The pharmacokinetics and absolute bioavailability of selegiline in the dog

Selegiline is beneficial to Parkinsonian patients as an adjunct to levodopa therapy. Currently no pharmacokinetic data are available for selegiline in the literature, mainly due to lack of analytical methods that can measure concentrations below 10 ng mL-1 in plasma. A sensitive fluorimetric assay based on inhibition of rat brain monoamine oxidase-B (MAO-B) in vitro has been developed to measure selegiline in plasma as low as 0.25 ng mL-1. The pharmacokinetics of selegiline were investigated following intravenous and oral administration to four female mongrel dogs. Each dog received 1 mg kg-1 selegiline in solution via gavage or by an intravenous route separated by one week. The mean terminal half-life, volume of distribution of the central compartment, and systemic clearance of selegiline were 60.24 +/- 9.56 min, 6.56 +/- 0.56 L kg-1, and 159.91 +/- 19.28 mL min-1 kg-1, respectively. After oral administration selegiline appeared to be absorbed rapidly with a tmax and Cmax of 25 +/- 5.8 min and 5.2 +/- 1.36 ng mL-1, respectively. The absolute bioavailability of selegiline in the dog was 8.51 +/- 3.31%.