Reserpine is an alkaloid, isolated from the Rauwolfia serpentina plant and developed by Ciba pharma. Reserpine was approved by FDA for the treatment of hypertension and psychotic disorders. The drug exerts its effect by blocking two vesicular monoamine transporters, VMAT1 and VMAT2. The blockade results in vesicles that lose their ability to store neurotransmitter molecules. Neurotransmitters, thus retained in cytosol, are then neutralized by MAO.

Trimethaphan (or Trimethaphan camsylate), a ganglionic blocking agent and an antihypertensive drug, was marketed under the brand name Arfonad. Arfonad is indicated to induce systemic arterial hypotension in patients undergoing major surgery and to treat severe systemic hypertension, and in the emergency treatment of pulmonary edema in patients with pulmonary hypertension associated with systemic hypertension. Trimethaphan prevents stimulation of postsynaptic receptors by competing with acetylcholine for these receptor sites. Additional effects may include direct peripheral vasodilation and release of histamine. This drug was discontinued because of the competition from newer drugs that are more selective in their actions and effects.

Ketanserin is a selective 5HT2A receptor antagonist which was initially developed as an anti-hypertensive medicine. However, now the drug is available as a topical gel formulation for the treatment of wounds, burns, ulcers and anal fissure (Sufrexal brand name). The drug action is explained by its ability to accelerate epithelialization.

Sitaxentan (TBC11251, trade name Thelin) is a potent and selective Endothelin A receptor antagonist. Sitaxentan was under development by Encysive Pharmaceuticals (now Pfizer) for use in the treatment of pulmonary hypertension, congestive heart failure and asthma. It was launched in the major markets of the European Union (EU) under name Thelin for the treatment of pulmonary arterial hypertension. In December 2010, Pfizer discontinued clinical trials of sitaxentan worldwide and initiated voluntary product withdrawal from markets where it is approved due to life-threatening idiosyncratic risk of liver injury.

Cadralazine is an antihypertensive of the hydrazinophthalazine chemical class. In hypertensive patients the optimal effect, based on the antihypertensive efficacy to tolerability ratio, is seen after a 15 mg dose when the drug is administered as monotherapy. When administered in combination with other antihypertensive agents, a 10 mg daily dosage seems appropriate. Noncomparative trials have shown that, in patients who had failed to respond adequately to a beta-blocker and/or diuretic, the addition of cadralazine 10 to 30 mg once daily reduced systolic/diastolic blood pressure by 11 to 19%/13 to 22%. This antihypertensive effect becomes evident over a 2- to 6-week period of therapy and persists during longer term administration. Comparative studies have shown that cadralazine is superior to placebo, and has a similar blood pressure lowering effect to hydralazine, dihydralazine and prazosin in patients not controlled by beta-blocker and/or diuretic but who continued to receive these treatments. Similarly, cadralazine and chlorthalidone were equally effective in reducing blood pressure in resting hypertensive patients but cadralazine shows an advantage in reducing the pressor response in exercising patients. Cadralazine is well tolerated when administered with a beta-blocker or diuretic. Most adverse effects become less frequent and severe with continued use, occur more frequently at dosages of 20 mg/day or more, and do not generally require withdrawal of therapy. Manifestations of the drug's vasodilating properties such as headache, asthenia, dizziness, palpitations and flushing are the most commonly reported symptoms during cadralazine monotherapy, but these may be reduced during combination therapy. The drug does not appear to induce a systemic lupus-like erythematosus syndrome, as may occur with hydralazine, but additional clinical experience is required to completely exclude this possibility. The therapeutic potential of cadralazine cannot be clearly established until the present limited clinical base is expanded to include comparisons with other classes of vasodilating drugs (ACE inhibitors and calcium antagonists), and its utility in the management of other indications such as severe hypertension during pregnancy has been adequately explored.

Methoserpidine is a synthetic isomer of reserpine, used in the 1960s as an antihypertensive drug. Initially, it was reported to be free from CNS side effects of reserpine (mild suppression of alertness, and mental depression). However, later clinical experience has shown that in a significant proportion of patients administration of the drug lead to episodes of depression.

Debrisoquin is an antihypertensive drug having guanethidine-like properties, which inhibits monoamine oxidase (MAO) and does not enter the brain. Debrisoquine was used for the treatment of hypertension. Debrisoquine hydroxylation phenotype has been the most used test in humans to evaluate CYP2D6 activity. Two debrisoquine hydroxylation phenotypes have been described: poor and extensive metabolizers. A group with a very low debrisoquine metabolic ratio within the extensive metabolizers, named ultrarapid metabolizers, has also been distinguished. This CYP2D6 variability can be for a large part alternatively determined by genotyping, which appears to be of clinical importance given CYP2D6 involvement in the metabolism of a large number of commonly prescribed drugs.

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).

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.

Rilmenidine (brand names Albarel, Hyperium, Iterium and Tenaxum) is an imidazoline derivative used for the treatment of hypertension. Rilmenidine, an oxazoline compound with antihypertensive properties, acts on both medullary and peripheral vasomotor structures. Rilmenidine shows greater selectivity for imidazoline receptors than for cerebral alpha2-adrenergic receptors, distinguishing it from reference alpha2-agonists. Rilmenidine is as effective in monotherapy as all other first line classes of drugs, including diuretics, beta-blockers, angiotensin converting enzyme (ACE) inhibitors, and calcium antagonists. It is well tolerated and can be taken in combination for greater efficacy. Sedation and dry mouth are not prominent side effects and withdrawal hypertension is not seen when treatment is stopped abruptly. In addition to a reduction in blood pressure, Rilmenidine has been shown to improve glucose tolerance, lipid risk factors, and insulin sensitivity.