Drug Absorption (PK) PDF

## Drug Absorption (PK) ### Route of Administration * Intravenous * Oral * Subcutaneous * Inhalation * Topical * Rectal ### Mechanism of Absorption * **Passive Diffusion:** Movement of drug across cell membranes from high to low concentration. * **Facilitated diffusion:** Movement of drug with...

## Drug Absorption (PK) ### Route of Administration * Intravenous * Oral * Subcutaneous * Inhalation * Topical * Rectal ### Mechanism of Absorption * **Passive Diffusion:** Movement of drug across cell membranes from high to low concentration. * **Facilitated diffusion:** Movement of drug with the help of carrier proteins. * **Active transport:** Movement of drug against concentration gradient requiring energy. * **Pinocytosis:** Uptake of drug by invagination of cell membrane. ### Factors Affecting Absorption * **PH:** Changes in PH can alter the ionization state of the drug, affecting its absorption. * **Blood Flow:** Increased blood flow to the absorption site increases the rate of absorption. * **Total Surface Area (TSA) and Contact Time:** A larger surface area and longer contact time increase absorption rate. ### Bioavailability * Bioavailability describes the fraction of administered drug that reaches systemic circulation unchanged, expressed as a percentage. The graph below shows the relationship between drug concentration ([drug]) and time. ### Factors Affecting Bioavailability * **Solubility:** The solubility of the drug can significantly affect its absorption. * **Instability:** Drugs that are chemically unstable can degrade in the gastrointestinal tract, decreasing their absorption. * **First Pass Effect:** This refers to the metabolism of a drug during its first pass through the liver, reducing its bioavailability. ### P-Glycoprotein * P-Glycoprotein is a transporter protein that pumps drugs out of cells. * It is present in various tissues, including the gastrointestinal tract, liver, and kidneys. * It can reduce the absorption and bioavailability of some drugs.