Analgesic effects of morphine in combination with adjuvant drugs in rats

Morphine is co-administered with adjuvant drugs to treat pain, nausea, vomiting, dyspnoea and delirium in cancer patients.

To investigate analgesic effects of morphine when co-administered with adjuvant drugs.

Two-month-old male Wistar rats received single morphine doses alone (0.45 and 0.9 mg/kg) or with midazolam (0.3 mg/kg), haloperidol (0.15 and 0.45 mg/kg), levomepromazine (0.35 mg/kg), metoclopramide (1.0 mg/kg), and hyoscine butylbromide (1.7 mg/kg) as single subcutaneous injections. Analgesia was measured by the tail-flick test after 15, 30, 45, 60, and 90 min of drug administration. In the case of significant analgesia enhancement, analgesic and sedative effects were explored in 3-, 5-, 6-, 8-, and 11-month-old rats.

Significant morphine (0.9 mg/kg) analgesia enhancement was observed 60 min after haloperidol (0.15 and 0.45 mg/kg) and hyoscine butylbromide co-administration. The addition of haloperidol to morphine significantly increased analgesia in 6-, 8- and 11-month-old rats while in the case of hyoscine butylbromide co-administration this effect was observed only in 11-month-old rats.

Haloperidol and hyoscine butylbromide enhanced morphine analgesia. Future studies may explore the repeated administration of these drug combinations in rats and humans.