Interacting drugs | Effects (probable mechanism) | Management |
Phenytoin or fosphenytoin, with: | ||
| Decreased brivaracetam effect (increased metabolism by CYP2C19) | Monitor clinical status |
Possible phenytoin toxicity (decreased metabolism by CYP2C19) | Monitor clinical status and phenytoin concentrations | |
| Decreased carbamazepine effect (increased metabolism) | Monitor carbamazepine and phenytoin concentrations |
Altered phenytoin effect may include decreased or increased phenytoin levels (mechanism not established) | ||
| Decreased clonazepam effect (increased metabolism) | Monitor clinical status |
Monitor phenytoin concentrations | ||
| Decreased eslicarbazepine concentrations (increased metabolism) | Monitor clinical status; eslicarbazepine dose may need to be increased |
Possible phenytoin toxicity (decreased metabolism by CYP2C19) | Monitor clinical status and phenytoin concentrations | |
| Decreased felbamate effect (increased metabolism) | Monitor felbamate effect; dose may need to be increased |
Possible phenytoin toxicity (mechanism not established) | Phenytoin dose reduction may be needed; refer to UpToDate Lexidrug for detail. Monitor clinical status and phenytoin concentrations. | |
| Decreased lamotrigine serum concentrations (increased metabolism; induction of glucuronidation by phenytoin) | Monitor clinical status and lamotrigine serum concentrations; lamotrigine dose may need to be adjusted |
| Possible decreased levetiracetam concentrations (increased metabolism) | Monitor clinical effect |
| Possible decreased oxcarbazepine effect (increased metabolism) | Monitor clinical status and oxcarbazepine concentration |
Possible phenytoin toxicity with oxcarbazepine doses of 1200 mg/day or higher (decreased metabolism by CYP2C19) | Monitor phenytoin concentrations especially when oxcarbazepine dosage is 1200 mg/day or higher; reduction of phenytoin dose may be needed | |
| Decreased perampanel effect (increased metabolism by CYP3A4) | Monitor clinical status; perampanel dose may need to be adjusted |
| Decreased tiagabine effect (increased metabolism by CYP3A4) | Monitor clinical status |
| Possible decreased topiramate effect (increased metabolism) | Monitor clinical status; may need to increase topiramate dose |
Possible phenytoin toxicity (decreased metabolism by CYP2C19) with high doses of topiramate | Monitor clinical status and phenytoin concentrations | |
| Possible phenytoin toxicity (displacement from binding and decreased metabolism, complex time course) | Monitor clinical status and phenytoin concentrations (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 | |
| Decreased zonisamide effect (increased metabolism by CYP3A4) | Monitor clinical status and zonisamide concentrations; zonisamide dose may need to be adjusted |
CYP: cytochrome P450.
* Not all potential interactions are listed. Additional interactions of antiseizure medications and management suggestions may be determined using the drug interactions program included within UpToDate.Do you want to add Medilib to your home screen?