Vioxx

[Rofecoxib]

Cytochrome P450 plays a minor role in metabolism of rofecoxib. Inhibition of CYP 3A activity by administration of ketoconazole 400 mg daily does not affect rofecoxib disposition. However, induction of general hepatic metabolic activity by administration of the non-specific inducer rifampin 600 mg daily produces a 50% decrease in rofecoxib plasma concentrations. (Also see Drug Interactions.)

Excretion

Rofecoxib is eliminated predominantly by hepatic metabolism with little (< 1%) unchanged drug recovered in the urine. Following a single radiolabeled dose of 125 mg, approximately 72% of the dose was excreted into the urine as metabolites and 14% in the feces as unchanged drug. The plasma clearance after 12.5-and 25-mg doses was approximately 141 and 120 mL/ min, respectively. Higher plasma clearance was observed at doses below the therapeutic range, suggesting the presence of a saturable route of metabolism (i. e., non-linear elimination). The effective half-life (based on steady-state levels) was approximately 17 hours.

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Special Populations

Gender

The pharmacokinetics of rofecoxib are comparable in men and women.

Geriatric

After a single dose of 25 mg VIOXX in elderly subjects (over 65 years old) a 34% increase in AUC was observed as compared to the young subjects. Dosage adjustment in the elderly is not necessary; however, therapy with VIOXX should be initiated at the lowest recommended dose.

Pediatric

VIOXX has not been investigated in patients below 18 years of age. Race
Meta-analysis of pharmacokinetic studies has suggested a slightly (10-15%) higher AUC of rofecoxib in Blacks and Hispanics as compared to Caucasians. No dosage adjustment is necessary on the basis of race.

Hepatic Insufficiency

A single-dose pharmacokinetic study in mild (Child-Pugh score 6) hepatic insufficiency patients indicated that rofecoxib AUC was similar between these patients and healthy subjects. A pharmacokinetic study in patients with moderate (Child-Pugh score 7-9) hepatic insufficiency indicated that mean rofecoxib plasma concentrations were higher (mean AUC: 55%; mean Cmax: 53%) relative to healthy subjects. Since patients with hepatic insufficiency are prone to fluid retention and hemodynamic compromise, the maximum recommended chronic dose of VIOXX for patients with moderate hepatic insufficiency is 12.5 mg daily. (See PRECAUTIONS, Hepatic Effects and DOSAGE AND ADMINISTRATION, Hepatic Insufficiency.) Patients with severe hepatic insufficiency have not been studied.

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