Pharmacology Flashcards
What is the definition of a drug?
“An external substance that acts on living tissue to produce a measurable change in the function of that tissue”
What do drugs do?
- Stimulate normal bodily communications
- Interrupt normal bodily communication
- Act on non-host organisms to aid body defences
What are the 2 types of communication within the human body?
- Hormones (slow acting) - regulatory substances secreted by glands produced to be transported via tissue fluids (e.g. blood), to stimulate specific cells into action
- Nerves (Fast acting) - Autonomic nervous system can be split into sympathetic (epinephrine) and parasympathetic (ACh)
e. g. HR is increased by adronergic stimulation of beta receptors, decreased by cholinergic stimulation of cholinergic receptors
What is an example of sympathetic nervous system?
Fast acting, localised
Epinephrine (beta agonist)
Atenolol (beta blocker)
What is an example of parasympathetic nervous system?
Pilocarpine (Cholinergic agonist) - makes you salivate
Atropine (cholinergic blocker)
How do antagonist drugs work?
They do not enact any intracellular change/reaction/morphological difference but instead inhibit an agonist from enacting a change
What do drug receptors act upon and what is an example?
In order of speed.
- Coupled to ion channels (i.e. nicotonic acetylcholine receptors - mediate synaptic transmission in the NS, have ion channels intrinsic to their structure which require agonists to open, they disrupt the ion balance in the cell which causes an ion influx, e.g. LA and anti-diabetic drugs, takes milliseconds)
- Coupled to G proteins - (i.e. muscarinic acetylcholine receptors, the drug has to pass its signal through layers of transmembrane helices to have a desired effect, takes seconds)
- Couple to Enzymes (i.e. these receptors incorporate an enzyme into their domain; either tyrosine kinase/guanyly cyclase. MOA - drug acts as substrate agonist to bind to enzyme e.g. aspirin and simvastatin - takes MINUTES.
- Coupled to Gene transcription - (i.e. regulate DNA transcription - characteristic of steroid/thyroid hormones - found in nucleus
glucocortcoid dna receptors found in cytoplasm - involved in protein synthesis - takes hours.
What is the law of mass action?
The priniciple that the rate of a chemical reaction is proportional to the concentrations of the reacting substances
In pharmacology - drug in the vicinity of a receptor will obey the law of mass action
What is “affinity” and what affects the affinity?
The strength with which the drug forms a complex with its receptor
- Size and shape of drug molecule
- Types, number and spatial arrangement of drug binding sites
- Intermolecular forces - Van der waals, hydrogen bonds (intermediate) , covalent bonds (strong)
What are drug effectors?
Agonists - bind to a receptor to cause an effect
Partial agonists - more difficult to produce drug/receptor interaction, in some instances increasing agonist conc. will increase efficacy, but in others doesnt
Antagonists -reversible - antagonist effect reduced by increasing conc. of the agonist (non-competitive) e.g. atenolol
irreversible - binds and reduces available receptors for the agonist (competitive) e.g. phenoxybenzamine (alpha 1 blocker)
What is the definition of pharmacokinetics?
Movement of drugs in the body
What are the different paths of absorption?
Oral - pills etc- socially acceptable, however slow onset, variable absorption, gastric acid might destory drug as well as subject to first pass metabolism - least reliable.
Intravenous - injections straight into systemic circulation
Intramuscular - injections into muscles to act directly on tissues
Subcutaneous - easy, safe and convenient, between skin and muscles (dermal injection) drug takes 24hrs sometimes to absorb
Inhalation - respiratory drugs
What are the pros and cons of non oral routes for drugs?
Pros:
- Predicatble plasma levels
No 1st pass metabolism
Cons:
Allergic reactions more severe
Difficult accessing if self medicating
Drug cost higher
What is first pass metabolism?
Liver metabolises the drug and it has one of two fates
- inactivates drug - more needed by oral route to achieve desired clinical effect (e.g. GTN)
- Activates drug - makes an active form of inactive drug in essence a pro-drug, therefore less is needed via oral route (e.g. valociclovir - aciclovir)
e.g. do not rely on 1st pass if the patient operates at extremes of life e.g. alcoholic or has liver disease and indeed with known drug interactions that would change normal metabolism
What is bioavailability?
Proportion of ingested drug that is available for clinical effect
