Peter asks:
Why do oral antibiotics cause diarrhea? Why do doctors not prescribe anti diarreal medicines such as Imodium or Kaolin and Morphine to counteract the undesirable side effect of getyting a bad dose of the runs when taking helpful antibiotic medicine?
Dr. Adams responds:
Oral antibiotics (or IV) usually will not cause diarrhea. There are many antibiotics available for prescription. Some are oral, others are intravenous (IV). Certain classes of antibiotics will be more likely to cause diarrhea than other classes. And to make things even more confusing, certain antibiotics are indicated to treat antibiotic-induced diarrhea.
To give you some more info as to how antibiotics could cause diarrhea.....remember that antibiotics kill bacteria. Also keep in mind that we have millions of natural bacteria in our colons. If these bacteria are destroyed (as does occur by most antibiotics), other bacteria which do not belong in our colons can grow and create havoc. One bacteria which can do this is Clostridium difficile. The diarrhea caused by C. difficile is known as pseudomembranous colitis, and is sometimes called C. diff colitis. After a course of antibiotics, our natural bacterial flora will be depleted, C. diff will take hold, start to grow, and create a pseudomembrane on the lining of the colon. The result will be profuse infectious diarrhea. So this is the basic on how an antibiotic could cause diarrhea.
Why do we not prescribe anti-diarrheal medications in the setting of pseudomebranous colitis (C. diff diarrhea)? The answer is because anti-diarrheal medications would only make the problem worse. C. diff secretes a toxin, and the last things you want is the toxin to increase and worsen the infectious and inflammatory process. Anti-diarrheal medicines will allow the C diff toxin to build up and the infectious process will worsen. Thus, anti-diarrheals are not used to treat antibiotic induced diarrhea. Rather, you would want the patient to pass the infectious toxins via the diarrhea.
What do we use to treat C. diff colitis? There are two main antibiotics that are used. They are Metronidazole and Vancomycin. Both of these antibiotics work well to kill C. diff and to treat the associated colitis.
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Dr. Adams is a resident in the Department of Internal Medicine at North Shore University Hopsital in Manhasset, NY. Got a question for him?