Pharmacokinetics Flashcards
What is Pharmacokinetics
How the drug is handled within the body
What is permeation
How the drug enters systemic circulation and barriers it goes through
What is facilitated diffusion
passive movement
molecules move across the cell membrane via the aid of a membrane protein.
It is utilised by molecules that are unable to freely cross the phospholipid bilayer (e.g. large, polar molecules and ions)
What is Pinocytosis
Cellular drinking
Big molecules - hormones and proteins
What are the main components of pharmacokinetics
Absorption
Distribution
Metabolism
Excretion
What is absorption
Drugs into systemic circulation
What’s effects absorption
PH
Food
Blood flow to the GI tract
Gastric emptying
Permeation
What is first pass effect
first pass effect occurs when a drug is metabolized at a specific spot in the body, resulting in a lower concentration of the active substance when it reaches its site of action or the systemic circulation.
What is Bioavailability
Proportion of drug available to the body
Drugs given orally under the curve
I’ve route 100% bioavailability
Is not a measurement of effectiveness
What is Bioequivalance
Therapeutic equivalence between two drugs - same clinical response - the same drug
What is Bioinequivalance
2 main brands - not swappable
What is drug half life
Drug concentration in plasma falls 50%
Metabolism and excretion determines half life
What is Steady State
Drug input is equal to drug elimination
5 half life’s = Steady State
What is flicks first law
Rate of permeation depends on surface area and concentration gradient
Small molecules
Small area
Gas exchange takes longer if fluid present in the lung, prolonging diffusion
What is distribution
Drug > plasma protein > good blood flow > lipid soluble > PH > degree of ionisation
If albumin low takes longer to distribute
What is Volume distribution
How far the drugs distribute
High volume - gets everywhere
Small VD (0.1-1l/kg) - does not go far
Large VD (1-10l/kg) reach wide and far
Exam:
What are the summary factors influencing drug distribution
Drugs need to cross cell membrane
1, low degree of ionisation
2, low molecular weight
3, high lipid solubility
4, high concentration gradient
What is Metabolism
Metabolism occurs in the liver
Lipophilic drugs
Gi tract > skin > lungs > kidneys
Metabolism may produce toxic metabolites
What is metabolism 2
Influence drug metabolism
Cytochrome p450 enzyme
Young and old age
Liver size and function
Circadian rhythm
Body temp
Smokers metabolise quicker
The role of the liver
Slide 44
Phase 1 - CP450 - Superfamily of enzymes
Phase 2 - reactions by enzymes
Phase 3 - active drug transport across cel membranes
What are the 2 phases of metabolism
Phase 1 - produces toxic metabolites
Phase 2 - turns toxic into soluble metabolites for excretion
What are the inhibitors and inducers of microsomal enzymes
Inhibitors- grapefruit, cimetidine, prolongs or stops
Inducers - barbiturates, carbamazepine
Speeds up drugs shortens therapy
What is renal excretion
Water soluble
Eliminated in urine
Small enough to fit through kidney glomerlus
Not rapidly diffused in lipid membranes
What is biliary secretion
Water soluble
Too large to fit through glomerular
Lipophilic
Can be excreted in bile
What is clearance
Clearance is the amount of drug given at any given time
Exam:
What is Zero order
The rate of excretion of a drug is independent of its concentration
5% - cannot be altered
Exam:
What is first order
The rate of excretion is directly proportional to its concentration
Most drugs - first order can be altered
95% of drugs at therapeutic level
