Duration of analgesia in mice after heroin by two testing methods

The analgestic action in mice of single injections of heroin hydrochloride ranging from 0.3-240mg/kg was measured by the tail-clip and by the hot-plate methods. The duration of analgesia increased as the dose of heroin increased. By the tail-clip technique, the mean effective dose (ED50) (and standard error of estimate) at 30 min was calculated as 1.0 (+/3.42) mg/kg while at 180 min it was 27.5 (+/3.05). By the hot-plate technique the ED50 at 30 min was 4.9 (+/3.13) mg/kg and at 180 min it was 173.8 (+/5.38) mg/kg. The hot-plate method, though less sensitive than the tail-clip method, yields a regression line derived from ED50 values at various testing times of the same slope; thus the two methods give comparable results for changes in analgesia with time. The rate of change of the median analgesic dose of heroin HC1 in mice was calculated to be 2% per minute. In similar mice the acute mean lethal dose for single, subcutaneous injections of heroin HC1 was calculated to be 190.5+/3.01 mg/kg (95% confidence limits).