Foscavir
Foscavir - General Information
An antiviral agent used in the treatment of cytomegalovirus retinitis. Foscavir also shows activity against human herpesviruses and HIV. [PubChem]
Pharmacology of Foscavir
Foscavir is an organic analogue of inorganic pyrophosphate that inhibits replication of herpes viruses in vitro including cytomegalovirus (CMV) and herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). Foscavir does not require activation (phosphorylation) by thymidine kinase or other kinases and therefore is active in vitro against HSV TK deficient mutants and CMV UL97 mutants. Thus, HSV strains resistant to acyclovir or CMV strains resistant to ganciclovir may be sensitive to foscarnet. However, acyclovir or ganciclovir resistant mutants with alterations in the viral DNA polymerase may be resistant to foscarnet and may not respond to therapy with foscarnet. The combination of foscarnet and ganciclovir has been shown to have enhanced activity in vitro.
Foscavir for patients
CMV Retinitis Patients should be advised that FOSCAVIR is not a cure for CMV retinitis,
and that they may continue to experience progression of retinitis during or following
treatment. They should be advised to have regular ophthalmologic examinations.
Mucocutaneous Acyclovir-Resistant HSV Infections Patients should be advised that FOSCAVIR
is not a cure for HSV infections. While complete healing is possible, relapse occurs in most
patients. Because relapse may be due to acyclovir-sensitive HSV, sensitivity testing of the
viral isolate is advised. In addition, repeated treatment with FOSCAVIR has led to the development
of resistance associated with poorer response. In the case of poor therapeutic response, sensitivity
testing of the viral isolate also is advised.
General Patients should be informed that the major toxicities of foscarnet are renal impairment,
electrolyte disturbances, and seizures, and that dose modifications and possibly discontinuation
may be required. The importance of close monitoring while on therapy must be emphasized. Patients
should be advised of the importance of reporting to their physicians symptoms of perioral tingling,
numbness in the extremities or paresthesias during or after infusion as possible symptoms of
electrolyte abnormalities. Should such symptoms occur, the infusion of FOSCAVIR should be stopped,
appropriate laboratory samples for assessment of electrolyte concentrations obtained, and a physician
consulted before resuming treatment. The rate of infusion must be no more than 1 mg/kg/minute.
The potential for renal impairment may be minimized by accompanying FOSCAVIR administration with
hydration adequate to establish and maintain a diuresis during dosing.
Foscavir Interactions
A possible drug interaction of FOSCAVIR and intravenous pentamidine has been described. Concomitant treatment of four patients in the United Kingdom with FOSCAVIR and intravenous pentamidine may have caused hypocalcemia; one patient died with severe hypocalcemia. Toxicity associated with concomitant use of aerosolized pentamidine has not been reported.
Because of foscarnet's tendency to cause renal impairment, the use of FOSCAVIR should be avoided in combination with potentially nephrotoxic drugs such as aminoglycosides, amphotericin B and intravenous pentamidine unless the potential benefits outweigh the risks to the patient.
Abnormal renal function has been observed in clinical practice during the use of FASCAVIR and ritonavir, or FOSCAVIR, ritonavir, and saquinavir.
Since FOSCAVIR decreases serum concentrations of ionized calcium, concurrent treatment with other drugs known to influence serum calcium concentrations should be used with particular caution.
Ganciclovir The pharmacokinetics of foscarnet and ganciclovir were not altered in 13 patients receiving either concomitant therapy or daily alternating therapy for maintenance of CMV disease.
Foscavir Contraindications
FOSCAVIR is contraindicated in patients with clinically significant hypersensitivity to foscarnet sodium.
Additional information about Foscavir
Foscavir Indication: For the treatment of CMV retinitis in patients with acquired immunodeficiency syndrome (AIDS) and for treatment of acyclovir-resistant mucocutaneous HSV infections in immunocompromised patients.
Mechanism Of Action: Foscavir exerts its antiviral activity by a selective inhibition at the pyrophosphate binding site on virus-specific DNA polymerases at concentrations that do not affect cellular DNA polymerases.
Drug Interactions: Not Available
Food Interactions: Not Available
Generic Name: Foscarnet
Synonyms: PFA; Foscarnet sodium; Forscarnet sodium; Dihydroxyphosphinecarboxylic acid oxide; Carboxyphosphonic acid; Phgosphonocarboxylic acid; Phosphonoformate; Phosphonoformic acid
Drug Category: Reverse Transcriptase Inhibitors; Antiviral Agents
Drug Type: Small Molecule; Approved
Other Brand Names containing Foscarnet: Foscarmet; Foscavir; Triapten;
Absorption: Poorly absorbed after oral administration (bioavailability from 12 to 22%).
Toxicity (Overdose): Oral, rat LD50: >2,000 mg/kg. Signs of overdose include renal impairment.
Protein Binding: 14-17%
Biotransformation: Not metabolized.
Half Life: 3.3-6.8 hours
Dosage Forms of Foscavir: Injection, solution Intravenous drip
Chemical IUPAC Name: phosphonoformic acid
Chemical Formula: CH3O5P
Foscarnet on Wikipedia: https://en.wikipedia.org/wiki/Foscarnet
Organisms Affected: Human Herpes Virus
