Cloxacillin

Cloxacillin	Last updated: 07/09/2025
(Not known by any other names)

GENERAL INFORMATION

Description

An antibiotic drug that is a chlorinated detivative of oxacillin

Examples of veterinary uses

Mainly used to treat many different types of infections caused by staphylococcus bacteria

Examples of species treated

Cattle; Dogs; Cats; Horses; Sheep

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved - usually available as a prescription only medicine to be authorised by a veterinarian (POM-V)

EU Regulatory approval status

Approved

Chemical structure

Isomerism

Cloxacillin exhibits stereoisomerism, specifically diastereomerism, due to its multiple chiral centres. As a semisynthetic beta-lactam antibiotic derived from oxacillin, cloxacillin contains a penam ring system with three key stereocentres at positions 2, 5, and 6 of the bicyclic structure. The biologically active form is the (2S,5R,6R) isomer, which is crucial for its ability to bind to bacterial penicillin-binding proteins (PBPs) and inhibit cell wall synthesis. Additionally, cloxacillin includes a chlorinated isoxazole side chain which can also give rise to positional isomers depending on the placement of the chlorine atom on the aromatic ring. However, in pharmaceutical formulations, the compound is standardised to a specific isomer to ensure consistent antibacterial activity and pharmacokinetics.

Chemical formula

C₁₉H₁₈ClN₃O₅S

Canonical SMILES

CC1=C(C(=NO1)C2=CC=CC=C2Cl)C(=O)NC3C4N(C3=O)C(C(S4)(C)C)C(=O)O

Isomeric SMILES

CC1=C(C(=NO1)C2=CC=CC=C2Cl)C(=O)N[C@H]3[C@@H]4N(C3=O)[C@H](C(S4)(C)C)C(=O)O

International Chemical Identifier key (InChIKey)

LQOLIRLGBULYKD-JKIFEVAISA-N

International Chemical Identifier (InChI)

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

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Antibiotic, Antibacterial, Medicinal drug

Substance groups

Isoxazolyl-penicillin

Minimum active substance purity

Known relevant impurities

Substance origin

Semi-synthetic

Mode of action

Interferes with the last stage of bacterial cell wall synthesis

Molecular targets

[Penicillin-binding proteins 1A/1B, Antagonist], [Beta-lactamase, Agonist], [Penicillin-binding protein 2a, Antagonist], [Penicillin-binding protein 2B, Antagonist], [Penicillin-binding protein 3, Antagonist], [Penicillin-binding protein 5, Antagonist]

CAS RN

61-72-3

EC number

200-514-7

CIPAC number

US EPA chemical code

PubChem CID

6098

Therapeutic Class

Antiinfectants for systemic use: Antibacterials for intramammary use; Sensory organs: Ophthalmologicals

ATCvet Code

QJ51CF02; QS01AA90

Controlled Drug?

Regulation 37/2010 MRL Classification

Allowed substance (Table 1: All food producing species)

Molecular mass

435.88

PIN (Preferred Identification Name)

IUPAC name

(2S,5R,6R)-6-[[3-(2-chlorophenyl)-5-methyl-1,2-oxazole-4-carbonyl]amino]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid

CAS name

6-(3-(o-Chlorophenyl)-5-methyl-4-isoxazolecarboxamido)penicillanic acid

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

White crystalline powder

Commercial

Property

Value

Availability status

Current

Introduction & key dates

Early 1960s, first synthesised; 1966, first US approvals; Circa 1969, first UK approvals

Example manufacturers & suppliers of products using this active now or historically

Norbrook Labs
Zoetis UK Ltd
Vetoquinol UK Ltd

Example products using this active

Bovaclox DC Intramammary Suspension
Kloxerate Gold Intramammary Suspension
Permaway Intramammaryn Suspension

Formulation and application details

Available in a variety of formulations including intramammary suspensions and infusions

Commercial production

Cloxacillin is produced through a semi-synthetic process starting with 6-aminopenicillanic acid (6-APA). First, 6-APA is reacted with sodium hydroxide to form its sodium salt. This intermediate then undergoes acylation with a chlorinated isoxazole derivative, specifically, o-chlorobenzoyl chloride, to introduce the bulky side chain that confers beta-lactamase resistance. The reaction mixture is then acidified with dilute sulphuric acid, followed by the addition of a salt-forming agent like sodium isooctanoate to yield cloxacillin sodium.

Impact on climate of production and use

Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

13.9

Moderate

Solubility - In organic solvents at 20 °C (mg l⁻¹)

Melting point (°C)

Boiling point (°C)

Degradation point (°C)

173

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

3.02 X 10⁰²

Calculated

Log P

2.48

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

2.78

Vapour pressure at 20 °C (mPa)

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Surface tension (mN m⁻¹)

Refractive Index

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

Rat as sodium salt

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary (LC₅₀/LD₅₀)

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹) (EC₅₀)

23.4

Raphidocelis subcapitata

Low

Algae - Chronic (growth rate, fresh; mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

Rat as sodium salt

Low

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intravenous LDLo = 1680 mg kg⁻¹

Human

Intracerebral LD₅₀ = 8.1 mg kg⁻¹

Mouse

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

Mammalian dose elimination route and rate

Around 50% of administered dose is rapidly (<6hrs) excreted in urine with additional losses via bile and faeces

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

May cause diarrhoea and abdominal cramps
May cause allergic reaction
May cause skin rashes and contact dermatitis

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

cloxacillin

French

cloxacilline

German

Danish

Italian

Spanish

cloxacilina

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	07/09/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242