What the label lists and what reports show
Nafcillin side effects
Nafcillin's FDA label lists its adverse reactions in its own words. FAERS holds 918 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 renal failure acute (64 reports).
- Generic listed
Check it at the source: the nafcillin FDA label on DailyMed (effective March 9, 2026, ONESOURCE SPECIALTY PHARMA LIMITED); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsBody as a Whole The reported incidence of allergic reactions to penicillin ranges from 0.7 to 10 percent (see WARNINGS ). Sensitization is usually the result of treatment, but some individuals have had immediate reactions to penicillin when first treated. In such cases, it is thought that the patients may have had prior exposure to the drug via trace amounts present in milk or vaccines. Two types of allergic reactions to penicillins are noted clinically, immediate and delayed. Immediate reactions usually occur within 20 minutes of administration and range in severity from urticaria and pruritus to angioedema, laryngospasm, bronchospasm, hypotension, vascular collapse, and death. Such immediate anaphylactic reactions are very rare (see WARNINGS ) and usually occur after parenteral therapy but have occurred in patients receiving oral therapy. …
Source: FDA drug label, ONESOURCE SPECIALTY PHARMA LIMITED, effective March 9, 2026 (SPL set 4b3b8e52-df96-4886-e063-6294a90ac63f), via openFDA; the full label on DailyMed
What do FAERS reports show?
918 reports list nafcillin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 110 are coded as a death and 465 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 23 reactions below, 5 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?
- Nafcillin: 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