Prazosin properties

In order to improve the properties of the well-known adrenergic antagonist, two chemical modulations on classical drugs including NO-donor moiety have been described. On the one hand, chemical modifications on Prazosin, an a 1-adrenergic antagonist, including furoxanyl moieties have been reported [70,182,183]. hi this approach, the 2-furanylcarbonyl moiety of Pra-... 

Prazosin and doxazosin are selective al blockers with similar properties. They are competitive antagonists that can be displaced from the al receptor by increases in catecholamine concentrations. This makes them unsuitable for use in the peri-operative management of phaeochromocytoma. Urapidil is an agonist at both central a2 and serotoninergic 5-HTlA receptors, and also has antagonist actions at cardiac pi adrenoceptors. 

The characteristics of individual alpha blockers are discussed in Chapter 20. Basically, these drugs can be differentiated according to their relative alpha-1 selectivity, their duration of action, and other pharmacokinetic properties. Prazosin (Minipress) has been the primary alpha blocker used in the past, but newer agents such as doxazosin and terazosin (Hytrin) are gaining acceptance in treating hypertension. Prazosin and other alpha blockers approved as antihypertensives are listed in Table 21-4. 

The main difference between prazosin, terazosin, and doxazosin lies in their pharmacokinetic properties. As men-lloncd above, these differences are dictated by the nature of the acyl moiety attached to the piperazine ring. A comparison of these three agents with respect to their oral bioavailability, half-life, and duration of action is shown in Table 16-2. These drugs are metabolized extensively, with the me-taNiies excreted in the bile. 

Terazosin Hydrochloride. Terazosin hydrochloride. I -l4-amino-f).7-dimethoxy-2-quinaz.olinyl)-4-(tetnihydro-2-fu-royllpipcrazinc monohydrochloride (Hytrin), is a structural congener of prazosin hydrochloride. It possesses similar selc-ctive properties of specincally inhibiting 0 -udrenergic receptors. The drug is slightly less potent than prazosin hydrochloride. Terazosin hydrochloride has a half-life of approximately 12 hours, which is much longer than that of prazosin. This lends itself to a once-daily dose to control hypertension in ntany patients. 

Clonidine hydrochloride has advantages over antihyper-icnsive drugs such asguanethidinc monosulfate and prazosin hydrochloride, in that it seldom produces orthostatic hypo-icndvc side effects. It does, however, have some sedative properties that ate undesirable it also may cau.se constipa-ilnn and dryness of the mouth. 

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