Prazosin dosing

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. 

Treatment Nonpharmacologic treatments of muscle cramping that occurs during hemodialysis include decreasing the ultrafiltration rate and accurately determining the dry weight. Pharmacologic measures include vitamin E, which is administered at doses of 400 IU daily. Other options that are not as well studied include oxazepam and prazosin. 

Plasma half-life. a-Adrenergic receptors with short plasma half-lives (e.g., prazosin) require multiple doses during the day. This is challenging for most patients, and, thus, prazosin is not recommended for BPH.11... 

Prazosin constipation First-dose orthostatic hypotension... 

Prazosin is a selective aradrenergic receptor antagonist that, at therapeutic doses, has little activity at a2-adrenergic receptors and clinically insignificant direct vasodilating activity The drug does not cause the other effects attributed to phentolamine. Most important, it produces less tachycardia than does phentolamine and, therefore, is useful in the treatment of essential hypertension. 

Reversible competitive antagonists, nonselective (phentolamine, tolazoline), and -selectively acting (prazosin, terazosin) that reversibly and competitively block a-receptive regions terazosin can last a few hours. At the same time, blockage of a-receptors can be interrupted and stopped by large doses of an agonist such as norepinephrine. 

First-dose effect Prazosin, terazosin, doxazosin, alfuzosin, and tamsulosin,... 

The first-dose phenomenon may be minimized by limiting the initial dose to 1 mg of terazosin or prazosin (given at bedtime) or doxazosin. 

Prazosin is readily absorbed after oral administration, peak serum levels occur approximately 2 hours after a single oral dose, and the antihypertensive effect of prazosin persists for up to 10 hours. Its half-life in plasma ranges from 2.5 to 4 hours, and elimination from plasma appears to follow first-order kinetics. The drug is extensively (perhaps as high as 97%) bound to plasma proteins this observation partially explains the lack of correlation between plasma drug levels and persistence of antihypertensive effect. 

The answer is e. (Katzung, pp 141, 168.) Prazosin blocks tti-adrenergic receptors in arterioles, thereby decreasing peripheral resistance and leading to a decrease in blood pressure. Orthostatic hypotension can occur, particularly after a first dose. 

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... 

Aside from the first-dose phenomenon, the reported toxicities of the a blockers are relatively infrequent and mild. These include dizziness, palpitations, headache, and lassitude. Some patients develop a positive test for antinuclear factor in serum while on prazosin therapy, but this has not been associated with rheumatic symptoms. The blockers do not adversely and may even beneficially affect plasma lipid profiles, but this action has not been shown to confer any benefit on clinical outcomes. 

Prazosin [P] Increased hypotensive response to first dose of prazosin. 

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