What is the first-line antibiotic for paronychia in a patient allergic to amoxicillin?

First-Line Antibiotic for Acute Paronychia with Amoxicillin Allergy

For an 18-year-old male with acute bacterial paronychia and amoxicillin allergy, use cephalexin 500 mg orally twice daily for 5-7 days if the allergy is non-Type I (e.g., rash only), or use doxycycline 100 mg orally twice daily if the allergy is severe/Type I hypersensitivity. 1, 2

Understanding the Clinical Context

This presentation—swelling, redness, and purulent discharge from the nail fold—indicates acute bacterial paronychia with abscess formation. 2, 3 The most common pathogens are Staphylococcus aureus and Streptococcus species, with occasional gram-negative organisms. 1, 4, 2

Algorithmic Approach Based on Allergy Type

Step 1: Classify the Penicillin Allergy Severity

• Non-Type I hypersensitivity (mild rash, delayed reaction): The patient can safely receive cephalosporins 5, 1
• Type I hypersensitivity (urticaria, angioedema, bronchospasm, anaphylaxis): Cephalosporins are contraindicated; alternative non-beta-lactam antibiotics are required 5, 6

Step 2: Select Antibiotic Based on Allergy Classification

For Non-Type I Penicillin Allergy:

• First choice: Cephalexin (first-generation cephalosporin) 500 mg orally twice daily 1, 6
• This provides excellent coverage against S. aureus and streptococci, the primary pathogens in acute paronychia 6, 3
• Cefazolin or cefuroxime are acceptable alternatives if cephalexin is unavailable 1, 6

For Type I Penicillin Allergy (Severe):

• First choice: Doxycycline 100 mg orally twice daily 1
• Alternative options include clindamycin 300-450 mg orally three times daily or trimethoprim-sulfamethoxazole 160-800 mg orally twice daily 1, 6
• Important caveat: Clindamycin has excellent activity against approximately 90% of S. aureus but lacks gram-negative coverage 5, 6

Step 3: Duration and Adjunctive Management

• Antibiotic duration: 5-7 days for uncomplicated paronychia 1, 2
• Mandatory drainage: If an abscess is present (fluctuant swelling with purulent discharge), incision and drainage must be performed before or concurrent with antibiotic therapy 2, 3, 7
• Warm soaks: Apply warm water or dilute vinegar soaks (50:50 dilution) for 10-15 minutes twice daily as adjunctive therapy 8, 2

Critical Management Pitfalls to Avoid

• Do not use oral antibiotics alone without drainage if an abscess is present—adequate drainage is the cornerstone of treatment, and antibiotics without drainage will fail 2, 3, 7
• Do not use first-generation cephalosporins in patients with Type I penicillin hypersensitivity—cross-reactivity can cause severe allergic reactions 5, 6
• Do not prescribe systemic antibiotics for chronic paronychia—this is typically an inflammatory/irritant dermatitis, not an infection, and antibiotics are ineffective 4, 2

When to Escalate Therapy

• If MRSA is suspected (prior MRSA infection, healthcare exposure, injection drug use): Add or switch to trimethoprim-sulfamethoxazole 160-800 mg orally twice daily or doxycycline 100 mg orally twice daily 1, 6
• If no improvement after 48-72 hours: Obtain wound cultures, reassess for adequate drainage, and consider MRSA or resistant organisms 1, 8, 3
• If grade 3 severity (severe pain, extensive erythema, systemic symptoms): Consider parenteral antibiotics and surgical consultation 8, 3

Special Considerations for This Patient

Since this is an 18-year-old male with purulent discharge, bacterial infection is confirmed and oral antibiotics are indicated alongside drainage. 2, 3 The presence of pus distinguishes this from chronic paronychia (which would not require antibiotics) and confirms the need for antimicrobial therapy. 4, 2