Foundations of medicine Flashcards
What determines the severity of the effect a drug has on the body; Time in body, OR time bonded to receptor?
Time in body.
What is an agonist?
A substance that can bind to a receptor and produce a response.
What is Efficacy?
The ability of the agonist to produce a cellular response - e.g. high efficacy means it produces more of a response.
What is Affinity?
The ability of an agonist to bind to a receptor.
If one drug is more potent than another what does that mean?
The more potent drug produces the same response at a lower dose.
What is Pharmacovigilance?
The detection, assessment, understanding and prevention of adverse side effects in association with a drug.
What does a wide therapeutic index mean? why?
That very few people taking an effective therapeutic dose (for the intended effect) will also experience adverse side effects.
This is because the efficacy of the drug in relation to the adverse side effect is much less than in relation to the therapeutic effect.
What is drug selectivity?
When a drug has a higher affinity and efficacy for one type of receptors over another type (which may cause a side effect)
What is a competitive (reversible) antagonist?
Does not produce a biological effect directly but competes with an agonist for binding.
When a competitive reversible antagonist is in effect at a receptor how can a full response still be achieved?
Increase the concentration of agonist.
A competitive reversible antagonist decreases what in the agonist?
Its potency
An antagonist that permanently stops an agonist from binding to a receptor is what kind of Antagonist?
A non-competitive antagonist.
If a non-competitive antagonist is present can a full response still be achieved? Therefore what is reduced in the agonist?
No. It’s efficacy.
What is an allosteric antagonist?
An antagonist that changes the shape of the receptor so that the agonist cannot bind, a type of non-competitive antagonist.
What two ways might a pharmokinetic antagonist work?
- by reducing its distribution.
- increasing its excretion.
What is a partial agonist?
An agonist in which the full response cannot be achieved even if 100% of receptors are occupied, due to low efficacy.
if a partial agonist is in the presence of a full agonist what happens?
The partial agonist acts as an antagonist and the full response is not achieved as easily if at all.
Three divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
Enteric (GI tract - no CNS involvement)
What is one of the reasons a multi-organ response can be achieved in the sympathetic nervous system? to do with post-ganglionic neurones.
Multiple post ganglionic neurones can be stimulated by one preganglionic neurone.
Give some examples of the effects of stimulating the sympathetic nervous system? (6)
Heart-rate increases
Blood vessels constrict apart from those in muscles.
Gi motility decreases
Pupils dilate
Salivary glands are stimulated and produce amylase.
Liver starts gluconeogenesis and glycogenolysis.
Effects of stimulating the parasympathetic nervous system?
Heart rate decreases - no effect on blood vessels.
Increased GI motility.
Pupil constriction.
Salivary glands secrete amylase
Liver and kidney are unaffected.
What is the receptor and neurotransmitter used when an impulse is transmitted at a ganglion in an efferent neurone in the autonomic nervous system.
Acetylcholine, type 1 nicotinic receptors.
Describe the two types of nicotinic receptors.
Both types are made up of 5 subunits.
Binding of Acetycholine to the å submits allows the influx of Na+
Both respond to Acetylcholine but differ in response to other neurotransmitter.
What is the receptor and transmitter at all parasympathetic post-ganglionic nerve endings?
Muscarinic receptors, and acetylcholine.
What is the receptor and transmitter at most sympathetic post-ganglionic nerve endings?
Noradrenaline and Adrenergic receptors.
Two examples of exceptions in the receptors and neurotransmitters used normally in the sympathetic nervous system?
Sweat glands - acetylcholine and muscarinic receptors are used.
Adrenal medulla - As adrenaline and noradrenaline produced here the neurotransmitter is acetylcholine and the receptor is nicotinic type 1.
Neurotransmitter and receptor in the somatic nervous system in efferent neurones to muscle fibres?
Acetylcholine and nicotinic.
Describe the synthesis and release of Acetylcholine at synapses.
- When action potential arrives vesicles containing Acetylcholine fuse with the presynaptic membrane and are released into the synaptic cleft.
- Acetylcholine interacts with muscarinic or nicotinic receptors.
- Acetylcholine is rapidly broken down by acetylcholinesterase.
- Choline is taken back into the presynaptic neurone and acetylated.
Examples of two drugs that mimic Acetylcholine and their uses.
Pilocarpine - used as eye drops to treat glaucoma.
Bethanecol - stimulates muscle contraction, occasionally used to return normal GI function after anaesthesia.
Four examples of drugs that block Acetylcholine and their uses.
Atropine - reduces secretions.
Ipatropium - bronchodilator.
Hyoscine - Motion sickness or to facilitate endoscopy.
Tropicamide - eyedrops to induce mydriasis (pupil dilation).
Will a drug that affects the synthesis, packaging, release or reabsorption of Acetylcholine affect Parasymapthetic/somatic/both? Why?
Both, due to the fact both use Acetylcholine as a neurotransmitter despite different receptors.
Give two examples of drugs that affect acetylcholinesterase.
Edrophonium - short acting - to diagnose myasthenia gravis (weakness of certain muscles)
Neostigmine - medium acting - to treat myasthenia gravis.
In what situation is Noradrenaline used as a neurotransmitter?
Stimulating blood vessels in sympathetic system and in cranial parasympathetic system, but not sacral parasympathetic system.
How is noradrenaline synthesised and released?
Synthesised as tyrosine is taken into the cell and converted to noradrenaline, then packaged into vesicles and released into the synaptic cleft.
How is noradrenaline removed? (3)
Metabolised by monoamine oxidase (MAO) when spare in the cytosol.
Taken back into the cell by specific transport mechanism when free in the synaptic cleft.
Also taken back into neighbouring cells and metabolised by catechol-O-methyl transferase (COMT)
Three drugs that affect noradrenaline synthesis or uptake?
Reserpine - blocks the packaging of Noradrenaline into granules
Amphetamine - displaces noradrenaline from the blood vessels.
Cocain and some antidepressants block the reuptake of NA from the synapse.
Drugs that block the metabolism of NA? their effects?
MAO inhibitors - Antidepressant - Atropine like affects (dry mouth, blurred vision)
COMT inhibitors - Used in parkinsons to stop the breakdown of dopamine.
Difference in pharmacodynamics and pharmacokinetics?
Dynamics is the study on what the drug does to the body and kinetics is the study of what the body does to the drug.
When would you use a rectal pill?
Vomiting patient.
When would you deliver drugs as a syrup?
Paediatrics
Whats an enteral formulation and a parenteral formulation?
Enteral - undergoes first pass metabolism in the liver before reaching the systemic circulation.
Parenteral - does not undergo first pass metabolism in the liver before reaching systemic circulation.
Two Parenteral formulations?
Liquid, and lyophilized (freeze-dried).
Examples of topical formulations?
Cutaneous (skin) Cream, ointment, gel, paste
Inhaled: Metered Dose inhaler (MDI), Breath actuated device, Nebuliser.
Eye drops, Nasal Sprays, Vaginal, urethral suppositories.
For most oral drugs where is the greatest absorption of a drug?
The small intestine (not the stomach).
What is Gastric emptying and how does it affect the absorption of drugs?
The amount of time it takes to empty the contents of the stomach. increased gastric emptying slows the absorption of the drug.
Ways in which gastric emptying is slowed?
A solid meal (distension)
High fat meal.
High protein meal,
Low gastric pH.
What’s first-pass metabolism?
When drugs undergo various degrees of metabolism in the liver before reaching the systemic circulation, Travels from the intestine in the portal vein and then out from the liver through the hepatic vein.
Disadvantages of Oral administration?
Delay in drug onset
Drug exposed to gastric acid and digestive enzymes
Portal vein —> The liver before reaching systemic circulation, where some drugs undergo first-pass metabolism.
Enteral routes that avoid first-pass metabolism?
Rectal, Buccal (mouth), sublingual (under tongue).
Three types of Parenteral routes? and their features?
Intravenous - instantaneous onset, high peak concentration (effect not over a long time)
Intramuscular - immediate onset, small volumes only, oil based depot formulations give a very long duration.
Subcutaneous - small volumes only, very slow onset.
What is intraosseous?
Injection into bone.
Disadvantages of Parenteral routes?
Avoid the GI tract and first-pass metabolism.
Features of transdermal topical administration?
Very slow onset, prolonged action.
Requires highly lipophilic drug.
Local irritation possibly.
Features of a topical inhaled administration? (5)
Rapid delivery.
No first-pass metabolism.
Acts locally.
Allows low-dose to local site.
Rarely used for systemic drugs.
What are the variables passive diffusion across a membrane depends on?
The concentration gradient across a membrane. C1-C2.
Area of the membrane available for diffusion (A)
Thickness of the membrane.
Permeability of the membrane to the drug.
What is the equation to calculate simple diffusion across a membrane
(C1-C2) x Area x permeability.
Diffusion= ——————————-
Thickness
How does a lipid-soluble drug cross a membrane?
Diffuses through the lipid membrane,
How does a Water-soluble drug with a molecular weight below 200 pass through a cell membrane?
Diffusion through an aqueous channel.
How does a water-soluble drug that resembles a natural molecule pass through the cell membrane?
Down it’s concentration gradient through a carrier molecule (facilitated diffusion).
Against it’s concentration gradient by energy-dependent (ATP) channel (active transport).
If a weak acid drug is at a low pH will it be non-ionised or ionised and therefore will it diffuse across membranes and be absorbed?
Weak acid at low pH will be mostly non ionised and will therefore diffuse effectively across the lipid membrane.
If a weak base drug is at a low pH will it be non-ionised or ionised and will it therefore diffuse across membranes and be absorbed?
Will be ionised (accepted H+) and will not be effectively absorbed across the lipid membrane.
In a drug concentration by time graph what does the area under the graph represent?
Bioavailability.
What is the definition for bioavailability?
The fraction of the drug reaching the circulation as the active drug. 1 represents an intravenous dose (fully available) 0 would be not available.
Whats the symbol for bioavailability?
F
How do you calculate the bioavailable dose?
Administered does in mg (D) X Bioavailability (F)
What affects oral bioavailability?
Drug solubility.
Extent of drug binding to gut contents.
Drug absorption.
Extent of drug degradation.
Name three drugs that mimic the effect of Noradrenaline on the sympathetic nervous system? their effects and uses? their collective name?
Salbutamol. Bronchdilator used in asthma.
Adrenaline. used in cardiac arrest, and in local anaesthetics to reduce diffusion
Dobutamine. stimulates heart.
Sympathomimetics.
Effects of Noradrenaline on the body?
Relaxation of smooth muscle.
Tachycardia - increased heart rate and force.
Decreased blood flow to the skin and GI tract.
Increased blood flow to the muscles.
Effect of decreasing NA levels on the body?
Bradycardia - slowing of the heart rate.
Hypotension - reduced cardiac output.
increased blood flow to skin and GI tract.
Name two drugs that block the actions of NA on the sympathetic nervous system? Their effects and uses?
Propranolol -used for angina, hypertension, anxiety.
Prazosin - Resistant hypertension and benign prostate hypertrophy.
How are peripheral adrenoreceptors divided up?
Alpha1 and alpha2
Beta1 and beta 2