Pharmacokinetics and cardio-respiratory effects of oral theophylline in exercised horses.

The researchers investigated the effects and behavior of the drug theophylline on exercised horses, uncovering key facts about its absorption, distribution, and impact on cardio-respiratory responses. There were significant changes in heart rate and blood lactate levels, and while no severe side effects were noted, individual variations in response suggest dosage adjustments may be needed.

Pharmacokinetics of Theophylline at Rest and During Exercise

• The research assessed the pharmacokinetics of theophylline in healthy Standardbred horses. This involves determining how the drug is absorbed, distributed, metabolized, and eliminated by the body.
• Every 12 hours, a dosage of 5mg/kg body weight was administered orally. The researchers analyzed the plasma concentrations of theophylline to confirm the predictions about its behavior in the body.
• The average half-life of theophylline’s elimination was approximately 17 hours, while its absorption was much faster, with a half-life of about 1.6 hours.
• The study also measured the volume of distribution (how well the drug spreads throughout the body) and the plasma clearance rate, both of which help to understand the drug’s behavior and implications for dose scheduling.

Effect of Theophylline on Cardio-Respiratory Responses

• The study observed significant increases in heart rate and blood lactate levels during and after exercise when the horse was under theophylline treatment.
• In addition, there was an increase in arterial oxygen tension after exercise, indicating improved oxygen uptake.
• Arterial carbon dioxide values both before and after exercise were notably lower than the values measured before the drug was administered, suggesting an effect of theophylline on respiration.
• No severe side effects of theophylline were observed, but due to inter-individual variation, some horses may require a different dose from the recommended 5 mg/kg every 12 hours.

Ideal Dose and Potential Impacts on Performance

• From the findings, the study concludes that a regular oral dose of 5mg/kg every 12 hours provides the desired cardio-respiratory effects without causing severe adverse effects.
• Nevertheless, possible variations in individual horses’ responses to the drug mean that some horses might need a different dosage.
• Importantly, the effects of theophylline on exercise parameters suggest that the drug could impair the performance capacity of a healthy horse, although further research would be needed to confirm and fully understand this impact.