General Pharmacology - Pharmacodynamics & Pharmacokinetics Flashcards

Question 1

What is Pharmacokinetics?

Accepted Answer

The study of how the body affects a drug. It describes the movement of a drug through the body, encompassing Absorption, Distribution, Metabolism, and Excretion (ADME).

Question 2

What is Pharmacodynamics?

Accepted Answer

The study of how a drug affects the body. It describes the biochemical and physiological effects of drugs and their mechanisms of action.

Question 3

What does ADME stand for in pharmacokinetics?

Accepted Answer

ADME is an acronym for:
*   **A**bsorption: Movement of drug from site of administration into the bloodstream.
*   **D**istribution: Movement of drug from the bloodstream to various tissues and organs.
*   **M**etabolism: Biotransformation of the drug into metabolites.
*   **E**xcretion: Elimination of the drug and its metabolites from the body.

Question 4

Define Absorption in pharmacokinetics.

Accepted Answer

The process by which an unchanged drug moves from its site of administration into the systemic circulation (bloodstream). Factors like route of administration, drug solubility, and blood flow at the site influence it.

Question 5

Define Bioavailability (F).

Accepted Answer

The fraction of an administered dose of unchanged drug that reaches the systemic circulation. It is often expressed as a percentage. For IV administration, bioavailability is 100% (F=1).

Question 6

Explain First-Pass Metabolism (or First-Pass Effect).

Accepted Answer

The metabolism of a drug by the liver or gut wall enzymes before it reaches the systemic circulation, primarily after oral administration. This reduces the drug's bioavailability.

Question 7

Define Distribution in pharmacokinetics.

Accepted Answer

The reversible transfer of a drug from the systemic circulation into the various tissues and organs of the body. It depends on blood flow, tissue permeability, and plasma protein binding.

Question 8

Define Volume of Distribution ($V_d$).

Accepted Answer

A hypothetical volume of fluid into which a drug is dispersed. It relates the total amount of drug in the body to the concentration of drug in the plasma: $V_d = \frac{	ext{Total amount of drug in body}}{	ext{Plasma drug concentration}}$. A high $V_d$ indicates extensive tissue distribution.

Question 9

Define Metabolism (Biotransformation) in pharmacokinetics.

Accepted Answer

The process by which the body chemically alters drugs, primarily in the liver, to facilitate their excretion. This usually converts lipid-soluble drugs into more water-soluble metabolites.

Question 10

Differentiate Phase I and Phase II Metabolic Reactions.

Accepted Answer

*   **Phase I Reactions:** Introduce or unmask polar functional groups (e.g., -OH, -NH2) via oxidation, reduction, or hydrolysis. Often mediated by cytochrome P450 (CYP) enzymes.
*   **Phase II Reactions:** Involve conjugation of the drug or its Phase I metabolite with an endogenous substrate (e.g., glucuronic acid, sulfate) to form highly polar, inactive metabolites, facilitating excretion.

Question 11

Define Excretion in pharmacokinetics.

Accepted Answer

The irreversible removal of a drug and its metabolites from the body. The primary routes are renal (kidneys, via urine) and hepatic (liver, via bile into feces), but also includes lungs, sweat, and breast milk.

Question 12

Define Drug Half-Life ($t_{1/2}$).

Accepted Answer

The time required for the concentration of a drug in the plasma to decrease by 50%. It is a key pharmacokinetic parameter determining dosing frequency and time to reach steady state. For first-order kinetics, $t_{1/2} = \frac{0.693 	imes V_d}{	ext{Clearance}}$.

Question 13

Define Steady State.

Accepted Answer

The point at which the rate of drug administration (input) is equal to the rate of drug elimination (output). At steady state, the average drug concentration in the plasma remains constant over time with repeated dosing.

Question 14

Approximately how many half-lives does it take for a drug to reach steady state concentration?

Accepted Answer

It generally takes approximately **4 to 5 half-lives** for a drug to reach about 94-97% of its steady-state concentration during continuous or repeated dosing.

Question 15

Define Drug Receptor.

Accepted Answer

A macromolecular component, usually a protein, on or within a cell that binds to a drug and initiates a biochemical or physiological change, leading to a drug effect.

Question 16

Differentiate Agonist and Antagonist.

Accepted Answer

*   **Agonist:** A drug that binds to a receptor and activates it, producing a pharmacological response. It has both affinity and intrinsic activity.
*   **Antagonist:** A drug that binds to a receptor but does not activate it. It blocks the action of an agonist, preventing a response. It has affinity but no intrinsic activity.

Question 17

Differentiate Competitive and Non-competitive Antagonism.

Accepted Answer

*   **Competitive Antagonism:** The antagonist binds reversibly to the same site as the agonist. It can be overcome by increasing the concentration of the agonist.
*   **Non-competitive Antagonism:** The antagonist binds to a different site on the receptor or binds irreversibly to the agonist site, preventing the agonist from producing a maximal effect, regardless of agonist concentration.

Question 18

Define Efficacy in pharmacodynamics.

Accepted Answer

The maximal effect ($E_{max}$) a drug can produce, regardless of the dose. It represents the drug's ability to produce a desired therapeutic effect. A drug with high efficacy produces a strong effect.

Question 19

Define Potency in pharmacodynamics.

Accepted Answer

The amount of drug needed to produce a given effect. It is often expressed as the $EC_{50}$ (effective concentration for 50% of maximal effect) or $ED_{50}$ (effective dose for 50% of maximal effect). A drug with high potency produces its effect at lower concentrations.

Question 20

Explain a Dose-Response Curve.

Accepted Answer

A graphical representation of the relationship between the dose of a drug and the magnitude of the pharmacological effect it produces. It typically shows an S-shaped (sigmoidal) curve, illustrating threshold, linear, and maximal effect phases.

Question 21

Define Therapeutic Index (TI).

Accepted Answer

A measure of a drug's safety, comparing the dose that produces a therapeutic effect to the dose that produces toxicity. A higher TI indicates a wider margin of safety.

Question 22

How is Therapeutic Index (TI) calculated?

Accepted Answer

The Therapeutic Index is typically calculated as the ratio of the median toxic dose ($TD_{50}$) or median lethal dose ($LD_{50}$) to the median effective dose ($ED_{50}$):
$TI = \frac{TD_{50}}{ED_{50}}$ or $TI = \frac{LD_{50}}{ED_{50}}$.
$ED_{50}$ is the dose producing a therapeutic effect in 50% of the population.
$TD_{50}$ is the dose producing a toxic effect in 50% of the population.
$LD_{50}$ is the dose producing a lethal effect in 50% of the population.

General Pharmacology - Pharmacodynamics & Pharmacokinetics

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