Antiviral Drugs

Viral skin infections, particularly those caused by the Herpesviridae family (herpes simplex virus HSV-1 and HSV-2, and varicella-zoster virus, VZV), are common acute conditions that can lead to postherpetic neuralgia (PHN), tissue necrosis, or widespread spread across already damaged skin (as in Kaposi varicelliform eruption). Systemic antivirals work by selectively blocking viral DNA replication through inhibition of the viral DNA polymerase.

At Haute-Derma, our antiviral protocols are built around three principles: starting treatment early, within the 72-hour "golden window"; making the most of the high bioavailability of newer prodrugs; and using preventive (suppressive or short-course) therapy for frequent recurrences and before invasive procedures such as laser, peels, and microneedling.

Mechanism of Action and Pharmacodynamics of Anti-Herpes Antivirals

Selective Inactivation of Viral DNA Polymerase

Nucleoside analogue antivirals (acyclovir, valacyclovir, famciclovir) must be phosphorylated in three steps before they become active:

Selective first step (thymidine kinase): Inside an infected cell, the virus's own thymidine kinase (TK) adds the first phosphate group, producing the monophosphate form. Healthy cells lack viral TK and do not activate the drug, which makes it highly selective.
Conversion to the triphosphate: Host-cell kinases then add two more phosphate groups, forming acyclovir triphosphate or penciclovir triphosphate.
DNA polymerase inhibition and chain termination: The triphosphate competes with natural dGTP and is built into the growing viral DNA strand. Because it lacks a free 3'-OH group, the strand cannot be extended any further (chain termination), and the virus can no longer replicate.

How the Newer Agents Differ

Acyclovir: The original molecule. Oral bioavailability is very low (only about 15–20%) and the half-life is short, so it has to be taken several times a day (4–5 doses daily).
Valacyclovir: The L-valyl ester prodrug of acyclovir. It is rapidly absorbed from the gut and almost completely converted to acyclovir in the liver by valacyclovir hydrolase, raising oral bioavailability to 55–70% (3–5 times that of acyclovir).
Famciclovir: The prodrug of penciclovir, with oral bioavailability of 77% and a much longer intracellular half-life (up to 10–20 hours in VZV), which suits it well to shingles treatment.

Clinical Indications in Dermatology

Herpes Simplex Infection (HSV-1, HSV-2)

Acute orolabial and genital herpes: Shortens the blistering phase, eases burning and stinging, and speeds up healing.
Frequently recurrent herpes (≥ 6 episodes a year): Continuous suppressive therapy prevents outbreaks and lowers the risk of passing the virus to a partner.
Prophylaxis before cosmetic procedures: Required before fractional CO2 laser, medium-to-deep chemical peels, mesotherapy injections, or microneedling in patients with a history of HSV.

Varicella-Zoster Virus (VZV) Infection

Shingles (herpes zoster): Reduces skin damage, limits the spread of blisters, and lowers the risk of postherpetic neuralgia (PHN).
Ophthalmic shingles (herpes zoster ophthalmicus): A combined dermatologic and ophthalmologic emergency that calls for high-dose oral antivirals right away to protect vision.

Pharmacology, Toxicity, and Drug Interactions

Kidney toxicity (crystalluria and renal failure): Acyclovir is cleared mainly unchanged by glomerular filtration. At high concentrations or in dehydrated patients, it can precipitate as crystals in the renal tubules and cause acute obstructive kidney injury.
- What we do: Advise patients to drink plenty of fluids (at least 2–2.5 L a day) throughout treatment, and reduce the dose according to creatinine clearance (eGFR) in people with kidney impairment.
Central nervous system side effects: Headache, dizziness, confusion, or hallucinations (rare, and usually seen in patients with kidney impairment whose dose has not been adjusted).
Drug interactions: Taking probenecid or cimetidine at the same time reduces the renal clearance of acyclovir and raises its blood levels.

Treatment and Monitoring at Haute-Derma

Assessment and Confirming the Diagnosis

The clinical diagnosis rests on clustered blisters on a red base, following a dermatome (shingles) or sitting around body openings (HSV).
For atypical presentations or immunocompromised patients, we perform a Tzanck smear to look for multinucleated giant cells, or HSV/VZV PCR testing.

Treating Within the "Golden Window"

Shingles: Start valacyclovir 1000 mg three times a day within 72 hours of the first blister for the best protection of the nerve.
Prophylaxis for cosmetic procedures: Start valacyclovir 500 mg once or twice a day from 1 day before the procedure and continue for 5–7 days afterward.

Review and Follow-Up After Treatment

Check how well the skin lesions have healed after 7 days.
Assess and manage pain with nerve-pain medications (gabapentin, pregabalin) if the patient has persistent stabbing or shooting pain after shingles.

Frequently Asked Questions (FAQs)

+Why is valacyclovir preferred over acyclovir for shingles?

Acyclovir and valacyclovir end up as the same active drug, but acyclovir has very low bioavailability (only 15–20%), so patients have to take it 5 times a day (every 4 hours), which makes it hard to stick with. Valacyclovir is a prodrug with bioavailability of up to 70%, so it keeps drug levels high and steady with just 3 doses a day. That makes it much easier to take consistently and gives better suppression of VZV.

+Is antiviral prophylaxis really necessary before fractional CO2 laser or a chemical peel?

Yes, it is required for anyone with a history of facial or lip herpes. Invasive procedures such as fractional CO2 laser, medium-to-deep peels, and microneedling cause thermal injury and break down the skin barrier over a wide area, which can trigger a sudden flare of herpes virus lying dormant in the trigeminal ganglion. Without prophylaxis, HSV can spread across the injured skin and cause permanent pitted scars and tissue necrosis.

+Can oral antivirals completely clear the herpes virus from the body?