Voriconazole (Page 10 of 19)

Patients at Risk of Aspergillosis

The observed voriconazole pharmacokinetics in patients at risk of aspergillosis (mainly patients with malignant neoplasms of lymphatic or hematopoietic tissue) were similar to healthy subjects.

Drug Interaction Studies

Effects of Other Drugs on Voriconazole

Voriconazole is metabolized by the human hepatic cytochrome P450 enzymes CYP2C19, CYP2C9, and CYP3A4. Results of in vitro metabolism studies indicate that the affinity of voriconazole is highest for CYP2C19, followed by CYP2C9, and is appreciably lower for CYP3A4. Inhibitors or inducers of these three enzymes may increase or decrease voriconazole systemic exposure (plasma concentrations), respectively.

The systemic exposure to voriconazole is significantly reduced or is expected to be reduced by the concomitant administration of the following agents and their use is contraindicated:

Rifampin (Potent CYP450 Inducer)

Rifampin (600 mg once daily) decreased the steady state C max and AUC τ of voriconazole (200 mg every 12 hours x 7 days) by an average of 93% and 96%, respectively, in healthy subjects. Doubling the dose of voriconazole to 400 mg every 12 hours does not restore adequate exposure to voriconazole during coadministration with rifampin. Coadministration of voriconazole and rifampin is contraindicated [see Contraindications (4) and Warnings and Precautions (5.13)] .

Ritonavir (Potent CYP450 Inducer; CYP3A4 Inhibitor and Substrate)

The effect of the coadministration of voriconazole and ritonavir (400 mg and 100 mg) was investigated in two separate studies. High-dose ritonavir (400 mg every 12 hours for 9 days) decreased the steady state C max and AUC τ of oral voriconazole (400 mg every 12 hours for 1 day, then 200 mg every 12 hours for 8 days) by an average of 66% and 82%, respectively, in healthy subjects. Low-dose ritonavir (100 mg every 12 hours for 9 days) decreased the steady state C max and AUC τ of oral voriconazole (400 mg every 12 hours for 1 day, then 200 mg every 12 hours for 8 days) by an average of 24% and 39%, respectively , in healthy subjects. Although repeat oral administration of voriconazole did not have a significant effect on steady state C max and AUC τ of high-dose ritonavir in healthy subjects, steady state C max and AUC τ of low-dose ritonavir decreased slightly by 24% and 14% respectively, when administered concomitantly with oral voriconazole in healthy subjects. Coadministration of voriconazole and high-dose ritonavir (400 mg every 12 hours) is contraindicated. Coadministration of voriconazole and low-dose ritonavir (100 mg every 12 hours) should be avoided, unless an assessment of the benefit/risk to the patient justifies the use of voriconazole [see Contraindications (4) and Warnings and Precautions (5.13)] .

St. John’s Wort (CYP450 Inducer; P-gp Inducer)

In an independent published study in healthy volunteers who were given multiple oral doses of St. John’s Wort (300 mg LI 160 extract three times daily for 15 days) followed by a single 400 mg oral dose of voriconazole, a 59% decrease in mean voriconazole AUC 0-∞ was observed. In contrast, coadministration of single oral doses of St. John’s Wort and voriconazole had no appreciable effect on voriconazole AUC 0-∞ . Because long-term use of St. John’s Wort could lead to reduced voriconazole exposure, concomitant use of voriconazole with St. John’s Wort is contraindicated [see Contraindications (4)] .

Carbamazepine and Long-acting Barbiturates (Potent CYP450 Inducers)

Although not studied in vitro or in vivo , carbamazepine and long-acting barbiturates (e.g., phenobarbital, mephobarbital) are likely to significantly decrease plasma voriconazole concentrations. Coadministration of voriconazole with carbamazepine or long-acting barbiturates is contraindicated [see Contraindications (4) and Warnings and Precautions (5.13)] .

Significant drug interactions that may require voriconazole dosage adjustment, or frequent monitoring of voriconazole-related adverse events/toxicity:

Fluconazole (CYP2C9, CYP2C19 and CYP3A4 Inhibitor)

Concurrent administration of oral voriconazole (400 mg every 12 hours for 1 day, then 200 mg every 12 hours for 2.5 days) and oral fluconazole (400 mg on day 1, then 200 mg every 24 hours for 4 days) to 6 healthy male subjects resulted in an increase in C max and AUC τ of voriconazole by an average of 57% (90% CI: 20%, 107%) and 79% (90% CI: 40%, 128%), respectively. In a follow-on clinical study involving 8 healthy male subjects, reduced dosing and/or frequency of voriconazole and fluconazole did not eliminate or diminish this effect. Concomitant administration of voriconazole and fluconazole at any dose is not recommended. Close monitoring for adverse events related to voriconazole is recommended if voriconazole is used sequentially after fluconazole, especially within 24 hours of the last dose of fluconazole [see Warnings and Precautions (5.13)] .

Minor or no significant pharmacokinetic interactions that do not require dosage adjustment:

Letermovir (CYP2C9/2C19 Inducer)

Coadministration of oral letermovir with oral voriconazole decreased the steady state C max and AUC 0-12 of voriconazole by an average of 39% and 44%, respectively [see Drug Interactions (7)] .

Cimetidine (Non-specific CYP450 Inhibitor and Increases Gastric pH)

Cimetidine (400 mg every 12 hours x 8 days) increased voriconazole steady state C max and AUC τ by an average of 18% (90% CI: 6%, 32%) and 23% (90% CI: 13%, 33%), respectively, following oral doses of 200 mg every 12 hours x 7 days to healthy subjects.

Ranitidine (Increases Gastric pH)

Ranitidine (150 mg every 12 hours) had no significant effect on voriconazole C max and AUC τ following oral doses of 200 mg every 12 hours x 7 days to healthy subjects.

Macrolide Antibiotics

Coadministration of erythromycin (CYP3A4 inhibitor; 1 gram every 12 hours for 7 days) or azithromycin (500 mg every 24 hours for 3 days) with voriconazole 200 mg every 12 hours for 14 days had no significant effect on voriconazole steady state C max and AUC τ in healthy subjects. The effects of voriconazole on the pharmacokinetics of either erythromycin or azithromycin are not known.

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