Pharmacology Question - Alpha Blockers

TCASII, ADN · Apr 22, 2010

More or less, alpha blockers would be alpha-adrenergic blockers (antagonists) in treating hypertension. The difference in alpha-adrenergic antagonists block the a1 type receptor, whereas the alpha-adrenergic agonists (e.g., clonidine) stimulate the a2 receptors in the brainstem to lower BP.

I don't know what they are wanting you to know about CAIs, but they are contraindicated in nephrolithiasis hx (kidney stones), worsened metabolic and/or respiratory acidosis therefore contraindicated in COPD or hyperchloremic acidosis, contraindication in hepatic encephalopathy. CAIs are used to treat edema, although the use as a single agent isn't very effective. CAIs are combined with diuretics that block Na+ reabsorption, although the long term use of CAIs is usually compromised by metabolic acidosis. The most useful application for CAIs is in open-angle glaucoma. They are also used in secondary glaucoma and preoperative acute angle closure glaucoma. Acetazolamide is also used in epilepsy, however, tolerance develops rapidly, so it isn't used much. Acetazolamide can be used in prophylactic treatment of altitude sickness too and even as treatment. It is also useful for familial periodic paralysis. CAIs are also good for reversing metabolic alkalosis, especially those caused by certain diuretics.

newbiepnp, MSN, RN, NP, CNS · Apr 22, 2010

Wow, thank you so much. Just a little clarification, if the alpha-adrenergic blocker is an antagonist (by definition), how are they stimulating a2 receptors? Wouldn't they be be alpha agonists?

CBsMommy · Apr 22, 2010

Alpha 2 receptors work the opposite of Alpha 1 receptors. Alpha1 is the fight or flight so when you block them, they have the same effect as beta agonists. If you stimulate A2 receptors, you are actually blocking epi and norepi, so again, you are bringing BP down. Hope that helps. That is the most confusing part of the whole thing for a lot of students. Writing it on a chart helped me a lot. Good luck!

newbiepnp, MSN, RN, NP, CNS · Apr 22, 2010

Great explanations. Thank you so much, as this clears up a lot of questions.

TCASII, ADN · Apr 23, 2010

Perhaps my post wasn't clear, sorry. Adrenergic pharmacology is tough. I mentioned alpha type 2 selective agonists because they are used for hypertension, and you said you were going over drugs used in HTN. They act (stimulate/potentiate) on postsynaptic and presynaptic receptors to lower BP (this is a highly simplified explanation). Alpha-adrenergic receptors come in different subtypes, as do beta-adrenergic receptors. The a2A and a2C subtype appear to mediate the hypotensive effects, whereas the a2B subtype seem to contribute to the sedative effects. These drugs are often referred to as "Centrally Acting Agents" in HTN textbooks.

The alpha type 1 selective antagonists, or simply alpha adrenergic antagonists in HTN therapy, block/inhibit peripheral a1 receptors. Keep in mind, a1 receptors are also found in the CNS as well. Same goes for the alpha type 1 receptors coming in different subtypes.

The autonomic nervous system is extremely complex. You have different receptors, subtypes, receptor locations, functions, and opposing actions. Then the drugs that work on one type of receptor or even those that have mixed activity.

So, in short, you have alpha 1 antagonists (blocking/inhibiting) to lower BP or alpha 2 agonists (stimulating/potentiating) to lower BP, among other things. BTW, alpha 1 antagonists aren't often preferred as a monotherapy, at least in long term cases, for HTN treatment.

For a fun fact of the day, your asking about CAIs prompted me to remember that topiramate (Topamax) is a weak carbonic anhydrase inhibitor. Topiramate is an anticonvulsant used for seizure disorders and migraine H/As, although the CAI effect seems to exacerbate kidney stone production in predisposed individuals.

~Mi Vida Loca~RN, ASN, RN · Apr 23, 2010

I think one of the biggest things to remember with anti hypertensives,(when it comes to nursing care) any of them from what we are taught, and besides contraindications is to ALWAYS check a BP before administering and you should ALWAYS check yourself. This was stressed so much in not just pharm but in med/surge as well.

newbiepnp, MSN, RN, NP, CNS · Apr 23, 2010

Thank you so much everyone, this really helps to understand the two types and the mechanisms that they work. This week we are moving on to treating CHF, so I'm glad that I have a better understanding of this whole system. I love this forum.

Anne36, LPN · Apr 23, 2010

Very smart group of people on here. This is very interesting to see where all this A&P 1 is leading. I am just starting to learn about this stuff as it pertains to the ANS.

Its all about the receptor type isnt it?

Sometimes I wonder why a nurse has to know all of this. A nurse doesnt diagnose and prescribe medication. Is all of this detail just to get through school or do Nurses really use this information in their daily job?

~Mi Vida Loca~RN, ASN, RN · Apr 24, 2010

Very smart group of people on here. This is very interesting to see where all this A&P 1 is leading. I am just starting to learn about this stuff as it pertains to the ANS.
Its all about the receptor type isnt it?
Sometimes I wonder why a nurse has to know all of this. A nurse doesnt diagnose and prescribe medication. Is all of this detail just to get through school or do Nurses really use this information in their daily job?

Nurses are the ones that are GIVING the meds, and they will be the first ones the finger pointed at. A nurse needs to know what they are giving, the reactions one might have for it, when to hold it. They are the patients advocate and if Doc. orders the wrong dose and the nurse gives it and it's not a normal dosage it will be the nurse that takes the fall because they should have known and questioned the order. You're never going to remember every drug and action and so on, Pharm is supposed to give you the foundation. They aren't expecting when you hit the floor 2 years later you will remember it all, although you will see the information on more common ones on exams outside of pharm class. But when you are on the floor you should NEVER give a med that you don't know about.

whichone'spink, BSN, RN · Apr 24, 2010

Is all of this detail just to get through school or do Nurses really use this information in their daily job?

Do we need to know all this? Hell yes we do. If I do not fill out the drug mechanism for drugs I'm giving to my patients in my care plans, I will be sent home.

~Mi Vida Loca~RN, ASN, RN · Apr 24, 2010

Do we need to know all this? Hell yes we do. If I do not fill out the drug mechanism for drugs I'm giving to my patients in my care plans, I will be sent home.

They are asking if nurses really need to know this, not students. Which of course the answer is still yes, but I think they get that students need the info, they just don't seem to make the connection why it's something nurses need to know that are in the field working.

No idea if this is true for that poster, but a lot of people still hold the notion that nurses just blindly follow orders and so we don't need to know about the drugs just need to give them.

I listened to a charge nurse go at it with a Doc for over 30 mins on the phone last night, she handled herself great, stood up for herself and her nurses and as a student it was such a great thing to see. Dr wanted to induce a 36 2/7 mom where baby had cleft palate and club feet and the nurse questioned it and dr got TICKED OFF.