Morphine in cancer pain management: a practical guide.

Morphine is the most practical and versatile analgesic for the relief of severe pain associated with advanced cancer. Information is available in the literature about its use in routine clinical practice. Morphine induces analgesia by reducing neurotransmitter release presynaptically and hyperpolarizing dorsal horn neurons at the postsynaptic level, thus preventing rostral transmission of nociception. Morphine has a unique metabolism via glucuronidation (UGT2B7), which results in an active metabolite (morphine-6-glucuronide). The pharmacokinetics of morphine relate to its hydrophilic characteristic, volume of distribution, route of administration and clearance. Renal failure alters its pharmacokinetics more than cirrhosis. The age of the patient and multiple medications will alter morphine pharmacokinetics. Morphine can be given by several different routes: oral, rectal, subcutaneous (s.c.), intravenous (i.v.), epidural and intrathecal. Recent experience confirms benefits of topical morphine for cutaneous pain associated with benign or malignant ulcers. Guidelines for morphine administration are reviewed, and in particular those of the Harry R. Horvitz Center for Palliative Medicine are outlined.