Phenytoin Cream for the Treatment of Neuropathic Pain

  • days left to enroll
  • participants needed
  • sponsor
    David J. Kopsky
Updated on 6 October 2021


Objectives: The main objective is to evaluate the efficacy and safety of phenytoin cream in patients with neuropathic pain due to chronic idiopathic axonal polyneuropathy (CIAP). The second objective is to determine the predictive value of a double-blind placebo-controlled response test (DOBRET) to identify sustained responders.

Study design: This is a 6-week enrichment randomized double-blind, placebo-controlled cross-over trial evaluating phenytoin cream in 72 participants with painful CIAP, whereafter an open label extension phase is offered with phenytoin 20 percent cream for up to one year.

At baseline a DOBRET with phenytoin 10 percent and placebo cream will be performed in each study participant to stratify participants according to their response to the DOBRET before entering the double-blind cross-over phase. DOBRET positive participants are those who experience at least two points pain reduction on the 11-point numerical rating scale (NRS) on the phenytoin 10 percent cream applied area within 30 minutes and at least one-point difference in pain reduction on the NRS between phenytoin 10 percent and placebo cream applied area, in favour of the former.

For the randomized cross-over trial phase, 48 DOBRET positive participants will enter the DOBRET positive group and 24 DOBRET negative participants the DOBRET negative group.

Participants will receive three treatments in a double blind fashion and in a randomized order: phenytoin 10 percent, phenytoin 20 percent and placebo cream. The duration of each treatment period is two weeks. Participants will cross-over two times to each of the other treatments. The study does not have wash-out periods between treatments, because the mean duration of analgesic effect after an application is expected to be less than nine hours. A blood sample will be collected at the end of the second week of the first treatment period to test for phenytoin plasma levels.

Study population: The investigators aim to include 72 participants, age 40 years or older, who have been diagnoses with painful CIAP at the University Medical Center Utrecht and fulfil the inclusion criteria and have given written informed consent.

Interventions: Phenytoin cream in concentrations of 10 percent and 20 percent cream compared to placebo cream.

Primary endpoint: Change in pain intensity from baseline NRS to the mean NRS in the second week in DOBRET positive participants.

Condition Chronic Idiopathic Axonal Polyneuropathy
Treatment Placebo Cream, phenytoin cream
Clinical Study IdentifierNCT04647877
SponsorDavid J. Kopsky
Last Modified on6 October 2021


Yes No Not Sure

Inclusion Criteria

Pregnancy or planned pregnancy in the study period (will only be asked)
Use of oral phenytoin
Open wounds in the neuropathic pain area
Current use of topical analgesics
Presence of other pain syndromes such as the widespread pain syndrome or pain in joints
Presence of serious psychological/psychiatric morbidity
Addiction to intoxicants
Hypersensitivity to the study medication (active substance and excipients)
Insufficient mastery of the Dutch language
Cognitive impairment and insufficiently capable to understand the purpose of the study

Exclusion Criteria

Painful (poly)neuropathy other than CIAP
Presence of neuropathic pain due to any other condition than CIAP
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