No. Keflex is a cephalosporin antibiotic which is chemically related to a penicillin. It does not contain a sulfa group in its structure, so it is not a sulfa drug.
The short answer is no. According to Wikipedia, this is part of the tetracycline class of antibiotics. They are not chemically related to Penicillins or Sulfates. However, one should always consult...
cranberries do contain sulfa. Sulfa is used in anti-biotics. Cranberry juice contains sulfa which is also a drug used in the manufacture of anti-biotics