Pharmacology Pharmacokinetics Quiz

Pharmacology: What the Body Does to Drugs (Pharmacokinetics)

• Pharmacology studies drug actions on the body (pharmacodynamics) and what the body does to drugs (pharmacokinetics).
• Pharmacokinetics describes how drugs are absorbed, distributed, metabolized, and excreted.
• Absorption refers to how drugs enter the body, tissues, and cells. Factors affecting absorption include physiochemical properties of the drug, environmental factors, membrane surface area, blood flow, presence of transporters, concentration gradients, pH, food, gastric emptying, age, genetic variation, health status, and diet.
• Distribution describes where drugs go in the body. This process is influenced by: plasma protein binding, lipophilicity, compartmental barriers (e.g., the blood-brain barrier) and the presence of transporters.
• Metabolism describes the chemical changes that occur to a drug in the body. There are three main types: oxidative, reductive, and conjugative.
• Excretion describes how the drug leaves the body.

Measuring and Calculating Drug Concentrations

• Drug concentrations are measured in moles/liter to determine the amount of drug present.
• A mole (mol) is 6.023 x 1023 molecules of a substance.
• Techniques like liquid-chromatography mass spectrometry (LC-MS) separate and quantify different compounds within a mixture.

Pharmacokinetic Parameters:

• Area under the curve (AUC): Represents total drug exposure.
• Half-life (t1/2): Time required for the drug concentration to decrease by half.
• Cmax: Maximum drug concentration in the body.
• Tmax: Time to reach maximum concentration.

How Drugs Work (Pharmacodynamics)

• Drugs work by interacting with cellular targets, affecting DNA, RNA, protein receptors, and enzymes.
• These interactions can activate or inhibit cellular function, alter gene expression, or stabilize/degrade proteins.
• Drugs can bind to specific receptors, which are often located on the cell membrane.

Types of Cellular Targets:

• Enzymes: Drugs can interact with enzymes by inhibiting or activating their activity. E.g., statins inhibit the enzyme HMG-CoA reductase, reducing cholesterol synthesis in the liver.
• Receptors: Drugs can bind to receptors, which are proteins that mediate cellular responses.
  • Ligand-gated ion channels: Ligand binding opens ion channels, allowing ions to flow across the membrane.
  • G-protein coupled receptors (GPCRs): A significant drug target, GPCRs initiate signaling pathways within cells. When an agonist binds to a GPCR, it triggers a cascade of events, involving the release of GDP and replacement with GTP, activation of downstream signaling pathways, and ultimately, the activation of target proteins.
  • Enzyme-linked receptors: These receptors have a domain for ligand binding and a catalytic domain that mediates phosphorylation (adding a phosphate group). This process can activate a cascade of downstream signaling events.
  • Nuclear receptors: These receptors are not membrane-bound and reside in the cytosol or nucleus. Ligand binding triggers their translocation to the nucleus and binding to DNA, ultimately regulating gene expression.

Receptor Summary

• There are various types of receptors, each with unique mechanisms of action.
• Understanding receptor function is essential for understanding how drugs work and their therapeutic effects.

Test your understanding of pharmacokinetics in pharmacology, focusing on how the body absorbs, distributes, metabolizes, and excretes drugs. Explore the various factors influencing these processes and the implications of drug actions within the body.