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.
