Best Antibiotic for Bacterial Nail Infection
For bacterial nail infections (paronychia), oral amoxicillin-clavulanate 500-875 mg twice daily or cephalexin 500 mg 3-4 times daily for 7-10 days are the first-line antibiotics, with topical antiseptics like povidone-iodine 2% for mild cases. 1
Understanding the Infection Type
The approach depends critically on distinguishing bacterial from fungal infection, as most nail infections are actually fungal (onychomycosis), not bacterial 2, 3. Bacterial nail infections primarily manifest as acute paronychia—painful, erythematous swelling of the lateral nail folds with potential purulent discharge 1, 4.
Key Clinical Distinctions:
- Bacterial paronychia: Acute onset, painful, red, swollen nail fold, possible pus formation 1, 4
- Fungal onychomycosis: Gradual onset, nail plate thickening/discoloration, typically painless 1
- Laboratory confirmation is essential before treatment to avoid inappropriate therapy and drug resistance 3, 5
Antibiotic Selection Algorithm
For Mild Bacterial Paronychia (Grade 1):
- Topical povidone-iodine 2% applied to affected area 1
- Topical antibiotics (gentamicin, nadifloxacin) with corticosteroids 1, 2
- Antiseptic soaks with octenidine 2
- Reassess after 2 weeks 1
For Moderate Bacterial Paronychia (Grade 2):
First-line oral antibiotics:
- Cephalexin 500 mg 3-4 times daily for 7-10 days 1, 6
- Dicloxacillin 500 mg 4 times daily for 7-10 days 1
- Amoxicillin-clavulanate 500-875 mg twice daily for 7-10 days 1
These agents provide excellent coverage against Staphylococcus aureus and Streptococcus species, the most common bacterial pathogens in nail infections 1.
For Severe Bacterial Paronychia (Grade 3):
- Obtain bacterial cultures before initiating therapy 1, 5
- Continue oral antibiotics as above 1
- Surgical drainage or partial nail avulsion may be required 1, 4
- Consider intravenous therapy if systemic signs present 4
Specific Pathogen Considerations
Pseudomonas Aeruginosa (Green/Black Nail Discoloration):
- Ciprofloxacin 500-750 mg twice daily orally 2
- Topical antiseptics 2
- This organism causes characteristic green-black nail discoloration 2, 3
Suspected MRSA Infection:
- Trimethoprim-sulfamethoxazole (TMP-SMZ) 1-2 double-strength tablets twice daily 1
- Clindamycin 300-450 mg 3 times daily 1
- Doxycycline 100 mg twice daily 1
Penicillin-Allergic Patients:
- Clindamycin 300 mg 3 times daily 1
- Fluoroquinolones (ciprofloxacin, levofloxacin) 1
- Avoid cephalosporins if immediate hypersensitivity reaction 1
Critical Pitfalls to Avoid
Do not treat presumed bacterial nail infections without mycological confirmation, as 80-90% of nail infections are actually fungal and will not respond to antibiotics 1, 2. Fungal infections require antifungal therapy (terbinafine or itraconazole), not antibiotics 1.
Do not confuse herpetic whitlow with bacterial abscess—viral infections require non-operative management, while bacterial abscesses need drainage 4, 5. Incision and drainage of herpetic whitlow can cause severe complications 4.
Obtain cultures if infection is severe, not responding to initial therapy, or if unusual organisms are suspected (e.g., Pseudomonas, gram-negative bacteria, or polymicrobial infection) 1, 2, 5.