Medications with known interactions with Keflex include blood thinners, probenecid, and Metformin. Take the full dosage schedule of Keflex, even if you're feeling better in a few days. Cephalexin is a broad-spectrum antibiotic used to treat a wide variety of bacterial infections. Cephalexin is used to treat infections caused by susceptible bacteria sinusitis, respiratory infections, otitis media, skin and soft tissue infections, bone infections, genitourinary tract infections. Keflex is effective antibiotic therapy for skin and skin structure infections and is the most commonly prescribed antibiotic for that reason. The infection. It's important to take the full dosage schedule of Keflex, even if you're feeling better in a few days.