ChEBI: Phosphonoformic acid is phosphoric acid in which one of the hydroxy groups is replaced by a carboxylic acid group. It is used as the trisodium salt as an antiviral agent in the treatment of cytomegalovirus retinitis (CMV retinitis, an inflamation of the retina that can lead to blindness) and as an alternative to ganciclovir for AIDS patients who require concurrent antiretroviral therapy but are unable to tolerate ganciclovir due to haematological toxicity. It has a role as an antiviral drug, a sodium-dependent Pi-transporter inhibitor and a HIV-1 reverse transcriptase inhibitor. It is a one-carbon compound, a member of phosphonic acids and a carboxylic acid. It derives from a phosphonic acid and a formic acid. It is a conjugate acid of a phosphonatoformate and a phosphonoformate(2-).NCI Thesaurus (NCIt): Foscarnet is a synthetic organic analog of inorganic pyrophosphate with activity against several types of viruses, but primarily used for the treatment of cytomegalovirus retinitis. Foscarnet selectively blocks the pyrophosphate binding site of virus-specific DNA polymerases at concentrations that do not affect cellular DNA polymerases. Because this agent crosses the blood brain barrier, it may be used in the treatment of viral infections of the central nervous system.