Introduction to General Pharmacology (Pharmacodynamics)
Once a drug is absorbed, it must act. This unit explains Pharmacodynamics—the molecular mechanics of how drugs bind to cellular Receptors (like GPCRs or kinase-linked receptors) to trigger changes inside the cell. It covers crucial charts like the Dose-Response Curve to gauge drug potency and efficacy. Because drugs are rarely perfect, this unit extensively details the dark side of pharmacology: Adverse Drug Reactions (side effects, toxicity, teratogenicity) and Drug Interactions (what happens when a patient takes multiple incompatible pills at once).
Syllabus & Topics
- 1Pharmacodynamics: Principles and mechanisms of drug action.
- 2Receptor theories and classification of receptors (GPCR, Ion channels, Kinase, Nuclear).
- 3Regulation of receptors and Dose-response relationship.
- 4Drug efficacy, Potency, Agonists, Antagonists (Competitive/Non-competitive), Partial agonists.
- 5Therapeutic Index and Drug safety margin.
- 6Adverse drug reactions: Idiosyncrasy, Teratogenicity, Mutagenicity, Carcinogenicity.
- 7Drug interactions: Pharmacokinetic and pharmacodynamic interactions.
- 8Basic concepts of drug discovery and clinical evaluation (Clinical trials Phase I-IV).
Learning Objectives
Frequently Asked Questions (FAQs)
Q1. What is an Agonist versus an Antagonist?
An agonist is a drug that binds to a receptor and produces a biological response because it possesses both affinity and intrinsic activity. An antagonist binds to the receptor but does not produce a response; instead, it blocks or prevents the action of an agonist. Thus, antagonists have affinity but no intrinsic activity.
Q2. Explain the Therapeutic Index (TI).
The Therapeutic Index (TI) is a measure of a drug’s safety margin and is calculated as TI = TD₅₀ / ED₅₀ (toxic dose for 50% of the population divided by effective dose for 50%). A high TI, as seen with Penicillin, indicates a wide margin of safety. A low TI, such as with Digoxin or Warfarin, means small dose changes can cause toxicity, requiring careful dose adjustment and blood monitoring.
Q3. What are Idiosyncratic and Teratogenic Adverse Effects?
An idiosyncratic reaction is an unpredictable, genetically determined abnormal response to a drug, such as hemolytic anemia caused by Primaquine in individuals with G6PD deficiency. A teratogenic effect refers to drug-induced harm to a developing fetus, resulting in congenital malformations, as historically observed with Thalidomide causing phocomelia.
Q4. What is an Enzyme Inducer vs Inhibitor in Drug Interactions?
Some drugs influence hepatic Cytochrome P450 enzymes. Enzyme inducers, such as Rifampin, increase enzyme activity, accelerating metabolism of co-administered drugs and potentially reducing their therapeutic effect. Enzyme inhibitors, such as Erythromycin, decrease enzyme activity, leading to elevated blood levels of other drugs and possible toxicity.