Overview
Hydralazine is a direct-acting vasodilator used primarily for the management of hypertension, including hypertensive emergencies and pregnancy-induced hypertension. It works by relaxing arterial smooth muscle, reducing peripheral vascular resistance without significantly affecting venous capacitance.
Mechanism of Action
Hydralazine directly relaxes arteriolar smooth muscle through multiple mechanisms, including activation of guanylate cyclase, increased cyclic GMP, and interference with calcium ion movement. This results in decreased peripheral vascular resistance and arterial blood pressure. It has minimal effect on venous capacitance vessels.
Indications
- Hypertension
- Hypertensive emergencies
- Pregnancy-induced hypertension (preeclampsia, eclampsia)
- Heart failure (as part of combination therapy with nitrates)
Dosage
Initial dose: 10 mg orally 4 times daily for 2-4 days, then increase to 25 mg 4 times daily for the remainder of first week. Maintenance: 50 mg orally 4 times daily. Maximum dose: 300 mg daily. For hypertensive emergencies: 10-20 mg IV/IM, repeated as needed. Adjust dose based on response and tolerance.
Contraindications
- Hypersensitivity to hydralazine or any component
- Coronary artery disease
- Mitral valvular rheumatic heart disease
- Systemic lupus erythematosus
- Severe renal impairment
Side Effects
- Headache
- Palpitations
- Tachycardia
- Nausea
- Vomiting
- Diarrhea
- Anorexia
- Dizziness
- Weakness
- Peripheral neuritis
- Drug-induced lupus-like syndrome
- Rash
- Fever
- Arthralgia
- Myalgia
- Nasal congestion
- Lacrimation
- Edema
Interactions
- MAO inhibitors: May potentiate hypotensive effect
- Beta-blockers: May increase heart rate
- Diuretics: Enhanced hypotensive effect
- NSAIDs: May reduce antihypertensive effect
- Sympathomimetics: May reduce antihypertensive effect
- Alcohol: Enhanced hypotensive effect