Lethality of opioid and antihistaminic combinations in mice

The lethality of morphine (37.5, 75, and 150 mg/kg) and tripelennamine (10,20,40 and 60 mg/kg), given alone and in combination, was evaluated in mice housed in groups of 16. When given alone, neither drug produced death at any dose. Combining the drugs produced supra-additive effects: some deaths occurred at all combination doses. The lethality of pentazocine (20, 40 and 80 mg/kg) and diphenhydramine (20, 40 and 80 mg/kg), given alone and in combination, also was evaluated. Neither drug alone produced death at any dose. Supra-additive effects were observed when the drugs were combined. These results are similar to earlier findings concerning the lethality of combinations of pentazocine and tripelennamine.