Foscarnet
Mechanism :
Foscarnet is an organic analogue of inorganic pyrophosphate that inhibits replication of herpesviruses including cytomegalovirus (CMV) and herpes simplex virus types 1 and 2. It 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.
Indication :
- CMV retinitis
- Herpes simplex virus muco-cutaneous lesions not responding to acyclovir
- Herpes zoster unresponsive to acyclovir
Contraindications :
Foscarnet is contraindicated in patients with clinically significant hypersensitivity to foscarnet sodium. Renal function should be monitored regularly during treatment as renal impairment may occur. Monitor serum calcium and magnesium as foscarnet may chelate divalent metal ions and lead to an acute decrease in ionized calcium/magnesium.
Dosing :
Safety and efficacy have not been established in the pediatric population.
CMV Retinitis:
Induction therapy:
60 mg/kg IV (Minimum 2 hour infusion) every 8 hours for 2 to 3 weeks.
Maintenance therapy:
90 to 120 mg/kg IV (Minimum 2 hour infusion) once a day.
Herpes Simplex:
40 mg/kg IV (Minimum 2 hour infusion) 3 times a day until clinical response.
Herpes-Zoster not responding to acyclovir:
40 to 60 mg/kg IV (Minimum 2 hour infusion) 3 times a day for 7 to 10 days.
In adolescents:
90 mg/kg IV (90 to 120 minute infusion) every 12 hours.
Adverse Effect :
Renal impairment, nausea, fever, diarrhea, anemia, headache, vomiting, seizures, bone marrow suppression, anemia, seizures.
Interaction :
Aminoglycosides, Amphotericin B and Intravenous Pentamidine: Foscarnet should be avoided in combination with potentially nephrotoxic drugs.
Serum Calcium Concentrations: Since foscarnet decreases serum concentrations of ionized calcium, concurrent treatment with other drugs known to influence serum calcium concentrations should be used with particular caution.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | 28 mg/kg every 8 hours |
| 10-20 | 15 mg/kg every 8 hours |
| <10 | 6 mg/kg every 8 hours |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Dialysed. Dose as in GFR<10 mL/ min. |
| HD | Dialysed. Dose as in GFR<10 mL/ min. |
| HDF/High flux | Dialysed. Dose as in GFR<10 mL/ min. |
| CAV/VVHD | Dialysed. Dose as in GFR=10– 20 mL/min. |
Hepatic Dose :
No dosage adjustments are needed.