Usage
Valacyclovir is prescribed for the treatment of infections caused by herpes simplex virus (HSV) types 1 and 2, varicella-zoster virus (VZV), including herpes labialis (cold sores), genital herpes, herpes zoster (shingles), and chickenpox. It is also used for prevention of cytomegalovirus (CMV) infection in transplant recipients. Its pharmacological classification is antiviral. The mechanism of action involves the inhibition of viral DNA polymerase, thus preventing viral replication.
Alternate Names
Valaciclovir is the international nonproprietary name (INN). Brand names include Valtrex.
How It Works
Pharmacodynamics: Valacyclovir is a prodrug of acyclovir. After oral administration, it is rapidly absorbed and almost completely converted to acyclovir. Acyclovir is then phosphorylated intracellularly to acyclovir triphosphate, the active form of the drug. Acyclovir triphosphate competitively inhibits viral DNA polymerase, leading to chain termination and preventing viral DNA replication. This action is highly selective for virus-infected cells.
Pharmacokinetics: Valacyclovir exhibits high oral bioavailability (approximately 54%) compared to acyclovir. Peak plasma concentrations are achieved 1-2 hours post-administration. Acyclovir is primarily eliminated by renal excretion, both as the unchanged drug and metabolites. The half-life of acyclovir is approximately 3 hours in patients with normal renal function.
Dosage
Standard Dosage
Adults:
- Cold Sores: 2 grams twice daily for 1 day (two doses 12 hours apart).
- Genital Herpes (Initial Episode): 1 gram twice daily for 10 days.
- Genital Herpes (Recurrent Episodes): 500 mg twice daily for 3 days or 1 gram once daily for 5 days.
- Herpes Zoster (Shingles): 1 gram three times daily for 7 days.
- Suppression of Genital Herpes: 500 mg to 1 gram once daily (depending on frequency of recurrence). Alternatively, 500 mg twice daily or 250 mg twice daily if ≥ 10 recurrences/year.
- CMV Prophylaxis: 2 grams four times daily. Dose adjustment is necessary for patients with impaired renal function.
Children:
- Chickenpox (2-18 years): 20 mg/kg (up to a maximum of 1 gram per dose) three times a day for 5 days. Dose should be determined by body weight.
- Cold Sores (≥12 years): 2 grams twice daily for 1 day.
- Genital Herpes: Use and dose must be determined by a doctor.
Special Cases:
- Elderly Patients: Dose adjustment may be necessary based on renal function.
- Patients with Renal Impairment: Dose reduction is required depending on creatinine clearance (see sources for specific adjustments).
- Patients with Hepatic Dysfunction: Dose adjustment is usually not necessary in mild to moderate hepatic impairment. Limited clinical data are available for severe hepatic impairment.
Clinical Use Cases
Dosing for specific clinical use cases beyond standard indications should be determined based on patient condition, severity of infection, and clinical experience.
Side Effects
Common Side Effects
Headache, nausea, vomiting, diarrhea, abdominal pain.
Rare but Serious Side Effects
Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), acute renal failure, hallucinations, confusion.
Long-Term Effects
No documented long-term side effects from recommended dosages.
Contraindications
Hypersensitivity to valacyclovir or acyclovir.
Drug Interactions
Probenecid, cimetidine, other nephrotoxic drugs (e.g., aminoglycosides, NSAIDs).
Pregnancy and Breastfeeding
Limited data are available on valacyclovir use during pregnancy. Acyclovir is excreted in breast milk. The decision to use valacyclovir during pregnancy or breastfeeding should be made after careful consideration of the potential risks and benefits.
Drug Profile Summary
- Mechanism of Action: Inhibits viral DNA polymerase.
- Side Effects: Headache, nausea, vomiting, diarrhea; rarely TTP/HUS, renal failure.
- Contraindications: Hypersensitivity to valacyclovir or acyclovir.
- Drug Interactions: Probenecid, cimetidine, nephrotoxic drugs.
- Pregnancy & Breastfeeding: Consult specialist for guidance.
- Dosage: See detailed section above.
- Monitoring Parameters: Renal function, particularly in patients with renal impairment.
Popular Combinations
No established “popular” combinations routinely employed.
Precautions
- Adequate hydration should be maintained, especially in patients with renal impairment and those receiving high doses.
- Close monitoring of renal function is recommended in patients with renal impairment.
- For cold sores, treatment should not exceed one day.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Valacyclovir?
A: See the Dosage section above for detailed information according to indication, age, and renal function.
Q2: Can Valacyclovir be used during pregnancy?
A: Limited data are available. Consult a specialist for guidance, considering potential risks and benefits.
A: It is converted to acyclovir by intestinal and hepatic metabolism.
Q4: What are the primary side effects of Valacyclovir?
A: Common side effects include headache, nausea, vomiting, diarrhea, and abdominal pain.
Q5: What are the serious side effects to watch out for with Valacyclovir?
A: Rare but serious side effects include thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) and renal failure.
Q6: What is the mechanism of action of valacyclovir?
A: Valacyclovir is a prodrug of acyclovir, which inhibits viral DNA polymerase, preventing viral replication.
Q7: What are the contraindications for Valacyclovir?
A: Hypersensitivity to valacyclovir or acyclovir.
Q8: Can Valacyclovir be crushed or chewed?
A: The tablets can be swallowed whole, or can be crushed and mixed with a small amount of liquid or soft food if needed. Consult a pharmacist for advice if necessary.
Q9: Does Valacyclovir interact with other medications?
A: Yes, it can interact with probenecid, cimetidine, and other nephrotoxic drugs. Co-administration should be carefully considered.
Q10: How should Valacyclovir be stored?
A: Store at room temperature away from moisture and heat.
