Postherpetic neuralgia: search for treatment

Two drugs are prescribed for the prevention of postherpetic neuralgia, the disabling pain that can persist long after the acute phase of shingles is over. The antiviral drug acyclovir and corticosteroids are believed to prevent or shorten the course of postherpetic pain. A new trial involving 349 people with shingles shows neither drug fulfills its promise (New England Journal of Medicine, 31 March 1994).

Earlier studies have demonstrated the benefit of acyclovir in relieving the pain of shingles. This is an acute viral infection (herpes zoster) that shows up as a rash of painful skin eruptions, tracing the course of the infected nerve. It is caused by a reactivation of the varicella-zoster virus that lies dormant in the body following a childhood bout of chicken pox. Among the triggering factors are exposure to someone with chicken pox, stress, fatigue, anticancer drugs, and diseases that destroy the immune system.

Three clinical trial show that people given acyclovir for seven to ten days have a lower incidence of prolonged pain, compared to people given a placebo. However, doubts surround the claims for acyclovir and steroids as a preventive against postherpetic neuralgia, a common complication of shingles. The incidence of postherpetic neuralgia following shingles ranges from 5-57% with the higher occurrence among the elderly and people in whom disease, such as AIDS, has impaired the immune system.

The pain can be severe, persisting for months and, in some cases even years. As this new study shows, postherpetic neuralgia is resistant to successful treatment. The goal was to determine whether 21 days of acyclovir or the addition of prednisolone offered any advantage over the standard seven-day treatment with acyclovir for shingles in reducing the incidence of postherpetic neuralgia.

Dr. Martin J. Wood and colleagues at several medical centers in the United Kingdom assigned 349 participants with a shingles rash of less than 72 hours' duration to receive acyclovir for seven days with either prednisolone (a steroid) or placebo, or acyclovir for 21 days with either prednisolone or placebo. The participants were examined often during the first 28 days of the study and then monthly until month six.

Neuralgia Not Affected

Results showed that the longer treatment course of acyclovir, with or without prednisolone, produced only a slight benefit over the standard seven-day course of acyclovir. Prednisolone healed a significantly higher proportion of the rash area on days seven through 14; it also lowered the incidence and severity of the shingles pain. Despite these improvements, the investigators concluded that the risks of steroid therapy outweigh the benefits. "Given that a short course of prednisolone is not without adverse effects, even in patients with no contraindications, the use of this steroid in herpes zoster cannot be recommended," wrote Dr. Wood and colleagues.

The study participants who took the steroid drug reported more adverse reactions, most frequently indigestion, hot flashes, and edema. There was one incidence of hematemesis (vomiting blood) reported by someone taking steroids, even though the study excluded people who were at risk for such an adverse effect.

As for the secondary purpose of these drug regimens--the prevention of postherpetic neuralgia--neither acyclovir nor steroids reduced the frequency of this painful condition. Steroids' ineffectiveness for the prevention of postherpetic neuralgia was demonstrated in an earlier placebocontrolled Scandinavian study published seven years ago in The Lancet. Yet they continue to be preprescribed for this purpose.

This study was supported by a grant from the Wellcome Research Laboratories, Beckenham, United Kingdom. Burroughs Wellcome is the manufacturer of acyclovir, which is sold under the brand name of Zovirax.

What Else is There?

Several other medical therapies are used in the treatment of postherpetic neuralgia, but there is little or no scientific evidence to demonstrate their efficacy. Among the most common are capsaicin (brand name: Zostrix), a topical analgesic cream whose active ingredient is a hot pepper derivative; local anesthetics like lidocaine; antidepressant drugs; anticonvulsants; and nerveblocks.

In the self-help category, people have used topically applied vitamin E oil, vitamin C supplements, and lysine (an amino acid) supplements, all of which can be purchased in health food stores.

The most promising research-backed treatment involves aspirin dissolved in chloroform and applied directly to the painful area. Two published studies show that this treatment relieves the pain of both shingles and postherpetic neuralgia (Pain, March 1992 and Archives of Neurology, October 1993). Each study involved about 45 participants.

The 1992 study, which was conducted in Milan, Italy, reported: "A striking reduction in the percentage of [shingles] patients developing postherpetic neuralgia was observed in the treated group, as compared with [untreated cases] reported in the medical literature (4% vs. 50-70%)." The 1993 study, which was conducted at the State University of New York Health Science Center, Syracuse, New York, showed that the aspirin/chloroform treatment helped people in the acute phase of shingles and those suffering postherpetic neuralgia. "All participants reported substantially decreased pain promptly after treatment, with maximum relief at 20 to 30 minutes and lasting two to four hours."