Metabolism of triamcinolone acetonide-21-phosphate in dogs, monkeys, and rats

The absorption, distribution and metabolic fate of triamcinolone acetonide-14C-21-phosphate were studied in the dog, monkey, and rat. A comparison of levels of radioactivity in blood or plasma, reached after intramuscular or intravenous administration, indicated that the drug was completely absorbed from the site of intramuscular injection within 10-15 min in all three species. Within 1-5 min after intramuscular or intravenous administration, the 21-phosphate ester was completely hydrolyzed to triamcinolone acetonide, which was present in the blood. The radioactivity was eliminated rapidly (t1/2 = 1-2 hr) from plasma (dogs, monkeys, and rats) and tissues (rats) after intramuscular or intravenous administration. In the three species, the major route of excretion was via the bile; however, the ratio of biliary to urinary excretion among the species varied considerably (from 1.5 to 15). In rats, excretion of radioactivity as expired carbon dioxide accounted for only 2-3 percent of the dose. 6beta-Hydroxytriamcinolone acetonide was the major metabolite in urine of the three species. Hydrolytic cleavage of the acetonide group did not appear to be significant.