Pharmacokinetic profile and behavioral effects of gabapentin in the horse.

This research investigated the pharmacokinetic profile and cardiovascular and behavioral impacts of administering gabapentin, a drug that is increasingly being used in horses but whose effects are not yet fully understood, to six horses. It was found that gabapentin was well tolerated by horses, although it had poor absorption when administered orally, and led to increased sedation and changes in behavior.

Study Design

• The researchers used a randomized crossover design for the study, involving six horses. They administered Gabapentin to each horse either intravenously (i.v.) or orally (p.o.).
• They collected plasma samples from the horses over a period of 48 hours after the drug was administered and analyzed the concentration of gabapentin using liquid chromatography-tandem mass spectrometry.
• In addition, they recorded the horses’ blood pressures and ECG, and assessed their level of sedation for 12 hours following gabapentin dosage.

Pharmacokinetics of Gabapentin in Horses

• After administering the drug intravenously, they found the reduction of drug level over time could be described by a 3-compartment mammillary model, a model used in pharmacology to represent the distribution of a drug in the body.
• The terminal elimination half-life, which is time needed to reduce the drug concentration to half its initial value in the terminal phase, was between 7.1 to 13.3 hours for intravenous administration, and between 6.7 to 11.9 hours for oral administration.
• The average oral bioavailability, which is the proportion of the drug that enters the circulation when introduced into the body and so is able to have an active effect, of gabapentin was found to be only 16.2 ± 2.8%, suggesting relatively poor absorption of the drug after it is administered orally to horses.

Behavioural and Cardiovascular Effects

• The research found that gabapentin caused a significant increase in sedation in horses for one hour after an intravenous dose.
• Their behavior also changed, with the horses drinking more frequently and resting while standing for shorter periods of time with intravenous gabapentin.
• Both the intravenous and orally administered doses were well-tolerated by the horses, with no significant changes in blood pressure and ECG.