Pharmacokinetic Evaluations of Sulpiride After Intravenous, Intramuscular, and Oral Single-Dose Administration in Jennies (Equus asinus)

Sulpiride is an antipsychotic human drug. It is commonly used to encourage ovulation in
noncycling mares and to stimulate lactation in adoptive mares. No pharmacokinetic data
are available for donkeys. The aim of this study was to assess the pharmacokinetics profile
of sulpiride after intravenous (IV), intramuscular (IM), and oral (PO) administrations in
healthy jennies. Animals (n ¼ 6) were treated with sulpiride, 1 mg/kg by IV, IM, and PO
routes according to a randomized cross-over design (3 3 Latin square). Blood samples
(5 mL) were collected at predetermined times and analyzed using a validated high performance
liquid chromatography with fluorescence detection method. IV and IM administrations
gave similar curves, but they were not bioequivalent. The IM average
bioavailability was 73.5%. After PO administration, the drug plasma concentrations were
low and consequently both area under the curve and bioavailability (9.4%) were low. This
finding could be because of the physicochemical features of the drug. Indeed, considering
that sulpiride is a weak base, existing in the ionized form at gastric and physiological pH, it
is unsurprising that it is poorly absorbable, especially in equine species whose gastric pH is
particularly acidic. In conclusion, injective routes are definitely preferable to PO dosing
because of the very low F% via this route.