Isometamidium in pigs : disposition kinetics, tissue residues and adverse reactions

The disposition and adverse effects of the anti-trypanosomal drug isometamidium in pigs were evaluated. Following intramuscular administration of the drug at doses of 0.5, 15 and 35 mg kg-1, the drug was rapidly absorbed within 15 to 30 minutes to reach maximum plasma concentrations of 12 to 477 (n = 6), 302 to 655 (n = 4) and 1620 (n = 1) ng ml-1, respectively. No drug was detectable in plasma (less than 5 ng ml-1) 24 hours after drug administration at the three doses used. The half-lives of disappearance of the drug from plasma during the terminal phase were 7.12 h for the pigs given a dose of 15 mg kg-1, and 7.20 h for the pig which received a dose of 35 mg kg-1. At all the intramuscular injection sites, high drug concentrations were found six weeks after administration. The most dramatic adverse reactions observed were: one death after intramuscular administration at a dose of 35 mg kg-1 to two animals, and two deaths after intravenous administration at a dose of 2 mg kg-1 to two animals. For all these cases, the immediate cause of death was acute cardiovascular collapse. Biochemical analyses and gross and histological examinations showed that the animals that tolerated the high doses of 15 and 35 mg kg-1 given intramuscularly had extensive and severe tissue damage at the injection sites. Significant increases in plasma gamma-glutamyltransferase and alanine aminotransferase following drug administration suggested a degree of hepatobiliary damage.