Hydralazine is a medication primarily used to treat high blood pressure and, in some cases, heart failure. It belongs to a class of drugs called vasodilators, meaning it works by relaxing and widening blood vessels. This action allows blood to flow more easily, which reduces blood pressure and decreases the workload on the heart. Hydralazine can be taken orally in tablet form or administered through injection.
Common and Immediate Side Effects
Patients starting hydralazine may experience common side effects shortly after beginning treatment. These frequently include headaches, which occur as blood vessels in the brain dilate. Another common effect is a fast heart rate or palpitations, known as reflex tachycardia. This happens because the body detects the sudden drop in blood pressure, triggering a compensatory increase in heart rate.
Dizziness and lightheadedness are also often reported. This sensation, called orthostatic hypotension, results from the drug’s blood pressure-lowering effect upon standing. Other gastrointestinal symptoms such as nausea, vomiting, decreased appetite, and diarrhea can occur. These common side effects are usually mild and often lessen as the body adjusts to the medication.
Hydralazine-Induced Lupus-like Syndrome
A serious side effect is drug-induced lupus erythematosus (DILE), a reversible condition mimicking systemic lupus erythematosus (SLE). Symptoms of this syndrome can include:
Joint pain
Muscle aches
Fever
A butterfly-shaped rash across the face
Fatigue
Loss of appetite
Chest pain
The development of DILE is linked to several risk factors, including higher daily doses (typically above 200 mg) and prolonged use (often exceeding three months). Genetic predispositions, such as being a “slow acetylator,” and female gender also increase the risk. While onset can vary, the syndrome usually resolves completely upon discontinuation of hydralazine.
Other Side Effects and When to Seek Medical Attention
Beyond common immediate effects and lupus-like syndrome, hydralazine can cause other side effects. Some individuals may experience peripheral neuropathy, characterized by numbness, tingling, burning, or weakness in the hands and feet. This nerve issue is thought to be related to the drug’s potential to lower vitamin B6 levels.
Blood disorders, such as anemia (low red blood cell count), leukopenia (low white blood cell count), or agranulocytosis (a severe drop in white blood cells), have also been reported. Additionally, hydralazine can affect the liver, leading to hepatitis. Symptoms of liver involvement may include yellowing of the skin or eyes (jaundice), dark urine, and severe stomach pain.
Seek medical attention if any side effects are persistent, severe, or concerning. Contact a healthcare provider immediately if you experience chest pain, pressure, or discomfort, especially if it spreads to the jaw or arm, as this could indicate a serious heart problem. Other signs requiring prompt medical evaluation include:
A fast or abnormal heartbeat
Trouble breathing
Unexplained bruising or bleeding
Fever with a sore throat
Symptoms of an allergic reaction (e.g., hives, swelling of the face, lips, or throat)
New or worsening numbness, tingling, or pain in the extremities