Lecture 2- Pharmacokinetics Flashcards
Pharmacokinetics is
-A subfield of pharmacology
-Absorption, distribution, bio transformation and excretion of drugs
-Movement of drug to and from its site action
Factors that determine the movement of drugs to terminals
-How much gets there
-How fast it gets there
-How long it’s there
Factors affecting absorption
-Drug solubility
-Ionisation
-Blood circulation at the site of administration
-Surface area of the absorbing surface
What factors of absorption are determined by route of administration
-Blood circulation at site of administration
-Surface area of absorbing surface
What is PO
PreOral
Absorption through gastrointestinal tract (not mouth)
Routes that avoid 1st pass metabolism
-Nasal
-Sublingual
-Rectal
-Transdermal
-Pulmonary absorption
Levels of transmission
-Subcutaneous
-Intramuscular
-Intravenous
Where is the subcutaneous
Just below the skin
Where is the intramuscular level
In the muscle
Where’s the intravenous level
Just the spinal cord
Putting a drug in an oil solution can
Slow down the release of the drug
What is peak effect
Highest point of concentration in the blood
Drug peak concentration and half life vary by
Route of administration
Half life is
Time for plasma drug concentrations to fall to half of peak effect
Effects of route administration
-Amount of drug destroyed by 1st metabolism
-Blood circulation at the site of administration
-Surface area available for absorption
-Binding to inactive sites
-Number of cell layers to blood
Drug movement across membranes is a key factor influencing
The dose available at site of action
Limiting factors of drug movement across membranes
-Size and shape of drug molecule
-Lipid solubility and ionisation
Which reaches the brain first heroin or morphine
Heroin
Drugs that are weak acids ionise more in
Basic (alkaline) environments (solvents)
Drugs that are weak bases ionise more in
Acidic environments (solvents)
The greater difference in environment and drug
The more ionised the drug is and less absorption
To know whether a drug is lipid soluble, you have to know
-Whether it’s a weak acid or base
-Pka value
-Solution your putting it in
What is ion trapping
Build up of a higher concentration of a chemical across a cell membrane due to the pka value of the chemical and difference of pH
What is the blood brain barrier
Special barrier protecting the brain, molecules travel everywhere but the brain
Brain areas outside the blood brain barrier
-Area postrema (vomiting center)
-Median eminence (hypothalamic hormones)
Features of typical capillary membranes
-Made of endothelial cells
-Fenestration
-Pinocytotic vesicles
-Lipid soluble transport
-Intracellular cleft
What can still diffuse through brain capillaries
Lipid soluble molecules such as psychoactive drugs
Features of brain capillaries
-Made of endothelial cell
-Tight junction
-Surrounded by astrocytes
Most of metabolism occurs in
The liver
Inactivation usually due to
Metabolism
What mechanism do psychoactive drugs most often move across cell membranes
Simple diffusion
True or false Metabolites are always inactive
False
True or false, there are sex differences in enzyme activity in the stomach
True
True or false, metabolism usually reduces the solubility
True
