What the label lists and what reports show
Foscarnet side effects
Foscarnet's FDA label: “clinical trials the most frequently reported adverse events in patients with AIDS and CMV retinitis are shown in Table 9 .” FAERS holds 3,971 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is drug resistance (508 reports).
- Generic listed
- Boxed warning
Check it at the source: the foscarnet FDA label on DailyMed (effective December 11, 2025, Clinigen Limited); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsclinical trials the most frequently reported adverse events in patients with AIDS and CMV retinitis are shown in Table 9 .
TABLE 10 Severe Adverse Events
| Reaction | n = 189 |
|---|---|
| Death | 14% |
| Abnormal Renal Function | 14% |
| Marrow Suppression | 10% |
| Anemia | 9% |
| Seizures | 7% |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedTHE MAJOR TOXICITY OF FOSCAVIR IS RENAL IMPAIRMENT (see WARNINGS section). Approximately 33% of 189 patients with AIDS and CMV retinitis who received FOSCAVIR (60 mg/kg TID), without adequate hydration, developed significant impairment of renal function (serum creatinine ≥ 2.0 mg/dL). The incidence of renal impairment in subsequent clinical trials in which 1000 mL of normal saline or 5% dextrose solution was given with each infusion of FOSCAVIR was 12% (34/280). FOSCAVIR has been associated with changes in serum electrolytes including hypocalcemia (15–30%), hypophosphatemia (8–26%) and hyperphosphatemia (6%), hypomagnesemia (15–30%), and hypokalemia (16–48%) (see WARNINGS section). The higher percentages were derived from those patients receiving hydration. FOSCAVIR treatment was associated with seizures in 18/189 (10%) AIDS patients in the initial five controlled studies (see WARNINGS section). Risk factors associated with seizures included impaired baseline renal function, low total serum calcium, and underlying CNS conditions predisposing the patient to seizures. The rate of seizures did not increase with duration of treatment. Three cases were associated with overdoses of FOSCAVIR (see OVERDOSAGE section). In five controlled U.S. clinical trials the most frequently reported adverse events in patients with AIDS and CMV retinitis are shown in Table 9 . …
Source: FDA drug label, Clinigen Limited, effective December 11, 2025 (SPL set 90e3da4e-3b1f-428b-99ca-e4bed1c80028), via openFDA; the full label on DailyMed
What do FAERS reports show?
3,971 reports list foscarnet among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,322 are coded as a death and 1,476 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 6 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Foscarnet: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions