Cidofovir use in acyclovir-resistant herpes infection

Herpes infections continue to be prevalent, especially in immunocompromised patients. Some of these patients will develop resistant HSV infections. Therefore, it is important to explore new treatment options. Animal studies have shown cidofovir to be effective in the treatment and prevention of HSV infections. Human data are limited, with only one randomized, double-blind, placebo-controlled trial performed to date. The results from this study look promising; however, due to the small sample size, a larger clinical trial is warranted. The human data available as case reports are suboptimal in the quality of reporting time frames for resolution of lesions/symptoms and outcomes of therapy. Another problem with the case report data is that the TK status of the herpes simplex isolates was not reported. This would have helped substantiate the acyclovir resistance seen in these patients. It was evident in these case reports that acyclovir resistance can be overcome, as acyclovir-resistant strains became sensitive following cidofovir therapy. This may be because TK(+) viruses have been shown to establish latency more readily than do TK(-) viruses. This pattern suggests that alternating between acyclovir and cidofovir therapies may provide a strategy to manage the emergence of alternatively acyclovir-sensitive and -resistant infections. At present, only the intravenous formulation of cidofovir is commercially available. Advantages of the intravenous formulation include weekly dosing and efficacy. Disadvantages are the complexity of administration and the adverse effect profile. The most common adverse effects with this formulation include nephrotoxicity manifested as proteinuria (12%), and increased creatinine (5%) and neutropenia (15%). Administration of probenecid and NaCl 0.9% hydration are used to reduce the incidence and severity of nephrotoxicity in patients who are receiving cidofovir. Probenecid also has toxicities, including nausea, vomiting, headache, fever, and flushing. The topical formulation of cidofovir looks promising for mucocutaneous HSV infection because it is usually undetectable in the blood following topical administration. Therefore, systemic adverse effects should be minimized. A cidofovir gel product (Forvade, Gilead Sciences) is currently being reviewed by the Food and Drug Administration for the treatment of refractory HSV. Ultimately, more controlled clinical studies are necessary to determine whether routine cidofovir use can be justified in patients with acyclovir-resistant HSV infection.

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