What antibiotic will cover common bacterial pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis for a patient presenting with ear and throat symptoms, considering potential penicillin allergy?

Antibiotic Coverage for Ear and Throat Infections

For ear and throat infections covering Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, amoxicillin-clavulanate (co-amoxiclav) is the preferred first-line antibiotic, with high-dose formulations (90 mg/kg/day amoxicillin component) recommended for moderate disease or recent antibiotic exposure. 1, 2

First-Line Antibiotic Selection

Amoxicillin-clavulanate provides optimal coverage because:

• It covers all three major pathogens (S. pneumoniae, H. influenzae, M. catarrhalis) 1
• The β-lactamase inhibitor (clavulanate) overcomes resistance in 20-30% of H. influenzae and 50-70% of M. catarrhalis strains that produce β-lactamase 1
• High-dose formulations (90 mg/kg/day or 1.75-4 g/250 mg daily in adults) achieve 90-91% clinical efficacy and 97-99% bacteriologic efficacy 2

Doxycycline is an equally preferred alternative for non-severe infections in adults and children >12 years (100 mg twice daily), particularly when broader coverage including Staphylococcus aureus is needed 1, 2, 3

Dosing Considerations by Severity

Mild Disease (No Recent Antibiotic Use)

• Standard-dose amoxicillin-clavulanate (45 mg/kg/day in children; 625 mg three times daily in adults) 1

Moderate Disease or Recent Antibiotic Exposure

• High-dose amoxicillin-clavulanate (90 mg/kg/day amoxicillin with 6.4 mg/kg/day clavulanate in 14:1 ratio, twice daily) 1, 2
• This higher dose is critical in areas with penicillin-resistant S. pneumoniae or for patients with risk factors for resistant pathogens 1

Penicillin Allergy Algorithm

Non-Type I Hypersensitivity (e.g., rash without anaphylaxis)

Cefdinir is the preferred agent due to superior patient acceptance and negligible cross-reactivity with penicillin 4

• Cefdinir: 14 mg/kg/day in 1-2 doses (children); 300 mg twice daily (adults) 4
• Alternative cephalosporins: cefuroxime (30 mg/kg/day divided twice daily) or cefpodoxime (10 mg/kg/day divided twice daily) 1, 4
• Cross-reactivity between penicillins and second/third-generation cephalosporins is only ~0.1% 4

Type I Hypersensitivity (Anaphylaxis History)

Clarithromycin is the preferred macrolide when β-lactams cannot be used 2, 5

• Clarithromycin: 500 mg twice daily (adults); 15 mg/kg/day divided twice daily (children) 1, 5
• Clarithromycin has superior activity against H. influenzae compared to azithromycin 2
• Alternative: Doxycycline 100 mg twice daily (if age >12 years and no tetracycline contraindications) 1, 2

Critical caveat: Macrolides and trimethoprim-sulfamethoxazole have limited effectiveness against major pathogens, with bacterial failure rates of 20-25%, and should only be used when β-lactams are contraindicated 1, 4

Coverage Limitations and Pitfalls

Common Mistakes to Avoid

• Never use plain amoxicillin or ampicillin empirically without susceptibility testing, as 18-42% of H. influenzae and 50-70% of M. catarrhalis produce β-lactamase 1, 2
• Do not assume all macrolides are equivalent: clarithromycin has clinically superior activity over azithromycin for H. influenzae 2
• Avoid cefuroxime axetil as first-line: >99% of H. influenzae and all M. catarrhalis show intermediate or resistant susceptibility 1, 6

Resistance Patterns

• Penicillin resistance in S. pneumoniae varies geographically but is present in all regions 7
• β-lactamase production: 42% of H. influenzae and >90% of M. catarrhalis in recent surveillance 6, 8
• Macrolide resistance in S. pneumoniae is high and increasing, particularly in serotype 19A strains 7, 8

Treatment Failure Management

If no improvement within 48-72 hours:

• Switch to high-dose amoxicillin-clavulanate if not already used 1
• Consider ceftriaxone 50 mg/kg IM/IV daily for 3-5 days (children) or 1-2 g daily (adults) 1
• Combination therapy for severe cases: high-dose amoxicillin or clindamycin PLUS cefixime 1

Duration of Therapy

• Standard duration: 7-10 days for most ear and throat infections 1, 3
• Severe infections: 10-14 days 2
• Clinical improvement should be evident within 48-72 hours of appropriate therapy 1

Special Populations

Children <5 Years

• Amoxicillin-clavulanate remains first-line (90 mg/kg/day amoxicillin component) 2
• For penicillin allergy: cefdinir, clarithromycin, or cefuroxime 1, 4

Children >12 Years and Adults

• Doxycycline 100 mg twice daily is an equally preferred alternative to amoxicillin-clavulanate 1, 2
• Provides additional S. aureus coverage when needed 1