CV pharmacology 2 Classes of drugs Flashcards
Class 1 b antidysrhythmics in practise e.g and when and how administered
LIDOCAINE
Local anaesthetic
HOW: topically, intradermally, spray, Parenteral - SLOW IV
WHEN:
1. Spray for intubation
2. animals with a raised intercranial pressure to reduce coughing. gagging reflex which is something we want to avoid in these animals. Given IV vvv slowly
3. Animals with ventricualr tachycardia
Main effect of class 1b Lidocaine
- Main effect of diseased cells due to use dependant blockade
Dog presents with ventricular tachycardia. What happens if you do nothing and What do you do?
Do nothing: high HR sustained over long period results in low CO, most likely death
- LIDOCAINE
- IV
- BOLUS
- Monitor ECG, may want to give another bolus is not converted back
- Aim: to convert HR back to normal rhythm
Side affects and adverse affects of LIDOCAINE
- Minimal haemodynamic effects – safer than class 1 a, fewer adverse affects on myocardium
- Hypotension at toxic levels (Low BP)
- Adverse effects
Mainly CNS – excitation, disorientation, seizures, nausea ☹
THEREFORE Give very slowly and monitored v closely
NOTE Horses and cats particularly sensitive
• Would want to admit patient tot the hospital
Class 2 drugs
- Beta blockers
- β1 receptors blocking
- Relatively selective drug at low doses, however lost at higher - can block beta 2 and alpha receptors.
What happens if give too high dosage of class 2 beta blockers?
NOT GOOD!
o Β2 blockage = some vasoconstriction on cardiac muscle
o 3rd generation drugs also some alpha blockade = vasodilation
Predicted effect of Class 2 Beta blockers
Blocking beta 1 receptors
Have an affect on the parasympathetic nervous system
1. Slow pacemaker potential by slowing Ca2+ influx
2. Slow conduction through AV node as increased refractory period
3. Negative inotropy and reduced lusitrophy
When in practise would you use Class 2 beta blockers
- Becuase Class 2 BB slow conduction in AVNode.
- if patient presents with Supraventricular or ventricular tachycardias
- Also to treat hypertension (high BP) with the beta blocker atenolol
Difference between Class 1 and class 2
Class 1 affects conduction through cardiomyocytes
Class 2 affects conduction through the conduction pathway, pacemaker cells
Why do you have to be careful when using beta blockers?
- Due to negative inotrophy (decreased contractility) and negative lusitrophy effects (reduced myocardial relaxation BB result in CO dropping as a result of slower HR.
- So if used in a healthy animal can trigger HYPOtension (Low BP)
Why would you sue class 2 BB if a patient had supraventricular tachycardia
- IN SV and Ventricular T cause = abnormal pacemaker ABOVE the Ventricles
- impulse to AV node, then AV bundle to be conducted to ventricles. Which means:
Very fast rhythm with NO P wave but the QRS complex looks normal. - V can’t fill properly so we use BB to slow down the conduction so to improve filling efficiency
Example of Class 2 antidysrhythmics in practise
- Beta blocker ATENOLOL (Tenormin)
About Class 2 Beta blocker ATENOLOL (Tenormin)
- It is β1 receptor selective
- Adverse effects mainly limited to CVS
- Can cause HyPOtension
- Used to treat animals with hypertension (atenolol BB)
Class 3 antidysrhythmics
drugs that prolong AP by blocking some K+ channels
MEchanism of action for class 3 antidysrhythmics
More than one Mechanism Of Action
- Main MOA:
a) blocking K+ channel
b) prevents/ slows down repolarisation of heart muscle
c) so Na+ channels stay refractory until next AP comes along, until heart has been repolarised - cell can’t be depolarised for a bit longer
d) therefore prolong the cardiac AP
e) slowing down HR - In skeletal muscle we have temporal summation but this doesn’t occur in myocardium!
