Lidocaine when applied topically in the form of a plaster produces a local analgesic effect.
The efficacy of lidocaine 5% medicated plaster has been assessed in several studies. A randomised, double-blind, vehicle-controlled trial1 was conducted in 32 patients with post-herpetic neuralgia (PHN). These patients had previously responded to topical lidocaine patches for at least one month prior to study enrolment.
In the cross-over design, patients received either 14 days treatment with lidocaine 5% medicated plaster followed by vehicle (placebo) patches, or vice versa. Pain relief was measured on a six-point verbal Pain Relief Scale (0 = worse, 5= complete relief). The primary endpoint was 'time to exit' where patients withdrew because their pain relief was two points lower for any two consecutive days as compared with the patient's pre-study pain relief.
The median time to exit with the lidocaine patch was greater than 14 days compared to the vehicle patch exit time of 3.8 days. Twenty-nine subjects reported moderate or greater pain relief for at least five days with lidocaine patches compared to 13 subjects with placebo patches.
Only seven subjects used concomitant rescue medications during the study for treatment of PHN, three during the lidocaine patch phase and four during the placebo phase. No serious adverse effects were reported that were deemed possibly or probably related to the study medication. Any adverse effects reported were either 'mild' or 'moderate' in severity.
1. Galer B, Rowbotham M, Perander J et al. Topical lidocaine patch relieves postherpetic neuralgia more effectively than a vehicle topical patch: results of an enriched enrolment study. Pain 1999: 80; 533-38.
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