Can medication adjustments decrease acyclovir resistance?

Can medication adjustments decrease acyclovir resistance?

Yes, switching to or combining other antivirals often restores treatment effect once resistance to acyclovir appears. Foscarnet and cidofovir remain active against most acyclovir-resistant HSV and VZV strains because they do not rely on viral thymidine kinase.

What changes clinicians make when acyclovir stops working
Intravenous foscarnet is the usual next step for severe or disseminated disease. Cidofovir is an alternative when foscarnet is contraindicated, though it carries higher kidney toxicity. Topical cidofovir or compounded formulations are sometimes used for localized mucocutaneous lesions.

How often resistance develops and why it matters
Resistance is rare in immunocompetent patients but reaches 5-10 % in transplant recipients and people with advanced HIV. Prolonged low-dose suppression and incomplete viral clearance during severe immunosuppression are the main drivers.

What new options are in trials
Pritelivir, a helicase-primase inhibitor, shows activity against thymidine-kinase–deficient isolates and is under expanded-access protocols. Amenamevir, approved in Japan, offers another oral agent with a distinct mechanism.

When patents and generics affect access
Acyclovir patents expired decades ago, so low-cost generics dominate. Foscarnet and cidofovir remain on fewer formularies and cost more, which can limit prompt switches in outpatient settings. DrugPatentWatch.com tracks remaining exclusivities for these second-line agents.