Trimazosin was originated by Pfizer and was licensed to Bristol-Myers Squibb worldwide except for Canada, Mexico and the USA. Trimazosin is a quinazoline antihypertensive agent structurally related to the selective alpha 1-adrenoceptor blocker prazosin. Trimazosin is an alpha adrenergic receptor antagonist. Compared with prazosin, trimazosin was a less potent but more efficacious hypotensive agent. At doses which caused equal or even greater hypotensive effects than those caused by prazosin, trimazosin caused less inhibition of pressor responses to phenylephrine. When administered during a maximum hypotensive response to prazosin, trimazosin caused an additional fall in pressure. Trimazosin is an effective antihypertensive when given by itself or in combination with a diuretic. Its ability to induce vasodilation without concomitant sodium retention or stimulation of the renin axis may be an important factor in its effectiveness. Trimazosin has the potential to cause sustained improvement in left ventricular function, both at rest and during exercise, in patients with chronic congestive heart failure (CHF).

Dimetofrine is a selective agonist of post-synaptic a1-adrenergic receptors. The drug was investigated as a cardiostimulant to treat orthostatic hypotension. Clinical investigation showed that dimetofrine relieves asthenia, paleness, drowsiness, fatigue, headache and other symptoms associated with hypotension. It was observed, that in acidic conditions similar to conditions in the stomach, dimetofrine is able to react with nitrites with the formation of highly mutagenic compound 2,6-dimethoxy-1,4-benzoquinone (DMBQ).

Urapidil is an anti-hypertensive agent approved in Europe for the treatment of the corresponding disease. The drug acts by activating 5HT1a receptor and inhibiting alpha1-adrenergic receptors.

Ifenprodil (marketed under the brands Vadilex; Dilvax; Creocral; Cerocral) is a selective NMDA receptor (glutamate) antagonist. Additionally, ifenprodil inhibits GIRK channels, and interacts with alpha1 adrenergic, serotonin, and sigma receptors. Ifenprodil acts as a vasodilator. Ifenprodil is a medicine available in a number of countries worldwide, but not in US.

Proroxan is a non-selective а-adrenoblocker. Proroxan was found to prevent the development of hypertensive crises and improve cerebral bioelectrical parameters in most of hypertensive patients. Proroxan has been used as an antihypertensive and in the treatment of Ménière’s disease, motion sickness, and allergic dermatitis.

Guanazodine is a new antihypertensive drug. Guanazodine caused a sustained decrease in the systemic blood pressure of spontaneously hypertensive rats, renal hypertensive dogs and normal cats. No tachyphylaxis developed when the drug was administered orally. The heart rate decreased. Guanazodine relaxed the cat nictitating membrane, attenuated the positive chronotropic response to sympathetic nerve stimulation in anesthetized dogs and in isolated rabbit aorta to transmural electrical stimulation. Guanazodine potentiated the pressor response to noradrenaline but attenuated the response to tyramine in anesthetized cats. It may be concluded that the hypotensive effect of guanazodine is related to adrenergic neuron blocking action, the noradrenaline-depleting action in peripheral tissues is similar to the effect of guanethidine and bethanidine. However, this drug is less potent than guanethidine. Toxicity and side effects appear to be less with guanazodine than with guanethidine and bethanidine.

Alinidine, a specific bradycardiac agent, which reduces myocardial oxygen consumption and improves exercise tolerance in patients with angina pectoris. In randomized controlled trial alinidine did not enhance myocardial salvage or preservation of left ventricular function of major arrhythmias in the early phase of infarction. The development of this drug was stopped because it was not sufficiently specific for its target.

Tolonidine, 2(2-chloro-p-toluidino)-2-imidazoline-nitrate, is a substance chemically related to clonidine. In the anesthetized dog, tolonidine administered i.v. decreased the amplitude of ventricular contractions, reduced aortic blood flow and increased peripheral vascular resistances. In the bivagotomized pithed rat, tolonidine induced a long-lasting increase in blood pressure with no secondary hypotension, thus suggesting peripheral sympathomimetic properties, however, contractions of seminal vesicles in vitro were not obtained. The product proved to have no peripheral sympatholytic or parasympatholytic properties.

Aganodine, an imidazoline/ alpha-2 receptor agonist, can lower intraocular pressure in the sympathetic neurons of the eye and possibly in the central nervous system.