Bioavailability of transdermal methimazole in a pluronic lecithin organogel (PLO) in healthy cats
Article first published online: 25 JUN 2002
Journal of Veterinary Pharmacology and Therapeutics
Volume 25, Issue 3, pages 189–193, June 2002
How to Cite
HOFFMAN, S. B. , YODER, A. R. and TREPANIER, L. A. (2002), Bioavailability of transdermal methimazole in a pluronic lecithin organogel (PLO) in healthy cats. Journal of Veterinary Pharmacology and Therapeutics, 25: 189–193. doi: 10.1046/j.1365-2885.2002.00405.x
- Issue published online: 25 JUN 2002
- Article first published online: 25 JUN 2002
Hoffman, S. B., Yoder, A. R., Trepanier, L. A. Bioavailability of transdermal methimazole in a pluronic lecithin organogel (PLO) in healthy cats. J. vet. Pharmacol. Therap.25, 189–193.
The antithyroid drug methimazole is widely used for the medical management of feline hyperthyroidism. Recently, custom veterinary pharmacies have offered methimazole in a transdermal gel containing pluronic and lecithin (PLO), with anecdotal evidence of efficacy. The purpose of this study was to determine the bioavailability, relative to i.v. and oral routes of administration, of transdermal methimazole in a PLO gel in cats. Six healthy adult cats were assigned to receive 5 mg of methimazole by the i.v., oral, or transdermal routes, in a randomized triple crossover protocol with 1 week washout between doses. Blood samples were taken for high performance liquid chromatography (HPLC) determination of serum methimazole, at 0, 5, 15, 30, 60 min, and 2, 4, 6, 12 and 24 h after dosing. Methimazole absorption following transdermal administration was poor and variable, with only two of six cats achieving detectable serum methimazole concentrations at any time point following transdermal administration. Area under the concentration–time curve (AUC), maximum concentration (Cmax), and absolute bioavailability were all significantly lower for the transdermal route (0.39 ± 0.63 μg h/mL, 0.05 ± 0.09 μg/mL, and 11.4 ± 18.7%, respectively) than for either i.v. (7.96 ± 4.38 μg h/mL, 3.34 ± 2.00 μg/mL, 100%) or oral routes (2.94 ± 1.24 μg h/mL, 0.51 ± 0.15 μg/mL, 40.4 ± 8.1%). The results of this study indicate generally low to undetectable bioavailability of methimazole in a lecithin/pluronic gel given as a single transdermal dose to healthy cats, although one individual cat did achieve nearly 100% transdermal bioavailability relative to the oral route.