Formulary
Amoxicillin: Uses, Dosing, Side Effects and Indian Brand Names
Amoxicillin is the most prescribed antibiotic globally, an aminopenicillin with 90% oral bioavailability, first-line for common respiratory, urinary, and dental infections, and the basis of H. pylori triple therapy.
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Amoxicillin: Uses, Dosing, Side Effects and Indian Brand Names
Amoxicillin is the most prescribed antibiotic globally, an aminopenicillin with 90% oral bioavailability, first-line for common respiratory, urinary, and dental infections, and the basis of H. pylori triple therapy.
NEET PG High-Yield: Aminopenicillin with 90% oral bioavailability (vs ampicillin 50%). Time-dependent killing (T>MIC matters, not peak). EBV + amoxicillin = rash (not allergy). Cross-reactivity with cephalosporins ~1-2% (not 10% as previously thought). Drug of choice for Listeria. Endocarditis prophylaxis dose: 2 g single dose. With clavulanate, covers beta-lactamase producers. H. pylori triple therapy component.
Clinical overview
Amoxicillin is the most widely prescribed antibiotic in India and globally, representing the workhorse of primary care antimicrobial therapy. It is a semi-synthetic aminopenicillin with improved oral bioavailability (approximately 90%) compared to ampicillin (~50%), though their spectrum of activity is identical. Amoxicillin covers most Gram-positive cocci (Streptococcus pneumoniae, Streptococcus pyogenes, Enterococcus faecalis), some Gram-negative organisms (Haemophilus influenzae, Escherichia coli, Proteus mirabilis, Helicobacter pylori), and Listeria monocytogenes. It is inactivated by beta-lactamase-producing organisms, which is why the combination with clavulanic acid (a beta-lactamase inhibitor) dramatically extends its utility. This combination (co-amoxiclav) covers beta-lactamase-producing H. influenzae, Moraxella catarrhalis, S. aureus (methicillin-sensitive), and many anaerobes. Amoxicillin is the drug of choice for acute otitis media, streptococcal pharyngitis, community-acquired pneumonia (mild-moderate), urinary tract infections (in susceptible organisms), dental infections, and as part of H. pylori triple therapy (with clarithromycin and a PPI). In endocarditis prophylaxis, a single dose of amoxicillin 2 g before dental procedures is standard for at-risk patients. The characteristic side effect is a maculopapular rash, which is NOT a true penicillin allergy -- it occurs in up to 70-100% of patients who take amoxicillin during EBV mononucleosis. True IgE-mediated penicillin allergy (urticaria, anaphylaxis) occurs in approximately 1-2% of patients.
Pharmacological class
Amoxicillin belongs to the Penicillins (Aminopenicillin) class. Binds to penicillin-binding proteins (PBPs, specifically transpeptidases) in the bacterial cell wall, inhibiting the final transpeptidation step of peptidoglycan synthesis. This weakens the cell wall, leading to osmotic lysis and bacterial death. Amoxicillin is bactericidal and exhibits time-dependent killing -- efficacy depends on the duration that drug concentration exceeds the MIC, not peak concentration.
Indian brand names and formulations
Available as: Mox (Ranbaxy/Sun), Novamox (Cipla), Amoxil (GSK), Wymox (Pfizer).
Capsules: 250 mg, 500 mg. Tablets: 500 mg, 875 mg. Suspension: 125 mg/5 mL, 250 mg/5 mL. Dispersible tablets (DT): 125 mg, 250 mg (WHO-recommended formulation for paediatric use). FDC with clavulanic acid: 375 mg (250+125), 625 mg (500+125), 1000 mg (875+125).
Regulatory status
Amoxicillin is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Prescription-only. India's most consumed antibiotic. Widely available at all pharmacies and Jan Aushadhi centres. Subject to antimicrobial stewardship regulations.
Indications
- Acute otitis media (first-line)
- Streptococcal pharyngitis/tonsillitis
- Community-acquired pneumonia (mild-moderate; empiric with clavulanate if beta-lactamase producers suspected)
- Urinary tract infections (uncomplicated, if local susceptibility permits)
- H. pylori eradication (with clarithromycin + PPI, or with metronidazole + PPI)
- Dental abscess and periodontal infections
- Endocarditis prophylaxis (high-risk patients before dental procedures)
- Lyme disease (early)
Dosing
Adults: 250-500 mg three times daily or 500-875 mg twice daily. High-dose for pneumonia or resistant pneumococcus: 1 g three times daily. Children: 25-50 mg/kg/day in 3 divided doses; high-dose AOM: 80-90 mg/kg/day in 2 divided doses. Endocarditis prophylaxis: 2 g single dose 30-60 min before procedure. Renal impairment (CrCl <30 mL/min): extend dosing interval to 12-hourly.
Contraindications
- Known IgE-mediated penicillin allergy (anaphylaxis, urticaria, angioedema)
- History of amoxicillin/penicillin-associated cholestatic jaundice
- Infectious mononucleosis (high risk of maculopapular rash -- not a true allergy but may be mistakenly labelled as one)
Adverse effects
- Diarrhoea (most common; disruption of gut flora)
- Maculopapular rash (not a true allergy; up to 70-100% incidence with concurrent EBV infection)
- Nausea and vomiting
- Antibiotic-associated Clostridioides difficile infection (less common than with clindamycin or fluoroquinolones)
- True allergic reactions: urticaria, angioedema, anaphylaxis (1-2%)
- Crystalluria (rare, at very high doses with poor hydration)
Drug interactions
- Methotrexate: amoxicillin reduces renal tubular secretion of methotrexate, risk of toxicity
- Warfarin: may increase INR by disrupting gut flora vitamin K synthesis; monitor INR
- Probenecid: reduces renal tubular secretion of amoxicillin, increasing levels (sometimes used therapeutically)
- Oral contraceptives: theoretical reduction in efficacy via gut flora disruption, though clinical significance is debated; advise additional contraception during short antibiotic courses
Pregnancy and lactation
Category B. Considered safe in pregnancy. One of the first-line antibiotics for infections during pregnancy (UTI, dental infections, respiratory infections). Crosses the placenta but no teratogenic effects demonstrated.
Exam-style clinical scenario
A 22-year-old presents with sore throat and fever. The clinician prescribes amoxicillin. Three days later, the patient develops a diffuse maculopapular rash. Monospot test is positive. Is this a penicillin allergy? No -- this is the characteristic non-allergic rash of amoxicillin given during EBV mononucleosis. It does NOT indicate true penicillin allergy and should not be labelled as such in the records.
Cost in India
Rs 30-70 for a strip of 10 capsules (500 mg). Suspension: Rs 40-80 for 60 mL bottle. Jan Aushadhi generic: approximately Rs 2 per capsule.
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
What is the difference between amoxicillin and ampicillin?
Both are aminopenicillins with identical antibacterial spectrums. The key difference is oral bioavailability: amoxicillin ~90% vs ampicillin ~50%. Amoxicillin is preferred for oral therapy because reliable absorption means consistent drug levels. Ampicillin is preferred IV (e.g., meningitis, endocarditis) where absorption is not a factor. Ampicillin also has a higher incidence of diarrhoea because unabsorbed drug disrupts colonic flora.
When should co-amoxiclav be used instead of amoxicillin alone?
Use co-amoxiclav when beta-lactamase-producing organisms are suspected: recurrent or treatment-failure otitis media, sinusitis, animal or human bites (covers Pasteurella and anaerobic oral flora), aspiration pneumonia, complicated UTIs, and diabetic foot infections. Do not use co-amoxiclav empirically for straightforward streptococcal pharyngitis -- amoxicillin alone is sufficient.
How to differentiate true penicillin allergy from the EBV rash?
True penicillin allergy is IgE-mediated: urticaria (raised, itchy wheals), angioedema, or anaphylaxis, occurring within minutes to hours. The EBV-amoxicillin rash is a delayed maculopapular eruption (flat, non-itchy or mildly itchy) appearing 5-10 days after starting amoxicillin, caused by immune complex formation during active EBV infection. The EBV rash should NOT be recorded as a penicillin allergy, as it does not recur with future penicillin use.
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