Foscavir

• Foscavir is an antiviral drug used to treat cytomegalovirus (CMV) retinitis and acyclovir-resistant herpes simplex virus (HSV).
• It works by directly inhibiting viral DNA polymerase, preventing the virus from replicating.
• Administration is typically intravenous, requiring careful monitoring of kidney function and electrolyte levels.
• Common Foscavir side effects include kidney impairment, electrolyte imbalances, and gastrointestinal issues.
• Precise Foscavir dosage and administration are critical due to its potential for toxicity and the need for hydration.

What is Foscavir: Uses and Mechanism of Action

Foscavir, also known by its generic name foscarnet sodium, is an antiviral agent that belongs to a class of drugs called pyrophosphate analogues. It is primarily indicated for the treatment of cytomegalovirus (CMV) retinitis in patients with acquired immunodeficiency syndrome (AIDS) and for the treatment of acyclovir-resistant herpes simplex virus (HSV) infections in immunocompromised patients. These conditions can be severe, especially in individuals with weakened immune systems, making effective antiviral therapy essential.

The way Foscavir works involves a direct inhibition of viral DNA polymerase and reverse transcriptase. Unlike some other antiviral drugs, Foscavir does not require activation by viral enzymes, which is particularly advantageous in treating resistant strains of viruses. It selectively blocks the pyrophosphate binding site on these viral enzymes, thereby preventing the synthesis of new viral DNA and RNA. This mechanism effectively halts viral replication without significantly interfering with human cellular DNA synthesis, although it can still affect host cells, leading to potential side effects.

Foscavir Dosage, Administration, and Side Effects

The Foscavir dosage and administration regimen are critical due to its potential for toxicity and the need for careful patient management. Foscavir is administered intravenously, typically through a central venous catheter, and requires a controlled infusion rate to minimize adverse reactions. Adequate hydration is often recommended before and during infusion to help protect the kidneys. The specific dosage depends on the patient’s kidney function, body weight, and the type of infection being treated. For CMV retinitis, an induction dose followed by a maintenance dose is common, while for acyclovir-resistant HSV, a specific induction course is usually prescribed.

Patients receiving Foscavir must be closely monitored for potential adverse effects. The most significant Foscavir side effects involve renal toxicity, which can range from mild impairment to acute renal failure. Regular monitoring of serum creatinine and creatinine clearance is essential to adjust the dosage and prevent severe kidney damage. Electrolyte imbalances are also common, including hypocalcemia, hypomagnesemia, hypokalemia, and hypophosphatemia, which can lead to serious cardiac arrhythmias or seizures. Other side effects may include:

• Nausea, vomiting, and diarrhea
• Anemia and leukopenia
• Headache and fatigue
• Genital ulceration (especially with higher concentrations)
• Paresthesia or numbness

Due to these potential toxicities, Foscavir is typically reserved for cases where other antiviral treatments are ineffective or contraindicated, and its use requires careful clinical judgment and vigilant patient monitoring.