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Anticonvulsant and proconvulsant effects of tramadol, its enantiomers and its M1 metabolite in the rat kindling model of epilepsy
Author(s) -
Potschka Heidrun,
Friderichs Elmar,
Löscher Wolfgang
Publication year - 2000
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0703562
Subject(s) - tramadol , pharmacology , metabolite , anticonvulsant , analgesic , chemistry , enantiomer , kindling , epilepsy , medicine , stereochemistry , biochemistry , psychiatry
The centrally acting analgesic tramadol has recently been reported to cause seizures at re‐commended dosages in patients, whereas animal experiments had indicated that seizures only occur in high, toxic doses. Tramadol has a dual mechanism of action that includes weak agonistic effects at the mu ‐opioid receptor as well as inhibition of monoamine (serotonin, norepinephrine) re‐uptake. Its major (M1) metabolite mono‐ O ‐desmethyltramadol, which is rapidly formed in vivo , has a markedly higher affinity for mu receptors and may thus contribute to the effects of the parent compound. Furthermore, the pharmacological effects of tramadol appear to be related to the different, but complementary and interactive pharmacologies of its enantiomers. In the present study, we evaluated (±)‐tramadol, its enantiomers, and its M1 metabolite ((+)‐enantiomer) in the amygdala kindling model of epilepsy in rats. Adverse effects determined in kindled rats were compared to those in nonkindled rats. At doses within the analgesic range, (±)‐tramadol and its enantiomers induced anticonvulsant effects in kindled rats. However, at only slightly higher doses seizures occurred. With (±)‐tramadol, generalized seizures were observed at 30 mg kg −1 in most kindled but not in nonkindled rats. The (−)‐enantiomer induced myoclonic seizures at 30 mg kg −1 in most kindled but not in nonkindled rats, although myoclonic seizure activity was observed in some nonkindled rats at 10 or 20 mg kg −1 . Seizures were also observed after the (+)‐enantiomer and the (+)‐enantiomer of the M1 metabolite, but experiments with higher doses of these compounds were limited by marked respiratory depression. The data demonstrate that kindling enhances the susceptibility of rats to convulsant adverse effects of tramadol and its enantiomers, indicating that a preexisting lowered seizure threshold increases the risk of tramadol‐induced seizures.British Journal of Pharmacology (2000) 131 , 203–212; doi: 10.1038/sj.bjp.0703562