(for veterinary information only)
BRAND NAME: MINIPRESS
The muscles of our body can be employed in voluntary activities (like running and playing) as well as in involuntary activities (like intestinal contraction and pupil constriction). Involuntary (automatic) activities are controlled by the autonomic nervous system and the autonomic nervous system is divided into the sympathetic and the parasympathetic nervous system. The sympathetic system supports the "fight or flight" response while the parasympathetic system supports the "status quo" or normal every day body functions.
The sympathetic system utilizes receptors called alpha and beta receptors to exert its effects. These receptors are located in all the organs controlled by the sympathetic nervous system, some organs using alpha receptors and some using beta receptors. Alpha and beta receptors are further divided into alpha-1 and alpha-2 and beta-1 and beta-2 receptors. These receptors can be enhanced or blocked by medication depending on the effect desired.
Prazosin is an alpha-1 blocker. The sympathetic system is in charge of urine storage (versus urination) and blocking the alpha-1 receptors in the urethral sphincter serves to relax the muscles and dilate the urethra allowing for easier urination.
Alpha-1 receptors are also present in the peripheral blood vessels. Prazosin serves to relax these muscles as well thus allowing for a reduction in blood pressure and dilation of blood vessels (both veins and arteries).
HOW THIS MEDICATION IS USED
The two scenarios where Prazosin is most commonly used are in cardiovascular disease and in promoting difficult urination.
Urinary Conditions: If a narrowing of the urethra is making urination difficult, the alpha-1 blockade of Prazosin may facilitate a more comfortable urination. It is commonly used in cats after an idiopathic cystitis blockage, in patients with bladder or prostate tumors, or patients with spinal disease.
Because one of its main functions is reducing blood pressure, some patients may be weak or tired if their blood pressure drops too low. A dosage adjustment may be necessary.
INTERACTIONS WITH OTHER DRUGS
In humans, tolerance has been a problem with Prazosin (meaning that after a while it does not work any more). Using the diuretic spironolactone seems to ameliorate this phenomenon.
Some patients require multiple drugs to control blood pressure but it is important to note that hypotensive agents should not be combined without realizing that their effects will likely be additive.
CONCERNS AND CAUTIONS
Prazosin may not be a good choice for patients with pre-existing low blood pressure.
Dogs with the ABCB1 (formerly called the MDR1) mutation may be sensitive to this drug as they are sensitive to many other drugs. Prazosin may not be a good choice for such individuals. Dogs with this mutation are usually of the collie family but individuals may be genetically screened by Washington State University. For more information on testing, visit:
Page posted: 9/29/2013