After intravenous injection, pentazocine (Talwin) (1 mg/kg) distributed relatively slowly in the horse, with an α phase half-time of 27 minutes, and a β, or metabolic phase, terminal half-life of about 138 minutes. After intramuscular injection of 0.66 mg/kg, peak plasma levels occurred at about 30 minutes and plasma levels thereafter declined in a multi-exponential fashion with a very slow terminal half-life. About 30% of a dose of pentazocine administered to horses was eliminated in urine as a glucuronide metabolite. When analyzed for this metabolite, pentazocine was detectable for up to five days after administration. Horsemen should be aware of this prolonged 'clearance time' for pentazocine and avoid racing within six days of pentazocine administration. The opiate receptor was demonstrated in equine brain tissue with highest activity observed in the cerebrum and thalamus. Using the opiate receptor in a radio-recepotr assay type experiment for fentanyl detection, equine urine was observed to contain material which displaced (3H) morphine from the opiate receptor, which interfered with this assay. The locomotor response to opiates was quantiated by counting footsteps of horses after dosing with fentanyl and pentazocine. After intravenous administration of fentanyl, a clear-cut dose response to this drug at 20 μg/kg was observed. Pentazocine was much less effective than fentanyl in producing this motor response.
|Number of pages||8|
|Journal||Irish Veterinary Journal|
|State||Published - 1979|
ASJC Scopus subject areas
- Veterinary (all)