Phenytoin Cream for the Treatment of Neuropathic Pain

Study Overview
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Brief Summary
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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.

Official Title
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Enrichment Randomized Double-blind, Placebo-controlled Cross-over Trial With PHEnytoin Cream in Patients With Painful Chronic Idiopathic Axonal polyNEuropathy

Conditions
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Chronic Idiopathic Axonal Polyneuropathy

Intervention / Treatment
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* Drug: phenytoin cream
* Other: Placebo cream


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients have been diagnosed with CIAP defined as: presence of symmetrical distal sensory or sensorimotor symptoms such as numbness, pins and needles, tightness, coldness, unsteadiness, muscle cramps, and weakness with onset in the feet, compatible with polyneuropathy; presence of symmetrical distal sensory or sensorimotor signs with evidence of large nerve fiber involvement such as decreased sense of touch, vibration, and proprioception, usually in the presence of decreased pin prick/temperature sense, decreased/absent tendon reflexes, or slight muscle weakness on neurologic examination, compatible with polyneuropathy; an insidious onset and slow or no progression of the polyneuropathy over the course of at least 6 months; no identifiable cause for the polyneuropathy after thorough history-taking, clinical examination, and extensive laboratory testing; no suggestion of a hereditary polyneuropathy based on detailed kinship history (i.e., one or more affected family member), neurologic examination, or confirmation by genetic analysis; and nerve conduction studies excluding a demyelinating polyneuropathy and confirming large nerve fiber involvement if the findings on neurologic examination are equivocal considering the patient's age. Presence of chronic localized neuropathic pain due to CIAP Neuropathic pain localized in two anatomically symmetrical areas of feet/lower legs Duration of neuropathic pain ≥3 months Duration of ≥1 hour neuropathic pain per day Neuropathic pain characteristics defined by the Douleur Neuropathique 4 questions (DN4) score ≥4 Mean pain score during daytime of ≥4 and <10 on the NRS at study entry (baseline) Difference of pain intensity between left and right foot and/or lower leg of not more than 1 point on the NRS No changes in neuropathic pain medication for at least 1 month Absence of any of the exclusion criteria outlined below Exclusion Criteria: Painful (poly)neuropathy other than CIAP Presence of neuropathic pain due to any other condition than CIAP Neuropathic pain (distribution, duration, characteristics, intensity) not fulfilling the 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

Ages Eligible for Study
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Minimum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Phenytoin 10 percent cream<br>Phenytoin 10 percent cream, 2 to 4 times daily application, 2 weeks long | Drug: phenytoin cream<br>* Phenytoin cream to be applied on the neuropathic pain area<br>|
| Experimental: Phenytoin 20 percent cream<br>Phenytoin 20 percent cream, 2 to 4 times daily application, 2 weeks long | Drug: phenytoin cream<br>* Phenytoin cream to be applied on the neuropathic pain area<br>|
| Placebo Comparator: Placebo cream<br>Placebo cream, 2 to 4 times daily application, 2 weeks long | Other: Placebo cream<br>* Placebo cream to be applied on the neuropathic pain area<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in mean pain intensity measured on the 11-point numerical rating scale (NRS) between baseline and week 2 for phenytoin 20% cream versus placebo cream. | 0 = no pain, 10 = worst imaginable pain. The bigger the mean change, the better the outcome | Mean baseline vs. mean of second week of each intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in mean pain intensity from baseline 11-point numerical rating scale (NRS) to the mean NRS in the second week in double-blind response test in positive and negative participants and all participants combined | 0 = no pain, 10 = worst imaginable pain. The bigger the mean change, the better the outcome | Mean baseline vs. mean of second week of each intervention | 
| Change of EuroQol (EQ5-5D-5L) from baseline to the end of the second week of each treatment period | EQ5-5D-5L consists of 5 quality of life questions assessed on a 5 point scale: the lower the score, the better quality of life. Furthermore, a visual analogue scale from 0 to 100 is included. The higher the score, the better quality of life. | Baseline vs. end of second week of each intervention | 
| Change of Neuropathic Pain Symptom Inventory (NPSI) from baseline to the end of the second week of each treatment period | The NPSI consists of 10 neuropathic pain descriptors on the NRS, and 2 items assessing the duration of spontaneous ongoing and paroxysmal pain. The lower the score, the less pain. | Baseline vs. end of second week of each intervention | 
| Change of subscales of the Brief Pain Inventory (sBPI) from baseline to the end of the second week of each treatment period | The sBPI consists of 7 quality of life questions, assessed on the NRS. The lower the score, the better quality of life. | Baseline vs. end of second week of each intervention | 
| Change of the 3 worst pain characteristics from baseline to the end of the second week of each treatment period | The 3 worst pain characteristics are scored on the NRS. The lower the score, the less pain. | Baseline vs. end of second week of each intervention | 
| Change of Patient Global Impression of Change Scale (PGIC) from baseline to the end of the second week of each treatment period | The PGIC is a 7-point satisfaction scale. The lower the score, the better. | Baseline vs. end of second week of each intervention | 
| 30 percent and 50 percent improvement or more on the NRS compared to placebo within one patient |  | Baseline vs. end of second week of each intervention | 
| Time of carry-over effects after a treatment period |  | First week of each intervention | 
| Onset of analgesic effect after application | The onset of analgesic effect will be noted in minutes. | At the end of second week of each intervention | 
| Duration of analgesic effect | The duration of analgesic effect will be noted in hours. | At the end of second week of each intervention | 
| Daily number of cream applications |  | At the end of second week of each intervention | 
| Percentage of analgesic effect as rated by the participant | The participant will be asked about the percentage of pain reduction at the end of the second week of each intervention. The higher, the better. | At the end of second week of each intervention. | 
| Local and/or systemic side effects | At each visit and telephone call participants will be asked about possibly occurring side effects. | During the 6 weeks of double-blind phase and 1 year open phase | 
| Detection of phenytoin in plasma | Two hours after last application phenytoin plasma level will be evaluated | At the end of second week of first treatment period | 
| Predictive value of DOBRET | Correlation with DOBRET response and mean pain reduction while using phenytoin 10 percent or 20 percent cream. The stronger the correlation, the more predictive the DOBRET is. | Baseline vs. mean of second week of each intervention | 
| Use of escape pain medication | The daily amount of acetaminophen and/or non-steroid anti-inflammatory drugs | During the 6 weeks of double-blind phase and 1 year open phase | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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CIAP, cryptogenic sensory polyneuropathy, neuropathic pain