Relative potency of pregabalin, gabapentin, and morphine in a mouse model of visceral pain

Purpose

Pregabalin is probably more effective than prototype gabapentin in different kinds of pain treatments. This study was performed to compare the potency of gabapentin, pregabalin, and morphine in a well-established model of visceral pain.

Methods

The number of abdominal contractions was counted for 30 min in adult male mice that received different doses of pregabalin, gabapentin, morphine, or placebo intraperitoneally 30 min before receiving 0.6% acetic acid 10 mL·kg^?1.The antinociceptive effect of each drug dose was determined as a percentage of the reduction in the number of acetic acid-induced writhes. The effective doses, for 20%, 50%, and 80% response (ED₂₀, ED₅₀, and ED₈₀, respectively), of each drug were calculated using least squares linear regression analysis, and then dose-response curves were compared.

Results

Pregabalin, gabapentin, and morphine produced a linear dose-dependent antinociceptive effect (coefficient of determination r²] > 0.9). No difference was observed between slopes of dose-response curves. The ED₅₀ estimates (95% confidence interval) for pregabalin, gabapentin, and morphine were 17.1 (12.9 to 22.1) mg·kg^?1, 87.1 (45.8 to 129.8) mg·kg^?1, and 0.2 (0.1 to 0.3) mg·kg^?1, respectively.

Conclusion

In this animal model of visceral pain, all three drugs exhibited parallel dose-response curves. Pregabalin had five times the potency of gabapentin and 1/85^th the potency of morphine. Similar potency ratios may apply in clinical practice. Despite some limitations of animal studies, this model could be useful for comparing new analgesics in visceral pain treatment.