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The efficacy of ketoconazole in dogs with PDH is debatable. A marked reduction in the serum cortisol concentration can occur within 30 minutes of administration and lasts from eight to 12 hours. In a single small study, 81% of dogs with PDH attained complete remission with ketoconazole.32 However, anecdotal evidence suggests the efficacy may be lower. In a survey of internists and dermatologists, most thought ketoconazole was effective in less than 25% of dogs with PDH.11 Only one of seven surveyed considered the efficacy of ketoconazole similar to that of mitotane.11 Treatment failure has been associated with poor bioavailability of orally administered ketoconazole.32 Assessing serum drug concentrations can differentiate between animals with poor intestinal absorption and those with true treatment failure.32