amoxicillin
Brand: Amoxil, Trimox
Prototype: penicillin-g
Drug Class: antibiotic
Drug Family: antibiotic
Subclass: aminopenicillin / beta-lactam
Organ Systems: infectious-disease
Mechanism of Action
Binds PBPs and inhibits bacterial cell wall synthesis; broader spectrum than penicillin G/V, covering gram-negative organisms (H. influenzae, E. coli) in addition to gram-positive coverage; susceptible to beta-lactamase hydrolysis.
penicillin-binding proteins (PBPs)
Indications
- community-acquired pneumonia
- otitis media (first-line)
- streptococcal pharyngitis
- sinusitis
- H. pylori eradication (component of triple therapy)
- UTI (susceptible organisms)
- Lyme disease (early localized)
- endocarditis prophylaxis
Contraindications
- penicillin or amoxicillin allergy
Adverse Effects
Common
- diarrhea
- nausea
- rash (maculopapular — especially in EBV mononucleosis)
- candidal overgrowth
Serious
- anaphylaxis
- Stevens-Johnson syndrome
- Clostridioides difficile colitis
- drug-induced hepatitis
Pharmacokinetics (ADME)
| Absorption | Well absorbed orally (~80%); not affected by food |
| Distribution | Protein binding ~20%; Vd ~0.26 L/kg |
| Metabolism | Minimal hepatic metabolism |
| Excretion | Renal; ~60% excreted unchanged; dose adjustment for CrCl <30 mL/min |
| Half-life | 1–1.5 hours |
| Onset | 30–60 minutes |
| Peak | 1–2 hours |
| Duration | 8–12 hours |
| Protein Binding | 20% |
| Vd | ~0.26 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| allopurinol | increases risk of amoxicillin rash (mechanism unclear) | moderate |
| warfarin | gut flora alteration reduces vitamin K synthesis; INR may rise | moderate |
| oral contraceptives | theoretical reduction in enterohepatic recycling of estrogen (clinical significance debated) | minor |
Nursing Considerations
- Amoxicillin rash in EBV mononucleosis: nearly all patients with mono who receive ampicillin/amoxicillin develop a characteristic maculopapular rash — this is not a true penicillin allergy
- Administer with or without food; suspensions should be refrigerated after reconstitution and discarded after 14 days
- For H. pylori eradication: amoxicillin is part of standard triple therapy (amoxicillin + clarithromycin + PPI) or quadruple therapy — take at evenly spaced intervals with meals
- Oral suspension: shake well before each dose; use calibrated measuring device, not household spoons
Clinical Pearls
- Amoxicillin is the drug of choice for uncomplicated community-acquired pneumonia in outpatient adults (ATS/IDSA guidelines 2019) because of excellent activity against Streptococcus pneumoniae with high oral bioavailability
- The amoxicillin-mononucleosis rash is not a true penicillin hypersensitivity reaction — it is immune-complex mediated and does not predict future penicillin allergic reactions
Safety Profile
Pregnancy generally-safe
Lactation safe
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.