Loyal Member
anti arrhythmic
Can someone please explain to me the difference betwen class 1 a and class 1 b antiarryhthmics?
Why does something like quinidine increase the duration of the action potential where as a class 2 like lidocaine decrease it when they are both sodium channel blockers... surely by blocking the sodium channel they both decrease the depolarisation phase in the cardiac cell action potential and thus both increase the action potential duration?!?
Loyal Member
hmmm is it because class 2 binds to inactivated sodium channels so takes these "out of play" so you only have those channels existing in the open and resting phase therefore a faster depolarisation is possible?!
Keep it surreal
Although type 1a's block Na+ channels, their actions are thought to be due to their ability to block K+ channels. Quinidine is predominantly open (or activated) Na+ blocker, whereas lidocaine primarily blocks Na+ current in the inactivated state. The reason why 1b's such as lidocaine were separated from 1a's is historical - early work with lidocaine suggested different electrophysiological properties. The other major difference is that 1a's increase the refractory period whereas lidocaine reduces the refractory period. The Vaughan Williams classification is not a brilliant classification system to be honest because of the overlap of actions of different drugs (propafenone is listed as 1c although it has some beta-blocking effects which are class 2) and drugs such as digoxin are not classified.
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Newly registered in 1981
Interesting...
Is there anywhere the explains this and its intricacies in a compact way?
Where am I?; In the Pharmacy.
Who are you?; The new Number 2.
Who is number 1?; You are number 6.
What do you want?;..................
Keep it surreal
Clinical Pharmacy and Therapeutics by Walker and Edwards is a very good clinical textbook often found in uni libraries, although I have my own copy. Been a while since I've done arrhythmia drugs so some of the above info was from Pharmacotherapy: A Pathophysiologic approach (US text but explains underlying disease and pathology mechanisms in more detail than Walker and Edwards).
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”We are real. We are not glam sh*t or anything else. We are Guns N’ Roses.”
Newly registered in 1981
I've yet to check out those references, so this is an uninformed comment.Originally Posted by Nik
It would be nice to see something that relates the physical symptoms and manifestations to the underlying pharmacology.
Starting at the low level and working outwards...
Most illness is the result of a cascade of events and it helps if the text highlights this and doesn't concentrate on describing cyclic AMP activation...
Where am I?; In the Pharmacy.
Who are you?; The new Number 2.
Who is number 1?; You are number 6.
What do you want?;..................
Keep it surreal
If you like I can scan the relevant pages from the former text and send over to you. Rang and Dale is a good pharmacology book to revisit early prinicples such as cardiac action potentials etc.
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”We are real. We are not glam sh*t or anything else. We are Guns N’ Roses.”
Newly registered in 1981
Thanks - might take you up on the offer.
Will see if library has it first.
Where am I?; In the Pharmacy.
Who are you?; The new Number 2.
Who is number 1?; You are number 6.
What do you want?;..................
Registered Pharmacist
bit of cpd coming on i think....
Rang,Dale and Ritter (as it was abck then) was a godsend at uni! covers the pharmacology of everything quite well, although in parts hs a tendency to go into cAMP and ATP quite heavily if my memory serves me correct. often a clinical textbook (Walker and Edwards) is good at explaining the background to medical conditions
Keep it surreal
The chapters in Walker and Edwards generally assume a good understanding of pharmacology, and they don't cover it much in their book. That's why I've also kept Rang and Dale from uni.
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”We are real. We are not glam sh*t or anything else. We are Guns N’ Roses.”
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