Penicillins with extended spectrum
ATC code: J01CA04 (Amoxicillin)
Brand names
Amoxil, Moxatag
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.
First line
Drug of choice in adults and children when bacterial etiology is suspected per 2012 and . 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.
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 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.
First line
In outpatients without comorbidity or resistant pathogen risk factors, amoxicillin 1 g TID for 5 days is first-line per /ATS 2019 and . With comorbidity or risk factors: amoxicillin/clavulanate or a respiratory fluoroquinolone. In severe cases or suspected atypical organisms, a macrolide or doxycycline is added.
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.
First line
GAS pharyngitis confirmed by rapid antigen test or culture requires antibiotic therapy to prevent acute rheumatic fever. Per 2012, adults receive amoxicillin 500 mg every 12 hours or 1000 mg once daily; children receive 50 mg/kg once daily (max 1000 mg). Course duration is 10 days. Alternatives: penicillin V, cephalexin. Macrolides are reserved for beta-lactam allergy given rising resistance.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
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. and explicitly recommend against antibiotics in viral URI.
7 pairs found. Sorted from critical to minor.
Mechanism
Amoxicillin and other penicillins compete with methotrexate for renal tubular secretion. Methotrexate clearance falls and plasma levels rise – risk of myelosuppression and toxicity at oncologic doses.
Symptoms
Mouth ulcers (mucositis), nausea, diarrhoea, hair loss. Blood counts fall: leukocytes, platelets, erythrocytes. Severe cases: fatal pancytopenia, nephrotoxicity.
Management
At oncologic methotrexate doses, avoid amoxicillin. Alternative antibiotics: a cephalosporin or macrolide (azithromycin, doxycycline). At low rheumatologic doses, a short amoxicillin course is acceptable with blood count monitoring.
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FDA category B. Cohort studies have not shown increased birth defect risk. Used in all trimesters when indicated.
Compatible with breastfeeding. Passes into milk in minimal amounts. Monitor the infant for diarrhea and sensitization.
Amoxicillin is evaluated for the following indications with varying evidence strength: Acute otitis media in children (evidence tier A), Community-acquired pneumonia (evidence tier A), Helicobacter pylori infection (evidence tier A). See the full indication matrix with dosing and citations above on this page.
Common side effects of Amoxicillin (≥ 1 in 100): Diarrhea (often self-limited), Nausea, vomiting, Oral and vaginal candidiasis, Skin rash. See the Safety section for uncommon and serious reactions.
FDA category B. FDA category B. Cohort studies have not shown increased birth defect risk. Used in all trimesters when indicated.
Compatible with breastfeeding. Passes into milk in minimal amounts. Monitor the infant for diarrhea and sensitization.
Amoxicillin is contraindicated in: Immediate hypersensitivity to penicillins and other beta-lactams (anaphylaxis, angioedema, bronchospasm); Infectious mononucleosis (relative, due to frequent rash). Full list in the Safety section.
Mechanism
A bacteriostatic agent (doxycycline) suppresses the bactericidal action of a beta-lactam (amoxicillin), which requires active bacterial division. Antibacterial efficacy drops.
Symptoms
Persistent fever, infection symptoms, and inflammation markers 48–72 hours after starting therapy. Resistant strain selection possible.
Management
Avoid the combination — choose a single antibiotic based on pathogen and infection site. For mixed infections (e.g. aspiration pneumonia), prefer switching to amoxicillin-clavulanate (broader spectrum) or a cephalosporin with metronidazole. For Lyme disease, use doxycycline monotherapy; for respiratory infections with confirmed sensitivity, amoxicillin.
Mechanism
Amoxicillin suppresses vitamin K-producing gut flora and enhances warfarin anticoagulation. Effect is unpredictable: INR may stay flat or rise by 1–2.
Symptoms
Gum bleeding, epistaxis, bruising without trauma, black or tarry stools, haematuria. Higher risk in older patients, prior peptic ulcer disease, and chronic kidney disease.
Management
For amoxicillin courses of 5–7 days, check INR 3–5 days after start and one week after stopping. If INR drifts outside target, adjust warfarin by 10–20%. Do not stop the antibiotic — complete the full course for the infection.
Sources
Mechanism
Same as the ethinylestradiol pair: meta-analyses did not confirm clinically significant reductions in hormone therapy efficacy with broad-spectrum antibiotics.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
For short amoxicillin courses (5–10 days) in women on menopausal hormone therapy, no adjustment needed. Vasomotor symptom monitoring follows the usual schedule.
Sources
Mechanism
Historical theory of reduced combined oral contraceptive efficacy via gut flora suppression. Cochrane meta-analysis (2017) did not confirm clinically significant reductions in ethinylestradiol levels with broad-spectrum antibiotics other than CYP3A4 inducers (rifampicin, rifabutin).
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
Additional contraception during short amoxicillin courses is not needed (updated Medical Eligibility Criteria 2015). The old "use a barrier method for the whole cycle" practice is outdated and applies only to rifampicin, rifabutin, CYP3A4-inducing anticonvulsants (carbamazepine, phenytoin), and most HIV antivirals.
Sources
Mechanism
Amoxicillin taken concurrently may slightly impair intestinal levothyroxine absorption. With separated dosing, the effect is clinically negligible.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
Take levothyroxine in the morning on an empty stomach, 30–60 minutes before food and other medications. Take amoxicillin 4 hours later or at lunch. For short amoxicillin courses (5–10 days), no special TSH monitoring needed.
Sources
Mechanism
Target combination in triple and quadruple Helicobacter pylori eradication (Maastricht VI/Florence Consensus 2022, Kyoto Global Consensus). Synergistic antibacterial action.
Symptoms
Possible combination side effects: metallic taste (from metronidazole), nausea, diarrhoea. In some patients, disulfiram-like reaction with alcohol on metronidazole.
Management
Standard combination in H. pylori eradication (amoxicillin 1000 mg twice daily + metronidazole 500 mg three times daily + PPI or bismuth for 10–14 days). Exclude alcohol throughout the course and for 48 hours after metronidazole. If metronidazole is intolerated, alternatives: tetracycline or levofloxacin.
Sources
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
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.
antibiotics affect gut microbiota but do not suppress immunity. When indicated, their use is necessary.
routine probiotic co-prescription with antibiotics lacks sufficient evidence of benefit in adults without specific C. difficile risk factors.