What is the most appropriate antibiotic for a patient with a skin infection, allergic to penicillin (Penicillin), and unresponsive to Roxithromycin (Erythromycin derivative)?

From the Guidelines

For a patient with a skin infection who is allergic to penicillin and has not responded to roxithromycin, clindamycin is the most appropriate antibiotic choice. The recommended dosage is typically 300-450 mg orally every 6-8 hours for 7-10 days, depending on infection severity, as suggested by the Infectious Diseases Society of America guidelines 1. Clindamycin provides excellent coverage against Staphylococcus aureus (including many MRSA strains) and Streptococcus species, which are common causes of skin infections. Since roxithromycin (a macrolide) has failed, clindamycin offers a different mechanism of action by inhibiting bacterial protein synthesis at the 50S ribosomal subunit. Some key points to consider when choosing an antibiotic for skin infections include:

• The presence of systemic inflammatory response syndrome (SIRS) or severely impaired host defenses, which may necessitate the use of an antibiotic active against MRSA, such as vancomycin or linezolid 1.
• The potential for cross-resistance and emergence of resistance in erythromycin-resistant strains when using clindamycin, highlighting the need for careful monitoring and potential adjustment of therapy 1. Alternative options include trimethoprim-sulfamethoxazole (TMP-SMX) or doxycycline if clindamycin cannot be used. It's essential to monitor for potential side effects of clindamycin, particularly diarrhea, which could indicate Clostridioides difficile infection. If the infection is severe or shows signs of systemic involvement (fever, extensive cellulitis), intravenous antibiotics and hospital admission may be necessary. The decision to administer antibiotics should be based on the presence or absence of systemic inflammatory response syndrome (SIRS) and the severity of the infection, as outlined in the guidelines 1.

From the FDA Drug Label

The cure rates in clinically evaluable patients were 90% in linezolid-treated patients and 85% in oxacillin-treated patients The cure rates by pathogen for microbiologically evaluable patients are presented in Table 18. Table 18 Cure Rates at the Test-of-Cure Visit for Microbiologically Evaluable Adult Patients with Complicated Skin and Skin Structure Infections Pathogen Cured ZYVOX n/N (%) Oxacillin/Dicloxacillin n/N (%) Staphylococcus aureus 73/83 (88) 72/84 (86) Methicillin-resistant S aureus 2/3 (67) 0/0 (-) Streptococcus agalactiae 6/6 (100) 3/6 (50) Streptococcus pyogenes 18/26 (69) 21/28 (75)

The most appropriate antibiotic to use in a patient with a skin infection who is allergic to penicillin and has not responded to roxithromycin is linezolid.

• Key points:
  • Linezolid has a cure rate of 90% in clinically evaluable patients with complicated skin and skin structure infections.
  • Linezolid is effective against a range of pathogens, including Staphylococcus aureus, methicillin-resistant S aureus, Streptococcus agalactiae, and Streptococcus pyogenes.
  • The patient's allergy to penicillin and lack of response to roxithromycin make linezolid a suitable alternative. 2

From the Research

Antibiotic Options for Skin Infections

Given the patient's allergy to penicillin and lack of response to roxithromycin, alternative antibiotics must be considered.

• Clindamycin is a suitable option for less serious methicillin-susceptible S. aureus (MSSA) infections, including skin and soft tissue infections, as stated in 3.
• For patients with methicillin-resistant S. aureus (MRSA) infections, lincosamides (clindamycin, lincomycin) or cotrimoxazole are recommended for less serious infections, according to 3.
• Oral tetracyclines, such as doxycycline, minocycline, and omadacycline, are also effective against skin and soft tissue infections, including those caused by MRSA, as discussed in 4.
• Cephalosporins, particularly third-generation and extended-spectrum cephalosporins like cefdinir, may be considered in penicillin-allergic patients, as the risk of cross-reactivity is less than 1%, as mentioned in 5.

Considerations for Antibiotic Choice

When selecting an antibiotic, factors such as infection severity, local susceptibility patterns, and drug-related safety, tolerability, and cost should be taken into account, as noted in 6.

• The choice of antibiotic should also consider the patient's specific allergy and medical history, as discussed in 7.
• In cases where treatment with penicillins is essential, desensitization may be an option, as mentioned in 7.

Treatment Duration and Expectations

Typically, 5 to 7 days of antibiotic therapy is adequate to achieve cure, with response to therapy expected within the first few days, as stated in 6.