Hydralazine
Apresolin · BiDil
Direct-acting arteriolar vasodilator with no effect on the venous circulation. The rapid afterload reduction triggers reflex sympathetic activation, making the drug unsuitable as first-line treatment in hypertensive crisis — but useful in pre-eclampsia and as afterload relief in combination with a nitrate and beta-blocker.
Reflex tachycardia can trigger or worsen angina pectoris and myocardial ischaemia. Combine with a beta-blocker in patients with coronary artery disease. Long-term use at high doses causes drug-induced lupus.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Hypertensive crisis, iv bolus | 10–40 mg iv every 4–6 hours | onset 10–30 minutes |
| Intramuscular | 10–20 mg im every 4–6 hours | when intravenous access is unavailable |
| Afterload reduction, infusion | Start 1 mg per hour, increase by 0,5 mg per hour every 20 minutes, maximum 5 mg per hour | for ventricular offloading |
| Antihypertensive infusion | Start 5 mg per hour, increase by 2,5 mg per hour every 20 minutes, maximum 25 mg per hour | titrated to target blood pressure |
eGFR below 30 ml/min: extend the dosing interval. Metabolites accumulate.
Reduce dose — extensive first-pass metabolism in the liver.
0,1–0,2 mg/kg iv every 4–6 hours, maximum dose 20 mg per dose.
Not the first choice in hypertensive crisis — onset is unpredictable, duration is long, and reflex tachycardia is dangerous in ischaemia and aortic dissection. Never give in suspected aortic dissection without prior beta-blockade.
Pharmacokinetics
- ONSET (iv)
- 10–30 minutes
- PEAK EFFECT
- 20–40 minutes
- DURATION
- below 4 hours
- t½
- 3–7 hours
- BIOAVAIL.
- 26–50 % orally
- METABOLISM
- N-acetylation (fast/slow acetylator status)
- PROTEIN BINDING
- 87 %
- EXCRETION
- Renal (metabolites)