Transdermal Formulation Development and Topical Administration of Atenolol to Cats

Atenolol diffusion through synthetic membrane, cloned human epidermis, and cat ear skin was performed utilizing a Franz diffusion cell. Transdermal drug diffusion enhancers’ ethanol, glycerol, propylene glycol, polysorbate 80 and Dimethyl isosorbide (DMI) were added to the topical formulations and tested for their ability to enhance drug permeation through the test membranes. Topical formulation with penetration enhancers showed a rapid burst of atenolol diffusion for the first two hours (35.5 to 40 μg/ml) followed by a zero-order sustained diffusion of 2.7 μg/cm2/h of atenolol for up to twenty-four hours after application to test membranes. Increased atenolol flux through different test membranes was greatest for synthetic membrane. The topical application of the optimized atenolol formulation to cat skin containing permeation enhancers aided transdermal atenolol drug delivery to treat cats with hypertrophic obstructive cardiomyopathy. The optimum topical formulation demonstrated two fluxes through cat skin, the burst flux (15.7 μg/cm2/h) and a sustained flux (2.7 μg/cm2/h). Measured atenolol concentrations in cats at 3, 6 and 12 hours after transdermal atenolol application were 432.7 ng/ml ± 323.3, 262.4 ng/ml ± 150.1, and 253.3 ng/ml ± 133.6 respectively. Six of 7 cats achieved therapeutic serum atenolol levels (200 ng/ml) for at least one time point. Five of 7 cats had therapeutic serum atenolol concentrations 3 hours post-atenolol. At the 6 hours post-atenolol time point, Four had a therapeutic serum atenolol concentration while at 12 hours post-atenolol dosing, 4 of 7 cats had therapeutic serum atenolol concentrations. Transdermal atenolol administered at 25 mg q12h resulted in clinically therapeutic serum atenolol concentrations in the majority of healthy cats. The optimum transdermal formulation enabled good drug delivery feasible for transdermal application in a clinical trial in cats.