Foscarnet for Acyclovir-Resistant Eczema Herpeticum in Infants
For an infant with eczema herpeticum resistant to acyclovir, foscarnet is the recommended antiviral medication at a dose of 40 mg/kg IV every 8 hours (or 60 mg/kg IV every 12 hours) until clinical resolution is achieved. 1, 2
Dosing and Administration
The specific pediatric dosing for acyclovir-resistant HSV infection is:
- Foscarnet: 40 mg/kg body weight per dose IV three times daily (every 8 hours)
- Alternative: 60 mg/kg body weight per dose IV twice daily (every 12 hours) 2
- Continue treatment until complete clinical resolution of the infection 1
Critical Administration Details
Infusion technique is essential to minimize toxicity:
- Administer slowly over 2 hours (no faster than 1 mg/kg/minute) 1
- Use saline fluid loading before and during infusion to minimize renal toxicity 1
- Adjust doses in patients with renal insufficiency 1
Understanding Acyclovir Resistance
When lesions persist despite acyclovir treatment, HSV resistance should be suspected 3. All acyclovir-resistant strains are also resistant to valacyclovir, and most are resistant to famciclovir 3, making foscarnet the only reliable alternative in this clinical scenario.
Alternative Considerations (Limited Evidence)
While foscarnet remains the gold standard, case reports suggest potential utility of:
- Topical cidofovir gel 1% applied daily for 5 consecutive days 3
- Brincidofovir and imiquimod (case report level evidence only) 4
However, these alternatives lack the robust evidence supporting foscarnet use in pediatric populations.
Important Caveats
Consultation with an infectious disease specialist is strongly advised when managing acyclovir-resistant HSV in infants, as this represents a complex clinical scenario requiring expert guidance 3.
Monitor closely for foscarnet toxicities:
- Renal toxicity (most common)
- Electrolyte disturbances (hypocalcemia, hypomagnesemia, hypokalemia)
- Seizures related to electrolyte abnormalities
The evidence base for foscarnet in acyclovir-resistant HSV is graded as AI (strong recommendation, high-quality evidence) across multiple CDC/NIH/IDSA guidelines 2, making it the definitive choice when acyclovir resistance is confirmed or strongly suspected.