Alpha blocker
Encyclopedia
Alpha-1 blockers constitute a variety of drugs which block α1-adrenergic receptors in arteries and smooth muscle
s.
Others include:
Non-selective Adrenergic blockers:
Silodosin shows high affinity and selectivity for α1A adrenergic receptors found in the prostate which ensures that it works quickly and effectively to relieve the symptoms of BPH. Silodosin's low affinity for α1B receptors in the blood vessels is thought to be reflected in its low incidence of orthostatic and vasodilatory side effects.
Tamsulosin is relatively selective for α1a-adrenergic receptors, which are mainly present in the prostate
. Hence, it may have a more selective action in BPH with minimal effects on blood pressure.
(low blood pressure) and interrupt the baroreflex
response. In doing so, they may cause dizziness, lightheadedness, or fainting when rising from a lying or sitting posture (known as orthostatic hypotension
or postural hypotension). For this reason, it is generally recommended that alpha blockers should be taken at bedtime. Additionally, the risk of first dose phenomenon
may be reduced by starting at a low dose and titrating upwards as needed.
Because these medications may cause orthostatic hypotension, as well as hypotension
in general, these agents may interact
with other medications that increase risk for hypotension
, such as other antihypertensive
s and vasodilators.
As discussed above, tamsulosin may have less risk for hypotension and orthostatic hypotension due to its selectivity for α1a-adrenergic receptors. On the other hand, the drug (a) elevates risk for floppy iris syndrome, and (b) might show adverse drug reactions (ADRs) characteristic of the sulfa
related drugs.
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
s.
Pharmacology
Reduce arteriolar resistance and increase venous capacitance causing reflex tachycardia.Depending on plasma concentration they may cause postural hypotension.Alpha-1 blockers may decrease LDL and triglycerides and increase HDL.Indications
These drugs may be used to treat:- benign prostatic hyperplasiaBenign prostatic hyperplasiaBenign prostatic hyperplasia also known as benign prostatic hypertrophy , benign enlargement of the prostate , and adenofibromyomatous hyperplasia, refers to the increase in size of the prostate....
(BPH)- Lower urinary tract symptomsLower urinary tract symptomsLower urinary tract symptoms are a common problem affecting approximately 40% of older men. LUTS is a recent term for what used to be known as prostatism.-Voiding or obstructive symptoms:*Poor stream*Hesitancy*Terminal dribbling...
- Post Transurethral microwave thermotherapyTransurethral microwave thermotherapyTransurethral microwave thermotherapy is one of a number of effective and safe procedures used in the treatment of lower urinary tract symptoms caused by benign prostatic hyperplasia . TUMT provides a one-time efficacious treatment of LUTS due to BPH...
(TUMT) and Transurethral needle ablation of the prostateTransurethral needle ablation of the prostateTransurethral needle ablation is a technique that uses low energy radio frequency energy delivered through two needles to ablate excess prostate tissue. It can be done with a local anesthetic on an outpatient basis...
(TUNA) procedures
- Lower urinary tract symptoms
- high blood pressure (hypertension). This is not typically the drug of choice unless the patient also has BPH.
- symptoms of non inflammatory chronic pelvic pain syndrome, a type of prostatitisProstatitisProstatitis is an inflammation of the prostate gland, in men. A prostatitis diagnosis is assigned at 8% of all urologist and 1% of all primary care physician visits in the United States.-Classification:...
. As a side effect they may reduce blood pressureBlood pressureBlood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
and result in lightheadedness.
Examples of alpha blockers
| Blocker | Use | Common Brand Name |
|---|---|---|
| Doxazosin Doxazosin Doxazosin mesylate, a quinazoline compound sold by Pfizer under the brand names Cardura and Carduran, is an α1a-selective alpha blocker used to treat high blood pressure and urinary retention associated with benign prostatic hyperplasia .... |
Hypertension Hypertension Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and... and benign prostatic hyperplasia Benign prostatic hyperplasia Benign prostatic hyperplasia also known as benign prostatic hypertrophy , benign enlargement of the prostate , and adenofibromyomatous hyperplasia, refers to the increase in size of the prostate.... (BPH) |
(Cardura) |
| Silodosin Silodosin Silodosin is a medication for the symptomatic treatment of benign prostatic hyperplasia... |
Benign prostatic hyperplasia | (Rapaflo) |
| Prazosin Prazosin Prazosin, trade names Minipress, Vasoflex, Pressin and Hypovase, is a sympatholytic drug used to treat high blood pressure and Anxiety, PTSD and Panic Disorder. It belongs to the class of alpha-adrenergic blockers. Specifically, prazosin is selective for the alpha-1 receptors on vascular smooth... |
Hypertension Hypertension Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and... |
(Minipress) |
| Tamsulosin Tamsulosin Tamsulosin is an α1a-selective alpha blocker used in the symptomatic treatment of benign prostatic hyperplasia . Tamsulosin was developed by Yamanouchi Pharmaceuticals and is marketed by various companies under licence, including Boehringer-Ingelheim and CSL... |
Benign prostatic hyperplasia | (Flomax) |
| Alfuzosin Alfuzosin Alfuzosin is an α1 receptor antagonist used to treat benign prostatic hyperplasia . It works by relaxing the muscles in the prostate and bladder neck, making it easier to urinate.... |
Benign prostatic hyperplasia | (Uroxatral) |
| Terazosin Terazosin Terazosin is a selective alpha 1 antagonist used for treatment of symptoms of an enlarged prostate... |
Hypertension and BPH | (Hytrin) |
Others include:
- TrimazosinTrimazosinTrimazosin is a sympatholytic drug.It is an alpha blocker.Hess, H. J.; 1972, .-References:...
Non-selective Adrenergic blockers:
- PhenoxybenzaminePhenoxybenzaminePhenoxybenzamine is a non-selective, irreversible alpha antagonist.-Uses:It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma...
- PhentolaminePhentolaminePhentolamine is a reversible nonselective alpha-adrenergic antagonist. -Mechanism:Its primary action is vasodilation due to α1 blockade....
(Regitine)
Silodosin shows high affinity and selectivity for α1A adrenergic receptors found in the prostate which ensures that it works quickly and effectively to relieve the symptoms of BPH. Silodosin's low affinity for α1B receptors in the blood vessels is thought to be reflected in its low incidence of orthostatic and vasodilatory side effects.
Tamsulosin is relatively selective for α1a-adrenergic receptors, which are mainly present in the prostate
Prostate
The prostate is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals....
. Hence, it may have a more selective action in BPH with minimal effects on blood pressure.
Adverse effects and interactions
By reducing α1-adrenergic activity of the blood vessels, these drugs may cause hypotensionHypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
(low blood pressure) and interrupt the baroreflex
Baroreflex
The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms for maintaining blood pressure. It provides a negative feedback loop in which an elevated blood pressure reflexively causes heart rate to decrease therefore causing blood pressure to decrease; likewise, decreased...
response. In doing so, they may cause dizziness, lightheadedness, or fainting when rising from a lying or sitting posture (known as orthostatic hypotension
Orthostatic hypotension
Orthostatic hypotension, also known as postural hypotension, orthostasis, and colloquially as head rush or dizzy spell, is a form of hypotension in which a person's blood pressure suddenly falls when the person stands up or stretches. The decrease is typically greater than 20/10 mm Hg, and may be...
or postural hypotension). For this reason, it is generally recommended that alpha blockers should be taken at bedtime. Additionally, the risk of first dose phenomenon
First dose phenomenon
The first dose phenomenon is a sudden and severe fall in blood pressure that can occur when changing from a lying to a standing position the first time that an alpha blocker drug is used or when resuming the drug after many months off. This postural hypotension usually happens shortly after the...
may be reduced by starting at a low dose and titrating upwards as needed.
Because these medications may cause orthostatic hypotension, as well as hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
in general, these agents may interact
Drug interaction
A drug interaction is a situation in which a substance affects the activity of a drug, i.e. the effects are increased or decreased, or they produce a new effect that neither produces on its own. Typically, interaction between drugs come to mind...
with other medications that increase risk for hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
, such as other antihypertensive
Antihypertensive
The antihypertensives are a class of drugs that are used to treat hypertension . Evidence suggests that reduction of the blood pressure by 5 mmHg can decrease the risk of stroke by 34%, of ischaemic heart disease by 21%, and reduce the likelihood of dementia, heart failure, and mortality from...
s and vasodilators.
As discussed above, tamsulosin may have less risk for hypotension and orthostatic hypotension due to its selectivity for α1a-adrenergic receptors. On the other hand, the drug (a) elevates risk for floppy iris syndrome, and (b) might show adverse drug reactions (ADRs) characteristic of the sulfa
SULFA
SULFA, short for Surrendered ULFA, i.e. members of the United Liberation Front of Asom that surrendered to the government.Beginning with 1990, the Government of India has attempted to wean away members of ULFA. In 1992 a large section of second rank leaders and members surrendered to government...
related drugs.
External links
- DrugDigest - Alpha blockers
- RxList.com - Tamsulosin