Nitrofurantoin is a commonly prescribed antibiotic used primarily to treat and prevent urinary tract infections (UTIs). It functions by stopping the growth of bacteria in the urinary tract, but like most antibiotics, it can affect other systems in the body. Diarrhea is a recognized side effect, though this digestive disturbance is generally temporary and mild.
How Often Diarrhea Occurs
The incidence of diarrhea attributed to nitrofurantoin is relatively low compared to other antibiotics, affecting approximately 1% to 6% of patients in clinical trials. Nausea and vomiting are more commonly reported gastrointestinal side effects than diarrhea with this medication. Gastrointestinal symptoms usually begin early in the course of treatment, often within the first few days of starting the medication.
Most cases of diarrhea are mild, characterized by loose stools that are self-limiting and resolve during treatment or shortly after completion. If mild symptoms occur, staying well-hydrated is important to replace lost fluids and electrolytes. It is advised not to use over-the-counter anti-diarrhea medicines without consulting a healthcare professional.
The Mechanism Behind Antibiotic-Associated Diarrhea
Antibiotics, including nitrofurantoin, can cause diarrhea through gut microbiota disruption, also known as dysbiosis. The medication kills the harmful bacteria causing the UTI, but it is not perfectly selective and also kills beneficial bacteria residing in the large intestine. These helpful bacteria maintain a balanced gut environment and aid in the digestion of certain carbohydrates.
When the population of beneficial gut bacteria is reduced, the digestive process becomes altered. This imbalance can lead to osmotic diarrhea because the colon is unable to properly absorb water and nutrients, resulting in loose stools. The disruption also allows naturally resistant bacteria or opportunistic pathogens to overgrow, which can further irritate the bowel lining.
Distinguishing Mild Diarrhea from a Serious Infection
It is important to distinguish between typical, mild antibiotic-associated diarrhea and a severe complication, such as a Clostridioides difficile (C. diff) infection. C. diff is a bacterium that takes advantage of the disrupted gut environment and produces toxins that cause inflammation in the colon. This infection can range from moderate to life-threatening.
Immediate medical attention is necessary if diarrhea is severe (occurring 10 to 15 times a day) or accompanied by concerning symptoms. Warning signs include fever, persistent or worsening abdominal pain and cramping, and the presence of blood or pus in the stool. These severe symptoms may appear while taking the antibiotic or up to two months after finishing the course of medication. If these signs develop, contact your healthcare provider immediately; do not stop the medication or take anti-diarrhea drugs without their instruction.