Generic Name

Amoxicillin

Mechanism

• Inhibition of bacterial cell‑wall synthesis: Amoxicillin binds to penicillin‑binding proteins (PBPs) on the bacterial cell membrane, blocking transpeptidation (cross‑linking) of peptidoglycan strands.
• Result: Bacterial cell lysis and death, particularly effective against susceptible anaerobes, *Streptococcus*, *Staphylococcus aureus* (except MRSA), and many *Enterobacteriaceae*.
• Penetration: β‑lactamase‑stabilized (e.g., clavulanate) combinations prevent degradation by common β‑lactamases.

Pharmacokinetics

Indications

• Upper and lower respiratory tract infections: sinusitis, pharyngitis, COPD exacerbations, lobar pneumonia
• Gastrointestinal infections: *Helicobacter pylori* eradication (combined with PPI + clarithromycin) and *Campylobacter* colitis
• Genitourinary infections: uncomplicated cystitis, pyelonephritis (in combination with gentamicin), trichomoniasis (in combination or as part of an oral therapy for *Neisseria gonorrhoeae*)
• Skin and skin‑structure infections: cellulitis, abscesses, furuncles
• Meningitis: when β‑lactamase–producing organisms are suspected, often combined with vancomycin or ceftriaxone

Contraindications

• Allergy to penicillins/β‑lactams (severe anaphylaxis, urticaria, angioedema)
• Allergy to amoxicillin itself (as per specific documented hypersensitivity)
• Severe hepatic impairment (due to accumulation of metabolite amoxicillin lactone)
• Concurrent use with high‑dose oral contraceptives – risk of decreased oral contraceptive efficacy
• Pregnancy Category B – safe; cautious use in lactating mothers
• Gastrointestinal disease (e.g., active flare of Crohn’s disease) where immune reaction may be exacerbated

Dosing

*Adjustments:*
• Renal impairment: 500 mg q12h if CrCl < 30 mL/min; 500 mg q8h if CrCl ≥ 30 mL/min; dose reduction or interval extension for severe renal failure.
• Weight‑based dosing for pediatric patients: 45 mg/kg/day (max 2 g/day) divided q8h or q12h.

Adverse Effects

• Common (≥ 1 % incidence): Nausea, vomiting, diarrhoea, rash, pruritus, hot‑flush, taste alteration
• Serious (≤ 0.5 % incidence):
• Hypersensitivity reactions (angioedema, anaphylaxis)
• Clostridioides difficile colitis (“superinfection”)
• Severe cutaneous adverse reactions (Stevens‑Johnson syndrome, toxic epidermal necrolysis)
• Hematologic: agranulocytosis, leukopenia, thrombocytopenia
• Hepatic: transient elevation of AST/ALT, rare hepatitis

Monitoring

• Renal function (CrCl, eGFR): baseline, weekly if dose ≥ 1 g daily
• Complete blood count (CBC): baseline, especially if prolonged therapy or comorbid immunosuppression
• Liver function tests (LFTs): baseline when indicated (e.g., concomitant hepatotoxic drugs)
• Adverse reaction surveillance: monitor for GI upset, rash, and signs of C. difficile; report severe reactions promptly.

Clinical Pearls

• Avoid use of amoxicillin as monotherapy in β‑lactamase‑producing organisms – always consider a β‑lactamase inhibitor or a broader β‑lactam when coverage is uncertain.
• Amoxicillin‑clavulanate can be almost as effective as amoxicillin alone for many infections; resist prescribing the combo for mild illnesses where simple amoxicillin suffices (drug‑cost, potential for over‑were).
• Timing with oral contraceptives: 16‑hour intermittent fasting (e.g., 6 am to 10 pm) reduces the impact of amoxicillin on oral contraceptive absorption; thereby mitigate contraceptive failure.
• Pediatric formulations: Chewable tablets and liquid suspensions are preferable for dosing flexibility and adherence.
• Synergy in H. pylori regimens: Amoxicillin is often paired with clarithromycin and a proton‑pump inhibitor – two doses daily for 14 days for maximum cure rates.
• Exclusion of H2‑blocker interaction: Some evidence suggests that H2‑blockers may reduce amoxicillin concentration; PPI is preferred in combination regimens for H. pylori.
• Probiotics and C. difficile prevention: Consider adjunctive probiotics to reduce antibiotic‑associated colitis risk, especially in older adults or high‑dose therapy.

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• *References managed via internal pharmacy database; clinicians should cross‑check dosing for local resistance patterns and regulatory guidelines.*