Foscarnet (marketed by AstraZeneca as foscarnet sodium under the trade name Foscavir®) is an antiviral medication used to treat herpes viruses, including cytomegalovirus (CMV) and herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2). It is particularly used to treat CMV retinitis.

Mechanism of action

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Foscarnet is an organic analog of inorganic pyrophosphate that selectively inhibits the pyrophosphate binding site on viral DNA polymerases at concentrations that do not affect human DNA polymerases. Because foscarnet is not activated by thymidine kinase, it maintains activity in some viruses which have lost thymidine kinase activity to gain resistance to aciclovir or ganciclovir. Therefore, foscarnet is often used in aciclovir- or ganciclovir-resistant disease. However, acyclovir or ganciclovir resistant mutants with alterations in viral DNA polymerase may be resistant to foscarnet.

Administration

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Intravenous only

Side effects

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• Renal failure
• Decreased calcium levels

Antivirals