Acyclovir

Selected oral labels treat herpes zoster, initial/recurrent genital herpes including suppressive therapy, and chickenpox; oral efficacy/safety below 2 is unestablished. Selected IV label treats initial/recurrent mucocutaneous HSV in immunocompromised patients, severe initial genital herpes, HSV encephalitis, neonatal/infant HSV and zoster in immunocompromised patients. Serious CNS/disseminated disease requires specialist management.

Cream 5% treats recurrent cold sores on external lips/face in immunocompetent adults/adolescents≥12. Ointment 5% label covers initial genital herpes and limited non-life-threatening mucocutaneous HSV in immunocompromised patients; pediatric use unestablished. Sitavig 50 mg treats recurrent cold sores in immunocompetent adults only. CDC discourages topical antiviral treatment for genital herpes because benefit is minimal, despite ointment’s labeled indication.

CDC recommends first episode 400 mg orally 3 times/day for 7–10 days (extend if incomplete healing); suppression 400 mg twice/day. Recurrent HSV-2 episodes:800 mg twice/day for 5 days or 800 mg 3 times/day for 2 days. The 200 mg five-times/day initial label regimen is effective but CDC avoids its dosing burden. These are guideline regimens, not a new claim of product approval.

CDC distinguishes encephalitis, requiring 14–21 days IV, from meningitis; do not use the selected IV label’s10-day encephalitis text as a routine treatment stop. CDC neonatal guidance uses 20 mg/kg every 8 hours for 14 days for skin/mucosa-limited disease or 21 days for CNS/disseminated disease; selected IV label separately stratifies premature neonates by PMA and gives 21 days. Infectious-disease/neonatal teams must select duration, renal/PMA interval and follow-up; no universal home algorithm is supplied.

Current oral tablets/suspension: clinically significant hypersensitivity, including anaphylaxis or SCARs, to acyclovir, valacyclovir or ingredients. Selected IV and cream: hypersensitivity to acyclovir/valacyclovir (cream also ingredients). Ointment: hypersensitivity to its components. Sitavig: acyclovir, milk protein concentrate or other components. Do not treat intolerance alone as identical to prior SCAR or ignore formulation excipients.

Selected systemic, dermal and buccal labels have no boxed warning. Renal failure, severe skin reactions and IV route warnings remain serious.

Oral reactions include nausea/vomiting, diarrhea, headache/malaise and dizziness; IV reactions include phlebitis, renal-lab elevations, nausea and hematologic abnormalities, including neonatal neutropenia. Local products can cause burning, stinging, dryness, itching or application-site pain; Sitavig headache/gingival symptoms reported. Postmarketing serious allergy, neurologic toxicity and renal injury have uncertain frequencies. Systemic overdose needs immediate Poison Help/medical assessment; renal failure/anuria may warrant clinician-directed hemodialysis. Local overdose is less likely because systemic exposure is low, but ingestion or severe reactions still require assessment.

Probenecid reduces renal clearance and increases acyclovir half-life/exposure in IV studies. Potentially nephrotoxic agents increase kidney injury and reversible CNS toxicity risk; review renal function, hydration and concomitant therapy. No universal interaction dose percentage is supplied.

Cream/ointment experience identified no clinically evident drug interactions; cream minimal systemic absorption makes systemic interactions unlikely. Sitavig interaction studies were not performed; competing tubular-secretion drugs could theoretically raise exposure, although its low dose/absorption makes systemic interactions unlikely. Avoid other topical products on the cold-sore area during cream use as directed.

Older patients often have reduced renal function and greater CNS/renal toxicity; adjust by renal status, not age alone. Oral below 2, cream below 12 and ointment pediatric use are unestablished; Sitavig adult immunocompetent only. IV has separate neonatal/pediatric regimens. Labels supply no routine hepatic percentage adjustment; IV cautions about serious hepatic, electrolyte or neurologic abnormalities and hypoxia. Resistant/persistent lesions need infectious-disease evaluation rather than unchecked escalation.

Systemic labels advise use when benefit justifies fetal risk; registry data did not show excess overall birth defects but cannot exclude uncommon harms. CDC supports acyclovir for maternal genital HSV and provides 36-week suppression guidance: 400 mg orally 3 times/day, under obstetric care; it does not guarantee neonatal transmission prevention. Milk exposure occurs with oral therapy; use when indicated with assessment. Cream has minimal absorption and reassuring limited pregnancy data; Sitavig has no pregnancy trials and breastfeeding caution. Avoid nursing with active herpetic lesions on/near breast per ointment label.

Viral thymidine kinase initiates phosphorylation, followed by cellular conversion to active acyclovir triphosphate, which inhibits viral DNA polymerase and terminates viral DNA chains. HSV/VZV kinase or polymerase changes can cause resistance, particularly in immunocompromised patients. Clinical nonresponse requires diagnostic/resistance review; no eradication of latent HSV is established.

Oral bioavailability about 10–20%, decreasing with dose; oral half-life about 2.5–3.3 hours with normal renal function. Protein binding 9–33%; unchanged renal elimination dominates. IV adult half-life about 2.5 hours with normal function, prolonged markedly in anuria; CSF levels about 50% of plasma. Food does not materially affect selected oral absorption. Renal adjustment is essential; oral, IV and topical concentrations cannot be equated.

Dermal cream/ointment and buccal Sitavig have low systemic exposure under studied conditions, with different skin/saliva absorption profiles. Sitavig slowly dissolves while adhering to gum; its 50 mg tablet is not an oral swallowed 50 mg systemic regimen. Limited adult cream absorption studies do not establish every pediatric or large-area exposure.

For systemic therapy assess renal function, hydration, urine output and neurologic status; monitor IV site, infusion duration and relevant blood counts, especially neonates. Tailor monitoring to risk; CDC does not require routine labs for otherwise uncomplicated long-term genital suppression, which does not remove monitoring needs with renal/IV risks. New severe rash, oliguria or mental-status change needs prompt care.

Measure suspension with calibrated device and verify mg/mL; maintain appropriate hydration, not a universal fluid volume. Begin prescribed recurrence treatment at prodrome. Wash hands around topical use; do not put cream in mouth/eyes/genitals or swallow a buccal tablet. HSV can transmit without visible lesions; avoid sexual contact during symptoms and discuss partner prevention. Persistent disease, neurologic symptoms, ocular concern or pregnancy requires clinical reassessment.

Selected product

200 mg/5 mL = 40 mg/mL; white/off-white banana-flavored suspension.

Package

ANI / Novitium · NDC 70954-188-10, 473 mL bottle.

Status

Prescription antiviral; no claim of current local stock or equivalent volumes across products.

Selected oral tablet

400 mg pink shield-shaped, J on one side, 49 in triangle on other; repack NDC 43063-928-30 bottle 30. Other 200/800 mg unit products require exact-package verification.

IV concentrate

50 mg/mL: 500 mg/10 mL and 1 g/20 mL single-dose vials; must dilute, not oral suspension.

Dermal

Cream and ointment 5% = 50 mg/g, distinct indications/vehicles. Cream selected 2/5 g tubes; ointment 5/15/30 g.

Buccal

Sitavig 50 mg off-white round, flat/rounded sides; AL21 marking, blister NDC 68712-049-02. Label chronology old; no inferred current availability.

Selected tablets 15–25°C, protect from light/moisture; suspension 15–25°C. IV 20–25°C, discard unused vial portion; dilute to about 7 mg/mL or less in appropriate electrolyte/glucose fluid and use within 24 hours per selected label, with sterile local policy. Cream 20–25°C (excursions 15–30); ointment 20–25°C in dry place; Sitavig 20–25°C (excursions 15–30), protect moisture. Retain exact-package instructions; no unsupported universal after-opening or refrigeration rule.