Transdermal absorption of four lidocaine (L) patches 5% was compared to the transdermal absorption of L cream 5% to evaluate the pharmacokinetics of the two formulations applied on the same anatomical region under dressing in eight horses. The animals were also assessed for the adequacy of analgesia after patches and cream removal, using a psychophysical method by pricking the patient?s skin to assess the response to pain according to a visual analogue scale. Horses were randomly assigned to four treatment groups: in groups I and II four L patches were applied for a period of 24 hours with and without alcohol pre-cleaning respectively; in group III, 5% L cream was applied every two hours over a period of 24 hours on the same anatomical site. Group IV was the control. No clinical side effects were noted with both formulations. L was detectable in plasma within 6 and 24 hours after patch application and the highest plasma concentrations were reached between 12 and 18 hours. The use of alcohol to pre-clean the skin appeared to reduce the transdermal drug absorption over time. The plasma drug level, after L cream application, reached the highest plasma concentration after 24 hours. Pain assessment after L patch or L cream application, revealed a decreased response when the L cream was used. The result of this study shows that there is an overall lower absorption from the L patches compared with the L cream in horses. Also the L cream treatment reduces significantly the intensity of pain quality as measured by the visual analogue scale.
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