Codeine intoxication associated with ultrarapid CYP2D6 metabolism

Area of Science:

• Pharmacogenomics
• Clinical Pharmacology
• Toxicology

Background:

• Codeine is a commonly prescribed opioid analgesic and antitussive.
• Codeine is metabolized to active morphine by the cytochrome P450 2D6 (CYP2D6) enzyme.
• Patient factors can significantly influence drug response and toxicity.

Observation:

• A patient developed severe opioid intoxication after receiving low-dose codeine for a cough associated with bilateral pneumonia.
• The patient's CYP2D6 genotype indicated ultrarapid metabolism, with three or more functional alleles.
• Concomitant medications potentially inhibited CYP3A4 activity, and the patient experienced a temporary decline in renal function.

Findings:

• The patient's ultrarapid CYP2D6 metabolizer status likely resulted in excessive morphine formation from codeine.
• Inhibition of CYP3A4 by other drugs may have altered codeine or metabolite pharmacokinetics.
• Reduced renal function could have impaired the excretion of codeine metabolites, contributing to toxicity.

Implications:

• This case highlights the critical role of pharmacogenomic testing (CYP2D6 genotyping) in predicting and preventing adverse drug reactions.
• Clinicians should consider patient genotype, concurrent medications, and organ function when prescribing codeine, especially in susceptible individuals.
• Understanding genetic variations in drug metabolism is essential for personalized medicine and improving patient safety in opioid therapy.