AMOXICILLIN — 250 mg / 500 mg capsules and tablets

Amoxicillin is a broad‑spectrum aminopenicillin antibiotic that has been a cornerstone of primary care prescribing since its introduction in 1972. It is a modification of ampicillin with improved oral bioavailability, allowing less frequent dosing and better gastrointestinal tolerance. Amoxicillin remains one of the most frequently prescribed antibiotics worldwide for community‑acquired infections.

Mechanism of action: Like all penicillins, amoxicillin exerts its bactericidal effect by inhibiting the synthesis of bacterial cell walls. It binds to penicillin‑binding proteins (PBPs) located inside the bacterial cell wall, inhibiting the final transpeptidation step of peptidoglycan synthesis. This leads to activation of autolytic enzymes, cell lysis, and death. Amoxicillin is active against a wide range of Gram‑positive and Gram‑negative bacteria, although bacterial resistance via beta‑lactamase production has become widespread.

Clinical indications: Amoxicillin is indicated for infections caused by susceptible strains of bacteria, including upper and lower respiratory tract infections (sinusitis, bronchitis, community‑acquired pneumonia), otitis media, pharyngitis and tonsillitis (especially streptococcal infections), skin and skin structure infections, urinary tract infections, and as part of Helicobacter pylori eradication therapy (with clarithromycin and a proton pump inhibitor). It is also used for Lyme disease (early localized), anthrax prophylaxis, and endocarditis prophylaxis in at‑risk patients undergoing dental procedures.

Key distinction from Augmentin: Amoxicillin alone is effective against bacteria that do not produce beta‑lactamase enzymes. If beta‑lactamase‑producing bacteria are suspected or confirmed (e.g., Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, many Enterobacteriaceae), amoxicillin is ineffective and amoxicillin/clavulanate (Augmentin) is required. Unnecessary use of clavulanate increases the risk of hepatotoxicity and diarrhea.

• History of serious hypersensitivity reaction (e.g., anaphylaxis) to amoxicillin, any penicillin, or other beta‑lactam antibiotics (cephalosporins, carbapenems).
• Known hypersensitivity to any component of the formulation.

• Probenecid: Decreases renal tubular secretion of amoxicillin, increasing and prolonging amoxicillin blood levels. May be used intentionally to increase amoxicillin levels.
• Oral anticoagulants (warfarin): May increase INR and bleeding risk. Monitor coagulation parameters closely, especially during and after treatment.
• Allopurinol: Concomitant use increases risk of rash.
• Oral contraceptives: Limited evidence suggests amoxicillin may rarely reduce efficacy of hormonal contraceptives due to disruption of gut flora affecting enterohepatic recirculation. Risk appears low, but advise patients to use additional non‑hormonal contraception during treatment and for 7 days after stopping if they have concerns or if diarrhea/vomiting occurs.
• Methotrexate: Penicillins may reduce methotrexate clearance, increasing toxicity risk. Monitor methotrexate levels.
• Mycophenolate mofetil: Amoxicillin may reduce mycophenolic acid concentrations. Monitor for reduced efficacy.
• Tetracyclines, macrolides, chloramphenicol: Bacteriostatic antibiotics may antagonize bactericidal action of penicillins. Avoid concurrent use if possible.
• Typhoid, cholera, BCG vaccines: Antibiotics may reduce vaccine effectiveness. Avoid concurrent administration.

• Pregnancy: Generally considered safe (FDA Category B). Animal studies do not indicate direct or indirect harmful effects. Widely used in pregnancy when indicated.
• Breastfeeding: Amoxicillin is excreted in breast milk in small amounts. Considered compatible with breastfeeding; monitor infant for diarrhea, rash, or thrush.
• Pediatric use: Safety established. Dosing based on weight and age. Neonates and young infants: 20‑30 mg/kg/day divided every 12 hours. Older children: 20‑50 mg/kg/day divided every 8‑12 hours depending on infection severity.
• Geriatric use: No specific problems demonstrated, but elderly more likely to have age‑related renal impairment; dose adjustment may be needed.
• Renal impairment: GFR 10‑30 mL/min: 250‑500 mg every 12 hours. GFR less than 10 mL/min: 250‑500 mg every 24 hours. Hemodialysis: 250‑500 mg during dialysis and after.
• Hepatic impairment: Use with caution in severe liver disease; monitor liver function tests.

• Symptoms: Nausea, vomiting, diarrhea, abdominal pain, agitation, drowsiness, crystalluria (with high doses).
• Management: Supportive care, fluid monitoring, correction of electrolyte imbalances. Activated charcoal may be considered if recent ingestion. Hemodialysis removes amoxicillin.