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Acyclovir is a guanine analog antiviral used to shorten HSV lesions and targeted varicella courses when started promptly in children.
Start within 72 hours of rash onset for VZV when treatment is indicated (e.g., chronic skin disease, immunocompromise, >12 years).
Dosing is weight based and typically given 4 or 5 times daily; adjust for reduced renal function.
Hydration reduces risk of crystalluria and renal adverse effects.
Suppressive regimens may be used for frequent HSV recurrences—coordinate follow-up.
Topical acyclovir is less effective for oral lesions than systemic therapy in children.
Acyclovir is the cornerstone antiviral for HSV and VZV in pediatrics. Rapid initiation limits viral replication, shortens symptom duration, and decreases complications such as dehydration, eczema herpeticum, and neonatal dissemination.
Use acyclovir when clinical presentation and risk factors indicate significant viral burden—particularly in severe primary infections, immunocompromised hosts, or high-risk varicella exposures.
| Condition | Age Range | First Line? | Notes |
|---|---|---|---|
| Primary herpetic gingivostomatitis | Children | No | Start within 72 hours of symptom onset to shorten oral lesion duration and improve feeding; consider for severe pain, dehydration risk, or immunocompromise. |
| HSV skin infections (e.g., eczema herpeticum) | Infants and children | Yes | Initiate promptly in coordination with dermatology or infectious disease to limit dissemination and hospitalisation. |
| Varicella in high-risk children | Children and adolescents | No | Consider for adolescents, chronic skin or lung disease, or immunocompromised hosts when started within 24 hours of rash onset. |
| HSV prophylaxis in immunocompromised patients | Transplant and oncology patients | Yes | Use under specialist guidance to prevent HSV reactivation during periods of profound immunosuppression. |
| Recurrent HSV labialis suppression | Children and adolescents | No | Individualize chronic suppressive therapy for frequent or severe recurrences impacting quality of life. |
FDA-approved primary uses with Level A evidence
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Quick selection guides and diagnostic pearls
When to consider other medications
How to explain treatment to families
Acyclovir is generally well tolerated; GI upset and headache are the most frequent pediatric complaints. Serious renal or neurologic effects are rare and usually linked to dehydration or impaired kidney function.
Hydration and renal monitoring in high-risk children mitigate most adverse effects.
Nausea
Common • mild
Diarrhea
Less common • mild
Headache
Common • mild
Dizziness or confusion
Rare • serious
Crystalluria/renal dysfunction
Rare • serious
Rash
Uncommon • variable
Organized by affected organ systems
How to discuss side effects with families
Management protocols and monitoring
Common concerns and practical guidance
Practical considerations for giving acyclovir to children.
Measure each dose with the oral syringe from the pharmacy for accuracy. Give with a small snack if stomach upset occurs. Encourage frequent fluids to keep the kidneys flushed while the medicine is in the system.
Start as soon as your clinician directs—ideally within 72 hours of symptom onset for varicella or at the first signs of a cold sore or HSV lesion. Set alarms for dosing every 4 to 6 hours while awake to avoid missed doses.
Emergency contact: Seek care urgently for trouble breathing, swelling of the face or lips, new confusion, severe lethargy, or if your child stops making urine.
Most children tolerate acyclovir well; staying hydrated and sticking with the dosing schedule keeps the course smooth.
Different formulations and concentrations
Safe preparation and measuring techniques
Tailored approaches for different ages
Solutions for common challenges
Storage guidelines and safety tips
Expert pearls and evidence-based tips
Acyclovir is a guanosine analog that selectively targets HSV and VZV-infected cells. Viral thymidine kinase converts acyclovir into its active triphosphate form, concentrating it where viral replication is occurring.
The activated metabolite competitively inhibits viral DNA polymerase and acts as a chain terminator, halting viral DNA synthesis without affecting host polymerases.
Simple explanations and helpful analogies
Receptors, enzymes, and cellular targets
Absorption, metabolism, and elimination
Age-related differences and special populations
Efficient acyclovir use depends on early initiation, careful renal dosing, and hydration to prevent nephrotoxicity.
These pearls help clinicians balance efficacy with safety in weekdays, ED, and inpatient settings.
Initiate within 72 hours of rash onset for varicella or prodromal symptoms for HSV to maximize lesion resolution and red…
Encourage ≥1 mL/kg/hour urine output; administer IV fluids when using high-dose IV regimens to prevent crystalluria and …
Use extended intervals for eGFR <50 mL/min/1.73 m² and consult neonatal dosing tables (e.g., 20 mg/kg IV q8h for neonata…
Confusion, tremors, or hallucinations may indicate neurotoxicity—check renal function, adjust dose, and consider discont…
Core insights every provider should know
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Recent updates that change how we practice
Organized by dosing, administration, and safety
How to explain treatments to families
Real-world cases with evidence-based approaches
Key numbers, algorithms, and decision tools
Understanding your child's medication is important. We've created comprehensive guides to help you safely administer Acyclovir and monitor your child's response to treatment.
For herpes sores, begin at the very first signs (tingling, burning, or new lesions). For chickenpox or shingles, start within 24–72 hours after the rash begins when your clinician recommends treatment.
Yes. Taking doses with a snack can lessen stomach upset and does not diminish effectiveness. Encourage good hydration during the course.
Give it as soon as you remember unless it is almost time for the next scheduled dose. Do not double up; return to the regular schedule and notify your clinician if multiple doses are missed.
Routine lab monitoring is not usually needed for short oral courses in healthy children. Children with kidney disease or prolonged suppressive therapy may need periodic lab checks as directed by their clinician.