Amoxicillin

Penicillins with extended spectrum

ATC code: J01CA04 (Amoxicillin)

Brand names

Amoxil, Moxatag

Mechanism of action

Beta-lactam antibiotic. Binds penicillin-binding proteins in the bacterial cell wall, inhibits transpeptidase, and disrupts peptidoglycan synthesis. Active against gram-positive organisms (Streptococcus pneumoniae, S. pyogenes, Enterococcus), select gram-negatives (beta-lactamase-negative H. influenzae, E. coli, Salmonella), and anaerobes. Susceptible to beta-lactamases, so in high-resistance regions it is combined with clavulanic acid.

Indications

Acute bacterial rhinosinusitis

First line

Drug of choice in adults and children when bacterial etiology is suspected per IDSA 2012 and NICE. Adults: amoxicillin 500 mg TID or 875 mg BID for 5–7 days. In regions with high S. pneumoniae resistance or with risk factors, amoxicillin/clavulanate is used. Indications for antibiotics: symptoms over 10 days, worsening after initial improvement, severe onset with fever ≥ 39 °C and purulent discharge.

Sources

Acute otitis media in children

First line

In children with acute otitis media, amoxicillin 80–90 mg/kg/day in two divided doses for 5–10 days (depending on age and severity) is first-line per AAP 2013. Children under 2 years with bilateral or severe disease receive antibiotics immediately. In milder unilateral cases in children over 2 years, 48–72 hour watchful waiting with a delayed prescription is acceptable.

Sources

AAP: The Diagnosis and Management of Acute Otitis Media (2013)

Community-acquired pneumonia

First line

In outpatients without comorbidity or resistant pathogen risk factors, amoxicillin 1 g TID for 5 days is first-line per IDSA/ATS 2019 and NICE. With comorbidity or risk factors: amoxicillin/clavulanate or a respiratory fluoroquinolone. In severe cases or suspected atypical organisms, a macrolide or doxycycline is added.

Sources

IDSA: Clinical Practice Guideline for the Diagnosis and Treatment of Adults with Community-acquired Pneumonia (2019)

Helicobacter pylori infection

First line

A core component of eradication regimens per Maastricht VI/Florence Consensus 2022. First-line empirical options include bismuth-based quadruple therapy (PPI + bismuth + tetracycline + metronidazole, amoxicillin not used), triple therapy with amoxicillin (PPI + clarithromycin + amoxicillin 1 g BID), and in regions with clarithromycin resistance above 15 %, bismuth quadruple or levofloxacin-based regimens with amoxicillin are preferred.

Sources

Maastricht VI/Florence Consensus: Maastricht VI/Florence Consensus Report on the Management of Helicobacter pylori Infection (2022)

Streptococcal pharyngitis

First line

GAS pharyngitis confirmed by rapid antigen test or culture requires antibiotic therapy to prevent acute rheumatic fever. Per IDSA 2012, amoxicillin 1 g BID in adults (or 50 mg/kg once daily in children) for 10 days is standard. Alternatives: penicillin V, cephalexin. Macrolides are reserved for beta-lactam allergy given rising resistance.

Sources

IDSA: Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis (2012)

Acute respiratory viral infection

Not recommended

Acute viral respiratory illness is an indication where amoxicillin and all other antibiotics should not be used. The etiology is viral; antibiotics do not shorten symptoms, do not prevent bacterial complications, and increase the risk of adverse effects and antimicrobial resistance. NICE and IDSA explicitly recommend against antibiotics in viral URI.

Sources

Practical notes

Timing and administration

Food does not affect amoxicillin bioavailability. Dispersible formulations (Flemoxin Solutab) dissolve in water — helpful for patients with swallowing difficulties and children. Respect the dosing interval: BID every 12 h, TID every 8 h. Complete the full course even if symptoms resolve earlier.

Special situations

A rash during amoxicillin therapy in a patient with infectious mononucleosis develops in 80–90 % and is not a true penicillin allergy. It is not a contraindication for future penicillin use. A documented immediate penicillin allergy (anaphylaxis, angioedema, bronchospasm) contraindicates the drug. Delayed cutaneous reactions (rash after several days without systemic symptoms) may allow re-challenge under allergy consultation.

Common myths

Myth: 'you need antibiotics for fever'. Fact: fever is a marker of infection of any kind, including viral. The decision to prescribe antibiotics is based on suspected etiology and clinical picture, not on temperature. Myth: 'antibiotics weaken the immune system'. Fact: antibiotics affect gut microbiota but do not suppress immunity. When indicated, their use is necessary. Myth: 'probiotics must be taken alongside antibiotics'. Fact: routine probiotic co-prescription with antibiotics lacks sufficient evidence of benefit in adults without specific C. difficile risk factors.

Safety

Contraindications

Immediate hypersensitivity to penicillins and other beta-lactams (anaphylaxis, angioedema, bronchospasm)
Infectious mononucleosis (relative, due to frequent rash)

Serious adverse effects

Anaphylaxis (rare but life-threatening)
C. difficile-associated pseudomembranous colitis
Stevens-Johnson syndrome, toxic epidermal necrolysis (very rare)
Acute interstitial nephritis
Hepatotoxicity (more often in combination with clavulanic acid)

Common adverse effects

Diarrhea (often self-limited)
Nausea, vomiting
Oral and vaginal candidiasis
Skin rash

PregnancyFDA B

FDA category B. Cohort studies have not shown increased birth defect risk. Used in all trimesters when indicated.

Breastfeeding

Compatible with breastfeeding. Passes into milk in minimal amounts. Monitor the infant for diarrhea and sensitization.