Foscarnet Injection and Pentamidine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Foscarnet Injection
Pentamidine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Symptomatic and severe hypocalcemia and nephrotoxicity
Interaction Deep Dive
Concurrent use of IV pentamidine and foscarnet has resulted in severe hypocalcemia and nephrotoxicity. In 4 patients coadministered these agents, symptomatic and severe hypocalcemia developed which resulted in a fatality in 1 patient13. Toxicity due to hypocalcemia has not been observed when foscarnet was used with aerosolized pentamidine. Avoid concomitant use of IV pentamidine and foscarnet unless the potential benefits outweigh the risks 1.
Why it happens (mechanism)
Reduction of ionized calcium by foscarnet and additive nephrotoxicity
Literature reports
2 reports — tap to read
a) Severe hypocalcemia occurred in 4 patients receiving pentamidine and foscarnet. Three patients were being treated for Pneumocystis pneumonia and the fourth for cytomegalovirus disease. Serum calcium returned to normal in 3 patients when one of the drugs was discontinued; the fourth patient died with severe hypocalcemia (1.42 mmol/L). All four patients experienced paresthesia in the hands and feet within 10 days of beginning combination therapy; 3 had Chvostek's and Trousseau's signs 23.
b) Toxicity due to hypocalcemia has not been observed when foscarnet was used with aerosolized pentamidine 1.
Common questions
Can I take Foscarnet Injection and Pentamidine together?
Symptomatic and severe hypocalcemia and nephrotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Foscarnet Injection and Pentamidine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Foscarnet Injection or Pentamidine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (3)
- Product Information: FOSCAVIR(R) intravenous injection solution, foscarnet sodium intravenous injection solution. Hospira, Inc. (per DailyMed), Lake Forest, IL, 2014. DailyMed
- Product Information: Foscavir(R), foscarnet sodium. AstraZeneca, Westborough, MA, 2002. DailyMed
- Youle MS, Clarbour J, Gazzard B, et al: Severe hypocalcaemia in AIDS patients treated with foscarnet and pentamidine. Lancet 1988; 1:1455-1456. PubMed
Keep reading about Foscarnet Injection
Keep reading about Pentamidine
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