Hydralazine

This is a drug used in the treatment of cardiac failure and hypertension.

Mode of action:

• direct relaxing effect on vascular smooth muscle resulting in peripheral arteriolar dilatation

There is a fall in blood pressure and consequent reflex tachycardia as a result of the peripheral arteriolar dilatation caused by hydralazine. Thus, in the treatment of hypertension, a beta-adrenoreceptor blocker is also is used. There is little reflex tachycardia when this drug is used to treat cardiac failure because there is no significant change in blood pressure.

Pharmacokinetics:

• t 1/2 - approximately 4 hours
• metabolised - mainly by acetylation

Side effects:

• palpitations, nausea, vomiting, tachycardia, postural hypotension
• with dosages over 200 mg then there may be the development of a lupus-like syndrome or an arthropathy resembling rheumatoid arthritis. The lupus-like syndrome that may occur with the use of hydralazine is more commonly seen in patients with HLA DR4.