[The concentration changes of different phenylbutazone formulations in horse plasma].

The research article studies how three formulations of phenylbutazone (injection, powder, and paste suspension) are distributed and absorbed in horse bodies. It provides insight into the half-life, optimal ingestion method, absorption rates, and other pharmacokinetic parameters of the drug in horses.

Methodology and Key Findings

• The study examines the absorption rate and overall pharmacokinetics of phenylbutazone, a non-steroidal anti-inflammatory drug, in various formulations in horses.
• Upon intravenous injection, the half-life of phenylbutazone was gauged to be between 6.6 to 6.7 hours.
• Oral administration via a stomach tube was found to be more efficient in terms of absorption than a direct application into the horse’s mouth.
• Among the oral formulations, the absorption rate constant of the paste suspension was markedly higher compared to the powder version.
• The maximum plasma concentrations were obtained within 0.5 to 3 hours and were found to be dose-dependent. Regardless of its dose and formulation, phenylbutazone’s elimination did not vary.

Drug Efficiency and its Clinical Implication

• Phenylbutazone’s bioavailability, the amount of the drug that reaches the systemic circulation intact, was estimated to be between 55.1 to 96.7% for the powder and paste formats. This percentage was higher when the drug was administered via a stomach tube.
• In certain horses, the absorption of the drug showed an atypical pattern, with a delayed duration suggesting that the drug might have been absorbed onto the food and later released in the large intestine.
• The least therapeutic level of 5 micrograms/ml was achieved between 0.2-0.8 hours after the drug’s administration, lasting between 8.2 to 22 hours, adjustably according to the administered dose.
• The study suggests that the paste suspension of phenylbutazone could present an alternative to horses that refuse to consume food mixed with the powder form of the drug.
• The authors also highlighted their positive clinical results using Butasan-Paste on 30 sick horses in their practice.