Hydralazine lowers blood pressure by relaxing the arteries directly. It comes as 10 mg, 25 mg and 50 mg tablets. It is an older medicine now used in specific situations — severe or resistant hypertension, high blood pressure in pregnancy, and heart failure — rather than as a first choice.
What is Hydralazine?
The South African Medicine Price Registry lists hydralazine as Schedule 3 tablets:
| Product | Form | Strength |
|---|---|---|
| Hyperphen | Tablet | Hydralazine 10 mg |
| Hydralazine HCl 25 Kiara (formerly Sandoz) | Tablet | Hydralazine 25 mg |
| Hydralazine HCl 50 Kiara, Hyperphen | Tablet | Hydralazine 50 mg |
Hydralazine is a direct-acting vasodilator. Most blood pressure medicines work indirectly — blocking a hormone, slowing the heart, removing fluid. Hydralazine acts on the smooth muscle in the artery walls themselves, relaxing it so the vessels widen and resistance falls.
It acts mainly on arteries rather than veins, which shapes both its usefulness and its problems.
The useful part: it reduces the resistance the heart pumps against, which is valuable in heart failure and in severe hypertension.
The problem: widening arteries without doing anything else triggers two reflex responses. The heart speeds up to compensate, and the kidneys retain salt and water. Left unchecked, these cancel much of the benefit and cause palpitations and swollen ankles.
That is why hydralazine is almost always combined — with a beta blocker to control the reflex tachycardia, and with a diuretic to control the fluid retention. Given alone it works poorly. This is not a limitation to work around; it is how the medicine is designed to be used.
What is Hydralazine commonly used for?
- Severe or resistant hypertension, where several other medicines have not achieved control.
- High blood pressure in pregnancy, including pre-eclampsia. This is one of its most important uses — hydralazine has a long record in pregnancy where many other antihypertensives are avoided, and the injectable form is a standard treatment for severe hypertension in pregnancy.
- Hypertensive emergencies, given intravenously in hospital.
- Heart failure, particularly combined with a nitrate. This combination reduces mortality in heart failure and is especially valuable in people who cannot take ACE inhibitors or ARBs because of kidney problems.
- Heart failure in patients of African ancestry, where trial evidence for the hydralazine-plus-nitrate combination is particularly strong.
It is not a first-line blood pressure medicine. Modern practice starts with ACE inhibitors, ARBs, calcium channel blockers and thiazide-like diuretics, all of which are once-daily and better tolerated. Hydralazine has to be taken two or three times a day and has more side effects.
Where it earns its place is exactly where those alternatives fall away — in pregnancy, in resistant hypertension, and in heart failure where kidney function rules out the usual options.
How Hydralazine fits into this medicine category
| Group | Examples | How it works |
|---|---|---|
| Direct vasodilators | Hydralazine, minoxidil | Relax artery walls directly |
| Calcium channel blockers | Amlodipine (Ciplavasc) | Relax arteries via calcium channels |
| ACE inhibitors | Enalapril, perindopril | Block a hormone that narrows vessels |
| ARBs | Losartan, telmisartan | Similar, without the cough |
| Diuretics | Hydrochlorothiazide (Ridaq), furosemide | Remove salt and fluid |
| Beta blockers | Carvedilol, bisoprolol | Slow the heart; used with hydralazine to control reflex tachycardia |
See the heart and blood pressure medicines hub.
What to check before using Hydralazine
Tell your doctor or pharmacist if you:
- Have coronary artery disease or angina. The reflex increase in heart rate raises the heart’s oxygen demand and can provoke chest pain.
- Have mitral valve disease, or certain other structural heart conditions.
- Have lupus, or a family history of it — see below.
- Have kidney or liver disease.
- Have had a stroke.
- Take other blood pressure medicines, nitrates, diuretics, or anti-inflammatories, which reduce its effect.
- Are pregnant or breastfeeding. Hydralazine is one of the antihypertensives with the best record in pregnancy — but the decision belongs to your clinician.
Practical points:
- Take it at the same times daily, usually two or three times a day. Consistency matters more with a short-acting medicine than a once-daily one.
- Take it with food for more consistent absorption.
- Get up slowly from sitting or lying.
- Do not stop suddenly, which can cause a rebound rise in blood pressure.
- Keep your appointments, including any blood tests.
- Do not stop because your reading is normal. That is the treatment working.
Possible cautions and when to ask a pharmacist or doctor
Common effects are headache, palpitations, a fast heartbeat, flushing, dizziness, nausea and fluid retention with swollen ankles. These follow directly from the way it works, and are usually managed by the accompanying beta blocker and diuretic rather than by stopping.
The distinctive risk of hydralazine is drug-induced lupus. With prolonged use — particularly at higher doses and in people who metabolise it slowly — it can trigger a condition resembling systemic lupus erythematosus. Watch for:
- Joint pain and swelling, especially in several joints
- Persistent fever
- A rash, particularly on sun-exposed skin
- Chest pain worse on breathing in
- Unexplained tiredness and weight loss
Report these promptly. Drug-induced lupus generally resolves once hydralazine is stopped, but it needs recognising rather than being attributed to something else.
Get emergency help for:
- Chest pain, especially with breathlessness or sweating.
- Fainting, or a very fast or irregular heartbeat.
- Severe breathlessness, particularly lying flat.
- Numbness or tingling in the hands and feet — hydralazine can cause a vitamin B6-related neuropathy, which is treatable.
- Swelling of the face, lips or tongue, difficulty breathing, or a widespread rash.
Contact your doctor if blood pressure stays high, if headaches or palpitations are persistent, if your ankles swell, if you notice joint pains or a rash, or if you are pregnant or planning pregnancy — hydralazine is often the medicine that stays when others must stop, and that is a discussion worth having early.
Related medicine guides
Frequently asked questions
What is hydralazine 25 mg used for? Lowering blood pressure — particularly severe or resistant hypertension, high blood pressure in pregnancy, and heart failure in combination with a nitrate.
How does it work? It relaxes the muscle in artery walls directly, so the vessels widen and blood pressure falls.
Why am I taking it with other tablets? Hydralazine alone triggers a reflex fast heartbeat and fluid retention. A beta blocker and a diuretic control those, which is why it is nearly always combined.
Why do I have to take it two or three times a day? It is short-acting, so evenly spaced doses are needed to keep blood pressure controlled.
Is it safe in pregnancy? It has one of the better records among blood pressure medicines in pregnancy and is used for pre-eclampsia — but the decision should be your doctor’s.
Why does it give me palpitations and headache? Both follow from widening the arteries. They usually settle, and the accompanying beta blocker helps.
What is drug-induced lupus? An uncommon reaction to prolonged hydralazine causing joint pain, fever, rash and tiredness. It usually resolves when the medicine is stopped — report those symptoms promptly.
Can I stop it if my blood pressure is normal? No. A normal reading means it is working. Stopping suddenly can cause a rebound rise.