Simvastatin prevents morphine antinociceptive tolerance and withdrawal symptoms in rats.

Background/purpose: Long-term exposure to opiates induces tolerance to the analgesic effect and dependence. In recent years, several studies have been conducted to find agents that can prevent the development of these two phenomena. The aim of the present study is to evaluate the effect of simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on morphine-induced tolerance and withdrawal symptoms.

Methods: Groups of male rats received daily morphine [for induction of tolerance (10 mg/kg) and for induction of dependence (additive doses: 5 mg/kg/12 h, 10 mg/kg/12 h, 15 mg/kg/12 h, 20 mg/kg/12 h, and 25 mg/kg/12 h)] in combination with propylene glycol or simvastatin [5 mg/kg, per os (p.o.), 10 mg/kg, p.o., and 20 mg/kg, p.o.]. Next, the nociception was assessed by the plantar test apparatus. The latency was recorded when the animal responded to the light stimulus. The animals received additional doses of morphine for 9 days in order to induce dependency. One hour after the last dose of the morphine injection, naloxone was administered and withdrawal symptoms were recorded for 1 hour.

Results: The results of the present study showed that chronic morphine administration induced tolerance to the analgesic effect for 19 days, whereas simvastatin (20 mg/kg, p.o.) delayed the day of the established tolerance by 5 days. The administration of simvastatin also prevented the morphine-induced shift to the right of the 50% effective dose (ED50) in the dose-response curve. Furthermore, the results showed that simvastatin decreased the total withdrawal score significantly.

Conclusion: We found that simvastatin attenuated morphine-induced tolerance and withdrawal symptoms.