Class 1B (Anti-Arrythmics) Flashcards
What is the general idea of Class 1B anti-arrythmics?
Blocking the inactive sodium channels, and thereby preventing it from reaching resting potential as fast as it would otherwise. Also, we block the slow Na “window” currents that help maintain the plateau phase, and as a result the plateau phase shrinks.
How does the AP diagram of cardiac myocytes look like for class 1b drugs?
Plateau phase decreases in size and decrease action potential duration.
What is one of the main situations where we use class 1B drugs and why?
Post MI, because the myocytes will be hypoxic and thus unable to pump out its sodium –> be depolarized and inactive and thus slower in the region of hypoxia than in region that’s normal. 1B drugs will allow for lower action potentials so the damaged area can lower its duration of AP’s and speed up to catch up to healthy tissues.
What is the prototype of Class 1b drugs? When do we use it?
Lidocaine which is also used as anasthesia. We use it for post MI, open heart surgery and for digoxin tox.
What’s notable of Lidocaine toxicities?
It has CNS toxicities however it is the least cardiotoxic among all the anti-arrythmics (though toxicities still exist).
How is Lidocaine administered?
Only through IV, due to extensive first pass metabolism if given orally.
Whats special about the class 1B drugs Mexiletine and Tocainide?
Lidocaine like drugs, but available in oral formulations.
