Proceedings of the Symposium "Updates of the Clinical Pharmacology of Opioids with Special Attention to Long-Acting Drugs"

Opioids provide excellent pain relief in most patients. Yet the responses of patients to individual opioids can vary markedly, even among the m opioids. Understanding this variability would greatly enhance our ability to treat patients appropriately. Classical pharmacological studies have long implied the existence of multiple subtypes of m opioid receptors. More recently, a number of variants of the cloned m opioid receptor have been described. These variants all show the same selectivity for m opioids, confirming their classification as m opioid receptors. Yet, they differ in their functional activation by opioids as well as in their localization within cells and regions in the brain. These multiple m opioid receptors may help explain the range of responses seen clinically among patients for the various opioid drugs. J Pain Symptom Manage 2005;29:S2–S9. 2005 U.S.