VALTREX 500MG 42 TAB

Indications

Approved Uses

Herpes zoster (shingles) treatment; genital herpes (initial episode, recurrent episodes, and chronic suppressive therapy) in immunocompetent adults; reduction of transmission of genital herpes in immunocompetent adults; herpes labialis (cold sores) treatment; chickenpox (varicella) treatment in pediatric patients (2 to <18 years).

Off-Label Uses

Off-label examples: CMV prophylaxis in some transplant settings (less common than valganciclovir), HSV prophylaxis in select immunocompromised patients, and adjunct use with corticosteroids for Bell’s palsy (evidence mixed).

Dosage & Administration

Dosing by Condition

Herpes zoster: 1 g PO three times daily for 7 days. Genital herpes-initial episode: 1 g PO twice daily for 10 days. Genital herpes-recurrent episode: 500 mg PO twice daily for 3 days. Genital herpes-suppressive therapy (immunocompetent): 500 mg PO once daily (or 1 g once daily for patients with very frequent recurrences). Reduction of transmission of genital herpes: 500 mg PO once daily (with safer sex practices). Herpes labialis: 2 g PO twice daily for 1 day (doses 12 hours apart). Chickenpox (2 to <18 years): 20 mg/kg PO three times daily for 5 days (max 1 g TID).

Initial Dose

500mg to 1000mg depending on indication

Maintenance Dose

500mg once daily (suppressive therapy) to 1000mg three times daily (herpes zoster)

Maximum Dose

Maximum labeled total daily dose is 8 g/day (2 g four times daily) for CMV prophylaxis in adult renal transplant patients; common maxima in other indications include 3 g/day for zoster and 4 g in 1 day for cold sores.

Children's Dosage

Pediatric use is limited to: Herpes labialis (cold sores) in adolescents ≥12 years: 2000 mg orally every 12 hours for 1 day (2 doses total). Chickenpox (varicella) in children 2 to <18 years: 20 mg/kg orally three times daily for 5 days (maximum 1000 mg per dose). Not established for genital herpes treatment/suppression or herpes zoster in pediatric patients.

Dose Adjustment Notes

Dose adjustment is required in renal impairment (dose/interval adjusted by creatinine clearance, including when CrCl <50 mL/min for several regimens); ensure adequate hydration, and use caution in elderly and with concomitant nephrotoxins.

How to Take

Swallow tablets whole with water; may be taken with or without food; maintain adequate hydration during therapy.

Side Effects

Common Side Effects

Headache, nausea, vomiting, diarrhea, abdominal pain, dizziness, fatigue

Side Effect Frequency

Common: headache, nausea (often the most frequent); also may include abdominal pain, vomiting, diarrhea, dizziness and rash. Serious but uncommon/rare: renal impairment/AKI (especially dehydration/renal disease), and CNS effects (confusion, hallucinations, agitation, tremor, encephalopathy/seizures), plus hypersensitivity reactions (e.g., angioedema/anaphylaxis) and severe cutaneous reactions (e.g., SJS/TEN-rare).

Safety & Warnings

Contraindications

Contraindicated in patients with hypersensitivity to valacyclovir, acyclovir, or any component (excipient) of the formulation.

Warnings & Precautions

Key precautions: adjust dose in renal impairment and in elderly; maintain adequate hydration; monitor for neurotoxicity and renal dysfunction; risk of TTP/HUS in immunocompromised patients at high doses; herpes transmission can still occur (not curative)-counsel on risk reduction/safer sex during genital herpes management.

Age Restriction

Pediatric approvals: Chickenpox (varicella) ≥2 to <18 years; Cold sores (herpes labialis) ≥12 years. Genital herpes and herpes zoster: adults (≥18 years). Not approved for varicella <2 years or cold sores <12 years; pediatric HSV suppression dosing not established.

Driving Warning

No effect on driving or machine operation reported

Drug Interactions

Drug Interactions

Key interactions: probenecid and cimetidine can increase acyclovir exposure (reduced renal tubular secretion); additive nephrotoxicity risk with other nephrotoxic agents (e.g., aminoglycosides, cyclosporine, tacrolimus, amphotericin B, IV contrast; NSAIDs may contribute especially with dehydration/renal risk); monitor closely in renal impairment/high doses.

Interaction Severity

MAJOR/clinically significant: concomitant nephrotoxic agents (e.g., aminoglycosides, amphotericin B, cyclosporine, tacrolimus, high-dose NSAIDs) increase risk of acute kidney injury; MODERATE: probenecid and cimetidine can increase acyclovir exposure by reducing renal tubular secretion; other interactions are generally limited but risk increases in renal impairment/high doses.

Food Interaction

No clinically significant food restriction; may be taken with or without food.

Special Populations

Pregnancy

B

Breastfeeding

Caution

Children

Pediatric use is limited to: Herpes labialis (cold sores) in adolescents ≥12 years: 2000 mg orally every 12 hours for 1 day (2 doses total). Chickenpox (varicella) in children 2 to <18 years: 20 mg/kg orally three times daily for 5 days (maximum 1000 mg per dose). Not established for genital herpes treatment/suppression or herpes zoster in pediatric patients.

Elderly

Standard adult dosing; however, renal function should be assessed and dose adjusted accordingly as renal clearance declines with age. Ensure adequate hydration. Monitor for neurological adverse effects

Kidney Impairment

Renal adjustment is required (dose/interval depend on indication and CrCl); examples consistent with labeling: Zoster-CrCl 30-49: 1 g q12h; 10-29: 1 g q24h; <10: 500 mg q24h. Cold sores (2 g q12h x 1 day regimen)-CrCl 30-49: 1 g q12h x 1 day; 10-29: 500 mg q12h x 1 day; <10: 500 mg once. Suppressive genital herpes-CrCl <30: 500 mg q24h. Give doses after hemodialysis on dialysis days.

Liver Impairment

No dose adjustment is needed in mild to moderate hepatic impairment; limited data in severe hepatic impairment-use caution, particularly with high total daily doses (e.g., around 4 g/day).

Storage & Patient Advice

Missed Dose

Take the missed dose as soon as remembered; if it is close to the next scheduled dose, skip the missed dose and resume the regular schedule; do not double doses.

Stopping the Medicine

Do not stop early for an acute episode-complete the prescribed course; suppressive therapy can be stopped when clinically appropriate but should be reassessed periodically (e.g., at least annually) and stopping may lead to recurrence.

Overdose

Overdose may cause acute renal failure (crystalluria/tubular precipitation) and neurotoxicity (confusion, hallucinations, agitation, seizures, coma) plus GI symptoms; management is supportive with aggressive hydration, renal function monitoring, and hemodialysis can enhance acyclovir removal-seek urgent medical care/poison center.

Patient Counseling

Start as early as possible at first symptoms; take exactly as prescribed and complete the course; maintain good hydration (especially important with renal impairment/older adults); it suppresses HSV but does not cure it and does not fully prevent transmission-use safer sex/condoms; if a dose is missed take it when remembered unless near next dose (do not double); seek urgent care for neurotoxicity (confusion/hallucinations) or reduced urination/renal symptoms; inform prescriber of kidney disease and other nephrotoxic drugs.

Monitoring Requirements

Monitor renal function (SCr/CrCl) in elderly, those with renal impairment, high-dose therapy, dehydration, or concomitant nephrotoxins; monitor for neurotoxicity (confusion, hallucinations, tremor) especially in renal impairment/elderly; ensure hydration.

Pharmacology

Mechanism of Action

Valacyclovir is converted to acyclovir; acyclovir is phosphorylated by viral thymidine kinase then by host kinases to acyclovir triphosphate, which competitively inhibits viral DNA polymerase and causes DNA chain termination, inhibiting herpesvirus replication.

Onset of Action

Acyclovir peak concentrations occur about 1-3 hours after an oral dose; clinical improvement typically begins within ~24-48 hours when started early (condition-dependent).

Duration of Effect

Effect is maintained over the dosing interval; suppressive benefit persists only while taken regularly (no lasting protection after discontinuation).

Half-Life

Acyclovir half-life ~2.5-3.3 hours with normal renal function; prolonged markedly in severe renal impairment/ESRD (up to ~14 hours).

Bioavailability

Approximately 54-55% (systemic availability of aciclovir after oral valaciclovir).

Metabolism

Valaciclovir is rapidly and nearly completely hydrolyzed (first-pass intestinal/hepatic valaciclovirase) to aciclovir and L-valine; aciclovir undergoes minimal metabolism to inactive metabolites (including CMMG).

Excretion

Primarily renal: most of the dose is recovered in urine as aciclovir and its metabolite 9-carboxymethoxymethylguanine (CMMG), with <1% excreted unchanged as valaciclovir.

Protein Binding

Low protein binding: ~13-18% (aciclovir).

Product Information

Available Dosage Forms

Oral tablet (film-coated).

Composition per Dose

Each film-coated tablet: 500mg valaciclovir (as valaciclovir hydrochloride)

Generic Availability

Yes

OTC Alternatives

Topical aciclovir 5% cream may be available OTC in some countries for herpes labialis (cold sores); there is no true OTC oral alternative to valaciclovir for genital herpes or systemic HSV/VZV infections.

Viral Target

Herpes (HSV-1, HSV-2, VZV)

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