Foscarnet
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.