Acyclovir

Acyclovir is an antiviral drug used mainly against herpes simplex (Herpes Simplex) . It is very effective against the two herpes viruses (HSV-1 and HSV-2), but less effective against the chickenpox or mononucleosis virus . Its efficacy against cytomegaloviruses is low.

Molecule names:
Acyclovir, acyclovir (US), Acyclovirum PhEur (Latin name)

About molecule:

Chemical name 2-amino-9-((2-hydroxyethoxy)methyl)-1H-purin-6(9H)-one.

Metabolism: 
The half-life of acyclovir is 2 to 3 hours. Elimination of acyclovir is renal. There is no active metabolite in the human body.

Effects:
Acyclovir is a guanine analogue. Acyclovir blocks viral DNA synthesis only in infected cells1 .
Mechanism of action of acyclovir :
Acyclovir is metabolized by viral thymidine kinase (HSV1 thymidine kinase), acyclovir is phosphorylated to acyclovir monophosphate (ACMP). As cells not infected with herpes cannot phosphorylate acyclovir, because only non-human viral thymidine kinase can give rise to ACMP, this molecule becomes selective for human cells infected with this virus.
Subsequently, monocyclovir monophosphate is again phosphorylated twice by human thymidine kinase, this time by acyclovir triphosphate, which acts as an antimetabolite or false substrate.
This ends up inhibiting the formation of viral DNA (herpes virus) and blocks the formation of new viruses.

Indications:
Note: It is important to start acyclovir therapy as soon as possible for herpes.
– Cold sores (applied as a cream – often sufficient for cold sores – or orally).
– Genital herpes (usually taken by mouth as a lozenge).
– Generalized herpes (usually taken by mouth or as a tablet).
– Herpes encephalitis or herpes simplex in newborns (taken as an injection).
– Herpes prophylaxis (usually taken by mouth).
– Herpes zoster (usually taken orally, not proven to prevent, see below under Observations).
– Chickenpox(usually taken orally, but acyclovir has a weak effect against the chickenpox virus, indicated in some cases of chickenpox, especially in complications).
– Mononucleosis .

Side Effects:
Internal Use:
More than 10% of people taking acyclovir complain of headaches and dizziness. Occasionally, acyclovir can lead to gastrointestinal complaints such as nausea, vomiting or diarrhea. In about 3% of cases, a hypersensitivity reaction with symptoms such as hives (eg, itching) may occur. Severe anaphylactic reactions or shock are very rare. Especially at high doses of aciclovir and in patients suffering from chronic renal failure, psychiatric or neurological disorders may appear such as: hallucinations, anxiety, confusion, insomnia, depression…2 .
External use:
Burning, itching, redness.
Intravenous :
In case of high dose, possible encephalopathy.
For more information, please read the medication leaflet.

Contraindications:
Existing neurological diseases.
For more information, please read the medication package insert.

Interactions:
With probenecid. Interactions with other drugs or molecules are possible.
For more information, please read the medication leaflet.

Presentation:
Acyclovir is marketed in the form of 200, 400 mg and 800 mg tablets (in some countries), 50 mg/g (5%) dermatological cream, 250 mg injectable solution and 0.03 g/g ophthalmic ointment . Depending on the use of acyclovir, its dose can be changed by the doctor.

Dosage:
– For the first herpes simplex infection, the oral dose of acyclovir for an adult is 200 mg every 4 hours (5 doses over 24 hours with an overnight break). The treatment lasts from 5 to 10 days.
– For genital herpes the dose can be 400 mg every 4 hours with an overnight break.
– For herpes zoster (herpes zoster), the dose is 800 mg taken orally or as a tablet, to be taken every 4 hours (or 5 times a day) with a break at night. The recommended or usual course of treatment is 7 days.
Herpes zoster (iv) injection is 5/10mg/kg every 8 hours3 . The recommended or usual treatment is also 7 days.

Notes:
– Acyclovir was first approved in the US by the FDA in 1982.
– Acyclovir is widely used against herpes and is considered a gold standard treatment.
– Acyclovir is on the WHO list of essential medicines (updated April 2013).
Prevention of herpes zoster (critical review):
Cochrane review (DOI: 10.1002/14651858.CD006866.pub3 ) published in 2014 found that acyclovir started within 72 hours of shingles onset was no more effective than placebo in prevention of post-terpetic neuralgia (PHN), the main complication of herpes zoster.
Alternatives: 
– For herpes zoster, valaciclovir and famciclovir are more appropriate than acyclovir because of their greater bioavailability.
– For herpes simplex, valaciclovir and famciclovir are also effective. But acyclovir has more scientific studies and is available in more different dosage forms. Penciclovir, available as a cream, can be used for cold sores.

Sources & References: 
Sources:  Pharmawiki.ch References and Literature: “100 wichtige Medikamente” – Infomed (2020).

Jeanne Kenney
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I’m a stylist trainer, a content creator, and an entrepreneur passion. Virgo sign and Pisces ascendant, I move easily between my dreams, the crazy world I want, and my feet on the ground to carry out my projects.

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