NCLEX Antihypertensives: Antiadrenergics – [Alpha and Beta Blockers]

NCLEX Antihypertensives: Antiadrenergics – [Alpha and Beta Blockers]

December 12, 2019 3 By Bertrand Dibbert


Welcome to this video tutorial – we’re going
to look at a group of antihypertensive drugs called antiadrenergics, which include alpha-adrenergic
blocking agents and beta-adrenergic blocking agents (better known as beta blockers). Be sure to check out our pharmacology playlist
for other antihypertensive videos, such as ACE inhibitors and ARBs, calcium channel blockers,
and diuretics. Antiadrenergic drugs inhibit or block the
activity of the sympathetic nervous system. So the goal of antiadrenergic drug therapy
is to suppress stimulation that is not the normal physiologic response to activity or
stress, such as increases in heart rate, increased force of myocardial contraction, increased
cardiac output, and increased blood pressure. When the nerve impulse is inhibited or blocked
at any location along the pathway, the result is lowered blood pressure. Antiadrenergic effects occur when either the
alpha or beta receptors are blocked by adrenergic antagonists. Alpha-1-adrenergic receptor blocking agents
dilate blood vessels and decrease peripheral vascular resistance. These include drugs such as prazosin, doxazosin,
and terazosin. In addition to treating hypertension, these
alpha-1 blocking drugs are also given for BPH (benign prostatic hyperplasia), a condition
characterized by obstructed urine flow as the enlarged prostate gland presses on the
urethra. Alpha-1 blocking agents relax muscles in the
prostate and urinary bladder, which decreases urinary retention and improves urine flow. One adverse effect is orthostatic hypotension
with palpitations, dizziness, and syncope, 1-3 hours after the first dose or an increased
dose. This is called the first-dose phenomenon,
and therefore it is best if first doses or an increased dose be taken at bedtime. Another adverse effect, after taking long-term
or higher doses, is the development of sodium and fluid retention, requiring diuretic therapy
also. Alpha-2 receptor agonists are centrally acting,
causing less norepinephrine to be released, which leads to decreased cardiac output, decreased
heart rate, lower peripheral vascular resistance, and lower blood pressure. Clonidine and methyldopa are both alpha-2
receptor agonists given for hypertension. Beta-adrenergic blocking agents prevent the
beta-adrenergic receptors from responding to the hormone epinephrine (adrenaline). The drugs are given to decrease heart rate,
decrease cardiac output, decrease the force of myocardial contraction, and decrease renin
release from the kidneys. Beta blockers are mainly given for cardiovascular
disorders, such as angina, hypertension, cardiac tachydysrhythmias, myocardial infarction,
and heart failure. They are also given for glaucoma and migraines. Common side effects of beta blockers include
fatigue, cold hands or feet, and weight gain. Less common side effects include trouble sleeping,
depression, and shortness of breath. Beta blockers are generally not given to patients
with asthma or COPD because of the risk of triggering severe asthma attacks. In patients with diabetes, beta blockers may
block signs of low blood sugar, such as rapid heartbeat. If a patient with diabetes or pulmonary disorders
needs to take beta blockers, the cardioselective beta blockers are preferred, such as metoprolol
(lopressor) and atenolol. Cardioselective just means that they have
more effect on beta-1 receptors and cause less bronchospasm and impairment of glucose
metabolism. Nonselective beta blockers are those drugs
that block both beta-1 and beta-2 receptors. Examples of nonselective blocking agents include
propranolol, nadolol, and timolol. Labetalol is an alpha-beta-blocking agent,
often given for hypertensive emergencies. Important education for patients taking beta
blockers includes counting their pulse daily and reporting if it is under 50 for
several days in a row, reporting weight gain, shortness of breath, excessive fatigue, ankle
edema, fainting spells, or difficulty breathing. Also, do not stop taking a beta blocker abruptly,
as it can result in chest pain, a heart attack, or other heart problems. Let’s take a look at some questions for
review… A patient with a history of COPD is prescribed
propranolol to treat hypertension. In this situation, the nurse should assess
for the presence of 1. Hyperglycemia
2. Tachycardia 3. Bronchoconstriction
4. Respiratory depression If you chose 3, bronchoconstriction, you’re
right! Propranolol is a nonselective beta blocker,
which has a risk of bronchoconstriction. A cardioselective beta blocker is preferred
because they cause less bronchospasm. Let’s try another one… Which of the following instructions should
be given to the hypertensive patient before taking his first dose of prazosin? 1. Take your medication with a glass of milk
2. Take your medication on an empty stomach. 3. Take your medication at bedtime. 4. Take your medication in the morning after
meals. If you chose 3, take the medication at bedtime,
you’re correct! Prazosin is an alpha-1 adrenergic blocking
agent that dilates blood vessels, and can result in the first-dose phenomenon of orthostatic
hypotension with dizziness and possibly syncope, and should therefore be taken at bedtime. Thank you for watching this video on Antiadrenergics
– Alpha & Beta Blockers! Be sure to check out our other videos!