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Acyclovir-Resistant Shingles Definition

Shingles is a reactivation of the chicken pox virus, herpes zoster. Acyclovir is a drug that treats---thought doesn't cure---herpes viruses, including herpes zoster. When acyclovir is ineffective even when properly administered it is typically a sign that the virus is resistant to the medicine.

  1. Why Is Shingles Resistant?

    • It is believed that when shingles are resistant to treatment by the antiviral drug acyclovir it is because of the emergence of new forms of the virus. In general, viruses can make small, gradual changes over time.

    Valacyclovir or Famciclovir

    • Valacyclovir and famciclovir are also antiviral drugs, and since they are similar to acyclovir, an acyclovir-resistant form of the shingles virus will most likely not be affected by treatment with either of them.

    Incidence of Resistant Viruses

    • According to aidsmed.com, drug-resistant forms of the shingles virus have occurred infrequently and only in HIV-positive patients.

    Alternative Treatment

    • Herpes zoster viruses resistant to acyclovir are usually treated with foscarnet instead. Foscarnet is marketed under the brand name Foscavir.

    Foscarnet Administration

    • Foscarnet is given intravenously through an I.V. line, usually three times daily, rather than orally.

    Cidofovir

    • Cidofovir is another antiviral medication that can treat acyclovir-resistant shingles. Both foscarnet and cidofovir act by inhibiting the viral polymerase (enzyme).

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