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Cloxacillin ball-and-stick.png
Trade namesCloxapen, others
  • (2S,5R,6R)-6-{[3-(2-chlorophenyl)-5-methyl-
    4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid or 5 methyl 3(2 chlorophenyl)4 isoxazoyl penicillin
Clinical data
  • US: B (No risk in non-human studies)
Routes of
By mouth, IM
Defined daily dose2 gm[1]
External links
AHFS/Drugs.comMicromedex Detailed Consumer Information
Bioavailability37 to 90%
Protein binding95%
Elimination half-life30 minutes to 1 hour
ExcretionKidney and biliary
Chemical and physical data
Molar mass435.88 g·mol−1
3D model (JSmol)
  • O=C(O)[C@@H]3N4C(=O)[C@@H](NC(=O)c2c(onc2c1ccccc1Cl)C)[C@H]4SC3(C)C
  • InChI=1S/C19H18ClN3O5S/c1-8-11(12(22-28-8)9-6-4-5-7-10(9)20)15(24)21-13-16(25)23-14(18(26)27)19(2,3)29-17(13)23/h4-7,13-14,17H,1-3H3,(H,21,24)(H,26,27)/t13-,14+,17-/m1/s1 checkY

Cloxacillin is an antibiotic useful for the treatment of a number of bacterial infections.[2] This includes impetigo, cellulitis, pneumonia, septic arthritis, and otitis externa.[2] It is not effective for methicillin-resistant Staphylococcus aureus (MRSA).[3] It is used by mouth and by injection.[2]

Side effects include nausea, diarrhea, and allergic reactions including anaphylaxis.[2] Clostridium difficile diarrhea may also occur.[3] It is not recommended in people who have previously had a penicillin allergy.[2] Use during pregnancy appears to be relatively safe.[2] Cloxacillin is in the penicillin family of medications.[3]

Cloxacillin was patented in 1960 and approved for medical use in 1965.[4] It is on the World Health Organization's List of Essential Medicines.[5] The wholesale cost in the developing world is about US$0.16 per day for the pills.[6] It is not commercially available in the United States.[3]

Medical uses


The defined daily dose is 2 gm by mouth and by injection.[1] In adults the typical dose is 1 gram three times per day by mouth while in children over the age of 10 the dose is 15 mg/kg three times per day.[7] Treatment duration for impetigo is 7 days.[7]

The injectable form is typically given as 2 gm every 6 hours in adults, though 3 grams every 6 hours may be used for certain cases.[8] In children over a month the dose is 25 to 50 mg/kg by injection every six hours.[8] When the injectable form is no longer required, switching to oral cloxacillin is not recommended. People should instead be switched from the injectable treatment to either oral cephalexin or amoxicillin/clavulanic acid as soon as possible, to complete the treatment course.[8]

For erysipelas and cellulitis, the doses of cloxacillin is usually half that for severe infections.[8]

Cloxacillin dosage for severe infections
Age category Weight (kg) By mouth By injection over 60 min (500 mg vial, diluted in 4 ml, 125 mg/ml)
1 to 3 mths 4 to 6 1 ml 4 times/day[8]
3 to 12 mths 6 to 10 2 ml 4 times/day[8]
1 to 5 yrs 10 to 20 4 ml 4 times/day[8]
5 to 8 yrs 20 to 28 8 ml 4 times/day[8]
8 to 12 yrs 28 to 38 12 ml 4 times/day[7]
12 to 13 yrs 38 to 45 500 mg 3 times/day[7] 16 ml 4 times/day[8]
13 to 15 yrs 45 to 55 750 mg 3 times/day[7] 16 ml 4 times/day[8]
Adult ≥ 55 1 gm three 3 times/day[7] 2 gm 4 times/day[8]

Mechanism of action

It is semisynthetic and in the same class as penicillin.[9] Cloxacillin is used against staphylococci that produce beta-lactamase. Cloxacillin's side chain acts as a barrier to the bacteria's enzyme and it works by breaking down the bacterial cell wall. Its absorption is reduced by food.[10] Staph. aureus has shown resistance to cloxacillin, hence requiring alternative antibiotics.[10]

Society and culture

Beecham (now GlaxoSmithKline) discovered and developed cloxacillin by making modifications to methicillin in the early 1960s.[9]

Cloxacillin is sold under a number of trade names, including Cloxapen,[11] Cloxacap,[12] Tegopen,[13] and commonly for veterinary use, Orbenin.[14] It is not commercially available in the United States.[3] It is available in Canada.[10]

See also


  1. 1.0 1.1 "WHOCC - ATC/DDD Index". Retrieved 30 August 2020. CS1 maint: discouraged parameter (link)
  2. 2.0 2.1 2.2 2.3 2.4 2.5 World Health Organization (2009). Stuart MC, Kouimtzi M, Hill SR (eds.). WHO Model Formulary 2008. World Health Organization. pp. 98, 100, 110–111, 586, 602, 614, 623. hdl:10665/44053. ISBN 9789241547659.
  3. 3.0 3.1 3.2 3.3 3.4 "Cloxacillin (Professional Patient Advice)". Archived from the original on 20 December 2016. Retrieved 10 December 2016. CS1 maint: discouraged parameter (link)
  4. Fischer, Janos; Ganellin, C. Robin (2006). Analogue-based Drug Discovery. John Wiley & Sons. p. 490. ISBN 9783527607495. Archived from the original on 2016-12-20. CS1 maint: discouraged parameter (link)
  5. World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
  6. "Cloxacillin Sodium". International Drug Price Indicator Guide. Retrieved 8 December 2016. CS1 maint: discouraged parameter (link)
  7. 7.0 7.1 7.2 7.3 7.4 7.5 "Cloxacillin oral - Essential drugs". Retrieved 30 August 2020. CS1 maint: discouraged parameter (link)
  8. 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 "Cloxacillin injectable - Essential drugs". Retrieved 1 September 2020. CS1 maint: discouraged parameter (link)
  9. 9.0 9.1 David Greenwood (2008). Antimicrobial drugs: chronicle of a twentieth century medical triumph. Oxford University Press US. pp. 124–. ISBN 978-0-19-953484-5. Archived from the original on 6 June 2013. Retrieved 18 November 2010. CS1 maint: discouraged parameter (link)
  10. 10.0 10.1 10.2 Sealock, Kara; Seneviratne, Cydnee; Lilley, Linda Lane; Collins, Shelly Rainforth; Snyder, Julie S. (2021). "43. Antibiotics Part 1. Sulfonamides, penicillins, cephalosporins, macrocodes and tetracyclines". Lilley's Pharmacology for Canadian Health Care Practice - E-Book (4th ed.). Elsevier. pp. 700–701. ISBN 978-0-323-69480-3.
  11. "Cloxapen". Retrieved 30 December 2020.
  12. "Cloxacap Full Prescribing Information, Dosage & Side Effects | MIMS Singapore".
  13. "Tegopen Drug Interactions". Retrieved 30 December 2020.
  14. "Orbenin". Retrieved 30 December 2020.

External links

External sites: