Analgesic potentiation and the distribution of morphine in the presence of triplennamine in mice.

Interest in the interaction of opioids and histamine antagonists arose from the observation that abusers of pentazocine and triplennamine experience a heroin-like euphoria that neither drug alone produces. The present study was conducted to evaluate the analgesic properties of the combination of the histamine antagonist, triplennamine (TRP), and morphine (MS). Analgesia was assessed using the hot plate at 55 degrees C and all drugs were administered intravenously. TRP had no analgesic effect. When a suboptimal dose of MS (3.5 mg/kg) was combined with TRP in a dosage range of 2.5-5 mg/kg, the latency in response to pain 10 minutes after drug administration was significantly increased and this potentiation was still evident 30 minutes after drug administration. Naloxone completely reversed the analgesia of MS and the MS-TRP combination. The distribution of 3H morphine in representative brain areas and plasma was not different in the presence or absence of triplennamine.