Pharmacokinetic studies of cimetidine hydrochloride in adult horses.

This research paper investigates the pharmacokinetics of the drug cimetidine, a medication used to treat gastric and duodenal ulcer disease, in adult horses. The study found that oral absorption of cimetidine appeared variable and slow, with dosage recommendations offered based on the desired average steady state plasma concentration.

Method of Study

• In this research, the adult horses were administered cimetidine either intravenously at a dose of 3.3 mg/kg or orally at doses of 3.3 mg/kg and 10 mg/kg.
• The plasma concentrations of cimetidine after oral administration at the lower dose were too low to measure.

Results of Intravenous Administration

• After intravenous administration, cimetidine showed two-compartment characteristics with a half-life (t1/2) varying between individuals.
• The total body clearance rate (how quickly the drug is removed from the body) was calculated to be 0.443 +/- 0.160 litre/h/kg and the mean residence time (the average time the drug stays in the body) was 2.74 +/- 1.11 hours.
• The volume of distribution (Vss) and the volume of the central compartment (Vc) were also identified, revealing how the drug spreads throughout the body’s tissues.

Results of Oral Administration

• The researchers found that after a single oral dose of 10 mg/kg, the peak plasma concentration occurred at approximately 1.4 hours.
• Oral absorption of cimetidine varied among individual horses and overall was slow, with an extent of absorption of 0.296 +/- 0.183 and a mean residence time for absorption of 1.99 +/- 0.79 hours.
• These measurements showed that the oral absorption was less effective in horses than in humans.

Conclusions and Recommendations

• Based on a desired average steady state plasma concentration of 1.0 microgram/ml, dosages of 11.0 mg/kg/day intravenously and 48 mg/kg/day orally are suggested for adult horses.
• The findings suggest that dosages in horses need to be adjusted to achieve effective treatment outcomes due to the slow and variable oral absorption observed in the study.