susan has an ear infection. The doctor prescribes a course of antibiotics. Susan is told to take 250mg dose of the antibiotic regularly every 12 hours for 20 days. Susan is curious and wants to know how much of the drug will be in her body over the course of the 20 days. She does some research online and finds out that at the end of 12 hours, about 4% of the drug is still in the body.