Amid all the bad publicity for AZT, acyclovir (or Zovirax, as it is known by brand name) is Wellcome’s big success story. This anti-viral drug inhibits a variety of human herpes viruses, including herpes simplex type 1 (cold sores), type 2 (genital herpes).
The drug works by inhibiting viral DNA replication and terminating DNA. When used for genital herpes, double-blind placebo-controlled studies have showed that orally administered acyclovir significantly reduced the duration of acute infection, pain and new lesion formation, and also the frequency and severity of recurrences in more than 95 per cent of patients. In another study almost half of patients remained free of recurrences in the first year and nearly two-thirds by the third year. This, of course, entails taking the drug continuously over that time.
As for shingles, scientific studies of 187 patients showed that the drug shortened the times for lesions, scabbing, healing and pain. A recent study shows no benefit to long-term Zovirax therapy with or without steroids over seven-day treatment with Zovirax alone (New Eng J of Med, 31 March 1994).
The biggest problem is with chronic use of acyclovir. This can lead to the formation of resistant viruses which will no longer respond to the drug. Furthermore, animal studies have shown that Zovirax can cause decreased production of sperm and in females, cause implantation difficulties, leading to infertility, and also possible chromosomal mutation and birth defects. Wellcome cautions that the drug shouldn’t be taken by pregnant women or nursing mothers. The most frequent adverse reactions were headache, numbness and tingling, general muscle weakness and pain, vomiting, diarrhea, dizziness, anorexia, swelling, leg pains, swollen glands in the groin, and lowered white blood cells.