We’re done with diuretics and now we’re moving onto Step 2 drug therapy and that includes sympatholytics. It sounds like it affects the sympathetic nervous system and that’s exactly what it does. There is another sympathetic receptor we didn’t talk about yet. We mentioned alpha, beta 1 and beta 2, but there’s also an alpha 2 adrenergic receptor.
If you remember in the sympathetic nervous system, if we stimulate an alpha receptor, it will cause vasoconstriction and blood pressure goes up.
The alpha-2 receptor is found in the post synaptic fiber and when this receptor is stimulated, it blocks the release of norepinephrine from the alpha fiber. So what happens to the alpha fiber? It’s not stimulated. This causes the vessels to dilate which decreases blood pressure. So this is how we decrease hypertension as a step 2 drug.
Side effects
- Sodium and water retention: Bad for diuretics. This is why it’s a step 2 drug, because they’re already on a diuretic to offset this sodium and water retention.
- Postural hypotension (because it affects the autonomic nervous system)
- Constipation
- Dry mouth
- Impotency
Sympatholytic Drug List
Methyldopa (Aldomet) – inj., p.o. – Not very commonly utilized but still out there. A tablet can also be used for acute hypertensive emergencies. They can be given a tablet every hour until their BP goes down.
Clonidine (Catapres) – p.o., topical – We have to be really good with educating a patient with this because otherwise they get rebound hypertension making it worse than before. To help patients become compliant, there’s a patch for this drug. It’s the only hypertensive drug that is available in patch form.
The caution for this patch, because there’s been too many nursing errors with this: This comes in 2 separate foils. The first foil has the drug. The second foil has the bandage that keeps the drug in place. Most patches have both the bandage and the drug in one, but with this, it’s not. Often times the bandage is present with no drug underneath it because the nurses don’t realize it.
Reserpine (Serpasil) – p.o. – Not very commonly utilized every since one study says it produces breast cancer.
Guanethidine (Ismelin) – p.o. – a 4th step drug – Causes severe diarrhea which is why it’s reserved as a 4th step drug. If this is used as a 4th step drug, what other drug will not be used? A sympatholytic.
Guanabenz (Wytensin) – p.o.
Guanfacine (Tenex, Intuniv) – p.o.
