[The effects of noscapine and chlorpheniramine on physical dependence and antitussive activity of dihydrocodeine]

The effects of noscapine and chlorpheniramine on physical dependence liability and antitussive activity of dihydrocodeine, a narcotic antitussive, were studied. For developing physical dependence, male Sprague-Dawley rats were treated with dihydrocodeine (DC), noscapine (N), and chlorpheniramine (CP) singly or simultaneously admixed with food (drug-admixed food method (DAF): DC: 0.125, N: 0.25, CP: 0.05 mg/g of food, for 7 days) or were intermittently medicated for 3 days at one-hour intervals through an implanted intravenous cannula (infusion method: DC: 0.5-2, N: 1-4, CP: 0.2-0.8 mg/kg x 24 times/day). Subsequently, rats were treated with naloxone (0.5 mg/kg, sc) and checked for withdrawal signs during 3 hours. Naloxone-precipitated body weight loss of DC was suppressed by simultaneous administration of N or CP. In combined group of DC, N, and CP, withdrawal signs, such as body weight loss, body shakes, and diarrhea, were more remarkably suppressed. Papaverine, the same kind of spasmolytic as N, was tested by the same schedule of DAF. Papaverine did not suppress the naloxone-precipitated withdrawal signs of DC. These results suggest that suppressive effect of N is not due to its spasmolytic action. On the other hand, the cough reflex was induced by electric stimulation in guinea pigs and the fifty percent of antitussive dose (AtD50) was estimated in order to evaluate the influence of N and CP on antitussive effect of DC. N and CP did not change the antitussive effect of DC. These results may suggest that N and CP suppress the development of physical dependence of DC without diminishing the pharmacological effects of DC.