Antihypertensive drugs
Antihypertensive drug therapy has been remarkably improved in the last 50 years. The aim of antihypertensive therapy is to prevent morbidity and mortality associated with persistently raised BP by lowering it to an acceptable level, with minimum inconvenience to the patient.
The cut-off manometric reading between normotensives and hypertensives is difficult to define. For practical purposes, Hypertension is graded as mild when diastolic BP is 90- 104 mm Hg, moderate when it is 105- 114 and severe when it is over 115 mm Hg. Isolated systolic hypertension is defined as systolic BP less than 160 mm Hg and diastolic BP more than 90 mm Hg. Epidemiological studies have confirmed that the higher the pressure (systolic or diastolic or both) greater is the risk of cardiovascular disease. Antihypertensive drug therapy by lowering the BP resets the barostat to function at the lower level of BP.
Nonpharmacological measures like diet, exercise can be tried concurrently with drugs. Nearly 50% - 75% hypertensives can be treated successfully with monodrug therapy. A simple regimen with once or twice daily drug dosing is most likely to be compiled with.
Classification:
The drugs are generally classified into:
Ace inhibitors: (Angiotensin converting enzyme) inhibitor
Examples are Captopril, Enalapril, Ramipril. These are considered to be most potential antihypertensives in patients with diabetes, nephropathy, angina, hypertrophy etc. Most patients require lower doses which are well tolerated ( enalapril 2.5-10mg/day).
Caution required in: patients with high dose diuretic therapy, preexisting dry cough and high salt intake.
Angiotensin antagonist: Losartin
A dose of 50 mg/ day of Losartin is an effective antihypertensive. Addition of 12.5 mg/ day of hydrochlorothiazide further reduces the BP. Losartin is free of side effects.
Calcium channel blockers: Verapamil, Diltiazem, Nifedipine, felodipine
They lower Bp by decreasing peripheral resistance without lowering cardiac output despite vasodilation, fluid retention is insignificant. Their antihypertensive action is quick. Most of the agents can be administered once or twice a day.
Suited for: Asthma, pregnant hypertensive, COPD patients
Diuretics: Hydrochlorothiazide, chlorthalidone
These are standard antihypertensive drugs over the past 3 decades. They do not lower Bp in normotensives. Furosemide, a high ceiling diuretic is also used but the fall in Bp is entirely dependent on reduction in plasma volume. The report of US committee on detection, evaluation and treatment of hypertension has recommended low doses(12.5- 25 mg) of diuretics alone or with added potassium sparring diuretics ( spironolactone, amiloride) as a first line treatment of essential hypertension.
Suited for: elderly patients, obese patients, isolated systolic hypertension
β- Adrenergic blockers: propranolol, metoprolol, atenolol
They are mild antihypertensives and are used mostly to moderate cases. They will be useful when combined with other drugs. Their hypotensive response develops over 1-3 weeks and is well sustained.
Suited for: angina patients, tense young patients non- obese, high rennin hypertensive
α- Adrenergic blockers: prazosin, terazosin
These are selective competitive anatagonist of the classical a1 receptors: dilates both resistance and capacitance vessels. Fainting and postural hypotension may occur initially so these are generally started at low doses and gradually increased.
Vasodilators: hydralazine, minoxidil, pinacidil, sodium nitroprusside
Hydralazine has a vascular smooth muscle relaxant action. It causes greater action in reducing diastolic rather than systolic BP. Sodium nitroprusside is rapidly acting and has brief duration of action (2-5 min). Minoxidil used alongside with loop diuretics and β blockers is effective foe severe hypertensives. Nitroprusside is highly useful in hypertensive emergencies due to its fast action.
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