Pharmacokinetics and Pharmacodynamics of Gabapentin in Horses: A Potentially Useful Analgesic Agent for the Treatment of Laminitis

Take Home Message 

Gabapentin (20 mg/kg) caused no major adverse effects in normal horses. Although the oral bioavailability is low, gabapentin is worthy of evaluation as an analgesic therapy for laminitis.

Introduction 

There is evidence of a neuropathic pain component to chronic equine laminitis1. Gabapentin has analgesic effects in neuropathic pain states. The aim of this study was to characterize the pharmacokinetics and pharmacodynamics of gabapentin in normal horses.

Materials and Methods 

Gabapentin (20 mg/kg) was administered orally (PO) or by intravenous (IV) infusion to 6 horses using a randomised crossover design. Plasma gabapentin concentrations were measured for 48 h. Blood pressure, ECG, and sedation scores, as well as quantitative measures of behaviour were recorded for 12 h after administration. Parametric and non-parametric statistical analyses were used to evaluate differences.

Results 

The IV pharmacokinetics were best described by a 3-compartment mammillary model; the maximum plasma concentration (Cmax) was 73.0 (66.2-76.3) mg/ml [median (range)] and terminal elimination half-life was 8.5 (7.1-13.3) h. After PO gabapentin Cmax was 3.75 (1.9-5.8) mg/ml, and terminal elimination half-life was 7.7 (6.7-11.9) h. The fractional absorption was 16.2±2.8%. There was no significant effect on cardiovascular parameters. Sedation scores were increased during the first hour after IV infusion (P < 0.05).

Discussion 

There were no major adverse effects noted after single dose IV or PO gabapentin. Bioavailability was only16% following PO administration.

Clinical Relevance 

Inability to control pain and subsequent euthanasia is the most common cause of treatment failure in laminitis cases. Gabapentin may be a useful analgesic agent in the treatment of laminitis.

Conclusion 

Gabapentin was safe and well tolerated. Further research is required to establish a dosage that will provide effective analgesia in horses with laminitis and to determine if combinations with other agents create an enhanced effect.

1. Jones E, et al. Neuropathic changes in equine laminitis pain. Pain 2007;132(3):321–331.