Pharmacology Cheat Sheet

The core ideas of Pharmacology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Pharmacokinetics

The study of how the body processes a drug over time, encompassing absorption, distribution, metabolism, and excretion (ADME). Pharmacokinetics determines the onset, duration, and intensity of a drug's effect by modeling how drug concentrations change in various body compartments.

Pharmacodynamics

The study of the biochemical and physiological effects of drugs on the body and their mechanisms of action. Pharmacodynamics examines how drugs bind to receptors, alter enzyme activity, or disrupt cellular processes to produce therapeutic or toxic effects.

Dose-Response Relationship

The quantitative relationship between the dose of a drug administered and the magnitude of its pharmacological effect. This relationship is typically represented by a sigmoidal curve and is characterized by parameters such as ED50 (the dose producing 50% of the maximum effect) and Emax (the maximum achievable effect).

Receptor Theory

The foundational concept that most drugs produce their effects by binding to specific protein molecules called receptors on or within cells. The drug-receptor interaction follows the law of mass action, and the nature of the response depends on whether the drug is an agonist, antagonist, partial agonist, or inverse agonist.

Therapeutic Index

A ratio comparing the dose of a drug that causes toxic effects (TD50) to the dose that produces the desired therapeutic effect (ED50). A high therapeutic index indicates a wide margin of safety, while a narrow therapeutic index means the effective and toxic doses are close together, requiring careful monitoring.

Drug Metabolism

The biochemical modification of drugs by the body, primarily carried out by enzymes in the liver. Phase I reactions (oxidation, reduction, hydrolysis) typically introduce or expose a functional group, while Phase II reactions (conjugation) attach polar molecules to make the drug more water-soluble for excretion.

Bioavailability

The fraction of an administered dose of a drug that reaches the systemic circulation in an unchanged form. Bioavailability is affected by the route of administration, drug formulation, first-pass metabolism, and physiochemical properties of the drug molecule.

Drug-Drug Interactions

Situations in which one drug alters the pharmacological effect of another drug when they are administered together. Interactions can be pharmacokinetic (one drug affects the absorption, distribution, metabolism, or excretion of another) or pharmacodynamic (two drugs produce additive, synergistic, or antagonistic effects at the same target or pathway).

Pharmacogenomics

The study of how an individual's genetic makeup influences their response to drugs, including variations in drug-metabolizing enzymes, transporters, and drug targets. Pharmacogenomics aims to optimize drug therapy by tailoring medication choice and dosage to a patient's genetic profile.

Tolerance and Dependence

Tolerance is the diminished response to a drug after repeated administration, requiring higher doses to achieve the same effect. Physical dependence is a state in which the body has adapted to the presence of a drug such that withdrawal symptoms occur when the drug is discontinued abruptly.

Key Terms at a Glance

Absorption:The process by which a drug moves from its site of administration into the systemic circulation. The rate and extent of absorption depend on the route of administration, drug formulation, and physiochemical properties of the drug.

Agonist:A substance that binds to a receptor and activates it to produce a biological response, mimicking the action of the endogenous ligand.

Antagonist:A substance that binds to a receptor without activating it, blocking the action of agonists and preventing the receptor from producing a biological response.

Bioavailability:The fraction of an administered drug dose that reaches the systemic circulation in an unchanged form, expressed as a percentage. Intravenous drugs have 100% bioavailability.

Clearance:The volume of plasma from which a drug is completely removed per unit time, typically expressed in mL/min or L/hr. It reflects the efficiency of the organs of elimination.

Cytochrome P450:A superfamily of heme-containing enzymes located primarily in the liver that catalyze Phase I oxidation reactions in drug metabolism. Major isoforms include CYP3A4, CYP2D6, CYP2C9, and CYP1A2.

Distribution:The process by which a drug is transported from the systemic circulation to various tissues and body compartments. It is influenced by blood flow, tissue binding, plasma protein binding, and lipid solubility.

Dose-Response Curve:A graphical representation of the relationship between drug dose (or concentration) and the magnitude of the pharmacological response, typically sigmoidal in shape.

Drug Interaction:A change in a drug's effect caused by the concurrent administration of another drug, food, or substance. Interactions may be pharmacokinetic or pharmacodynamic in nature.

ED50:The effective dose of a drug that produces 50% of the maximum possible therapeutic response. It is a standard measure of drug potency -- a lower ED50 indicates greater potency.

Enzyme Induction:The process by which a drug or substance increases the synthesis or activity of drug-metabolizing enzymes, leading to faster metabolism and decreased effectiveness of other drugs.

Enzyme Inhibition:The process by which a drug or substance decreases the activity of drug-metabolizing enzymes, leading to slower metabolism and potentially toxic accumulation of other drugs.

Excretion:The process of removing a drug and its metabolites from the body, primarily via the kidneys (renal excretion) but also through bile, lungs, sweat, and breast milk.

First-Pass Metabolism:The initial metabolism of an orally administered drug by intestinal and hepatic enzymes before it reaches the systemic circulation, which can significantly reduce the amount of active drug available.

Half-Life:The time required for the plasma concentration of a drug to decrease by 50%. It is a key determinant of dosing frequency and the time to reach or lose steady-state concentrations.

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