Those allergic to penicillin should use caution when taking Keflex, as allergic reactions to the drug occur in up to 10 percent of individuals with penicillin allergies, cite the medical experts at RxList. Patients are advised to discuss any concerns about allergic reactions beforehand with their doctor.
The cephalosporin antibiotic is prescribed to treat a variety of bacterial infections. Signs of allergic reactions to Keflex include rash, itching and hives. Difficulty breathing and swelling of the lips, tongue or throat may also occur, according to RxList. Patients experiencing any of these symptoms are advised to stop taking Keflex and seek medical attention immediately.