6 - Introduction to Pharmacokinetics Flashcards
What does pharmacokinetics study
What the body does to the drug (Absorption, Distribution, Metabolism, Excretion – ADME)
What are key pharmacokinetic concepts
Bioavailability
Clearance
Half-life
Volume of Distribution
What does a Drug Plasma Curve help determine
The right dose and dosing frequency
What is bioavailability (F)
Fraction of unchanged drug that reaches systemic circulation
What is the bioavailability of IV drugs
F = 1 (100%)
Why is oral bioavailability usually less than 1
Due to first-pass metabolism in the liver and gut
What is the First Pass Effect
% of drug lost during the first liver passage, lowering bioavailability
Name 4 causes of incomplete oral bioavailability
Failure of disintegration/dissolution
Enzymatic/bacterial breakdown
Absorption failure (e.g., p-glycoprotein)
First-pass metabolism
Name 4 causes of incomplete oral bioavailability
Failure of disintegration/dissolution
Enzymatic/bacterial breakdown
Absorption failure (e.g., p-glycoprotein)
First-pass metabolism
What is first-order kinetics
Elimination rate is proportional to drug concentration
What is zero-order kinetics
Constant amount of drug is eliminated, independent of concentration
What does Volume of Distribution (VD) indicate
How extensively a drug distributes in body tissues
What does a large VD mean
Drug distributes widely into tissues
What does a small VD mean
Drug remains mostly in plasma
What is a Loading Dose (LD)
A single high dose to quickly reach therapeutic drug levels
What is Clearance (CL)
Volume of plasma cleared of drug per unit time
What is the formula for Total Clearance
CL = Hepatic CL + Renal CL
How is Hepatic Clearance calculated
Blood Flow × Extraction Ratio
What is the Elimination Rate Constant (K)
Fraction of drug eliminated per unit time
What is half-life (t½)
Time it takes for drug concentration to drop by 50%
How many half-lives to reach steady state
~4–5 half-lives
Why is steady state important
Keeps drug levels within the therapeutic window with repeated dosing
Calculation of F
AUC oral / AUC (i.v.)
If something is <100% bioavailable the F value will be
<1
What does AUC stand for
Area under the curve
What does area under the curve mean
Amount of drug which enters the systemic circulation
Volume of distribution (V) calculation
Amount in body (A) / Plasma concentration (C)
LD equation
(C x V) / F
Renal excretion
Glomerular filtration of plasma water and unbound drug (in glomeralus)
Active tubular secretion of organic acids and bases
Reabsorption of lipid soluble drugs
