Pharmacokinetics and pharmacodynamics of clemastine in healthy horses.

The study investigates the pharmacokinetics and pharmacodynamics of the drug Clemastine in horses. The findings reveal that, although the drug shows efficacy in reducing histamine-induced skin reactions, its low oral bioavailability and short half-life render it impractical for oral administration in equine populations.

Introduction to Clemastine and It’s Study in Horses

• The research paper focuses on Clemastine, an H1 antagonist that is typically used in treating certain allergic conditions in humans.
• Though its use has been considered in horses, there has been a lack of research into the drug’s pharmacology in this animal species. To address this concern, a study was carried out to determine the basic pharmacokinetic parameters and compare the effect of the drug in inhibiting histamine-induced cutaneous wheal formation in horses.

Methodology and Results

• The study involved intravenously injecting Clemastine into six horses and observing the effects. The dosage given was 50 micrograms per kilogram body weight.
• Following the administration, the researchers reported a rapid initial decrease in the drug’s plasma concentration, subsequently followed by a terminal phase, during which the half-life of Clemastine was found to be about 5.4 hours.
• The volume of distribution was found to be quite large, with a value of 3.8 L/kg, and the total body clearance rate was clocked at 0.79 L/h kg.
• A notably low oral bioavailability of just 3.4% was observed. This means that when administered orally, only a very minimal amount of the drug gets absorbed into the body, making it essentially ineffective.
• However, there was a strong relationship between plasma concentrations and effect, with a 65% reduction in histamine-induced cutaneous wheal formations compared to when saline was injected. The duration of the effect was about five hours post intravenous dosage.

Conclusion and Recommendations

• Based on the findings, oral administration of Clemastine to horses was determined to be inappropriate due to its low bioavailability.
• If administered intravenously, the drug needs to be given at least three to four times a day to maintain effective plasma concentrations due to its short half-life.
• The study concludes that when sufficient plasma concentrations are maintained, Clemastine can effectively reduce histamine-induced wheal formations.