Antihypertensive Drugs

Hypertension

WHO defines hypertension as:

“Level of systolic blood pressure more than 140 mmHg and diastolic blood pressure more than 90 mmHg, done by repeated measurements over a period of several weeks”.

Hypertension is a common disorder especially after middle age. It is an important risk factor for cardiovascular diseases (mortality and morbidity).

BP Scheme for Adults (in mm Hg)

Normal:

systolic BP <120 and diastolic BP <80

Pre hypertension:

SBP 120-139 or DBP 80-89

Stage 1 hypertension:

SBP 140-159 or DBP 90-99

Stage 2 hypertension:

SBP> 160 or DBP> 100

Predisposing factors

Diabetes mellitus
Renal diseases
Hyperlipidemias
Cardiovascular diseases
Smoking

Types

1. Primary (Essential)

Most common, where non cause is known.

2. Secondary

Secondary to other diseases present in patient e.g. kidney diseases, heart diseases, pheochromocytoma.

BP = CO x PVR

Cardiac output and total peripheral resistance are controlled by moment to moment control.

There are four sites at which blood pressure is regulated:

Arterioles
Venules
Heart
Kidney

In addition, there is baroreceptor reflex system and control of blood pressure through rennin-angiotensin system.

Most of the drugs controlling blood pressure act at one of these sites.

Some drugs act at arterioles causing dilatation, decreasing the after load.
Drugs acting on venules cause decrease in preload.
Drugs acting on heart decrease heart rate and cardiac output.
Drugs acting on kidney decrease peripheral vascular resistance, decreasing water retention and blood volume.

Most of these drugs control blood pressure completely

Some drugs do cause postural hypotension e.g. alpha blockers and adrenergic neuron blockers.

Choice of drugs involves those interfering minimally with hemodynamic mechanism.

On prolonged use, increase in blood pressure due to reflex increase in sympathetic activity occurs. This is because of increase in noradrenaline and increase in renin. Thus antihypertensives are used in combination with diuretics and ACE inhibitors.