Valaciclovir

# Valaciclovir ## Overview - **Classification**: Antiviral, nucleoside analog (prodrug of acyclovir) - **Mechanism**: Converted to acyclovir, which inhibits viral DNA synthesis and replication by interfering with viral DNA polymerase. ## Primary Indications 1. **Herpes Labialis (Cold Sores)** - Treatment of recurrent episodes. 2. **Genital Herpes** - Treatment of initial/recurrent episodes and chronic suppression. 3. **Herpes Zoster (Shingles)** - Treatment of herpes zoster. 4. **Chickenpox (Varicella)** - Treatment in immunocompetent children. ## Adult Dosing ### Standard Dosing **Herpes Labialis (Cold Sores)** - **Dose**: **2000 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral - **Duration**: 1 day **Genital Herpes (Initial Episode)** - **Dose**: **1000 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral - **Duration**: 7-10 days **Genital Herpes (Recurrent Episode)** - **Dose**: **500 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral - **Duration**: 3 days **Genital Herpes (Suppression)** - **Dose**: **1000 mg** - **Frequency**: Once daily (OD) - **Route**: Oral - **Consideration**: **500 mg** OD for frequent recurrences or immunocompromised. **Herpes Zoster (Shingles)** - **Dose**: **1000 mg** - **Frequency**: Three times daily (TID) - **Route**: Oral - **Duration**: 7 days ### Dose Adjustments - **Renal Impairment**: Dose reduction required due to acyclovir excretion. - CrCl 30-49 mL/min: Reduce frequency (e.g., BID to OD). - CrCl 10-29 mL/min: Reduce dose and/or frequency significantly. - CrCl <10 mL/min or Hemodialysis: Further significant reduction. Consult specific guidelines. - **Hepatic Impairment**: No dose adjustment generally required. - **Elderly Patients**: Monitor renal function closely; dose adjustment based on CrCl. ## Pediatric Dosing ### Neonates (0-28 days) - **Special Notes**: Valaciclovir is generally **not recommended**. Oral acyclovir or IV acyclovir is preferred. Safety and efficacy not established. ### Infants (1-12 months) - **Special Notes**: Valaciclovir is generally **not recommended**. Oral acyclovir or IV acyclovir is preferred. Limited data for specific indications (e.g., recurrent HSV suppression) may exist in specialized settings. ### Children (1-12 years) **Herpes Labialis (Cold Sores) - For children >= 12 years:** - **Dose**: **2000 mg** - **Frequency**: Twice daily (BID) - **Maximum**: **2000 mg** BID - **Special Notes**: For 1 day only. **Chickenpox (Varicella) - For children 2 to <18 years:** - **Dose**: **20 mg/kg/dose** - **Frequency**: Three times daily (TID) - **Maximum**: **1000 mg** per dose - **Duration**: 5 days - **Special Notes**: Initiate within 24 hours of rash onset. ### Adolescents (13-18 years) - **Dose**: Generally follows **adult dosing** guidelines. - **Maximum**: Adult maximum doses apply. - **Special Notes**: Consider renal function, especially in younger adolescents. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to valaciclovir, acyclovir, or any component of the formulation. ### Common Adverse Effects - **Very Common (>10%)**: Headache, Nausea. - **Common (1-10%)**: Diarrhea, Vomiting, Abdominal pain, Dizziness, Fatigue. - **Serious but Rare**: Acute renal failure, Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) in immunocompromised patients, Neurotoxicity (agitation, confusion, hallucinations, seizures). ### Key Drug Interactions - **Nephrotoxic Drugs**: Increased risk of renal dysfunction. Monitor renal function. - **Cimetidine/Probenecid**: May increase acyclovir plasma levels by reducing renal clearance. Monitor for acyclovir toxicity. - **Mycophenolate Mofetil**: May increase plasma concentrations of acyclovir and MMF's active metabolite. Monitor for toxicity. ## Monitoring & Follow-up - **Before Treatment**: Assess baseline renal function (CrCl). - **During Treatment**: Monitor renal function, especially in elderly, renally impaired, or those on high doses. - **Clinical Signs**: Watch for signs of neurotoxicity (confusion, agitation, seizures). Monitor for worsening rash or lack of response. ## Clinical Pearls - 💡 **Timing Matters**: For shingles and chickenpox, initiate therapy as early as possible (within 24-72 hours of rash onset) for best efficacy. - 💡 **Hydration**: Advise patients to maintain adequate hydration to prevent renal effects, especially with higher doses. - 💡 **Missed Dose**: If a dose is missed, take it as soon as remembered. If it's almost time for the next dose, skip the missed dose and resume regular schedule. Do not double dose. - 💡 **Dispensing**: For herpes labialis, the 1-day **2000 mg BID** regimen can be helpful for patient adherence. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.