Friday, February 6, 2009
Supportive Care in Cancer has published a randomized, double-blind, placebo-patch controlled trial of the 5% lidocaine patch for postsurgical incisional pain in cancer patients. It involved an unfortunately small number of patients (28 randomized, 18 completed the trial) who had greater than one month of pain in/near their surgical site (most had breast or lung surgeries), at least 4/10, and with some 'neuropathic features' (had to have burning, paresthesias, or allodynia). They received active (up to 3 at a time, worn 18 hours a day) or placebo patch each for a month, then switched. The study was powered for 50 patients per arm.
There were no statistically significant differences in pain between groups at any times (reported worst, least, average, current pain intensity) - and even eye-balling the graphs it's tough to say there were consistent trends. Pain interference was modestly (and statistically significantly) improved with the active patch (e.g. interference with work), but that was it. Unfortunately I don't think we can conclude anything from these data. This seemed to be a well-thought out, well-designed study, with reasonable outcomes, but there just weren't sufficient number of subjects to tell a difference. Even in the best studies on the patch (all involving post-herpetic neuralgia) which showed significant improvement in the active patch subjects - the average improvement was modest (in the ballpark of 1.5 points on a 0-10 pain scale) - and one is never going to show a significant difference with these small numbers.
This raises the question - why even pay attention to a symptomatic therapy whose effects are so modest you need 100+ patients to even demonstrate a little improvement? Especially one as costly as the lidocaine patch? Cost concerns aside, I continue to use the patch because 1) it's incredibly safe and well tolerated (no drug interactions or really no demonstrable side effects other than skin stuff), and 2) a small minority of my patients who use it report tremendous benefit - solid pain relief, opioid sparing, etc. etc. (a substantial minority in addition report modest improvements with it). It's possible that the #2 phenomenon is largely placebo (especially since there's yet to be any controlled data clearly demonstrating the patch is beneficial outside of postherpetic neuralgia), and in some ways the lidocaine patch seems to be a perfect storm of a placebo: a prescription-only treatment containing a 'numbing medicine' with fancy packaging that you apply right where it hurts. Sounds good to me. #2 is why I keep using it, but I remain agnostic about what I'm actually prescribing, and I'm curious as to what others think of the patch. From a health-systems standpoint I understand why many insurers and hospices won't use it.
Andrea L. Cheville, Jeff A. Sloan, Donald W. Northfelt, Anand P. Jillella, Gilbert Y. Wong, James D. Bearden III, Heshan Liu, Paul L. Schaefer, Benjamin T. Marchello, Bradley J. Christensen, Charles L. Loprinzi (2009). Use of a lidocaine patch in the management of postsurgical neuropathic pain in patients with cancer: a phase III double-blind crossover study (N01CB) Supportive Care in Cancer DOI: 10.1007/s00520-008-0542-x