What antibiotics are used to treat a pus abscess?

Antibiotic Management for Pus Abscesses

For simple, uncomplicated abscesses treated with adequate incision and drainage, antibiotics are generally unnecessary unless specific high-risk features are present. 1

When Antibiotics Are NOT Needed

For simple superficial abscesses or boils where adequate incision and drainage is performed, antibiotics should be withheld if all of the following criteria are met 1:

• Erythema and induration limited to ≤5 cm from the wound edge 1
• Temperature <38.5°C 1
• Pulse rate <100 beats/min 1
• No systemic signs of infection 1
• Immunocompetent patient 1
• Complete source control achieved 1

Incision and drainage alone is the primary treatment for simple abscesses, and antibiotics provide no additional benefit in these cases. 1

When Antibiotics ARE Indicated

Mandatory Antibiotic Indications

Antibiotics must be administered in the following situations 1:

• Sepsis or systemic signs of infection (temperature ≥38.5°C, pulse ≥100 beats/min) 1
• Surrounding cellulitis extending >5 cm from abscess borders 1
• Immunocompromised patients (HIV, neutropenic, transplant recipients) 1
• Incomplete source control or inability to adequately drain 1
• High-risk cardiac conditions (prosthetic valves, previous endocarditis, congenital heart disease, transplant recipients with valve pathology) 1

Special Considerations for Anorectal Abscesses

For drained anorectal abscesses specifically, antibiotics reduce fistula formation and recurrence 1:

• A 5-10 day course of antibiotics following drainage reduces fistula formation from 24% to 16% 1
• Among patients with surrounding cellulitis, induration, or systemic sepsis, drainage alone results in 2-fold increased recurrent abscess 1

Antibiotic Selection

For Simple Skin Abscesses (When Antibiotics Are Indicated)

First-line options targeting MRSA 1, 2, 3:

• Trimethoprim-sulfamethoxazole (TMP-SMX): 1-2 double-strength tablets (160/800 mg) twice daily for 5-7 days 1, 2, 3
• Clindamycin: 300-450 mg orally three times daily for 5-7 days 1, 2

TMP-SMX and clindamycin demonstrate equivalent efficacy (83.1% vs 81.7% cure rates), both superior to placebo (68.9%). 2 However, clindamycin causes more adverse events (21.9% vs 11.1% with TMP-SMX) but provides lower recurrence rates at 1 month (6.8% vs 13.5%). 2

Alternative options in areas with low CA-MRSA prevalence 1:

• Cephalexin: 500 mg every 6 hours 1
• Dicloxacillin: Standard dosing for penicillinase-resistant coverage 4

For Complex Abscesses (Perianal, Perirectal, Injection Sites)

Empiric broad-spectrum coverage is mandatory, targeting Gram-positive, Gram-negative, and anaerobic bacteria. 1

Recommended regimens 1:

• Piperacillin-tazobactam: 3.375 g IV every 6 hours or 4.5 g every 8 hours 1
• Ceftriaxone 1 g IV daily PLUS metronidazole 500 mg IV every 8 hours 1
• Levofloxacin 750 mg IV daily PLUS metronidazole 500 mg IV every 8 hours 1
• Ertapenem: 1 g IV every 24 hours 1

For axilla or perineum locations, add anaerobic coverage with metronidazole to any regimen 1.

MRSA Coverage Considerations

If MRSA is suspected (hospital-acquired or community-acquired), add vancomycin, daptomycin, or linezolid. 1 MRSA prevalence in anorectal abscesses can reach 35%, warranting culture in high-risk patients. 1

Treatment Duration

5-7 days is the optimal duration for uncomplicated abscesses with adequate drainage. 1, 2, 3 Treatment for ≥10 days represents avoidable antibiotic exposure in 42% of cases and should be avoided. 5

For anorectal abscesses with antibiotics indicated, 5-10 days is recommended. 1

Culture Recommendations

Routine cultures are unnecessary for simple cutaneous abscesses. 1 However, sampling of drained pus is indicated in 1:

• High-risk patients (HIV, immunocompromised) 1
• Risk factors for multidrug-resistant organisms 1
• Recurrent infections or non-healing wounds 1
• Treatment failure 1

Critical Pitfalls to Avoid

Do not prescribe antibiotics for adequately drained simple abscesses without high-risk features - this represents unnecessary exposure and promotes resistance. 1, 5

Do not use fluoroquinolones or broad gram-negative coverage for simple skin abscesses - these represent avoidable broad-spectrum exposure occurring in 4% of cases. 1, 5

Do not extend treatment beyond 7 days for uncomplicated cases - prolonged courses (≥10 days) occur unnecessarily in 42% of cases. 5

Do not rely on oral antibiotics alone for complex abscesses - parenteral broad-spectrum therapy is required. 1