FLUCONAZOLE (Page 7 of 12)

Coumarin-Type Anticoagulants

Prothrombin time may be increased in patients receiving concomitant fluconazole and coumarin-type anticoagulants. In postmarketing experience, as with other azole antifungals, bleeding events (bruising, epistaxis, gastrointestinal bleeding, hematuria, and melena) have been reported in association with increases in prothrombin time in patients receiving fluconazole concurrently with warfarin. Careful monitoring of prothrombin time in patients receiving fluconazole and coumarin-type anticoagulants is recommended. Dose adjustment of warfarin may be necessary (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Phenytoin

Fluconazole increases the plasma concentrations of phenytoin. Careful monitoring of phenytoin concentrations in patients receiving fluconazole and phenytoin is recommended (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Cyclosporine

Fluconazole may significantly increase cyclosporine levels in renal transplant patients with or without renal impairment. Careful monitoring of cyclosporine concentrations and serum creatinine is recommended in patients receiving fluconazole and cyclosporine (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Rifampin

Rifampin enhances the metabolism of concurrently administered fluconazole. Depending on clinical circumstances, consideration should be given to increasing the dose of fluconazole when it is administered with rifampin (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Theophylline

Fluconazole increases the serum concentrations of theophylline. Careful monitoring of serum theophylline concentrations in patients receiving fluconazole and theophylline is recommended (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Terfenadine

Because of the occurrence of serious cardiac dysrhythmias secondary to prolongation of the QTc interval in patients receiving azole antifungals in conjunction with terfenadine, interaction studies have been performed. One study at a 200 mg daily dose of fluconazole failed to demonstrate a prolongation in QTc interval. Another study at a 400 mg and 800 mg daily dose of fluconazole demonstrated that fluconazole taken in doses of 400 mg per day or greater significantly increases plasma levels of terfenadine when taken concomitantly. The combined use of fluconazole at doses of 400 mg or greater with terfenadine is contraindicated (see CONTRAINDICATIONS and CLINICAL PHARMACOLOGY, Drug Interaction Studies). The coadministration of fluconazole at doses lower than 400 mg/day with terfenadine should be carefully monitored.

Cisapride

There have been reports of cardiac events, including torsade de pointes, in patients to whom fluconazole and cisapride were coadministered. A controlled study found that concomitant fluconazole 200 mg once daily and cisapride 20 mg four times a day yielded a significant increase in cisapride plasma levels and prolongation of QTc interval. The combined use of fluconazole with cisapride is contraindicated (see CONTRAINDICATIONS and CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Astemizole

Concomitant administration of fluconazole with astemizole may decrease the clearance of astemizole. Resulting increased plasma concentrations of astemizole can lead to QT prolongation and rare occurrences of torsade de pointes. Coadministration of fluconazole and astemizole is contraindicated.

Rifabutin

There have been reports that an interaction exists when fluconazole is administered concomitantly with rifabutin, leading to increased serum levels of rifabutin up to 80%. There have been reports of uveitis in patients to whom fluconazole and rifabutin were coadministered. Patients receiving rifabutin and fluconazole concomitantly should be carefully monitored (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Voriconazole

Avoid concomitant administration of voriconazole and fluconazole. Monitoring for adverse events and toxicity related to voriconazole is recommended; especially, if voriconazole is started within 24 h after the last dose of fluconazole (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Tacrolimus

Fluconazole may increase the serum concentrations of orally administered tacrolimus up to 5 times due to inhibition of tacrolimus metabolism through CYP3A4 in the intestines. No significant pharmacokinetic changes have been observed when tacrolimus is given intravenously. Increased tacrolimus levels have been associated with nephrotoxicity. Dosage of orally administered tacrolimus should be decreased depending on tacrolimus concentration (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Short-acting Benzodiazepines

Following oral administration of midazolam, fluconazole resulted in substantial increases in midazolam concentrations and psychomotor effects. This effect on midazolam appears to be more pronounced following oral administration of fluconazole than with fluconazole administered intravenously. If short-acting benzodiazepines, which are metabolized by the cytochrome P450 system, are concomitantly administered with fluconazole, consideration should be given to decreasing the benzodiazepine dosage, and the patients should be appropriately monitored (see CLINICAL PHARMACOLOGY, Drug Interaction Studies).

Fluconazole increases the AUC of triazolam (single dose) by approximately 50%, Cmax by 20 to 32%, and increases t½ by 25 to 50% due to the inhibition of metabolism of triazolam. Dosage adjustments of triazolam may be necessary.

Oral Contraceptives

Two pharmacokinetic studies with a combined oral contraceptive have been performed using multiple doses of fluconazole. There were no relevant effects on hormone level in the 50 mg fluconazole study, while at 200 mg daily, the AUCs of ethinyl estradiol and levonorgestrel were increased 40% and 24%, respectively. Thus, multiple dose use of fluconazole at these doses is unlikely to have an effect on the efficacy of the combined oral contraceptive.

Pimozide

Although not studied in vitro or in vivo , concomitant administration of fluconazole with pimozide may result in inhibition of pimozide metabolism. Increased pimozide plasma concentrations can lead to QT prolongation and rare occurrences of torsade de pointes. Coadministration of fluconazole and pimozide is contraindicated.

Hydrochlorothiazide

In a pharmacokinetic interaction study, coadministration of multiple dose hydrochlorothiazide to healthy volunteers receiving fluconazole increased plasma concentrations of fluconazole by 40%. An effect of this magnitude should not necessitate a change in the fluconazole dose regimen in subjects receiving concomitant diuretics.

Alfentanil

A study observed a reduction in clearance and distribution volume as well as prolongation of T½ of alfentanil following concomitant treatment with fluconazole. A possible mechanism of action is fluconazole’s inhibition of CYP3A4. Dosage adjustment of alfentanil may be necessary.

Amitriptyline, Nortriptyline

Fluconazole increases the effect of amitriptyline and nortriptyline. 5- nortriptyline and/or S-amitriptyline may be measured at initiation of the combination therapy and after one week. Dosage of amitriptyline/nortriptyline should be adjusted, if necessary.

Amphotericin B

Concurrent administration of fluconazole and amphotericin B in infected normal and immunosuppressed mice showed the following results: a small additive antifungal effect in systemic infection with C. albicans , no interaction in intracranial infection with Cryptococcus neoformans , and antagonism of the two drugs in systemic infection with A. fumigatus. The clinical significance of results obtained in these studies is unknown.

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