Topiramate Phenytoin

Topiramate Phenytoin 2006 Elsevier B.V. All rights reserved. Interaction inconsistent, usually of little clinical significance Inhibition of phenytoin metabolism Continued... 

The last few years has seen an explosion in AEDs. Some of those mentioned above may fall by the wayside and others appear. At the time of writing, we could include felbamate, zonisamide oxcarbazepine and topiramate. They all appear to have a phenytoin-like action on sodium channels, although topiramate appears to also potentiate the action of GABA on GABAa receptors like the benzodiazepines but through a different site. 

Epilepsy is a clinical disorder characterized by spontaneous, recurrent seizures arising from excessive electrical activity in certain parts of the brain [51]. Currently available drugs, such as phenytoin, carbamazepine, valproic acid, lamotrigine, and topiramate (for molecular structures see Fig. 6), provide symptomatic seizure suppression in only 60-70% of those receiving treatment [52-54]. These drugs are also associated with unwanted side... 

Phenobarbital Phenytoin Topiramate Valproate Oxcarbazepine Topiramate Second-line Clobazam6 Gabapentin Levetiracetam Phenytoin Tiagabine... 

Risperidone Aripiprazole 2D6 > 3A4 2D6, 3A4 Carbamazepine and phenytoin topiramate hypericum (St. John s Wort). Paroxetine, fluoxetine, sertraline (high dose) grapefruit juice 2D6 or 3A4 substrates acting as competitive inhibitors. 

Quetiapine 3A4 2D6, 2C9 Carbamazepine and phenytoin topiramate prednisolone. Fluvoxamine fluoxetine sertraline (high dose) CYP3A4 substrates grapefruit juice. 

Carbamazepine, phenytoin, valproate, gabapentin, lamotrigine, levetiracetam, tiagabine, topiramate, zonisamide... 

Commonly used drugs that induce liver enzymes (rifampin, phenytoin, carbamazepine, barbiturates, primidone, topiramate) and reduce efficacy of CHC... 

Anticonvulsants (barbiturates, including phenobar-bital and primidone carbamazepine felbamate phenytoin topiramate vigabatrin)... 

Phenobarbital Phenytoin Topiramate Valproic acid Valproic acid... 

U.S. Expert Panel 2005 Valproic acid Carbamazepine Lamotrigine Oxcarbazepine Phenobarbital Phenytoin Topiramate Valproic acid Children Carbamazepine Phenobarbital Phenytoin Topiramate Valproic acid Lamotrigine... 

Valproic acid may cause less cognitive impairment than phenytoin and phenobarbital. Some of the newer agents (e.g., gabapentin and lamotri-gine) have been shown to cause fewer cognitive impairments than the older agents (e.g., carbamazepine). Topiramate may cause substantial cognitive impairment. 

Mood stabilizers phenytoin, valproate, topiramate Sedative/anxiolytics diazepam, barbiturates Beta-blockers propranolol... 

Concomitant therapy On occasion, the addition of topiramate to phenytoin may require an adjustment of the dose of phenytoin to achieve optimal clinical outcome. The addition or withdrawal of phenytoin and/or carbamazepine during adjunctive therapy with topiramate may require adjustment of the dose of topiramate. 

Phenobarbital Phenytoin (Dilantin) Tiagabine (Gabitril) Topiramate (Topamax) Valproic Acid (Depakene, Depakote) Zonisamide (Zonegran)... 

II.e. 5.2. Interactions between first and second generation AEDs. Felbamate raises plasma concentrations of phenytoin, valproic acid and carbamazepine. Clearance of tiagabine, topiramate and zon-isamide is increased in the presence of an enzyme inducer. Vigabatrin reduces phenytoin concentrations after 4-5 weeks of comedication (via an unknown mechanism). For tiagabine, the elimination half-life may be reduced by 2-3 hours in the presence of an enzyme-induction AED. Lamotrigine elimination is slower if given with valproic acid. Topiramate reduces elimination of phenytoin. 

Topiramate, a sulfamate-substituted derivative of the monosaccharide cf-fructose, is an anticonvulsant agent (AHFS, 2000). The spectrum of topiramate s anticonvulsant activity resembles that of CBZ and phenytoin (Shank et ah, 2000). Topiramate has shown preliminary antimanic (McElroy et al., 2000) and possibly antidepressant efficacy in treatment-refractory, manic patients with BD type I (Calabrese et ah, 1998). 

Reduced ethinyl estradiol concentrations have been associated with concomitant use of substances that induce hepatic microsomal enzymes, such as rifampin, rifabutin, barbiturates, phenylbutazone, phenytoin sodium, griseofulvin, topiramate, some protease inhibitors, modafinil, and possibly St. John s wort ... 

Specific myoclonic syndromes are usually treated with valproate an intravenous formulation can be used acutely if needed. It is nonsedating and can be dramatically effective. Other patients respond to clonazepam, nitrazepam, or other benzodiazepines, although high doses may be necessary, with accompanying drowsiness. Zonisamide and levetiracetam may be useful. Another specific myoclonic syndrome, juvenile myoclonic epilepsy, can be aggravated by phenytoin or carbamazepine valproate is the drug of choice followed by lamotrigine and topiramate. 

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