|Trade names||Minipress, Vasoflex, Lentopres, others|
|Onset of action||30–90 minutes|
|Elimination half-life||2–3 hours|
|Duration of action||10–24 hours|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||383.408 g·mol−1|
|3D model (JSmol)|
Prazosin is an alpha-1 blocker medication primarily used to treat high blood pressure, symptoms of an enlarged prostate, and posttraumatic stress disorder (PTSD). It is a less preferred treatment of high blood pressure. Other uses may include heart failure and Raynaud syndrome. It is taken by mouth.
Common side effects include dizziness, sleepiness, nausea, and heart palpitations. Serious side effects may include low blood pressure with standing and depression. Prazosin is an α1-blocker. It works to decrease blood pressure by dilating blood vessels and helps with an enlarged prostate by relaxing the outflow of the bladder. How it works in PTSD is not entirely clear.
Prazosin was patented in 1965 and came into medical use in 1974. It is available as a generic medication. In 2017, it was the 227th most commonly prescribed medication in the United States, with more than two million prescriptions.
Prazosin is active after oral administration and has a minimal effect on cardiac function due to its alpha-1 adrenergic receptor selectivity. When prazosin is started, however, heart rate and contractility can increase in order to maintain the pre-treatment blood pressures because the body has reached homeostasis at its abnormally high blood pressure. The blood pressure lowering effect becomes apparent when prazosin is taken for longer periods of time. The heart rate and contractility go back down over time and blood pressure decreases.
The antihypertensive characteristics of prazosin make it a second-line choice for the treatment of high blood pressure.
Prazosin is also useful in treating urinary hesitancy associated with benign prostatic hyperplasia, blocking alpha-1 adrenergic receptors, which control constriction of both the prostate and urethra. Although not a first-line choice for either hypertension or benign prostatic hyperplasia, it is a choice for people who present with both problems concomitantly.
During its use for urinary hesitancy in military veterans in the 1990s, Murray A. Raskind and colleagues discovered it appeared to be effective in reducing nightmares. Subsequent reviews indicate prazosin is effective in improving sleep quality and treating nightmares related to PTSD.
Common (4–10% frequency) side effects of prazosin include dizziness, headache, drowsiness, lack of energy, weakness, palpitations, and nausea. Less frequent (1–4%) side effects include vomiting, diarrhea, constipation, edema, orthostatic hypotension, dyspnea, syncope, vertigo, depression, nervousness, and rash. A very rare side effect of prazosin is priapism. One phenomenon associated with prazosin is known as the "first dose response", in which the side effects of the drug – specifically orthostatic hypotension, dizziness, and drowsiness – are especially pronounced in the first dose.
Orthostatic hypotension and syncope are associated with the body's poor ability to control blood pressure without active alpha-adrenergic receptors. People on prazosin should be told to rise to stand up slowly, since their poor baroreflex may cause them to faint if their blood pressure is not adequately maintained during standing. The nasal congestion is due to dilation of vessels in the nasal mucosa.[medical citation needed]
Mechanism of action
Prazosin is an α1-blocker that acts as an inverse agonist at alpha-1 adrenergic receptors, including α1A-, α1B-, and α1D-receptor subtypes. These receptors are found on vascular smooth muscle, where they are responsible for the vasoconstrictive action of norepinephrine. They are also found throughout the central nervous system. Alpha-1 adrenergic receptors have been found on immune cells, where catecholamine binding can stimulate and enhance cytokine production.
Prazosin has been shown to prevent death in animal models of cytokine storm. As a repurposed drug, prazosin is being investigated for the prevention of cytokine storm syndrome and complications of COVID-19 where it is thought to decrease cytokine dysregulation.
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This sympatholytic drug is used in the treatment of hypertension, anxiety and post-traumatic stress disorder. ... Antagonist of alpha-1 adrenoceptors on vascular smooth muscle, thereby inhibiting the vasoconstrictor effect of circulating and locally-released adrenaline and noradrenaline, resulting in peripheral vasodilation.
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