Angiotensin Converting Enzyme (ACE) inhibitors are getting more and more popular because of their effective hypotensive action as well as relative freedom form adverse side-effects. Captopril (e.g., Aceten’), Enlapril (e.g., ‘Envas’) Lisinopril (e.g..
Lipril ) Ramipril (e.g.. Ramace’) are the available ACE-inhibitors commonly used. Enlapril is now generally preferred because of the lower dosage requirement and convenient dosage schedule of once or twice instead of twice or thrice dosage required for Captopril and the price is also within the means of ordinary people. However, according to the various therapeutic assessment reports, the preferred ACE-inhibitors of today are Ramipril and Lisinopril.
Mode of action : The enzyme Renin’ is liberated by the juxtaglomerular apparatus of the kidney in response to the low circulatory blood volume or low level of serum Sodium with tendency to lowering the blood pressure. Renin acts on the plasma protein alpha-two variety of globulin producing ‘Angiotensin I’. Subsequently, an enzyme called ‘Dipeptidil carboxypeptidase’ present in plasma converts the inert ‘Angiotensin I’ into ‘Angiotensin II’. The latter is a very potent vaso-constrictor acting directly as well as through the potentiating effect on the peripheral sympathetic action.
ACE-inhibitors act by way of competitive inhibition of the enzyme ‘Dipeptidil carboxypeptidase’ and thus prevents the conversion of Angiotensin I to Angiotensin II. The pharmacological effects are—reduction of peripheral resistance and aldosterone mediated retention of sodium. The net result is lowering of blood pressure.
The reduction of peripheral resistance occurs partly by direct pharmacological effect and partly by reducing the aldosterone secretion (responsible for sodium and water retention). Renal vascular resistance also falls with increase in renal blood flow. The results are fall of both systolic and diastolic pressure and increase in cardiac output with reduction of heart rate (hence useful in cases of hypertension associated with congestive cardiac failure). ACE-inhibitors by virtue of own specific action as well as by anti-aldosterone action help in improving kidney function and prevention of sodium retention with tendency to oedema.
Indications : ACE-inhibitors are now considered suitable in moderate or severe grades of hypertension and of value in cases of hypertension associated with congestive cardiac failure. Initial treatment should be started with minimum dose. In appropriate cases, combination with some other suitable hypotensive drug e.g.. Beta-blockers, Thiazide diuretics may be found therapeutically rewarding.
Side-effects : Urticaria, irritating cough, proteinuria, agranulocytosis, hypotension etc. are possible.
Precautions : These drugs should be avoided in patients with renal impairment or renal failure. (The durg is excreted through the kidneys).
Comments : These drugs do not interfere with the serum lipids, blood glucose or uric acid.
Only the Physicians well-aware of this group of drugs should prescribe such drugs particularly in combination with other anti-hypertensive drug (in appropriate cases).