Ramtace Mechanism of Action

Pharmacology: Pharmacodynamics: Mechanism of action: Ramiprilat, the active metabolite of the prodrug ramipril, inhibits the enzyme dipeptidylcarboxypeptidase I (synonyms: angiotensin-converting enzyme; kininase II). In plasma and tissue this enzyme catalyses the conversion of angiotensin I to the active vasoconstrictor substance angiotensin II, as well as the breakdown of the active vasodilator bradykinin. Reduced angiotensin II formation and inhibition of bradykinin breakdown lead to vasodilation. Since angiotensin II also stimulates the release of aldosterone, ramiprilat causes a reduction in aldosterone secretion. The average response to ACE inhibitor monotherapy was lower in black (Afro-Caribbean) hypertensive patients (usually a low-renin hypertensive population) than in non-black patients.
Pharmacodynamic effects: Antihypertensive properties: Administration of ramipril causes a marked reduction in peripheral arterial resistance. Generally, there are no major changes in renal plasma flow and glomerular filtration rate. Administration of ramipril to patients with hypertension leads to a reduction in supine and standing blood pressure without a compensatory rise in heart rate. In most patients the onset of the antihypertensive effect of a single dose becomes apparent 1 to 2 hours after oral administration. The peak effect of a single dose is usually reached 3 to 6 hours after oral administration. The antihypertensive effect of a single dose usually lasts for 24 hours. The maximum antihypertensive effect of continued treatment with ramipril is generally apparent after 3 to 4 weeks. It has been shown that the antihypertensive effect is sustained under long term therapy lasting 2 years. Abrupt discontinuation of ramipril does not produce a rapid and excessive rebound increase in blood pressure.
Heart failure: In addition to conventional therapy with diuretics and optional cardiac glycosides, ramipril has been shown to be effective in patients with functional classes II-IV of the New-York Heart Association. The drug had beneficial effects on cardiac haemodynamics (decreased left and right ventricular filling pressures, reduced total peripheral vascular resistance, increased cardiac output and improved cardiac index). It also reduced neuroendocrine activation.
Pharmacokinetics: Absorption: Following oral administration, ramipril is rapidly absorbed from the gastrointestinal tract; peak plasma concentrations of ramipril are reached within 1 hour. Based on urinary recovery, the extent of absorption is at least 56% and is not significantly influenced by the presence of food in the gastrointestinal tract. The bioavailability of the active metabolite, ramiprilat, after oral administration of 2.5 mg and 5 mg ramipril is 45%. Peak plasma concentrations of ramiprilat, the sole active metabolite of ramipril are reached 2-4 hours after ramipril intake. Steady state plasma concentrations of ramiprilat after once daily dosing with the usual doses of ramipril are reached by about the 4th day of treatment.
Distribution: The serum protein binding of ramipril is about 73% and that of ramiprilat about 56%.
Metabolism: Ramipril is almost completely metabolised to ramiprilat and to the diketopiperazine ester, the diketopiperazine acid and the glucuronides of ramipril and ramiprilat.
Elimination: Excretion of the metabolites is primarily renal. Plasma concentrations of ramiprilat decline in a polyphasic manner. Because of its potent, saturable binding to ACE and slow dissociation from the enzyme, ramiprilat shows a prolonged terminal elimination phase at very low plasma concentrations.
After multiple once-daily doses of ramipril, the effective half-life of ramiprilat concentrations was 13-17 hours for the 5-10 mg doses and longer for the lower 1.25-2.5 mg doses. This difference is related to the saturable capacity of the enzyme to bind ramiprilat. A single oral dose of ramipril produced an undetectable level of ramipril and its metabolite in breast milk. However, the effect of multiple doses is not known.
Patients with Renal Impairment: Renal excretion of ramiprilat is reduced in patients with impaired renal function and renal ramiprilat clearance is proportionally related to creatinine clearance. This result in elevated plasma concentrations of ramiprilat, which decrease more slowly than in subjects with normal renal function.
Patients with Hepatic Impairment: In patients with impaired liver function, the metabolism of ramipril to ramiprilat was delayed, due to diminished activity of hepatic esterases and plasma ramipril levels in these patients were increased. Peak concentrations of ramiprilat in these patients, however, are not different from those with normal hepatic function.