|Synonyms||Minipress, Vasoflex, Lentopres, others|
|Onset of action||30–90 minutes|
|Elimination half-life||2–3 hours|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||383.408 g·mol−1|
|3D model (JSmol)|
Prazosin is a 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 avaliable as a generic medication. A month supply in the United Kingdom costs the NHS about 3.50 £ as of 2019. In the United States the wholesale cost of this amount is about 20 USD. In 2016 it was the 220th most prescribed medication in the United States with more than 2 million prescriptions.
Prazosin is orally active and has a minimal effect on cardiac function due to its alpha-1 receptor selectivity. When prazosin is started, however, heart rate and contractility go up 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 prostatic hyperplasia, blocking alpha-1 receptors, which control constriction of both the prostate and urethra. Although not a first line choice for either hypertension or prostatic hyperplasia, it is a choice for patients who present with both problems concomitantly.
There is some evidence that this medication is effective in treating nightmares, mixed results in randomized control trials. Prazosin was, however, shown to be more effective when 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. Patients 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.
Mechanism of action
Prazosin is an α1-blocker that acts as an inverse agonist at alpha-1 adrenergic receptors. 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.
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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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