Alpha Adrenergic Blockers: Drugs & Side Effects

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

We will describe the different drugs that are under the category of alpha adrenergic blockers and what they are used for. We will also look at the most commonly reported side effects of this category of drugs.

Alpha-Adrenergic Blockers

Sky diving. Roller coasters. Bungee jumping. Cliff diving. They all serve to do one thing for most peopleā€¦.give a nice adrenaline rush! The adrenaline rush comes from the release of two different hormones, adrenaline and noradrenaline, into the bloodstream. The hormones work together to cause smooth muscles that line the blood vessels and organs in the body to tighten up and the heart to beat faster.

The result of the fight-and-flight response is that our blood pressure increases. While higher blood pressure is a great in certain circumstances, it can be dangerous for long periods of time.

There is a category of drugs that are designed to block these actions. Alpha-adrenergic blockers, also frequently called alpha blockers, are drugs that stop noradrenaline from being able to affect the walls of our blood vessels and internal organs.

You may see a few different names for this category of drugs to include: alpha blocking agents, alpha adrenergic antagonists, and adrenergic blocking agents.

Alpha blockers treat BPH
Diagram showing BPH

All of these names refer to the same category of drugs that are used in the treatment of hypertension, which is a disease of having persistent high blood pressure as well as benign prostatic hyperplasia (BPH), which is an enlarged prostate gland.


Long-Acting Alpha Blockers

There are quite a few different drugs that fall into the category of alpha blockers. Some are long-acting while others are short-acting and some are non-selective while others are specific. Let's begin with the long-acting since these are the ones that tend to be used most often for treatments.

Doxazosin is an extended release alpha blocker meaning that it gives a continuous dose to maintain the blocking activity over a longer period of time. Doxazosin is one of the specific alpha blockers since it blocks alpha 1 only as opposed to both alpha 1 and 2. This extended release drug is used to treat both hypertension and BPH.

Terazosin , tamulosin, and alfuzosin, are all long-acting alpha 1 blockers as well, but in this case they are not extended release tablets. These are also used to treat the prostate gland. They relax the muscles in the prostate gland which allows urine to flow through more easily.

Our next drug in the category of long-acting adrenergic blockers is phenoxybenzamine. Phenoxybenzamine is not selective like the other drugs that we have covered so far. This means its actions work relatively well against both alpha 1 and alpha 2, but not extremely effectively for either one. In this case, we use phenoxybenzamine to treat high blood pressure rather than BPH.

Short-Acting Alpha Blockers

We also have the use of short-acting alpha blockers which are good in the event that conditions in the body need to be reversed very quickly or just temporarily. Our first short-acting adrenergic blocker is phentolamine. Phentolamine is not specific to either alpha 1 or 2. Since it is needed to act quickly in the body, it gets injected either directly into the muscles or intraveneously into the bloodstream. It is used to prevent high blood pressure during some surgeries and diagnose tumors in the adrenal glands that are responsible for releasing adrenaline and noradrenaline. Another interesting use for phentolamine is the reversal of erectile dysfunction in men. It still gets injected, but it is injected directly into the penis.

The last of the adrenergic blocking agents that we are covering is prazosin. This short-acting alpha blocker is used to treat hypertension, BPH, and some symptoms of post-traumatic stress disorder. It is also not specific just like phentolamine. Unlike phentolamine, prazosin is not injected and can be used for long periods of time or temporarily.

Side Effects

By now you have probably learned that very few things come without any drawbacks. Just like there are things that we want to happen with taking adrenergic blocking agents, there are things that we didn't exactly plan on happening when taking these drugs. Some are minor while others are more concerning.

Mild Side Effects

So let's start with a side effect that actually isn't a bad thing. Hard to believe, right? Well every now and then we get lucky! You know how you keep hearing about cholesterol being bad and that there is only one good kind of cholesterol to have in our bodies? Alpha blockers can sometimes help to lower your total cholesterol levels as well as low-density cholesterol levels, which is the 'bad' cholesterol.

Time to get to the undesirable side effects. These drugs are associated with causing weakness, weight gain, dizziness, fatigue, headache and a pounding heartbeat.

Nausea and vomiting are side effects of alpha blockers
Drawing of a person with stomach discomfort

Some less common side effects that are mild include slow heartbeat, constipation, frequent urination, nausea, vomiting and diarrhea. These side effects will often disappear once the body gets use to the alpha blocker.

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