How to Write a Prescription for Hydralazine 10 mg Four Times Daily
For chronic hypertension management, write: "Hydralazine 10 mg by mouth four times daily" as the FDA-approved starting dose, with plans to titrate upward every 2-4 days based on blood pressure response. 1
Standard Prescription Format
Write the prescription as follows:
- Drug name: Hydralazine (or hydralazine hydrochloride)
- Dose: 10 mg
- Route: PO (by mouth)
- Frequency: Four times daily (QID)
- Quantity: #120 tablets (30-day supply)
- Refills: As appropriate for your practice
The FDA label explicitly states to "start with 10 mg four times daily for the first 2 to 4 days" for hypertension management. 1
Critical Titration Schedule
After the initial 2-4 days at 10 mg four times daily, you must plan to increase the dose to 25 mg four times daily for the remainder of the first week, then to 50 mg four times daily for the second and subsequent weeks. 1 The 10 mg four times daily dose is intentionally subtherapeutic and serves only as an initial starting point to assess tolerance. 1
The target maintenance dose is typically 50 mg four times daily (200 mg/day total), though some patients may require up to 300 mg daily in divided doses for resistant hypertension. 1
Mandatory Concurrent Medications
You must prescribe a beta-blocker concurrently if the patient is not already taking one, as hydralazine causes reflex tachycardia that can be severe and counterproductive. 2, 3, 4 Additionally, ensure adequate diuretic therapy is in place to address sodium and water retention caused by hydralazine. 3, 4
The FDA label specifically recommends combining hydralazine with a thiazide and/or beta-blocker when higher doses are needed. 1
Important Clinical Context
Hydralazine four times daily dosing is appropriate only for chronic hypertension management, not for heart failure. 4, 5 For heart failure with reduced ejection fraction, the dosing is different: 37.5 mg three times daily (combined with isosorbide dinitrate), titrating to 75 mg three times daily. 2, 4
Four times daily dosing is necessary because hydralazine has a short duration of action (2-4 hours for peak effects), and once-daily or twice-daily conventional formulations provide inadequate 24-hour control, especially in rapid acetylators. 4, 6 Research demonstrates that once-daily conventional hydralazine results in significant waning of hypotensive effect at 24 hours. 6
Critical Safety Monitoring
Monitor blood pressure at 10-30 minutes, 1 hour, and 2-4 hours after the first dose to assess response and detect excessive hypotension. 3, 4 The risk of drug-induced lupus-like syndrome increases significantly at cumulative daily doses exceeding 200 mg/day, so avoid exceeding this threshold without compelling indication. 3, 4, 1
Common Pitfall to Avoid
Do not use hydralazine as a first-line, second-line, or even third-line agent for hypertension. 3 It should be positioned as a fourth-line or fifth-line agent for resistant hypertension after maximizing ACE inhibitors/ARBs, calcium channel blockers, and diuretics. 3 The unpredictability of response and need for multiple daily doses make it less desirable than other antihypertensive options. 2