Hydralazine

Hydralazine: Uses, Dosage and Side Effects

Overview

• Hydralazine primarily acts on arteriolar smooth muscle, inducing vasodilation; it can reduce systemic vascular resistance to around 50% of the baseline value.
• Hydralazine reduces afterload while increasing heart rate, stroke volume, and cardiac output.

Uses of Hydralazine

• Afterload reducer as adjunctive therapy for canine congestive heart failure due to severe or refractory mitral insufficiency.
• .It may be used to treat systemic hypertension (though not as a first-line medication).

Dose of Hydralazine in Dogs and Cats

Dogs:

• 0.5–3 mg/kg p.o. q8–12h. Start at low dose (0.5–1 mg/kg q12h).
• Monitor blood pressure regularly and increase to 2 mg/kg or even 3 mg/kg q12h if necessary.

Cats:

• 2.5–10 mg/cat p.o. q12h.
• Start at low dose and titrate upwards cautiously as above if necessary.

Side Effects of Hydralazine in Dogs and Cats

• Reflex tachycardia.
• severe hypotension
• Anorexia and vomiting (commonly seen in cats).

Contraindications of Hydralazine in Dogs and Cats

• Hypovolaemia.
• Hypotension.
• Renal impairment.
• Cerebral bleeding

Some Notes:

• Hospitalization with frequent monitoring of blood pressure is advised during its use.
• As hydralazine may cause sodium and water retention, concomitant use of diuretic therapy is often necessary.
• Give with food if possible.
• ACE inhibitors (e.g., enalapril, benazepril), anaesthetics, beta-blockers (e.g., propranolol), calcium-channel blockers (e.g., diltiazem, verapamil), corticosteroids, diuretics, and NSAIDs can increase hydralazine’s hypotensive effects.
• Tachycardia can be caused by sympathomimetics such as phenylpropanolamine.
• Adrenaline’s pressor reaction may be diminished.