Appropriate Antibiotic for Infected Ingrown Groin Hair
For an infected ingrown groin hair (furuncle) in a man in his late 60s, incision and drainage is the primary treatment, and antibiotics are only indicated if systemic signs of infection are present (fever >38°C, tachycardia >90 bpm, or signs of surrounding cellulitis >5 cm). If antibiotics are warranted, oral cephalexin 500 mg four times daily or dicloxacillin 500 mg four times daily for 5-7 days are the first-line choices. 1
Primary Treatment Approach
Incision and drainage is the definitive treatment for furuncles (infected hair follicles), and most cases do not require antibiotics. 1, 2 The decision to add antibiotics should be based on specific clinical criteria rather than routine administration. 1
When Antibiotics Are NOT Needed
Antibiotics should be withheld after drainage if the patient meets ALL of the following criteria: 1, 2
- Temperature <38.5°C
- Heart rate <100 beats per minute
- White blood cell count <12,000 cells/µL
- Erythema and induration extending <5 cm from the lesion
When Antibiotics ARE Indicated
Antibiotics directed against S. aureus should be added when any of the following are present: 1
- Temperature >38°C or <36°C
- Tachycardia >90 beats per minute
- Tachypnea >24 breaths per minute
- White blood cell count >12,000 or <400 cells/µL
- Significant surrounding cellulitis (>5 cm extension)
- Immunocompromised status
- Diabetes mellitus or other impaired host defenses
Antibiotic Selection for Groin Location
For groin/perineal furuncles requiring antibiotics, broader coverage is needed due to mixed flora from adjacent areas. 1, 2
First-Line Oral Regimens
Cephalexin 500 mg four times daily for 5-7 days is the preferred first-line agent, providing excellent coverage against both S. aureus and streptococci. 1, 3
Alternative first-line options include: 1
- Dicloxacillin 500 mg four times daily
- Amoxicillin-clavulanate 875/125 mg twice daily (provides additional anaerobic coverage appropriate for groin location)
Coverage for Perineal/Groin-Specific Flora
Because the groin is adjacent to the perineum, consider adding metronidazole 500 mg three times daily to cephalexin if there is concern for anaerobic involvement. 1, 2 This combination provides coverage for the mixed aerobic-anaerobic flora characteristic of this anatomical region. 1
MRSA Considerations
MRSA coverage is NOT routinely needed for typical furuncles unless: 1
- Previous MRSA infection documented
- Failure to respond to initial beta-lactam therapy after 48-72 hours
- Known MRSA colonization
- Recent hospitalization or long-term care facility residence
If MRSA coverage is indicated, use: 1, 2
- Doxycycline 100 mg twice daily for 7 days 4
- Trimethoprim-sulfamethoxazole 160-800 mg (one double-strength tablet) twice daily for 7 days 1
- Clindamycin 300-450 mg three times daily for 7 days 2
Treatment Duration
A 5-7 day course is appropriate for uncomplicated infections with clinical improvement. 1, 2 Patients showing ongoing signs of infection beyond 7 days warrant diagnostic re-evaluation including repeat examination and consideration of inadequate drainage or resistant organisms. 2
Critical Pitfalls to Avoid
Do not treat with antibiotics alone without drainage - this will fail in the vast majority of cases as the purulent collection must be evacuated. 1, 2
Do not use metronidazole as monotherapy - it lacks activity against S. aureus and streptococci, the primary pathogens in furuncles. 2 It should only be used as part of combination therapy for groin/perineal locations. 1
Do not routinely cover for MRSA - typical cellulitis and furuncles are rarely caused by MRSA, and beta-lactam therapy is successful in 96% of cases. 1 Reserve MRSA coverage for the specific indications listed above.
Avoid needle aspiration - this has only a 25% success rate overall and <10% success with MRSA infections. 1
Special Considerations for This Patient Population
In a man in his late 60s, assess for diabetes mellitus and other immunocompromising conditions that would lower the threshold for antibiotic use. 1 These patients may require antibiotics even with minimal systemic signs due to impaired host defenses. 1
Culture the drained material if antibiotics are prescribed to guide therapy adjustment if the patient fails to improve. 1, 2