Opioid analgesics in cancer pain: current practice and controversies.

Pain is a complex somato psychic experience that requires a multimodality approach to treatment. Pharmacologically, pain in cancer can be divided into opioid non-responsive, opioid partially responsive, opioid responsive (but do not use opioids) and opioid responsive (do use opioids). Three concepts govern the use of analgesics in opioid responsive pains: 'by the mouth', 'by the clock' and 'by the ladder'. Adjuvant drugs may also be necessary. Morphine is the strong opioid of choice for cancer pain. In patients unable to take oral medication, morphine can be administered by suppository, by injection or peridurally. Useful alternative strong opioids include phenazocine, hydromorphone and buprenorphine. A number of controversial issues are discussed. These include the oral to parenteral potency ratio of morphine; the main site of metabolism of morphine; the relative merits of morphine and diamorphine; the risk of respiratory depression; the development of tolerance; and the risk of addiction.