Randomized, Placebo-controlled Crossover Trial Evaluating Topical Lidocaine Patch(es) for Mechanical Neck Pain

Neck pain is one of the 5 most common pain conditions and leading causes of disability worldwide. According to one systematic review, the estimated mean point, annual, and lifetime prevalence rates were 7.6%, 37.2% and 48.5%, respectively. In the Global Burden of Disease 2010 study, neck pain was ranked as the fourth most common cause of disability in the United States.

Among individuals with chronic neck pain, injections work for only a small percentage of patients and their effects are generally short-lived, while studies evaluating the long-term effectiveness of surgery are mixed. Among randomized, placebo-controlled trials evaluating medications for chronic neck pain, only topical diclofenac has been shown to be effective, suggesting that muscles and other superficial tissues play an important role.

Topical local anesthetics have been shown in randomized trials to alleviate some forms of neck pain (trapezius muscle) associated with myofascial trigger points, but a well-designed placebo- controlled trial found no evidence of efficacy for low back pain. This suggests that the pain generators in the neck may be more superficial than in the low back. The erector spinae and deep intrinsic muscles in the low back generally lie several inches beneath the surface, while the penetration of topical lidocaine is typically limited to around 1 cm without penetration enhancers.

A drawback of topical local anesthetic creams is that they can adhere to clothing, making absorption unreliable. They may also be messy and, on exposed skin, unsightly. This has led to the widespread adoption of topical local anesthetics embedded in patch form. Limitations of the current, commercially available formulations of topical lidocaine patches (Lidoderm, Endo Pharmaceuticals, Chadds Ford, PA) include poor bioavailability, estimated at 3%, and poor adherence. A newer formulation of topical lidocaine (ZT Lido, Scilex, San Diego, CA) that contains higher bioavailability (36 mg provides equivalent exposure to 700 mg of Lidoderm) and less variability, along with better adherence (> 90% adherence in 75% of individuals at 12 hours vs. 13.6% for Lidoderm), was recently approved for post-therapeutic neuralgia. A high adherence rate is necessary to maximize benefit in a physically active (i.e. military and VA population) cohort.

In this randomized, double-blind, placebo-controlled crossover study, patients with non-radicular neck pain will be allocated in a 1:1 ratio to receive up to three topical lidocaine or placebo patches, to be applied 12 hours per day. At the end of four weeks, patients will return for their post-phase I treatment evaluation. One to two weeks after the initial treatment, patients will crossover to receive the treatment they did not receive originally, to be applied in the same fashion for the same 4-week period. The primary outcome measure will be average neck pain over the past week, 4 weeks post-treatment.