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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
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

Biopsy showing drug induced liver injury-lobular necrosis and portal tract inflammation with a mixed inflammatory infiltrate of neutrophils, eosinophils, lymphocytes.[7]

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.[9]

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". Archived from the original on 24 January 2021. Retrieved 11 November 2021.
  2. "Nafcillin Use During Pregnancy". Archived from the original on 4 December 2020. Retrieved 11 November 2021.
  3. "Nafcillin Prices, Coupons & Patient Assistance Programs". Archived from the original on 27 September 2017. 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. Archived from the original on April 16, 2018. Retrieved August 5, 2021. 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. Khatib, Sohaib; Sabobeh, Taher; Bock, Michael D; Masoud, Amgad; Alallaf, Jwan (20 January 2021). "Nafcillin-Induced Hepatic Injury: A Case Report and Literature Review". Cureus. doi:10.7759/cureus.12817.
  8. JA Mohr. (1979). Nafcillin-associated hypokalemia. JAMA
  9. 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