From the Guidelines
Alpha adrenergic blockers can be either selective or non-selective, with most commonly prescribed agents like doxazosin, terazosin, alfuzosin, and tamsulosin being relatively selective for alpha-1 receptors and not significantly blocking beta receptors. However, some agents like phenoxybenzamine (a non-selective alpha blocker) and labetalol and carvedilol (which are primarily marketed as beta blockers) have mixed activity 1. The selectivity profile of these medications is crucial in guiding appropriate selection based on the patient's condition and desired hemodynamic effects.
Key Points to Consider
- Most alpha blockers are selective for alpha-1 receptors and do not significantly block beta receptors 1
- Agents like phenoxybenzamine, labetalol, and carvedilol have mixed alpha and beta blocking activity 1
- The choice of alpha blocker should be influenced by the patient's cardiovascular and sexual status 1
- Pure alpha blockers can cause reflex tachycardia due to decreased peripheral resistance without beta blockade, whereas agents with combined alpha and beta activity may prevent this reflex increase in heart rate
Clinical Implications
- Understanding the selectivity profile of alpha adrenergic blockers is essential in clinical practice to minimize adverse effects and optimize treatment outcomes 1
- Alpha blockers with mixed activity, such as labetalol and carvedilol, may be beneficial in patients with certain cardiovascular conditions, but their use should be carefully considered in patients with obstructive airways disease due to the risk of beta-2 antagonism 1
- The frequency of side effects, such as dizziness, asthenia, and orthostatic hypotension, may vary among individual alpha blockers, and the choice of agent should be tailored to the individual patient's needs 1
From the FDA Drug Label
The mechanism of action of doxazosin is selective blockade of the alpha 1 (postjunctional) subtype of adrenergic receptors. The parent compound doxazosin is primarily responsible for the antihypertensive activity The vasodilatory hypotensive action of terazosin appears to be produced mainly by blockade of alpha-1 adrenoceptors.
Alpha Adrenergic Blockers are selective for the alpha 1 subtype of adrenergic receptors.
- There is no mention of beta blockade in the provided drug labels for doxazosin 2 and terazosin 3 and 3.
- The mechanism of action of these drugs is primarily through the blockade of alpha 1 adrenoceptors, which results in a decrease in systemic vascular resistance and an improvement in urinary flow rates in patients with BPH.
- The lack of beta blockade is consistent with the fact that these drugs do not significantly affect heart rate at therapeutic doses.
From the Research
Alpha Adrenergic Blockers
- Alpha adrenergic blockers are a class of medications used to treat symptomatic benign prostatic hyperplasia (BPH) and hypertension 4, 5, 6, 7.
- These blockers work by relaxing the muscles in the prostate and bladder neck, making it easier to urinate 4, 6.
Purity of Alpha Adrenergic Blockers
- Not all alpha adrenergic blockers are pure, some may have beta-blocking activity as well 8.
- However, studies have shown that some alpha blockers, such as silodosin, exhibit true selectivity for the α1-adrenoceptor subtypes, with minimal beta-blocking activity 6.
- Other alpha blockers, such as terazosin and doxazosin, may have more pronounced beta-blocking effects, which can lead to cardiovascular side effects like hypotension and dizziness 4, 5, 7.
Comparison of Alpha Adrenergic Blockers
- Different alpha adrenergic blockers have varying degrees of selectivity for alpha-adrenergic receptors, which can affect their efficacy and side effect profiles 4, 6.
- For example, tamsulosin and alfuzosin are considered uroselective, meaning they have a higher affinity for alpha-adrenergic receptors in the prostate, which can reduce the risk of cardiovascular side effects 4, 6.
- Silodosin, on the other hand, has a unique selectivity profile, which may account for its favorable cardiovascular safety profile 6.