Comparisons of the analgesic effects of oral and intramuscular oxymorphone and of intramuscular oxymorphone and morphine in patients with cancer.

The relative analgesic potency of oral and intramuscular oxymorphone was evaluated in a double-blind crossover comparison of graded single doses in patients with chronic pain due to cancer. When both duration and intensity of analgesia are considered (total effect), oral oxymorphone was 1/6 as potent as the intramuscular form. In terms of peak effect, however, oral oxymorphone was only 1/14 as potent. These values are almost identical to those obtained in a previous study comparing oral with intramuscular morphine. The analgesic effect of oral oxymorphone rose to a peak later and had a longer duration than the effect of intramuscular oxymorphone. Intramuscular oxymorphone and morphine were also compared in a similar patient group. Intramuscular oxymorphone proved to be 8.7 times as potent as morphine in terms of total analgesic effect and 13 times as potent in terms of peak effect. In roughly equinalgesic doses, the occurrence of side effects was qualitatively and quantitatively similar for oral and intramuscular oxymorphone and for intramuscular oxymorphone and morphine.