Terazosin hypotension caused

Q60 When a patient who is receiving atenolol is started on terazosin, there is an increased risk of first-dose hypotension. Terazosin is an alpha-adrenoceptor agonist which causes vasodilatation. 

Terazosin is an alpha-adrenoreceptor blocker that causes vasodilation and is used in the management of hypertension and benign prostatic hypertrophy. Beta-blockers and alpha-blockers can interact to induce hypotension since both act to reduce the blood pressure. Patients already on beta-blockers and who are started on alpha-blockers such as terazosin should be advised to take the terazosin dose at night to reduce the implications (falls) of first-dose hypotension. 

Altered homeostasis in older persons can lead to important and common adverse drug effects the less robust homeostatic milieu may be stressed by drugs, causing adverse effects. Examples include orthostatic hypotension due to antihypertensives and other agents that cause a-adrenergic blockade (e.g. terazosin, doxazosin, tricyclic antidepressants and phenothiazines) in those with barorecep-tor dysfunction. Diuretics can cause hyponatraemia or hypokalaemia in older patients, whereas ACE inhibitors and NSAIDs can cause hyperkalaemia. 

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

Terazosin can often be given once daily, with doses of 5-20 mg/d. Doxazosin is usually given once daily starting at 1 mg/d and progressing to 4 mg/d or more as needed. Although long-term treatment with these -blockers causes relatively little postural hypotension, precipitous drop in standing blood pressure develops in a number of patients shortly after the first dose is absorbed. For this reason, the first dose should be small and should be administered at bedtime. While the mechanism of this first-dose phenomenon is not clear, it occurs more commonly in patients who are salt- and volume-depleted. 

Prazosin, oxazosin and terazosin (see p. 73) produce a competitive block of oci adrenoceptors. They decrease peripheral vascular resistance and lower arterial blood pressure by causing the relaxation of both arterial and venous smooth muscle. These drugs cause only minimal changes in cardiac output, renal blood flow, and glomerular filtration rate. Therefore, long-term tachycardia and increased renin release do not occur. Postural hypotension may occur in some individuals. Prazosin is used to treat mild to moderate hypertension and is prescribed in combination with propranolol or a diuretic for additive effects. Reflex tachycardia and first dose syncope are almost universal adverse effects. Concomitant use of a p-blocker may be necessary to blunt the short-term effect of reflex tachycardia. 

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. 

Direct information is limited. Acute hypotension (dizziness, fainting) sometimes occurs unpredictably with the first dose of some alpha blockers (particularly, alfuzosin, prazosin and terazosin but see Alpha blockers , (p.83)), and this can be exaggerated if the patient takes or is already taking a beta blocker or a calcium-channel blocker (see Alpha blockers + Beta blockers , below, and Alpha blockers + Calcium-channel blockers , p.85). It would therefore seem prudent to apply the same precautions to ACE inhibitors, namely reducing the dose of the ACE inhibitor to a maintenance level if possible, then starting the alpha blocker at the lowest dose, with the first dose given at bedtime. Note that the acute hypotensive reaction appears to be short-lived. There is limited evidence that terazosin and tamsulosin may not cause an additional hypotensive effect in the longer term in patients with BPH who have hypertension already well-controlled with ACE inhibitors. Nevertheless, caution should be exercised in this situation, and a dose reduction of the ACE inhibitor may be required. 

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