Hydralazine (Apresoline)

Hydralazine - lowers the BP by reducing arterial resistance through a direct relaxation of arteriolar smooth muscle. This effect is limited by reflex tachycardia and so it is best combined with a B-blocker. Metabolism occurs by hepatic acetylation, the rate of which is genetically determined. Fast acetylators show a reduced therapeutic effect until the enzyme system is saturated.

Uses
All grades of hypertension
Pre-eclampsia

Contraindications
Systemic lupus erythematosus
Dissecting aortic aneurysm
Right ventricular failure due to pulmonary hypertension (cor pulmonale)
Severe tachycardia and heart failure with a high cardiac output state, e.g.
thyrotoxicosis
Severe aortic outflow obstruction (aortic stenosis, mitral stenosis, constrictive
pericarditis)

Administration
• IV bolus: 10–20 mg over 3–5 min
Reconstitute the ampoule containing 20 mg powder with 1 ml WFI, further dilute with 10 ml sodium chloride 0.9% give over 3–5 min
Expect to see response after 20 min Repeat after 20–30 min as necessary

• IV infusion: 2–15 mg/h
Reconstitute three ampoules (60 mg) of hydralazine with 1 ml WFI each. Make up to 60 ml with 0.9% sodium chloride (1 mg/ml) Give at a rate between 2 and 15 mg/h depending on the BP and pulse Rapid acetylators may require higher doses

• PO: hypertension 25 mg twice daily (up to 50 mg twice daily) Heart failure 25 mg 6–8 hourly, increased every 2 days to 50–75mg
6 hourly.

How not to use hydralazine
Do not dilute in fluids containing glucose (causes breakdown of
hydralazine)
Adverse effects
Headache
Tachycardia
Hypotension
Myocardial ischaemia
Sodium and fluid retention, producing oedema and reduced urinary
volume (prevented by concomitant use of a diuretic)
Lupus erythematosus (commoner if slow acetylator status,women and
if treatment >6 months at doses >100 mg daily)

Cautions
Cerebrovascular disease
Cardiac disease (angina, immediately post-MI)
Use with other antihypertensives and nitrate drugs may produce additive
hypotensive effects

Organ failure
Hepatic: prolonged effect
Renal: increased hypotensive effect (start with small dose)