Controlled Double-Blind Trial of Phenytoin vs. Fluoxetine in Major Depressive Disorder

Background: Phenytoin was the first nonsedative anticonvulsant introduced and is still the anticonvulsant most widely used worldwide in neurology. Given the efficacy of the anticonvulsant lamotrigine in the depressed phase of bipolar disorder, a critical theoretical question is whether other anticonvulsants used in treating bipolar disorder might be similarly effective. We therefore undertook a controlled trial of phenytoin versus fluoxetine in major depressive disorder.

Method: Data were collected from July 2001 to July 2003. Thirty-three subjects entered the study. All patients met DSM-IV criteria for major depressive disorder and scored a minimum of 18 on the 24-item Hamilton Rating Scale for Depression (HAM-D) at baseline. After a 3-day washout of any previous medications, patients were randomly assigned to fluoxetine or phenytoin in identical capsules. Each capsule contained phenytoin 100 mg or fluoxetine 7 mg plus cornstarch. Patients started with 1 tablet daily and increased every other day until they were taking 1 tablet 3 times daily with meals. Blood phenytoin levels were taken after 1 week, 3 weeks, and 6 weeks, and dosage was adjusted to achieve blood levels of 10 to 20 mg/mL, to a maximum dose of 4 capsules per day or a minimum dose of 2 capsules per day. Fluoxetine patients were assigned dummy blood phenytoin levels by the control psychiatrist such that the treating physician would raise the number of capsules to at least 3 per day (20 mg of fluoxetine).

Results: Thirty-three patients entered the study, and 28 (N = 14 in each treatment group) completed at least 3 weeks and were included in the data analysis. Patients who dropped out after week 3 (3 patients) were included in the study as last value carried forward. There was no difference between treatment groups in overall rate of response or speed of response.

Conclusion: The absence of a placebo arm in our study allows for the possibility that neither treatment was more effective than placebo. However, the exclusion of past fluoxetine nonresponders and the minimum HAM-D score at baseline of 18 make this possibility unlikely.​​

J Clin Psychiatry 2005;66(5):586-590