title: Physiological disposition and metabolism of timolol in man and laboratory animals.
abstract: Timolol [3-(3-tert.-butylamino-2-hydroxypropoxy)-4-morpholino-1,2,5-thiadiazole], was rapidly absorbed, metabolized, and effectively excreted in man, rats, and dogs. Peak plasma levels of timolol-14C were observed in these species 1-2 hr after oral administration. Generally, less than 20% of the radioactivity was present in the plasma in the unmetabolized form. The intact drug had a plasma half-life of 28 min in the rat, 48 min in the dog, and 5.5 hr in man. After oral administration of timolol-14C to humans approximately 72% of the dose was excreted in 84 hr, with 66% in the urine and 6% in the feces. In the rat, 58% of an oral dose was excreted in the urine and 26% in the feces. The dog excreted 68% of an oral dose in the urine and 19% in feces in 72 hr. Following intravenous administration, rats excreted 50% in the urine and 28% in the feces, which suggests that extensive biliary excretion occurred. Timolol was extensively metabolized. Approximately 50% of the radioactivity was identified in dog urine as the lactic acid metabolite. An additional metabolite was tentatively identified as the 3-oxomorpholino derivative of timolol. Approximately 20% of the dose in man was excreted in the urine unchanged. Two metabolites, resulting from cleavage of the morpholine ring, were identified as 1-tert-butylamino-3-[4-(2-hydroxyethylamino)-1,2,5-thiadiazol-3-xloxyl-2-propanol, accounting for 10% of the urine radioactivity, and t-tert-butylamino-[4-(N-2-hydroxyethylglycolamido)-1,2,5-thiadiazol-3-yloxy]-2-propanol, accounting for 30%. A minor metabolite, resulting from hydroxylation of a terminal methyl group, accounted for an additional 3% of the urine radioactivity.
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D002849:Chromatography, Gas; D003377:Countercurrent Distribution; D004285:Dogs; D004590:Electrophoresis, Paper; D006801:Humans; D008297:Male; D013058:Mass Spectrometry; D011412:Propanolamines / Q000097:blood / Q000378:metabolism* / Q000652:urine; D051381:Rats; D013045:Species Specificity; D013830:Thiadiazoles / Q000097:blood / Q000378:metabolism / Q000652:urine
chemical_list: D002250:Carbon Radioisotopes; D011412:Propanolamines; D013830:Thiadiazoles