The other factor that needs to be considered should be allergic reaction history, the function of liver and kidney, and another medication was taken. If the patient has a history of allergic reaction to the drug, the physician should not use it. Some drug is excreted by the liver and other mostly by the kidney, so the function of both organ should be monitored. A disease of the liver/kidney can decrease the drug clearance.
Some drug might interact with the antibiotic and increase its toxicity.