Diarrhea can significantly impact the absorption of an oral drug due to its effect on the gastrointestinal (GI) tract. When a person experiences diarrhea, the normal functioning of the GI tract is disrupted, and this can affect the way drugs are absorbed into the body. Here's how diarrhea can influence drug absorption:
Decreased Transit Time: Diarrhea leads to increased motility of the intestines, resulting in a shorter transit time for food and drug substances. As a result, the drug may not spend enough time in the GI tract to be adequately absorbed before being expelled from the body through loose stools. This reduced contact time between the drug and the absorbing surfaces of the intestines can lead to decreased drug absorption.
Reduced Surface Area for Absorption: The small intestine is the primary site for drug absorption in the GI tract, as it provides a large surface area for the drug to cross into the bloodstream. Diarrhea can damage the lining of the intestines or cause inflammation, reducing the effective surface area available for drug absorption. This can result in less drug being absorbed, leading to a potential decrease in therapeutic efficacy.
Changes in pH and Ionization: Diarrhea can alter the pH of the intestines, which may impact the ionization of certain drugs. The ionization state of a drug affects its ability to cross membranes and be absorbed. Changes in pH can lead to altered drug solubility and absorption patterns.
Altered Drug Solubility: Some drugs' solubility is affected by the presence of water in the GI tract. Diarrhea increases the amount of water in the intestines, which can potentially alter the drug's solubility. This can affect how well the drug dissolves and subsequently gets absorbed into the bloodstream.
Effect on Drug Transporters: The GI tract contains various drug transporters that help regulate drug absorption. Diarrhea may affect the expression or function of these transporters, leading to altered drug absorption.
Systemic Changes: Diarrhea can cause dehydration and electrolyte imbalances, which may impact the overall physiology of the body, potentially affecting drug absorption and distribution.
Due to these factors, oral drugs taken during an episode of diarrhea may have reduced bioavailability and efficacy. In some cases, healthcare providers may need to adjust the dosing or consider alternative routes of drug administration (e.g., intravenous) to ensure adequate drug delivery and effectiveness, especially in critical situations where maintaining therapeutic drug levels is essential. If you experience diarrhea while taking medication, it is essential to contact your healthcare provider for guidance on managing your treatment effectively.