Amoxicillin Chemical Structure

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1. Identification

Summary
A β-lactam, aminopenicillin antibiotic used across primary care and hospital settings for common bacterial infections; often chosen for ENT, lower respiratory, skin/soft-tissue, urinary, and H. pylori combination therapy.

Brand Names
Amoxil, Trimox, Moxatag; regional variants and numerous generics

Name
Amoxicillin

Background
A semisynthetic derivative of 6-APA (developed in the 1960s) with improved oral absorption versus ampicillin. Available as immediate-release and extended-release tablets/capsules, oral suspension, and in fixed-dose combinations (e.g., with clavulanate).

Modality
Small molecule

Groups
Approved; prescription

Structure
(Insert your 2D SVG/PNG skeletal formula here—black-and-white or labeled recommended.)

Weight
~365.4 g/mol (anhydrous base)

Chemical Formula
C₁₆H₁₉N₃O₅S

Synonyms
Amoxycillin; amoxicillin anhydrous (base); amoxicillin trihydrate (hydrate form)

External IDs
CAS (base): 26787-78-0; PubChem CID: 33613; UNII (anhydrous): 9EM05410Q9; KEGG: D07452; ChEBI: 2676; ChEMBL: 1082

2. Pharmacology

Indication
Treatment of susceptible infections: otitis media, pharyngitis/tonsillitis, sinusitis, LRTIs (e.g., community-acquired pneumonia when appropriate), uncomplicated skin/soft-tissue and urinary tract infections; part of H. pylori eradication regimens with a PPI and another antibiotic per local guidelines.

Associated Conditions
ENT infections, CAP/bronchitis (when indicated), dental/odontogenic infections, uncomplicated UTI, H. pylori disease (combination therapy).

Associated Therapies
Frequent combinations with clavulanate (β-lactamase inhibitor), macrolides or nitroimidazoles in H. pylori regimens, and other agents per stewardship guidance.

Contraindications & Blackbox Warnings
Contraindicated in serious hypersensitivity to penicillins (risk of immediate anaphylaxis) and in patients with prior severe reactions to β-lactams. Monitor for serious cutaneous adverse reactions. Use caution with severe renal impairment and adjust dose per label.

Pharmacodynamics
Bactericidal time-dependent killing by inhibiting transpeptidase (penicillin-binding proteins) → blocks peptidoglycan cross-linking, compromising cell-wall integrity. Optimal effect relates to %fT>MIC.

Mechanism of action
β-Lactam acylation of active-site serine on PBPs → halted cell-wall synthesis; autolytic enzyme activation contributes to lysis. Active against many streptococci, enterococci, and some gram-negatives; β-lactamase production confers resistance (hence clavulanate combinations).

Absorption
Good oral absorption; typical oral bioavailability ~60% (formulation/food dependent). Food may delay peak but aids GI tolerability; many labels allow dosing with meals.

Volume of distribution
Approx. 0.26–0.41 L/kg in adults; penetrates various tissues/fluids relevant to labeled indications.

Protein binding
Low, roughly ~17–20% at therapeutic concentrations.

Metabolism
Limited hepatic metabolism; multiple minor metabolites reported. Parent drug predominates in plasma and urine.

Route of elimination
Primarily renal (glomerular filtration + tubular secretion) as unchanged drug; substantial fraction excreted in urine within hours after dosing.

Half-life
About ~1 hour in healthy adults; prolonged with renal impairment.

Clearance
High renal clearance; transporter interactions (e.g., probenecid) can increase systemic exposure.

Adverse Effects
Common: GI upset, diarrhea (more with clavulanate), rash. Less common: tooth discoloration in pediatrics (usually reversible with cleaning), elevated transaminases. Serious: immediate hypersensitivity, SCARs, antibiotic-associated colitis.

Toxicity
Wide therapeutic window; main risks are severe allergic reactions and C. difficile–associated diarrhea with broad antibiotic exposure.

Pathways
PBPs/cell-wall synthesis inhibition; renal tubular secretion (notably impacted by probenecid).

Pharmacogenomic Effects/ADRs
No routine pharmacogenomic testing; hypersensitivity risk relates more to β-lactam allergy history than known germline variants.

3. Interactions

Drug Interactions

  • Probenecid: decreases renal tubular secretion → higher/prolonged amoxicillin levels.
  • Oral anticoagulants (e.g., warfarin): reports of INR elevation/bleeding risk; monitor if co-used.
  • Allopurinol: increased incidence of rash when co-administered.
  • Bacteriostatic agents (chloramphenicol, macrolides, sulfonamides, tetracyclines): may antagonize β-lactam bactericidal activity in vitro (clinical significance varies).

Food Interactions
May be taken with food to minimize GI intolerance; food can delay tₘₐₓ without major reduction in exposure for common oral products.

4. Categories

ATC Codes
J01CA04 (Penicillins with extended spectrum)

Drug Categories
β-Lactam antibiotics; Aminopenicillins; Small molecule

Chemical Taxonomy
Aromatic aminopenicillin with β-lactam and thiazolidine rings; phenolic side chain; amphiphilic profile.

Affected organisms
Humans (therapeutic use); target bacteria susceptible to aminopenicillins

5. Chemical Identifiers

UNII
9EM05410Q9 (amoxicillin anhydrous)

CAS number
26787-78-0 (anhydrous base)

InChI Key
LSQZJLSUYDQPKJ-NJBDSQKTSA-N

InChI
InChI=1S/C16H19N3O5S/c1-16(2)11(15(23)24)19-13(22)10(14(19)25-16)18-12(21)9(17)7-3-5-8(20)6-4-7/h3-6,9-11,14,20H,17H2,1-2H3,(H,18,21)(H,23,24)/t9-,10-,11+,14-/m1/s1

IUPAC Name
(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid

SMILES
O=C(O)[C@@H]2N3C(=O)[C@@H](NC(=O)[C@@H](c1ccc(O)cc1)N)[C@H]3SC2(C)C

6. References

  1. PubChem: Amoxicillin compound summary—formula, identifiers, general properties (CID 33613). PubChem
  2. WHO Essential Medicines: Amoxicillin listed on EML; 2025 overview and AWaRe resources. World Health Organization
  3. ATC/DDD Index: J01CA04 (amoxicillin), DDD and route details. atcddd.fhi.no+1
  4. DailyMed labels (multiple): administration with food for GI tolerance; interaction warnings (probenecid; oral anticoagulants); pediatric tooth discoloration note. DailyMed+4DailyMed+4DailyMed+4
  5. Peer-reviewed PK: protein binding ~17%; Vd and clearance ranges; half-life ≈1 h. PMC+2ASM Journals+2
  6. ChEBI / UNII FDA GSRS: InChI, InChIKey LSQZJLSUYDQPKJ-NJBDSQKTSA-N; UNII 9EM05410Q9. sitem.herts.ac.uk+1
  7. Fisher Scientific / spec sheets: MW 365.404 g/mol; CAS confirmation; InChIKey. Fisher Scientific
  8. Drug interaction literature (clinical/observational): warfarin effects with amoxicillin or amox-clav; allopurinol rash signal. FDA Access Data+3PMC+3JAMA Network+3

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