Dose-effect relationships of extradural morphine.

The effectiveness of three different doses of extradural morphine (4, 6 and 8 mg) in relieving post-operative pain was compared in 24 patients. Although there was no significant difference in the efficacy of the three doses, increasing dosage increased the average duration of analgesia provided by the drug (4 mg--593 min; 6 mg--772 min; 8 mg--885 min). All three doses increased the average peak expiratory flow rate, the greatest increases being seen at the higher dosages. Increasing dosage was not accompanied by an increase in the occurrence of adverse effects.