Terazosin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in essential hypertension.

Terazosin is a post-synaptic alpha 1-adrenoceptor antagonist with a similar pharmacodynamic profile to prazosin. It differs from prazosin in having a longer duration of action, with an elimination half-life some 2 to 3 times that of prazosin, allowing the convenience of once daily administration. Moreover, its absorption from the gastrointestinal tract is more complete and predictable than that of prazosin which may facilitate dose titration. Terazosin therapy results in a significant reduction in blood pressure in patients with mild to moderate essential hypertension, with little influence on heart rate. The drug is an effective antihypertensive when administered as monotherapy or in combination with a range of antihypertensive agents including beta-blockers, diuretics and combinations of the two. In the few patients with congestive heart failure studied, terazosin produced an increase in cardiac output with a reduction in ventricular filling pressure and systemic vascular resistance, but no studies have been performed to assess the therapeutic potential of terazosin in this indication. Reductions in total plasma cholesterol and low density plus very low density lipoprotein cholesterol fractions have been reported after terazosin therapy, while high density lipoprotein cholesterol concentrations have tended to increase. Should such beneficial changes be confirmed in long term clinical studies they would suggest a therapeutic advantage of terazosin over some other antihypertensive drugs, particularly diuretics, which have been reported to adversely affect the plasma lipid profile. The most common side effects associated with terazosin treatment are dizziness, headache, asthenia and nasal congestion, but these are usually mild and do not require treatment discontinuation. Terazosin is normally administered once daily, starting at a dose of 1 mg/day and gradually titrating upwards as the blood pressure stabilises at each new dose, until blood pressure is adequately controlled or to a maximum dose of 20mg daily. First-dose syncope occurs rarely after terazosin, and can largely be avoided by giving the first dose at bedtime. Thus, terazosin offers a useful alternative to the drugs currently available for the management of mild to moderate essential hypertension either as monotherapy or in combination with other antihypertensive drugs.