Antiviral – nucleoside analogue
Updated · Methodology
First line
First-line for HSV-1 and HSV-2 infections of various locations: primary and recurrent genital herpes, herpes encephalitis (IV), neonatal herpes. In primary genital herpes 400 mg three times daily for 7–10 days; recurrences – 800 mg three times daily for 2 days or 400 mg five times daily for 5 days. Suppressive therapy 400 mg twice daily for more than 6 recurrences per year reduces them by 70–80%.
Sources
ICD-10: B00 · ICD-11: 1F00.Z
First line
First-line for herpes zoster per 2024 and 2007. Dose 800 mg five times daily for 7 days. Starting within 72 hours of rash onset reduces pain intensity, skin lesion duration, and postherpetic neuralgia risk. Valacyclovir and famciclovir have more convenient three-times-daily dosing with equivalent efficacy and are often preferred.
Sources
ICD-10: B02 · ICD-11: 1E91
First line
Used in recurrent herpes labialis. Topical 5% cream is applied 5 times daily for 4 days, starting in prodrome. The Cochrane 2007 meta-analysis showed topical aciclovir reduces episode duration by 0.5–1 day with minimal toxicity. Oral aciclovir 400 mg three times daily for 5 days is more effective in severe recurrences. In patients with more than 6 episodes per year, suppressive therapy 400 mg twice daily long-term is used.
Sources
ICD-10: B00.1 · ICD-11: 1F00.01
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Aciclovir is an antiviral drug active against herpesviruses (HSV-1, HSV-2, VZV). It is prescribed for infections caused by these viruses – genital and orolabial herpes, chickenpox, and shingles (AEMPS Ficha Técnica). For common colds or flu, aciclovir does not work – respiratory virus pathogens (rhinoviruses, adenoviruses, coronaviruses, influenza) are not susceptible to this drug. Taking aciclovir at the first signs of a cold is not justified. The drug can cause nausea, headache, and acute kidney injury with intravenous administration. If aciclovir was prescribed for a cold, consider seeking a second opinion.
A guanosine analogue. In virus-infected cells, viral thymidine kinase (TK) phosphorylates aciclovir to the monophosphate; cellular enzymes then convert it to active triphosphate. Aciclovir triphosphate competitively inhibits viral DNA polymerase and incorporates into growing DNA, terminating synthesis. Selectivity comes from absence of viral TK in uninfected cells. Effective against HSV-1, HSV-2, and VZV; less so against EBV and CMV. Half-life 2.5–3 hours.
AEMPS summary of product characteristics (section 4.6): a post-marketing pregnancy registry of women exposed to any aciclovir formulation found no increase in birth defects compared with the general population, and the defects that occurred showed no consistent or unique pattern pointing to a common cause. In internationally accepted standard tests, systemic aciclovir caused no embryotoxic or teratogenic effects in rabbits, rats or mice. One non-standard rat study found fetal abnormalities together with maternal toxicity after high subcutaneous doses; the clinical relevance of this finding is uncertain. Aciclovir is used in pregnancy only when the potential benefits outweigh the possibility of unknown risks.
Compatible with breastfeeding. Moderate milk concentrations but low infant GI absorption.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Verbatim lines from the interaction sections, in the language of the label
«Un estudio experimental en cinco sujetos masculinos indicó que la terapia concomitante con aciclovir aumenta el AUC de teofilina totalmente administrada en aproximadamente el 50%. Se recomienda medir…»AEMPS, section 4.5 · Open on CIMA
«Antivirales: ritonavir aumenta significativamente las concentraciones plasmáticas de norpetidina, por lo que está contraindicada la administración concomitante de petidina y ritonavir (ver sección…»AEMPS, section 4.5 · Open on CIMA
«Aciclovir: Se observaron concentraciones plasmáticas más altas de aciclovir cuando micofenolato de mofetilo se administró con aciclovir, en comparación con la administración de aciclovir sólo. Los…»AEMPS, section 4.5 · Open on CIMA
«No se han observado interacciones farmacocinéticas clínicamente significativas entre sirolimus y ninguna de las siguientes sustancias: aciclovir, atorvastatina, digoxina, glibenclamida…»AEMPS, section 4.5 · Open on CIMA
«Recomendaciones relativas a la a dministración simultánea: Productos con efectos nefrotóxicos o neurotóxicos conocidos: aminoglicósidos, inhibidores de girasa, vancomicina sulfametoxazol +…»AEMPS, section 4.5 · Open on CIMA
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Aciclovir is evaluated for the following indications with varying evidence strength: Herpes simplex (evidence tier A), Herpes zoster (evidence tier A), Cold sores (herpes labialis) (evidence tier B). See the full indication matrix with dosing and citations above on this page.
Common side effects of Aciclovir (≥ 1 in 100): Nausea, vomiting, Diarrhea, Headache, Fatigue, Skin rash. See the Safety section for uncommon and serious reactions.
AEMPS summary of product characteristics (section 4.6): a post-marketing pregnancy registry of women exposed to any aciclovir formulation found no increase in birth defects compared with the general population, and the defects that occurred showed no consistent or unique pattern pointing to a common cause. In internationally accepted standard tests, systemic aciclovir caused no embryotoxic or teratogenic effects in rabbits, rats or mice. One non-standard rat study found fetal abnormalities together with maternal toxicity after high subcutaneous doses; the clinical relevance of this finding is uncertain. Aciclovir is used in pregnancy only when the potential benefits outweigh the possibility of unknown risks.
Compatible with breastfeeding. Moderate milk concentrations but low infant GI absorption.
Aciclovir is contraindicated in: Hypersensitivity to aciclovir or valacyclovir; Severe renal impairment without dose adjustment. Full list in the Safety section.
Direct links to regulator labels. Open in a new tab.
Atazanavir, Brivudine, Darunavir, Efavirenz, Famciclovir, Meglumine acridone acetate, Tilorone, Entecavir