Prothipendyl: detection and elimination in the horse–a case report.

This study focused on the detection and elimination of the neuroleptic drug prothipendyl in racehorses where it is suspected of being illegally administered at low doses to enhance performance. It specifically examined its elimination from blood and urine in a standard-bred mare, how its effects varied between subtherapeutic and therapeutic doses, and how effectively it could be detected in blood and urine via gas chromatography-mass spectrometry (GC-MS).

Study Methodology

Experiments were carried out using a standard-bred mare, to whom prothipendyl was administered intravenously:

• A low (subtherapeutic) dose of 0.24 mg/kg resulted in the horse appearing less excited, though its locomotor activity and attention appeared to remain unaffected.
• A therapeutic dose of 1 mg/kg resulted in the noticeable effects of sedation and ataxia (lack of voluntary coordination of muscle movements) in the horse.

Detection of Prothipendyl in Blood and Urine

Gas chromatography-mass spectrometry (GC-MS) was used to identify prothipendyl in the horse’s bloodstream:

• At the lower dose, the drug could only be detected in the blood using this method.
• At the therapeutic dose, prothipendyl was detected in both blood and urine.

In order to quantify the amount of the drug, triflupromazine was used as an internal standard. The mass spectrometer was operated in the selected ion monitoring (SIM) mode. The detection limit under these conditions was found to be 10 ng/ml of body fluid.

Elimination of Prothipendyl from Blood

The rate at which prothipendyl was eliminated from the horse’s bloodstream was measured. The half-life (t1/2) of the drug was found to be 2.4 hours.

Conclusions

Based on these results, the researchers concluded that when testing for prothipendyl use in horses, blood screening appears to be more effective than urine testing, as the drug was not found in urine following the administration of subtherapeutic doses.