Lecture 1 Pharmacokinetics: Absorption and Distribution

Vocabulary-style flashcards covering the basic principles of pharmacokinetics, specifically focused on absorption and distribution as presented in the Rocky PA Program lecture.

Pharmacokinetics (PK)

The study of drug movement through the body, divided into five stages: liberation, absorption, distribution, metabolism, and excretion.

LADME

An acronym for the five stages of pharmacokinetics: Liberation, Absorption, Distribution, Metabolism, and Excretion.

Metabolism (M)

The chemical conversion of a drug into compounds which are easier to eliminate.

Excretion (E)

The elimination of unchanged drug or its metabolite from the body via renal, biliary, or pulmonary processes.

Liberation (L)

How a drug is released from its administered form, including immediate, delayed, or extended release types.

Immediate Release

A drug formulation that releases the active ingredient without delay.

Delayed Release

A drug formulation that releases the drug sometime after it is taken.

Extended Release

A drug formulation that releases the drug over a prolonged period; these formulations typically cannot be split or crushed.

Route of Administration (ROA)

The way a medication gets into the body, which can have a profound effect on the drug's onset of action.

Enteral Route

A route of administration where drug absorption occurs in the gastrointestinal (GI) tract by active or passive transport.

Sublingual (SL)

An enteral route where medication is placed under the tongue.

Buccal (Buc)

An enteral route where medication is placed between the gums and the cheek.

Intrathecal Route

A route where drug is injected directly into the cerebrospinal fluid, such as via the epidural space.

Absorption (A)

The process by which a drug enters the bloodstream without being chemically altered, or the movement of a drug from its site of administration into the blood or lymphatic system.

Hydrophilic

The tendency of a polar substance to mix with or dissolve in water.

Hydrophobic

The tendency of non-polar substances to aggregate in aqueous solution and exclude water molecules.

Lipophilic

The ability of a substance to combine with or dissolve in lipids or fats.

Lipophobic

A substance that is not soluble in lipids or other non-polar substances.

Polar Molecule

A molecule where the electrons are unevenly distributed in a bond, creating dipoles with unequal charges.

Ionized

A molecule with a positive or negative charge, where the number of protons does not equal the number of electrons.

Protonation

The addition of a proton ($H^+$) to an atom, molecule, or ion, commonly occurring in acid-base reactions.

Fick's Law of Diffusion

Describes the passive movement of molecules down their concentration gradient across a lipid membrane.

pKa

The pH at which $50\%$ of the drug is non-ionized.

pH Trapping

A process where a drug diffuses easily into a compartment but becomes ionized due to the pH of that compartment (e.g., plasma at $pH\,7$ vs. stomach at $pH\,1$), trapping it there.

Passive Transport

Transport across a membrane requiring no energy, following a concentration gradient; it can be simple diffusion or facilitated by a carrier protein.

Active Transport

Transport across a membrane that requires energy in the form of $ATP$ to move substances, often against an electrochemical gradient.

First-Pass Metabolism

The hepatic metabolism of a drug absorbed from the GI tract that is delivered to the liver via portal circulation before reaching the systemic circulation.

Extraction Ratio (ER)

A value used to quantify the magnitude of first-pass metabolism, calculated as $ER = CL_H / Q$, where $CL_H$ is hepatic clearance and $Q$ is hepatic blood flow.

Bioavailability (F)

The fraction of administered drug that reaches systemic circulation, calculated by the formula $F = f \times (1 - ER)$.

Area Under the Curve (AUC)

A representation of the actual body exposure to a drug after a dose has been administered.

Cmax

The maximum concentration of a drug achieved in the body.

Tmax

The time at which the maximum concentration of a drug ($Cmax$) is reached.

Distribution (D)

The movement of drug to and from the blood and various tissues of the body, such as fat, muscle, and brain tissue.

Vessel-Rich Group (VRG)

Tissues with high blood flow (brain, heart, kidneys) that receive significant drug amounts in a short time.

Blood-Brain Barrier (BBB)

An astrocytic sheath and tight junctions between endothelial cells that regulate the flow of substances from blood into the brain.

Volume of Distribution ($V_d$)

A proportionality constant ($L/kg$) defining the theoretical fluid volume required to contain the total amount of drug in the body at the same concentration as in the plasma.

Loading Dose

A higher initial dose required for drugs with a high $V_d$ to saturate tissues and establish therapeutic plasma levels quickly.