Acyclovir for Herpes Labialis (Cold Sores)
Acyclovir, the first of the nucleoside analogues, was discovered by a team led by Gertrude B. Elion in the late 1970s. Acyclovir is a synthetic purine analogue active against herpes simplex viruses HSV-1 and HSV-2, and varicella-zoster.
Acyclovir is used to treat genital herpes simplex virus, herpes labialis (cold sores), herpes zoster (shingles), HSV encephalitis, neonatal HSV, mucocutaneous HSV in immunocompromised patients, and varicella-zoster (chickenpox).
Acyclovir is available as a topical cream, as oral capsules, tablets, and suspension, and as a powder for intravenous administration.
Herpes labialis (also known as cold sores or fever blisters) is caused mainly by herpes simplex virus type 1 (HSV-1). Infection occurs when virus penetrates through abraded skin or mucosal surfaces. HSV-1 is transmitted via direct contact with contaminated saliva or secretions. After primary infection the virus travels through sensory nerves and establishes chronic, lifelong, latent infection within neurons in sensory ganglia.
Symptoms of initial HSV-1 infection usually develop within two weeks after infection and include painful, itchy lesions on the lips and skin around the mouth. The first episode of cold sores may also be accompanied by fever, malaise, and muscle pain.
Severe herpes infection in which the lesions extend into the oral cavity, is called herpetic gingivostomatitis.
Recurrent outbreaks of cold sores are often preceded by a prodrome characterized by burning, tenderness, and tingling at the site of HSV-1 reactivation. The lesions of recurrent infections are rarely as severe as those of initial infections.
Acyclovir is effective in shortening the duration of symptoms and lesions of HSV-1 infections. The beneficial effects of antiviral therapy are more pronounced if the medication is started early after the onset of infection (during prodrome or erythema lesion stage).
Benefits of treatment
Topical acyclovir provides less benefits then oral.
Acyclovir dosage for episodic treatment14
Acyclovir is also used to prevent recurrences of herpes infection. Prophylactic daily use of acyclovir reduces reactivation of HSV17, but does not eliminate asymptomatic viral shedding.
Indications for prophylactic acyclovir therapy:
Benefits of prophylactic therapy:
Acyclovir dosage for prophylaxis14: 400 mg 2 times per day.
How long can you take Acyclovir?
Acyclovir has been shown to prevent recurrent herpes outbreaks even after more than 5 years of continuous suppressive therapy16.
1. Acyclovir does NOT cure the herpes infection or free the body of latent HSV.
2. Treatment of primary or recurrent cold sores does NOT reduces the frequency of future recurrences.
3. Acyclovir acts only during active viral replication, which largely precedes visible blisters. Therefore the drug is effective if started during prodromal stage.
Mechanism of action
Acyclovir, an acyclic guanine nucleoside analog, prevents the growth and multiplication of the herpes virus. Acyclovir can insert itself into virus DNA during virus replication. However, the drug does not prevent death of the infected cells.
Acyclovir is selectively phosphorylated only within virus-infected cells by viral thymidine kinase (TK). Further phosphorylation by cellular enzymes leads to the production of acyclovir triphosphate, which competes with the natural nucleotide, dGTP, resulting in the selective inhibition of viral DNA polymerase. Incorporation of the analogue triphosphate into the growing DNA chain prevents continued extension of the DNA chain.
HSV type 1 is the most sensitive virus to acyclovir followed by HSV type 2, varicella-zoster virus is even less sensitive.
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