In vitro comparison of the dermal penetration of three different topical formulations containing lasalocid

Background: Topical antimicrobial preparations are of utmost importance in treating suspected and confirmed meticillin-resistant Staphylococcus pseudintermedius (MRSP) infections due to the increasing incidence of widespread resistance to systemic antimicrobials. Lasalocid is active against MRSP in vitro and this may become an important topical antimicrobial for the treatment of canine pyoderma. Hypothesis/Objectives: To determine effects of various formulation types on penetration and retention of lasalocid applied to canine skin in vitro. Animals: Normal canine skin was collected from the thorax of five dogs that had been euthanized on the basis of health and/or intractable behavioural issues. Methods: Solution, lotion and ointment containing 2% lasalocid were applied to ex vivo canine skin. Transdermal penetration was assessed for a 24 h period and retention of lasalocid was assessed at the conclusion of the study. Results: The solution had significantly higher skin retention of lasalocid and proportion of applied dose retained in skin than lotion and ointment (Tukey–Kramer Honest Significant Difference test, P < 0.01). Lasalocid could not be detected in the receptor fluid of any Franz cell at any time point. Conclusions and clinical importance: Lasalocid was not identified in the receptor fluid of any sample, indicating that systemic absorption of the active ingredient in vivo is unlikely. Lasalocid may be useful in the treatment of MRSP infections if in vivo studies support safety and efficacy