Azithromycin

Azithromycin	Last updated: 13/09/2025
(Also known as: hemomycin)

GENERAL INFORMATION

Description

A broad-spectrum antibiotic, derived from erythromycin. Also exhibits anti-inflammatory, immune-modulating, and gastrointestinal motility effects.

Examples of veterinary uses

Used for a variety of bacterial, rickettsial, and parasitic infections including streptococci, staphylococci and bartonella henselae

Examples of species treated

Dogs; Cats; Horses; Birds

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

Azithromycin exhibits stereoisomerism, specifically multiple chiral centres that define its three-dimensional structure and biological activity. As a 15-membered azalide macrolide, it contains numerous asymmetric carbon atoms, each contributing to its precise spatial configuration.

Chemical formula

C₃₈H₇₂N₂O₁₂

Canonical SMILES

CCC1C(C(C(N(CC(CC(C(C(C(C(C(=O)O1)C)OC2CC(C(C(O2)C)O)(C)OC)C)OC3C(C(CC(O3)C)N(C)C)O)(C)O)C)C)C)O)(C)O

Isomeric SMILES

CC[C@@H]1[C@@]([C@@H]([C@H](N(C[C@@H](C[C@@]([C@@H]([C@H]([C@@H]([C@H](C(=O)O1)C)O[C@H]2C[C@@]([C@H]([C@@H](O2)C)O)(C)OC)C)O[C@H]3[C@@H]([C@H](C[C@H](O3)C)N(C)C)O)(C)O)C)C)C)O)(C)O

International Chemical Identifier key (InChIKey)

MQTOSJVFKKJCRP-BICOPXKESA-N

International Chemical Identifier (InChI)

InChI=1S/C38H72N2O12/c1-15-27-38(10,46)31(42)24(6)40(13)19-20(2)17-36(8,45)33(52-35-29(41)26(39(11)12)16-21(3)48-35)22(4)30(23(5)34(44)50-27)51-28-18-37(9,47-14)32(43)25(7)49-28/h20-33,35,41-43,45-46H,15-19H2,1-14H3/t20-,21-,22+,23-,24-,25+,26+,27-,28+,29-,30+,31-,32+,33-,35+,36-,37-,38-/m1/s1

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
azithromycin dihydrate	Hydrate

General status

Veterinary substance type

Antibiotic

Substance groups

Unclassified substance

Minimum active substance purity

[Azithromycin B may form during storage]

Known relevant impurities

Substance origin

Synthetic

Mode of action

Inhibits protein synthesis by susceptible bacteria

Molecular targets

[Protein synthesis, Inhibitor]

CAS RN

83905-01-5

Alternative/old CAS RN

104491-80-7; 142556-82-9

EC number

617-500-5

CIPAC number

US EPA chemical code

PubChem CID

447043

Therapeutic Class

Antibacterials for systemic use, macrolides

ATCvet Code

QJ01FA10

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

749.0

PIN (Preferred Identification Name)

(2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-11-[(2S,3R,4S,6R)-4-(dimethylamino)-3-hydroxy-6-methyloxan-2-yl]oxy-2-ethyl-3,4,10-trihydroxy-13-[(2R,4R,5S,6S)-5-hydroxy-4-methoxy-4,6-dimethyloxan-2-yl]oxy-3,5,6,8,10,12,14-heptamethyl-1-oxa-6-azacyclopentadecan-15-one

IUPAC name

CAS name

Forever chemical

Other status information

Possible surface and groundwater pollutant. Identified in raw effluents.

Relevant Environmental Water Quality Standards

Physical state

Amorphous white powder

Related substances & organisms

erythromycin

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1980, discovered Croatia; 1988, first introduced in market

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

Pfizer Animal Health
James Brown Pharma

Example products using this active

Zithromax
Zmax
Azitro-Vet

Formulation and application details

Usually supplied as an oral solution, tablet, or suspension which is often administered via drinking water

Commercial production

Azithromycin is produced through a semi-synthetic process that begins with the fermentation-based production of erythromycin A, its natural precursor. Erythromycin A is biosynthesised by the actinomycete Saccharopolyspora erythraea in a carefully controlled industrial fermentation process. This involves inoculum development, nutrient optimization, and pH and temperature regulation to maximise yield. Once fermentation is complete, erythromycin is extracted from the broth using solvent extraction, followed by acid-base purification and crystallization to isolate erythromycin A. The purified erythromycin A then undergoes chemical transformation to become azithromycin. This involves converting erythromycin into an oxime derivative, which is subjected to a Beckmann rearrangement to form a 15-membered ring structure known as 9-deoxo-9a-aza-9a-homoerythromycin A. Subsequent steps include reduction and N-methylation, yielding azithromycin with its characteristic azalide structure.

Impact on climate of production and use

As microbial-based products tend to use fermentation-based production processes rather than chemical synthesis, they typically have a lower fossil fuel input in formulation and active ingredient creation, and also have reduced downstream emissions due to biodegradability and minimal soil disruption, their life-cycle GHG emissions are expected to be low. Whilst hard and precise data is not available, broad estimates suggest that typically emissions are likely to be below 5 kg CO₂e/kg. However, the semi-synthetic production process of azithromycin will push emissions higher.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

7.09

Low

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

Melting point (°C)

114

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

451

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

1.05 X 10⁰⁴

Calculated

Log P

4.02

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

8.74

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)

Slightly mobile

K_oc (mL g⁻¹)

3100

Notes and range

Q2 estimated

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)

> 2000

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 dw soil)

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

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)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 2000

Rat

Low

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

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

Pattern of use is unlikely to result in toxicological relevant exposure

Occupational

Pattern of use is unlikely to result in toxicological relevant exposure

Mammalian dose elimination route and rate

Main excretion route is biliary as the unmetabolised drug

Health issues

Specific human health issues (hazard-based)

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

Eye irritant

Phototoxicant

No data found

General human health issues

May cause abdominal discomfort, vomiting, and diarrhea
Possible liver toxin

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

Health: H372, H334, H317
Environment: H400, H410

WHO Classification

Not listed (Not listed)

UN Number

Not registered

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

Stable for around 4 years

TRANSLATIONS

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Name

English

azithromycin

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Record last updated:	13/09/2025
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