Control of radiation-induced emesis with promethazine, cimetidine, thiethylperazine, or naloxone

Promethazine (2 mg/kg), cimetidine (4 mg/kg), thiethylperazine (0.86 mg/kg), and naloxone (0.08 mg/kg) were each evaluated for their ability to increase the threshold of radiation-induced emesis in the dog. Each dog was fed a can of dog food (ca 0.4 kg) and then injected IM with the appropriate drug 1 hour before being irradiated by a 60Co teletherapy unit. The total radiation dose given an individual dog was determined by an up-and-down exposure schedule. Dogs were then observed continuously for 10 hours while the number, time of onset, and duration of each emetic episode were monitored. The dose of radiation causing emesis in 50% (ED50 +/- SEM) of control dogs was 170 +/- 38.5 rad. The ED50 +/- SEM was increased to 402 +/- 18.6 rad by promethazine, to 331 +/- 27.3 rad by cimetidine, and to 320 +/- 38.5 rad by thiethylperazine. This increased tolerance was significant at P less than 0.05 for each drug. The ED50 for naloxone was 262.5 +/- 92.9 rad, which was not a statistically significant increase in threshold.