From the Guidelines
Appropriate Dosing for Hydralazine
The appropriate dosing for Hydralazine is an initial dose of 10 mg via slow IV infusion, with a maximum initial dose of 20 mg, and can be repeated every 4-6 hours as needed 1.
Key Considerations
- Blood Pressure Reduction: BP begins to decrease within 10-30 minutes, and the fall lasts 2-4 hours.
- Unpredictability of Response: The unpredictability of response and prolonged duration of action do not make hydralazine a desirable first-line agent for acute treatment in most patients.
- Contraindications and Precautions: While the provided evidence does not explicitly list contraindications for hydralazine, it is crucial to consider the patient's overall clinical picture, including potential interactions with other medications and underlying health conditions.
Evidence Summary
The dosing information for hydralazine is consistently reported across the guidelines from the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines 1, emphasizing the importance of careful dose adjustment and monitoring in the management of hypertensive emergencies.
Clinical Application
In clinical practice, hydralazine should be used judiciously, taking into account its pharmacological properties and the patient's specific condition, to minimize potential adverse effects while effectively managing blood pressure. Given the lack of high-quality RCT evidence comparing different antihypertensive drug classes in hypertensive emergencies 1, the choice of hydralazine should be based on individual patient factors and clinical judgment.
From the FDA Drug Label
The usual recommended oral starting dosage is 0.75 mg/kg of body weight daily in four divided doses. Dosage may be increased gradually over the next 3 to 4 weeks to a maximum of 7. 5 mg/kg or 200 mg daily. The appropriate dosing for Hydralazine is:
- Starting dosage: 0.75 mg/kg of body weight daily in four divided doses
- Maximum dosage: 7.5 mg/kg or 200 mg daily 2
From the Research
Dosing Regimens for Hydralazine
The appropriate dosing for Hydralazine can be considered based on the following evidence:
- A study published in 1983 3 compared the efficacy and tolerability of slow-release hydralazine administered once daily with conventional hydralazine given two to four times a day, and found that blood pressure control achieved with multiple doses of conventional hydralazine was maintained with slow-release hydralazine.
- Another study from 1982 4 assessed the effects of hydralazine formulation and dose interval in 20 patients with hypertension, and found that once-daily treatment with conventional hydralazine was unsatisfactory, while twice-daily conventional hydralazine and once-daily slow-release hydralazine gave satisfactory control for 24 hours.
- A study from 1983 5 compared the hypotensive effect of prazosin and hydralazine, and found that 1 mg of prazosin was equivalent to 12.5 mg of hydralazine, and that increasing the dose of prazosin or hydralazine did not consistently reduce blood pressure.
- A randomized double-blind comparison of conventional and slow-release formulations of hydralazine, as well as b.i.d. and q.i.d. dosage regimens, found no statistically significant differences in blood pressure and pulse rate between the three treatment regimens 6.
- An earlier study from 1975 7 found that a daily dose of 300 mg of hydralazine was as effective and free of side effects given in 2 as in 4 divided doses.
Dosage Intervals and Formulations
The evidence suggests that:
- Twice-daily conventional hydralazine and once-daily slow-release hydralazine can provide satisfactory control for 24 hours 4.
- Slow-release hydralazine can be given once daily without increased risk of side effects 3.
- Conventional hydralazine can be replaced by the same preparation or slow-release formulation in a b.i.d. dosage 6.
- The acetylator phenotype may have some influence on the results, but it is not significant 6.
Equivalent Doses
- 1 mg of prazosin is equivalent to 12.5 mg of hydralazine 5.