Phenytoin Cream for the Treatment of Neuropathic Pain

Summary

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 84 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. 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 84 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 measured on the NRS between baseline and week 2 for phenytoin 20% cream versus placebo cream.

Timeline

Start

2020-09-17

Primary completion

2023-06-15

Completion

2023-06-15

Publications

• Background Kopsky DJ, Vrancken AFJE, Keppel Hesselink JM, van Eijk RPA, Notermans NC. Usefulness of a Double-Blind Placebo-Controlled Response Test to Demonstrate Rapid Onset Analgesia with Phenytoin 10% Cream in Polyneuropathy. J Pain Res. 2020 May 1;13:877-882. doi: 10.2147/JPR.S243434. eCollection 2020.
• Background Kopsky DJ, Keppel Hesselink JM. Single-Blind Placebo-Controlled Response Test with Phenytoin 10% Cream in Neuropathic Pain Patients. Pharmaceuticals (Basel). 2018 Nov 12;11(4):122. doi: 10.3390/ph11040122.
• Background Kopsky DJ, Keppel Hesselink JM. Phenytoin Cream for the Treatment for Neuropathic Pain: Case Series. Pharmaceuticals (Basel). 2018 May 28;11(2):53. doi: 10.3390/ph11020053.
• Background Kopsky DJ, Keppel Hesselink JM, Russell AL, Vrancken AFJE. No Detectable Phenytoin Plasma Levels After Topical Phenytoin Cream Application in Chronic Pain: Inferences for Mechanisms of Action. J Pain Res. 2022 Feb 9;15:377-383. doi: 10.2147/JPR.S345347. eCollection 2022.
• Kopsky DJ, van Eijk RPA, Warendorf JK, Keppel Hesselink JM, Notermans NC, Vrancken AFJE. Enriched enrollment randomized double-blind placebo-controlled cross-over trial with phenytoin cream in painful chronic idiopathic axonal polyneuropathy (EPHENE): a study protocol. Trials. 2022 Oct 22;23(1):888. doi: 10.1186/s13063-022-06806-8.

Drugs

Indications