Nafcillin: uses, dosing, side effects & brands
Nafcillin is a penicillin-class antibacterial sold in the U.S. under 4 brand and generic names, for cellulitis, bacterial endocarditis and osteomyelitis. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Drug class
- Penicillin-Class Antibacterial
- Treats
- Cellulitis, Bacterial Endocarditis and Osteomyelitis
- Available as
- Injectable
- Sold as
- 4 products — Nafcillin Sodium, Nallpen in Plastic Container and Unipen, and others
- Prescription?
- Prescription only
- Generic available?
- Yes
How nafcillin is dosed
From the FDA label for Nallpen in Plastic Container (application NDA050655). Other nafcillin products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.
Nafcillin Injection, USP supplied as a premixed frozen solution is to be administered as an intravenous infusion. The usual I.V. dosage for adults is 500 mg every 4 hours. For severe infections, 1 g every 4 hours is recommended. Administer slowly over at least 30 to 60 minutes to minimize the risk of vein irritation and extravasation. Bacteriologic studies to determine the causative organisms and their susceptibility to nafcillin should always be performed. Duration of therapy varies with the type and severity of infection as well as the overall condition of the patient; therefore, it should be determined by the clinical and bacteriological response of the patient. In severe staphylococcal infections, therapy with nafcillin should be continued for at least 14 days. The treatment of endocarditis and osteomyelitis may require a longer duration of therapy. No dosage alterations are necessary for patients with renal dysfunction, including those on hemodialysis. Hemodialysis does not accelerate nafcillin clearance from the blood. With intravenous administration, particularly in elderly patients, care should be taken because of the possibility of thrombophlebitis. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration whenever solution and container permit. Do not add supplementary medication to Nafcillin Injection,…
Nafcillin side effects
Body 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. Another type of immediate reaction, an accelerated reaction, may occur between 20 minutes and 48 hours after administration and may include urticaria, pruritus, and fever. Although laryngeal edema, laryngospasm, and hypotension occasionally occur, fatality is uncommon. Delayed allergic reactions to penicillin therapy usually occur after 48 hours and sometimes as late as 2 to 4 weeks after initiation of therapy. Manifestations of this type of reaction include serum sickness-like symptoms ( i.e., fever, malaise, urticaria, myalgia,…
Who shouldn’t take nafcillin
CONTRAINDICATION A history of a hypersensitivity (anaphylactic) reaction to any penicillin is a contraindication. Solutions containing dextrose may be contraindicated in patients with known allergy to corn or corn products.
Nafcillin drug interactions
Tetracycline, a bacteriostatic antibiotic, may antagonize the bactericidal effect of penicillin, and concurrent use of these drugs should be avoided. Nafcillin in high dosage regimens, i.e., 2 grams every 4 hours, has been reported to decrease the effects of warfarin. When nafcillin and warfarin are used concomitantly, the prothrombin time should be closely monitored and the dose of warfarin adjusted as necessary. This effect may persist for up to 30 days after nafcillin has been discontinued. Nafcillin when administered concomitantly with cyclosporine has been reported to result in subtherapeutic cyclosporine levels. The nafcillin-cyclosporine interaction was documented in a patient during two separate courses of therapy. When cyclosporine and nafcillin are used concomitantly in organ transplant patients, the cyclosporine levels should be monitored.
Every nafcillin product we track (4)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
| # | Drug | Rating | Type | Form | Generic? | Pharmacy pays | |
|---|---|---|---|---|---|---|---|
| 1 | Not yet rated | Prescription | Injectable | No data | — | View → | |
| 2 | Not yet rated | Prescription | Injectable | No data | — | View → | |
| 3 | Not yet rated | Prescription | Injectable | No data | — | View → | |
| 4 | Not yet rated | Prescription | Injectable | No data | — | View → |
Nafcillin and breastfeeding
From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.
Full LactMed record for nafcillin: levels in milk, effects in breastfed infants, and the drugs it would consider insteadAlthough no information is available on the use of nafcillin during breastfeeding, penicillins are generally not expected to cause adverse effects in breastfed infants. Occasionally disruption of the infant's gastrointestinal flora, resulting in diarrhea or thrush have been reported with penicillins, but these effects have not been adequately evaluated. Nafcillin is acceptable in nursing mothers.
National Institute of Child Health and Human Development, record revised November 15, 2024. LactMed states its information is not a substitute for professional judgement.
What people report to the FDA about nafcillin
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 218 reports naming nafcillin, and the FDA flagged 78% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- renal failure acute29 reports
- nephritis interstitial14 reports
- blood creatinine increased13 reports
- rash13 reports
- pruritus10 reports
- pyrexia10 reports
- hepatotoxicity9 reports
- diarrhoea7 reports
Read these as a signal, not a rate. A report does not mean nafcillin caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.
Source: openFDA drug/event (FAERS), retrieved July 25, 2026.
Related calculators
Frequently asked questions
What is nafcillin?
Nallpen in Plastic Container (Nafcillin Sodium) is a penicillin-class antibacterial used to treat Cellulitis, Bacterial Endocarditis, Osteomyelitis, Postoperative Complications.
What kind of drug is nafcillin?
The FDA classifies nafcillin as a penicillin-class antibacterial. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.
Can you take nafcillin with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run nafcillin against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What brand names is nafcillin sold under?
We track 4 nafcillin-containing products in the U.S.: Nafcillin Sodium, Nallpen in Plastic Container, Unipen and Unipen in Plastic Container. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.
What forms does nafcillin come in?
Across the brands we track, nafcillin is currently marketed as injectable, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic nafcillin?
Yes. Our catalog lists 1 generic nafcillin product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.
Cite this page
- APA
- pharmaranks. (2026, July 24). Nafcillin: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/nafcillin
- MLA
- “Nafcillin: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/nafcillin.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for nafcillin on DailyMed (NIH) ↗.