Drugs Flashcards
What is the Vaughan Williams classification?
1- Na channel blockers
2 - Beta blockers
3 - K channel blockers
4 - Ca channel blockers
How do class 1 drugs work?
Stabilising the cell membrane via decreased excitogenicity
What do type 1a drugs do? Name an example
Slow conduction velocity in both atrial and ventricular cells. Higher doses slows AV conduction. Block K leading to slower repolarisation.
Procainamide
When are type 1a drugs used?
Ventricular and atrial arrhythmias especially post MI
What do type 1b drugs do? Example.
Reduces AP duration in abnormal ventricular cells. Slows recovery of sodium channels.
Does not shorten effective refractory period
Lignocaine
When are type 1b drugs used?
Ventricular arrhythmias post MI or dig toxicity
What do type 1c drugs do? Example
Depressants of sodium current. Markedly slows conduction velocity in atria and ventricles.
Increased QRS duration.
Flecainide
Used for refractory arrhythmias
How do beta blockers work?
Block cardiac beta receptor response to sympathetic nervous system stimulation.
Decreased G-protein S responses and decreased cAMP.
Also interfere with the binding of epinephrine and other stress hormones ro receptors
B1 receptors are located in?
The heart and kidneys
B2 receptors are located in?
Lungs, GI, liver, uterus, smooth muscle, skeletal muscle
How do B blockers affect action potential
Decreased rate of phase 4 depolarisation + slows SA node rate.
Prolonged PR on ecg
How do potassium channel blockers affect the AP?
What is an example?
Prolongs by blockade of K - aka lengthed repolarisation
Amiodarone
Potassium blockers do what to the refratory period?
Increase in the effective refractory period
What can potassium channel blockers cause?
Torsades, by QT prologation
Amiodarone affects atrial or ventricular tissues?
Both, including AV node and SA node
Half life of amiodarone?
29 days
Which receptors does amiodarone work on?
Beta
Potassium
Sodium
Calcium
What are the effects of amiodarone?
Slow AV and SA node conduction
Increased refractory period
Slowed intracardiac AP conduction
Side effects of amiodarone?
Interstitial lung disease
Hyper/hypothyroid
Corneal microdeposits
Jaundice/hepatitis
Blue grey skin discolouration
Peripheral neuropathy
Epididymitis
Gynaecomastia
When is amiodarone contraindicated?
Pregnancy + breast feeing
Sinus node bradycardia
AV block
2/3rd degree HB
How does digoxin work?
Inhibits Na/K ATPase of cell membrane
This increases intracellular sodium levels, reverses sodium-calcium exchanger, increases intracellular calcium and therefore increases myocardial contraction
How is the baro-receptor effected by digoxin?
Improves baroreceptor sensitivity by inhibition of sodium pump
Cardiac effects of digoxin?
Increased ventricular ejection, decreased ED size, higher CO, increased renal perfusion
How does it affect sthe autonomic nervous system?
Decreases symp. Increases parasymp via vagus (AV node delay)
How does digoxin affect the refractory period?
Increases in the SA and AV nodes. Decreased in atria and ventricles
Side effects of digoxin?
Anorexia, N/V, diarrhoea, blurred vision, confusion, drowsiness, dizziness, insomnia, agitation, depression.
Rare - psychosis, delirium, amnesia, convulsions
Shortened QRS, A or V extrasystoles, VF/VT, heart block, paroxysmal atrial tachycardia with AV block
How does digoxin affect the ecg?
Increased PR, decreased QT, flattened T waves.
Can cause AV junctional rhythm and ectopics
How does adenosine work?
Affects A1 adenosine receptors in SA and AV. Inhibits adenylyl cyclase, reducing cAMP -> cell hyperpolarisation
How does high dose adenosine work?
Hyperpolarisation through outward potassium flux and reduced calcium current leading to a temporary block in conduction
Also causes vascular dilation
Side effects of adenosine
Facial flushing, chest rash, light headedness, diaphoresis, nausea, metallic taste
When is adenosine contraindicated?
2nd/3rd degree HB
sick sinus syndrome
Long QT
severe hypotension
Decompensated HF
Asthma
Drug induced tachycardia
What % of body magnesium is in heart and smooth muscle
35%
What are the effect of Mg
Inhibits acetylcholine and noradrenaline release. Antagonises NDMA
How does Mg affect the cell membrane?
Stabilises it via acting as a cofactor for Na/K ATPase.
Is bound to cellular ATP
What are the effects of Mg on cardiac tissue?
Prolongs sinus node recovery, reduced automaticity and AV node/His conduction
What does low Mg cause in patients with myocardial ischaemia?
Facilitates Ca2 influx, which causes cellular death
