1.3 Absorption.docx

1.3 Absorption **Drug Absorption and Administration Routes** **1. Absorption Overview:** - **Absorption** is the initial stage in pharmacokinetics where drugs enter the bloodstream from the site of administration. **2. Common Routes of Administration:** - **Oral**: Swallowed medications...

1.3 Absorption **Drug Absorption and Administration Routes** **1. Absorption Overview:** - **Absorption** is the initial stage in pharmacokinetics where drugs enter the bloodstream from the site of administration. **2. Common Routes of Administration:** - **Oral**: Swallowed medications (e.g., aspirin tablets). These face challenges in the gastrointestinal (GI) tract, including enzyme degradation and the first pass effect in the liver. - **Enteral**: Administered to the GI tract (e.g., NG tube). Similar issues as oral administration, with additional risks of tube complications. - **Rectal**: Administered via suppositories (e.g., acetaminophen). Can be useful if oral administration is not possible but may be less reliable. - **Inhalation**: Medications breathed in (e.g., inhalers). Bypasses the GI tract and liver, allowing for rapid effects, especially in respiratory conditions. - **Intramuscular (IM)**: Injected into muscle (e.g., flu shots). Provides steady absorption but can be painful and cause localized effects. - **Subcutaneous (SC)**: Injected into fat tissue (e.g., insulin). Allows for gradual absorption but can be uncomfortable and cause localized reactions. - **Transdermal**: Applied to the skin (e.g., nicotine patches). Delivers medication steadily over time, avoiding the first pass effect but limited to small molecules. **3. First Pass Effect:** - Oral and enteral medications often undergo significant metabolism in the liver before reaching systemic circulation, reducing their bioavailability. Alternate routes (e.g., IV, transdermal) can bypass this effect. **4. Alternative Routes:** - **Intravenous (IV)**: Delivers medication directly into the bloodstream for immediate effect and complete bioavailability. Risks include pain, infection, and need for sterile technique. - **Transdermal**: Provides a slow and steady drug release but is limited to small molecules. Suitable for long-term medication management (e.g., fentanyl, nitroglycerin). - **Inhalation**: Provides rapid drug delivery, particularly effective for respiratory conditions. New technologies include inhaled insulin powders. **5. Lifespan Considerations:** - **Neonates and Pediatrics**: Immature GI function and liver metabolism can affect drug absorption and metabolism. Increased drug levels in the bloodstream may be observed. - **Older Adults**: Decreased GI blood flow, altered gastric pH, and reduced plasma protein levels can affect drug absorption and metabolism. Reduced fat and blood flow can impact the effectiveness of transdermal patches and injectable medications. **6. Route Considerations:** - **Oral/Enteral**: Convenient but affected by the first pass effect. Variability in absorption based on formulation, stomach acidity, and other factors. - **Parenteral (IM, SC, IV)**: Direct administration into tissues, varying from painful and costly injections to immediate IV access with risks of infection and toxicity. - **Pulmonary Inhalation**: Rapid absorption but dependent on particle size and patient inhalation technique. - **Topical/Transdermal**: Local or systemic effects, with absorption influenced by skin blood flow and drug molecule size.