Understanding the Absorption of Oral Drugs.docx

**Understanding the Absorption of Oral Drugs** When you administer a drug orally, the journey it takes through the body starts with absorption. Absorption is a critical phase in pharmacokinetics---the study of how drugs move through the body. Understanding this process is essential for safe and eff...

**Understanding the Absorption of Oral Drugs** When you administer a drug orally, the journey it takes through the body starts with absorption. Absorption is a critical phase in pharmacokinetics---the study of how drugs move through the body. Understanding this process is essential for safe and effective patient care. Let\'s dive into the key concepts. **I. Advantages of the Oral Route** **Why Oral Drugs?** - **Safety:** Oral administration is generally the safest way to deliver medication. - **Convenience:** It\'s easy and requires no special equipment. - **Cost-Effective:** Oral drugs are often the most economical option for patients. **II. Gastrointestinal (G.I.) Absorption: The Process** **A. How Oral Drugs Are Absorbed** For most oral medications, absorption begins in the gastrointestinal (G.I.) tract. Here\'s how the process unfolds: 1. **Dissolution:** The drug dissolves in the G.I. fluids. 2. **Membrane Passage:** It passes through the G.I. membrane. 3. **Interstitial Fluid:** The drug dissolves in interstitial fluid. 4. **Capillary Membrane:** Finally, it passes through the capillary membrane to enter the bloodstream. **B. Importance of Absorption** - **Rate and Extent:** How quickly and how much of the drug is absorbed affects its effectiveness. - **Bioavailability:** This term refers to the percentage of the administered drug that actually reaches the bloodstream or the target body system. **III. Factors Affecting Bioavailability (Absorption)** **A. Drug Form or Preparation** - **Capsules:** How fast a capsule disintegrates affects absorption. - **Tablets:** Starch or buffers in tablets help them expand and break apart. - **Film/Sugar Coatings:** These dissolve quickly in the stomach. - **Enteric Coatings:** Designed to dissolve in the intestine, not the stomach. *Do not crush or break these!* - **Sustained/Delayed Release Forms:** These should not be crushed or chewed. Doing so could cause a rapid release and potential overdose. - **Soluble Liquid Forms:** Generally more bioavailable than solid forms. - **Non-Soluble Liquids:** These are cloudy and suspended; absorption is slow or doesn't occur. **B. Nature of the Absorbing Surface** - **Cell Membranes:** Drugs pass through the mucosal lining of the stomach or small intestine into interstitial fluid and then into the bloodstream. - **Membrane Composition:** Membranes are primarily made of lipids (fats) and proteins. Some drugs dissolve in these lipids to pass through the membrane. - \*\*Lipid-Soluble Drugs:\*\* These dissolve in the lipid material of the cell membrane and pass through more easily. The higher the drug concentration, the faster it diffuses into the bloodstream. - **Water-Soluble Drugs:** These are ionized (carry an electrical charge) and move through small pores in the membrane. Their absorption is generally slower compared to lipid-soluble drugs because the pores might repel them based on their charge. **C. Chemical and Physical Characteristics of the G.I. System** - **pH Levels:** The stomach is acidic, while the intestine is alkaline. The drug's ionization depends on the pH, which affects how well it dissolves and is absorbed. - **Non-Ionized (Lipid-Soluble):** Passes easily through membranes but is harder to dissolve in fluids. - **Ionized (Water-Soluble):** Dissolves easily but passes through membranes less readily. - **Surface Area for Absorption:** The small intestine has a large surface area due to its length, folds, and villi, making it the primary site for drug absorption. The stomach has a smaller surface area, leading to less absorption. **D. Food and Other G.I. System Factors** - **Food Interactions:** Some drugs interact with food or other substances, reducing their absorption. - **Digestive Enzymes:** Insulin, for example, is broken down by digestive enzymes and cannot be given orally. - **Stomach Emptying:** Delays in stomach emptying (due to fatty foods or lying on the left side) slow down absorption, while rapid emptying (due to laxatives) limits absorption time. - **pH Changes:** Foods or drugs that change the pH of the stomach or intestine can alter where and how well a drug is absorbed. - **Fasting:** Prolonged fasting can cause vasoconstriction of blood vessels in the G.I. tract, delaying drug absorption. **Key Takeaways** Understanding how oral drugs are absorbed is crucial in pharmacokinetics. The form of the drug, the environment of the G.I. tract, and even the presence of food can all influence how much and how quickly a drug is absorbed. As a nursing student, recognizing these factors will help you better anticipate the effects of medications and ensure that your patients receive the intended therapeutic outcomes.