Opmærksomhed på mulig øget blødningsrisiko og evt. dosisreducering af warfarin.
En enkelt kasuistik viser øget virkning af warfarin ved samtidig behandling med itraconazol, mens en anden kasuistik beretter at S-warfarin steg med en faktor 7,3, mens R-warfarin ikke ændredes.
Warfarin og fluconazol
Kliniske studier
Et prospektivt studie med syv patienter viste, at patienternes middel prothombin tid (PT) steg fra 15.8 +/- 1.0 sekunder (s) på dag 1 til 18,9 +/- 1,9 s på 5. dagen og til 21,9 +/- 2,2 s på 8. dagen. Stigningen i patienternes prothrombintid var beskeden, men dog signifikant. Desuden stoppede fluconazol behandlingen for tre af patienterne pga høj PT. Den største ændring i PT var på 9.7 s. Mekanismen formodes at være en hæmning af warfarins metabolisme, Crussell-Porter LL, Rindone JP et al, 1993.
I et retropsektivt studie af fire patienter, observeredes kun stigninger i prothrombintiden for to af patienterne, Tett S, Carey D et al, 1992.
Et prospektivt farmakokinetisk studie med seks raske frivillige sås en 275% stigning i halveringstiden for S-warfarin, og en 210% stigning i halveringstiden for R-warfarin ved samtidig behandling med fluconazol. Desuden viser forsøget store variationer i plasma halveringstiden for S-warfarin varierende fra 23-60 timer i kontrolgruppen, og fra 63-151 timer i behandlingsgruppen. Den gennemsnitlige prothrombintid ved samtidig behandling med warfarin og fluconazol steg fra normalt 21,3 +/- 2,4 sekunder til 26,6 +/- 3,6 sekunder efter fire dages behandling. Efter syv dages behandling sås et lille, men ikke statistisk signifikant fald i prothrombintiden. Clearance af R-warfarin faldt fra 1,84 ml/hr/kg til 0,87 ml/hr/kg, og for S-warfarin sås et fald i clearance fra 2,59 til 0,89. Fluconazol en kendt hæmmer af CYP2C9 in vitro. CYP2C9 omsættes warfarin, hvilket understøtter formodningen om en mulig interaktion mellem warfarin og fluconazol, Black DJ, Kunze KL et al, 1996b
I et farmakokinetisk studie med syv raske frivillige blev effekten af fluconazol på warfarins metabolisme undersøgt for tre forskellige doser af fluconazol. Ved henholdsvis 100, 200 og 300 mg fluconazol daglig blev omdannelsen af S-warfarin til S-7-hydroxywarfarin hæmmet med henholdsvis 31, 55 og 77%. Varigheden af den antikoagulerende effekt steg med stigende doser af fluconazol. Efter et enkelt dosis warfarin var den 4-7 dage og efter 100, 200 og 300 mg fluconazol var den henholdsvis 5-9, 6-11, og 8-15 dage, Neal JM, Kunze KL et al, 2003.
I et studie observeres efter indgift af en enkelt dosis fluconazol (150 mg) hos seks kvinder i stabil behandling med warfarin (54 mg/uge) en ikke-statistisk signifikane stigning i patieternes PT på mellem 2-34%. Hos tre af kvinderne sås en klinisk relevant stigning i INR > 4 eller udvikling af blødninger, således at patieternes warfarin dosis skulle reduceres, Turrentine MA, 2006
Et andet studie undersøgte hvorvidt en potentiel farmakokinetisk interaktion imellem warfarin og forskellige anti-infektiøse midler øger risikoen for hospitalisering og gastro-intestinal blødning hos warfarinbrugere. Resultaterne er baseret på US Medicaid data, behandlet vha. to forskellige studiedesigns – et nested case control og et case-crossover studie, hvor man i alt har kigget på 308.100 warfarin brugere. I forsøget testede man bl.a. fluconazol mod ingen samtidig behandling og behandling med cephalexin, som ikke forventes at have indflydelse. Sammenlignet med co-adminsitration med cephelaxin viste fluconazol co-administreret med warfarin en signifikant øget risiko for gastrointestinal blødning (odds ratio 2.09, 95%CI 1.34-3.26). Dette kan forklares ved at fluconazol hæmmer enzymet CYP2C9, som er primært ansvarlig for metaboliseringen af (S)-warfarin i leveren, Schelleman H, Bilker WB et al, 2008.
I et retrospektivt single-center cohorte studie, bestående af 21 cases og 957 kontroller, sås en relativ risiko på 9,11 for stigning i INR til >4,5 ved kombinationsbehandling med warfarin og fluconazol sammenlignet med warfarin alene. Hos 2 af patienterne blev der observeret blødninger, Daniels LM, Barreto JN et al, 2015
Supplerende litteratur: Lane MA, Zeringue A et al, 2014
Kasuistikker
Derudover er der i litteraturen mindst seks kasuistikker omhandlende patienter i behandling med warfarin og fluconazol, hvor der observeres stigning i patienternes koagulationsfaktorer og blødninger, heraf to patienter med gastrointestinale blødninger, Allison EJ, McKinney TJ et al, 2002; Baciewicz AM, Menke JJ et al, 1994; Kerr HD, 1993; Seaton TL, Celum CL et al, 1990a; Gericke KR, 1993a.
Warfarin og itraconazol
En kasuistik beretter om næse og hudblødninger fire dage efter at en patient har fået tillagt itraconazol til sin warfarinbehandling. INR måltes til > 8, Yeh J, Soo SC et al, 1990. En anden kasuistik beretter om en patient der modtog itraconazol 200mg/dag og warfarin 2mg/dag, hvor S-warfarin blev fundet at stige med en faktor 7,3, mens R-warfarin ikke ændredes. Miura M, Takahashi N et al, 2011
Warfarin og ketoconazol
En kasuistik viser ved samtidig behandling med warfarin og ketoconazol, en formodet interaktion mellem warfarin og ketoconazol på grundlag af observerede stigninger i en patients INR fra 1,9 til 5,4 over en periode på tre uger efter opstart af ketoconazol 200 mg 2 gange daglig. Der observeres ingen blødninger, Smith AG, 1984.
En kausuistik beskriver en 59-årig mand med en mekanisk aortaklap hvor det var nødvendigt at reducere warfarin dosis med 43% efter at høj-dosis ketoconazol (1200 mg daglig) behandling blev begyndt, Jackevicius CA og Ton MN, 2009.
Warfarin og miconazol
Kliniske studier
I et prospektivt studie med raske forsøgspersoner i kombinationsbehandling med warfarin og miconazol tabletter 125 mg daglig, ses en tredobbelt, signifikant stigning i halveringstiden fra 35 til 135 timer for S-warfarin, 39% gennemsnitligt signifikant fald i clearance for R-warfarin og 80% fald i clearance for S-warfarin, O'Reilly RA, Goulart DA et al, 1992a.
Et retrospektivt studie omhandlede 35 patienter, der alle var i stabil AK behandling med warfarin inden de påbegyndte topikal behandling med miconazol. Herefter steg INR gennemsnitligt fra 2.4 til 8.8 (p<0.0001), og flere af patienterne oplevede større eller mindre blødninger, Kovac M, Mitic G et al, 2012a. Et andet retrospektivt studie med 6 patienter, der alle var i stabil AK behandling med warfarin inden de påbegyndte oral behandling med miconazol. Under miconazol-behandlingen sås ingen stigning i INR, mens INR efter seponering af miconazol i gennemsnit steg fra 1,67 til 3,83 (p<0,01). INR var gennemsnitlig forhøjet i 15 dage efter seponering af oral miconazol. Dette kan muligvis skyldes, at miconazol ophobes i leveren pga. nedsat renal clearance. Murakami S, Tanaka A et al, 2016.
I et kohorte overkrydsningsstudie inkluderes 7.400 individer, der i perioden 1998-2012 har fået warfarin. Hos 17 warfarinbehandlede, der samtidig er behandlet med miconazol oral gel, stiger gennemsnitlig INR statistisk signifikant fra 2,5 før eksponering til 3,8 efter, Hellfritzsch M, Pottegard A et al, 2016
Kasuistikker
Derudover er der i litteraturen fundet adskillige kasuistikker, der beskriver en formodet interaktion mellem warfarin og topikal/vaginal/oral miconazol. Der rapporteres i kasuistikkerne om supraterapeutiske stigninger i patienternes INR (INR på op til 24 er rapporteret), samt forekomst af blødninger, såsom hudblødninger, hæmatomer, hæmaturi, melæna og hamatokesi, hos en del af patienterne ved co-administration, Ogard CG og Vestergaard H, 2000; Shenfield GM og Page M, 1991; Ariyaratnam S, Thakker NS et al, 1997; Silingardi M, Ghirarduzzi A et al, 2000a; Pemberton MN, Oliver RJ et al, 2004; Devaraj A, O'Beirne JP et al, 2002; Colquhoun MC, Daly M et al, 1987; Tajima-Okubo R, Tsuruoka S et al, 2012; Thirion DJ og Zanetti LA, 2000b; Ufondu CC, Ferrins P et al, 2013; Miki A, Ohtani H et al, 2011a; Pendlimari R, Anaparthy R et al, 2010; Marco M og Guy AJ, 1998; Pillans P og Woods DJ, 1996; De PA og De BT, 2015; Thomas JL, Dunn D et al, 2010;Pemberton MN, Sloan P et al, 1998; Murty M, 2001; Hook J, Millsopp L et al, 2016a;
Supplerende litteratur; Pemberton MN, 2016
Mekanisme
Miconazol er en potent hæmmer af CYP2C9, som metaboliserer warfarin.
Warfarin og voriconazol
I en prospektiv undersøgelse konstateres efter samtidig indgift af en enkelt dosis warfarin og flerdosis voriconazol (600 mg) en signifikant stigning i patienternes prothrombin tid fra 8 til 17 sekunder og en stigning i arealet under effekt kurven (AUEC) for prothrombin tiden på ca. 30% (fra 2282 til 3211 sekunder/time). I forhold til behandling med warfarin alene, observeres samtidig øget forekomst af blødninger. Mekanisme: hæmning af warfarins (S-warfarins) omsætning i CYP2C9 i leveren, Purkins L, Wood N et al, 2003c.
Supplerende litteratur: Mootha VV, Schluter ML et al, 2002; Harder S og Thurmann P, 1996.
Ogard CG;Vestergaard H, Ugeskr Laeger, 2000, 162:5511; [Interaction between warfarin and oral miconazole gel]
We report a case of a 76 year-old woman who had been taking warfarin for seven years because of relapsing deep venous thrombosis. Her daily maintenance dose was 5 mg. Monthly measurements of international normalised ratio (INR) were stable between 2-3. She developed oral candidiasis and miconazole gel was prescribed. One week later she developed bleeding gums. Eight days later she was admitted to the hospital with haematuria. INR was > 10. Warfarin and the miconazole gel were withdrawn. She was treated with phytonadione. INR normalised after four days and she continued warfarin treatment. Caution should be exercised whenever the combination of warfarin and miconazole gel are prescribed
Kerr HD, Am J Med Sci, 1993, 305:164-165; Case report: potentiation of warfarin by fluconazole
Described is an elderly woman who developed gastrointestinal bleeding probably potentiated by the interaction of fluconazole with warfarin. Because varied clinical uses are being found for fluconazole, clinicians should be aware of this potential interaction
Harder S;Thurmann P, Clin Pharmacokinet, 1996, 30:416-444; Clinically important drug interactions with anticoagulants. An update
Coumarin derivatives combine 3 unfavorable properties which make them prone to potentially life threatening drug-drug interactions: (i) high protein binding; (ii) cytochrome P450 dependent metabolism; and (iii) a narrow therapeutic range. An entire list of drugs which are supposed to interact with coumarins (mostly with warfarin) comprises about 250 different compounds. Noteworthy are the interactions with cardiovascular or antilipidaemic drugs which are often coadministered with coumarins: amiodarone, propafenone and fibrates. Cardiovascular drugs which are obviously devoid or proven to be devoid of an interaction are angiotensin converting enzyme (ACE) inhibitors, calcium antagonists, beta-blockers and cardiac glycosides. There are several other drugs which enhance the hypoprothrombinaemic response to coumarins by various mechanisms: inhibitors of the elimination of the eutomer S-(-)-warfarin (e.g. miconazole, phenylbutazone), combined with protein binding displacement (e.g., sulfinpyrazone, phenylbutazone), synergistic hypoprothrombinaemia (e.g. cefazoline). Furthermore, bleeding complications may occur with drugs affecting platelet function [aspirin (acetylsalicylic acid) and several nonsteroidal anti- inflammatories (NSAIDs)]. Strong inducers of coumarin metabolism are rifampicin (rifampin) and carbamazepine. Biphasic interactions may occur where a drug first enhances the hypoprothrombinaemic response to a coumarin but has a sustained inducing effect on coumarin metabolism (e.g. phenytoin or sulfinpyrazone). The complex response of coumarins to concomitant drug therapy makes it difficult to predict the occurrence and degree of a deterioration of anticoagulant control in individual patients. For clinical practice, it seems advisable that one should monitor for changes in prothrombin time when adding or deleting any newly approved drug or any drug suspected (e.g. on the basis of this review) to cause an interaction to patients on coumarin therapy. The onset of the adverse prothrombin time response might be from between 1 to 2 days up to 3 weeks (in case of phenprocoumon) after starting a concomitant drug regimen. With amiodarone, an adverse prothrombin time response might occur up to 2 months after initiating therapy. For heparins, only a drug interaction with aspirin or nitroglycerin seems clinically relevant due to the possibility of coadministration during acute cardiac events. Both drugs are shown to enhance the activated partial thromboplastin time response to heparin
Pemberton MN;Sloan P;Ariyaratnam S;Thakker NS;Thornhill MH, Br Dent J, 1998, 184:68-69; Derangement of warfarin anticoagulation by miconazole oral gel
The potentiation of the anticoagulant effects of warfarin by miconazole, when used in oral gel form, is described in three patients. The associated morbidity is examined, emphasising the importance of considering this potentially serious interaction when prescribing antifungal agents to patients on oral anticoagulants
Miura M;Takahashi N;Kanno S;Kato S;Nara M;Itoh M;Saitoh H;Yoshioka T;Kameoka Y;Fujishima N;Tagawa H;Hirokawa M;Sawada K, Tomt indhold, 2011;09; Drug interaction of (S)-warfarin, and not (R)-warfarin, with itraconazole in a hematopoietic stem cell transplant recipient
Background: Itraconazole is a potent inhibitor of CYP3A4 and P-glycoprotein, but not CYP2C9. Herein, we report a case study in which the plasma concentration of the CYP2C9 substrate (S)-warfarin, and not the CYP3A4 substrate (R)-warfarin, increased with itraconazole coadministration. Case: A 67-y-old man received an allogenic bone marrow transplant for acute lymphoid leukemia. He was taking oral itraconazole (200. mg/day) and was started on a warfarin dose of 2.0. mg/day. The plasma concentrations of (S)- and (R)-warfarin 3. days after starting warfarin administration were 216 and 556. ng/mL, respectively (INR 0.98), and after 10. days, the concentrations were 763 and 545. ng/mL, respectively (INR 2.43). On day 11 after withdrawal of itraconazole, the concentrations of (S)- and (R)-warfarin were 341 and 605. ng/mL, respectively (INR 1.38). The concentration of (R)-warfarin was not affected by itraconazole; however, the final (S)-warfarin concentration had increased 7.3-fold. The (S)-warfarin/(S)-7-hydroxywarfarin ratio decreased to 2.45 from 8.40 after discontinuation of itraconazole. The permeability of warfarin enantiomers across Caco-2 cells was not influenced by itraconazole and showed no difference between enantiomers. Conclusions: Careful INR monitoring is necessary for warfarin co-administration with itraconazole. Further examination is necessary to elucidate mechanisms of the interaction between warfarin and itraconazole. 2011 Elsevier B.V
Pendlimari R;Anaparthy R;Sugumar A, World J Gastrointest Pharmacol Ther , 2010, 1:40-42; Drug interaction presenting as acute abdomen
Warfarin is the most common oral anticoagulant prescribed around the world. Adverse drug interactions with warfarin are a huge problem especially in the elderly and in patients who take multiple medications. Most adverse drug interactions involve concomitantly prescribed oral or intravenous medications. Occasionally, topical or mucosally absorbed drugs can interact, leading to fluctuations in warfarin levels with adverse consequences. In this case report, we describe a case of intestinal intramural hematoma, a rare but known consequence of a supra therapeutic international normalized ratio (INR). The supra therapeutic INR was a consequence of mucosally absorbed miconazole, prescribed for vaginal candidiasis. We wish to highlight this rare and potentially fatal drug interaction, along with the need for frequent INR monitoring when new drugs are added or removed in patients taking warfarin
Tett S;Carey D;Lee HS, Med J Aust, 1992, 156:365; Drug interactions with fluconazole
Observationsstudieover en 12 ugers periode af patienter i langtidsbehandling med fluconazol. Retrospektiv undersøgelse.Kun 2 af patienterne oplevede en mulig interaktion mellem warfarin og fluconazol.
Jackevicius CA;Ton MN, Case Rep Med , 2009, 2009:315687; Enhanced Interaction between Warfarin and High-Dose Ketoconazole: A Case Report
This case describes the increased anticoagulation effect associated with the use of high-dose ketoconazole. A 59-year-old man treated with warfarin for aortic valve replacement was prescribed high-dose ketoconazole and hydrocortisone for the treatment of prostate cancer. Despite lowering the warfarin dosage by 35% during the start of high dose ketoconazole, an additional dose reduction was required subsequently when the INR rose from 2.62 to 3.82 within nine days. After a total dose reduction of 43%, the INR returned to therapeutic range within two weeks. The Naranjo probability scale revealed a probable adverse reaction of increased anticoagulant effect associated with high dose ketoconazole. Due to the inhibition of warfarin metabolism by ketoconazole, patients taking high dose ketoconazole concomitantly with warfarin may need their warfarin dosage reduced by more than is currently recommended, as well as receive more frequent INR monitoring to avoid over anticoagulation
Daniels LM;Barreto JN;Kuth JC;Anderson JR;Zhang B;Majka AJ;Morgenthaler TI;Tosh PK, Am J Health Syst Pharm, 2015, 72:1195-1203; Failure mode and effects analysis to reduce risk of anticoagulation levels above the target range during concurrent antimicrobial therapy
PURPOSE: A failure mode and effects analysis (FMEA) was conducted to analyze the clinical and operational processes leading to above-target International Normalized Ratios (INRs) in warfarin-treated patients receiving concurrent antimicrobial therapy. METHODS: The INRs of patients on long-term warfarin therapy who received a course of trimethoprim-sulfamethoxazole, metronidazole, fluconazole, miconazole, or voriconazole (highly potentiating antimicrobials, or HPAs) between September 1 and December 31, 2011, were compared with patients on long-term warfarin therapy who did not receive any antimicrobial during the same period. A multidisciplinary team of physicians, pharmacists, and a systems analyst was then formed to complete a step-by-step outline of the processes involved in warfarin management and concomitant HPA therapy, followed by an FMEA. RESULTS: Patients taking trimethoprim-sulfamethoxazole, metronidazole, or fluconazole demonstrated a significantly increased risk of having an INR of >4.5. The FMEA identified 134 failure modes. The most common failure modes were as follows: (1) electronic medical records did not identify all patients receiving warfarin, (2) HPA prescribers were unaware of recommended warfarin therapy when HPAs were prescribed, (3) HPA prescribers were unaware that a patient was taking warfarin and that the drug interaction is significant, and (4) warfarin managers were unaware that an HPA had been prescribed for a patient. CONCLUSION: An FMEA determined that the risk of adverse events caused by concomitantly administering warfarin and HPAs can be decreased by preemptively identifying patients receiving warfarin, having a care process in place, alerting providers about the patient's risk status, and notifying providers at the anticoagulation clinic
Baciewicz AM;Menke JJ;Bokar JA;Baud EB, Ann Pharmacother, 1994, 28:1111; Fluconazole-warfarin interaction
Kasuistik omhandlende en patient i kombinationsbehandling med warfarin og fluconazol.
Thomas JL;Dunn D;Pelletier A;Franks AS, South Med J, 2010, 103:1063-1065; Hyperprothrombinemia as a result of a possible warfarin and intravaginal miconazole interaction
Warfarin, a commonly prescribed anticoagulant, has many potential drug interactions. We describe a case of intravaginal miconazole potentiating the effects of warfarin in a patient previously stable on a consistent dose of 8.5 mg warfarin daily. Following a course of intravaginal miconazole and a dosage increase to 9 mg daily, her international normalized ratio (INR) increased from 2.0 to 5. After the course of miconazole was complete, the patient was stable with a therapeutic INR (mean INR 2.9) on 9 mg warfarin daily. Clinicians should consider the possibility of systemic absorption of intravaginal miconazole, and a resultant increase in warfarin's anticoagulant effect
Pillans P;Woods DJ, N Z Med J, 1996, 109:346; Interaction between miconazole oral gel (Daktarin) and warfarin
Colquhoun MC;Daly M;Stewart P;Beeley L, Lancet, 1987, 1:695-696; Interaction between warfarin and miconazole oral gel
Kauistik omhandlende en patient i kombinationsbehandling med warfarin og miconazol oral gel. Efter 10 dages kombinationsbehandling ses stigninger i patientens INR fra normalt 2,5 til 17,9. Patienten klager desuden over blodig aff°ring.
Devaraj A;O'Beirne JP;Veasey R;Dunk AA, BMJ, 2002, 325:77; Interaction between warfarin and topical miconazole cream
Tajima-Okubo R;Tsuruoka S;Moriyama N;Kaneda T;Yamagata K, Tomt indhold, 2012, 1:May; Interaction of miconazole oral gel with warfarin and cyclosporine in a patient with nephrotic syndrome
It is well known that miconazole inhibits cytochrome P450 (CYP). However, this drug in oral gel form is believed not to absorb into systemic circulation, and therefore not to inhibit CYP. We experienced a case of increased oral bioavailability of warfarin and cyclosporine with this gel for treatment of oral candidiasis in a patient with nephrotic syndrome. Her prothrombin time-international normalized ratio (PT-INR) increased from 2 to 7. 25, and the cyclosporine concentration at 2 h after final dosing (C2) increased from 633. 8 to 1396. 5 ng/ml 6 days after the coadministration. These problems were resolved by termination of the gel and switching to amphotericin B gargle. We further detected a significant amount of miconazole in her plasma, directly showing for the first time in a patient with this interaction that oral miconazole gel was actually absorbed into systemic circulation. Because warfarin and cyclosporine are often used simultaneously by nephrologists, caution should be applied with combined use of these drugs and oral miconazole gel to avoid adverse reaction. 2012 Japanese Society of Nephrology
Mootha VV;Schluter ML;Das A, Arch Ophthalmol, 2002, 120:94-95; Intraocular hemorrhages due to warfarin fluconazole drug interaction in a patient with presumed Candida endophthalmitis
Fluconazole is a triazole antifungal effective agains Candida endophthalmitis. It potentiates the anticoagulant effect of warfarin sodium.
Neal JM;Kunze KL;Levy RH;O'Reilly RA;Trager WF, Drug Metab Dispos, 2003, 31:1043-1048; Kiiv, an in vivo parameter for predicting the magnitude of a drug interaction arising from competitive enzyme inhibition
The goal of the study was to test the assumption that a competitive inhibition constant determined in vivo, Kiiv, like its corresponding in vitro counterpart, Ki, is independent of inhibitor concentration. Inhibition of the CYP2C9-dependent formation of (S)-7-hydroxy-warfarin from (S)-warfarin was measured in seven healthy subjects at three different doses of fluconazole. Prothrombin time measurements showed increasing anticoagulant activity with increasing fluconazole dose. The pharmacokinetic parameters calculated from the (S)- and (R)-warfarin plasma levels were consistent with previous studies. Fluconazole reduced the clearance of (S)-warfarin to a greater extent than that of (R)-warfarin. The decrease in clearance of both warfarin enantiomers was fluconazole dose-dependent. The formation of (S)-7-hydroxy-warfarin was inhibited by 31, 55, and 77% at the 100, 200, and 300 mg daily doses of fluconazole, respectively. Kiiv, values calculated from these data based on plasma fluconazole levels at each dose and data from earlier work at 400-mg daily doses of fluconazole were 30.7 +/- 23.7, 19.6 +/- 3.8, 17.9 +/- 7.5, and 19.8 +/- 3.5 microM, respectively. These results confirm the hypothesis that Kiiv is independent of inhibitor concentration
Crussell-Porter LL;Rindone JP;Ford MA;Jaskar DW, Arch Intern Med, 1993, 153:102-104; Low-dose fluconazole therapy potentiates the hypoprothrombinemic response of warfarin sodium
BACKGROUND: Fluconazole has been reported to interact with many medications. This study examined the effect of low-dose fluconazole therapy on the hypoprothrombinemic response of warfarin sodium in patients. METHODS: Patients receiving low-intensity anticoagulation therapy with warfarin were recruited. All patients were taking stable doses of warfarin and had two baseline prothrombin times (PTs) within 10% of each other. Each patient received 100 mg of fluconazole daily for 7 days. Prothrombin times were measured on days 2, 5, and 8 during fluconazole administration. RESULTS: All patients had a progressive increase in PTs. Mean (+/- SD) of PTs increased from 15.8 +/- 1 seconds before the administration of fluconazole to 18.9 +/- 1.9 seconds on day 5 and 21.9 +/- 2.2 seconds on day 8. Fluconazole therapy was stopped early in the three patients due to high PTs. The largest change in PT was 9.7 seconds. No bleeding was noted during the study. CONCLUSION: Fluconazole predictably potentiates the hypoprothrombinemic response of warfarin. Prothrombin times must be monitored when fluconazole is administered to patients taking warfarin
O'Reilly RA;Goulart DA;Kunze KL;Neal J;Gibaldi M;Eddy AC;Trager WF, Clin Pharmacol Ther, 1992, a, 51:656-667; Mechanisms of the stereoselective interaction between miconazole and racemic warfarin in human subjects
Miconazole decreased the total body clearance of both (R)- and (S)-warfarin in normal subjects but did not change volumes of distribution. Miconazole inhibited the oxidation of both (R)- and (S)-warfarin to phenolic metabolites, although (S)-warfarin was inhibited to the greater extent. In particular, (S)-7-hydroxylation, the pathway primarily responsible for termination of the anticoagulant effect, was most strongly inhibited. Inhibition of warfarin hydroxylation by miconazole in human liver microsomes and the in vivo results showed a good rank order correlation. The enhanced anticoagulant effect observed when miconazole and warfarin are coadministered may result from inhibition of P4502C9, the isozyme of P450 primarily responsible for the conversion of (S)-warfarin to (S)-7-hydroxy-warfarin. Because miconazole inhibits a number of P450 isozymes, in addition to P4502C9, it can be expected to lead to interactions with other drugs whose primary metabolism is controlled by these enzymes
Kovac M;Mitic G;Kovac Z, J Clin Pharm Ther, 2012, a;February; Miconazole and nystatin used as topical antifungal drugs interact equally strongly with warfarin
What is known and Objective: Medline search disclosed 10 case reports of interactions between oral anticoagulants and miconazole oral gel, but none so far between nystatin solution and anticoagulants. We report on change in anticoagulant activity with use of different topical antifungal drugs, miconazole oral gel and vaginal suppositories, and nystatin solution. Methods: We conducted a retrospective study that included 43 patients on stable anticoagulation before the introduction of topical antifungal drugs. Miconazole oral gel was prescribed for 32 patients, nystatin solution for eight patients and miconazole vaginal suppositories for three patients. Results and Discussion: Nineteen (442%) of the patients reported bleeding complications and some of these were severe. Fifteen of 32 who used miconazole oral gel and four of 8 of those who used nystatin solution were affected. Before use of the antifungal drugs, the mean weekly warfarin dose in the nystatin group was 145 mg, and after antifungal drugs, 9 mg, P = 0038, while the mean international normalized ratio (INR) before antifungal drugs was 25 (range 19-35) and afterwards it was 106 (range 45-193), P = 00001. In the miconazole oral gel group the mean weekly warfarin dose was 157 mg, and after 108 mg, P = 0008, while the mean INR before antifungal drugs was 244 (range 192-318) and afterwards it was 88 (range 49-169), P < 00001. What is new and Conclusion: Miconazole oral gel and topically applied nystatin solution have equally strong effects on warfarin activity and can provoke major bleeding. Prospective evaluation of this effect is called for. However, based on our results the warfarin dose adjustment appears necessary when the anticoagulant is used concomitantly with those topical antifungals. 2011 Blackwell Publishing Ltd
Prescrire Int, 2015, 24:19; Miconazole and oral anticoagulants: bleeding
Increases in the INR and cases of bleeding have been reported during concomitant use of miconazole oral gel or mucoadhesive buccal tablets and a vitamin K antagonist (fluindione or warfarin)
De PA;De BT, Acta Clin Belg, 2015, 70:121-123; Miconazole buccal gel and risk for systemic bleeding: how certain topical formula can interfere with anticoagulants
The association of miconazole and oral anticoagulants should be carried out with great caution because of potentially serious side effects. This phenomenon is well known in the case of systemic administration of miconazole, but there is limited awareness that also topical oral administration of miconazole can provoke these effects. In this paper we describe four patients followed at the Cardiology Department of the Ghent University Hospital, who used an oral mucosal miconazole preparation, and who developed an increased international normalized ratio
Pemberton MN;Oliver RJ;Theaker ED, Br Dent J, 2004, 196:529-531; Miconazole oral gel and drug interactions
Miconazole oral gel is frequently prescribed for the treatment of oral Candidal infections. Its ability to be systemically absorbed and interact with other drugs has previously been recorded but is not universally known. As a reminder, a further case of derangement of anticoagulation following concomitant use of warfarin and miconazole is reported. Other potential drug interactions of miconazole and fluconazole are highlighted
Silingardi M;Ghirarduzzi A;Tincani E;Iorio A;Iori I, Thromb Haemost, 2000, a, 83:794-795; Miconazole oral gel potentiates warfarin anticoagulant activity
Kasuistik omhandlende to patienter i kombinationsbehandling med warfarin og miconazol.Efter 10-14 dages kombinationsbehandling stiger begge patienters INR kraftigt.
Murty M, CMAJ, 2001, 165:81-86; Miconazole-warfarin interaction: increased INR
Pemberton MN, Oral Dis , 2016, 22:761-765; Nystatin and miconazole: pharmacological and clinical evidence regarding interactions with warfarin
OBJECTIVE: A retrospective case series published in 2012 concluded that miconazole and nystatin used as topical antifungal drugs appear to interact equally strongly with warfarin. If confirmed, this finding has significant implications for clinical practice. This study evaluates the evidence. MATERIALS AND METHODS: Evidence from the pharmacology literature, the medical literature and the 'yellow card' adverse drug reaction surveillance reports was analysed regarding possible interactions of nystatin and miconazole with warfarin. RESULTS: There is strong evidence to support the derangement of warfarin anticoagulation by miconazole oral gel in all areas of evidence studied. No postulated mechanism of interaction, no additional published reported cases and no supportive data from adverse drug reports were identified which would corroborate the case for a significant interaction between nystatin and warfarin. CONCLUSION: Miconazole and nystatin used as topical antifungal drugs do not interact equally strongly with warfarin. Miconazole oral gel can clearly interact with warfarin to cause derangement of anticoagulation. Nystatin appears unlikely to interact with warfarin
Gericke KR, Pharmacotherapy, 1993, a, 13:508-509; Possible interaction between warfarin and fluconazole
Fluconazole is a triazole antifungal agent reported to have a low affinity for human cytochrome P-450, and thus would not be expected to interact with drugs metabolized through the cytochrome P-450 system, including phenytoin, cyclosporine, and warfarin. A potential interaction between warfarin and fluconazole occurred in a 39-year-old man with chronic renal insufficiency. He was receiving anticoagulant therapy for a lower extremity thrombus and oral fluconazole 50 mg/day for a fungal urinary tract infection. After attaining consistent international normalized ratio (INR) values between 2.0 and 2.7 with warfarin, the INR increased to 5.2 four days after fluconazole was started, despite decreasing the dosage of warfarin. There were no changes in the patient's other medications, and the INR decreased to 1.5 on discontinuation of fluconazole. The possible mechanism of an interaction may be dose-related inhibition of warfarin metabolism, and may be more pronounced in patients with decreased renal clearance of fluconazole
Seaton TL;Celum CL;Black DJ, DICP, 1990, a, 24:1177-1178; Possible potentiation of warfarin by fluconazole
Fluconazole, a new triazole antifungal agent, interacts with a number of drugs. Only one study to date has examined the potentiation of warfarin's anticoagulant effect by fluconazole. To our knowledge, this is the first published case report of this interaction in the clinical setting. The patient had received a stable dosage regimen of warfarin for a number of months. Fluconazole 100 mg bid was added for a candidal wound infection. The prothrombin time increased from 19 to 65 seconds eight days later and the patient experienced a gastrointestinal bleeding episode. Fresh-frozen plasma was administered and warfarin was discontinued while the patient completed a planned 21-day course of fluconazole. The patient eventually resumed the original warfarin dosage with stable coagulation parameters. Until the influence of fluconazole on the anticoagulant effect of warfarin is studied in further detail, careful monitoring of coagulation parameters is recommended for all patients receiving the combination
Yeh J;Soo SC;Summerton C;Richardson C, BMJ, 1990, 301:669; Potentiation of action of warfarin by itraconazole
Kasuistik omhandlende en patient i kombinationsbehandling med warfarin og itraconazol. Efter 4 dages kombinationsbehandling måles patientens INR til større end 8. Desuden klager patienten over tilbagevendende kraftig næseblod samt hudblødninger.
Smith AG, Br Med J (Clin Res Ed), 1984, 288:188-189; Potentiation of oral anticoagulants by ketoconazole
Kasuistik omhandlende en patient i behandling med warfarin og ketoconazol. Efter 3 ugers kombinationsbehandling med warfarin og ketoconazol ses stigninger i patientens INR fra 1,9 til 5,4.
Shenfield GM;Page M, Aust N Z J Med, 1991, 21:928; Potentiation of warfarin action by miconazole oral gel
Kasuistik omhandlende en kvindelig patient i kombinationsbehandling med warfarin og miconazol oral gel. Efter 11 dages kombinationsbehandling opdager patienten hudbl°dninger, rygsmerter og hµmaturi. Patients INR er steget fra 2,0 til 13,1.
Ariyaratnam S;Thakker NS;Sloan P;Thornhill MH, BMJ, 1997, 314:349; Potentiation of warfarin anticoagulant activity by miconazole oral gel
Kasuistik omhandlende en patient i kombinationsbehandling med warfarin og miconazol. Efter 2 ugers kombinationsbehandling stiger patientens INR fra 1,5 til 10.
Thirion DJ;Zanetti LA, Pharmacotherapy, 2000, b, 20:98-99; Potentiation of warfarin's hypoprothrombinemic effect with miconazole vaginal suppositories
A 53-year-old woman being treated for a vaginal yeast infection experienced ecchymosis. Laboratory evaluation revealed a prolonged prothrombin time. It is possible that the bleeding was due to an interaction between warfarin and miconazole. Health care professionals should be aware of the potential for drug interactions with vaginally administered miconazole, especially in women receiving anticoagulation therapy
Murakami S;Tanaka A;Ido K;Tanaka M;Araki H, Int J Clin Pharmacol Ther, 2016, a, 54:474-476; Prolonged effects of miconazole oral gel on warfarin anticoagulation even after treatment withdrawal
OBJECTIVE: We investigated the effect of terminating miconazole oral gel (MOG) treatment on the anticoagulant activity of warfarin by evaluating changes in international normalized ratio levels (INR). METHODS: Data were collected from the medical records of 6 patients treated with warfarin and MOG. RESULTS: Following cessation of MOG treatment, increased INR and INR/dose levels were observed for an average of 15 days, showing that the anticoagulant activity of warfarin was increased for ~ 2 weeks. CONCLUSIONS: Closer monitoring of INR levels for at least 2 weeks may be required upon withdrawal of MOG treatment in patients treated with warfarin
Marco M;Guy AJ, Int J Oral Maxillofac Surg , 1998, 27:485; Retroperitoneal haematoma and small bowel intramural haematoma caused by warfarin and miconazole interaction
Lane MA;Zeringue A;McDonald JR, Tomt indhold, 2014, 127:July; Serious bleeding events due to warfarin and antibiotic co-prescription in a cohort of veterans
Background Antibiotics may interact with warfarin, increasing the risk for significant bleeding events. Methods This is a retrospective cohort study of veterans who were prescribed warfarin for 30 days without interruption through the US Department of Veterans Affairs between October 1, 2002 and September 1, 2008. Antibiotics considered to be high risk for interaction with warfarin include: trimethoprim/sulfamethoxazole (TMP/SMX), ciprofloxacin, levofloxacin, metronidazole, fluconazole, azithromycin, and clarithromycin. Low-risk antibiotics include clindamycin and cephalexin. Risk of bleeding event within 30 days of antibiotic exposure was measured using Cox proportional hazards regression, adjusted for demographic characteristics, comorbid conditions, and receipt of other medications interacting with warfarin. Results A total of 22,272 patients met inclusion criteria, with 14,078 and 8194 receiving high- and low-risk antibiotics, respectively. There were 93 and 36 bleeding events in the high- and low-risk groups, respectively. Receipt of a high-risk antibiotic (hazard ratio [HR] 1.48; 95% confidence interval [CI], 1.00-2.19) and azithromycin (HR 1.93; 95% CI, 1.13-3.30) were associated with increased risk of bleeding as a primary diagnosis. TMP/SMX (HR 2.09; 95% CI, 1.45-3.02), ciprofloxacin (HR 1.87; 95% CI, 1.42-2.50), levofloxacin (HR 1.77; 95% CI, 1.22-2.50), azithromycin (HR 1.64; 95% CI, 1.16-2.33), and clarithromycin (HR 2.40; 95% CI, 1.16-4.94) were associated with serious bleeding as a primary or secondary diagnosis. International normalized ratio (INR) alterations were common; 9.7% of patients prescribed fluconazole had INR value >6. Patients who had INR performed within 3-14 days of co-prescription were at a decreased risk of serious bleeding (HR 0.61; 95% CI, 0.42-0.88). Conclusions Warfarin users who are prescribed high-risk antibiotics are at higher risk for serious bleeding events. Early INR evaluation may mitigate this risk. 2014 Elsevier Inc. All rights reserved
Turrentine MA, Obstet Gynecol, 2006, 107(2 I): 310-313-313; Single-dose fluconazole for vulvovaginal candidiasis: Impact on prothrombin time in women taking warfarin
OBJECTIVE: To estimate the effect of a single oral 150-mg dose of fluconazole on the prothrombin time of women on long-term warfarin therapy. METHODS: Women on warfarin therapy for 6 months or more with no change in dose within 4 weeks of the study, and a prothrombin time (PT) with an International Normalized Ratio (INR) between 2 and 3 were invited to participate. Two consecutive baseline PTs were obtained (days -1 and 0), and women were given 150 mg of fluconazole. Prothrombin times were measured on days 2, 5, and 8 of the study. The change in PT was calculated from the difference between the baseline PT on day 0 and the PT during the study period. To detect a 10% difference in a PT (approximately 2.1 seconds) of a patient with an INR of 2.0, at P < .05 and a power of 90%, 5 subjects are required. RESULTS: Six women participated. The mean (± standard deviation) PT for day 0 was 27.7 ± 4.1 seconds or INR 2.6 ± 0.4. The PT increased 11% at day 2, 34% at day 5, and 2% at day 8; these differences were not statistically significant. However, one half of the women had either a clinically relevant increase of the INR greater than 4, or bleeding that required their dosage of warfarin to be decreased. CONCLUSION: A single 150-mg oral dose of fluconazole may increase the PT to a clinically relevant level in a woman on chronic warfarin therapy. Clinicians should monitor the PT carefully after a single dose of fluconazole. < copyright > 2006 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins
Allison EJ;McKinney TJ;Langenberg JN, Eur J Emerg Med, 2002, 9:175-177; Spinal epidural haematoma as a result of warfarin/fluconazole drug interaction
This is the first reported case in the emergency medicine literature of a drug interaction between warfarin and fluconazole. We present a case of spinal epidural haematoma and summarize four other case reports reported elsewhere from 1988 to 1996. We admonish emergency physicians to be aware of this dangerous drug combination. Warfarin and fluconazole are frequently encountered drugs in the emergency department and thus any interaction between these drugs is of considerable importance
Hellfritzsch M;Pottegard A;Pedersen AJ;Burghle A;Mouaanaki F;Hallas J;Grove EL;Damkier P, Basic Clin Pharmacol Toxicol, 2016; Topical Antimycotics for Oral Candidiasis in Warfarin Users
Treatment for oral candidiasis in warfarin users may be complicated by drug-drug interactions (DDIs) between warfarin and topically applied antimycotics. However, current knowledge of these putative DDIs is merely based on case series. We therefore performed a cohort cross-over study with the objective to evaluate the potential DDIs between warfarin and miconazole oral gel or nystatin oral solution. The cohort consisted of individuals using warfarin in the period of 1998-2012 (n approximately 7400). We collected data on cohort members' measurements of the international normalized ratio (INR) from a clinical database, and obtained information on their use of topically applied miconazole and nystatin from a regional prescription register. Potential DDIs were assessed by comparing INR values before and after initiation of an antimycotic drug. Among 17 warfarin users exposed to miconazole oral gel, the mean INR increased from 2.5 (95% CI: 2.1-2.8) to 3.8 (95% CI: 2.8-4.8) after exposure, corresponding to a mean INR increase of 1.4 (95% CI: 0.3-2.4). Among 30 warfarin users exposed to nystatin oral solution, the mean INR was 2.7 (95% CI: 2.3-3.1) before and 2.5 (95% CI: 2.2-2.9) after exposure. In conclusion, we found evidence supporting a clinically relevant drug-drug interaction between warfarin and miconazole oral gel. In contrast, we did not find any indication of an interaction between warfarin and nystatin oral solution. Nystatin rather than miconazole should be preferred when treating warfarin users for oral candidiasis
Purkins L;Wood N;Kleinermans D;Nichols D, Br J Clin Pharmacol, 2003, c, 56 Suppl 1:24-29; Voriconazole potentiates warfarin-induced prothrombin time prolongation
AIMS: Voriconazole is a novel triazole with broad-spectrum antifungal activity. It is likely that some patients receiving voriconazole may also require treatment with the anticoagulant warfarin. Cytochrome P450 isoenzymes are important in the metabolism of both these drugs. This study investigated the effect of voriconazole on the pharmacodynamics of warfarin by measuring prothrombin time, and also evaluated the safety and tolerability of the coadministered drugs. METHODS: This was a double-blind, placebo-controlled, two-way crossover study in which healthy male subjects received either 300 mg voriconazole or placebo twice daily on days 1-12, plus a single oral dose of 30 mg warfarin on day 7 of each study period. Volunteers were randomized to one of the following treatment sequences: voriconazole + warfarin followed by placebo + warfarin or placebo + warfarin followed by voriconazole + warfarin. There was a washout of at least of 7 days between treatment periods. RESULTS: The mean Cmax, AUCtau and tmax for voriconazole were 3736 ng ml-1, 25 733 ng.h ml-1, and 1.66 h, respectively. Both the mean maximum change from baseline prothrombin time and the mean area under the effect curve (AUEC) for prothrombin time during coadministration with voriconazole (17 s and 3211 s.h, respectively) were statistically significantly greater than the mean values observed during the placebo period (8 s and 2282 s.h ). Prothrombin times were still increased by a mean value of 5.4 s 144 h post warfarin dose following coadministration with voriconazole compared with a mean value of 0.6 s in the placebo treatment period. CONCLUSIONS: Coadministration of voriconazole and warfarin potentiates warfarin-induced prothrombin time prolongation. Regular monitoring of prothrombin time is recommended if these drugs are coadministered, with appropriate adjustment of the dose of warfarin
Hook J;Millsopp L;Field EA, Dent Update , 2016, a, 43:34-36; Warfarin and Drug Interactions: Prescribing Vigilance
A patient taking warfarin presented to the Oral Medicine Clinic at Liverpool University Dental Hospital, having been prescribed metronidazole and miconazole by his general dental practitioner (GDP) for his oral mucosal problem. He subsequently developed bruising on his torso following mild trauma. Having read the drug information leaflet provided with his metronidazole and miconazole, he noted the potential drug interactions between these and warfarin. He therefore stopped his warfarin. The details of this case are outlined, and the potential for significant drug interactions with warfarin are highlighted. The need for dental practitioners to be vigilant concerning drug interactions is emphasized, together with the importance of CPD in relation to drug prescribing. CPD/CLINICAL RELEVANCE: This case report, which is of relevance to all dental practitioners, highlights the importance of up-to-date medical and drug histories and the continuing awareness of potential drug interactions. In this case, patient intervention after checking drug information leaflets prevented serious consequences. The importance and potentially serious consequences of significant drug interactions needs to be understood.
Miki A;Ohtani H;Sawada Y, J Clin Pharm Ther, 2011, a, 36:642-650; Warfarin and miconazole oral gel interactions: Analysis and therapy recommendations based on clinical data and a pharmacokinetic model
Summary What is known and Objective: Miconazole is a strong inhibitor of CYP2C9, one of the main enzymes involved in the metabolism of warfarin. Concurrent use of the two drugs leads to potentially serious adverse effects. Although it is often assumed that use of the oral miconazole gel is acceptable with concomitant warfarin, because of the low bioavailability following buccal administration, drug-drug interactions have been reported following such use. We aimed to investigate case reports of such interactions and develop a pharmacokinetic model to model such interactions. Methods: The Medline database from 1966 to October 2010 was used for literature search. Case reports of the potentiation of the anticoagulant effects of warfarin, such as the elevation of prothrombin time (INR), by concomitant administration of warfarin and miconazole oral gel were collected. We quantitatively estimated the extent of inhibition of warfarin metabolism by orally administered miconazole gel and compared our findings with case reports. Results and Discussion: Metabolism of (S)-warfarin is inhibited potently following administration of a standard dose (200-400 mg/day in Japan) of miconazole gel. This may lead to in an increase in the blood concentration of warfarin and lead to serious adverse effects. The literature reports of clinical interactions with concomitant use of those drugs show that other factors may amplify the effects of any increase in blood concentration. What is new and Conclusion: We summarize all reported, clinically significant, cases of drug interaction between miconazole oral gel and warfarin. Pharmacokinetic modelling shows that concomitant administration of warfarin and miconazole oral gel can lead to substantial increase in warfarin concentration. However, our PK/PD model fails to capture the dramatic increases seen in INR values, and hence bleeding complications, reported in the literature. Taken together, the evidence suggests that concomitant use of miconazole gel and warfarin should be avoided. Even over-the-counter products containing miconazole should be used with caution by patients receiving warfarin. 2010 Blackwell Publishing Ltd
Ufondu CC;Ferrins P;Cushen A;Quinn J, Ir J Med Sci, 2013, 182:March; Warfarin and topical miconazole: The potential for a clinically significant interaction
Schelleman H;Bilker WB;Brensinger CM;Han X;Kimmel SE;Hennessy S, Clin Pharmacol Ther, 2008, 84:581-588; Warfarin with fluoroquinolones, sulfonamides, or azole antifungals: interactions and the risk of hospitalization for gastrointestinal bleeding
The aim of this study was to determine whether a potential pharmacokinetic interaction between warfarin and orally administered anti-infectives increases the risk of hospitalization for gastrointestinal (GI) bleeding in warfarin users. We conducted a nested case-control and case-crossover study using US Medicaid data. Logistic regression was used to determine the association between GI bleeding and prior use of ciprofloxacin, levofloxacin, gatifloxacin, co-trimoxazole, or fluconazole vs. no exposure and also vs. use of cephalexin, which would not be expected to interact with warfarin. All of the anti-infectives examined were associated with elevated odds ratios (ORs) when compared to no exposure to these drugs. With cephalexin data as the reference, the ORs for co-trimoxazole (OR: 1.68 (95% confidence interval (CI): 1.21-2.33) in the prior 6-10 days) and fluconazole (OR: 2.09 (95% CI: 1.34-3.26) in the prior 11-15 days) were significantly elevated. Warfarin users who had received an anti-infective agent showed a substantially increased risk of GI bleeding. However, a drug-drug interaction with warfarin was evident only for co-trimoxazole and fluconazole
Black DJ;Kunze KL;Wienkers LC;Gidal BE;Seaton TL;McDonnell ND;Evans JS;Bauwens JE;Trager WF, Drug Metab Dispos, 1996, b, 24:422-428; Warfarin-fluconazole. II. A metabolically based drug interaction: in vivo studies
Consistent with expectations based on human in vitro microsomal experiments, administration of fluconazole (400 mg/day) for 6 days to six human volunteers significantly reduced the cytochrome P450 (P450)- dependent metabolic clearance of the warfarin enantiomers. In particular, P4502C9 catalyzed 6- and 7-hydroxylation of (S)-warfarin, the pathway primarily responsible for termination of warfarin's anticoagulant effect, was inhibited by approximately 70%. The change in (S)-warfarin pharmacokinetics caused by fluconazole dramatically increased the magnitude and duration of warfarin's hypoprothrombinemic effect. These observations indicate that co-administration of fluconazole and warfarin will result in a clinically significant metabolically based interaction The major P450-dependent, in vivo pathways of (R)-warfarin clearance were also strongly inhibited by fluconazole. 10-Hydroxylation, a metabolic pathway catalyzed exclusively by P4503A4, was inhibited by 45% whereas 6-, 7-, and 8- hydroxylations were inhibited by 61, 73, and 88%, respectively. The potent inhibition of the phenolic metabolites suggests that enzymes other than P4501A2 (weakly inhibited by fluconazole in vitro) are primarily responsible for the formation of these metabolites in vivo as predicted from in vitro kinetic studies. These data suggest that fluconazole can be expected to interact with any drug whose clearance is dominated by P450s 2C9, 3A4, and other as yet undefined isoforms. Overall, the results strongly support the hypothesis that metabolically based in vivo drug interactions may be predicted from human in vitro microsomal data