Studies on metabolism of prazepam. IV. Metabolic fate of prazepam in monkeys

Kabuto, S.; Tamaki, T.; Koide, T.; Ishihama, H.

Yakugaku Zasshi Journal of the Pharmaceutical Society of Japan 98(7): 944-949


ISSN/ISBN: 0031-6903
PMID: 101652
DOI: 10.1248/yakushi1947.98.7_944
Accession: 068520741

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Metabolism of orally administered [5-14C] prazepam, a muscle relaxant, was investigated in cynomolgus monkeys. The radioactivity in the plasma reached a peak level at 3-6 h after dosing, and thereafter declined gradually with a half-life of about 21 h. Major metabolites in the plasma were dealkylprazepam (DPZ), 3-hydroxyprazepam (3-HPZ) glucuronide and oxazepam (OX) glucuronide. These glucuronides were rapidly excreted and DPZ accounted for more than 70% of the total plasma metabolites after 12 h. More than 70% of the radioactivity were excreted mostly in the urine within 3 days. Major metabolites in the urine were OX glucuronide and 3-HPZ glucuronide. The amount of these glucuronides did not decrease markedly until 48 h after dosing. 4'-Hydroxydealkylprazepam sulfate accounted for only 2-4% of the total urinary metabolites. A very small amount of prazepam (PZ) was detected in the plasma and urine. Most of fecal metabolites was unabsorbed PZ, which indicated that the fecal excretion via bile had little significance in monkeys. The PZ metabolism in the monkey resembled that in man, though the rate of metabolism in the monkey was faster than that in man.