So let's talk about those drugs that directly act on the
receptors. Let's cover the blockers of those receptors first.
So alpha blockers are nonselective and selective. The
nonselective alpha blockers are Phenoxybenzamine and Phentolamine.
I want you to remember this drugs. I'm only going to pick the
ones that you are going to be tested on. There are literally
hundreds within each class. So let's just focus on the
important ones but you do need to know them. The alpha 1
selective agent of choice is Prazosin and the alpha 2 selective
agent is Yohimbine. I have never used Yohimbine in clinical
practice but I always remember it because it's the one that
we had to memorise for exams. Let's talk about beta blockers now.
The nonselective prototypical beta blocker is Propanolol. Beta
1 selective agent, the example that we always use is Atenolol
which is kind of an older beta blocker and replaced by newer
ones. But it's the prototypical one that I want you to remember.
Beta 2 selective beta blockers is Butoxamine which is almost
never used clinically but it's important for research.
And it is the prototypical drug so you do need to know it. Beta
blockers that start with the letters A-M are generally those
drugs that tend to be beta 1 selective and useful for cardiac
inhibition. Acebutolol, atenolol, bisoprolol, esmolol, labetolol,
metoprolol. Those are the commonly used clinical ones. But if
you remember A-M is beta 1 selective and for the heart
you'll be a long way. The beta blockers that start with C, C
stands for cardiac. And these are the drugs we tend to use
in cardiac failure. So the prototypical drug of the heart
failure beta blockers is carvedilol. And the reason why
carvedilol is so unique is because it has combined alpha and
beta activity. So it helps those patient in heart failure
seemingly more than the other beta blockers. Now beta blockers
that start with letters between N and Z tend to be nonselective
beta blockers. Nadolol, nebivolol, pindolol, propanolol,
timolol, these are all nonselective beta blockers.
Let's go into more detail with the beta 1 blockers. Remember
that the more selective the drug is for the beta 1 receptor,
the better it is for the lung because you have fewer lung side
effects. Remember you don't want to have beta 2 blocking activity
with your beta blocker. With rhythm control it's great for
breaking supraventricular tachycardias, preventing ventricular
tachycardias and it helps with rate control in atrial
fibrillation. We also use beta 1 blockers in heart failure
but only after the patient has been stabilised. I often use
beta blockade in blood pressure control and interestingly
enough we can use propanolol for anxiety. Propanolol is one
of the first drugs of the beta blocker class and we discovered
that people who tended to get stage fright or anxious in front
of a crowd would often take propanolol, it would help calm down
that thumping heart sensation and people did quite well. I
still use this in my practice to treat patients who gets
stage fright and you'd be suprised how many times I have to
treat people for it. A little secret that's kind of fun
if you take propanolol before a lie detector test, it's
possible that you will pass the lie detector test without
getting in trouble. But just don't tell the FBI I said that.
What about beta blockers in pregnancy. So labetolol is the
most used blood pressure drug in pregnancy. We have over a
million women years of experience using labetolol as blood
pressure control. I use it all the time in my pregnant
hypertensive patients. It's a beautiful drug. It's nice,
it's balanced, it's got both alpha and beta activity, and
the nice thing about that, is that it prevents reduced
placental flow. It has a huge wide therapeutic window. So
we can go anywhere from a 100mg a day to 2400mg a day
and people have tolerated it based on their dose.