What is the drug of choice for a patient with acute tonsillitis, considering potential bacterial or viral causes and possible allergies to penicillin (PCN)?

Drug of Choice for Acute Tonsillitis

Penicillin V or amoxicillin are the drugs of choice for acute bacterial tonsillitis, with penicillin V dosed at 250 mg twice or three times daily for 10 days in children (or 250 mg four times daily/500 mg twice daily in adolescents and adults), and amoxicillin at 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg) for 10 days. 1, 2, 3

When to Test and Treat

• Do not prescribe antibiotics for viral pharyngitis, which presents with cough, rhinorrhea, hoarseness, or oral ulcers 1, 2
• Test patients with 3-4 Centor criteria (fever, tonsillar exudates, tender anterior cervical adenopathy, absence of cough) using rapid antigen detection test or throat culture before prescribing antibiotics 1, 2
• Patients with fewer than 3 Centor criteria do not need testing or antibiotics 1
• Testing is not recommended for children under 3 years old unless special risk factors exist (e.g., older sibling with Group A Streptococcus infection) 1

First-Line Treatment for Non-Allergic Patients

Penicillin and amoxicillin are chosen based on their narrow spectrum, proven efficacy, safety profile, and low cost 1, 2, 3:

• Penicillin V: 250 mg 2-3 times daily for children, or 250 mg four times daily/500 mg twice daily for adolescents and adults, for 10 days 1, 2, 3
• Amoxicillin: 50 mg/kg once daily (max 1000 mg) or 25 mg/kg twice daily (max 500 mg) for 10 days—particularly useful in younger children due to better palatability 1, 2, 3
• Benzathine penicillin G: Single intramuscular dose of 600,000 U for patients <27 kg or 1,200,000 U for patients ≥27 kg 1, 2, 3

The 10-day duration is critical to eradicate Group A Streptococcus and prevent rheumatic fever 1, 2, 3. Shorter courses show inferior bacteriologic eradication rates 1.

Treatment for Penicillin-Allergic Patients

For patients with penicillin allergy, the choice depends on the type of reaction 1, 2, 3:

Non-Anaphylactic Allergy

• Cephalexin: 20 mg/kg/dose twice daily (max 500 mg/dose) for 10 days 1, 2, 3
• Cefadroxil: 30 mg/kg once daily (max 1 g) for 10 days 1, 3

Avoid cephalosporins in patients with immediate-type hypersensitivity (anaphylaxis) to penicillin 1, 2, 3.

Any Penicillin Allergy (Including Anaphylaxis)

• Clindamycin: 7 mg/kg/dose three times daily (max 300 mg/dose) for 10 days 1, 2, 3
• Azithromycin: 12 mg/kg once daily (max 500 mg) for 5 days 1, 2, 3, 4
• Clarithromycin: 7.5 mg/kg/dose twice daily (max 250 mg/dose) for 10 days 1, 3

Important caveat: Macrolide resistance in Group A Streptococcus varies geographically and temporally, making them less reliable than first-line agents 1, 2, 5. Azithromycin showed clinical superiority over penicillin in some trials (95% vs 73% bacteriologic eradication at Day 14), but approximately 1% of susceptible isolates became resistant following therapy 4.

When to Use Broader-Spectrum Agents

Reserve amoxicillin-clavulanate and second-generation cephalosporins for treatment failures or patients with multiple culture-positive episodes despite appropriate penicillin therapy 2, 3. These situations may involve beta-lactamase-producing bacteria "shielding" Group A Streptococcus 2.

Do not use broad-spectrum agents as first-line therapy, as this unnecessarily increases antibiotic resistance and side effects without providing additional clinical benefit 1, 2.

Common Pitfalls to Avoid

• Do not treat viral pharyngitis with antibiotics—most sore throats are viral and require only symptomatic treatment 1, 2
• Do not prescribe antibiotics empirically without testing in patients with 3-4 Centor criteria 1
• Do not use shorter treatment courses (less than 10 days for most antibiotics, except azithromycin's 5-day course)—this increases treatment failure rates 1, 2
• Do not use macrolides as first-line therapy due to increasing resistance patterns 1, 2
• Avoid amoxicillin in older children with suspected Epstein-Barr virus (infectious mononucleosis) due to risk of severe rash 1

Delayed Prescribing Strategy

For patients with equivocal presentations, consider "delayed antibiotic prescribing" with 2-3 day observation 1, 6. This strategy shows no significant difference in complication rates compared to immediate antibiotics and reduces unnecessary antibiotic use 1.