HSV-1 Antiviral Shortage: What Providers and Prescribers Need to Know in 2026

The ongoing availability challenges surrounding HSV-1 antiviral medications — particularly IV acyclovir — continue to create clinical management challenges across a range of specialties. This article provides practical guidance for prescribers and healthcare teams on navigating the current shortage, managing therapeutic substitutions, and counseling patients on what to expect in 2026.

Current Supply Status at a Glance

As of 2026, providers should be aware of the following supply conditions for HSV-1 antiviral agents:

• IV Acyclovir: Intermittent shortage ongoing since 2020. Improving but still constrained. Recommend switching immunocompetent patients to oral valacyclovir where clinically appropriate to preserve IV supply for high-acuity cases (encephalitis, neonatal HSV, severely immunocompromised).
• Oral acyclovir: Generally available nationally. Individual pharmacy stock varies. Patients on suppressive therapy may encounter spot shortages.
• Valacyclovir: Widely available. Preferred first-line choice for most outpatient HSV-1 management given superior bioavailability, convenient dosing, and broad availability.
• Famciclovir: Available. An appropriate first-line or substitution option for outpatient HSV-1 management.

Therapeutic Substitution Guidance

All three first-line nucleoside analogues (acyclovir, valacyclovir, famciclovir) have demonstrated comparable efficacy in randomized trials for treating and suppressing HSV-1 in immunocompetent patients. When switching is clinically appropriate, the following dose equivalences apply for common indications:

Suppressive therapy:

• Acyclovir 400 mg BID ≈ Valacyclovir 500 mg QD (or 1g QD for ≥10 recurrences/year) ≈ Famciclovir 250 mg BID

Episodic treatment (recurrent genital HSV-1):

• Acyclovir 400 mg TID x5d OR 800 mg BID x5d ≈ Valacyclovir 500 mg BID x3d ≈ Famciclovir 125 mg BID x5d

Herpes labialis (cold sores):

• Valacyclovir 2g BID x1 day ≈ Famciclovir 1,500 mg single dose (for immunocompetent adults)

Prioritizing IV Acyclovir During Shortage Conditions

When IV acyclovir supply is constrained, the CDC and ASHP recommend prioritizing IV therapy for the highest-acuity indications:

1. HSV encephalitis: IV acyclovir 10 mg/kg q8h x21 days is standard of care and has no oral equivalent for CNS disease
2. Neonatal HSV: High-dose IV acyclovir is the only proven treatment for neonatal HSV disease
3. Severe HSV in immunocompromised hosts: Disseminated HSV, visceral involvement, or failure to absorb oral therapy

For patients with uncomplicated herpes zoster or genital/oral HSV in immunocompetent individuals who are admitted to hospital, consider early switch to oral valacyclovir once clinical improvement is evident to conserve IV supply.

Acyclovir Resistance: What to Know

Acyclovir resistance remains uncommon in immunocompetent patients (0.1%–0.7% with long-term suppressive therapy) but is clinically significant in immunocompromised patients (3.5%–10%). Resistance typically arises through thymidine kinase (TK) mutations. Key clinical points:

• TK-negative acyclovir-resistant strains are also cross-resistant to famciclovir/penciclovir
• Foscarnet is the preferred second-line treatment for acyclovir-resistant HSV (does not require TK for activation)
• Cidofovir IV is an alternative for foscarnet-resistant or -intolerant patients

Patient Counseling During Shortage Conditions

When counseling patients about potential medication shortages, providers should emphasize:

• Do not abruptly stop suppressive antiviral therapy — if primary medication is unavailable, contact the office for a substitution prescription before running out
• Refill prescriptions 7–10 days early, especially for patients on daily suppressive therapy
• Consider directing patients to medfinder.com to locate pharmacies with their medication in stock before calling around on their own
• Mail-order pharmacies often maintain better stock of generic antivirals — appropriate for stable patients on long-term suppressive therapy

Resources for Providers

For a practical guide on helping your patients find medications during shortage conditions, visit medfinder for providers. medfinder calls local pharmacies on behalf of patients to check availability and texts results — reducing the administrative burden on your staff while helping patients find their medications faster. See also our provider guide to helping patients find HSV-1 antivirals in stock.