For an otherwise healthy adult with an acute fingertip abscess (felon), how many days should trimethoprim‑sulfamethoxazole (Bactrim) be prescribed?

Antibiotic Duration for Felon (Fingertip Abscess)

For an otherwise healthy adult with a felon that has been adequately drained, prescribe trimethoprim‑sulfamethoxazole (Bactrim DS 160/800 mg) twice daily for 7–10 days.

Primary Treatment Principle

• Incision and drainage is the definitive treatment for a felon; antibiotics serve only as adjunctive therapy after surgical drainage. 1, 2
• Antibiotics are recommended for facial and fingertip abscesses even in immunocompetent patients because of the anatomical difficulty of achieving complete drainage and the higher risk of complications. 2

Antibiotic Selection and Dosing

First‑Line Empiric Therapy (MRSA Coverage)

• Trimethoprim‑sulfamethoxazole (Bactrim DS) 1–2 double‑strength tablets (160/800 mg) twice daily for 7–10 days is the most effective first‑line oral option for MRSA skin infections. 2, 3
• Clindamycin 300–450 mg three times daily for 7–10 days is preferred when coverage for both MRSA and β‑hemolytic streptococci is needed, but should only be used if local MRSA clindamycin resistance is <10%. 2, 3
• Doxycycline 100 mg twice daily for 7–10 days is an alternative when TMP‑SMX fails or is contraindicated. 2, 3

If MSSA Is Confirmed by Culture

• Dicloxacillin or cephalexin 500 mg four times daily for 7 days is first‑line treatment once methicillin‑susceptible Staphylococcus aureus (MSSA) is confirmed. 2, 3

Treatment Duration Evidence

• 7–10 days of oral antibiotic therapy is recommended for uncomplicated fingertip abscesses after adequate drainage. 2, 3
• In a randomized controlled trial of 786 patients with skin abscesses ≤5 cm, clindamycin or TMP‑SMX for 10 days after incision and drainage achieved cure rates of 83.1% and 81.7%, respectively, compared to 68.9% with drainage alone. 4
• A separate trial of 212 patients found that TMP‑SMX after drainage did not reduce 7‑day treatment failure (17% vs 26%, P=0.12) but did reduce new lesion formation at 30 days (9% vs 28%, P=0.02). 5

Microbiologic Considerations

• Obtain a culture of the abscess drainage before initiating antibiotics to identify the pathogen and guide definitive therapy. 2, 3
• MRSA accounts for approximately 50% of skin abscess isolates, making empiric MRSA coverage essential. 2, 4
• In fingertip infections specifically, Staphylococcus aureus is isolated in 58.3% of cases, with polymicrobial flora (16.5%) and Streptococcus (12.6%) as the next most common pathogens. 6

When Antibiotics May Not Be Necessary

• In a series of 103 acute fingertip infections treated with excision and extensive lavage alone (no routine antibiotics), there were zero recurrences regardless of bacterial type. 6
• Only 5 patients (8.2%) required delayed antibiotics at day 5 for wound complications (hypergranulation or maceration), not for infection recurrence. 6
• If complete surgical resection is achieved and the patient has no severe comorbidities, antibiotics may not be necessary—reassess at the first dressing change (5–7 days) and prescribe antibiotics only if progression is inadequate. 6

Dosing Considerations for TMP‑SMX

• The standard dose of 160/800 mg (one double‑strength tablet) twice daily is as effective as higher doses (320/1600 mg twice daily) for MRSA skin infections. 7
• In a prospective cohort of 291 patients with MRSA skin infections, clinical resolution rates were identical between standard‑dose (75%) and high‑dose (73%) TMP‑SMX groups (P=0.79). 7

Indications for Hospitalization and IV Therapy

• Hospital admission with intravenous vancomycin (15–20 mg/kg IV every 8–12 hours) is advised for patients with systemic infection signs (fever >38°C, tachycardia, leukocytosis), rapid clinical deterioration despite oral therapy, or immunocompromise. 2, 3
• Severe fingertip infections with necrotic or cavitated lesions, or concern for deeper structures (flexor tenosynovitis, septic arthritis, osteomyelitis), warrant more aggressive IV management and surgical consultation. 2, 8

Common Pitfalls to Avoid

• Do not prescribe antibiotics without performing adequate incision and drainage; drainage is the cornerstone of felon treatment. 1, 2
• Do not use beta‑lactam agents (amoxicillin, cephalexin, dicloxacillin) empirically until MRSA is excluded by culture, as nearly 50% of skin abscesses harbor MRSA. 2, 3
• Do not use clindamycin empirically for MRSA without verifying local resistance rates; if resistance exceeds 10%, choose TMP‑SMX or doxycycline instead. 2, 3
• Rifampin should not be used as monotherapy or as an adjunct for skin infections due to rapid resistance development. 2

Follow‑Up and Reassessment

• Reassess the patient at the first dressing change (5–7 days) to monitor progression and determine whether the initial antibiotic course should be extended or changed. 6
• Clindamycin is associated with a higher rate of adverse events (≈22%) compared to TMP‑SMX (≈11%), although reported events are generally self‑limited. 2, 4