Amoxicillin

What is Amoxicillin?

Amoxicillin is a broad-spectrum beta-lactam antibiotic belonging to the penicillin class. It is used to treat a wide range of bacterial infections caused by susceptible organisms.

It is structurally related to ampicillin but has improved oral absorption, making it one of the most commonly prescribed antibiotics worldwide.

History & Development

Amoxicillin was developed to enhance the antibacterial spectrum and bioavailability of earlier penicillin antibiotics. Its effectiveness and safety profile led to widespread use in both adult and pediatric populations.

Chemical Structure & Medicinal Chemistry

• IUPAC Name: (2S,5R,6R)-6-[(R)-2-amino-2-(4-hydroxyphenyl)acetamido]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
• Molecular Formula: C₁₆H₁₉N₃O₅S
• Molar Mass: 365.40 g/mol
• Key Functional Groups: Beta-lactam ring, amide, phenolic group

The beta-lactam ring is essential for antibacterial activity. Disruption of this ring by bacterial beta-lactamases leads to antibiotic resistance.

Mechanism of Action

Amoxicillin exerts its antibacterial effect by inhibiting bacterial cell wall synthesis.

• Binds to penicillin-binding proteins (PBPs)
• Prevents cross-linking of peptidoglycan chains
• Weakens bacterial cell wall integrity
• Leads to osmotic lysis and bacterial death

Because human cells lack cell walls, this mechanism provides selective toxicity against bacteria.

Pharmacokinetics

• Excellent oral absorption
• Peak plasma concentration within 1–2 hours
• Minimal hepatic metabolism
• Short plasma half-life (~1 hour)
• Primarily excreted unchanged in urine

Clinical Uses

• Respiratory tract infections
• Otitis media and sinusitis
• Urinary tract infections
• Skin and soft tissue infections
• Helicobacter pylori eradication (combination therapy)

Dosage Principles

Dosage depends on the type and severity of infection, patient age, and renal function.

Completion of the full prescribed course is essential to prevent treatment failure and resistance.

Common Side Effects

• Nausea and diarrhea
• Skin rash
• Abdominal discomfort

Warnings & Contraindications

• Contraindicated in penicillin allergy
• Use cautiously in renal impairment
• May cause rash in infectious mononucleosis

Antibiotic Resistance

Misuse or incomplete courses of amoxicillin can promote the development of resistant bacteria. Combination with beta-lactamase inhibitors is used to overcome certain resistance mechanisms.

Drug Interactions

• Allopurinol — increased risk of skin rash
• Oral contraceptives — reduced effectiveness
• Anticoagulants — altered bleeding risk

References

• World Health Organization (WHO)
• U.S. Food and Drug Administration (FDA)
• PubChem Drug Database
• National Center for Biotechnology Information (NCBI)