Amoxicillin

 

1. Generic & Brand Names

• Generic: Amoxicillin

• Brands: Amoxil®, Trimox®, Moxatag® (ER)

• Combinations: Augmentin® (amoxicillin + clavulanate)

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2. Drug Class & Mechanism

• Class: Penicillin-type β-lactam antibiotic

• Mechanism: Inhibits bacterial cell wall synthesis → bactericidal

• Spectrum: Gram-positive & some Gram-negative bacteria

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3. FDA-Approved Uses

Infection Type	Key Pathogens
Otitis media	S. pneumoniae, H. influenzae
Strep throat	S. pyogenes (Group A Strep)
Sinusitis	S. pneumoniae, H. influenzae
Pneumonia	S. pneumoniae (community)
UTIs	E. coli, Enterococcus
Skin infections	S. aureus (non-MRSA)
H. pylori eradication	With clarithromycin + PPI

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4. Dosage & Administration

Infection	Standard Adult Dose	Duration
Mild/Moderate infections	500 mg q8h OR 875 mg q12h	7-10 days
Severe infections	875 mg q12h	7-14 days
Strep throat	500 mg BID or 1000 mg QD	10 days
ER formulation (Moxatag)	775 mg once daily	7-10 days

Pediatric Dosing (Oral Suspension):

• 20-90 mg/kg/day divided q8-12h (max 3 g/day)

• Example: 45 mg/kg/day for AOM → 22.5 mg/kg/dose BID

Critical Notes:

• Take with/without food (food reduces nausea)

• Shake suspension well; refrigerate after reconstitution (discard after 14 days)

• Complete full course even if symptoms resolve

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5. Side Effects

Common (>10%)	Serious (Stop & Seek Help)
Diarrhea	Anaphylaxis (hives, swelling)
Nausea/vomiting	Severe skin reactions (SJS, TEN)
Rash	Clostridioides difficile colitis
Vaginal yeast infection	Hepatitis (jaundice, dark urine)

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6. Black Box Warnings & Contraindications

• 🚫 Contraindications:

  • Penicillin/β-lactam allergy (cross-reactivity: 10%)

  • Infectious mononucleosis (↑ rash risk)

  • History of amoxicillin-associated cholestatic jaundice

• High-Risk Groups:

  • Renal impairment: ↓ dose if CrCl <30 mL/min

  • Pregnancy (Category B): Use if benefit > risk

  • Breastfeeding: Low excretion in milk (generally safe)

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7. Drug Interactions

Medication	Risk
Probenecid	↑ Amoxicillin levels (blocks excretion)
Oral Contraceptives	↓ Efficacy (use backup contraception)
Warfarin	↑ INR (monitor bleeding)
Methotrexate	↑ Toxicity (competes for excretion)

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8. Missed Dose

• Take ASAP if <2 hours late

• Skip if >2 hours late; resume next scheduled dose

• Never double dose

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9. Overdose Management

• Symptoms: Crystalluria, hematuria, seizures

• Treatment:

  • Supportive care + hydration

  • Hemodialysis (removes 50-70% of drug)

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10. Storage

• Tablets/Capsules: 20-25°C (68-77°F) in dry place

• Suspension:

  • Unreconstituted: Room temperature

  • Reconstituted: Refrigerate (2-8°C/36-46°F)

  • Discard after 14 days

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Critical Clinical Insights

⚠️ Allergy Alert:

• Cross-reacts with cephalosporins (3-7%) – avoid if penicillin allergy history includes anaphylaxis.

• Rash in mono is non-allergic (maculopapular, not urticarial).

⚠️ Resistance Concerns:

• β-lactamase producers (e.g., H. influenzae, E. coli): Use Augmentin®.

• S. pneumoniae resistance: High-dose (90 mg/kg/day) for AOM in regions with resistance >10%.

✅ Stewardship Tips:

• Avoid for viral infections (no effect on cold/flu).

• Use strep test before treating pharyngitis.

• For UTIs: Reserve for susceptible strains (↑ resistance in E. coli).

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Amoxicillin vs. Augmentin®

Parameter	Amoxicillin Alone	Amoxicillin/Clavulanate
Spectrum	Narrower (no β-lactamase coverage)	Broad (covers β-lactamase producers)
Diarrhea Risk	8%	25%
Cost	$	$$$
Best For	Strep, uncomplicated AOM	Sinusitis, bite wounds, recurrent AOM

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📊 Efficacy Data:

• Strep eradication: 85-95% with 10-day course (vs. 35% for 5-day).

• AOM failure rate: 15% for standard dose vs. 8% for high-dose (NEJM).

Prescribing Note: First-line for uncomplicated infections; switch to Augmentin® if no improvement in 48-72 hours.