Prazosin

Prazosin, trade names Minipress, Vasoflex, Lentopres and Hypovase, is a sympatholytic drug used to treat high blood pressure and anxiety, PTSD, and panic disorder. It is an alpha-adrenergic blocker that is specific for the alpha-1 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. As of 2013, prazosin is off-patent in the US, and the FDA has approved at least one generic manufacturer.

In addition to its alpha-blocking activity, prazosin is an antagonist of the MT₃ receptor (which is not present in humans), with selectivity for this receptor over the MT₁ and MT₂ receptors.

Medical use

Prazosin is orally active and has a minimal effect on cardiac function due to its alpha-1 receptor selectivity. However, when prazosin is started, 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.