Intravenous acyclovir significantly reduced postherpetic neuralgia in half of the older patients who received it in an open-label pilot study, reported Dr. Dianna Quan and her associates at the University of Colorado Health Sciences Center, Denver.
These “promising” results will pave the way for a large clinical trial of the drug, the researchers said.
For most patients who develop herpes zoster (shingles) decades after childhood varicella infection, pain resolves within 4–6 weeks. But among patients over age 70, 40% have postherpetic neuralgia that persists for months or years. The exact cause is unknown, but there is evidence that low-grade varicella infection within the ganglia is a contributing factor. Noting that postherpetic neuralgia may reflect such chronic infection, Dr. Quan and her associates assessed whether antiviral therapy would help to quiet any low-grade infection and diminish pain.
They treated 12 men and 3 women aged 53–82 years whose postherpetic neuralgia had persisted for a median of 1 year and had not responded to numerous treatments including opioids, tricyclic antidepressants, and gabapentin. The subjects received 10 mg/kg IV acyclovir every 8 hours for 14 days. Three subjects withdrew from the study: one who had mild, reversible creatinine elevation likely caused by the drug, one who became ill from unrelated causes, and one who could not tolerate the IV.
The remaining 12 subjects completed the intravenous therapy and then received a 1-month course of oral valacyclovir. It was hoped that the oral antiviral would provide continued viral suppression and prolong the period of pain relief (Arch. Neurol. 2006;63:[doi:10.1001/archneur.63.7.noc60049]).
In the intention-to-treat analysis, 7 of the 15 subjects (47%) reported clinically significant pain relief after the intravenous therapy. At the conclusion of the study after the course of valacyclovir, 8 of 15 (53%) reported clinically significant pain relief.
“Based on our findings, we now believe that a large, randomized, double-blind, placebo-controlled trial is warranted,” the authors said.