Tramadol produces analgesia by two distinct mechanisms. In a patient with cytochrome P450 2D6 poor metabolizer status, tramadol analgesia is significantly reduced. The reason is:

• A CYP2D6 is required for tramadol's reuptake inhibition of serotonin and norepinephrine
• B Poor metabolizers cannot convert tramadol to its SNRI metabolite which provides 80% of analgesic effect
• C CYP2D6 converts tramadol's parent compound to O-desmethyltramadol (M1), which has 200-fold higher mu-opioid receptor affinity than the parent ✓
• D CYP2D6 generates an active metabolite that inhibits substance P release in the dorsal horn

Explanation

Tramadol exerts weak mu-opioid agonism directly, but its primary opioid analgesic contribution comes from CYP2D6-mediated O-demethylation to M1 (O-desmethyltramadol), which has approximately 200-fold greater mu-receptor affinity. CYP2D6 poor metabolizers (approximately 7-10% of Caucasians) cannot generate adequate M1 concentrations, significantly reducing the opioid component of tramadol analgesia. Conversely, CYP2D6 ultrarapid metabolizers can generate toxic M1 levels.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.