Hydralazine belongs to the class of medications called vasodilators. It is used alone or with other medications to reduce blood pressure. It works to lower blood pressure by relaxing veins and arteries.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The dose of hydralazine is based on the individual and depends on the condition being treated and the person's response to the medication. The starting dose of hydralazine tablets is 10 mg taken 4 times a day for the first 2 to 4 days. Depending on how well it is working for you and how well it is tolerated, your doctor will gradually increase the dose. The usual recommended maintenance dose of hydralazine to treat high blood pressure varies from 10 mg to 50 mg 4 times daily. The dose should not be increased over 100 mg per day without further testing by your doctor to determine your acetylator phenotype.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from heat and moisture, and keep it out of the reach of children.

10 mg
Each light yellow, coated, round, biconvex tablet, debossed "10" on one side and plain on the other side, contains 10 mg of hydralazine. Nonmedicinal ingredients: microcrystalline cellulose, croscarmellose sodium, colloidal silicon dioxide, magnesium stearate, polyvinyl alcohol, polyethylene glycol, titanium dioxide, talc, D&C Yellow No. 10 Aluminum Lake, and Sunset Yellow Aluminum Lake.

25 mg
Each blue, coated, round, biconvex tablet, debossed "25" on one side and plain on the other side, contains 25 mg of hydralazine. Nonmedicinal ingredients: microcrystalline cellulose, magnesium stearate, croscarmellose sodium, colloidal silicon dioxide, polyethylene glycol, polyvinyl alcohol, titanium dioxide, talc, FD&C Blue No. 1, and yellow iron oxide.

50 mg
Each pink, coated, round, biconvex tablet, debossed "50" on one side and plain on the other side, contains 50 mg of hydralazine. Nonmedicinal ingredients: microcrystalline cellulose, magnesium stearate, croscarmellose sodium, colloidal silicon dioxide, polyethylene glycol, polyvinyl alcohol, titanium dioxide, talc, FD&C Blue No. 1, and D&C Red No. 27.

Do not use hydralazine if you:

• are allergic to hydralazine or any ingredients of the medication
• have an untreated aneurysm in the aorta (large artery leaving the heart)
• have certain heart conditions (e.g., aortic stenosis, mitral stenosis, constrictive pericarditis, cor pulmonale, or a very fast heartbeat combined with heart failure)
• have coronary artery disease
• have lupus (also called systemic lupus erythematosus or SLE)
• have mitral valve rheumatic heart disease

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• blurred vision
• chest pain
• constipation
• decreased appetite
• diarrhea
• dizziness
• fast heart rate
• fever
• flushing
• headache
• increased tear production
• low blood pressure (e.g., fainting, dizziness, lightheadedness, blurred vision, nausea)
• muscle cramps
• nasal congestion
• nausea
• pounding heartbeat
• rash
• tremor
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• fluid retention (e.g., swelling of the feet, ankles, or lower leg)
• increased frequency of infections
• shortness of breath
• signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of heart problems (e.g., fast, irregular heartbeat or pulse, chest pain, sudden weight gain, difficulty breathing, leg swelling)
• signs of kidney problems (e.g., change in the amount or colour of urine, increased urination at night, blood in the urine, swelling in the feet or legs)
• symptoms of angina (e.g., chest pain, sudden wheeziness, difficulty breathing, or shortness of breath)
• symptoms of liver problems (e.g., nausea, loss of appetite, yellowing of the skin and eyes, abdominal pain, dark urine)
• tingling or numbness in the hands and feet
• unexplained joint pain with fever and skin rash
• unusual tiredness

Stop taking the medication and seek immediate medical attention if any of the following occur:

• symptoms of a serious allergic reaction (such as hives; swelling of the face, eyes, and throat; and difficulty breathing)
• symptoms of lupus (e.g., joint pain, fever, generalized rash)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Blood tests: Rarely, this medication can decrease the number of neutrophils (a type of white blood cell that helps fight infection), red blood cells (which carry oxygen), and platelets (which help your blood to clot). Your doctor will do regular blood tests to monitor your blood cell levels while you are taking this medication.

Drowsiness/reduced alertness: Hydralazine may cause drowsiness or dizziness, affecting your ability to drive or operate machinery. Avoid driving, operating machinery, or performing other potentially hazardous tasks until you have determined how you are affected by this medication.

Kidney disease: Decreased kidney function can cause this medication to build up in the body, causing side effects. If you have decreased kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Low blood pressure: Some people taking hydralazine may experience sudden blood pressure drops when getting up from a sitting or lying position. These blood pressure drops could lead to dizziness, lightheadedness, and falls. If you experience this problem, try getting up more slowly. If it persists or if you faint, contact your doctor.

Lupus: Hydralazine may cause lupus-like symptoms (e.g., joint pain, fever, generalized rash). If these symptoms develop, contact your doctor immediately.

Pregnancy: This medication should only be used during pregnancy when the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking hydralazine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

Seniors: Seniors may be more sensitive to the blood-lowering effects of hydralazine. It should be used with more caution.

There may be an interaction between hydralazine and any of the following:

• aldesleukin
• alpha-blockers (e.g., alfuzosin, terazosin, tamsulosin)
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• antipsychotics (e.g., aripiprazole, cariprazine, chlorpromazine, lurasidone, olanzapine, paliperidone, quetiapine)
• apomorphine
• barbiturates (e.g., butalbital, phenobarbital)
• bortezomib
• brigatinib
• brimonidine
• bromocriptine
• diazoxide
• diuretics (water pills; e.g., bumetanide, furosemide)
• duloxetine
• epinephrine
• flunarizine
• general anesthetics (medications used to put people to sleep before surgery)
• iron sucrose
• levodopa
• methylphenidate
• monoamine oxidase inhibitors (MAOIs; e.g., rasagiline, selegiline, tranylcypromine)
• morphine
• nabilone
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• non-steroidal anti-inflammatory medications (NSAIDs; e.g., celecoxib, diclofenac, ibuprofen, naproxen)
• obinutuzumab
• pentoxifylline
• pergolide
• phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pramipexole
• primidone
• riociguat
• ropinirole
• rotigotine
• sacubitril
• sotalol
• tizanidine
• tretinoin
• tricyclic antidepressants (e.g., clomipramine, imipramine)
• yohimbine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.