Effect of drug formulation and feeding on the pharmacokinetics of orally administered quinidine in the horse.

The study focuses on how different formulations of the drug quinidine and feeding conditions affect the drug’s absorption in horses. It reveals that different formulations of orally administered quinidine, along with feeding, greatly influence the drug’s pharmacokinetics, with an oral solution preferred due to its consistent bioavailability.

Objective and Methodology

• The research examined the influence of two quinidine formulations (an oral solution and an oral suspension paste) and feeding conditions (fed and non-fed conditions) on the drug’s pharmacokinetics in horses.
• Quinidine is a medication commonly used for treating heart arrhythmias in horses.
• Nine horses were studied, receiving multiple administrations of quinidine under varying conditions. A loading dose and maintenance dose were used at set intervals.

Findings

• The study found that the bioavailability of the oral solution under fed conditions compared to non-fed conditions was 75.0 +/- 10.2% for the loading dose and 97.18 +/- 31.66% after the fourth dose.
• No values for the bioavailability of the paste formulation were provided because steady-state levels were not achieved, indicating inconsistent absorption levels with this formulation.
• There was a considerable variation in plasma quinidine levels when the paste formulation was administered. This inconsistency raises concerns about the reliability of the paste version in delivering the necessary drug levels.
• The study also found that feeding conditions significantly impacted the maximum concentration (Cmax) values after the administration of the loading dose. However, the time it took to reach the maximum concentration (Tmax) was not affected by food intake.

Conclusion

• The researchers concluded that an oral solution of quinidine should be preferred over the paste formulation. This preference is due to the inconsistent bioavailability from the paste formulation and its poor acceptability by the horse.
• The findings may provide valuable information for manufacturers to improve their drug production and for veterinary practitioners in prescribing the most effective form of medication.