Pharmacokinetics and drug metabolism Flashcards
What are the 4 stages of a drugs journey through the body?
Absorption
Distribution
Metabolism
Excretion
What are the possible ways of administering drugs?
Ingestion Dermal Intramuscular Subcutaneous Intraperitoneal Intravenous Inhalation
What is a systemic drug and give a common example?
Affects entire organism and aspirin
What is a local drug and give a common example?
Restricted to one area of the organism and salbutamol
What is an enteral drug and give a common example?
Gastro-intestinal administration
What are the two ways that drugs move around the body?
Bulk flow transfer e.g. bloodstream
Diffusional transfer e.g. molecule by molecule over short distance
What are the compartments and barriers that drugs have to traverse?
Compartments= aqueous e.g. blood, lymph, extracellular fluid and intracellular fluid Barriers= Lipid e.g. cell membranes (epithelium/endothelium)
How can drugs cross these barriers?
Diffusing through lipid
Carrier molecules
Diffusing through aqueous pores in lipid
Pinocytosis
How do most drugs exist?
Weak acids (ionised) or weak bases (non-ionised)
What is the difference between ionised and non-ionised drugs?
Non ionised/non polar can freely dissolve in non-polar substances e.g. penetrate lipid membranes freely
What factors affect drug distribution?
Regional blood flow
Extracellular binding (plasma proteins)
Capillary permeability
Localisation in tissues
How does metabolism affect blood flow?
Higher metabolically active tissues lead to denser capillary networks
What percentage of acidic drugs are plasma protein bound?
50-80%
What are the two major routes of drug excretion?
Kidney- responsible for elimination of most drugs
Liver- Some drugs are concentrated in bile
What happens to drug-protein complexes when they reach the glomerulus?
They are not filtered
What happens at the proximal tubule in terms of excretion?
There is active secretion of acids and bases
What happens at the proximal and distal tubules in terms of reabsorption?
Lipid soluble drugs are reabsorbed
How does treatment with intravenous sodium bicarbonate increase aspirin excretion?
It increases urine pH which ionises the aspirin making it less lipid soluble and less reabsorbed from the tubule increasing its rate of excretion
Apart from the two main routes, what other routes of excretion are there?
Lungs Skin Gastrointestinal secretions Saliva Sweat Milk Genital secretions
What is bioavailability?
Proportion of administered drug that is available within the body to exert its pharmacological effect
What is the apparent volume of distribution?
The volume in which a drug appears to be distributed- an indicator of the pattern of distribution
What is biological half life?
The time taken for the concentration of the drug in the blood to fall to half its original value
What is clearance?
Blood clearance is the volume of blood cleared of a drug in a unit time
What is first order kinetics?
The rate of elimination of a drug where the amount of drug decreases at a rate that is proportional to the concentration of drug remaining in the body
What is the volume of distribution?
Dose divided by the initial concentration of the drug in the plasma
What is zero order kinetics?
A constant amount of drug is removed per unit time (something is saturating the rate of removal, usually an enzyme)
What common sort of drug follows zero order kinetics?
Alcohol
What kinetics do most drugs follow?
First order
