Questions
3–5 questions per semester paper
Difficulty
Medium-Hard
Importance
Essential core knowledge for clinical rotations and licensing exams
Overview
General Pharmacology is the foundation of clinical medicine and pharmacy, focusing on the interactions between drugs and biological systems. It covers how the body processes substances (Pharmacokinetics) and how drugs exert their effects (Pharmacodynamics), which are critical for safe therapeutic decision-making in any health profession.
Pharmacokinetics (ADME)
Pharmacokinetics describes the movement of a drug through the body, summarized by the acronym ADME: Absorption, Distribution, Metabolism, and Excretion. Understanding these processes is essential to determine drug dosage, frequency, and the route of administration for optimal efficacy.
- Absorption: Movement of drug from site of administration into the systemic circulation
- Bioavailability (F): The fraction of unchanged drug that reaches systemic circulation
- Volume of Distribution (Vd): Extent of drug distribution into body tissues
- First-pass metabolism: Hepatic degradation of oral drugs before reaching systemic circulation
- Zero-order kinetics: Constant amount of drug eliminated per unit time
- First-order kinetics: Constant fraction of drug eliminated per unit time
Pharmacodynamics
Pharmacodynamics explores the biochemical and physiological effects of drugs on the body and their mechanisms of action. This includes the study of drug-receptor interactions, dose-response relationships, and the therapeutic index, which dictates the safety profile of any medication.
- Agonist: Drug that binds to a receptor and activates it
- Antagonist: Drug that prevents the activation of a receptor
- Therapeutic Index: Ratio of Toxic Dose (TD50) to Effective Dose (ED50)
- Potency: Concentration of drug required to produce 50% of maximal effect (EC50)
- Efficacy: Maximum effect (Emax) a drug can produce
- Spare receptors: Receptors remaining unoccupied when maximal effect is achieved
Drug Interactions
Drug interactions occur when the pharmacological effect of one drug is altered by the concomitant administration of another drug, food, or environmental factor. Recognizing these interactions is vital to prevent adverse events and therapeutic failure in polypharmacy settings.
- Pharmacokinetic interaction: Interference with absorption, distribution, metabolism, or excretion
- Pharmacodynamic interaction: Drugs acting on the same or opposing physiological systems
- Enzyme Induction: Increased metabolism leading to decreased therapeutic effect
- Enzyme Inhibition: Decreased metabolism leading to potential toxicity
- Synergism: Combined effect is greater than the sum of individual effects (1+1=3)
- Antagonism: Combined effect is less than the sum of individual effects
Formula Sheet
Vd = Amount of drug in body / Plasma drug concentration
Half-life (t1/2) = 0.693 / Ke
Therapeutic Index = TD50 / ED50
Loading Dose = (Target concentration * Vd) / Bioavailability
Exam Tip
Always draw the semi-logarithmic dose-response curve when discussing Potency and Efficacy, as examiners highly value graphical representation.
Common Mistakes
- Confusing Potency with Efficacy in exam definitions
- Mixing up Enzyme Induction with Enzyme Inhibition regarding drug plasma levels
- Failing to mention the 'first-pass effect' when discussing oral bioavailability
More Revision Notes
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