Foscarnet is the conjugate base of the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....



This phosphonic acid derivative (marketed by Clinigen as foscarnet sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 under the trade name Foscavir) is an antiviral medication used to treat herpes viruses, including drug resistant cytomegalovirus
Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...

 (CMV) and herpes simplex
Herpes simplex
Herpes simplex is a viral disease caused by both Herpes simplex virus type 1 and type 2 . Infection with the herpes virus is categorized into one of several distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever...

 viruses types 1 and 2 (HSV-1 and HSV-2). It is particularly used to treat CMV retinitis. Foscarnet can be used to treat highly treatment experienced patients with HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

 as part of salvage therapy
Salvage therapy
Salvage therapy is a form of treatment given after an ailment does not respond to standard treatment. The most common diseases that require salvage therapy are HIV and various tumors...


Mechanism of action

Foscarnet is a structural mimic of the anion pyrophosphate
In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Any salt or ester containing two phosphate groups is called a diphosphate. As a food additive, diphosphates are known as E450.- Chemistry :...

 that selectively inhibits the pyrophosphate binding site on viral DNA polymerase
DNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

s at concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

s that do not affect human DNA polymerases. Because foscarnet is not activated by viral kinases it maintains activity against viruses like HSV and VZV that have respectively developed mutant thymidine kinase
Thymidine kinase
Thymidine kinase is an enzyme, a phosphotransferase : 2'-deoxythymidine kinase, ATP-thymidine 5'-phosphotransferase, . It can be found in most living cells. It is present in two forms in mammalian cells, TK1 and TK2...

 and UL97 encoded protein kinase, to gain resistance to other DNA polymerase inhibitors, like acyclovir and ganciclovir
Ganciclovir INN is an antiviral medication used to treat or prevent cytomegalovirus infections.Ganciclovir sodium is marketed under the trade names Cytovene and Cymevene . Ganciclovir for ocular use is marketed under the trade name Vitrasert...

. Therefore, foscarnet is often used in acyclovir- or ganciclovir-resistant disease.

However, acyclovir- or ganciclovir-resistant mutants with alterations in viral DNA polymerase may be resistant to foscarnet.

Side effects

  • Nephrotoxicity
    Nephrotoxicity is a poisonous effect of some substances, both toxic chemicals and medication, on the kidneys. There are various forms of toxicity. Nephrotoxicity should not be confused with the fact that some medications have a predominantly renal excretion and need their dose adjusted for the...

     - Increase in serum creatinine levels occurs on average in 45% of patients receiving foscarnet. Other nephrotoxic drugs should be avoided. Nephrotoxicity is usually reversible and can be reduced by dosage adjustment and adequate hydration.

  • Electrolyte
    In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

     disturbances - Changes in calcium, magnesium (Harisson 16th ed page2244) potassium and phosphate levels occurs commonly and regular monitoring of electrolytes is necessary to avoid clinical toxicity.

  • Genital ulceration - Occurs more commonly in men and usually occurs during induction use of foscarnet. It is most likely a contact dermatitis due to high concentrations of foscarnet in urine. It usually resolves rapidly following discontinuation of the drug.

  • CNS - Paraesthesias,irritability and hallucinations
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