Hydralazine
Mechanism :
Hydralazine is an antihypertensive. Hydralazine lowers blood pressure by exerting a peripheral vasodilating effect through a direct relaxation of vascular smooth muscle. Hydralazine, by altering cellular calcium metabolism, interferes with the calcium movements within the vascular smooth muscle that are responsible for initiating or maintaining the contractile state.
Indication :
- Chronic hypertension
- Hypertensive crisis
- Severe Essential Hypertension
Contraindications :
Hypersensitivity to hydralazine; coronary artery disease; mitral valvular rheumatic heart disease are contraindications for its use.
Dosing :
Hypertensive Crisis:
3 months-12 months:
0.1-0.5 mg/kg/dose given intravenously 3-4 times a day; maximum dose is 2 mg/kg given intravenously 4 times a day. Doses must be titrated accordingly for blood pressure control.
>12 months:
0.1-0.2 mg/kg IV/IM every 4-6 hours. Can increase to 1.7-3.5 mg/kg/day in 4-6 divided doses. Max: 20 mg/dose or 200 mg/day.
Chronic Hypertension:
Start with 0.75-1 mg/kg/day given orally 2-4 times a day.
For <12 months:
5 mg/kg/day taken orally 2-4 times a day or 20 mg/dose or 200 mg/day as the maximum dose.
For >12 months:
7.5 mg/kg/day taken orally divided into 4 daily doses. Max: 200 mg/day.
Adverse Effect :
Common reactions: Fluid retention, headache, peripheral neuritis, tachycardia, palpitation.
Rare: Anemia, leukopenia, thrombocytopenia, neutropenia, SLE-like syndrome.
Serious Reactions: Hypersensitivity reaction, anaphylaxis, erythema multiforme.
Interaction :
MAO Inhibitors: Should be used with caution in patients receiving hydralazine.
Diazoxide: Profound hypotensive episodes may occur.
Beta-blockers (Metoprolol, Propranolol): Serum concentrations and pharmacologic effects may be increased.
NSAIDs: May decrease the hemodynamic effects of hydralazine; avoid use if possible or closely monitor cardiovascular status.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | Start at low dose and adjust in accordance with response |
| 10-20 | Start at low dose and adjust in accordance with response |
| <10 | Start at low dose and adjust in accordance with response |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Not dialysed. Dose as in GFR<10 mL/min |
| HD | Not dialysed. Dose as in GFR<10 mL/min |
| HDF/High flux | Not dialysed. Dose as in GFR<10 mL/min |
| CAV/VVHD | Not dialysed. Dose as in GFR=10– 20 mL/min |
Hepatic Dose :
No dosage adjustments are recommended. However, hydralazine undergoes extensive hepatic metabolism.