Identification of an N-oxide as the major metabolite of the analgesic O-(diethylaminoethyl)-4-chlorobenzaldoxime hydrochloride in dogs.

1. After oral administration to dogs of the analgesic O-(diethylaminoethyl)-4-chloro[7-14C]benzaldoxime hydrochloride together with piperazine hydrochloride (2:1, w/w), at a dose of 4.5 mg/kg, the radioactivity was well absorbed and rapidly excreted. During 5 days, 81 percent of the dose (ca. 50 percent in 12 h) was excreted in urine and 10 percent in faeces. 2. Rates and routes of excretion of radioactivity were not altered in animals pre-treated with the drug for fourteen days. 3. Peak mean plasma concentrations of radioactivity (5.5 microgram equiv./ml) occurred at 90 min after an oral dose and were higher than those at 2 min following an equivalent intravenous (3.4 microgram equiv./ml) or rectal (4.0 microgram equiv./ml) dose which gave a max. at 45 min. 4. The drug was rapidly and extensively metabolized and no unchanged drug was detected in the plasma or urine. The major urinary metabolite was the N-oxide of the parent compound accounting for 34 percent and 23 percent dose excreted in the urine of males and females respectively during 12 h after administration.