Foscarnet is an antiviral medication used to treat CMV retinitis in immunocompromised patients. Most often, these patients have symptoms which have persisted beyond ganciclovir treatment.
Foscarnet is also indicated for use in the treatment of acyclovir-resistant HSV.
This medication does not require phosphorylation or activation by thymidine kinases.
This med works by inhibiting viral DNA polymerase by binding to the pyrophosphate-binding site of this enzyme. Thus, foscarnet inhibits elongation of viral DNA.
Foscarnet is a pyrophosphate analog, mimicking its structure. It works by binding to the pyrophosphate-binding site of viral DNA polymerase.
Viruses can gain resistance to Foscarnet when they mutate their DNA polymerase enzyme. By mutating the enzyme, Foscarnet is no longer able to bind to it and inhibit its effects.
This drug is known to cause nephrotoxicity, and leads to increased creatinine levels in patients. This side effect, however, is reversible with adequate hydration and decreased dosage.
Foscarnet can lead to electrolyte abnormalities, such as hypokalemia, hypocalcemia, and hypomagnesemia. These abnormalities can lead to mental status changes, paresthesias, irritability, hallucinations, or even seizures.
Hypokalemia is a potassium level less than 3.5 mEq/L. It is characterized by muscle weakness, arrhythmias, presence of U waves, constipation, and hyporeflexia.
Foscarnet can cause hypocalcemia, and less frequently hypercalcemia. Decreased levels of calcium below 8.5 mg/dL are termed hypocalcemia. It is characterized with decreased bone density, muscle spasms, tetany, increased deep tendon reflexes, and a prolonged QT interval.
Hypomagnesemia is characterized by a serum magnesium level of less than 1.5 mEq/L. It is characterized by increased deep tendon reflexes, seizures, muscle cramps, tremors, insomnia, and tachycardia.
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