Orthostatic hypotension prazosin

Generally, arblockers are considered as second-line agents to be added on to most other agents when hypertension is not adequately controlled. They may have a specific role in the antihypertensive regimen for elderly males with prostatism however, their use is often curtailed by complaints of syncope, dizziness, or palpitations following the first dose and orthostatic hypotension with chronic use. The roles of doxazosin, terazosin, and prazosin in the management of patients with hypertension are limited due to the paucity of outcome data and the absence of a unique role for special populations or compelling indications from JNC 7. 

The decrease in the ability of the aging body to respond to baroreflexive stimuli can result in very serious consequences for elderly patients [115-117]. Because of this decrease in sensitivity and the decreased cardiac output witnessed in elderly patients, they are predisposed to the effects of orthostatic hypotension that can occur when one is taking antihypertensive medication (e.g., prazosin). Indeed, the fact that elderly persons are prone to accidental falls may be due to this change in sensitivity [115-117]. 

Prazosin constipation First-dose orthostatic hypotension... 

The answer is e. (Katz ng, pp HI, I6 ) Prazosin blocks a -adrenergic receptors in arterioles, thereby decreasing peripheral resistance and leading to a decrease in blood pressure. Orthostatic hypotension can occur, particularly after a first close... 

Prazosin was the first example of a selective O -blocker. Its main application is hypertension, usually in combination with a -blocker and/or a diuretic. Orthostatic hypotension readily occurs as a result of venous dilatation. The problem may be avoided by a gradual increase of the dosage. The drug has a short duration of action and must be administered 2-3 times daily in order to achieve adequate control of blood pressure. 

Doxazosin, also a selective a i-blocker, resembles prazosin in most aspects, but it has a better pharmacokinetic profile, at least for long-term use as in essential hypertension. Owing to its slow onset of action, doxazosin causes far less orthostatic hypotension and reflex tachycardia than prazosin. As a result of its long duration of action, it can be administered once daily in the long-term treatment of essential hypertension. 

In the treatment of hypertension a selective O -adrenoceptor agent is preferable to the older, non-selective (ai - - a2)-blockers. Doxazosin is preferable to prazosin, because it has a slower onset and longer duration of action. It therefore causes less or no reflex tachycardia and orthostatic hypotension. 

Geriatric Considerations - Summary Alpha-adrenergic blockers are modestly effective alone, and in combination with 5-alpha reductase inhibitors (e,g, finasteride) in the treatment of urinary obstructive symptoms related to benign prostatic hyperplasia. Alfuzosin is a "uroselective" alpha-blockerwhich appears to cause less orthostatic hypotension than nonselective alpha-blockers such as terazosin, prazosin, and doxazosin. 

Prazosin, doxazosin, and terazosin are all efficacious in patients with BPH. These drugs are particularly useful in patients who also have hypertension. Considerable interest has focused on which -receptor subtype is most important for smooth muscle contraction in the prostate subtype-selective K1A-receptor antagonists might lead to improved efficacy and safety in treating this disease. As indicated above, tamsulosin is also efficacious in BPH and has relatively minor effects on blood pressure at a low dose. This drug may be preferred in patients who have experienced orthostatic hypotension with other -receptor... 

Prazosin Doxazosin Terazosin Block , but not a2 Lower BP Hypertension benign prostatic hyperplasia Larger depressor effect with first dose may cause orthostatic hypotension... 

Prazosin Selectively block 04 adrenoceptors Prevent sympathetic vasoconstriction reduce prostatic smooth muscle tone Hypertension benign prostatic hyperplasia Oral Toxicity Orthostatic hypotension... 

The doctor is sympathetic cough is sometimes a problem for patients taking captopril she prescribes an alpha-adrenoceptor (a-adrenoceptor) antagonist, prazosin, instead. Sam has problems initially with orthostatic hypotension however, after dosage reduction, prazosin is well tolerated and Sam s BP settles at 143/87 mmHg. 

Prazosin is an a i-selective adrenoceptor antagonist which causes vasodilation and a fall in BP. Alpha-adrenoceptor antagonists also have a favourable effect on blood lipids and are useful for people with raised cholesterol. However, orthostatic hypotension may occur during treatment because prazosin interferes with the postural reflexes, which are triggered when a patient stands up from a supine or sitting position. 

The first-dose effect (profound postural hypotension and reflex tachycardia) is a weU-recognized complication of the first dose of prazosin and related agents. This phenomenon is dose-related and can usually be avoided by using a low initial dosage taken at bedtime. During long-term treatment, orthostatic hypotension and dizziness is reported by about 10% of patients. 

Second-generation agents include prazosin, terazosin, doxazosin, and alfuzosin. These differ in terms of duration of action and dosing schedule. Whereas prazosin requires dosing two to three times a day, terazosin, doxazosin, and alfuzosin offer more convenient once-daUy dosing. Prazosin, terazosin, and doxazosin antagonize peripheral vascular ai-adrenergic receptors, in addition to those in the prostate, at the usual doses used to treat BPH. As a result, first-dose syncope, orthostatic hypotension, and dizziness are... 

Prazosin, terazosin, doxazosin, tamsulosin, and alfuzosin have been studied extensively and used widely in patients with benign prostatic hyperplasia. With the exception of tamsulosin, the comparative efficacies of each of these drugs, especially in comparison with relative adverse effects such as postural hypotension, appear similar, although direct comparisons are limited. Tamsulosin at the recommended dose of 0.4 mg daily is less likely to cause orthostatic hypotension than the other drugs. There is growing evidence that the predominant a,-receptor subtype expressed in the human prostate is the a,-receptor. Developments in this area will provide the basis for the selection of Ct receptor antagonists with specificity for the relevant subtype of aj-receptor. However, the possibility remains that some of the symptoms of BPH are due to aj-receptors in other sites, such as bladder, spinal cord, or brain. 

Propranolol—but not prazosin—may decrease cardiac output. Prazosin may increase renin output (a compensatory response), but beta-blockers inhibit its release by the kidney. By reducing blood pressure, both may increase central sympathetic outflow (a compensatory response). Propranolol does not cause orthostatic hypotension. The answer is (D). 

Alfuzosin (91) is a prazosin-like hypotensive adrenergic a-1 receptor blocker with the special structural feature that two carbons have been excised conceptually from the piperazine ring normally present in this series. Following the usual sequence for this series, reaction of 4-amino-2-chloro-7-dimethoxyquinazoline (89) with the tetrahydro-2-furyl amide of 3-methylaminopropyla-mine (90) gives alfuzosin (91) [25], Alfuzosin is claimed to cause less orthostatic hypotention (dizziness or fainting upon sudden rising) than prazosin. 

An adverse effect of prazosin and its congeners is the first-dose effect marked postural hypotension and syncope may occur 30-90 minutes after the initial dose. The mechanisms responsible for exaggerated hypotensive response and the subsequent development of tolerance to the effect are not clear an action in the CNS to reduce sympathetic outflow may contribute. Risk of the first-dose phenomenon is minimized by limiting the initial dose (e.g., 1 mg at bedtime), by increasing the dosage slowly, and by introducing additional antihypertensive drugs cautiously. Since orthostatic... 

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