GI disease and drug absorption Flashcards
Explain intestinal drug absorption
The small intestine is the primary site of drug absorption because it has a large surface area, which allows for efficient absorption of drugs. The inner lining of the small intestine is composed of millions of tiny finger-like projections called villi, which are covered in even smaller hair-like structures called microvilli. These structures increase the surface area of the small intestine and provide a large area for drug absorption.
Drug absorption occurs through several mechanisms, including passive diffusion, facilitated diffusion, active transport, and endocytosis. Passive diffusion is the most common mechanism and involves the drug moving from an area of high concentration to an area of low concentration across the intestinal wall. Facilitated diffusion occurs when a carrier protein assists in the movement of the drug across the intestinal wall. Active transport is a process that requires energy and involves the movement of the drug against its concentration gradient. Finally, endocytosis is a mechanism in which the drug is engulfed by the intestinal cell and transported into the body.
What patient factors could affect intestinal drug absorption
Age: Intestinal drug absorption can be affected by age-related changes in the gastrointestinal tract. For example, as people age, the surface area of the intestinal lining may decrease, which can reduce the efficiency of drug absorption.
Genetics: Genetic variations can affect the expression and activity of drug transporters and enzymes in the gastrointestinal tract, which can influence drug absorption. For example, some individuals may have variations in genes that affect the expression of P-glycoprotein, a transporter that pumps drugs out of intestinal cells and back into the lumen of the intestine, reducing their absorption.
Disease states: Certain disease states can affect intestinal drug absorption. For example, conditions that cause inflammation or damage to the intestinal lining, such as inflammatory bowel disease or celiac disease, can reduce the efficiency of drug absorption.
Gastrointestinal motility: The rate of gastrointestinal motility can affect drug absorption in patients with conditions that affect the motility of the gastrointestinal tract, such as irritable bowel syndrome or gastroparesis.
Nutritional status: Nutritional deficiencies, such as vitamin deficiencies or malnutrition, can affect intestinal drug absorption by altering the pH of the stomach and small intestine or by reducing the surface area of the intestinal lining.
Drug interactions: Finally, drug interactions with other medications or substances can affect intestinal drug absorption in patients. For example, drugs that reduce gastric acid secretion, such as proton pump inhibitors, can increase the pH of the stomach and reduce the solubility of certain drugs, reducing their absorption.
How can GI disease affect intestines
Inflammatory bowel disease (IBD), such as Crohn’s disease and ulcerative colitis, can lead to changes in the intestinal epithelium, resulting in decreased drug absorption. This is because the inflammation can disrupt the tight junctions between the epithelial cells, which can lead to increased permeability of the intestine and reduced absorption of drugs. Additionally, the presence of diarrhea in these conditions can cause rapid transit of drugs through the intestine, resulting in reduced exposure time for absorption.
Celiac disease, a condition in which individuals are unable to tolerate gluten, can also affect drug absorption. The damage to the intestinal villi that occurs in celiac disease can decrease the surface area available for drug absorption, leading to reduced bioavailability of some drugs.
Other GI diseases, such as gastroesophageal reflux disease (GERD) and peptic ulcer disease, can also affect drug absorption. In these conditions, changes in the pH of the stomach can alter the solubility and stability of drugs, leading to reduced absorption.
Furthermore, certain medications used to treat GI diseases can also affect drug absorption. For example, proton pump inhibitors (PPIs) used to treat GERD can decrease the acidity of the stomach, which can affect the absorption of drugs that require an acidic environment for dissolution and absorption.
