Antibiotics are medications designed to treat bacterial infections. While highly effective, they frequently cause gastrointestinal upset, with diarrhea being one of the most common side effects. This reaction, known as antibiotic-associated diarrhea (AAD), occurs in approximately 5% to 35% of adults taking these drugs. AAD can range from a mild inconvenience to a serious medical problem, making management crucial for patients to complete their necessary course of treatment.
How Antibiotics Affect Gut Health
Antibiotics are often non-selective, killing both the harmful bacteria causing the infection and the large populations of beneficial bacteria residing in the gut. This mass elimination disrupts the delicate balance of the gut microbiota, a condition known as dysbiosis.
The gut’s microbial community is responsible for fermenting undigested food particles. When beneficial bacteria are significantly reduced, the process of carbohydrate metabolism changes, and excess carbohydrates remain in the intestinal lumen.
This accumulation of undigested material increases the osmotic load within the colon, drawing more water into the bowel. The resulting excess water content leads to the characteristic loose, watery, and frequent stools associated with AAD. This mild diarrhea typically begins within hours or days of starting the medication and often resolves shortly after treatment is completed.
Managing Diarrhea While Taking Medication
For mild to moderate AAD, patients can take specific steps to help restore balance and manage symptoms. Probiotic supplements, which contain live microorganisms, help reduce the risk of AAD. Strains like Saccharomyces boulardii or Lactobacillus rhamnosus GG are often recommended.
When taking probiotics, it is important to space consumption from the antibiotic dose by at least two hours. This timing prevents the antibiotic from killing the beneficial bacteria before they can colonize the gut. Starting the probiotic at the same time as the antibiotic and continuing for at least a week after the course finishes is generally advised.
Dietary adjustments can also help soothe the irritated digestive tract and firm up stools. Temporarily focusing on bland, easily digestible foods can be beneficial:
- Rice
- Bananas
- Applesauce
- Toast
Avoiding foods high in fat, excessive spice, or poorly absorbed fibers may reduce symptom severity. Maintaining hydration with water, broths, and electrolyte-containing beverages is also important, as diarrhea causes a loss of fluid and electrolytes.
Identifying Serious Complications
While most AAD is mild and self-limiting, certain symptoms indicate a serious underlying complication requiring immediate medical attention. These red flags include persistent, severe, watery diarrhea, especially when accompanied by a fever or intense abdominal cramping. Passing blood or pus in the stool, or experiencing signs of severe dehydration like dizziness or dark urine, also requires prompt medical evaluation.
The most concerning complication is an infection with the bacterium Clostridioides difficile (C. diff). Antibiotic-induced dysbiosis allows C. diff to overgrow and produce toxins that cause severe inflammation. C. diff infection accounts for a significant portion of serious AAD cases and can lead to life-threatening conditions. If severe symptoms develop or diarrhea persists for more than two days, medical evaluation is necessary to test for this infection.