What antibiotic is recommended for a skin infection in a patient with an allergy to penicillin, considering Keflex (Cephalexin) as a potential option?

From the Guidelines

If you have a penicillin allergy and need an antibiotic for a skin infection, Keflex (cephalexin) is not the safest choice due to the risk of cross-reactivity, and alternative antibiotics such as clindamycin, doxycycline, or trimethoprim-sulfamethoxazole should be considered instead. According to the 2022 practice parameter update on drug allergy 1, the cross-reactivity between penicillins and cephalosporins is lower than previously thought, with a rate of around 2-4.8% in patients with confirmed penicillin allergies. However, this still poses a significant risk, especially for patients with a history of severe reactions like anaphylaxis.

Some key points to consider when choosing an alternative antibiotic include:

• The type and severity of the skin infection
• Local resistance patterns
• The patient's medical history, including the nature of their penicillin allergy
• The potential for cross-reactivity with other beta-lactam antibiotics, as outlined in TABLE XII of the study 1

Alternative treatment options for skin infections in patients with penicillin allergies may include:

• Clindamycin (300-450mg orally four times daily for 7-10 days)
• Doxycycline (100mg twice daily for 7-10 days)
• Trimethoprim-sulfamethoxazole (one double-strength tablet twice daily for 7-10 days) These options may be preferred over cephalosporins like Keflex due to their lower risk of cross-reactivity and potential for effective treatment of skin infections, as suggested by the study 1.

From the FDA Drug Label

Clindamycin is also indicated in the treatment of serious infections due to susceptible strains of streptococci, pneumococci, and staphylococci Its use should be reserved for penicillin-allergic patients or other patients for whom, in the judgment of the physician, a penicillin is inappropriate. Anaerobes: Serious respiratory tract infections such as empyema, anaerobic pneumonitis, and lung abscess; serious skin and soft tissue infections; Streptococci: Serious respiratory tract infections; serious skin and soft tissue infections. Staphylococci: Serious respiratory tract infections; serious skin and soft tissue infections.

For a patient with a skin infection who is allergic to penicillin, clindamycin may be considered as an alternative antibiotic option, as it is indicated for the treatment of serious skin and soft tissue infections caused by susceptible strains of streptococci, staphylococci, and anaerobes 2.

• Key considerations:
  • Bacteriologic studies should be performed to determine the causative organisms and their susceptibility to clindamycin.
  • The use of clindamycin should be reserved for penicillin-allergic patients or other patients for whom a penicillin is inappropriate.
  • The risk of colitis associated with clindamycin should be considered, and less toxic alternatives should be evaluated before selecting clindamycin. Keflex (cephalexin) is a penicillin-like antibiotic and may not be suitable for patients with a penicillin allergy.

From the Research

Skin Infection Antibiotic Alternatives

If a patient is allergic to penicillin, alternative antibiotics can be considered for skin infections.

• Cephalexin (Keflex) is a commonly used antibiotic for skin and soft-tissue infections, including streptococcal and staphylococcal infections 3.
• However, it is essential to note that patients with a penicillin allergy may also be allergic to cephalosporins, although the cross-reactivity is lower with newer generation cephalosporins 4, 5.
• For patients with a low risk of severe allergic reactions, cephalosporins like cephalexin may be a relatively safe treatment option 5.

Assessment and Prescribing

When assessing a patient's penicillin allergy, it is crucial to consider the severity and type of reaction, as well as the time elapsed since the reaction occurred 5.

• Patients with a history of delayed non-severe reactions, such as mild childhood rashes, may be suitable for an oral rechallenge with low-dose penicillin in a supervised hospital environment 5.
• Penicillin skin testing and graded challenge can also be used to assess the patient's allergy and determine the safest course of treatment 4, 6, 7.

Considerations for Keflex Prescription

Before prescribing Keflex (cephalexin) to a patient with a penicillin allergy, consider the following:

• The patient's allergy history and severity of reaction 4, 5.
• The potential for cross-reactivity with cephalosporins 4, 5.
• Alternative treatment options, such as other antibiotics or desensitization protocols 7.