Interactions of morphine and methotrimeprazine in mouse and man with respect to analgesia, respiration and sedation

Interactions between morphine and methotrimeprazine have been studied in mice and man with respect to analgesia or antinociceptive activity, respiratory effects and sedation. The volunteer study was a double-blind cross-over trial with 10 volunteers. In mice, methotrimeprazine only possessed antinociceptive activity in doses which caused marked sedation. However, small non-sedative doses of methotrimeprazine potentiated the analgesic action of morphine. The volunteer study did not confirm this finding in man. Methotrimeprazine 7.5 mg i.m. caused significant sedation, but did not alter the effects of morphine 5 mg on pain threshold or ventilatory response to carbon dioxide.