Flashcards in Pharmacology Deck (74)
What is pharmacokinetics?
How the body affects the drug - absorption, distribution, metabolism and excretion of the drug
What is pharmacodynamics?
How the drug affects the body
What are the different kinds of receptors?
GPCRs e.g. beta-adrenoceptors
Ligand-gated ion channels e.g. nAchR
Kinase-linked receptors e.g. VEGFR
Cytosolic/nuclear receptors e.g. oestrogen receptor
What is an agonist?
A compound that binds to receptors and activates it; it can reverse the effect of an antagonist in competitive inhibition
What is an antagonist?
A compound that reduces the effect of an agonist; it does not activate the receptor and can reverse the effects of an agonist in competitive inhibition.
What is EC50?
The concentration of the drug that gives half the maximal response.
What is Emax?
The maximum possible effect of the agonist
What is intrinsic activity?
Intrinsic activity = Emax of partial agonist + Emax of full agonist
What is affinity?
How well a ligand binds to a receptor; it is a property shown by both agonists and antagonists
What is efficacy?
How well a ligand activates a receptor; only agonists have efficacy
What is tolerance?
A reduction in drug effect over time with continuous, repeated high concentrations of the drug. This is a clinical description.
What is desensitisation?
The mechanism through which tolerance occurs. It happens though:
Desensitisation of the receptors either by uncoupling them, internalising them or degrading them.
What is receptor-reserve?
An integrative measure of the response-inducing capacity of an agonist and of the signal amplification capacity of the corresponding receptor.
What are the three phases of plasma levels?
Uptake into plasma
Distribution from plasma
Elimination from plasma
What is the rate of diffusion for a dissolved drug?
Rate of diffusion is proportional to the concentration gradient (first order process with respect to concentration)
1/ distance to diffuse
Rate of diffusion is proportional to temperature
What are the compartments of the body and how much fluid is in there?
Plasma - 5L
Interstitial - 15L
Intracellular - 45L
What are the different mechanisms of movement?
Through extracellular spaces
What is bioavailability?
The amount of drug taken up as a proportion of the amount administered.
What are the two main routes of elimination for drugs?
Hepatic elimination and renal elimination.
What is clearance?
The volume of plasma that can be completely cleared of the drug per unit of time.
The rate at which the plasma drug is eliminated per unit of plasma concentration.
Both are measures of efficiency and are measured in ml/min
How are water soluble molecules eliminated in the kidneys?
They pass through the glomerular endothelial gaps and are eliminated by glomerular filtration.
How are larger water soluble eliminated in the kidneys?
Through active tubular secretion
How is clearance calculated?
The rate of appearance in urine / plasma concentration
What does clearance assume?
The rate of elimination is equal to the rate of appearance in the urine
What causes impaired renal clearance?
Acutely - reduced perfusion causing AKI
Chronically - HTN or DM causing CKD
What effect does hypoalbuminaemia have on drug clearance?
Lipid soluble drugs have higher freely diffusible fractions and greater effects. Elevated plasma creatine and urea compete for lipid binding sites on protein and displace more drug.
What adjustments need to be made for renal impairment?
Choose drugs not eliminated renally
Avoid nephrotoxic drugs
Measure plasma concentrations if there's a toxicity risk
Haemodialysis and give normal doses as usual
How are drugs eliminated renally?
Through active transport systems; they vary in efficiency for different compounds.
What is the hepatic extraction ratio?
The proportion of the drug that is removed by one pass through the liver.
How are drugs with a high HER limited?
How are drugs with a low HER limited?
What are phase I reactions?
Non-specific reactions that attack specific side chains on large molecules
What does cytochrome P450 do?
Catalyses oxidative hydroxylation in the liver
What are phase II reactions?
Conjugation reactions to glucaronic acid
How much liver needs to function needs to be lost for it to have an effect on drug metabolism?
More than or up to 70% of functioning liver
Why are IV drugs used?
For drugs that are ineffective administered by other routes or for patients who can't absorb oral medications
What features does the ideal IV drug have?
Drug is broken down by tissue/plasma enzymes irrespective of liver or renal function
Obvious and predictable dose response relationship
Low risk of toxicity
High therapeutic window
Easy to assay plasma drug concentration quickly
For drugs with a high VD, what is needed before a constant infusion?
A loading bolus dose to speed up the saturation of all compartments.
How is ACh synthesised?
At the NMJ through choline acetyltransferase
What enzyme breaks ACh down?
How does botox work?
It inhibits ACh release at the NMJ causing paralysis, it is a protease. It degrades vesicle proteins preventing the vesicle fusing to the presynaptic membrane.
What are reversible cholinesterase inhibitors used for?
Treating myasthenia gravis as if increases the amount of ACh at the NMJ.
What are mAChR agonists used to treat?
What are the adverse effects of mAChR agonists?
Miosis - excessive constriction of the pupil
What are mAChR antagonists used to treat?
Eye examinations to dilate the pupils
Used in asthma and COPD as bronchodilators
Used to treat urinary frequency
How many alpha adrenoceptors are there?
Alpha1 and alpha2
How many beta adrenoceptors are there?
beta1, beta2 and beta3
What effects do beta 1 adrenoceptors have upon activation?
Cardiac effects - increased force, rate and contraction
Renal effects - increased renin secretion and BP
What effects do beta 2 adrenoceptors have upon activation?
Bronchodilation, vasodilation and decreased GI motility
What effects do beta 3 adrenoceptors have upon activation?
Increased lipolysis and relaxation of the bladder
What are the three classifications of pain?
Acute, chronic non-cancer pain and cancer pain
How long does acute pain generally last?
What causes acute pain?
Activation of nociceptors, pain is carried by A-delta fibres and C fibres
What are the effectors of acute pain?
Behaviour, reaction and emotions
What are the different types of noxious stimuli?
Mechanical, thermal and chemical
What kind of pain do C fibres carry?
Diffuse, dull, intense pain
What kind of pain do A-delta fibres carry?
Localised, sharp pain
What is wind-up?
A perceived increase in pain intensity over time; stimulation by non-noxious input can suppress pain
How do local anaesthetics work?
They're sodium channel blockers which block the conduction of nerve impulses that carry the pain signal.
What is chronic pain?
Ongoing, persistent pain >3-6 months in duration
What are the principles of chronic pain treatment?
Pain perception, function/mobility, sleep, emotional and psychological consequences of pain and quality of life
What are adverse drug reactions?
A response to a drug which is noxious and unintended
What are augmented adverse drug reactions?
An extension of the clinical effect of the drug. It is predictable, dose-related and self-limiting. They can occur in patients with renal or hepatic impairment or elderly patients.
What are bizarre adverse drug reactions?
They're unrelated to dosage and not expected from the known pharmacological action. They're unpredictable and have mostly immunological mechanisms - hypersensitivity.
What are chronic adverse drug reactions?
Drug reactions that occur after long term therapy, they may not be immediately obvious with new medicines.
What are are delayed adverse drug reactions?
They also occur after long term therapy but the adverse reaction is delayed, for example teratogenesis or neoplasia.
What are end of use adverse drug reactions?
Withdrawal reactions that are serious complications related to the clinical effect. They occur after relatively long use.
What are the symptoms of anaphylaxis?
Rash, characteristic blotches, swelling of lips, face, oedema, central cyanosis, wheeze, hypotension, cardiac arrest
What are the blood markers for drug allergy?
Type A - serum concentration
Type B - tryptase, RAST, urine methyl histamine
What are the different types of drug interaction?
Synergy e.g. clavulanic acid and amoxicillin
What are the risk factors for a drug interaction?
A narrow therapeutic index
Steep dose/response curve
Saturable metabolism e.g. paracetamol or alcohol
How does pharmacodynamics play a role in drug interactions?
Agonists of the same receptor e.g. benzodiazepines and alcohol so the effect is potentiated
Partial agonists e.g. buprenorphine for opioid addiction
Antagonist e.g. beta blockers and asthma
How does pharmacokinetics play a role in drug interactions?
Absorption e.g. motility, acidity, solubility, complex formation or direct action on enterocytes
Distribution e.g. protein binding
Metabolism e.g. CYP450 - alcohol dehydrogenase and metronidazole
Excretion e.g. renal or biliary