MIAMI BEACH — There are many options for antibiotic treatment of uncomplicated and complicated skin infections, each with its own advantages and disadvantages, according to a presentation by Richard K. Scher, M.D., at a symposium sponsored by the Florida Society of Dermatology and Dermatologic Surgery.
Major goals of therapy include prompt eradication of the infection, reduction of potential antibiotic resistance, and lower risk of recurrence. Safety, efficacy, cost, compliance, managed care formularies, and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) are important considerations when individualizing therapy, according to Dr. Scher, professor of clinical dermatology at Columbia University, New York.
Uncomplicated infections affect superficial skin tissue and include furuncles, cellulites, folliculitis, simple abscesses, and impetiginous lesions. Complicated infections affect deeper soft tissue or require significant surgery, such as infected ulcers, burns, or major abscesses. Infections are also complicated in the presence of significant underlying disease or if the affected site carries a higher risk for anaerobic or gram-negative infection, such as the rectal area.
Severe atopic dermatitis, poorly controlled diabetes, and patients with kidney failure may be predisposed to skin infections. Other risk factors are leukemia or lymphoma; malnutrition and low serum iron; alcohol abuse; intravenous drug use; and medications including systemic steroids, retinoids, cytotoxic agents, and immunosuppressants.
Dr. Scher discussed these options for treating skin structure infections:
▸ Cephalosporins. These drugs have good tolerability and good sensitivity. The risk of hypersensitivity is low, probably less than 2%, for a patient with a history of nonanaphylactic penicillin allergy.
First-generation drugs in this class include cephalexin and cefadroxil. They have good activity against S. pyogenes and MRSA. Dosing is t.i.d. to q.i.d.
Second-generation cephalosporins include cefaclor and cefuroxime, which have expanded activity against gram-negative bacteria and a longer half-life than the first-generation drugs. Dosing is b.i.d.
Third-generation agents include cefixime and ceftibuten. They are good for gram-negative organisms but not as good for gram-positive bacteria, Dr. Scher noted. Dosing is once daily or b.i.d.
Extended-spectrum cephalosporins include cefdinir and cefpodoxime, which are active against gram-negative and gram-positive bacteria. Cefdinir is administered b.i.d.
▸ Penicillins. S. pyogenes is always sensitive to treatment with penicillins, but because of cross resistance from MRSA, S. aureus is no longer sensitive. Drugs in this class that are β-lactamase stable exhibit good antistaphylococcal activity. Most dosing is t.i.d. or q.i.d.
▸ Macrolides. These drugs include erythromycin, clarithromycin, and azithromycin. They are less likely to be used because of concerns about resistance, Dr. Scher said. Increasing resistance to S. pyogenes and S. aureus have been reported.
▸ Tetracyclines. The tetracyclines have some coverage for community-acquired MRSA. However, there are some resistance issues, and these agents can discolor childrens' teeth and cause photosensitivity.
▸ Fluoroquinolones. These drugs have a long half-life, and early studies suggest they are as efficacious as β-lactams for erysipelas, cellulitis, impetigo, surgical wounds, and diabetic foot infections. However, resistance is increasing. Possible adverse effects include tendonitis and tendon rupture in adults. They are contraindicated in pediatric patients.
▸ Lincosamides. Clindamycin has good activity against S. pyogenes and methicillin-susceptible strains of S. aureus. It is also active against some MRSA strains. Resistance to erythromycin could signal inducible resistance to clindamycin, Dr. Scher said. A higher risk of pseudomembranous colitis is associated with Clostridium difficile. Dosing is t.i.d.
▸ Trimethoprim-sulfamethoxazole. This combination covers some community-acquired MRSA infections. There is some resistance among staphylococci and no coverage for streptococci. Possible adverse reactions include rash and photosensitivity.
Factors that may alter antimicrobial decision making include emerging macrolide resistance among the β-hemolytic or viridans-group streptococci, Dr. Scher noted. Community-acquired MRSA might also be resistant to β-lactams, macrolides, and quinolones, further limiting choices.