Aciclovir

Aciclovir (ACV), also known as acyclovir in the US, is an antiviral medication designed for herpesviruses. It is mostly used to treat herpes simplex virus (cold sores or genital sores) and varicella zoster virus (chickenpox or shingles). It also has weaker activity against cytomegalovirus and Epstein-Barr virus. Aciclovir is a nucleic acid analogue derived from guanosine. It works by blocking the production of the viral DNA. Use of aciclovir has largely been replaced with use of the newer version, valaciclovir.

Mechanism of action
Aciclovir inhibits replication of the herpesvirus by targeting the viral DNA polymerase, a viral enzyme which makes copies of the viral genome. The viral DNA polymerase mistakenly incorporates aciclovir into the viral genome instead of guanosine, which effectively terminates the copying of the genome.

Clinical Use
Aciclovir is prescribed for active infections of herpes simplex virus (cold sores, genital sores) as well as for active infections of varicella zoster virus (chickenpox, shingles). It is also used to prevent reactivation of these viruses while the viruses are in the latent, inactive state. Even when the virus appears to be in the latent, inactive state, aciclovir can reduce the proinflammatory cytokines produced by infected cells.

Aciclovir as a treatment for ME/CFS
In 1988, Straus et al. conducted a double-blind, placebo-controlled study of the efficacy of aciclovir in patients with CFS. One group was given a course of IV aciclovir followed by oral aciclovir. The other group received a placebo. Patients with and without antibodies to Epstein-Barr virus early antigens were included in the study. The researchers concluded that aciclovir, as used in this study, did not ameliorate the symptoms of chronic fatigue syndrome: "Of the 24 patients who completed the trial, similar numbers improved with acyclovir therapy and with placebo (11 and 10, respectively). Neither acyclovir treatment nor clinical improvement correlated with alterations in laboratory findings, including titers of antibody to Epstein-Barr virus."

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 * Wikipedia - Aciclovir