Basic Information
ID DDInter1511 and DDInter12
Interaction Additive hypotensive effects may occur when beta-blockers are used in combination with alpha-blockers. In the presence of beta-blockade, the risk and/or severity of first-dose effects associated with alpha-blockers such as postural hypotension and syncope may be increased. Beta-blockers may also blunt the reflex tachycardia that occurs in response to postural hypotension. Theoretically, the interaction may also occur with beta-blocker ophthalmic preparations, since they may be systemically absorbed and can produce clinically significant systemic effects even at low or undetectable plasma levels.
Management Caution is advised during coadministration of these agents, particularly when initiating an alpha-blocker in the presence of a beta-blocker, including ophthalmic formulations. Small initial dosages of the alpha-blocker should be considered and gradually titrated to desired effect, while the systemic beta-blocker dosage may also need to be reduced. Hemodynamic responses should be monitored, especially during the first few weeks of therapy. Taking the alpha-blocker at bedtime may minimize the occurrence of orthostatic effects. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia.
References [1] Holtzman JL, Kaihlanen PM, Rider JA, Lewin AJ, Spindler JS, Oberlin JA "Concomitant administration of terazosin and atenolol for the treatment of essential hypertension." Arch Intern Med 148 (1988): 539-43 [2] Chrysant SG "Experience with terazosin administered in combination with other antihypertensive agents." Am J Med 80 (1986): 55-61 [3] "Product Information. Xatral (alfuzosin)." Sanofi-Synthelabo Canada Inc, Markham, ON. [4] Pool JL "Combination antihypertensive therapy with terazosin and other antihypertensive agents: results of clinical trials." Am Heart J 122 (1991): 926-31 [5] Rubin P, Jackson G, Blaschke T "Studies on the clinical pharmacology of prazosin II: the influence of indomethacin and of propranolol on the action and disposition of prazosin." Br J Clin Pharmacol 10 (1980): 33-9 [6] Elliott HL, McLean K, Sumner DJ, Meredith PA, Reid JL "Immediate cardiovascular responses to oral prazosin: effects of concurrent beta-blockers." Clin Pharmacol Ther 29 (1981): 303-9 [7] Seideman P, Grahnen A, Haglund K, Lindstrom B, Von Bahr C "Prazosin first dose phenomenon during combined treatment with a B-adrenoceptor blocker in hypertensive patients." Br J Clin Pharmacol 13 (1982): 865-70 [8] Stokes GS, Mennie BA, Gellatly R, Hill A "On the combination of alpha- and beta-adrenoceptor blockade in hypertension." Clin Pharmacol Ther 34 (1983): 576-82
Alternative for Prazosin C02L
Deserpidine

C02C
Alternative for Acebutolol -
Potential Metabolism Interactions
Substrate-Substrate Interaction：If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction：Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction：Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.