Foscarnet and Pentamidine interaction
Foscarnet and Pentamidine: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Foscarnet (Foscavir) label · effective 2025-12-11
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, cyclosporine, acyclovir, methotrexate, tacrolimus and intravenous pentamidine (see above) unless the potential benefits outweigh the risks to the patient.
(See DOSAGE and ADMINISTRATION. ) Because of the risk of QT prolongation and the potential for torsades de pointes, the use of FOSCAVIR should be avoided in combination with agents known to prolong the QT interval including Class IA (e.g., quinidine or procainamide) or Class III (e.g., dofetilide, amiodarone, sotalol) antiarrhythmic agents, phenothiazines, tricyclic…
Toxicity associated with concomitant use of aerosolized pentamidine has not been reported.
Because FOSCAVIR can reduce serum levels of ionized calcium, extreme caution is advised when used concurrently with other drugs known to influence serum calcium levels (e.g., intravenous pentamidine).
Use with caution in patients who have a history of QT prolongation, in patients who are taking medications known to prolong the QT interval (see PRECAUTIONS section), in patients with electrolyte disturbances, or in patients who have other risk factors for QT prolongation.
From the Pentamidine (Pentamidine Isethionate) label · effective 2026-06-12
Because the nephrotoxic effects may be additive, the concomitant or sequential use of Pentamidine Isethionate and other nephrotoxic drugs such as aminoglycosides, amphotericin B, cisplatin, foscarnet, or vancomycin should be closely monitored and avoided, if possible.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.