What happens if I just took cephalexin 500 mg. again after the first one 4 hours ago. This is my?

three times a day usually means 06h00, 12h00, 18h00 that is 6 hours apart. taking one dose early should be ok but dont do it again and if you feel anything unusual go to a doc or pharmacist. good luck

Ideally you would want to take them every 8 hours. For three times a day, you are dividing the 24 hours in a day by 3 and that comes out to every 8 hours. For some people this is not feasable or they dont choose to get up in the night. In that case, you want to space doses at least 4 hours apart. For best results, every 8 hours is best though. This keeps the blood drug levels at a more continuous level.