What is the role of phenytoin in the treatment of trigeminal neuralgia (TN)?

Updated: Jul 11, 2019
  • Author: Manish K Singh, MD; Chief Editor: Robert A Egan, MD  more...
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Phenytoin, although not approved by the US Food and Drug Administration (FDA) for idiopathic trigeminal neuralgia (TN) and believed to be less effective than carbamazepine, is probably effective for some patients with this disorder. [39]

Phenytoin has the same mechanism of action as carbamazepine and poses a similar risk panel, except for the risk of aplastic anemia. Of those patients who fail to attain relief with carbamazepine alone, an additional 8-20% of patients may have an adequate response if phenytoin is added to the treatment regimen.

According to a small study by Braham, phenytoin produced complete relief of pain in 30-40% of 43 patients and partial relief in an additional 30-40% at 300-600 mg/d. [40] Blom stated that doses of 300 mg/d were less effective, although doses of 400-600 mg caused more adverse effects. [27]

No correlation has been found between blood levels of phenytoin and therapeutic effect. Loeser recommended that the dose can be increased until relief is obtained or undesirable adverse effects appear (eg, dizziness, ataxia, diplopia, nystagmus, nausea). [39]

Raskin reported relief of intolerable pain with 250 mg of intravenous phenytoin over 5 minutes, allowing relief for hours to 3 days, sufficient for an adequate history and reexamination. [41]

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