Selected Alpha-1 Blockers/Verapamil
How the interaction occurs:
The cause of the interaction is not known. When these two medicines are taken together, the effects of both medicines to lower your blood pressure may increase.
What might happen:
The effects of these medicines to lower blood pressure may be greater than with either drug alone. This may be an advantage. However, additional problems due to excess effects may occur.
What you should do about this interaction:
If you experience weakness or dizziness when you sit up or stand up, contact your doctor.Your healthcare professionals (e.g. doctor or pharmacist) may already be aware of this drug interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Pasanisi F, Elliott HL, Meredith PA, McSharry DR, Reid JL. Combined alpha adrenoceptor antagonism and calcium channel blockade in normal subjects. Clin Pharmacol Ther 1984 Dec;36(6):716-23.
2.Meredith PA, Elliott HL, Pasanisi F, Reid JL. Prazosin and verapamil: a pharmacokinetic and pharmacodynamic interaction. Br J Clin Pharmacol 1985 Sep;21(1):85P.
3.Elliott HL, Meredith PA, Campbell L, Reid JL. The combination of prazosin and verapamil in the treatment of essential hypertension. Clin Pharmacol Ther 1988 May;43(5):554-60.
4.Meredith PA, Elliott HL. An additive or synergistic drug interaction: application of concentration-effect modeling. Clin Pharmacol Ther 1992 Jun;51(6):708-14.
5.Hytrin (terazosin hydrochloride) US prescribing information. Abbott Laboratories July, 2009.