Core pharmacology

Class Group

Direct Vasodilator

Legacy Cicm Level

Level 3

Introduction

direct vasodilator whose mechanism of action is poorly
understood.

Indications Uses

sometimes used intravenously in the treatment of hypertensive
emergencies, and in the management of severe hypertension associated with
pregnancy

Presentation

PO 25-50mg IV 20mg powder for reconstitution and inj. Should not be reconstituted with 5% dex as this degrades the drug quickly.

Mechanism of action

Poorly understood.
It is possible that hydralazine activates guanylyl cyclase,
increasing cAMP and decreasing Ca, causing vasodilation. NO may play a role. IP3 may be a second messenger involved.

Onset Peak Duration

PO 25-100mg BD PO, IV 5-10mg over 20mins, titrated

Physiological effects

Arteriole vasodilation with
preserved venous tone, and minimal eff¬ect on epicardial vasculature. Reflex increase in HR, CO and activation of the RAAS → peripheral oedema.

Adverse Effects Toxicity

activation of the RAAS and the increase in HR and Co make this drug less
efficacious. Because of this reason it is often given in combination with a thiazide
or betablocker. Long term use is associated with lupus like syndrome

Absorption

PO,IV
BA 30% well absorbed but high first pass metabolism

Protein binding

87%

Volume of distribution

4.2 L/kg

Metabolism

N-acetylated in the bowel and/or the liver

Excretion

Mostly excreted in urine, primarily as metabolites

Half-life

greatly dependent on genetically acetylation
rates, ranging from 1-8 hours

Route And Dose

PO 25-100mg BD PO, IV 5-10mg over 20mins, titrated