Role of codeine in palliative care.

Codeine is designated as one of the essential medicines of palliative care for symptoms such as pain and diarrhea. Essential drugs for palliative care are drugs that are effective for the treatment of common symptoms in palliative medicine, easily available, and are affordable. Codeine is recommended for the management of mild to moderate pain and is available as a combination product or as a stand-alone opioid. It is a prodrug and exhibits an affinity to micro-opioid receptors 200 times lower than morphine. Codeine is metabolized in the liver to inactive metabolites, which account for 90 percent of the transformed product, and morphine, which accounts for 10 percent of the transformed product and provides the main analgesic effect. The production of morphine is dependent on cytochrome oxidase 2D6 enzyme activity, which may not be fully active in some populations. The purpose of this review is to examine the efficacy of codeine for common symptoms encountered in palliative medicine, which has led to its designation as an essential medicine for palliative care.