HYDRALAZINE INTRODUCTION
Direct acting arteriolar vasodilator Hydralazine is available in the market under the trade name apresoline.vasoldilation attained by hydralazine is depended upon the presence of an intact blood vessel endothelium.Thats what leads to the naming "direct".
metabolism,absorbtion and excretion of hydralazine
in oral administration,hydralazine is well absorbed,approximately upto 65-90 %.the peak pharmacological action is attained in some 6 hours of apresoline's administration.
hydralazine undergo metabolism through some common metabolic pathways like ring hydroxylation,glucoronide conjugation and N-acetylation.
morever the first pass effect is also exhibited by this potent vasodilator in intestinal mucosa through N-acetylation.
its primary excretory route is in urine however about 10% of the drug is found unchanged in the faeces.
its worthwhile to note that the half life of the drug is less than their pharmacological effect.
that's because some drugs remain accumulated in arterial endothelium even after the serum level is low.
MECHANISM OF ACTION
The mechanism of action of hydralazine is called EDRF(endothelial derived relaxing factor) mechanism.the pharmacodynamics of hydralizine is summed up in the sketch below.
as shown in diagram above hydralazine acts of vessels endothelium to release EDRF which is chemically nitric oxide's endogenous source.the EDRF released excites guanyl cyclase which furthur leads to the oxidation of GTP to cyclicGMP.the increased serum levels of cyclic-gmp furthur sparks up the dephosphorylation of MLCPO4 (myosin light chain phosphate) to MLC.
the final effect of hydralazine is vasodilation hence decreasing peripheral vascular resistance and so as the blood pressure is decreased.
CLINICAL USES of hydralazine
hydralazine is used basically in moderate hypertensive crisis and in ambulatory patients.generally used in combination with diuretics or beta blockers for better antehypertensive response and to avoid reflex renel hyperperfusion and reflex sympathetic activity due to excessive hypotension.
SIDE EFFECTS OF APRESOLINE
hyrdalazine like all other drugs of same genre is accompanied by some common side effects which are not serious at all.some of them are..
- throbbing headache (this maybe due to the dilation of meningeal artery)
- anorexia
- sweating (possibly due to reflex symapthetic stimulation).
- reflex barometric mechanism.
