Prescriptions: Complying with the Doctor's Orders (cont.)

Effects of Medicines on Disease

Medicines have different purposes in treating illnesses, including:

  • quieting and stopping the illness;

  • keeping the illness inactive;

  • preventing new illnesses; and

  • treating the symptoms of illnesses (such as pain).

For each of these purposes the medicines must be taken according to the doctor's directions in order for the patient to benefit. If the medication is inappropriately taken or discontinued, illnesses can persist unnecessarily, inactive illness can become active again, complications of the illness can develop, or an illness that was being prevented may occur.


The effectiveness of antibiotics to kill bacteria in the body depends on continuous, adequate concentrations of the antibiotics in the blood. Only adequate concentrations of the antibiotic will kill the bacteria in the tissues that are infected (for example, the ears, sinuses, throat, lungs, skin, etc.). If the antibiotic is not taken in adequate doses or doses are not taken regularly, the bacteria can survive and multiply. The infection can then persist unnecessarily and complications of the infection can develop.

Also, if the entire prescribed course of antibiotics is not completed, the bacteria may only be reduced in numbers, not eradicated, and the infection may return in full force after the antibiotics are stopped. Another potentially serious response to an incomplete course of antibiotics is bacterial resistance. Bacterial resistance occurs when a small number of bacteria survive because the course of antibiotics was not completed. The bacteria that survive are likely to be resistant to the antibiotic, that is, they have developed ways to block the effect of the antibiotic. When the antibiotic is next used, for example, to treat the infection when it recurs, the antibiotic is no longer effective. In this situation, the next infection can be more serious and it may be necessary to change to other antibiotics to stop the infection.

Timing of Medications

Although the timing of medicines is often dictated by the need to maximize benefits and limit side effects, doctors also might specify particular timing of doses and length of treatment in order to avoid interactions with other medicines. In addition, certain procedures or tests may require special timing of the prescribed medicines. Finally, doctors may recommend that medicines be discontinued because they may interfere with certain procedures or tests. Not heeding the doctor's directions could lead to side effects from interactions with medications or complications from a procedure or test.

Medically Reviewed by a Doctor on 12/9/2014

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