Cefalexin

Cefalexin	Last updated: 06/09/2025
(Also known as: cephalexin; ceporexin-E; cephanasten; cophalexin; CEX)

GENERAL INFORMATION

Description

A broad spectrum antibiotic commonly used in veterinary medicine

Examples of veterinary uses

Used to treat bacterial infections of the skin, urinary tract, respiratory tract, bones and joints

Examples of species treated

Dogs; Cats; Cattle; Pigs; 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

Cefalexin exhibits stereoisomerism, specifically optical isomerism, due to the presence of chiral centres in its molecular structure. The key site of isomerism lies at the alpha-amino group on the 7-position of the cephalosporin nucleus. This position allows for the existence of D- and L-isomers. Studies have shown that the D-isomer of cefalexin (D-CEX) is well absorbed in the intestine and remains stable in serum and urine, while the L-isomer (L-CEX) is poorly absorbed and rapidly degraded into inactive metabolites like 7-aminodeacetoxycephalosporanic acid. Only the D-isomer contributes to the compounds antibiotic’s therapeutic effect. So, while cefalexin can theoretically exist as stereoisomers, only one is pharmacologically active and used in clinical formulations.

Chemical formula

C₁₆H₁₇N₃O₄S

Canonical SMILES

CC1=C(N2C(C(C2=O)NC(=O)C(C3=CC=CC=C3)N)SC1)C(=O)O

Isomeric SMILES

CC1=C(N2[C@@H]([C@@H](C2=O)NC(=O)[C@@H](C3=CC=CC=C3)N)SC1)C(=O)O

International Chemical Identifier key (InChIKey)

ZAIPMKNFIOOWCQ-UEKVPHQBSA-N

International Chemical Identifier (InChI)

InChI=1S/C16H17N3O4S/c1-8-7-24-15-11(14(21)19(15)12(8)16(22)23)18-13(20)10(17)9-5-3-2-4-6-9/h2-6,10-11,15H,7,17H2,1H3,(H,18,20)(H,22,23)/t10-,11-,15-/m1/s1

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
Cephalexin hydrate	-

General status

Veterinary substance type

Antibiotic, Medicinal drug, Antibacterial, Antimicrobial

Substance groups

Cephalosporin

Minimum active substance purity

Known relevant impurities

Substance origin

Semi-synthetic

Mode of action

Interferes with the bacteria's cell wall formation, causing it to rupture, and killing the bacteria.

Molecular targets

[Penicillin-binding protein 3, Antagonist], [Penicillin-binding protein 2a, Antagonist], [Penicillin-binding protein 1b, Antagonist], [Penicillin-binding protein 2B, Antagonist], [Penicillin-binding protein 1A, Antagonist]

CAS RN

15686-71-2

EC number

239-773-6

CIPAC number

US EPA chemical code

PubChem CID

27447

Therapeutic Class

Antiinfectants for systemic use: Antibacterials for intramammary use

ATCvet Code

QJ51DA01

Controlled Drug?

Regulation 37/2010 MRL Classification

Allowed substance (Table 1: Bovine)

Molecular mass

347.39

PIN (Preferred Identification Name)

IUPAC name

(6R,7R)-7-{[(2R)-2-amino-2-phenylacetyl]amino}- 3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene- 2-carboxylic acid

CAS name

7-(D-2-amino-2-phenylacetamido)-3-methyl-delta(sup 3)-cephem-4-carboxylic 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

1967, introduced

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

Le Vet Beheer B.V.
Eucphar NV
TVM UK Animal Health Ltd

Example products using this active

Cefabactin Tablets
Cephacare tablets
Cephorium Film-coated Tablets

Formulation and application details

Available as tablets, capsules and powder for oral suspension

Commercial production

Cefalexin is typically produced through a semi-synthetic process starting from the core beta-lactam structure, 7-amino-3-deacetoxycephalosporanic acid (7-ADCA). In one widely used method, 7-ADCA undergoes a condensation reaction with an acyl donor such as D-phenylglycine methyl ester, catalysed by penicillin G acylase, either free or immobilised. This enzymatic synthesis is favoured for its mild reaction conditions and high selectivity, yielding cefalexin with minimal byproducts. After the reaction, the mixture is subjected to purification steps, including solvent extraction, pH adjustment, and crystallisation to isolate high-purity cefalexin. Advanced techniques like microreactor systems and aqueous two-phase separation have also been explored to enhance yield and efficiency.

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)

1790

High

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

Melting point (°C)

197

Boiling point (°C)

727

Degradation point (°C)

Flashpoint (°C)

394

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

4.47 X 10⁰⁰

Calculated

Log P

0.65

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

5.2

pKa(2) = 7.3

Vapour pressure at 20 °C (mPa)

4.31 X 10^-10

Low volatility

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

Max: 260nm = 7750

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)

> 20000

Rat

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)

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)

> 20000

Rat

Low

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 4000 mg kg⁻¹

Rat

Subcutaneous LD₅₀ > 6100 mg kg⁻¹

Rat

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

Majority (~80-90%) is excreted unchanged in urine within 6 hours of administration, remainder lost in bile and faeces

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

No data found

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, dizziness, headache, indigestion, joint pain, stomach pain and tiredness

Handling issues

Property

Value and interpretation

General

Hazardous combustion or decomposition products are produced in a fire

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

cefalexin

French

cefalexine

German

Danish

Italian

Spanish

cefalexina

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	06/09/2025
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