Gabapentin May Help Prevent Postherpetic Neuralgia

Megan Brooks

April 14, 2011

April 14, 2011 — Treating patients with acute herpes zoster with the anticonvulsant gabapentin may help prevent postherpetic neuralgia (PHN), according to results of an uncontrolled, open-label study conducted at a private dermatology clinic in Texas.

Whitney Lapolla, MD, of the Center for Clinical Studies in Houston, Texas, and colleagues report their findings online April 11 in the Archives of Dermatology.

Based on her experience, Dr. Lapolla told Medscape Medical News, she would advise clinicians to "consider prescribing gabapentin in addition to standard antiviral therapy and analgesics for patients with moderate to severe shingles pain on presentation."

Whitney Lapolla, MD

PHN "Exceedingly" Hard to Treat

Each year, more than 1 million adults in the United States contract acute herpes zoster, and a large proportion of them will go on to have PHN several months after the acute infection subsides.

It is "exceedingly" difficult to treat and can severely impair quality of life, Dr. Lapolla and colleagues note in their article.

Current therapies for PHN include tricyclic antidepressants, anticonvulsants, and various oral and topical analgesics; however, these are only partially effective at alleviating the excruciating pain of PHN, which has been described as burning or throbbing pain, sharp stabs, or electric shocks.

Gabapentin has been shown to be effective for PHN, and some animal studies suggest that it may be more effective when given acutely than when after PHN develops.

To investigate if it might help prevent PHN, Dr. Lapolla and her colleagues recruited 133 men and women (mean age, 64.6 years) who presented with herpes zoster within 72 hours of vesicle appearance. At presentation, 38% of patients complained of moderate pain (4 to 6 on the 10-point Likert scale), and 62% complained of severe pain (7 to 10 on the Likert scale).

During acute treatment, patients received 1000 mg of valacyclovir 3 times daily for 7 days plus gabapentin at a starting dose of 300 mg daily, titrated for 4 weeks up to a maximum of 3600 mg daily, adverse effects permitting.

Gabapentin was discontinued at the end of 4 weeks in patients reporting mild or no pain (< 4 on the Likert scale). At 4 weeks, patients with an average pain score of 4 or higher could continue gabapentin for another 4 weeks. After 4 or 8 weeks, the dose of gabapentin was tapered for 1 week. No patient received the drug beyond week 9.

Record Low PHN Levels

The clinicians found that the proportion of patients reporting pain decreased steadily. At week 12, the prevalence of zoster pain (> 0 on the Likert scale) was 20.3%; at week 16, it was 18.0%; and at week 24, it was 9.8%.

Also, at week 24, the incidence of PHN (> 3 on the Likert scale at 90 days after zoster infection) was 6.8%. The researchers say that, to their knowledge, these are the lowest levels "ever reported in a formal study." The literature cites PHN prevalence ranging from 9% to 73%, Dr. Lapolla and colleagues note.

The study team also reports that patients with moderate pain at baseline were less likely to have pain at weeks 12, 16, and 24, than patients with severe pain at the outset. The first visit with complete cessation of pain was 8 weeks for patients with moderate pain initially and 12 weeks for patients with severe initial pain. Quality of life improved during the course of the study in all patients.

The study included patients most likely to have PHN: those aged 50 years and older with worse acute pain. Because none of the patients used gabapentin beyond 9 weeks, and zoster pain assessments were made much later (at 12, 16, and 24 weeks), gabapentin "did not mask PHN pain, it prevented PHN from developing," the researchers note.

They acknowledge that without a placebo control, it is not possible to confirm the benefit of acute gabapentin therapy; "therefore, larger-scale blinded studies are necessary," they write.

"In the meantime, gabapentin should be considered as an adjunct to antiviral therapy for acute herpes zoster management, particularly in patients at highest risk for PHN," the study authors conclude.

The study was supported by the Foundation for Advances in Therapeutics and Prevention. GlaxoSmithKline provided valacyclovir for the study. Dr. Lapolla and 5 colleagues have disclosed participation in grant-supported research for Pfizer-Wyeth, Inhibitex, and NeurogesX.

Arch Dermatol. Published online April 11, 2011. Full text

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