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Current Approaches to the Management of Post Herpetic Neuralgia: Part 2 Non-Systemic

ABSTRACT

In the last issue of Skin Therapy Letter, we described oral therapies which are useful in the management of post herpetic neuralgia (PHN), a common manifestation of herpes zoster (shingles) in the elderly1. These therapies included the nucleoside analogue antiviral agents, acyclovir (Zovirax®, Glaxo Wellcome), valaciclovir (Valtrex®, Glaxo Wellcome) and famciclovir (Famvir®, SmithKline Beecham); corticosteroids; tricyclic antidepressants; and anticonvulsants.

In this article, we examine the other approaches to PHN management. Claims have been made for products ranging from vitamins to snake venom for patients who develop PHN. However, few controlled clinical trials have been conducted and, of non-oral approaches to the treatment of PHN, only topical lidocaine, capsaicin, and various nonpharmacologic techniques have been shown to be effective2. This article describes these approaches to the treatment of PHN.


Key Words: post herpetic neuralgia, PHN, herpes zoster, shingles, acyclovir, valaciclovir, famciclovir, tricyclicantidepressants, anticonvulsants

Topical Therapy

Idoxuridine

Idoxuridine dissolved in dimethysulfoxide (DMSO) is available in many European countries for the treatment of herpes zoster. This product may reduce the time to rash healing and duration of acute pain, but its effect against the development of PHN is inconclusive.3,4

Capsaicin

Capsaicin cream (Zostrix®, GenDerm), which depletes the peptide neurotransmitter substance P, is approved by the US FDA for the treatment of PHN. Capsaicin, applied 3 -4 times daily for four weeks, was shown to reduce the duration of PHN by 21%, compared to 6% with placebo (p <0.05), in patients who had suffered from PHN for at least six months. However, 61% of patients in the capsaicin group experienced burning on application of the cream, compared with 33% of placebo recipients. This burning can be intolerable for up to one-third of patients who receive the product in clinical practice.2

Other Topical Therapies

Topical lidocaine was tested in one trial and found to confer short-term benefit in patients with PHN. Ethyl chloride spray has also been found to provide some relief.2 Topical acyclovir was found to be ineffective against herpes zoster.1

Electrical Stimulation and Surgical Procedures

Electrical stimulation of the thalamus and transcutaneous electrical nerve stimulation (TENS) have provided relief in patients with intractable PHN.2 TENS has been used for over 20 years, but there is still a controversy over its utility, with some studies showing only a transient effect and others showing a prolonged benefit.3

Anterolateral cordotomy has provided relief in some patients, as have other surgical approaches. However, none have shown consistent benefit against PHN.2,3

Vaccination

Herpes zoster is caused by a reactivation of the latent varicella zoster virus (VZV), the causative agent of chickenpox. A VZV (live Oka-strain) vaccine is approved for inoculation against chickenpox, although it is not 100% effective.5 However, if chickenpox could be prevented for life then zoster would eventually become a disease of the past.

Furthermore, a VZV vaccine may also be useful in reinvigorating the humoral and cellular responses to the virus in the elderly. An exploratory study with the Oka vaccine on 200 healthy adults over 60 years of age suggested that enhancement of cell mediated immune response (CMIR) in the elderly can lead to a decrease in the incidence and/or severity of reactivated zoster. The vaccine elevated CMIR to the levels seen in 40-year-olds and, after four years, none of the subjects had experienced true cases of zoster when at least eight cases would have been expected. A large, double-blind, placebocontrolled clinical trial of the vaccine in an elderly population is currently underway.6

Recommendation

As we recommended in the last article, the prevention of PHN is the best strategy in herpes zoster. Oral antiviral therapy offers patients the best opportunity to minimize zoster pain, particularly if initiated within 72 hours of rash onset. In patients who develop PHN, however, tricyclic antidepressants are the mainstay of therapy in patients who do not respond to conventional analgesics.7,8 Topical lidocaine-prilocaine cream, or lidocaine gel (5%)have also been recommended. Non-pharmacologic approaches can be used to complement the medical treatment. For very severe pain, patients may need to be referred to painmanagement specialists.2

References

  1. Wood MJ, Easterbrook P. Shingles, scourge of the elderly. The acute illness. In: Sacks SL, Straus SE, Whitley RJ, Griffiths PD. Clinical management of herpes viruses. Washington DC: IOS Press, 1995: 193-209.
  2. Kost RG, Straus SE. Postherpetic neuralgia pathogenesis, treatment, and prevention. N Engl J Med 1996; 335: 32-42.
  3. Easterbrook P, Wood M. Post-herpetic neuralgia. What do drugs really do? In: Sacks SL, Straus SE, Whitley RJ, Griffiths PD. Clinical management of herpes viruses. Washington DC: IOS Press, 1995: 211-235.
  4. Wood MJ, Ogan PH, McKendrick MW, et al. Efficacy of oral acyclovir treatment of acute herpes zoster. Am J Med 1988; 85 (suppl 2A): 79-83.
  5. Hardy I, Gershon AA, Steinberg SP, et al. The incidence of zoster after immunization with live attenuated varicella vaccine. N Engl J Med 1991; 325: 1545-1550.
  6. Levin M. Presentation given at the 34th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Orlando, Florida, USA, 4-7 October 1994.
  7. Rowbotham MC. Treatment of postherpetic neuralgia. Semin Dermatol 1992; 11: 218-225.
  8. Relieving the misery of herpes zoster and its sequelae. Drugs Therapy Perspect 1995; 6: 6-9.

In this issue:

  1. Human Skin Equivalent, Apligraf Cellular technology benefits wound repair
  2. Current Approaches to the Management of Post Herpetic Neuralgia: Part 2 Non-Systemic
  3. Update on Sunscreens
  4. Update on Drugs and Drug News - Number 5 1997