Clinical Pharmacology Flashcards
What 2 areas are drugs distributed?
Tissue reservoirs
Protein-bound drug
What is bioavailability?
Measure of drug absorption where it can be used (F) as compared to when given IV
What things can affect absorption of drugs?
Formulation
Age (luminal changes)
Food (chelation, gastric emptying)
Vomiting/ malabsorption (Crohn’s)
What areas are included in first pass metabolism?
Gut lumen, gut wall and liver
What factors affect distribution of medication throughout the body?
Blood flow/ capillary structure Lipophilicity/ hydrophilicity Acidic/ Basic drugs Protein binding - Albumin - acidic drugs Globulins - hormones Lipoproteins - basic drugs Glycoproteins - basic drugs Volume of distribution
What is the equation for volume of distribution?
Vd = Dose/ [Drug]plasma
How would you interpret a volume of distribution?
A lower Vd is indicative of more drug in the blood and less in the tissues
A higher Vd is indicative of less drug in the blood and more in the tissues
What is the units for volume of distribution?
mg/litre
How can dose be calculated from the volume of distribution and the drug concentration in the plasma?
Dose = Vd x [Drug]plasma
How many phases of metabolism are there?
2 phases
What happens in the phases of metabolism?
Phase 1- oxidation - dealkylation or reduction - hydrolysis
Phase 2- Glucuronidation, sulphation, glutathione added, N-cetyl added
What is another name for phase 1 enzymes?
Cytochrome P450 enzymes
What found in grapefruit juice is a cyp inhibitor?
Furanocoumarins irreversibly inhibit CYP 3A4 which is responsible for metabolising 50% of drugs.
What is the importance of CYP2D6 in caucasians and east africans?
Absent in 7% of caucasians
Hyperactive/ increased induction in ~30% of East Africans
Apart from the kidneys what are the other routes of drug elimination?
Sweat, tears, genital secretions, saliva, breast milk, faeces, hair, gases - volatile compounds
How can enterohepatic circulation affect drug elimination?
When the drug is absorbed and then metabolised by the liver it can then become conjugated with bilirubin and released into the GI system. This would then cause some of the conjugated drug and bilirubin to be reabsorbed with fats and so the drug would then potentially be reabsorbed distal to the common bile duct.
What is zero order kinetics for drug elimination?
The drug is eliminated at a constant rate over time
What is first order kinetics for drug elimination?
The drug elimination is exponentially decreasing. As time increases the elimination decreases. Log of the drug concentration produces a straight curve
How is half life related to kinetics?
Half life is related to first order kinetics
It is independent of concentration
1/time
Define the clearance of drugs?
Constant proportion not amount of drug that is cleared
Volume of blood cleared per unit time (mL/min)
How do you calculate clearance?
Rate of elimination from body / drug concentration in plasma
What is the relationship between drug concentration and clearance?
The higher the drug concentration the higher the elimination rate and more drug cleared
At therapeutic doses what type of kinetics do most drugs have?
First order kinetics therefore half life is constant
What effect does a high dose have on the kinetics?
As the enzymes become saturated at high doses the elimination can become zero order and so a set amount of the drug is eliminated at a constant rate
What factors of PK affect elimination of a drug?
Vd
Clearance
Half life
How quickly is steady state achieved in most drugs?
5.5 half lives
What equation calculates dosing interval?
[Dose x Bioavailability correction] /
Dose interval
What calculation gives the loading dose for most drugs?
Loading dose = Steady state plasma concentration x Vd
How do clearance and elimination rate differ?
Clearance takes into account the rate of elimination from the body/drug concentration in plasma
Clearance is a constant proportion and not an amount but the elimination rate is the volume of blood cleared per unit time so is variable and an amount not a proportiob
To increase or decrease the Css, what dosing parameters could you change?
Volume of distribution
Dose of drug
Loading dose
What equation gives the mean arterial pressure?
Cardiac output x total peripheral resistance
What equation gives the cardiac output?
Stroke volume x heart rate
How is the radius of blood vessels related to the resistance?
As the radius increases by a number the resistance to flow increases by a factor of 4 (radius to the power of 4)
What are 3 subcategories of elevated blood pressure?
Essential
Primary
Idiopathic
What is NICE’s definition of HTN?
Elevated blood pressure that is associated with an increase in risk of some harm
>140/90 mmHg = HTN
When do we treat HTN?
140/90 <80yrs old including type 2 diabetics
150/90 >80 years old
135/85 type 1 diabetics
What is stage 1 of HTN?
Clinic BP = 140/90 - 159/99mmHg
ABPM average or HBPM average from 135/85 to 149/94mmHg
What is stage 2 HTN?
Clinic BP = 160/100 to 180/120
ABPM or HBPM average of >150/95
What is stage 3 HTN?
Clinic SBP = >180 or
Clinic DBP = >120
What is prehypertension?
> 120/80 <140/90 mmHg
What enzyme does Ramipril inhibit?
Angiotensin converting enzyme
What angiotensin receptor do ARB’s block?
Angiotensin 1 receptor
What are the 5 effects of Angiotensin 2?
1- Increased sympathetic activity
2- Tubular Na Cl reabsorption and K retention. H20 retention
3- Adrenal cortex release of renin - H20 retention
4- Arteriolar vasoconstriction. Increase in blood pressure
5- Posterior Pituitary gland - ADH secretion - H20 absorption in the collecting duct
Where are the ACE found predominantly?
Luminal surface of capillary endothelial cells, predominantly in the lungs
How do ACEi cause hyperkalaemia?
Lowers aldosterone which causes an increase in K+
How can ACEi cause renal failure?
Renal artery stenosis - constriction of efferent arterioles
How do ACEi work in the vasculature?
Potentiates bradykin - vasodilation via NOS/NO and PGIs. ACEi causes vasodilation in low-renin hypertensives
How do ARBs work?
Block AT1 and AT2 receptors - no effect on bradykinin
In low-renin hypertensives which drug is better ACEi or ARBs?
ACEi because it works at the rate limiting step stage from Ang1 to Ang2 conversion. The more renin the more Ang1 there is and so the more ACE converts 1 to 2 but ACEi will stop this. If there is a low renin then the pathway is not upregulated anyway and so won’t have much of an effect by blocking the receptors in ARBs
By targeting AT1 receptors with ARBs what is the result?
Inhibiting Ang-2 mediated vasoconstriction - chymase production
What type of CCB is amlodipine?
dihydropyridine
What type of CCB is diltiazem?
Non-dihydropyridine
What is an uncommon but important side effect of dihydropyridine CCBs?
Palpitations (compensatory tachycardia)
Name a phenylalkylamine CCB
Verapamil
How does verapamil work?
Class IV anti-arrhythmic agent/ prolongs action potentials/ effective refractory period
How does verapamil affect chronotropic and ionotropic results on the heart?
Negative chronotropic and ionotropic
Name a benzothiazine CCB
Diltiazem
Where in the nephron do thiazide and thiazide-like diuretics work?
distal tubule
How do thiazide and thiazide-like diuretics work?
Block sodium chloride co-transporter which then reduces sodium resorption and therefore water
What are common side effects of thiazides and thiazide-like diuretics?
Hypokalaemia, hyponatraemia, hyperuricaemia, hyperglycaemia, hypercholesterolaemia, hypertriglyceridaemia
What is the difference in the pathway of treating HTN in diabetics and non-diabetics?
First line in diabetics is ACEi regardless of age rather than CCB in non-diabetics
How does hydralazine work?
Arteriolar vasodilation and reduction in TPR - actual MAO is unknown
How does ivabradine work?
Blocks the If current that controls spontaneous depolarisation in SA node
Does furosemide affect preload or afterload?
reduces preload
How does spironolactone work?
Aldosterone receptor antagonist
How does secubitril work?
Inhibits natriuretic inactivating enzymes - potentiates effects of ANP and BNP
Why are beta blockers given in heart failure?
Reduce HR and therefore allow blood to enter the ventricles during diastole. They therefore increase diastole and allow enough perfusion of the cardiac myocytes
What is the medical term for water loss without electrolytes?
Aquaretic
What is the medical term for increased production of urine?
Diuretic
Where do carbonic anhydrase inhibitors work?
PCT of the renal tubule
Where do osmotic diuretics work?
PCT
Where do SGLT2 inhibitors work?
PCT
Where do loop diuretics work?
Ascending loop of henle
Where do thiazides work?
DCT
Where do potassium sparing diuretics work?
CD
What do carbonic anydrase inhibitors do?
Block CA which prevents bicarbonate breaking down into water and CO2 and so bicarb is lost
By what mechanism do CA inhibitors cause hypokalaemia?
On the basolateral surface Na/K ATPase brings sodium into the cell and potassium out of the blood into the cell. CA reduces the H2CO3 break down intracellularly which therefore means less H+ dissociates in the cell and so less Na enters cell by the Na/H+ exchanger on the luminal surface. More Na delivery to the CD and more Na reabsorbed through the ENaC channels in exchange for K+. Causing Hypokalaemic metabolic acidosis
Give an example of an osmotic diuretic
Mannitol
How do SGLT2 inhibitors work?
Prevent the glucose entering the cell through the SGLT2 channel in the PCT therefore osmotic effect more water is retained in the lumen and so more water is lost plus glucose.
How do loop diuretics work?
Block NKCC2 channel in basolateral side in thick ascending limb. Therefore more Na in the lumen and therefore more water loss.
What is a problem with loop diuretics in relation to K+ and pH?
Hypokalaemic metabolic alkalosis. Na/H channel works too effectively as more Na in lumen and therefore more H+ is lost from the cell and so creating alkalosis
How do thiazide diuretics work?
Block Na/Cl co-transporter in DCT. Reduced Na entry into cell therefore increased calcium reabsorption through Na/Ca antiporter on basolateral surface
What effect does aldosterone have on ENaC and Na/K ATPase channels?
Increases their expression in principal cells of the CD therefore increased reabsorption of Na and therefore H2O
Name an aquaretic and how would it work?
Tolvaptan - ADH antagonist
What are aquaretics used for?
Treat hyponatreamia (and prevent cyst enlargement in Adult polycystic CDK)
How does alcohol work as a diuretic?
Inhibits ADH release and doesnt block the receptor
What is nephrotic syndrome characterised by?
Nephrotic syndrome classically presents with heavy proteinuria, minimal hematuria, hypoalbuminemia, hypercholesterolemia, edema, and hypertension
What are the stages of kidney disease and what are their respective % renal function?
Stage 1 - 90% Stage 2 - 89-60% Stage 3 - 59-30% Stage 4 - 29-15% Stage 5 - <15%
What is Bartter’s syndrome?
NKCC2 channel reduced or no function in the thick ascending loop of henle.
What is Gitelman’s syndrome?
Reduced or no functioning NaCl co-transporter in the DCT
How could Bartter’s and Gitelman’s syndrome be treated?
Loop diuretics for Bartter’s and thiazide diuretics for Gitelman’s
What are broadly the four mechanisms of an ADR?
Exaggerated response
Desired pharmacological effect at an alternative site
Additional/ secondary pharmacological effect (QT prolongation)
Triggering immunological response (anaphylaxis)
What is a split antigen?
A subset of the antigen that may cause a reaction
Why are ACEi not first line in African Caribbean populations?
They have typically lower renin levels and so they wouldnt be making much of the Ang1 anyway plus angioedema is more prevalent than in young white caucasians
Why are east asians less able to metabolise alcohol?
They have a mutated aldehyde dehydrogenase enzyme - single amino acid mutation
Why is CYP2D6 an important enzyme?
approx 25% drug are metabolised by it. 6% of caucasians carry two null alleles therefore decreased first pass metabolism for metoprolol for example.
What do oestrogens, progestagens and androgens have in common?
They are all sex steroid hormones
What chemical structures make the steroid hormone base?
3 benzene rings and 1 pentameric ring
In outline how are steroid hormones made?
Cholesterol to pregnenolone to then 2 pathways one leads to androstenedione then to estrone and the second pathway to testosterone then to estradiol. At the level of the androsetenedione and testosterone there can be a conversion
Using what enzyme can androstenedione be made into testosterone?
17beta-HSD
Where do steroid hormones mainly act?
Intracellularly by causing changes in gene transcription and expression hence the lag in the effects
Why do steroid hormones take long to exert its effects?
causing changes in gene transcription and expression hence the lag in the effects
Which steroid hormone also has a membrane bound receptor?
Oestrogen
What is the major effect of oestradiol?
Growth of endometrium and breast also stimulates production of progesterone receptor
What is the major effect of progesterone?
Stimulates growth of endometrium and breast, maintains pregnancy, inhibits production of oestrogen receptor
What is the major effect of testosterone?
Stimulates male characteristics, anabolism
How does oestrogen affect HDL and LDL?
It lowers LDL and raises HDL
Name a side effect of progesterone on mood?
Can get irritability depression and pms, lack of concentration
Name a side effect of testosterone?
Male secondary characteristics, anabolic, acne, voice changes, increases aggression, adverse effects on lipid profile particularly HDL-C/LDL-C ratio
Why does carbamazepine interact with COCP?
Increase production of CPY enzymes and therefore reduces their efficacy
Name 2 indications for prescribing of HRT?
Symptoms of menopause - hot flushes, sweats and dyspareunia
Oesteoporosis
What are the risks of opposed oestrogen?
Increases risk of developing breast cancer
What are the risks of unopposed oestrogen?
Increases risks of developing endometrial and ovarian cancers
How do oestrogens increase risk of VTE?
Increased activated protein C resistance, increased thrombin activation, decreased anti-thrombin 3 activity, decreased protein S levels, decreased factor VII levels and decreased tissue factor pathway inhibitor - only for oral delivery systems. - in essence, it puts the blood into a procoagulative state
What is mifepristone and how does it work?
progesterone receptor antagonist, sensitising the myometrium to prostaglandin-induced contractions. Used for termination of pregnancy
What is clomiphene used for?
Anovulation - competes with oestrogen for ER binding, leads to ovulation induction through increased production of anterior pituitary hormones
How does ulipristal work?
Selective progesterone receptor modulator
What is ulipristal used for?
EHC
why do we treat high total cholesterol?
It is linked to CHD
For how much LDL cholesterol needs to be reduced for a 20% reduction in CVD risk?
1mmol/L
MOA of statins?
HMG-CoA reductase inhibitor - upregulation of hepatic LDL receptors therefore increased clearance of LDL
Apart from the common MOA of statins how else to they work?
Increased NO release, VEGF release and decreased endothelin production
Stabilization of atherosclerotic plaque - reduced SMC proliferation and increased collagen
Improved hemostasis - decreased fibrinogen, platelet aggregation and increased fibrinolysis
Is Simvastatin a prodrug or active ingredient?
Prodrug
Is Atorvastatin a prodrug or active ingredient?
Active ingredient
What scoring system is used to determine if someone should be on a statin?
QRISK
At what QRISK score to we give someone statins for primary prevention?
10 year 10% QRISK and above
What % reduction at we looking for in a patients bloods post statin therapy?
> 40% reduction in non-HDL-C after 3 months
Why is simvastatin taken at night?
Circadian rhythm of LDL receptor synthesis/ activity is at night and so this is when you want it to take effect
How do fibrates work?
Peroxisome proliferation-activation receptor activator - PPARalpha is a nuclear transcription factor that regulates expression of genes that control lipoprotein metabolism - increased production of lipoprotein lipase
Give an example of a cholesterol absorption inhibitor
Ezetimibe
MOA of cholesterol absorption inhibitor?
Inhibit NPC1L1 transporter which reduces absorption of cholesterol by the gut ~50%, hepatic LDLD receptor expression increased and therefore lowers total cholesterol ~15% and LDL ~20%.
As a guide for those being treated for secondary prevention with statins what is the target LDL-C and total cholesterol?
2mmol/L - LDL-C
4mmol/L - Total
How do PCSK9 inhibitors work?
Protein that binds internalised LDL-R directing them for degradation
Name a PCSK9 inhibitor?
Alirocumab
What are rough NNT for statins?
17-20
What is insulin secreted in response to?
Increased glucose, Increased incretins (GLP-1 and GIP)
Glucagon, Parasympathetic activity M3
What inhibits the release of insulin?
Decreased glucose, cortisol, sympathetic activity (Alpha2)
What 4 categories of insulins are there in relation to their onset of action?
Rapid, shore, intermediate and long
How quickly do rapid acting insulins act?
within 10-20minutes
How quickly do short acting insulins act?
within 30-60mins
How quickly do intermediate acting insulins act?
within 60-120mins
How quickly do long acting insulins act?
60-90mins
When do short acting insulins peak in their activity?
2-5hours
When do rapid acting insulins peak in their activity?
40-50mins
When do intermediate acting insulins peak in their activity?
4-12hours
When do long acting insulins peak in their activity?
plateau between 2-20hours
How long do rapid acting insulins act for?
3-5hours
How long do short acting insulins act for?
5-8hrs
How long do intermediate acting insulins act for?
18-24hrs
How long do long acting insulins act for?
20-24hrs
What is the most common insulin dosing regimen?
basal bolus regimen
Give a name for a rapid acting insulin
Insulin aspart
Give a name for a fast acting insulin
Soluble insulin, humulin S, actrapid
Give a name for an intermediate acting insulin
Isophane insulin
Give a name for long acting insulin
Insulin glargine
What is DKA?
Ketonaemia, hyperglycaemia, acidosis. Although DKA can present with low blood ketones and hyperglycemia may not always present
On the NICE T2DM guidelines when do you consider adding medication?
If HbA1c is above 48mmol/mol (6.5%)
What is the first line treatment for T2DM?
Metformin
After which HbA1c result after starting metformin would you consider adding a second agent?
HbA1c level above 58mmol/mol (7.5%)
What drugs can be used second line in T2DM?
DDP-4i, pioglitazone, SU, SGLT-2
If HbA1c rises above 58mmol/mol(7.5%) after 2 agents used what else can you use?
combination of any of these with a metformin backbone which includes an insulin based treatment, or a GLP-1 analogue
Name a GLP-1 analogue
Liraglutide, dulaglutide, semaglutide
MOA of biguanides
decrease hepatic glucose output (gluconeogenesis, glycogenolysis) and increase glucose utilisation in skeletal muscles, suppress appetite so limit weight gain
MOA of sulfonylureas
stimulate beta-cell pancreatic insulin secretion blocking ATP-dependent potassium channels
What is a problem with sulfonylurea use?
Need residual pancreatic function
How is insulin normally released from the pancreatic beta cell?
Glucose enters the cell through GLUT-2 transporters on the cell membrane. Glucose is metabolised and causing a rise in ATP. This then causes ATP-dependent potassium channels to start to close which causes cell membrane depolarisation allowing calcium to enter the cell. The calcium entering the cell will cause the vesicles which house the insulin to fuse with the cell membrane then release the insulin
What is a side effect of sulfonylureas that is potentially unpleasant?
Weight gain as there is more insulin being released and so you get anabolic effects
MOA of thiozolidinediones?
Insulin sensitisation in muscle and adipose tissues. Decreased hepatic glucose output. Activation of PPAR-gamma which cause increased gene transcription to allow glucose to be made into triglycerides in the cells.
Why do thiozolidinediones take so long to work?
Affect gene transcription and so this takes 6-8weeks for effect
Why do you get weight gain when using pioglitazone?
Fat cell differentiation - increase in the physical number of fat cells
MOA of SGLT-2 inhibitors
Block the sodium-glucose 2 transporter in the renal PCT. Causes decreased glucose absorption from tubular filtrate and so increased urinary glucose
What is a risk of SGLT-2 inhibitors?
As they physically prevent glucose re-entering the blood they can cause hypoglycaemia but much less compared to the other oral antihyperglycaemic agents
What is a side effect of the SGLT-2 inhibitors that would potentially require treatment with antibiotics?
UTI and genital infections as there is more glucose present and so would allow bacteria to grow faster
What are the 5 effects of GLP-1 analogues?
Pancreas- increased insulin biosynthesis and secretion, decreased glucagon secretion
Bain - decreased food intake through increased satiety
Liver (indirect) - decreased glucose production
Stomach- delayed gastric emptying
Muscle (indirect) - increased glucose uptake
MOA of DPP4- inhibitors
Prevent incretin degradation which are glucose dependent (therefore post-prandial) action. Do not stimulate insulin secretion at normal blood glucose - therefore lower hypoglycemic rik
What is good about DPP4-i for normal weight patients?
Weight neutral - suppresses appetite so no changes in weight
MOA of GLP-1 analogues
Increase glucose dependent synthesis of insulin secretion from beta-cells activate GLP-1 receptors and therefore are not degraded by DPP-4
What is added to insulin preparations to alter their release from the site of injection?
Zinc or protamine or a combination of the two
Looking at a cardiac cause what can cause a blackout?
Bradyarrhythmias —> palpitations —> blackout
Tachyarrhythmias can also cause the same
In a fast cardiac action potential what ionic change causes the upstroke of the potential?
Sodium influx into the cell
In a fast cardiac action potential what ionic change causes the first (1) downward stroke of the potential?
Opening of potassium channels causing potassium to leave the cells
In a fast cardiac action potential what ionic change causes the second (2) downstroke of the potential?
Calcium entry into the cell causes the maintenance of AP temporarily
In a fast cardiac action potential what ionic change causes the third (3) downstroke of the potential?
The exit of potassium from inside the cell to outside maintains the downward stroke of the AP
In a fast cardiac action potential what ionic change causes the fourth (4) downstroke of the potential?
Plateau phase where the sodium/potassium ATPase pump is exchanging sodium to leave the cell and potassium to enter the cell making it even more negative
What is a class 1 anti-arrhythmic?
Sodium channel blocker that causes a marked slowing conduction of the tissue (phase 0) - minor effects on AP duration
What is a class 2 anti-arrhythmic?
Beta blockers - diminish phase 4 depolarisation and automaticity (focal arrhythmia).
They work on phase 2 of the cardiac AP
What is a class 3 anti-arrhythmic?
Potassium channel blocker - block the 3rd phase. This would extend the refractory period.
Increases action potential duration and so would extend the QT - pro-arrhythmic agent.
What is a class 4 anti-arrhythmic?
Calcium channel blockers decrease inward calcium currents resulting in a decrease of phase 4 spontaneous depolarisation. Effect is a plateau phase of action potential. This would affect phase 2 of the cardiac AP
There is a slow cardiac action potential which can be found in which part of the heart?
SA and AV node
What is stage 4 of the funny current?
Sodium and potassium entry into the cell
What is stage 0 of he slow cardiac AP?
Upward stroke - calcium entry into the cell
What is stage 2 of the slow cardiac AP?
Calcium entry into the cell causes a peak in the current
What is stage 3 of the slow cardiac AP?
Potassium leaving the cell causes a downward trend
How would calcium channel blockers affect the funny current?
Slope of phase 0 is more flat which is the conduction velocity. Due to slow conduction through the SA and AV node. This would then mean that the refractory period is shifted to later causing a bradycardia
How could drugs affect automaticity of the SA and AV nodes?
B agonists would increase the slope at phase 4 of the funny current. This increases the speed of action potential.
Muscarinic agonists or adenosine would cause phase 4 slope of the funny current to become flatter and a longer period of time before AP activation
Name two abnormal impulse generations
Automatic rhythms
Triggered rhythms
Name the subsets of the automatic rhythms
Enhanced normal automaticity - increase AP from SA node - tachycardia
Ectopic focus - AP arises from sites other than SA node. Abnormal electrical conduction due to ventricular ectopic foci
Name the subtypes of triggered rhythms
Delayed afterdepolarisation - arises from the resting potential that doesn’t result in a full AP
Early afterdepolarisation - AP arises from the plateau phase
Name the two subsets of abnormal conduction
Conduction blocking
Re-entry
Name the subtypes of conduction blocking during an AP
1st, 2nd and 3rd degree heart block.
This is when the impulse is not conducted from the atria to the ventricles
Name the 2 subtypes of re-entry rhythms
Circus movement and reflection
What is a bundle of Kent and what is the result?
Accessory pathway in the heart that leads to preexcitation and then Wolf-Parkinson-White syndrome (WPW)
What is a re-entry rhythm in cardiology?
In a circuit the pathway leaves and comes back around another conduction pathway back around on itself
What is the worst side effect of a re-entrant rhythm?
SVT - a constant re-entry of AP through the AV node that has some APs leaving and entering the Bundle of His through the ventricles
What drugs can be used for abnormal AP generation?
Beta blockers of CCB - decreases phase 4 slope in the pacemaker cells and rises the threshold
In case of abnormal conduction what drugs can be used to treat it?
Decrease in conduction velocity phase 0 is affected which would be a sodium channel blocker.
Effective refractory period would increase (so the cell wont be reexcited again) - class 3
What are the Vaughan-Williams Classification classes and how do they affect action potentials?
Class: 1A - moderate phase 0 effects 1B - no change in phase 0 1C - marked phase 0 effects 2 - beta-blockers 3 - prolonged repolarisation 4 - CCB
What drugs are in the Vaughan-WIlliams Classification classes?
1A - Quinidine and procainamide 1B - Lidocaine 1C - Flecainide and propafenone 2 - Bisoprolol, metoprolol, propranolol 3 - Amiodarone and sotalol 4 - Verapamil and diltiazem
How do class 1A antiarrhythmics work and their effects on ECGs?
Decrease conduction in phase 0
Increase refractory period (increase APD and sodium inactivation)
Decrease automaticity (decrease slope of phase 4, fast potentials)
Increase threshold for sodium
Increase QRS and QT
What can class 1A anti-arrhythmics be used for?
Quinidine - Maintain sinus rhythm in AF and A flutter and to prevent recurrence
Procainamide - acute IV Tx of supreventricular and ventricular arrhythmias
How do class 1B anti-arrhythmics effect cardiac activity?
Fast binding
No change in phase 0 in normal tissue
APD slightly decreased
Increased threshold for sodium channels
Decreased phase 0 conduction in fast beating or ischaemic tissue
How do class 1B anti-arrhythmics affect the ECG?
None in normal tissues, in fast beating or ischaemic tissues increases the QRS width
What can class 1B antiarrhythmics be used for?
VT especially during ischaemia
Not used in atrial arrhythmias or AV junction arrhythmias
How do class 1C antiarrhythmics effect cardiac activity?
Very slow binding
Significantly decrease phase 0 (sodium)
Decrease automaticity (increased threshold)
Increased APD (potassium) and increased refractory period especially in depolarising atrial tissue
How do class 1C antiarrhythmics effect ECGs?
Increased PR and QRS and QT
What can class 1C antiarrhythmics be used for?
Supraventricular arrhythmias (fibrillation and flutter)
Premature ventricular contractions
WPW syndrome
What are class 2 antiarrhythmics cardiac affects?
Increase APD and refractory period in AV node to slow AV conduction velocity
Decreased phase 4 depolarisation (catecholamine dependent)
How do class 2 antiarrhythmics affect ECGs?
Increased PR and decreased HR
What can class 2 antiarrhythmics be used to treat?
Sinus and catecholamine dependent tachycardia
Converting restraint arrhythmias at AV node
Protecting the ventricles from high atrial rates (slow AV conduction) in atrial flutter/ fibrillation
What are class 3 antiarrhythmics cardiac affects?
Increase refractory period and increase APD (potassium channels)
Decreased phase 0 and conduction (sodium)
Increased threshold
Decrease phase 4 (beta blocking and calcium channel block)
Decreased speed of AV conduction
How do class 3 antiarrhythmics affect ECGs?
Increase PR, QRS and QT
Decreased HR
What can class 3 antiarrhythmics be used for?
Effective for most arrhythmias e.g. VT and SVT
What are the ECG changes seen with class 3 antiarrhythmics?
Increased APD and refractory period in atrial and ventricular tissues
Slow phase 4 (beta blocker at lower doses)
Slow AV conduction
What are class 4 antiarrhythmics cardiac effects?
Slow conduction through AV (calcium channels)
Increase refractory period in AV node and increase slope of phase 4 in SA node to slow HR
What are class 4 antiarrhythmics effects on the ECG?
Increase PR
Increase/decrease HR depending on blood pressure response and baroreflex
What can class 4 antiarrhythmics be used for?
Control ventricles during SVT
Convert SVT (re-entry around AV)
How does adenosine work as an antiarrhythmic?
Natural nucleoside that binds A1 receptors and activates potassium currents in AV and SA node decreasing APD
Hyperpolarisation causing decreased HR
Decreased calcium currents - increase refractory period in AV node
What can adenosine be used for?
Convert re-entrant SVT
Diagnosis of coronary artery disease (scans - give to slow the HR)
How does vernakalant work?
Blocks atrial specific potassium channels (outward channel class 3)
How does vernakalant affect the heart?
Slows atrial conduction
Increases potency with higher heart rates
What is vernakalant used for?
Convert recent onset AF to normal sinus rhythm
How does ivabradine work?
Blocks If ion current highly expressed in sinus node
What can ivabradine be used for?
Reduce inappropriate sinus tachycardia
Reduce heart rate in HF and angina (avoiding blood pressure drops)
How does digoxin work?
Enhances vagal activity (increases potassium currents, decreases calcium currents and increases refractory period)
Slows AV conduction and slows HR
What can digoxin be used for?
Reduces ventricular rates in AF and Aflutter
How does atropine work?
Selective muscarinic antagonist
Blocks vagal activity to speed AV conduction and increase HR
What is atropine used for?
Treat vagal bradycardia
Should flecainide be used alone in atrial flutter and if not with what?
No, give AV nodal blocking drugs to reduce ventricular rates in Atrial Flutter