Title: Cloxacillin
CAS Registry Number: 61-72-3
CAS Name: (2S,5R,6R)-6-[[[3-(2-Chlorophenyl)-5-methyl-4-isoxazolyl]carbonyl]amino]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
Additional Names: [3-(o-chlorophenyl)-5-methyl-4-isoxazolyl]penicillin; [5-methyl-3-(o-chlorophenyl)-4-isoxazolyl]penicillin; 6-[3-(o-chlorophenyl)-5-methyl-4-isoxazolecarboxamido]penicillanic acid
Molecular Formula: C19H18ClN3O5S
Molecular Weight: 435.88
Percent Composition: C 52.35%, H 4.16%, Cl 8.13%, N 9.64%, O 18.35%, S 7.36%
Literature References: Semi-synthetic antibiotic related to penicillin; chlorinated deriv of oxacillin, q.v. Prepn: F. P. Doyle, J. H. C. Nayler, US 2996501 (1961); F. P. Doyle et al., J. Chem. Soc. 1963, 5838. Manuf: Ind. Chem. 39, 513 (1963), C.A. 60, 1543a (1964). Properties and pharmacology: J. H. C. Nayler et al., Nature 195, 1264 (1962). Toxicity data: E. I. Goldenthal, Toxicol. Appl. Pharmacol. 18, 185 (1971). Comprehensive description: D. L. Mays, Anal. Profiles Drug Subs. 4, 113-136 (1975).
Derivative Type: Sodium salt monohydrate
CAS Registry Number: 7081-44-9; 642-78-4 (anhydrous)
Additional Names: Sodium cloxacillin
Manufacturers' Codes: BRL-1621
Trademarks: Cloxapen (GSK); Cloxypen (BMS); Ekvacillin (AstraZeneca); Latocillin (Chassot); Orbenin (GSK); Methocillin-S (Meiji); Tegopen (BMS)
Molecular Formula: C19H17ClN3NaO5S.H2O
Molecular Weight: 475.88
Percent Composition: C 47.95%, H 4.02%, Cl 7.45%, N 8.83%, Na 4.83%, O 20.17%, S 6.74%
Properties: Microcryst powder, dec 170°. [a]D20 +163° (c = 1 in water). pH of 1% aq soln = 6.0-7.5. Sol in water, methanol, ethanol, pyridine, ethylene glycol. LD50 in rats, mice (mg/kg): 1630 ±112, 1280 ±50 i.p. (Goldenthal).
Optical Rotation: [a]D20 +163° (c = 1 in water)
Toxicity data: LD50 in rats, mice (mg/kg): 1630 ±112, 1280 ±50 i.p. (Goldenthal)
Derivative Type: Benzathine salt
CAS Registry Number: 23736-58-5
Trademarks: Dry Clox (Wyeth); Noroclox (Norbrook)
Molecular Formula: C54H56Cl2N8O10S2
Molecular Weight: 1112.11
Percent Composition: C 58.32%, H 5.08%, Cl 6.38%, N 10.08%, O 14.39%, S 5.77%
Therap-Cat: Antibacterial.
Therap-Cat-Vet: Antibacterial.
Keywords: Antibacterial (Antibiotics); ?Lactams; Penicillins.
Cloxazolam Cloxotestosterone Cloxyquin Clozapine Clupeine

Cloxacillin ball-and-stick.png
Systematic (IUPAC) name
4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
Clinical data
Trade names Cloxapen
AHFS/ Micromedex Detailed Consumer Information
Pregnancy cat. B (US)
Legal status  ?
Routes Oral, IM
Pharmacokinetic data
Bioavailability 37 to 90%
Protein binding 95%
Half-life 30 minutes to 1 hour
Excretion Renal and biliary
CAS number 61-72-3 YesY
ATC code J01CF02 QJ51CF02 QS01AA90
PubChem CID 6098
DrugBank DB01147
ChemSpider 5873 YesY
KEGG D07733 YesY
ChEBI CHEBI:49566 YesY
Chemical data
Formula C19H18ClN3O5S 
Mol. mass 435.88 g/mol
 YesY (what is this?)  (verify)

Cloxacillin is a semisynthetic antibiotic in the same class as penicillin. Cloxacillin was discovered and developed by Beecham.[1] It is sold under a number of trade names, including Cloxapen, Cloxacap, Tegopen and Orbenin.

Cloxacillin is used against staphylococci that produce beta-lactamase, due to its large R chain, which does not allow the beta-lactamases to bind.

This drug has a weaker antibacterial activity than benzylpenicillin, and is devoid of serious toxicity except for allergic reactions.

It has been suggested, in one study, that increased use of cloxacillin may permit reduced use of vancomycin.[2]