OBJECTIVE To determine the pharmacokinetics of florfenicol, terbinafine, and betamethasone acetate after topical application to canine auricular skin and the influence of synthetic canine cerumen on pharmacokinetics.
SAMPLE Auricular skin from 6 euthanized shelter dogs (3 females and 3 neutered males with no visible signs of otitis externa).
PROCEDURES Skin adjacent to the external opening of the ear canal was collected and prepared for use in a 2-compartment flow-through diffusion cell system to evaluate penetration of an otic gel containing florfenicol, terbinafine, and betamethasone acetate over a 24-hour period. Radiolabeled 14C-terbinafine hydrochloride and 3H-betamethasone acetate were added to the gel to determine dermal penetration and distribution. Florfenicol absorption was determined by use of high-performance liquid chromatography–UV detection. Additionally, the effect of synthetic canine cerumen on the pharmacokinetics of all compounds was evaluated.
RESULTS During the 24-hour experiment, mean ± SD percentage absorption without the presence of synthetic canine cerumen was 0.28 ± 0.09% for 3H-betamethasone acetate, 0.06 ± 0.06% for florfenicol, and 0.06 ± 0.02% for 14C-terbinafine hydrochloride. Absorption profiles revealed no impact of synthetic canine cerumen on skin absorption for all 3 active compounds in the gel or on skin distribution of 3H-betamethasone acetate and 14C-terbinafine hydrochloride.
CONCLUSIONS AND CLINICAL RELEVANCE3H-betamethasone acetate, 14C-terbinafine hydrochloride, and florfenicol were all absorbed in vitro through healthy auricular skin specimens within the first 24 hours after topical application. Synthetic canine cerumen had no impact on dermal absorption in vitro, but it may serve as a temporary reservoir that prolongs the release of topical drugs.
OBJECTIVE To investigate the cytotoxic effects of azathioprine, 6-mercaptopurine, and 6-thioguanine on canine hepatocytes.
SAMPLE Commercially available cryopreserved canine primary hepatocytes.
PROCEDURES The study consisted of 2 trials. In trial 1, hepatocytes were incubated with azathioprine, 6-mercaptopurine, or 6-thioguanine at 1 of 6 concentrations (0.468, 0.937, 1.875, 3.750, 7.500, or 15.000 μmol/L) for 24, 48, or 72 hours. At each time, cell viability and lactate dehydrogenase (LDH) activity were determined for each thiopurine-concentration combination, and alanine aminotransferase (ALT) activity was determined for cells incubated with each thiopurine at a concentration of 15 μmol/L. In trial 2, hepatocytes were incubated with azathioprine, 6-mercaptopurine, or 6-thioguanine at 1 of 3 concentrations (18.75, 37.50, or 75.00 μmol/L) for 24 hours, after which the free glutathione concentration was determined for each thiopurine-concentration combination and compared with that for hepatocytes incubated without a thiopurine (control).
RESULTS Incubation of hepatocytes with each of the 3 thiopurines adversely affected cell viability in a time- and concentration-dependent manner; however, this decrease in cell viability was not accompanied by a concurrent increase in LDH or ALT activity. Likewise, free glutathione concentration for hepatocytes incubated for 24 hours with supratherapeutic thiopurine concentrations (> 18.75 μmol/L) did not differ significantly from that of control cells.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that thiopurines adversely affected the viability of canine hepatocytes in a time- and concentration-dependent manner but had a nonsignificant effect on the LDH and ALT activities and free glutathione depletion of those hepatocytes.