The plasma concentrations of mebendazole and its metabolites have been monitored in twelve patients after receiving a 10 mg/kg dose for cystic hydatid disease. The mebendazole plasma concentration-time profiles differed considerably between patients; elimination half-lives ranged from 2.8-9.0 h, time to peak plasma concentration after dosing ranged from 1.5-7.25 h and peak plasma concentrations ranged from 17.5 to 500 ng/ml. The mean peak plasma concentration of mebendazole after an initial dose (69.5 ng/ml) was lower than found in patients during chronic therapy (137.4 ng/ml). The plasma AUCTS for the major metabolites of mebendazole (methyl 5-(alpha-hydroxybenzyl)-2-benzimidazole carbamate and 2-amino-5 benzoylbenzimidazole) were about five times the plasma AUCT found for mebendazole in patients on chronic therapy. It is suggested that the slower clearance of these polar metabolites relative to mebendazole results from enterohepatic recycling. Since mebendazole is also highly plasma protein bound, caution should be observed in administering mebendazole to patients with liver disease. Concentrations of mebendazole found in the tissue and cyst material collected from two patients during surgery ranged from 59.5 to 206.6 ng/g wet weight.
The majority (85%) of 394 monarch butterflies sampled from overwintering sites in Mexico contain the same epoxy cardenolide glycosides, including most conspicuously a novel polar glycoside with a single genin-sugar bridge (aspecioside), as occur in the milkweedsAsclepias speciosa andA. syriaca. This cardenolide commonality was established by isolating aspecioside and syriobioside from the wings of overwintering monarchs and the two plant species, and comparing Chromatographie and NMR spectrometric characteristics of the isolates. When combined with the migratory pattern of monarchs and the distribution of these two milkweed species, this chemical evidence lends strong support to the hypothesis thatA. syriaca is the major late summer food plant of monarchs in eastern North America. This finding may be of ecological importance, forA. syriaca contributes less cardenolide and cardenolides of lower emetic potency to monarchs than most milkweeds studied to date.
1 Five volunteers, whose ages ranged between 37 and 64 years, took part in a crossover study to determine the pharmacokinetics and bioavailability of mebendazole in man following intravenous and oral administration of a tracer dose of [3H]-mebendazole. 2 Following intravenous administration, the average distribution half-life, elimination half-life and rate of clearance were 0.20 h, 1.12 h, and 1.063 min respectively. 3 After oral administration of the solution, the average elimination half-life was 0.93 h, the apparent rate of clearance was 0.846 /min, the average time to peak plasma concentration was 0.42 h, and the bioavailability of mebendazole was 22%. 4 Comparison of metabolite area under the plasma concentration vs time data from each route of administration indicates that absorption of mebendazole from the gastrointestinal tract at this dose level is almost complete. The low bioavailability observed following oral administration at this dose level is postulated to be due to high first pass elimination. 5 Approximately half of the administered dose of radioactivity following intravenous and oral administration was detected in the urine, and the major unconjugated metabolite of mebendazole was found to be 2-amino-5(6) [ot-hydroxybenzyl]benzimidazole (IV), not 2-amino-5(6)benzoylbenzimidazole (II), as previously reported.
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