Many dentists will ask you to premedicate before your dental visit because of a heart condition or joint replacement, or even because of an immunodeficiency, but why is this so important? Premedication prior to an appointment is extremely important if you have any type of medical condition that lowers the amount of white blood cells, and can make you more susceptible to an infection. The problem lies in even simple dental cleanings that can temporarily elevate the bacteria in the bloodstream, and attach itself to a heart valve, or compromise the health of the bone attached to the joint that has been replaced. The bacterium, once it has entered your bloodstream, from your gums, is known as Bacterial Endocaditis, and can lead to a fatal infection. The antibiotics weaken the bacteria, before it enters your bloodstream, and makes it easier for your weakened white blood cells to fight.