According to AboutKidsHealth, it may take several days before cephalexin improves the symptoms of the condition for which it is prescribed. It may take several days after that before the full benefit of the medication is seen. Keflex is a brand name for the antibiotic cephalexin.
AboutKidsHealth says that it is important to take the entire prescription of cephalexin, even if the symptoms go away before finishing the medication. WebMD explains that cephalexin is an antibiotic used to treat a wide variety of bacterial infections. Cephalexin is commonly used to treat ear, throat and urinary tract infections. Diarrhea is a common side effect of the medication.