Role of active metabolites in the use of opioids

• Published in: European journal of clinical pharmacology Vol. 65; no. 2; pp. 121 - 139
• Main Authors: Coller, Janet K, Christrup, Lona L, Somogyi, Andrew A
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01-02-2009; Springer-Verlag; Springer; Springer Nature B.V
• Subjects: Analgesics, Opioid - metabolism; Analgesics, Opioid - pharmacology; Analgesics, Opioid - therapeutic use; Animals; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; genetic polymorphism; Humans; Medical sciences; Metabolic Networks and Pathways; Metabolism; metabolites; Molecular Structure; Mu opioid receptor; Narcotics; Pain - drug therapy; Pain management; Pharmacology; Pharmacology. Drug treatments; Pharmacology/Toxicology; Receptors, Opioid, mu - drug effects; Review Article; Side effects; Mu opioid receptor; Metabolites; Genetic polymorphisms; Opioids; Human; Genetic variability; Metabolite; μ Opioid receptor; Genotype; Opiates; Opioid peptide; Polymorphism
• ISSN: 0031-6970; 1432-1041
• DOI: 10.1007/s00228-008-0570-y

The opioid class of drugs, a large group, is mainly used for the treatment of acute and chronic persistent pain. All are eliminated from the body via metabolism involving principally CYP3A4 and the highly polymorphic CYP2D6, which markedly affects the drug's function, and by conjugation reactions mainly by UGT2B7. In many cases, the resultant metabolites have the same pharmacological activity as the parent opioid; however in many cases, plasma metabolite concentrations are too low to make a meaningful contribution to the overall clinical effects of the parent drug. These metabolites are invariably more water soluble and require renal clearance as an important overall elimination pathway. Such metabolites have the potential to accumulate in the elderly and in those with declining renal function with resultant accumulation to a much greater extent than the parent opioid. The best known example is the accumulation of morphine-6-glucuronide from morphine. Some opioids have active metabolites but at different target sites. These are norpethidine, a neurotoxic agent, and nordextropropoxyphene, a cardiotoxic agent. Clinicians need to be aware that many opioids have active metabolites that will become therapeutically important, for example in cases of altered pathology, drug interactions and genetic polymorphisms of drug-metabolizing enzymes. Thus, dose individualisation and the avoidance of adverse effects of opioids due to the accumulation of active metabolites or lack of formation of active metabolites are important considerations when opioids are used.