What the FDA labels say about taking them together
Acyclovir and foscarnet
Foscarnet's FDA label of December 11, 2025 names acyclovir in its drug interactions section; the acyclovir labels PlainMeds reads (4) do not name foscarnet.
Check it at the source: the acyclovir FDA label on DailyMed (effective July 24, 2026, Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc.); the foscarnet FDA label on DailyMed (effective December 11, 2025, Clinigen Limited).
What does the acyclovir label say about foscarnet?
Acyclovir's label (effective July 24, 2026) and its 3 other brand-application labels do not name foscarnet in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (ACYCLOVIR), Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc., effective July 24, 2026 (SPL set 0de2f5c7-9e75-4bdf-9c28-e026cc6694b4), via openFDA; the full label on DailyMed
What does the foscarnet label say about acyclovir?
Foscarnet label, drug interactionsBecause 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.
Source: FDA drug label (Foscavir), Clinigen Limited, effective December 11, 2025 (SPL set 90e3da4e-3b1f-428b-99ca-e4bed1c80028), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Acyclovir | Foscarnet | |
|---|---|---|
| Labeled for | Herpes and shingles | n/a |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.0962 per tablet 400 mg tablet | n/a |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once