What is the first-line oral medication for a nail bacterial infection?

Oral Medication for Bacterial Nail Infections

For bacterial nail infections, oral antibiotics targeting Staphylococcus aureus are first-line, with dicloxacillin or cephalexin being the preferred agents for methicillin-sensitive infections. 1, 2, 3

Critical Diagnostic Distinction

Before initiating any treatment, you must confirm the infection is bacterial rather than fungal, as the vast majority of nail infections (>90%) are fungal in origin 1. Treatment should not be commenced before mycological and bacteriological confirmation 1:

• Bacterial infections typically present with acute paronychia (swollen, erythematous, painful periungual tissue), often with purulent drainage 4, 5
• Pseudomonas infections cause characteristic green or black nail discoloration 6
• Fungal infections (onychomycosis) present more insidiously with nail plate thickening, discoloration, and subungual debris without acute inflammation 1

First-Line Oral Antibiotics

For Staphylococcus aureus (Most Common Bacterial Pathogen)

Dicloxacillin is the preferred agent 1, 2:

• Provides anti-staphylococcal and gram-positive coverage
• Should be taken on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption 2
• Requires monitoring for allergic reactions, particularly in patients with penicillin allergy history 2

Cephalexin is an effective alternative 1, 3:

• Particularly useful in patients with minor penicillin allergies (not anaphylaxis)
• Dosing should be adjusted in renal impairment 3
• Can be taken with or without food 3

For Pseudomonas aeruginosa Infections

Ciprofloxacin is the treatment of choice 6:

• Specifically targets gram-negative organisms including Pseudomonas
• Essential when green/black nail discoloration is present 6

Treatment Duration and Monitoring

Continue oral antibiotics for 7-14 days depending on severity 1:

• Reassess after 2 weeks; if no improvement, obtain bacterial cultures with sensitivity testing 1, 6
• If painful subungual abscess or hematoma is present, partial or total nail avulsion is required before antibiotics will be effective 1
• Bacterial cultures should guide antibiotic selection if initial empiric therapy fails 2, 6

Critical Pitfalls to Avoid

Do not treat empirically without confirming bacterial infection 1, 7:

• Fungal infections require entirely different treatment (terbinafine or itraconazole for dermatophytes, not antibiotics) 1
• Chronic paronychia is often contact dermatitis with secondary colonization, not primary infection requiring systemic antibiotics 4
• Herpetic whitlow (viral) can mimic bacterial abscess but requires non-operative management, not antibiotics or drainage 5

Avoid systemic antibiotics for ingrown nails unless proven infection 4:

• Paronychia from ingrown nails is mechanical inflammation, not infection in most cases
• Antibiotics are ineffective and promote resistance unless bacterial infection is documented 4

Do not use topical antibiotics as monotherapy for established nail infections 6:

• Topical agents (nadifloxacin, gentamicin) are reserved for superficial colonization only
• Antiseptics like octenidine are appropriate for mild cases 6

When Surgical Intervention is Needed

Drainage is mandatory if abscess is present 1, 5:

• Antibiotics alone will not resolve a closed-space infection
• The nail bed must be cleaned and cultured at the time of drainage 1
• Continue oral antibiotics post-drainage to prevent recurrence 1