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| Clinical data | |
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| Trade names | Apresoline, BiDil, others |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a682246 |
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| Routes of administration | By mouth,intravenous |
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| Pharmacokinetic data | |
| Bioavailability | 26–50% |
| Protein binding | 85–90% |
| Metabolism | Liver |
| Onset of action | 5–30 minutes[2] |
| Eliminationhalf-life | 2–8 hours, 7–16 hours (renal impairment) |
| Duration of action | 2–6 hours[2] |
| Excretion | Urine |
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| CompTox Dashboard(EPA) | |
| ECHA InfoCard | 100.001.528 |
| Chemical and physical data | |
| Formula | C8H8N4 |
| Molar mass | 160.180 g·mol−1 |
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Hydralazine, sold under the brand nameApresoline among others, is a medication used to treathigh blood pressure andheart failure.[2] This includeshigh blood pressure in pregnancy andvery high blood pressure resulting in symptoms.[3] It has been found to be particularly useful in heart failure, together withisosorbide dinitrate, for treatment ofpeople of African descent.[2] It is given by mouth orby injection into a vein.[3] Effects usually begin around 15 minutes and last up to six hours.[2]
Common side effects includeheadache andfast heart rate.[2] It is not recommended in people withcoronary artery disease or in those withrheumatic heart disease that affects themitral valve.[2] In those withkidney disease a low dose is recommended.[3] Hydralazine is in thevasodilator family of medications, so it is believed to work by causing thedilation of blood vessels.[2]
Hydralazine was discovered while scientists atCiba were looking for a treatment for malaria.[4] It was patented in 1949.[5] It is on theWorld Health Organization's List of Essential Medicines.[6] In 2023, it was the 109th most commonly prescribed medication in the United States, with more than 6 million prescriptions.[7][8]
Hydralazine is not used as a primary drug for treating hypertension because it elicits a reflexsympathetic stimulation of the heart (thebaroreceptor reflex).[9] The sympathetic stimulation may increase heart rate andcardiac output, and in people with coronary artery disease may causeangina pectoris ormyocardial infarction.[10] Hydralazine may also increaseplasmarenin concentration, resulting in fluid retention. To prevent these undesirable side effects, hydralazine is usually prescribed in combination with abeta blocker (e.g.,propranolol) and adiuretic.[10]
Hydralazine is used to treat severe hypertension, but is not a first-line therapy foressential hypertension. Hydralazine is often used to treat hypertension in pregnancy together with eitherlabetalol and/ormethyldopa.[11]
Hydralazine is commonly used in combination withisosorbide dinitrate for the treatment ofcongestive heart failure in black populations. This preparation,isosorbide dinitrate/hydralazine, was the first race-based prescription drug.[12]
It should not be used in people who havetachycardia, heart failure, constrictivepericarditis,lupus, a dissectingaortic aneurysm, orporphyria.[13]
Prolonged treatment may cause asyndrome similar to lupus, which can become fatal if the symptoms are not noticed and drug treatment stopped.[13] Hydralazine is within the top three drugs that is known to induce systemic lupus and this adverse drug event is dose dependent yet significant.
Very common (>10% frequency) side effects include headache, tachycardia, andpalpitations.[13]
Common (1–10% frequency) side effects includeflushing,hypotension, anginal symptoms, aching or swelling joints, muscle aches, positive tests foratrial natriuretic peptide, stomach upset, diarrhea, nausea and vomiting, andswelling (sodium and water retention).[13]
Hydralazine may potentiate the antihypertensive effects of:[13]
Drugs subject to a strongfirst-pass effect, such asbeta blockers, may increase thebioavailability of hydralazine.[13] The heart rate-accelerating effects ofepinephrine (adrenaline) are increased by hydralazine, and coadministration may lead to toxicity.[13]
Hydralazine is a direct-actingsmooth muscle relaxant and acts as avasodilator primarily inresistance arterioles, also known as the smooth muscle of the arterial bed. The molecular mechanism involves inhibition of inositol trisphosphate-induced Ca2+ release from the sarcoplasmic reticulum in arterial smooth muscle cells.[14][15] By relaxingvascular smooth muscle, vasodilators act to decreaseperipheral resistance, thereby loweringblood pressure and decreasing afterload.[10] The exactmechanism of action of hydralazine is unknown, at least as of 1981.[16]
Metabolic products include theN-acetyl derivative,pyruvic acid hydrazone, andacetone hydrazone, each of which may also contribute to reducing blood pressure.[17]
Hydralazine belongs to thehydrazinophthalazine class of drugs.[18]
The antihypertensive activity of hydralazine was discovered by scientists at Ciba, who were trying to discover drugs to treat malaria; it was initially called C-5968 and 1-hydrazinophthalazine; Ciba's patent application was filed in 1945 and issued in 1949,[19][20][21] and the first scientific publications of its blood pressure-lowering activities appeared in 1950.[4][18][22] It was approved by the FDA in 1953.[23]
It was one of the first antihypertensive medications that could be taken by mouth.[9]
Hydralazine has also been studied as a treatment formyelodysplastic syndrome in its capacity as aDNA methyltransferase inhibitor.[24]
