Downsides

If you are between the ages of 18 and 60, do not take any other medications, and have no other medical conditions, you are more likely to experience the following side effects:

• The most commonly reported symptoms are diarrhea, dyspepsia, abdominal pain, and nausea. Some laboratory tests may be affected. Seizures have only been reported in a few cases.
• Cephalosporins are also allergic to about 10% of people who are allergic to penicillin. Tell your doctor if you've ever had an antibiotic allergy.
• Positive direct Coombs tests have been reported in patients receiving cephalosporin antibacterials such as cephalexin.
• Cephalexin dosage must be adjusted for people with moderate-to-severe kidney disease.
• Severe diarrhea, caused by Clostridium difficile overgrowth, is a potential side effect of almost all antibacterial agents, including cephalexin. Diarrhea that is persistent, watery, and sometimes bloody is one of the symptoms.
• It may lengthen the time it takes for blood to clot. People who have liver or kidney disease, are malnourished, are on a long course of therapy, or are already on anticoagulants are more vulnerable.
• Some drugs, including metformin, probenecid, and some urinary glucose tests, may interact.

Note: People over the age of 65, children, people with certain medical conditions (such as liver or kidney disease, heart disease, diabetes, seizures), or people who take other medications are more likely to experience a broader range of side effects.