This study aimed to investigate pharmacokinetics of fluoxetine in horses and validate a method for liquid chromatography mass spectrometry analysis of serum levels. Fluoxetine pharmacokinetics were determined using 10 healthy, adult horses. Fluoxetine pharmacokinetics following a single oral dose (0.25 mg/kg) were determined using blood samples collected prior to and at several time points over 7 days following administration. Serum concentrations of fluoxetine and its bioactive metabolite norfluoxetine were measured using liquid chromatography coupled to an accurate mass/high-resolution mass spectrometer. Pharmacokinetic parameters were estimated using a noncompartmental model. Time to maximum serum concentration and serum half-life of fluoxetine was 1.5 and 15.6 h, respectively. Steady-state serum concentrations were evaluated using five horses each receiving fluoxetine (0.25 mg/kg, PO, q24hrs) for 8 weeks and were found to be 62.9 ± 25.5 ng/ml on average. Norfluoxetine was not detected in any sample.
Keywords: SSRI; fluoxetine; horse; liquid chromatography; mass spectrometry.
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