Effect of calcium channel blockers on withdrawal syndrome of lorazepam in rats.

Effects of calcium channel blockers were investigated on withdrawal signs in lorazepam dependent rats. Physical dependence was produced by giving lorazepam admixed with the food in the following dose schedule: 10 x 4, 20 x 4, 40 x 4, 80 x 4 and 120 x 7 (mg/kg daily x days). Parameters such as body weight, food intake, spontaneous locomotor activity (SLA), body temperature, reaction time to pain, foot shock-aggression (FSA) and audiogenic seizures were observed during the period of administration of lorazepam and after its withdrawal. Calcium channel blockers viz. verapamil, nifedipine and nimodipine in different doses were administered orally twice daily in separate groups during the withdrawal period. The withdrawal signs observed in control group (without calcium channel blockers) were hyperkinesia, hyperthermia, hyper-aggression and audiogenic seizures. The administration of verapamil (5-20 mg/kg), nifedipine (1.75-7 mg/kg) and nimodipine (5-20 mg/kg) during the withdrawal period of lorazepam showed dose dependent significant blockade of all the withdrawal signs. Audiogenic seizures were completely blocked by 20 mg/kg dose of verapamil and nimodipine while nifedipine was partially effective. It may be concluded that calcium channel blockers exert protective effects on benzodiazepine withdrawal syndrome.