Alpha-1 adrenergic blockers: Nursing pharmacology

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ALPHA-1 BLOCKERS
DRUG NAME
prazosin (Minipress), terazosin, doxazosin (Cardura)
CLASS
Peripheral adrenergic antagonists
α1 selective adrenergic blockers
MECHANISM of ACTION
Block peripheral α1-adrenergic receptors → dilates peripheral blood vessels → lowers peripheral resistance → reduces blood pressure
INDICATIONS
Hypertension
Benign prostate hyperplasia (to decrease urine outflow obstruction)
ROUTE(S) of ADMINISTRATION
  • PO
SIDE EFFECTS
  • Dizziness, headache, and drowsiness
  • Anxiety, CNS depression
  • Palpitations, orthostatic hypotension, reflex tachycardia, and edema
  • Blurred vision
  • Dry mouth
  • Nausea, diarrhea, and constipation
  • Urinary frequency, incontinence, impotence, and priapism
  • Doxazosin: arrhythmias and hepatitis
CONTRAINDICATIONS & CAUTIONS
  • Pregnancy and breastfeeding
  • Children and elderly clients
  • Prazosin and Terazosin: prostate cancer
  • Doxazosin: hepatic disease
  • Drug interactions: vasodilators, beta blockers, and PDE5 inhibitors
NURSING CONSIDERATIONS
Assessment and monitoring
Assessment
  • Weight, vital signs, orthostatic blood pressure

Monitoring
  • Side effects
  • Evaluate for the therapeutic response: blood pressure control

Client education
  • Purpose of medication: blood pressure control
  • Take with or without food
    • Take consistently; do not abruptly stop medication to avoid rebound hypertension
  • Take first dose at bedtime to avoid severe orthostatic hypotension and syncope
  • Continue to make position changes slowly, sit down if dizziness occur
    • Contact healthcare provider if hypotension and dizziness persist
  • Avoid alcohol
  • Check with healthcare provider before taking over-the-counter medications
  • Blood pressure self-monitoring technique
    • Desired blood pressure; readings that require medical attention
  • Lifestyle modifications: maintaining a healthy weight, smoking cessation, reducing their intake of sodium, increasing physical activity as tolerated 
Author: Victoria S. Recalde, MD
Illustrator: Elizabeth Nixon-Shapiro, CMI, MSMI

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Content Reviewers

Antonella Melani, MD,Lisa Miklush, PhD, RNC, CNS,Gabrielle Proper, RN, BScN, MN

Alpha-1 adrenergic blockers are medications that oppose the effects of the sympathetic nervous system, ultimately decreasing smooth muscle contraction. Hence, these medications can be used to treat hypertension and benign prostate hyperplasia, and include prazosin, terazosin, and doxazosin, which are administered orally.

Normally, the sympathetic nervous system triggers the fight or flight response by secreting catecholamines, which activate alpha-1 adrenergic receptors on the different organs. This results in smooth muscle contraction, in turn leading to an increase in the heart rate and blood pressure, as well as decreasing gastrointestinal motility and urination by contracting the sphincters.

So, once administered, alpha-1 adrenergic blockers bind and inhibit these alpha-1 adrenergic receptors. As a result, alpha-1 blockers cause vasodilation, which in turn decreases blood pressure. In the urinary tract, they help relax the sphincters, which helps relieve the symptoms of benign prostate hyperplasia by decreasing the urine outflow obstruction.

Now, since alpha-1 receptor inhibition causes vasodilation, common side effects include orthostatic hypotension and reflex tachycardia, especially after the first dose; as well as palpitations and edema. Other side effects include anxiety, CNS depression, and blurred vision.

Often, clients may also experience dizziness, headaches, and drowsiness, as well as nausea, diarrhea or constipation, urinary frequency, incontinence, and impotence. Rarely, these medications may lead to priapism. Finally, clients taking doxazosin may develop arrhythmias or hepatitis.

There are no major contraindications for alpha-1 blockers, but they must be used cautiously in pregnancy, breastfeeding, children, and elderly clients. In addition, prazosin and terazosin should be used with caution in clients with prostate cancer, and doxazosin in those with hepatic disease. Finally, these medications may have dangerous interactions with vasodilators, beta blockers, and PDE5 inhibitors, potentially resulting in hypotension and syncope.

Okay, if you’re caring for a client who has been prescribed the alpha-1 blocker prazosin for hypertension, begin by performing a baseline assessment of their weight and vital signs, as well as an orthostatic blood pressure assessment.

Summary

Alpha-1 blockers are a type of medication used to treat high blood pressure, prostate problems, and heart failure. By blocking the action of alpha-1 receptors in the body, these medications can help to lower blood pressure and improve symptoms related to benign prostatic hyperplasia (BPH), and heart failure. Examples of alpha-1 blockers include drugs like alfuzosin, doxazosin, and terazosin.