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Other namesNafcillin sodium
  • (2S,5R,6R)-6-[(2-ethoxy-1-naphthoyl)amino]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
Clinical data
Drug classAntibiotic (penicillin)[1]
Main usesTreat and prevent straphylococcal infections[1]
Side effectsPain at injection site, anaphylaxis, Clostridioides difficile infection[1]
  • US: B (No risk in non-human studies)
Routes of
External links
US NLMNafcillin
Legal status
  • In general: ℞ (Prescription only)
Protein binding90%
Metabolism<30% liver
Elimination half-life0.5 hours
ExcretionBiliary and kidney
Chemical and physical data
Molar mass414.48 g·mol−1
3D model (JSmol)
  • O=C(O)[C@@H]3N4C(=O)[C@@H](NC(=O)c2c1ccccc1ccc2OCC)[C@H]4SC3(C)C
  • InChI=1S/C21H22N2O5S/c1-4-28-13-10-9-11-7-5-6-8-12(11)14(13)17(24)22-15-18(25)23-16(20(26)27)21(2,3)29-19(15)23/h5-10,15-16,19H,4H2,1-3H3,(H,22,24)(H,26,27)/t15-,16+,19-/m1/s1 checkY

Nafcillin, sold under the brand name Unipen among others, is an antibiotic used to treat and prevent straphylococcal infections.[1] This includes includes of the skin, respiratory tract, urine, and blood.[1] It is not effective against MRSA.[1] It is given by injection into a vein or muscle.[1]

Common side effects include pain and inflammation at the site of injection.[1] Other side effects may include anaphylaxis and Clostridioides difficile infection.[1] There is no evidence of harm with use in pregnancy, though such use has not been well studied.[2] It is a beta-lactam antibiotic of the penicillin type.[1] It is penicillinase resistant.[1]

Nafcillin was approved for medical use in the United States in 1965.[1] In the United States 10 doses of 2 grams costs about 90 USD as of 2021.[3] In 2012, out of 38 countries it was only available in one.[4]

Medical uses

Nafcillin is used to treat staphylococcal infections, except those caused by MRSA.[5]

Medical guidelines recommend either nafcillin or oxacillin as the first-line treatment for staphylococcal endocarditis in people without artificial heart valves.[6]


It is given at a dose of 500 to 2,000 mg every 4 to 6 hours.[1]

Side effects

Serious life-threatening allergic reactions can occur.

Milder side-effects include:


There is evidence that nafcillin induces cytochrome P-450 enzymes, specifically CYP2C9. Several drugs with a narrow therapeutic window, such as warfarin and nifedipine, are metabolized by CYP2C9.[8]

Nafcillin contains salts added as stability media. These added salts could cause edema or fluid accumulation. It would be prudent to avoid this medication if there were a concern for a congestive heart failure or kidney disease.[citation needed]


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 "Nafcillin Monograph for Professionals". Retrieved 11 November 2021.
  2. "Nafcillin Use During Pregnancy". Retrieved 11 November 2021.
  3. "Nafcillin Prices, Coupons & Patient Assistance Programs". Retrieved 11 November 2021.
  4. Pulcini, Céline; Bush, Karen; Craig, William A.; Frimodt-Møller, Niels; Grayson, M. Lindsay; Mouton, Johan W.; Turnidge, John; Harbarth, Stephan; Gyssens, Inge C. (15 January 2012). "Forgotten Antibiotics: An Inventory in Europe, the United States, Canada, and Australia". Clinical Infectious Diseases. 54 (2): 268–274. doi:10.1093/cid/cir838.
  5. Pham P, Bartlett JG (January 2, 2009). "Nafcillin". Point-of-Care Information Technology ABX Guide. Johns Hopkins University. Retrieved on July 10, 2009. Freely available with registration.
  6. Bonow RO, Carabello BA, Kanu C, et al. (August 2006). "ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (writing committee to revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease): developed in collaboration with the Society of Cardiovascular Anesthesiologists: endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons". Circulation. 114 (5): e84–231. doi:10.1161/CIRCULATIONAHA.106.176857. PMID 16880336.
  7. JA Mohr. (1979). Nafcillin-associated hypokalemia. JAMA
  8. Lang CC, Jamal SK, Mohamed Z, Mustafa MR, Mustafa AM, Lee TC (June 2003). "Evidence of an interaction between nifedipine and nafcillin in humans". Br J Clin Pharmacol. 55 (6): 588–90. doi:10.1046/j.1365-2125.2003.01789.x. PMC 1884262. PMID 12814453.

External links