Valacyclovir (Valtrex)

Valacyclovir (brand name Valtrex) is an oral antiviral medication used to treat and prevent ocular infections caused by herpes simplex virus (HSV) and varicella zoster virus (VZV). It is the prodrug of acyclovir - converted to acyclovir in the body - and offers better oral bioavailability and less frequent dosing than acyclovir itself. In ophthalmology, valacyclovir is commonly used as systemic antiviral treatment for HSV keratitis, herpes zoster ophthalmicus, and recurrence prevention.

How It Works

Valacyclovir is rapidly converted to acyclovir in the intestinal wall and liver. Acyclovir is selectively phosphorylated by viral thymidine kinase, which preferentially activates the drug in HSV- and VZV-infected cells. The activated drug interferes with viral DNA polymerase, halting viral replication.

Common Ophthalmic Uses

Acute HSV Keratitis

• Stromal HSV keratitis - oral antiviral dosing and duration are tailored to severity and the topical steroid taper; courses often last weeks rather than 7-10 days, and higher-dose regimens may be used for stromal/endothelial disease or HSV uveitis
• Iridocyclitis (HSV uveitis) - similar dosing
• Acute epithelial HSV keratitis - oral valacyclovir 500 mg three times daily for 7-10 days is effective as monotherapy, with comparable resolution to topical antivirals; it can also be used as an adjunct in severe or recalcitrant cases

Long-Term HSV Prophylaxis

• For patients with frequent recurrences, valacyclovir 500 mg once daily (or BID for higher recurrence risk) reduces recurrence rates substantially. The HEDS Acyclovir Prevention Trial used acyclovir 400 mg twice daily for 12 months; valacyclovir 500 mg once daily provides comparable systemic exposure and is widely used because of its convenience. Many specialists continue prophylaxis longer than 12 months in patients with stromal disease, bilateral disease, or high recurrence frequency

Herpes Zoster Ophthalmicus

• Valacyclovir 1 g three times daily for 7 days is the labeled herpes zoster regimen; many ophthalmologists extend treatment to 10 days for HZO, especially with eye involvement, in older patients, or in immunocompromised hosts
• Start as soon as possible, ideally within 72 hours of rash onset for maximal skin and pain benefit; treatment is still often used later when there are new lesions, eye involvement, or immune compromise
• Reduces acute viral replication and disease severity; prevention of post-herpetic neuralgia or ocular complications is not guaranteed

Other

• HSV/VZV uveitis
• Acute retinal necrosis - traditional regimen is IV acyclovir 10 mg/kg every 8 hours for 7-10 days followed by oral valacyclovir; alternatively, high-dose oral valacyclovir (commonly 2 g four times daily) achieves comparable vitreous levels in studies. Adjunctive intravitreal foscarnet or ganciclovir is often given. Treatment is individualized at retina specialty centers

Dosing Considerations

• Renal function - dose reductions are required at creatinine clearance below 50 mL/min, with stratified adjustments by indication at CrCl 30-49, 10-29, and below 10 mL/min; your prescriber will adjust based on labs
• Hydration - important to prevent crystalline nephropathy at high doses
• Pregnancy - acyclovir and valacyclovir have a long history of use in pregnancy without evidence of increased teratogenicity; use when indicated in coordination with the prescribing physician and obstetric clinician

Side Effects

Common

• Headache
• Nausea, vomiting
• Abdominal pain
• Dizziness

Less Common

• Rash
• Fatigue

Serious (Rare)

• Crystal-associated kidney injury / acute renal failure - risk is higher with dehydration, kidney disease, older age, nephrotoxic drugs, or doses that are too high for renal function
• Thrombotic thrombocytopenic purpura / hemolytic uremic syndrome (TTP/HUS) - rare; reported in immunocompromised patients on high doses
• CNS toxicity - confusion, hallucinations, particularly in renal impairment

Drug Interactions

• Probenecid - increases acyclovir levels
• Mycophenolate - increases acyclovir/valacyclovir levels
• Generally low interaction profile

Frequently Asked Questions

Why am I being prescribed both eye drops and oral medication?

For stromal disease, recurrent disease, or HSV uveitis, topical antivirals alone are often inadequate. Oral valacyclovir reaches deeper tissues and provides systemic coverage that topical trifluridine or ganciclovir gel cannot. Topical steroids should not be used for suspected herpetic eye disease unless an eye clinician is supervising antiviral coverage.

How long will I need to take it?

For many epithelial HSV or shingles episodes, treatment is typically 7-10 days. Stromal/endothelial keratitis or uveitis often requires longer antiviral coverage coordinated with the steroid taper. For recurrence prevention, at least 12 months and often longer is used in patients with frequent flares, bilateral disease, or stromal disease history.

Are there interactions with my other medications?

Few significant interactions. Renal function matters for dosing. Tell your prescriber if you take probenecid, mycophenolate, or have kidney disease.

Is valacyclovir the same as acyclovir?

Valacyclovir is the prodrug - better absorbed orally, less frequent dosing. Once in the body, it becomes acyclovir, the active drug. Either may be used; valacyclovir is more convenient.

What about famciclovir?

Famciclovir is an alternative prodrug that becomes penciclovir in the body. Effective for HSV and VZV. Usually selected for patient tolerance issues with valacyclovir.

References