According to Drugs.com, Cephalexin does not contain penicillin. It is a cephalosporin antibiotic. It is mainly prescribed to treat urinary tract infections, upper respiratory infections, skin infections and ear infections.
Although it is in a different class of antibiotics from penicillin, some individuals may still have an allergic reaction to the medication, states Drugs.com. Signs of an allergic reaction include swelling of the face and throat and difficulty breathing. Other serious side effects include seizures, confusion, unusual weakness, vomiting and diarrhea.
According to MedlinePlus, Cephalexin is available in tablet, capsule or liquid form. Doctors usually direct patients to take the medication for seven to 10 days.