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 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.

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 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

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 /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.

Sources

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

Streptococcal pharyngitis

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.

Sources

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

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. and explicitly recommend against antibiotics in viral URI.

Sources

NICE: Hypertension in adults: diagnosis and management (NG136) (2023)

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.

Drug–drug interactions

7 pairs found. Sorted from critical to minor.

Major

Methotrexate

Antimetabolites, folic acid analogues

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.

Sources

FDA: Methotrexate Sodium Tablets prescribing information (2016)

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Moderate

Doxycycline

Tetracyclines

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.

Sources

FDA: Bactrim (sulfamethoxazole and trimethoprim) prescribing information (2013)

Pair details →

Moderate

Warfarin

Vitamin K antagonist anticoagulants

Mechanism

Amoxicillin may reduce gut flora vitamin K synthesis – INR mildly rises. Effect usually moderate.

Symptoms

INR above target, occasional bleeding.

Management

Check INR on day 5 if course longer than 5 days.

Sources

Pair details →

Minor

Estradiol

Estrogens — natural and semisynthetic

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

KDIGO: KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD (2024)

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Minor

Ethinylestradiol

Estrogens. Natural and semisynthetic estrogens, plain

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

KDIGO: KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD (2024)

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Minor

Levothyroxine sodium

Thyroid hormones

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

Pair details →

Minor

Metronidazole

Imidazole derivatives (antiprotozoal / antibacterial)

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

Pair details →

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Official sources

Direct links to regulator labels. Open in a new tab.

AEMPS / CIMA

Spanish Medicines Information Centre (CIMA)

Label dated: 05/12/2026

FDA / DailyMed

FDA — DailyMed Drug Labels

Label dated: 01/19/2026

GRLS

Russian State Register of Medicines

Label dated: 01/27/2026

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

Hale L1 · Compatible

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

RID, infant dose via milk: 1%
Maternal half-life: 1.7 h
Maternal peak time: 1.5 h
Peak milk concentration: 0.9 mg/L
Milk-to-plasma ratio: 0.04

Calculate RID Safe feeding window Full profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Amoxicillin used for?

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.

What are the side effects of Amoxicillin?

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.

Is Amoxicillin safe during pregnancy?

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

Is Amoxicillin compatible with breastfeeding?

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

Who should not take Amoxicillin?

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.

you need antibiotics for fever

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 weaken the immune system

antibiotics affect gut microbiota but do not suppress immunity. When indicated, their use is necessary.

probiotics must be taken alongside antibiotics

routine probiotic co-prescription with antibiotics lacks sufficient evidence of benefit in adults without specific C. difficile risk factors.

Mechanism of action

Practical notes

Timing and administration

Special situations

Common myths

Drug–drug interactions

7 pairs found. Sorted from critical to minor.

Major

Methotrexate

Antimetabolites, folic acid analogues

Mechanism

Symptoms

Mouth ulcers (mucositis), nausea, diarrhoea, hair loss. Blood counts fall: leukocytes, platelets, erythrocytes. Severe cases: fatal pancytopenia, nephrotoxicity.

Management

Sources

FDA: Methotrexate Sodium Tablets prescribing information (2016)

Pair details →

Moderate

Doxycycline

Tetracyclines

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

Sources

FDA: Bactrim (sulfamethoxazole and trimethoprim) prescribing information (2013)

Pair details →

Moderate

Warfarin

Vitamin K antagonist anticoagulants

Mechanism

Amoxicillin may reduce gut flora vitamin K synthesis – INR mildly rises. Effect usually moderate.

Symptoms

INR above target, occasional bleeding.

Management

Check INR on day 5 if course longer than 5 days.

Sources

Pair details →

Minor

Estradiol

Estrogens — natural and semisynthetic

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

KDIGO: KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD (2024)

Pair details →

Minor

Ethinylestradiol

Estrogens. Natural and semisynthetic estrogens, plain

Mechanism

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

Sources

KDIGO: KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD (2024)

Pair details →

Minor

Levothyroxine sodium

Thyroid hormones

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

Sources

Pair details →

Minor

Metronidazole

Imidazole derivatives (antiprotozoal / antibacterial)

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

Sources

Pair details →

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

Hale L1 · Compatible

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

RID, infant dose via milk: 1%
Maternal half-life: 1.7 h
Maternal peak time: 1.5 h
Peak milk concentration: 0.9 mg/L
Milk-to-plasma ratio: 0.04

Calculate RID Safe feeding window Full profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Amoxicillin used for?

What are the side effects of Amoxicillin?

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.

Is Amoxicillin safe during pregnancy?

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

Is Amoxicillin compatible with breastfeeding?

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

Who should not take Amoxicillin?

you need antibiotics for fever

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 weaken the immune system

antibiotics affect gut microbiota but do not suppress immunity. When indicated, their use is necessary.

probiotics must be taken alongside antibiotics

routine probiotic co-prescription with antibiotics lacks sufficient evidence of benefit in adults without specific C. difficile risk factors.