Pharmacology Flashcards
What are the enteral routes of systemic drug administration?
Via the GI tract:
- oral (PO)
- rectal (PR)
- sublingual
What are the parenteral routes of systemic drug administration?
(Not via the GI tract)
- Intravenous (IV)
- Intramuscular (IM)
- Subcutaneous (SC)
- Inhalation (Inh)
- Transdermal
What the routes of local drug administration?
- Topical
- Intranasal
- Eye drops
- Inhalation (Inh)
- Transdermal
Give 4 groups of drug targets.
Receptors, enzymes, transporters, ion channels
What is a receptor?
A component of a cell that interacts with a specific ligand and initiates a change of biochemical events leading to the ligands observed effects.
What are ligands?
Molecules that bind to receptors to cause an effect, they can be exogenous (drugs) or endogenous (hormones, neurotransmitter, etc.)
Name and give an example of 4 types of receptor.
- Ligand-gated ion channels (nicotinic ACh receptor)
- G protein coupled receptors (beta-adrenoreceptors)
- Kinase-linked receptors (receptors for growth factors)
- Cytosolic/nuclear receptors (steroid receptors)
How do ligand-gated ion channels work?
They are pore-forming membrane proteins that allow ions through the pore so that the cell undergoes a shift in electric charge distribution.
How do GPCRs work?
G protein coupled receptors are integral membrane proteins that are used by cells to convert extracellular signals into intracellular responses, including responses to hormones, neurotransmitters, as well as responses to vision, olfaction and taste signals
How do kinase-linked receptors work?
Transmembrane receptors are activated when the binding of an extracellular ligand causes kinases on the intracellular side to catalyse phosphorylation and cause a change in the cell.
How do nuclear receptors work?
They modify gene transcription when ligands bind.
Steps of therapeutic development
- Identify the receptor involved in a pathophysiological response.
- Develop drugs that act at that receptor.
- Quantify drug action at that receptor.
What is an agonist?
A compound that binds to a receptor and activates it.
- mimics endogenous ligand
- can be full or partial
What is an antagonist?
A compound that reduces the effect of an agonist.
Define affinity
How well a ligand binds to the receptor.
Define efficacy
How well a ligand activates the receptor.
What is inverse agonism?
When a drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist.
Define tolerance
Reduction in agonist effect over time, usually after repeated or continuous use, or high concentrations of the drug.
Define specificity
The measure of a receptors ability to respond to a single ligand.
Define selectivity
The degree to which a drug acts on a given site relative to other sites.
What is the difference between competitive vs non-competitive inhibition?
A competitive inhibitor structurally resembles the substrate for a given enzyme and competes to bind to the enzyme active site whereas non-competitive inhibitors bind at a different site to the substrate.
Define bioavailability
The proportion of a drug which enters the circulation and so is able to have an active effect in the body.
What is an irreversible enzyme inhibitor?
A molecule that reacts with an enzyme, causing it to change chemically so that it cannot catalyse its reaction.
What is a reversible enzyme inhibitor?
A molecule that binds non-convalently to an enzyme producing different types of inhibition depending on whether these inhibitors bind to the enzyme, the enzyme-substrate complex, or both.
What is the action of statins?
They inhibit the HMG-CoA reductase enzyme, blocking the rate limiting step in the cholesterol pathway so less cholesterol is produced.
What is EC50?
The concentration of drug that gives half the maximal response.
Would a drug with a lower EC50 have a lower or greater potency?
Great potency
What does Emax tell us about a drug?
Efficacy
Which is more efficacious, a full or partial agonist?
A full agonist is more efficacious because it can give a 100% response.
Would an antagonist shift a dose-response curve to the left or right?
The antagonist would shift the dose-response curve to the right because it reduces the potency of the drug.
Describe allosteric modulation.
An allosteric modulator binds to a different site on a receptor and influences the role of an agonist.
Does an antagonist show efficacy?
No, an antagonist has affinity but zero efficacy. An agonist however demonstrates affinity and efficacy.
What 3 ways can a receptor be desensitised?
- Uncoupled (an agonist would be unable to interact with a GPCR).
- Internalised (endocytosis, the receptor is taken into vesicles in the cell).
- Degraded.
Define pharmacodynamics
The effect the drug has on the human body.
Define pharmacokinetics
The action of the body on the drug (how it’s broken down).
What is first pass metabolism?
Reduced bioavailability of an orally administered drug due to metabolism of the drug by the gut and liver before it reaches the systemic circulation.
What is an example of a physicochemical drug reaction?
The adsorption of paracetamol by activated charcoal which is used to treat a paracetamol overdose.
What is the action of an inducer on drug metabolism?
Increase activity of cytochrome P450 and speed up metabolism of other drugs - may result in sub-therapeutic dose.
What are 3 examples of inducers?
- Anti-epileptics (Phenytoin, carbamazepine)
- Rifampicin (antibiotic)
- Chronic alcohol intake
What is the action of an inhibitor on drug metabolism?
Decrease cytochrome P450 activity and reduce metabolism of other drugs - may result in toxicity.
What are 3 examples of inhibitors?
- Ciprofloxacin, erythromyocin (antibiotics)
- Isoniazid (antibiotic)
- Amiodarone (for arrythmia)
What is first order elimination?
Catalysed by enzymes, rate of metabolism directly proportional to drug concentration.
What is zero order elimination?
Enzymes saturated by high drug doses, rate of metabolism is constant
What is synergy?
Interactions between drugs where the combined effect is greater than the sum of the individual effects. (1+1>2)
Define summation
Different drugs used together to have the same effect as a single drug would (1+1=1)
Define potentiation
Enhancement of one drug by another so that the combined effect is greater than the sum of each one alone. (1+1=1+1.5)
What are the pharmacokinetic actions? (ADME)
Absorption
Distribution
Metabolism
Excretion
What factors affect drug absorption?
- Motility
- Acidity
- (Physicochemical)
What are pro-drugs and what is an example of one?
Drugs that need to be activated enzymatically e.g. ACE inhibitors, enalapril.
How do ACE inhibitors work?
ACE inhibitors prevent angiotensin I binding to ACE so it can’t be converted to angiotensin II. (Prevents narrowing of blood vessels and so reduces BP)
Define adrenergic receptors
Receptors activated by catecholamines (adrenaline and noradrenaline) that help to trigger the fight or flight response.
Define cholinergic receptors
Receptors on the cell surface membrane that bind acetylcholine.