A 35-year-old man with acute bacterial tonsillitis (fever 38.8°C, pharyngeal exudate, positive rapid strep test) reports a history of severe penicillin allergy (anaphylaxis). Which antibiotic is the preferred first-line alternative?

Explanation

## Acute Bacterial Tonsillitis in Penicillin-Allergic Patients **Key Point:** In penicillin-allergic patients with acute bacterial tonsillitis (typically Group A Streptococcus), clindamycin is the preferred first-line alternative because it provides excellent streptococcal coverage, reliable tissue penetration, and a favorable safety profile. ### Why Clindamycin? **High-Yield:** Clindamycin is the gold standard alternative in penicillin allergy because: - **Excellent streptococcal coverage:** highly active against Group A Streptococcus (>95% susceptibility in most regions) - **Tissue penetration:** achieves high concentrations in pharyngeal tissue and saliva - **Oral bioavailability:** 150–300 mg three times daily is effective for acute tonsillitis - **Low cross-reactivity:** <1% cross-reactivity with penicillins (safe even in non-anaphylactic penicillin allergy) - **Proven efficacy:** comparable cure rates to penicillin V in acute streptococcal tonsillitis **Clinical Pearl:** Clindamycin dosing for acute tonsillitis is 300 mg PO three times daily for 10 days. It is also effective for peritonsillar abscess in penicillin-allergic patients. ### Antibiotic Alternatives in Penicillin Allergy | Antibiotic | GAS Coverage | Tissue Penetration | Cross-Reactivity Risk | Suitable? | |---|---|---|---|---| | **Clindamycin** | ✓✓ (excellent) | ✓✓ (excellent) | <1% | **YES, First-line** | | Fluoroquinolone | ✓ (adequate) | ✓ (good) | None | Alternative (not preferred) | | TMP-SMX | ✓ (adequate) | ✓ (good) | None | Alternative (less preferred) | | Tetracycline | ✓ (adequate) | ✓ (good) | None | Alternative (resistance emerging) | | Cephalosporin (3rd gen) | ✓✓ (excellent) | ✓✓ (excellent) | 1–3% | Only if non-anaphylactic allergy | **Mnemonic:** **CAP** = **C**lindamycin is the **A**lternative **P**enicillin-sparing choice for streptococcal tonsillitis. ### Decision Tree for Penicillin-Allergic Tonsillitis ```mermaid flowchart TD A[Acute Bacterial Tonsillitis + Penicillin Allergy]:::outcome --> B{Type of Allergy?}:::decision B -->|Anaphylaxis/Severe| C[Clindamycin 300 mg TDS]:::action B -->|Non-anaphylactic Rash| D[Cephalosporin 3rd gen OR Clindamycin]:::action C --> E[10-day course]:::action D --> E E --> F[Clinical cure]:::outcome A --> G{Macrolide Resistance High?}:::decision G -->|Yes| H[Avoid azithromycin]:::urgent ``` **Warning:** Avoid macrolides (azithromycin, erythromycin) in regions with high Group A Streptococcus resistance to macrolides (>25%). Fluoroquinolones are suboptimal as first-line due to cost and unnecessary broad spectrum. Tetracyclines are increasingly unreliable due to resistance.