Adrenergic antagonists: Alpha blockers

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Adrenergic antagonists: Alpha blockers

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A 55-year-old man presents for evaluation of insomnia. The patient has been having trouble sleeping for the past 3 weeks. He has also lost appetite for the past three months, which resulted in a 10 lb (4.5 kg) weight loss. A review of systems is significant for difficulty concentrating at work and loss of interest in activities he previously enjoyed. He spends most of the day lying in bed. His relationship with his spouse is “not working too well right now.” The patient has no chronic medical conditions and takes no medications. BMI is 20 kg/m2. Vitals are within normal limits. Baseline workup, including thyroid function testing, is unremarkable. Which of the following medications would be most appropriate to treat this patient’s condition?  

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Doxazosin p. 245


Alpha blocker and beta blockers are two types of postsynaptic anti-adrenergic medications that prevent their respective receptors from being stimulated by catecholamines, like norepinephrine and epinephrine.

The nervous system is divided into the central nervous system, so the brain and spinal cord; and the peripheral nervous system, which includes all the nerves that connect the central nervous system to the muscles and organs.

The peripheral nervous system can be divided into the somatic nervous system, which controls voluntary movement of our skeletal muscles; and the autonomic nervous system, which is further divided into the sympathetic and the parasympathetic, and controls the involuntary movement of the smooth muscles and glands of our organs.

Now, the autonomic nervous system - which includes both the sympathetic and parasympathetic nervous system - is made up of a relay that includes two neurons.

We’ll focus on just the sympathetic nervous system.

Signals for the autonomic nervous system start in the hypothalamus, at the base of the brain.

Hypothalamic neurons have really long axons that carry signals all the way down to the thoracic and lumbar spinal cord nuclei, where they synapse with preganglionic neuron cell bodies.

From there, the signal goes from the preganglionic neurons down its relatively short axon, exits the spinal cord, and reaches the nearby sympathetic ganglion, which is made up of lots of postganglionic neuron cell bodies.

The postganglionic neurons are also called adrenergic neurons because they release the neurotransmitter norepinephrine, which is also called noradrenalin; and to a much lesser degree, epinephrine, or adrenaline.


Adrenergic antagonists are a type of drug that blocks the action of adrenaline in the body. Adrenaline is a hormone that is released in response to stress or excitement, and it causes the heart rate to speed up and the blood vessels to narrow.

Alpha-blockers are a type of adrenergic antagonist that blocks the action of adrenaline on the alpha receptors. The alpha receptors are found in the muscles around the blood vessels, and when they are activated, they cause the blood vessels to narrow. Alpha-blockers, therefore, cause the blood vessels to widen, which lowers blood pressure and improves symptoms of congestive heart failure.


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