Mechanism of action:
It causes activation of α2 receptors in the vasomotor center of brain that causes a decrease in sympathetic outflow to the peripheral vascular bed.
Its intravascular injection causes a direct activation of peripheral α-adrenergic receptors resulting in a short time elevated systolic and diastolic pressure. After this, there is a reduction of cardiac output and cardiac rate resulting in the fall of blood pressure.
It causes a decrease in plasma renin activity.
It causes an elevated vagal discharge along with promoted baroreceptor reflex sensitivity.
It causes a reduction of renal vascular resistance but does not affect renal blood flow.
It causes sodium and water retention and that is why they are taken along with diuretics.
It is well absorbed orally and is excreted by the kidney.
It is used for hypertensive patients especially in patients of renal impairment.
Sedation, drowsiness, drying of the nasal mucosa, fluid retention, headache and sweating,
It may be given in the dose of 0.2-1.2 mg/day. Its transdermal patches can give dose for up to 1 week.