Drug Interactions between Psychoactive Agents and Antiepileptic Agents

[Drug interactions with antiepileptic agents]

Drug interactions with antiepileptic agents are based in large part on pharmacokinetic mechanisms. Most prominent are induction or inhibition of enzymes of the cytochrome P450 (CYP) system, which is of central importance for metabolic elimination of lipophilic xenobiotics. Potent inductors of CYP isoenzymes are carbamazepine, phenobarbital, phenytoin, and primidone, thereby decreasing not only their own plasma levels and efficacy but also that of other antiepileptics and other drugs. Felbamate, oxcarbazepine, and topiramate are weak inductors of the CYP isoenzyme 3A4, whereas they inhibit CYP2C19. Valproic acid is a potent inhibitor of several CYP isoenzymes and glucuronyltransferases, resulting in an increase in plasma concentrations and toxicity of antiepileptics and other drugs. Antiepileptics that are not involved in drug interactions include gabapentin, levetiracetam, and vigabatrine. The P-glycoprotein may mediate the exit of antiepileptics from the brain. This transport mechanism is inhibited by carbamazepine, which may explain the enhanced clinical efficacy of a combination of carbamazepin with other antiepileptics. Other possible pharmacokinetic interactions are precipitation of antiepileptics in the stomach by antacids or sucralfate and displacement from plasmaprotein binding of one antiepileptic agent by another. Therapeutic drug monitoring (TDM) may be helpful in assessing pharmacokinetic drug interactions. Pharmacodynamic interactions appear to be responsible for the enhanced efficacy of antiepileptic combination therapy. In prescribing drugs, their spectrum of interactions has to be known.

Effects of acute topiramate dosing on open field behavior in mice

Although topiramate (TPM) has been used to treat human disease, there are few studies of its effects on the behavior of animal models. Objective. This study aimed to assess the effect of acute TPM administration on the behavior of mice undergoing the open-field test. Method. The animals were divided in two groups: the treatment group (n = 10), which received 10 mg/kg TPM intraperitoneally, and the control group (n = 10), which received saline. 30 minutes after drug administration, the animals were assessed for 5 minutes in the open-field. The following parameters were analyzed: number of squares explored, immobility time, central area permanence time, peripheral apparatus permanence time, rearing frequency and time, grooming frequency and time, rearing frequency during the last minute, number of fecal boli, and estimated speed. Results. The treatment group had a higher number of squares explored (p = 0.02) and greater estimated speed (p = 0.01). Conclusion. The results suggest that acute TPM administration increases the locomotor activity of mice without interfering with learning, anxiety, stress, and exploratory behavior.