Pharmacokinetics
Dr. Nawazishi Husain Syed
Pharm D 2nd Prof
Pharmacology
1
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Pharmacokinetics 1 - Introduction Study notes, Study notes of Pharmacology
In this notes, Pharmacokinetics is briefly described, what body do when drug enters in the body - the process of Absorption, Metabolism, Distribution, and Elimination is briefly described
Typology: Study notes
2021/2022
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Pharmacokinetics
Dr. Nawazishi Husain Syed
Pharm D 2
nd
Prof
Pharmacology
Pharmacokinetics
“What the body does to the drug”
The study of the disposition of a drug
It includes the processes of ADME
A bsorption
D istribution
M etabolism
E xcretion
T oxicity
Elimination
Why drugs fail
Significance
Patients may suffer
Toxic drugs may accumulate
Useful drugs may have no benefit because
doses are too small to establish therapeutic
efficacy
A drug can be rapidly metabolized
Drug Absorption
Absorption is the process by which a drug
enters the bloodstream without being
chemically altered
or
The movement of a drug from its site of
application into the blood or lymphatic system
Drug Absorption
Factors which influence the rate of absorption
types of transport
the physicochemical properties of the drug
protein binding
routes of administration
dosage forms
circulation at the site of absorption
concentration of the drug
Drug Absorption
Mechanisms of solute transport across
membranes
passive diffusion
filtration and bulk flow
endocytosis
ion-pairing
active transport
Absorption relies on
Passage through membranes to reach the blood
passive diffusion of lipid soluble species.
Absorption
Membranes
Types of Membranes:
Cell Membranes: This barrier is permeable to many drug
molecules but not to others, depending on their lipid
solubility. Small pores, 8 angstroms, permit small
molecules such as alcohol and water to pass through.
Walls of Capillaries: Pores between the cells are larger
than most drug molecules, allowing them to pass freely,
without lipid solubility being a factor.
Blood/Brain Barrier: This barrier provides a protective
environment for the brain. Speed of transport across this
barrier is limited by the lipid solubility of the psychoactive
molecule.
Placental Barrier: This barrier separates two distinct
human beings but is very permeable to lipid soluble drugs.
Distribution
The movement of drug from the blood to and from the tissues
Distribution
Determined by
partitioning across various membranes
binding to tissue components
binding to blood components (RBC, plasma protein)
physiological volumes
Total Body water
Vascular
3 L
4% BW
Extravascular
9 L
13% BW
Intracellular
28 L
41% BW
Distribution
Apparent volume of distribution (Vd) = Amount of drug in
body/plasma
Volume of Distribution for some drugs
Drugs Vd (L)
cocaine 140
clonazepam 210
amitriptyline 1050
amiodarone 5000