What is the antibiotic of choice for an adult patient with infected psoriasis?

Antibiotic Treatment for Infected Psoriasis

For infected psoriasis in adults, anti-staphylococcal antibiotics targeting Staphylococcus aureus are the antibiotics of choice, with macrolides (erythromycin, azithromycin) or rifampin being preferred when possible, as these agents may provide dual benefit by treating the infection while potentially improving psoriasis severity through immunomodulatory effects.

Primary Antibiotic Selection

First-Line Options for Bacterial Superinfection

• Anti-staphylococcal coverage is essential since secondary bacterial infection of psoriatic plaques is most commonly caused by S. aureus and beta-hemolytic streptococci 1
• Macrolide antibiotics (erythromycin, azithromycin, clarithromycin) are preferred when clinically appropriate, as they have demonstrated reduction in Psoriasis Area and Severity Index (PASI) scores in plaque-type psoriasis through immunomodulatory mechanisms beyond simple bacterial inhibition 2
• Rifampin has shown benefit in decreasing PASI scores in plaque-type psoriasis and may be considered for infected lesions 2

Alternative Options

• Penicillins or cephalosporins can be used for anti-staphylococcal coverage, though they lack the additional immunomodulatory benefits seen with macrolides 2
• Culture-directed antibiotics should be used when streptococcal infection is confirmed (particularly group A beta-hemolytic Streptococcus), as this is a known trigger for guttate psoriasis exacerbations 1

Critical Antibiotics to Avoid

Tetracyclines Should Be Avoided

• Tetracyclines (doxycycline, minocycline) are considered triggering factors for psoriasis exacerbation and should be avoided when treating infected psoriasis, though the evidence comes primarily from case reports and retrospective studies 2
• Other triggering antibiotics include beta-lactams in some patients, antimalarials, and certain NSAIDs, though these are rarely inciting agents 1

Treatment Algorithm

Step 1: Assess Infection Severity

• Obtain bacterial cultures from pustular or crusted lesions, particularly from pharyngeal, anal, or vulvar sites if guttate psoriasis is present 1
• Evaluate for systemic signs of infection (fever, lymphadenopathy, spreading erythema) that would necessitate more aggressive treatment 3

Step 2: Initiate Empiric Antibiotic Therapy

• Start with a macrolide (azithromycin 500 mg day 1, then 250 mg daily for 4 days, or clarithromycin 500 mg twice daily for 7-10 days) for mild-to-moderate infected psoriasis 2
• Consider rifampin (600 mg daily) in combination with other antibiotics for more severe infections, given its dual antimicrobial and anti-psoriatic effects 2
• Use anti-staphylococcal penicillins or first-generation cephalosporins (cephalexin 500 mg four times daily) if macrolides are contraindicated 1

Step 3: Adjust Based on Culture Results

• Narrow antibiotic spectrum once culture and sensitivity results are available 1
• Extend treatment duration to 10-14 days for confirmed streptococcal infections, as inadequate treatment may lead to psoriasis flares 1

Concurrent Psoriasis Management

Continue Baseline Psoriasis Therapy

• Maintain topical corticosteroids (high-potency class 1-3) during antibiotic treatment for infected areas 4
• Avoid systemic immunosuppression escalation until infection is controlled, particularly with biologics that increase infection risk 1

Special Considerations for Biologic Users

• Screen for infections carefully in patients on TNF-α inhibitors, IL-17 inhibitors, or IL-23 inhibitors, as these agents suppress immune surveillance 1
• Consider temporary biologic hold if severe bacterial superinfection is present, particularly with TNF-α inhibitors which carry higher infection risk 1
• Abatacept may be preferred over other biologics in patients with recurrent or serious infections, based on indirect evidence from rheumatoid arthritis populations showing fewer hospitalized infections 1

Common Pitfalls to Avoid

• Do not use tetracyclines as first-line therapy, as they may worsen psoriasis 2
• Do not assume penicillin efficacy for guttate psoriasis without culture confirmation, as studies show no statistically significant improvement with empiric penicillin therapy 2
• Do not overlook streptococcal screening in pediatric patients with guttate psoriasis, as pharyngeal and perianal group A beta-hemolytic Streptococcus is a major trigger 1
• Do not delay culture collection before starting antibiotics, as this guides definitive therapy and identifies triggering organisms 1