Percutaneous absorption of methimazole: An in vitro study of the absorption pharmacokinetics for two different vehicles

Hill, K. E., Mills, P. C., Jones, B. R., Bolwell, C. F., Aberdein, D., Chambers, J. P.Percutaneous absorption of methimazole: an in vitro study of the absorptionpharmacokinetics for two different vehicles. J. vet. Pharmacol. Therap. doi:10.1111/jvp.12213.The use of transdermal medications in cats has become popular in veterinarymedicine due to the ease of administration compared to oral medication.However, the research to support systemic absorption of drugs applied to thepinna after transdermal administration in cats is limited. The aim of thisstudy was to characterize the percutaneous absorption pharmacokinetics ofmethimazole in a lipophilic vehicle compared to methimazole in Pluroniclecithin organogel (PLO) using a finite dose applied to feline ear skin in an invitro Franz cell model. The two formulations of methimazole (10 mg) wereapplied to the inner stratum corneum of six pairs of feline ears. The receptormedium was sampled up to 30 h post–administration, and methimazole con-centrations were measured using high-performance liquid chromatography(HPLC). Histological examination of all ears was undertaken as small differ-ences in the thickness of ear skin may have contributed to inter-individualdifferences in methimazole absorption between six cats. Methimazole wasabsorbed more completely across the pinnal skin when administered in thelipophilic vehicle compared to administration in the PLO gel (P < 0.001).(Paper received 11 September 2014; accepted for publication 19 January2015)Kate E. Hill, IVABS, Massey University, Tennent Drive, Private Bag 11-222,Palmerston North 4442, New Zealand. E-mail: k.hill@massey.ac.nz