Adult: Particularly in cases associated with pre-eclampsia and toxaemia of pregnancy: Initially, 5-10 mg via slow IV inj, may repeat after 20-30 minutes if necessary; or 200-300 mcg/min via continuous IV infusion, adjust individually according to response to usual maintenance dose of 50-150 mcg/min. Alternatively, give 20-40 mg via IV push or IM inj then repeat if necessary. Treatment and dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).
Oral Congestive heart failure
Adult: In combination with nitrates for moderate to severe chronic cases: Initially, 25 mg 3-4 times daily, may increase if needed. Usual maintenance: 50-75 mg 4 times daily. Dose is individualised based on patient's clinical response. Treatment recommendations may vary among individual products and between countries (refer to specific product guidelines).
Oral Hypertension
Adult: Alone or in combination with other antihypertensives (e.g. β-blockers, diuretics) for moderate to severe cases: Initially, 40-50 mg daily in divided doses, increase gradually if needed. Max: 200 mg daily. Dose is individualised based on patient's clinical response.
Special Patient Group
Pharmacogenomics:
Hydralazine undergoes metabolism via acetylation, ring oxidation and conjugation with endogenous compounds including pyruvic acid. Acetylation occurs mainly during the first-pass metabolism which explains the dependence of the absolute bioavailability on the N-acetyltransferase 2 (NAT2) phenotype. Individuals who are fast acetylators may have decreased exposure to hydralazine, whereas individuals who are slow acetylators may have increased exposure to hydralazine. Therefore, it is recommended to give lower doses to slow acetylators.
Renal Impairment
Dose reduction may be required.
Hepatic Impairment
Dose reduction may be required.
Administration
Should be taken with food.
Reconstitution
IV inj: Dissolve contents in 1 mL water for inj, then further dilute with 10 mL NaCl 0.9% inj. IV infusion: Add reconstituted IV inj to 500 mL NaCl 0.9% inj, sorbitol 5% solution, or Ringer's solution. Instruction for reconstitution may vary among individual products and between countries (refer to specific product guidelines).
Incompatibility
Solution for inj or infusion: Incompatible with dextrose infusion solutions.
Contraindications
Idiopathic SLE and related diseases, severe tachycardia, heart failure with high cardiac output (e.g. thyrotoxicosis), myocardial insufficiency due to mechanical obstruction (e.g. aortic or mitral stenosis, constrictive pericarditis), isolated right ventricular failure due to pulmonary hypertension, dissecting aortic aneurysm, CAD, mitral valvular rheumatic heart disease, porphyria.
Special Precautions
Patient with cerebrovascular disease, suspected CAD, mitral valvular disease, other autoimmune disease, blood dyscrasias, pronounced arteriosclerosis, severe myocardial disease. Women and slow acetylators. Not recommended as initial treatment of hypertension. Patient undergoing surgery. Avoid abrupt withdrawal. Renal and hepatic impairment. Pregnancy and lactation.
This drug may cause dizziness or hypotension, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor blood pressure and heart rate; CBC and antinuclear antibody (ANA) titre prior to therapy and periodically thereafter; urine analysis at intervals of approx 6 months (long-term treatment).
Overdosage
Symptoms: Hypotension, tachycardia, headache, generalised skin flushing, myocardial ischaemia, cardiac arrhythmias, shock, coma. Management: Symptomatic and supportive treatment. Perform gastric lavage or administer activated charcoal (oral). May give IV fluids or plasma expanders as indicated. If hypotension occurs, raise the blood pressure without increasing the tachycardia.
Drug Interactions
Enhanced hypotensive effect with other antihypertensive agents (e.g. vasodilators, Ca antagonists, ACE inhibitors, diuretics), TCAs (e.g. imipramine, clomipramine), levodopa, anaesthetics, nitrates, major tranquillisers, CNS depressants, MAOIs, diazoxide. May increase bioavailability of β-blockers (e.g. propranolol). Antagonised hypotensive effect with estrogens, NSAIDs (e.g. ibuprofen, diclofenac), or corticosteroids (e.g. hydrocortisone, prednisolone).
Food Interaction
Increased bioavailability with food. Enhanced hypotensive effect with alcohol.
Action
Description: Hydralazine is a direct-acting vasodilator which acts predominantly on the arterioles. The exact mechanism of action is unknown, but it is thought to exert its vasodilating effect through direct relaxation of vascular smooth muscle by inhibition of Ca release from the sarcoplasmic reticulum and inhibition of myosin phosphorylation in the arterial smooth muscle cells. Onset: 10-80 minutes (IV). Duration: Up to 12 hours (IV/IM). Pharmacokinetics: Absorption: Rapidly absorbed from the gastrointestinal tract. Increased bioavailability with food. Bioavailability: Approx 22-69%; increased in slow acetylators and decreased in rapid acetylators. Time to peak plasma concentration: 1-2 hours (oral). Distribution: Widely distributed in the body, particularly into arterial walls. Crosses the placenta and enters breast milk (small amounts). Plasma protein binding: 87%. Metabolism: Undergoes extensive first-pass metabolism in the liver via acetylation. Excretion: Via urine (as metabolites). Elimination half-life: 3-7 hours.
Chemical Structure
Hydralazine Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 3637, Hydralazine. https://pubchem.ncbi.nlm.nih.gov/compound/Hydralazine. Accessed Nov. 25, 2022.
Storage
Tab: Store between 15-30°C. Solution for inj or infusion: Store below 25°C. Protect from light. Storage recommendations may vary among individual products and between countries (refer to specific product guidelines).
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