Receptor theories explain how drugs produce effects by binding to receptors and activating or blocking them. Receptor Theories These theories explain how drugs interact with receptors and how this leads to a response: Historically, various theories have been proposed to explain how drugs interact with receptors and elicit responses: Occupancy Theory (Clark’s Theory) The intensity … Read more
Pharmacodynamics Pharmacodynamics refers to what the drug does to the body – including the biochemical and physiological effects of drugs and their mechanisms of action. Principles of Drug Action Stimulation Increases the activity of a specific organ or system. Example: Adrenaline stimulates β1-receptors to increase heart rate and contractility. Depression Decreases the activity of a … Read more
Absorption of Drugs refers to the process by which a drug enters the bloodstream from its site of administration. Factors Affecting Absorption: Route of Administration: Oral, IV, IM, subcutaneous, transdermal, inhalational, etc. IV route bypasses absorption as the drug is delivered directly into the bloodstream. Physicochemical Properties of the Drug: Solubility (lipid vs. water solubility) … Read more
Allergy (Drug Hypersensitivity) is an abnormal immune reaction to a drug, causing effects like rash, swelling, or anaphylaxis. Definition of Drug Hypersensitivity: A drug allergy is an immune system-mediated adverse drug reaction. It can occur at low doses, is unpredictable, and is not related to the pharmacologic action of the drug. Types of Hypersensitivity Reactions … Read more
Distribution is the reversible transfer of a drug from the bloodstream to various tissues and organs. Once absorbed, drugs distribute throughout the body, moving into different tissues and fluids. Distribution depends on: Blood Flow (Perfusion Rate) Organs with higher blood flow (brain, liver, kidneys) get drug supply more rapidly. Skeletal muscle, adipose tissue, and skin … Read more
Metabolism of drugs involves enzymatic conversion into active or inactive metabolites for easier elimination. Definition to Metabolism of drugs: It is the process by which drugs are chemically altered (usually in the liver) to make them more water-soluble for excretion. Sites: Primary: Liver (most important). Others: Kidney, lungs, intestines, plasma. Phases of Metabolism: Phase I … Read more
Enzyme induction and inhibition alter drug metabolism, affecting drug activity, duration, and interactions. Enzyme Induction: Certain drugs increase the activity of CYP450 enzymes. Leads to faster metabolism of the drug and/or other drugs. Effect: Reduced plasma levels and therapeutic effect. Examples of Enzyme Inducers: Rifampin Phenobarbital Carbamazepine Phenytoin Enzyme Inhibition: Some drugs inhibit CYP450 enzymes. … Read more
Excretion of drugs is the process of eliminating drugs and metabolites mainly via kidneys, bile, or lungs. Excretion of Drugs Excretion is the process by which the drug or its metabolites are removed from the body. Renal Excretion (most common) Glomerular Filtration: Depends on the free drug fraction in plasma (unbound drug is freely filtered). … Read more
Kinetics of drug elimination explains how drugs are removed from the body, following zero or first-order processes. Drug elimination kinetics describe how the concentration of a drug decreases over time. Clearance and Half-Life Clearance (CL): The volume of plasma completely cleared of drug per unit time (mL/min or L/hr). Total body clearance is the sum … Read more
Idiosyncrasy in pharmacology refers to an unusual and unpredictable drug reaction that is not dose-dependent and often genetically determined. Such drug responses vary among individuals, where most patients tolerate the medicine, but certain susceptible people may experience harmful effects. For example, Primaquine can cause hemolysis in individuals with G6PD deficiency, highlighting how genetic factors influence … Read more
