Intro to pharmacology Flashcards
Pharmacology
Science of drug action
Drug
Anything w/ positive or desired effect
Substance used in diagnosis, treatment or prevention of disease or as a component of a medication
Poison
Anything w/ negative or undesired effect
Legal status of drugs
POM
PM
GSL
POM
Prescription only medication
PM
Pharmacy medication
GSL
General sales medication
Branches of pharmacology
Pharmacokinetics
Pharmacodynamics
Pharmacokinetics
How the body affects the drug
Pharmacodynamics
How the drug affects the body
Drugs can be …
Agonist
Antagonist
Agonist
Activate receptors and elicit a response e.g. drugs, hormones, neurotransmitters bitter, signalling molecules
Antagonist
Prevent (block) effect of agonist; can be competitive or non-competitive
Examples of agonist/antagonist interactions
Morphine is released at a synapse (agonist) and naloxone fits into the dips on the other neurone (antagonist) blocking the morphine
Receptors
Proteins located on cell membranes, respond to endogenous compounds (hormones)
Transport systems
Ion channels, either voltage gated (Ca2+, K+, Na+) or ligand gated
G coupled proteins
Located in cell membranes and bounds extracellular substances to an intracellular molecule
Affinity
How well does the drug bind to receptor
What does drug affinity depend on
Conc of drug [D]
What does removal of a drug depend on
How well it bound in 1st place
Receptor binding
How many receptors are occupied
How is rship between drug conc and receptor binding calculated
p = [D]/ [D] + Kd
Dose
How much drug is needed for therapeutic response
What should drug + receptor =
Chemical response but this depends on efficacy
Efficacy
2 drugs Same concept Same receptor binding ability (affinity) Different efficacy Diff chemical effects
Examples of drugs w/ diff efficacy
Benzodiazepines, lorazepam and temazepam have a 10-fold diff in dose
Key point about efficacy and dosage
Not all drugs in the same class and receptor site will have similar doses As a result, medication ha sits own currency
Stages of pharmacokinetics
Absorption
Distribution
Metabolism (after body realises drug is exogenous)
Excretion
Absorption in pharmacokinetics
Getting drug into body - so it can work
Everything given via mouth will go through dissolution phase
Pass through gut wall into bloodstream —> even distribution around the body
What does absorption depend on
Drug solubility - lipophilic or hydrophilic
Why is drug solubility important
Allows us to decipher how to get the drug into the body
Lipid soluble drugs
Pass through the gut and enter the bloodstream a lot quicker e.g. hormones
What happens when drugs are distributed unto water compartments in the blood
Exposed to plasma proteins - where once bound can become ineffective (unable to traverse cell membranes)
Routes of administration
Oral (po) Inhaled (inh) Topical (top) Sub lingual (s/l) Rectal (pr) Parental
Oral administration
po
Most common, ease of administration
Inhaled administration
Volatile anaesthetics/ local delivery in asthma
Topical administration
Skin/eyes/ears - local delivery
Sub lingual administration
Rapid onset action
Under tongue
Example of drug given sub lingually
GTN - Glyceryl trinitrate
Used to treat angina
Rectal administration
Bypass portal circulation
Parental administration
Bypassing GI system
Straight into blood stream
Types of parental administration
Subcutaneous Intramuscular Intravenous Transdermal Implantation
Subcutaneous parental administration
Drug infected into fat at 90 degrees, usually in stomach
Drugs given by subcutaneous parental adminstarion
Insulin
LMWH
LMWH
Low molecular weight heparin
Intramuscular parental administration
Less common mode of administration
Usually done in big muscles e.g. thigh
Not many licensed to do
Used when we want to give drugs slowly i.e. give the drug in a neuroleptic preparation (depressing nerve functions)
Transdermal parental administration
Continual drug release
Examples of drugs given by transdermal parental administration
Morphine
NRT
NRT
Nicotine replacement therapy
Intravenous parental administration
100% bioavailability
Good for infusions, rapid access and drug delivery in large volumes
Bioavailability
% unchanged drug that reaches the systemic circulation
Implantation parental administration
Hormones/steroids
Targeted and continual drug release
What allows us to figure out the dose of a drug
Half life
Vd
Clearance
Half life
Time it takes drug conc to drop to half of orig
Vd
Volume of distribution
How much volume the drug has to distribute itself into
Clearance
Volume of plasma/ blood cleared of drug
Metabolism in pharmacokinetics
Occurs throughout body - usually in liver (lipophilic)
Important because determines therapeutic and toxic effects of drugs and allows you too optimise therapy, minimise harm
Metabolites
Products of metabolism
Commonly less potent than the drug but can be more potent - prodrugs
Prodrugs
The drug given to patient is partially active, once metabolised becomes a more potent agent that can provide local relief
Offshoots are active drugs
Excretion in pharmacokinetics
Principally occurs in kidneys
Kidney = hydrophilic agents
Clearance via glomerular filtration
Why do we aim to make drugs more hydrophilic
More water soluble –> more easily excreted by the kidneys
Kinase linked receptors
Ligand binding activates an intracellular protein that triggers a cascade of phosphorylation reactions
Selectivity
Propensity for a drug to bind to one target rather than an other
Partial agonists
Activate the receptor but cannot produce a maximal signalling effect equivalent to that of a full agonist, even when all receptors are occupied
Potency
Amount of drug required for a given response
What do more potent drugs produce
Biological effects at lower doses
ED 50
Dose producing half the value of the maximum response
Therapeutic index
Ratio of the ED50 for therapeutic efficacy and for a major adverse effect
Indicates how much margin prescribers have when choosing a dose that will provide beneficial effects w/ out causing adverse effects
Toxic effects
Adverse effects that occur at doses above the therapeutic range
Side effects
Adverse effects that occur within the therapeutic range
Hyper-susceptible effects
Adverse effects occurring below the therapeutic range
Why do we have to give drugs on a frequent basis
The body will wash it out
Factors to consider when choosing a drug
Absorption Distribution Metabolism Excretion Efficacy Avoiding adverse effects and drug interactions Features of the disease Severity of disease Coexisting disease Cost Patient adherence to therapy