Pharmacokinetics and bioavailability of theophylline in horses.

This research investigates the absorption, distribution, and elimination of the drug theophylline in horses. After being given intravenously and digestion, theophylline quickly distributed in the horse’s body, then eliminated at a slower rate. The proposed dosage of theophylline for horses is 5mg/kg every 12 hours.

Research Methodology

• The researchers explored the pharmacokinetics – how the body absorbs, distributes, metabolizes, and excretes drugs – and bioavailability – the extent and rate at which a drug is absorbed into a living system and becomes available at the site of physiological activity – of theophylline in horses.
• Theophylline was administered to horses in doses equivalent to 15 and 10 mg/kg theophylline base, via two routes: intravenous (direct into the bloodstream) and intragastric (within the stomach).

Theophylline Distribution and Elimination

• After administration of theophylline, a quick distribution phase with a half-life of 15-30 minutes was observed. The half-life of a drug refers to the time taken by the body to reduce the concentration of the drug by half. This quick phase was followed by a slower elimination phase, where the drug is removed from the body with an average half-life of 15-17 hours.
• The apparent volume of distribution, a hypothetical volume that a drug would need to distribute throughout the body to provide the same concentration as in the blood, was on average 850-900 milliliters per kilogram.

Absorption of Theophylline and Dosage Recommendation

• Theophylline, administered as aminophylline solution, was rapidly and completely absorbed from the horse’s digestive tract, suggesting a high degree of bioavailability.
• Basing on the observed bioavailability and pharmacokinetics, the researchers proposed an intragastric dosage regimen for aminophylline (the drug theophylline is delivered in) consisting of an administration of 5 mg/kg every 12 hours. This dosage was expected to maintain plasma theophylline concentrations within the therapeutic range thus ensuring an optimal treatment benefit.