Codeine

Obstructive sleep apnea, COPD, Severe asthma, Respiratory failure

Patients with pre-existing respiratory insufficiency face amplified respiratory depression risk. Obstructive sleep apnea is particularly concerning as opioid-induced muscle relaxation further compromises airway patency.

Hepatic impairment may alter the ratio of codeine metabolic pathways, producing unpredictable morphine and metabolite plasma levels. Both increased toxicity (if CYP2D6 activity is preserved while conjugation is impaired) and decreased efficacy are possible.

Renal impairment leads to accumulation of renally-cleared morphine metabolites, particularly morphine-6-glucuronide (M6G), which is a potent mu-opioid agonist. This accumulation can produce prolonged respiratory depression and sedation.

Known CYP2D6 ultrarapid metabolizers should not receive codeine. Standard doses produce morphine exposure equivalent to supratherapeutic morphine dosing. Prevalence varies by ethnicity: ~1-2% of Northern Europeans, up to ~18% in some Latin American and African populations.

FDA advisory contraindicates codeine during breastfeeding. However, Zipursky and Juurlink (2020) critically reassessed the landmark case and argued the causal link to neonatal death is implausible based on the small quantities of opioids in breast milk regardless of CYP2D6 genotype. This contraindication remains scientifically disputed.

FDA black box warning contraindicates codeine in children under 12 for any indication. Three fatal/life-threatening pediatric cases post-adenotonsillectomy were linked to CYP2D6 ultrarapid metabolizer status.

Codeine is contraindicated at any age following tonsillectomy or adenoidectomy. The combination of post-surgical airway vulnerability and unpredictable CYP2D6-mediated morphine production creates unacceptable respiratory depression risk.