Unexceptional Seizure Potential of Tramadol or Its Enantiomers or Metabolites in Mice

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 325; no. 2; pp. 500 - 506
• Main Authors: Raffa, Robert B, Stone, Jr, Dennis J
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.05.2008
• Subjects: Analgesics, Opioid - adverse effects; Analgesics, Opioid - therapeutic use; Animals; Codeine - adverse effects; Codeine - therapeutic use; Cytochrome P-450 CYP2D6 Inhibitors; Drug Interactions; Hot Temperature; Male; Mice; Mice, Inbred Strains; Morphine - adverse effects; Morphine - therapeutic use; Naloxone - adverse effects; Naloxone - pharmacology; Narcotic Antagonists - adverse effects; Narcotic Antagonists - pharmacology; Oxycodone - adverse effects; Oxycodone - therapeutic use; Pain - drug therapy; Quinidine - pharmacology; Reserpine - pharmacology; Seizures - chemically induced; Stereoisomerism; Tramadol - adverse effects; Tramadol - therapeutic use
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.108.137273

Tramadol is one of the most widely used centrally acting analgesics worldwide. Because of its multimodal analgesic mechanism (opioid plus nonopioid), the adverse effects profile of tramadol, similar to its analgesic profile, can be atypical compared with single-mechanism opioid analgesics. The comparison is often favorable (e.g., less respiratory depression or abuse), but it is sometimes cited as unfavorable in regard to seizure potential. As part of a broader study of this analgesic, we compared seizure induction in mice produced by administration of tramadol, the enantiomers and metabolites [M1 ( O -desmethyl tramadol), M2 ( N -desmethyl tramadol), M3 ( N,N- didesmethyl tramadol), M4 ( O,N,N- tridesmethyl tramadol), and M5 ( O,N- didesmethyl tramadol)] of tramadol, and opioid and nonopioid reference compounds. We found that tramadol, its enantiomers, and M1 to M5 metabolites were of intermediate potency in this endpoint (on either a milligram per kilogram or millimole per kilogram basis). The SD 50 (estimated dose required to induce seizures in 50% of test group) of tramadol to antinociceptive ED 50 ratio was almost identical to that of codeine. The enantiomers of tramadol were about equipotent to tramadol on this endpoint. The M1 to M5 metabolites (and M1 enantiomers) of tramadol were less potent than tramadol. The relative potency of tramadol to opioids was not altered by quinidine (an inhibitor of CYP4502D6), noxious stimulus (48°C hot-plate), multiple dosing, or in reserpinized mice. Tramadol seizures were increased by naloxone, principally at high tramadol doses and due to an effect on the (–)enantiomer that overcame the opposite effect on the (+)enantiomer. No synergistic effect on seizure induction was observed between concomitant tramadol and codeine or morphine.