Acyclovir is an antiviral most commonly used to
treat shingles, chickenpox, or genital herpes. The
effect of acyclovir is based on a selective
inhibition of the replication of herpes viruses.
The drug is phosphorylated by viral thymidine kinase.
As a triphosphate acyclovir inhibits the DNA
polymerase and thus the formation of viral DNA. The
host cells are not considerably affected. Varicella-zoster
viruses are not as sensitive as herpes simplex
viruses. Resistant herpes viruses, that lack the
thymidine kinase, have been observed almost
exclusively in immunocompromised subjects.
For the
treatment of immunocompetent subjects
acyclovir only plays a minor role. Herpes simplex:
For genital primary infections, oral acyclovir
entails a considerably faster healing rate than a
placebo or an acyclovir ointment. For herpes simplex
keratitis, local or oral therapy is successful.
Herpes simplex encephalitis and herpes simplex
neonatorum must be treated intravenously. Patients
with frequently relapsing herpes simplex
(labial or genital) benefit from long-term,
prophylactic acyclovir administration. However,
treatment of an isolated (labial or genital) herpes
relapse is not indicated.
The
effect of acyclovir against most forms of the
varicella-zoster disease is marginal. A herpes
zoster of the cornea should be treated as early as
possible with high doses of acyclovir. Acyclovir
only brings limited benefit for zosters (and
varicella) in other localisations. Specialists do
not agree on its advantages as far as post-herpetic
neuralgias are concerned.
The case
is different for immunocompromised subjects (chemotherapy,
HIV infection, lymphoma) whose herpes simplex and
varicella-zoster infections should all be
treated with oral or parenteral acyclovir.
