General Principles of Pharmacology

Vocabulary practice flashcards covering fundamental concepts in pharmacokinetics, pharmacodynamics, receptor theory, and drug administration routes.

Pharmacology

The science that deals with the effects of drugs on living systems.

Pharmacokinetics

The study of the movement of a drug within the body, encompassing absorption, distribution, metabolism, and excretion (ADME), summarized as 'what the body does to the drug'.

Pharmacodynamics

The study of drugs, their mechanisms of action, pharmacological actions, and adverse effects, summarized as 'what the drug does to the body'.

Drug Absorption

The movement of a drug from its site of administration into the blood stream.

Bioavailability

The fraction of an administered drug dose that reaches the systemic circulation in an active, unchanged form.

First-Pass Metabolism

The presystemic metabolism and inactivation of an orally administered drug as it passes through the gut wall and liver prior to entering the systemic circulation.

Enterohepatic Cycling

The recurring cycle where a drug excreted in bile into the intestine is reabsorbed back into the portal circulation and returned to the liver, increasing bioavailability and duration of action.

Bioequivalence

A condition where two drug formulations containing identical active ingredients at identical doses and dosage forms differ in bioavailability by less than $20\%$, producing similar plasma concentrations.

Apparent Volume of Distribution ($\text{aVd}$)

The hypothetical volume of body fluid into which a drug is uniformly distributed at a concentration equal to that in plasma, calculated as $\text{aVd} = \frac{\text{Total administered amount of drug}}{\text{Concentration of the drug in plasma}}$.

Blood-Brain Barrier (BBB)

A capillary boundary between blood and brain tissue formed by endothelial tight junctions that restricts entry to lipid-soluble, unionized molecules.

Plasma Protein Binding

The reversible attachment of drugs to plasma proteins (such as albumin for acidic drugs and $\alpha_1$-acid glycoprotein for basic drugs), rendering the bound fraction pharmacologically inactive and serving as a temporary reservoir.

Biotransformation

The chemical alteration of a drug in a living organism, typically converting lipid-soluble and unionized compounds into water-soluble and ionized metabolites for excretion.

Prodrug

An inactive form of a drug that requires metabolic conversion within the body to form an active, pharmacologically effective metabolite.

Phase I Reactions

Non-synthetic metabolic processes—including oxidation, reduction, hydrolysis, cyclization, and decyclization—that alter drug structures using microsomal or non-microsomal enzymes.

Phase II Reactions

Conjugation reactions in which a drug or Phase I metabolite combines with an endogenous substrate (e.g., glucuronic acid, sulfate, acetate, glutathione) to form a polar, water-soluble, inactive conjugate.

Plasma Half-Life ($t_{1/2}$)

The time required for the plasma concentration of a drug to decrease by $50\%$ of its original value.

Clearance (CL)

The volume of plasma from which a drug is completely removed per unit of time, defined as $\text{Clearance} = \frac{\text{Rate of elimination}}{\text{Plasma concentration of the drug}}$.

First-Order Kinetics

Elimination kinetics in which a constant fraction of the drug is eliminated per unit time, with the elimination rate being directly proportional to plasma concentration.

Zero-Order Kinetics

Elimination kinetics in which a constant amount of the drug is eliminated per unit time, making the elimination rate independent of plasma drug concentration.

Affinity

The ability of a drug to bind specifically to its receptor.

Intrinsic Activity

The ability of a drug to activate the receptor and elicit a pharmacological action after binding.

Agonist

A drug that binds to a receptor and produces a maximal pharmacological response, having both high affinity and high intrinsic activity.

Antagonist

A drug that binds to a receptor and prevents an agonist from acting, possessing high affinity but zero intrinsic activity.

Partial Agonist

A drug that binds to a receptor but produces a lower maximal response than a full agonist, possessing receptor affinity with lower intrinsic activity.

Inverse Agonist

An agent that binds with full affinity to a receptor but induces a pharmacological response directionally opposite to that of an agonist.

Ligand-Gated Ion Channels

Ionotropic cell-surface receptors directly coupled to ion channels that alter ion permeability (hyperpolarization or depolarization) upon agonist binding.

G Protein-Coupled Receptors (GPCRs)

Seven-transmembrane metabotropic receptors that regulate intracellular effectors (e.g., adenylyl cyclase, phospholipase C) through heterotrimeric G proteins comprising $\alpha$, $\beta$, and $\gamma$ subunits.

Transmembrane Enzyme-Linked Receptors

Cell-surface receptors possessing an extracellular ligand-binding domain and an intracellular enzymatically active domain, predominantly demonstrating tyrosine kinase activity.

Nuclear Receptors

Intracellular receptors located in the cytoplasm or nucleus that bind lipophilic ligands (such as steroids or thyroxine) to regulate DNA transcription and protein synthesis.

Therapeutic Index (TI)

An index of drug safety defined as the ratio of the median lethal dose to the median effective dose ($\text{TI} = \frac{\text{LD}_{50}}{\text{ED}_{50}}$).

Median Lethal Dose ($\text{LD}_{50}$)

The dose of a drug that produces death in $50\%$ of a tested population.

Median Effective Dose ($\text{ED}_{50}$)

The dose of a drug that produces the specified desired effect in $50\%$ of the population.

Additive Effect

A combined drug effect that equals the algebraic sum of the individual effects of the administered drugs ($\text{Effect of } A + B = \text{Effect of } A + \text{Effect of } B$).

Potentiation

The enhancement of the therapeutic action of an active drug by another compound that is inactive on its own ($\text{Effect of } A + B > \text{Effect of } A + \text{Effect of } B$).

Synergism

A phenomenon where the simultaneous administration of two or more drugs yields a combined response greater than that elicited by either drug alone.

Physiological Antagonism

A state where two drugs act on distinct receptors or mechanisms within the same physiological system to produce mutually opposing actions.

Competitive Antagonism

A form of receptor antagonism where an agonist and antagonist reversibly compete for the same receptor binding site, producing a parallel rightward shift in the log dose-response curve.

Non-Competitive Antagonism

A form of antagonism where an antagonist binds to an allosteric site on the receptor, preventing agonist-mediated activation and causing flattening of the maximal dose-response curve.

Drug Tolerance

The requirement for increasingly larger doses of a drug to produce a given pharmacological response.

Tachyphylaxis

A rapidly developing reduction in pharmacological response following repeated administration of a drug at short intervals (acute tolerance).