CYP2D6 in the metabolism of opioids for mild to moderate pain.

In most cancer patients, pain is successfully treated with pharmacological measures using opioid analgesics for moderate to severe pain (strong opioids) alone or in combination with adjuvant analgesics (coanalgesics). Opioids for mild to moderate pain (weak opioids) are usually recommended in the treatment of cancer pain of mild to moderate intensity. There is a debate whether the second step of the WHO analgesic ladder comprising weak opioids such as tramadol, codeine and dihydrocodeine is still needed for the treatment of cancer and chronic pain since low doses of strong opioids show similar efficacy. However, many patients with mild, moderate and in some cases strong pain intensity are still successfully treated with weak opioids. All these drugs are metabolized through CYP2D6, an important enzyme for approximately 25% of all drugs administered in clinical practice. The aim of this review is to summarize data on the impact of CYP2D6 polymorphism on pharmacokinetics, pharmacodynamics and adverse effects of weak opioids.