• David J Kopsky, VranckenAlexander F J EAFJE0000-0003-4649-6534Department of Neurology, Brain Centre University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands., Keppel HesselinkJan MJM0000-0002-0186-8050Institute for Neuropathic Pain, Bosch En Duin, the Netherlands., van EijkRuben P ARPA0000-0002-7132-5967Department of Neurology, Brain Centre University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands.Biostatistics & Research Support, Julius Center for Health Sciences and Primary Care, University M, and Nicolette C Notermans.
• Institute for Neuropathic Pain, Amsterdam, the Netherlands.
• J Pain Res. 2020 Jan 1; 13: 877-882.

PurposeTopical analgesics are an upcoming treatment option for neuropathic pain. In this observational study, we performed a double-blind placebo-controlled response test (DOBRET) in patients with polyneuropathy to determine the personalized analgesic effect of phenytoin 10% cream.Patients And MethodsIn a double-blind fashion, 12 consecutive adult patients with symmetrical painful polyneuropathy and equal pain intensity of ≥4 on the 11-point numerical rating scale (NRS) applied phenytoin10% cream on one painful area and a placebo cream on the corresponding contralateral area. We defined responders as patients who experienced a pain reduction ≥2 NRS points from baseline and ≥1 NRS point difference in pain reduction in favour of phenytoin 10% cream compared with placebo cream within 30 minutes after application. We also evaluated the percentage of pain reduction and frequency of 30% and 50% pain relief from baseline.ResultsSix patients (50%) were responders. Compared with placebo cream, pain reduction was higher in phenytoin 10% cream-applied areas with mean difference in pain reduction of 1.3 (95% CI: 1.1 to 1.8; p<0.001) on the NRS and mean percentage difference in pain reduction of 22% (95% CI: 13% to 32%; p =0.03). All responders had at least 30% pain reduction, and 4 out of 6 had at least 50% pain reduction in the phenytoin 10% cream applied area. All non-responders had less than 30% pain reduction. No side effects were reported.ConclusionA DOBRET is easy to perform, quickly identifies an analgesic effect in responders and could be a useful tool to personalize neuropathic pain treatment with topical formulations.© 2020 Kopsky et al.

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