Pharmacokinetics and Metabolism of the New Analgesic Meptazinol in Rats and Patas Monkeys

1. The absorption of meptazinol following oral administration to rats and monkeys was extensive, 63-88% of the administered dose being recovered in the urine. However, the rate of absorption was slower in the monkey than that in the rat. 2. Distribution studies showed higher concentrations of unchanged drug in tissues and plasma of rats than in those of monkeys after the same dosage. 3. Elimination of the drug from plasma occurred rapidly in both species. The major route of excretion was the urine, over 60% of the dose appearing in the 0-24 h collection. 4. Metabolism of the drug was extensive, less than 6% being excreted unchanged by either rats or monkeys. The major route of biotransformation in both species was conjugation of parent drug with glucuronic acid. Only male rats exhibited demethylation of the drug.