A 28-year-old woman presents to the emergency department with a 2-day history of severe sore throat, fever (39.5°C), and difficulty swallowing. On examination, she has bilateral exudative pharyngitis with enlarged tonsils, petechial rash on the soft palate, and tender cervical lymphadenopathy. A rapid antigen detection test (RADT) is positive. She has no history of penicillin allergy. Which antibiotic is the first-line treatment for this condition?

## Diagnosis and Treatment of Group A Streptococcal Pharyngitis ### Clinical Presentation The patient presents with classic features of acute streptococcal pharyngitis: - Exudative pharyngitis with tonsillar enlargement - Petechial rash on soft palate (characteristic of GAS) - Fever and cervical lymphadenopathy - Positive RADT confirming Group A Streptococcus (GAS / *Streptococcus pyogenes*) ### First-Line Antibiotic Therapy **Key Point:** Penicillin V (oral) or amoxicillin are the gold-standard first-line agents for GAS pharyngitis in non-allergic patients [cite:Harrison 21e Ch 297]. **High-Yield:** The rationale for penicillin is: 1. Excellent in vitro activity against GAS (no resistance reported) 2. Proven efficacy in preventing suppurative and non-suppurative sequelae (acute rheumatic fever, post-streptococcal glomerulonephritis) 3. Narrow spectrum (reduces dysbiosis) 4. Cost-effective 5. Oral bioavailability adequate for pharyngitis ### Dosing - **Penicillin V:** 250 mg PO QID for 10 days - **Amoxicillin:** 500 mg PO BID–TID for 10 days (preferred in children due to palatability) ### Why 10 Days? **Clinical Pearl:** A full 10-day course is mandatory to eradicate GAS from the pharynx and prevent acute rheumatic fever (ARF). Shorter courses are associated with higher ARF recurrence rates. ### Alternative Agents (for Penicillin-Allergic Patients) | Allergy Type | First-Line Alternative | Second-Line | |---|---|---| | Non-severe (rash) | First-generation cephalosporin (cephalexin 500 mg QID) | Azithromycin (if cephalosporin contraindicated) | | Severe (anaphylaxis, Stevens-Johnson) | Azithromycin 500 mg day 1, then 250 mg daily × 4 days | Clindamycin 300 mg TID × 10 days | **Warning:** ~10% cross-reactivity between penicillins and cephalosporins in severe IgE-mediated allergy; safe in non-severe rash allergy. ### Why NOT the Other Options See distractor explanations below.