From the Guidelines
For cellulitis caused by streptococcal infection in a patient with penicillin allergy, Keflex (cephalexin) can be used with caution, with a typical adult dose of 500 mg orally four times daily, or 1 gram twice daily, for 7-10 days, as recommended by the Infectious Diseases Society of America 1. However, it is essential to consider the potential cross-reactivity between penicillins and cephalosporins, which is estimated to be around 2% to 4.8% according to a 2022 practice parameter update 1. For patients with severe or immediate-type penicillin allergies, alternative antibiotics like clindamycin (300-450 mg orally four times daily) or doxycycline (100 mg twice daily) would be safer options. The medication should be taken with food if stomach upset occurs, and the full course should be completed even if symptoms improve. Patients should seek immediate medical attention if they develop signs of an allergic reaction such as rash, itching, swelling, severe dizziness, or trouble breathing.
Some key points to consider when treating cellulitis caused by streptococcal infection in patients with penicillin allergy include:
- The use of antibiotics active against streptococci, such as penicillin, amoxicillin, amoxicillin-clavulanate, dicloxacillin, cephalexin, or clindamycin 1.
- A 5-day course of antimicrobial therapy may be as effective as a 10-day course if clinical improvement has occurred by 5 days 1.
- The potential for cross-reactivity between penicillins and cephalosporins, and the need to consider alternative antibiotics in patients with severe or immediate-type penicillin allergies 1.
- The importance of completing the full course of antibiotic therapy, even if symptoms improve, to ensure complete resolution of the infection 1.
From the FDA Drug Label
The usual adult dose is 250 mg every 6 hours For the following infections, a dosage of 500 mg may be administered every 12 hours: streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age.
The dose of Cephalexin (Keflex) for streptococcal cellulitis, which is a type of skin and skin structure infection, is 500 mg every 12 hours in adults, as it falls under the category of skin and skin structure infections. 2
From the Research
Cephalexin Dosing for Streptococcal Cellulitis
- The dose of Cephalexin for streptococcal cellulitis is not explicitly stated in the provided studies 3, 4, 5, 6, 7.
- However, study 4 mentions that patients with uncomplicated skin and skin structure infections, including cellulitis, were treated with cephalexin 250 mg four times daily (QID) for 10 days.
- Study 5 used cephalexin 500 mg four times daily for 7 days to treat uncomplicated cellulitis.
- Study 7 compared the effectiveness of cephalexin, trimethoprim-sulfamethoxazole, and clindamycin for outpatient treatment of cellulitis, but does not specify the dose of cephalexin used.
Considerations for Penicillin Allergy
- Study 3 notes that cross-reactivity between penicillin and cephalosporins is extremely low, estimated at 2% to 3% among patients with a verified penicillin allergy.
- Study 6 confirms that the overall cross-reactivity rate between penicillins and cephalosporins is approximately 1% when using first-generation cephalosporins or cephalosporins with similar R1 side chains.
- Therefore, cephalexin may be a suitable alternative for patients with a penicillin allergy, but caution and careful evaluation are still necessary 3, 6.