Pharmacokinetics of pirazolac--a new anti-inflammatory drug--in human volunteers. I. Absorption, disposition, biotransformation and excretion.

The absorption, disposition, biotransformation and excretion of the nonsteroidal anti-inflammatory drug pirazolac were investigated in 6 volunteers (3 males, 3 females, age 50 greater than years) after intravenous and oral administration of 50 mg 14C-pirazolac as an aqueous solution of the sodium salt. Pirazolac was very rapidly and completely absorbed and bioavailable when orally administered in a dose of 50 mg in solution. Maximum pirazolac levels in plasma of 6 micrograms/ml (30% of dose in total plasma volume) were already reached after approx. 20 minutes. No metabolites were detectable in the plasma. Pirazolac was eliminated from the plasma in two phases with half-lives of 3 hours and 16 hours, respectively, regardless of administration route. After intravenous and oral administration approximately 80% of the dose was excreted with the urine and approximately 15% with the feces within 7 days, indicating a complete excretion of 14C-radioactivity. In urine, approximately 10% of the dose was identified as unchanged pirazolac and 70% as pirazolac ester glucuronide.