Hydralazine Apresoline vs clonidine Catapres Kapvay

Hydralazine Apresoline vs clonidine Catapres Kapvay

Hydralazine vs. Clonidine: A Comparison

Hydralazine is a medication used to treat high blood pressure, hypertensive crisis, and congestive heart failure (CHF). It works by relaxing blood vessels, which reduces arterial blood pressure and peripheral vascular resistance. Hydralazine is selective for arterioles and affects calcium movement within blood vessels.

Clonidine, on the other hand, is used primarily for the treatment of high blood pressure. It is also used off-label for alcohol withdrawal, smoking cessation, restless leg syndrome, Tourette’s syndrome, and opioid withdrawal. Clonidine functions by stimulating receptors in the brain that reduce the transmission of messages to other areas of the body, resulting in slowed heart rate and lowered blood pressure.


What are the side effects of hydralazine and clonidine?


The common side effects of hydralazine include:

  • headache,
  • anorexia,
  • nausea,
  • vomiting,
  • diarrhea,
  • palpitations,
  • tachycardia (rapid heartbeat), and
  • angina pectoris (chest pain).

Other less common side effects include:

  • constipation,
  • paralytic ileus,
  • low blood pressure,
  • edema,
  • paradoxical pressor response,
  • dyspnea (shortness of breath),
  • peripheral neuritis,
  • numbness,
  • tingling,
  • tremors,
  • muscle cramps,
  • psychotic reactions,
  • difficulty urinating,
  • blood disorders,
  • hypersensitivity type reactions,
  • nasal congestion,
  • flushing,
  • abnormal tear production (lacrimation) , and
  • conjunctivitis.
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The most common side effects include:

Other side effects include:

  • Skin redness,
  • Itching,
  • Impotence,
  • Darkening of skin,
  • Decreased sexual desire,
  • Ejaculatory dysfunction,
  • Severe rebound high blood pressure,
  • Severe low blood pressure,
  • Slow heart rate,
  • Withdrawal symptoms,
  • Depression,
  • Angioedema,
  • Severe allergic reactions,
  • Slow heart rate,
  • Fainting,
  • Abnormal heart conduction.

Severe rebound hypertension can occur following sudden withdrawal from clonidine. Symptoms include increased salivation, nervousness, headache, heart palpitations, agitation, anxiety, sweating, nausea, muscle pain, and abdominal pain. To prevent these symptoms, it is important to gradually reduce the dose of clonidine over several days.

What is the dosage of hydralazine vs. clonidine?


The starting regimen is 10 mg orally four times daily for the first 2 to 4 days, followed by an increase to 25 mg four times daily for the remainder of the first week. For the second and subsequent weeks, the dosage is increased to 50 mg four times daily, with a gradual increase of 10-25 mg/dose every 2-5 days. The maximum daily dose used in clinical studies is 300 mg.

For congestive heart failure, the initial dose is 10 to 25 mg orally 3 to 4 times daily. The usual dose is 225 to 300 mg daily in 3 to 4 divided doses. For pediatric hypertensive emergencies, the dose is 0.5 mg/Kg IV every 4 hours.


The usual oral adult dose is 0.1–0.3 mg twice daily. The maximum oral dose is 2.4 mg daily. Topical patches should be applied once every 7 days to an area of hairless skin on the upper arm or torso. When applying a new patch, a different area of skin should be used.

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What drugs interact with hydralazine and clonidine?


Sympathomimetics such as cocaine, dobutamine, dopamine, norepinephrine, epinephrine, metaraminol, methoxamine, phenylephrine, phenylpropanolamine, ephedra, and ephedrine may reduce the effectiveness of hydralazine treatment by blocking its antihypertensive benefits.


Clonidine can increase the sedating effects of medications that also cause sedation, such as narcotic pain relievers, barbiturates, sedatives, and ethanol. Additionally, tricyclic antidepressants can block the blood pressure lowering effects of clonidine, leading to an increase in blood pressure. It is important to use clonidine cautiously in combination with drugs that lower heart rate, as abnormal heart rhythms can occur. Furthermore, clonidine can interact with cyclosporine, nonsteroidal anti-inflammatory drugs (NSAIDs), cocaine, pseudoephedrine, phenylephrine, and phenylpropanolamine.

Are hydralazine and clonidine safe to take while pregnant or breastfeeding?


Hydralazine should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. It is classified as FDA pregnancy risk category C. It is excreted in breast milk, so caution should be exercised when used during breastfeeding.


There are no adequate studies of clonidine during pregnancy. It is excreted into breast milk and could potentially cause adverse effects in the infant.


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Hydralazine (Apresoline) and clonidine (Catapres, Kapvay) are both used to treat high blood pressure. Hydralazine is also used for hypertensive crisis and congestive heart failure (CHF). Clonidine, in addition to treating high blood pressure, has off-label uses for alcohol withdrawal, smoking cessation, restless leg syndrome, Tourette’s syndrome, and opioid withdrawal. Although they belong to different drug classes, they serve similar purposes in managing hypertension.

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