Measurement of pain and analgesia in cancer patients.

Measurement of pain in cancer patients requires all the procedural safeguards essential for the measurement of subjective responses, including the employment of active and inactive controls, double-blind techniques, randomization, and statistical verification of results. Pain is traditionally measured in analgesic studies by employing verbal descriptors of intensity, but more recently visual analogues of pain intensity have been used and generally provide more sensitive measures of pain intensity. Patients with chronic pain tend to rate the categories representing more intense pain as lower in the visual analogue scale than do patients with postoperative pain. This may well reflect differences in the prior pain experiences of the two groups. Patients with chronic cancer pain have greater positive mood effects after the narcotic, morphine, than after the non-steroidal antiinflammatory analgesic, zomepirac, and this appears to be independent of analgesic activity. It is possible to design crossover analgesic studies in cancer patients so as to minimize carry-over effects, and such studies are more efficient than parallel group assays. Crossover studies also provide the ability to measure carry-over when it occurs.