AAPWeight-Based Antibiotic Dosing
Input Parameters
Amoxicillin Calc
Calculate accurate weight-based dosing for standard or high-dose amoxicillin therapy.
Guidelines & Evidence
Verified
Last Review: 2026
When to Use
Primary Indications (FDA-Approved)
Acute otitis media (AOM) - most common indication in children
Community-acquired pneumonia (CAP) - mild to moderate, outpatient
Group A streptococcal pharyngitis (strep throat)
Acute bacterial sinusitis
Acute exacerbations of chronic bronchitis (AECB) - adults
Dental abscess and odontogenic infections (frequently combined with metronidazole)
Helicobacter pylori eradication (part of triple therapy with clarithromycin + PPI)
Lyme disease (early localized, erythema migrans) - alternative to doxycycline in children <8 years and pregnant women
Urinary tract infections (UTI) - uncomplicated cystitis (E. coli susceptible)
Typhoid fever (Salmonella typhi) - susceptible strains
Endocarditis prophylaxis (dental procedures, AHA guidelines)
Listeria monocytogenes infections (usually combined with ampicillin IV, amoxicillin oral step-down)
Clinical Utility
Amoxicillin is the most commonly prescribed outpatient antibiotic for children in the United States, accounting for over 20 million prescriptions annually. Its popularity stems from excellent oral bioavailability (75-80%, unaffected by food), palatable suspension formulations, relatively narrow spectrum (preserves gut flora better than broader agents), low cost, and well-established safety profile. Compared to ampicillin (its parenteral counterpart), amoxicillin has superior oral absorption (ampicillin only 40-50% bioavailable) and lower incidence of diarrhea. Amoxicillin is bactericidal, time-dependent (efficacy correlates with time above MIC, target >40-50% of dosing interval). High-dose regimens (80-90 mg/kg/day) were introduced to overcome penicillin-intermediate and penicillin-resistant Streptococcus pneumoniae (MIC 2-4 μg/mL), which emerged in the 1990s-2000s. The addition of clavulanate (co-amoxiclav, Augmentin) extends activity to beta-lactamase-producing organisms (S. aureus, H. influenzae, M. catarrhalis, E. coli, Bacteroides fragilis) but increases GI side effects (diarrhea 20-30% vs 5-10% for amoxicillin alone).
Comparison with Other Oral Antibiotics for Common Pediatric Infections
| Antibiotic | Class | Bioavailability | Dosing Frequency | Spectrum | S. pneumoniae Coverage (High Dose) | AOM Efficacy | Diarrhea Risk | Cost (Generic 10-day course) |
|---|---|---|---|---|---|---|---|---|
| Amoxicillin (alone) | Aminopenicillin | 75-80% | BID-TID | Gram + (strep, pneumo, enterococcus), some Gram - (E. coli, H. influenzae, Salmonella) | Good (80-90% at 80-90 mg/kg/day) | First-line (high-dose) | 5-10% | $4-8 |
| Amoxicillin-clavulanate (Augmentin) | Aminopenicillin + BLI | 75-80% | BID (ES formulation) | Same as amoxicillin + beta-lactamase producers (S. aureus, M. catarrhalis, H. influenzae, Bacteroides) | Good (covers resistant H. influenzae) | Second-line (first-line if beta-lactamase suspected) | 20-30% (high) | $25-40 |
| Cefdinir (Omnicef) | 3rd gen cephalosporin | 25% (low, but active) | QD-BID | Broader Gram - (including ceftriaxone-sensitive) | Good | Alternative (second-line) | 15-20% | $30-50 |
| Cefpodoxime (Vantin) | 3rd gen cephalosporin | 50% | BID | Broader Gram - | Good | Alternative (not first-line) | 10-15% | $40-60 |
| Cefuroxime (Ceftin) | 2nd gen cephalosporin | 50% (poor taste) | BID | Moderate Gram - | Moderate (cephalosporin-resistant pneumococcus emerges) | Alternative (second-line) | 10-15% | $35-55 |
| Azithromycin (Zithromax) | Macrolide | 37% | QD x5 days | Atypicals (mycoplasma, legionella, chlamydia), some S. pneumoniae (resistance >40% in many regions) | Poor (high pneumococcal resistance) | Not recommended for AOM (resistance) | 5-10% | $15-25 |
| Clindamycin | Lincosamide | 90% | TID-QID | Gram + (strep, staph, pneumo, anaerobes) | Fair (resistance emerging, 10-30%) | Alternative (penicillin allergy, MRSA coverage) | 15-20% (C. diff risk) | $20-35 |
Last Comprehensive Review: 2026