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

Abstract

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 o 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 (ϩ)enantiomer. No synergistic effect on seizure induction was observed between concomitant tramadol and codeine or morphine.Tramadol is a centrally acting analgesic that is widely used throughout the world (in more than 100 countries). Tramadol produces its multimodal antinociceptive and analgesic effects via two mechanisms (Raffa and Friderichs, 1996): one is opioid, and the other is nonopioid (Hennies et al., 1988;Friderichs et al., 1991Friderichs et al., , 1992Raffa et al., 1992Raffa et al., , 1993Raffa et al., , 1995Dayer et al., 1997;Ide et al., 2006). The opioid component involves weak affinity (approximately 1 M) of the parent drug and approximately 300-fold greater affinity of the M1 metabolite of tramadol (Wu et al., 2002) for -opioid receptors (Hennies et al., 1988;Raffa et al., 1992;Lai et al., 1996;Gillen et al., 2000). The nonopioid component is related to inhibition of neuronal 5-hydroxytryptamine (5-HT; serotonin) and norepinephrine reuptake (Friderichs et al., 1991;Codd et al., 1995). The opioid component, predominant in the (ϩ)enantiomer, and the nonopioid component, predominant in the (-)enantiomer Raffa et al., 1992;Codd et al., 1995), combine in a complementary and sometimes synergistic manner to produce antinociception, but in an additive or subadditive manner in several side-effect measures (Raffa et al., 1993). The total contribution from all ...

Factors Related to Seizure in Tramadol Poisoning and Its Blood Concentration

“…Tramadol may also increase the seizure risk in patients receiving other medications such as tricyclic antidepressants, phenothiazines, and selective serotonin reuptake inhibitors [11]. While tramadol-related seizures can be controlled by diazepam, they are not responsive to naloxone, and tramadol-induced seizures can be precipitated by administration of naloxone, at high tramadol doses [18].…”

Comparative Toxicity of Tapentadol and Tramadol Utilizing Data Reported to the National Poison Data System

“…There are human cases and animal models that attempt to characterize this adverse effect. 7,[14][15][16][17][18][19][20] In a rat and a mouse model, TRA, its enantiomers, and active metabolite were shown to induce seizures in rats with a lowered seizure threshold and at a seizure dose to antinociceptive dose ratio similar to that of codeine. 14,15 TRA has structural similarities and may possess some antidepressant activity similar to venlafaxine, which has been associated with seizures in several studies.…”

Tramadol Intoxication in an 8-Months-Old Infant through Breastfeeding: A Case Report

“…There is a large individual variation in the activity of CYP2D6 enzyme within a population and between ethnic groups [10][11][12][13]. The ethnic groups from the Middle East and East Africa are more likely to be ultrarapid metabolizers compared with those from Middle Europe and North America (incidence 21%-29% vs. 0.5%-1% respectively) so people in the Middle East are more susceptible to opioid effects, including dependency, seizure, sedation, and respiratory depression [10][11][12][13][14][15][16]. Ultrarapid metabolizer (UMs) have increased CYP2D6 enzymatic activity and may experience different degrees of pain relief and side effects of tramadol by converting it into its active metabolite; M1(O-desmethyl tramadol) more rapidly and completely than other people.…”