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Hydralazine side effects and how to avoid them

Hydralazine side effects include tachycardia, Lupus-like symptoms, and frequent urination
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By | Sep. 6, 2022 Medically reviewed by Keith Gardner, R.Ph.

Common hydralazine side effects | Serious side effects | Tachycardia | Lupus-like symptoms | Frequent urination | Fatigue | Hair loss | Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects | How to treat side effects

Hydralazine is a generic prescription drug FDA-approved for the treatment of high blood pressure (hypertension). However, it may be used off-label to treat congestive heart failure or, as an IV injection, to manage dangerously high blood pressure in an emergency. As a vasodilator, hydralazine widens peripheral blood vessels, reducing blood pressure. Outside of emergency situations, hydralazine is not the most commonly used blood pressure drug. It’s usually prescribed as an add-on drug when other drugs don’t work. That’s because there are concerns about its effectiveness and its side effects. Many of these adverse effects involve the heart.

Common side effects of hydralazine

The most common side effects of hydralazine have an incidence rate that may be as high as 1 in 10 people:

  • Headache
  • Diarrhea
  • Nausea
  • Vomiting
  • Loss of appetite (anorexia)
  • Chest pain (angina)
  • Palpitations
  • Fast heartbeat
  • Fluid retention
  • Constipation

Serious side effects of hydralazine

The most serious side effects of hydralazine are:

  • Heart attack
  • Dangerously low blood pressure
  • Blood disorders
  • Lupus-like symptoms
  • Severe allergic reactions

Tachycardia

Rapid heartbeat, or tachycardia, is estimated to occur in 10% of people taking hydralazine. That’s because hydralazine causes the body to stimulate the heart through the blood pressure reflex; the body releases substances to make the heart beat faster because peripheral blood pressure is low. If your heart rate increases when taking hydralazine, talk to your prescribing healthcare provider. A beta blocker or a diuretic may be prescribed to resolve this side effect.

Lupus-like symptoms

Drug-induced lupus-like symptoms occur in 5–10% of patients taking hydralazine. Symptoms include joint pain (arthralgia), muscle pain (myalgia), and fever. Other organs normally affected by lupus, such as lungs and kidneys, are usually spared and heart involvement is rare. Stopping hydralazine typically resolves the symptoms. If symptoms continue after discontinuing hydralazine then therapy with corticosteroids or other immunosuppressant medications may be started.

Frequent urination

Frequent urination is not a listed side effect of hydralazine, but difficulty with urination is. However, hydralazine is frequently prescribed with other blood pressure medications called thiazide diuretics, popularly known as “water pills.” Diuretics do significantly increase urination because they increase the amount of water and salts eliminated through the kidneys. Frequent urination is the intended and beneficial effect of diuretic treatment, and it can have dramatic effects on blood pressure.

Fatigue

Hydralazine is not associated with fatigue as a side effect. However, it is commonly used with other blood pressure drugs that may cause fatigue, such as beta blockers. Fatigue is also a symptom of a rare side effect of hydralazine: drug-induced systemic lupus erythematosus (SLE), a condition in which the body’s immune system attacks healthy cells and tissues. However, drug-induced SLE has other symptoms, including skin rash, fever, and weight loss. If fatigue is a problem or accompanied by other symptoms, talk to the prescriber.

Hair loss

Hydralazine is not associated with hair loss. On the contrary, drugs like hydralazine that widen peripheral blood vessels usually promote hair growth. The hair growth drug minoxidil, for instance, is a vasodilator like hydralazine and was originally used to treat high blood pressure. Remember: hydralazine is often prescribed with other blood pressure drugs. Some, like beta blockers, may cause hair to thin.

Hydralazine side effects in elderly patients

Hydralazine has been used since 1949. There is no clinical evidence that hydralazine is less effective or less safe in elderly people than in younger adults. Because older adults may clear the drug more slowly than younger adults, healthcare providers usually start the drug at a lower dose.

How soon do hydralazine side effects start?

Hydralazine begins working on the first dose, so some side effects, such as headache, palpitations, or rapid  heartbeat, may begin one or two hours after taking a dose as a direct response to the drug’s vasodilating effects. Other side effects such as diarrhea or vomiting may appear in a few days. The more serious problems caused by hydralazine are generally delayed side effects that occur after long-term use.

How long do hydralazine side effects last?

Some of hydralazine’s minor side effects may get better as the body adapts to the drug or the side effect. Most side effects will reverse when the drug is stopped, typically in a day or two. Some side effects, such as heart attack or stroke, may have long-term consequences.

What are the long-term side effects of hydralazine?

Hydralazine is intended for long-term treatment, often in combination with other drugs. There are no side effects due to the long-term use of hydralazine, but delayed side effects may include heart problems and drug-induced lupus. 

Hydralazine contraindications

Hydralazine should not be taken by people with:

  • A known allergic reaction to the drug
  • Coronary artery disease
  • Mitral valve disease caused by rheumatic heart disease

Pregnancy

The safety of hydralazine taken during pregnancy has not been studied. Healthcare professionals are cautious in prescribing the drug to pregnant women for high blood pressure, particularly in the third trimester. However, hydralazine IV injections may be used off-label for hypertensive emergencies in pregnant women, but their use is intended to save the life of the mother and the baby.

Breastfeeding

Hydralazine is present in human breast milk and is considered an acceptable drug to be used in women who are breastfeeding.

Children

Hydralazine is not approved for use in children or adolescents, though some healthcare providers may prescribe it off-label to treat hypertension or chronic hypertension in pediatric patients. 

Hydralazine warnings

Hydralazine is not considered a first-line blood pressure treatment because of its reflex effects on the heart. These and other issues are concerning enough to give prescribers pause when considering using this drug.

Cautions

Hydralazine could worsen some medical conditions, particularly heart or blood vessel conditions. These include:

  • Congestive heart failure (unless combined with isosorbide dinitrate)
  • Aortic aneurysm
  • History of stroke
  • Increased intracranial pressure
  • Low blood pressure

In addition, people with kidney disease eliminate hydralazine from the body more slowly than others, so hydralazine doses may need to be reduced.

Abuse and dependence

Hydralazine is not associated with drug abuse and is not known to cause physical dependence or withdrawal symptoms. 

Overdose

If too much hydralazine is taken, get medical attention or call a poison control center. Although there are no known fatalities, an overdose can cause shock or serious heart problems such as heart attack. Symptoms of an overdose include flushing, headache, low blood pressure, and rapid heartbeat. The maximum daily hydralazine dose for high blood pressure is 300 mg but may be higher when prescribed off-label. The best rule to avoid an overdose is to never exceed the prescribed dose.

Recalls

Hydralazine itself has never been recalled, but individual batches from individual manufacturers have been periodically recalled because of manufacturing or impurity concerns. 

Hydralazine interactions

Hydralazine has some drug interactions. Most concern lowering blood pressure or affecting the way other drugs work. These include:

  • MAO inhibitors (MAOIs). This small family of drugs can either increase the blood pressure lowering effects of hydralazine or, in some cases, hydralazine can increase the side effects of these drugs. Marplan (isocarboxazid), an MAO inhibitor prescribed as an antidepressant, is never used with blood pressure-reducing drugs.
  • Drugs that affect heart rhythm or heart rate. Hydralazine can speed up the heart, so it’s used cautiously with drugs that can change the heart’s rhythm, such as antiarrhythmics or antipsychotics. Because of the risk of irregular heartbeats, it is never prescribed with the antipsychotic thioridazine.
  • Drugs that lower blood pressure. Hydralazine is usually prescribed with other antihypertensives. However, some of these combinations can result in blood pressure dropping too low. Other drugs such as opioids, sleeping aids, and alcohol also lower blood pressure, but the effects aren’t a cause for concern unless blood pressure is not being regularly monitored.
  • Drugs that raise blood pressure. Many drugs will push blood pressure up, including stimulants, migraine drugs, attention-deficit hyperactivity disorder (ADHD) medications, over-the-counter decongestants, nonsteroidal anti-inflammatory drugs (NSAIDs), and caffeine. These aren’t dangerous drug interactions, but taking these drugs will compromise the therapeutic benefits of taking blood pressure medications like hydralazine.

How to avoid hydralazine side effects

Side effects are fairly common in people taking hydralazine. The most worrisome side effects involve the heart, so there are a few things everyone should do to minimize the possibility of side effects.

1. Give the prescriber a complete medical history

Avoiding serious side effects is most effectively accomplished by giving the prescribing healthcare provider a complete medical history. For hydralazine, the prescriber especially needs to know about:

  • Low blood pressure
  • Heart disease
  • Heart failure
  • Kidney problems
  • Lupus

2. Give the prescriber a complete rundown on drugs being taken

Another way to avoid side effects is to avoid drug interactions. Start by giving the prescribing healthcare provider a complete picture of all the prescription drugs, over-the-counter medications, or dietary supplements being used. The prescriber may make adjustments or advise on what to avoid. When getting a new prescription, make sure the prescriber or pharmacist knows that you’re taking hydralazine.

3. Take hydralazine as prescribed

Another tried and true way of avoiding a prescription drug’s side effects is to follow the instructions. Take the dose as instructed. Take each dose when it’s scheduled. Do not skip doses. Use a smartphone app or alarm to help remember when to take a dose. This is especially important for a drug like hydralazine that needs to be taken four times a day. 

4. Do not take extra doses

Do not exceed the prescribed dose. The risk of side effects, especially drug-induced lupus, goes up when higher doses are taken. If a dose is missed, take it when remembered. If it’s almost time for the next dose, skip the missed dose and take the next dose as scheduled. Remember: hydralazine is typically taken four times a day. That’s once every four hours. On such a tight timeline, chances are that most missed doses will have to be skipped.

5. Be consistent in how hydralazine is taken

Hydralazine can be taken with a meal or on an empty stomach. To prevent side effects, be consistent in how it’s taken. Either always take the dose with food or always take it without food.

How to treat side effects of hydralazine

Some of hydralazine’s side effects can be managed at home, but others will require professional medical advice or medical attention.

Headache

Drinking fluids and rest can help. It’s safe to take a pain reliever such as acetaminophen, but NSAIDs like aspirin or ibuprofen can raise blood pressure a bit. If headaches persist or get worse, talk to the prescribing healthcare provider.

Nausea

Eat smaller meals and stick to bland foods. Avoid greasy and heavy foods.

Vomiting

Drink fluids to avoid dehydration and avoid solid foods until vomiting stops. If vomiting persists or gets worse, contact a healthcare provider.

Diarrhea

Drink fluids to avoid dehydration. If diarrhea persists or gets worse, contact a healthcare provider.

Swelling

Fluid retention is commonly caused by vasodilators like hydralazine and typically involves swelling in the feet and lower legs. If this happens, elevate the feet and rest. If swelling persists or gets worse, talk to the prescribing healthcare provider.

Nerve problems

Hydralazine can cause problems with peripheral nerves, so contact the prescribing healthcare provider if there are any unexplained or bizarre sensations in the hands or feet such as tingling, burning, or pain.

Chest pain or rapid heartbeat

If palpitations, rapid heartbeat, or chest pain is experienced, immediately call the prescribing healthcare provider or get medical attention. 

Low blood pressure

Unless regularly checking blood pressure, the only way to spot low blood pressure are the symptoms: lightheadedness, dizziness, and feeling like you’re going to pass out. Get medical attention if any of these symptoms are experienced.

Lupus-like symptoms

Hydralazine can cause a lupus-like reaction a few weeks or months into treatment. In fact, hydralazine is one of the drugs most commonly associated with drug-induced lupus, and it is more likely if the doses are large. Drug-induced lupus is a serious side effect and requires that the drug be stopped and that immediate medical attention be sought out. Watch for symptoms such as:

  • Skin rash
  • Fever
  • Chest pain
  • Tiredness
  • Joint pain and swelling
  • Muscle pain

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