Hydralazine Dosing for Hypertension
For hypertension, hydralazine should be initiated at 10 mg four times daily for 2-4 days, then increased to 25 mg four times daily for the remainder of the first week, followed by 50 mg four times daily for maintenance, with a typical total daily dose of 100-200 mg divided into 2-3 administrations. 1, 2
Initial Dosing Protocol
- Start with 10 mg four times daily for the first 2-4 days to assess tolerance 1
- Increase to 25 mg four times daily for the balance of the first week 1
- Advance to 50 mg four times daily for the second and subsequent weeks 1
- Adjust to the lowest effective maintenance dose once blood pressure control is achieved 1
Standard Maintenance Dosing
- Total daily dose: 100-200 mg divided into 2-3 doses per day is the recommended range per ACC/AHA guidelines 2
- Twice-daily dosing is adequate for most patients when combined with a beta-blocker and diuretic, as there is no need to administer hydralazine more than twice daily 3
- Three times daily dosing may be necessary in rapid acetylators or those requiring higher doses 2
Resistant Hypertension
- Up to 300 mg daily may be required in a few resistant patients for significant antihypertensive effect 1
- Higher doses (≥150 mg daily) carry increased risk of drug-induced lupus-like syndrome, particularly in elderly white women on chronic therapy 4, 2
- Consider combination therapy at lower doses rather than maximizing hydralazine monotherapy to reduce toxicity risk 1
Critical Dosing Considerations
Mandatory Concurrent Therapy
- Always combine with a diuretic and beta-blocker to counteract sodium/water retention and reflex tachycardia 2, 5
- Hydralazine monotherapy is inappropriate due to compensatory mechanisms that limit efficacy 6, 5
Acetylator Status Impact
- Slow acetylators require lower doses: D50 of 0.87 mg/kg versus 1.68 mg/kg for fast acetylators 7
- Slow acetylators have larger hypotensive effects and longer duration of action 3, 7
Renal Impairment Adjustments
- Duration of action is significantly prolonged in patients with creatinine clearance <35 mL/min (14.3 hours vs 7.9 hours) 8
- Extend dosing intervals in renal dysfunction to avoid accumulation 8
- Consider hydralazine as alternative when ACE inhibitors/ARBs are contraindicated due to renal insufficiency, but use with caution 2
Heart Failure Dosing Context
- For heart failure with reduced ejection fraction: Hydralazine must be combined with isosorbide dinitrate (not used alone) 6
- Variable dosing required: In severe heart failure, doses of 100-200 mg may be needed, with some patients requiring 150-200 mg for hemodynamic response 8
- Individualized titration essential based on hemodynamic response in heart failure patients 8
Safety Parameters for Holding Doses
- Hold if systolic BP <100 mmHg or diastolic BP <60 mmHg due to hypotension risk and compromised coronary perfusion 6, 9
- Hold if heart rate >110 bpm as reflex tachycardia can precipitate anginal attacks and myocardial ischemia 6
- Hold if signs of drug-induced lupus develop: arthralgia, fever, chest pain, or unexplained malaise 6
Important Clinical Pitfalls
- Do not use for acute hypertensive emergencies due to unpredictable response and prolonged duration of action (2-4 hours) 6, 9
- Avoid in advanced aortic stenosis (absolute contraindication) due to unpredictable hemodynamic effects 6
- Monitor for lupus-like syndrome especially at doses ≥150 mg daily in elderly patients 4, 2
- Hydralazine preferentially lowers diastolic more than systolic pressure, which can compromise coronary perfusion in CAD patients 6