Let's move on to those drugs that act on the
sympathetic nervous system,
specifically we are just going to focus on
alpha blockers right now.
So, these alpha agonists are often very good drugs.
There we have the alpha 1 agonists like phenylepherine,
and alpha 2 agonists like alpha-methyldopa and clonidine.
Now, phenylepherine is an alpha 1 agonist and that will
actually cause constriction of the blood vessel
and it causes high blood pressure.
So, we put it there just to remind you that
alpha 1 and alpha 2 have very different effects.
Obviously, we don't use phenylepherine to treat hypertension
because it causes high blood pressure.
Let's go on to the alpha 2 agonists.
So, alpha-methyldopa and clonidine.
Let's compare and contrast alpha-methyldopa and clonidine.
The alpha-methyldopa or I'm going to call it Aldomet
for simplicity sake, decreases central sympathetic outflow.
Similarly, clonidine does the same thing.
Aldomet is a prodrug.
It is metabolized to the active agent.
Both will decrease central sympathetic outflow,
cardiac output, and vascular resistance.
Both have a compensatory reaction of salt retention.
They both do this.
There are some idiosyncratic reactions
which distinguish the two drugs.
The idiosyncratic reaction of note with Aldomet
is hemolytic anemia.
The idiosyncratic reaction of clonidine
is rebound hypertension.
Both of course cause sedation
cause they're working centrally.
extensively in pregnant patients.
In fact, Aldomet is the second most common
antihypertensive drug used in pregnant women,
whereas clonidine is definitively categorically
not used in pregnancy.
So, these two drugs are very very different
in one very important respect,
is that Aldomet is used in pregnancy,
clonidine is never used in pregnancy.