Coadministration of voriconazole with the following agents results in increased exposure or is expected to result in increased exposure to these drugs. Therefore, careful monitoring and/or dosage adjustment of these drugs is needed:

Cyclosporine (CYP3A4 substrate): In stable renal transplant recipients receiving chronic cyclosporine therapy, concomitant administration of oral voriconazole (200 mg Q12h for 8 days) increased cyclosporine Cmax and AUC_τ an average of 1.1 times (90% CI: 0.9, 1.41) and 1.7 times (90% CI: 1.5, 2.0), respectively, as compared to when cyclosporine was administered without voriconazole. When initiating therapy with voriconazole in patients already receiving cyclosporine, it is recommended that the cyclosporine dose be reduced to one-half of the original dose and followed with frequent monitoring of the cyclosporine blood levels. Increased cyclosporine levels have been associated with nephrotoxicity. When voriconazole is discontinued, cyclosporine levels should be frequently monitored and the dose increased as necessary (see PRECAUTIONS - DRUG INTERACTIONS).

Methadone (CYP3A4, CYP2C19, CYP2C9 substrate): Repeat dose administration of oral voriconazole (400mg Q12h for 1 day, then 200mg Q12h for 4 days) increased the Cmax and AUC_τ of pharmacologically active R-methadone by 31% (90% CI: 22%, 40%) and 47% (90% CI: 38%, 57%), respectively, in subjects receiving a methadone maintenance dose (30-100 mg QD). The Cmax and AUC of (S)-methadone increased by 65% (90% CI: 53%, 79%) and 103% (90% CI: 85%, 124%), respectively. Increased plasma concentrations of methadone have been associated with toxicity including QT prolongation. Frequent monitoring for adverse events and toxicity related to methadone is recommended during coadministration. Dose reduction of methadone may be needed (see PRECAUTIONS - DRUG INTERACTIONS).

Short Acting Opiates (CYP3A4 substrate): In an independent publication, steady-state administration of oral voriconazole significantly increased the AUC∞ of a single dose of alfentanil by 6-fold. Reduction in the dose of alfentanil and other short acting opiates metabolized by CYP3A4 (e.g., sufentanil) should be considered when co-administered with voriconazole (see PRECAUTIONS – DRUG INTERACTIONS). As the half-life of alfentanil is prolonged in a 4-fold manner when alfentanil is coadministered with voriconazole, a longer respiratory monitoring period may be necessary.

Tacrolimus (CYP3A4 substrate): Repeat oral dose administration of voriconazole (400 mg Q12h x 1 day, then 200 mg Q12h x 6 days) increased tacrolimus (0.1 mg/kg single dose) Cmax and AUC_τ in healthy subjects by an average of 2-fold (90% CI: 1.9, 2.5) and 3-fold (90% CI: 2.7, 3.8), respectively. When initiating therapy with voriconazole in patients already receiving tacrolimus, it is recommended that the tacrolimus dose be reduced to one-third of the original dose and followed with frequent monitoring of the tacrolimus blood levels. Increased tacrolimus levels have been associated with nephrotoxicity. When voriconazole is discontinued, tacrolimus levels should be carefully monitored and the dose increased as necessary (see PRECAUTIONS - DRUG INTERACTIONS).

Warfarin (CYP2C9 substrate): Coadministration of voriconazole (300 mg Q12h x 12 days) with warfarin (30 mg single dose) significantly increased maximum prothrombin time by approximately 2 times that of placebo in healthy subjects. Close monitoring of prothrombin time or other suitable anticoagulation tests is recommended if warfarin and voriconazole are coadministered and the warfarin dose adjusted accordingly (see PRECAUTIONS - DRUG INTERACTIONS).

Oral Coumarin Anticoagulants (CYP2C9, CYP3A4 substrates): Although not studied in vitro or in vivo, voriconazole may increase the plasma concentrations of coumarin anticoagulants and therefore may cause an increase in prothrombin time. If patients receiving coumarin preparations are treated simultaneously with voriconazole, the prothrombin time or other suitable anti- coagulation tests should be monitored at close intervals and the dosage of anticoagulants adjusted accordingly (see PRECAUTIONS - DRUG INTERACTIONS).

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