It does really depend. Some organisms are more hardy, and some areas of the body are harder for antibiotics to reach. One of the most important things though, is that even if you feel completely better after a few days, always take the complete dose of your medicine for the full number of days that you were prescribed. If you don't, some of the bacteria could still be alive, and could make you sick again, or become resistant to the antibiotic you just took.
