Hydralazine Oral (PO) Dosing for PRN Hypertension Management
For PRN (as-needed) management of hypertension, hydralazine should be dosed at 10-25 mg orally every 4-6 hours, with a maximum daily dose of 200 mg for most patients. 1
Initial Dosing and Titration
- Start with 10 mg four times daily for the first 2-4 days, then increase to 25 mg four times daily for the remainder of the first week 1
- For subsequent weeks, dosage may be increased to 50 mg four times daily if needed 1
- Maintenance dosage should be adjusted to the lowest effective level 1
- In resistant hypertension cases, up to 300 mg daily may be required, but this higher dose increases risk of adverse effects 1
PRN Administration Guidelines
- Hydralazine is frequently prescribed as a PRN medication for acute blood pressure management in hospitalized patients 2
- PRN oral hydralazine should generally be reserved for systolic blood pressure ≥180 mmHg or diastolic blood pressure ≥110 mmHg (threshold for acute severe hypertension) 2
- Caution is advised as studies show 36% of PRN administrations occur at lower thresholds than recommended 2
Pharmacokinetics and Dosing Frequency
- Hydralazine has a relatively short plasma half-life but demonstrates prolonged antihypertensive effects 3
- Despite its short half-life, hydralazine shows a multiexponential pattern of elimination with a prolonged terminal phase 3
- For scheduled (non-PRN) dosing, twice-daily administration is generally sufficient for blood pressure control 4
- Once-daily conventional hydralazine is not recommended as its hypotensive effect wanes at 24 hours 4
Special Considerations
- Response to hydralazine varies based on acetylator status - slow acetylators experience greater hypotensive effects and more side effects 5
- When using hydralazine PRN, monitor for excessive blood pressure reduction, especially when combined with other antihypertensive medications 1
- Profound hypotensive episodes may occur when hydralazine is used concomitantly with other potent antihypertensives 1
- Administration with food results in higher plasma levels 1
Combination Therapy
- Lower dosage of hydralazine combined with a thiazide diuretic and/or beta blocker may be more effective with fewer side effects than high-dose hydralazine monotherapy 1
- Combination with beta-blockers (such as propranolol) can mitigate reflex tachycardia and provide more stable blood pressure control 6
- Hydralazine is classified as a direct vasodilator and is associated with sodium/water retention and reflex tachycardia; consider using with a diuretic 7
Cautions and Monitoring
- Monitor for common side effects including headache, tachycardia, fluid retention, and lupus-like syndrome (particularly at higher doses) 7
- Hydralazine can cause drug-induced lupus-like syndrome, especially in slow acetylators on higher doses 7
- Avoid abrupt discontinuation after prolonged use 7
- Regularly assess blood pressure response and adjust dosing accordingly 1
Pediatric Dosing
- Safety and effectiveness in pediatric patients have not been established in controlled clinical trials 1
- If needed in pediatric patients, the usual recommended oral starting dosage is 0.75 mg/kg daily in four divided doses, with gradual increase over 3-4 weeks to a maximum of 7.5 mg/kg or 200 mg daily 1