The present study was undertaken to compare the anticonvulsant effect of various antiepileptic drugs on the intravenous pentylenetetrazol (PTZ)-induced seizure threshold in mice. Minimal doses of PTZ needed to induce different phases (myoclonic jerks, generalized clonus and tonic extensor) of convulsions were recorded as an index of seizure threshold. Furthermore, TID50 (the dose of an anticonvulsant drug required to increase the PTZ seizure threshold for tonic extensor by 50%) was calculated for all drugs, and from these values the potency ratio was determined. Pentobarbital (10-40 mg/kg i.p.), phenobarbital (5-20 mg/kg i.p.), phenytoin (20-40 mg/kg i.p.), carbamazepine (5-20 mg/kg i.p.), diazepam (0.5-2 mg/kg i.p.), chlordiazepoxide (1-4 mg/kg i.p.), triazolam (0.02-0.08 mg/kg i.p.), clonazepam (0.03125-0.25 mg/kg i.p.), GABA (25-100 mg/kg i.p.), ethanol (1000-4000 mg/kg of 10% v/v p.o.), ashwagandha (50-200 mg/kg p.o.), tiagabine (20 and 40 mg/kg i.p.), gabapentin (50-200 mg/kg i.p.), pregabalin (10-40 mg/kg i.p.), progesterone (20-80 mg/kg s.c.), adenosine (25-200 mg/kg i.p.) and rofecoxib (1-4 mg/kg i.p.) exhibited dose-dependent anticonvulsant effects. The TID50 of triazolam was found to be the lowest among all the drugs tested, indicating higher potency. The relative potency of standard drugs to increase the PTZ seizure threshold for tonic extensor was found to be: triazolam > clonazepam > diazepam > rofecoxib > chlordiazepoxide > phenobarbital > carbamazepine > pentobarbital > pregabalin > phenytoin > progesterone > tiagabine > GABA > adenosine > gabapentin > ashwagandha > ethanol. The results of the present study indicate that the intravenous PTZ seizure threshold may be useful for assessing the anticonvulsant effect of drugs effective against different stages of convulsions.
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