Browse the corpus

NOTE: Not all potential interactions are listed. Additional interactions of antiepileptic drugs and management suggestions may be determined using the drug interactions tool (Lexi-Interact Online) included in UpToDate. The Lexi-Interact program can be accessed from the UpToDate new search tab or through the individual drug information topics in the section on Drug interactions. Adapted with permission from: Drugs for Epilepsy. Treatment guidelines from The Medical Letter 2008; 6(70):37-46. Copyright © 2008 The Medical Letter. Some interactions between phenytoin and other antiepileptic drugs* Interacting drugs Effects (probable mechanism) Management Phenytoin, with: Carbamazepine Decreased carbamazepine effect (increased metabolism) Monitor carbamazepine and phenytoin concentrations Altered phenytoin effect (mechanism not established) Clonazepam Decreased clonazepam effect (increased metabolism) Monitor clonazepam effect or concentrations Variable effects on phenytoin concentrations (mechanism not established) Monitor phenytoin concentrations Lamotrigine Decreased lamotrigine serum concentrations (increased metabolism; induction of glucuronidation by phenytoin) Monitor lamotrigine serum concentrations and clinical status; lamotrigine dosage may need to be adjusted Oxcarbazepine Possible decreased oxcarbazepine effect (increased metabolism) Monitor clinical status and serum concentration Possible phenytoin toxicity with oxcarbazepine doses of 1200 mg/day or higher (decreased metabolism) Monitor phenytoin concentrations especially when oxcarbazepine dosage is 1200 mg/day or higher Perampanel Decreased perampanel effect (increased metabolism by CYP3A4) Monitor clinical status; perampanel dosage may need to be adjusted Tiagabine Decreased tiagabine effect (increased metabolism) Monitor clinical status Topiramate Possible decreased topiramate effect (increased metabolism) Monitor topiramate concentrations and clinical status; may need to increase topiramate dose Possible phenytoin toxicity (decreased metabolism by CYP2C19) Monitor phenytoin concentrations and clinical status Valproate Possible phenytoin toxicity (displacement from binding) Monitor phenytoin concentrations and clinical status (unbound concentrations may be more helpful than total) Possible decreased valproate effect and increased toxicity (increased metabolism and formation of toxic metabolite) Monitor clinical status and valproate serum concentrations Zonisamide

Possible phenytoin toxicity (displacement from binding) Monitor phenytoin concentrations and clinical status (unbound concentrations may be more helpful than total) Possible decreased valproate effect and increased toxicity (increased metabolism and formation of toxic metabolite) Monitor clinical status and valproate serum concentrations Zonisamide Decreased zonisamide effect (increased metabolism by CYP3A4) Monitor zonisamide concentrations and clinical status; zonisamide dosage may need to be adjusted *

NOTE: Not all potential interactions are listed. Additional interactions of antiepileptic drugs and management suggestions may be determined using the drug interactions tool (Lexi-Interact Online) included in UpToDate. The Lexi-Interact program can be accessed from the UpToDate new search tab or through the individual drug information topics in the section on Drug interactions. Adapted with permission from: Drugs for Epilepsy. Treatment guidelines from The Medical Letter 2008; 6(70):37-46. Copyright © 2008 The Medical Letter. Some interactions between valproate and other antiepileptic drugs* Interacting drugs Effects (probable mechanism) Management Valproate, with: Carbamazepine Decreased valproate effect and possible increased toxicity (increased metabolism and formation of toxic metabolite) Monitor valproate concentrations and clinical status Carbamazepine toxicity (decreased metabolism of carbamazepine epoxide and displacement from binding) Monitor carbamazepine and carbamazepine epoxide concentrations Clonazepam Clonazepam may precipitate absence status (mechanism not established) Monitor clinical status Ethosuximide Possible ethosuximide toxicity (decreased metabolism) Monitor ethosuximide concentration Possible decreased valproate effect (mechanism not established) Monitor valproate concentration Lamotrigine Possible lamotrigine toxicity (decreased metabolism; glucuronidation) Decrease lamotrigine dose; monitor lamotrigine concentrations and clinical status Oxcarbazepine Possible decreased oxcabazepine concentration (increased metabolism) Monitor oxcarbazepine concentrations and clinical status Phenytoin Phenytoin toxicity (displacement from binding and decreased metabolism) Monitor phenytoin concentrations and clinical status (unbound concentrations may be more helpful than total) Possible decreased valproate effect and increased toxicity (increased metabolism and formation of toxic metabolite) Monitor clinical status and valproate serum concentrations Topiramate Possible increased hepatotoxic effect of valproate (mechanism not established) Monitor clinical status *

NOTE: Not all potential interactions are listed. Additional interactions of antiepileptic drugs and management suggestions may be determined using the drug interactions tool (Lexi-Interact Online) included in UpToDate. The Lexi-Interact program can be accessed from the UpToDate new search tab or through the individual drug information topics in the section on Drug interactions. Reproduced with permission from: Drugs for Epilepsy. Treatment guidelines from The Medical Letter 2008; 6(70):37-46. Copyright © 2008 The Medical Letter.

NOTE: Not all potential interactions are listed. Additional interactions of antiepileptic drugs and management suggestions may be determined using the drug interactions tool (Lexi-Interact Online) included in UpToDate. The Lexi-Interact program can be accessed from the UpToDate new search tab or through the individual drug information topics in the section on Drug interactions. Adapted with permission from: Drugs for Epilepsy. Treatment guidelines from The Medical Letter 2008; 6(70):37-46. Copyright © 2008 The Medical Letter.