Drugs Flashcards
What are the basic classes of anti-arrhythmic drugs
I - drugs that block voltage-sensitive sodium channels
II - antagonists of B-adrenoreceptors
III - drugs that block potassium channels
IV - drugs that block calcium channels
Name some class I drugs
Lidocaine
Describe liocaines use and how it works
Sometimes used following an MI - only if signs of ventricular tachycardia. Areas of damaged myocardium may be depolarised and fire automatically, drug suppresses this
Blocks voltage gated Na channels in open or inactive state (preferentially blocks damaged depolarised tissue)
Blocks during depolarisation but dissociates in time for next AP so can help to prevent premature depolarisation while allowing normal depolarisation to take place
Name some Class II drugs
Propranolol
Atenolol
How do class II drugs function and when are they used
Block sympathetic action (B1 adrenoreceptors in heart)
They decrease slope of pacemaker potential and slow AV node conduction by blocking L type Ca channels
Can prevent supraventricular tachycardia
Used following myocardial infarction - MI often increases sympathtic activity so B-blockers used to reduce chance of arrhythmias occuring due to this
To reduce oxygen demand by making the heart have to work less hard
Describe the action of class III drugs
Prolong the action potential mainly by blocking K channels, lengthening absolute refractory period
Not generally used as can also be pro-arrhythmic
What class III drug is used, what for and why
Amiodarone
Treat tachycardia associated with Wolff-Parkinson-White syndrome
Also effective in suppressing ventricular arrhythmias post MI
The drug blocks Na, Ca and K channels so can be used
Name some class IV drugs
Verapamil
Ditiazem
What do class IV drugs act to do
Decrease slope of action potential at SA node
Decrease AV nodal conduction
Cause negative inotropy
What is adenosine and what can it be used for
It is a nucleoside, it is produced endogenously at physiological levels
Acts on A1 receptors at AV node to enhance K conductance causing hyperpolarisation of the cells
This can be used to suppress conduction at the AV node and is used to terminate re-entrant SVT
What other dugs act on the CVS
ACE inhibitors and AngII receptor blockers
Diuretics
Ca channel antagonists
Positive inotropes
Alpha adrenoreceptor blocker and beta blocker
Antithrombotic drugs
Name an ACE inhibitor and describe how they work and what they are used in
Perindopril
Inhibit action of angtiotensin converting enzyme
Treatment of hypertension and heart failure
What is heart failure
Chronic failure of the heart to provide sufficient output to meet the body’s requirements
Can cause peripheral and pulmonary oedema
What changes do ACE inhibitors cause in the body
Decrease vasomotor tone (decrease BP), reducing afterload
Decrease fluid retention (decrease blood volume), reducing preload
Why are angiotensin II receptor blockers (ARBs) used and what are they used for
Used to treat hypertension and heart failure in patients who cannot tolerate ACEi
What are diuretics used for and how do they achieve this
Used in treatment of heart failure and hypertension
They reduce fluid volume which decreases BP and volume, reducing the preload and afterload
What are dihydropyridine blockers and how do they work
Ca channel blockers that act on vascular smooth muscle
They reduce Ca influx causing a relaxation of blood vessels
This decreases peripheral resistance and arterial BP which reduces afterload and workload of the heart
What are Ca channel blockers used to treat
Hypertension
Angina
Coronary artery spasm
SVTs
What are the types of postivie inotropes and what do positive inotropes do
Increase contractility and cardiac output
Types: cardiac glycosides, B-adrenergic agonists
How do cardiac glycosides work
They block Na/K ATPase
This increases intracellular Na, so Na-Ca exchanger activity decreases leading to a rise in intracellular Ca
More Ca in the cell means a greater force of contraction
Also cause increased vagal activity which slows AV conduction and slows heart rate
When are cardiac glycosides used
Heart failure
e.g. arrhythmia such as AF
How do B-adrenoreceptors agonists work and what are they used for
They are selective B1-adrenoreceptors which stimulate receptors at the SA node, AV node and on ventricular myocytes (dobutamine)
Used in cardiogenic shock and acute but reversible heart failure
What are organic nitrates used for
Used to treat angina
They undergo reaction and reduction to NO which is released from endothelial cells to cause vasodilation, especially in veins
This then lowers preload and so reduces the workload on the heart, lowering oxygen demand
How does NO cause vasodilation
NO activates guanylate cyclase
This acts to increase cGMP
This lower intracellular [Ca]
This relaxes vascular smooth muscle
What types of drugs are used in treating angina and what do they do
Reduce workload of the heart
- Organic nitrates
- B-adrenoreceptor blockers
- Ca channel antagonists
Improve blood supply to the heart
- Ca channel antagonists
- Organic nitrates (minor effect)
What heart conditions carry an increased risk of thrombus formation
Atrial fibrillation
Acute MI
Mechanical prosthetic heart valves
What types of antithrombotic drugs are used
Anticoagulants
Drugs that prevent venous thromboembolism
Antiplatelet drugs
