Guanethidine (Oral)

Guanethidine is part of a group of medicines called antihypertensives. It is used to treat high blood pressure (hypertension).

High blood pressure puts extra strain on the heart and arteries. If it lasts for a long time, the heart and arteries may not work properly. This can harm the blood vessels in the brain, heart, and kidneys, leading to a stroke, heart failure, or kidney failure. High blood pressure may also raise the chance of heart attacks. These issues may be less likely to happen if blood pressure is managed.

Guanethidine helps by controlling nerve signals along specific nerve pathways. This action relaxes the blood vessels, allowing blood to flow through them more easily. This helps to lower blood pressure.

Guanethidine is available only with a prescription from your doctor.

It is important for your doctor to check your progress during regular visits to ensure that this medicine is working properly.

Dizziness, lightheadedness, or fainting may happen, especially when you get up from lying down or sitting. This is more likely to occur in the morning. Getting up slowly may help. When you get up from lying down, sit on the edge of the bed with your feet hanging for 1 or 2 minutes. Then stand up slowly. If the issue continues or worsens, check with your doctor.

Dizziness, lightheadedness, or fainting is also more likely to happen if you drink alcohol, stand for long periods, exercise, or if the weather is hot. While taking this medicine, be cautious about how much alcohol you consume. Also, be extra careful during exercise, in hot weather, or if you need to stand for long periods.

Do not take other medicines unless your doctor has discussed them with you. This includes over-the-counter (nonprescription) medicines for appetite control, asthma, colds, cough, hay fever, or sinus problems, as they may increase your blood pressure.

Before having any type of surgery (including dental surgery) or emergency treatment, inform the medical doctor or dentist that you are taking this medicine.

Tell your doctor if you develop a fever, as this may affect the amount of medicine you need to take.

Male patients: This medicine may interfere with ejaculation.

In deciding to use a medicine, you and your doctor will weigh the risks against the benefits. For this medicine, consider the following:

Allergies

Inform your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also, let your healthcare professional know about any other allergies you may have, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

There is no specific information comparing the use of guanethidine in children with its use in other age groups. This medicine is not expected to cause different side effects or problems in children compared to adults.

Geriatric

Many medicines have not been specifically studied in older individuals. Therefore, it may not be known if they work the same way in older adults as they do in younger adults. While there is no specific information comparing the use of guanethidine in the elderly with other age groups, dizziness, lightheadedness, or fainting may be more likely to occur in older adults, who may be more sensitive to the effects of guanethidine.

Breast Feeding

There are no adequate studies in women to determine the risk to infants when using this medication during breastfeeding. Consider the potential benefits against the potential risks before taking this medication while breastfeeding.

Interactions with Medicines

Some medicines should not be used together at all, while others may be used together even if an interaction might occur. In these cases, your doctor may change the dose or take other precautions. It is especially important for your healthcare professional to know if you are taking any of the medicines listed below while using this medicine. The following interactions are significant and may not include all possible interactions.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to prescribe this medication or may change some of your other medicines.

• Brofaromine
• Clorgyline
• Furazolidone
• Iproniazid
• Isocarboxazid
• Lazabemide
• Linezolid
• Moclobemide
• Nialamide
• Pargyline
• Phenelzine
• Procarbazine
• Rasagiline
• Selegiline
• Toloxatone
• Tranylcypromine

Using this medicine with any of the following medicines is usually not recommended, but may be necessary in some cases. If both medicines are prescribed together, your doctor may adjust the dose or how often you use one or both medicines.

• Iobenguane I 123
• Phenylpropanolamine
• Pseudoephedrine

Using this medicine with any of the following medicines may increase the risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may adjust the dose or how often you use one or both medicines.

• Amitriptyline
• Doxepin
• Phenylephrine
• Semaglutide
• Yohimbine

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used around the time of eating food or certain types of food due to potential interactions. Using alcohol or tobacco with certain medicines may also cause interactions. Discuss the use of your medicine with food, alcohol, or tobacco with your healthcare professional.

Other Medical Problems

Having other medical problems may affect the use of this medicine. Be sure to inform your doctor if you have any other medical issues, especially:

• Asthma (history of) or
• Diarrhea or
• Pheochromocytoma or
• Stomach ulcer (history of)—Guanethidine may make these conditions worse

• Type 2 diabetes mellitus—Guanethidine may increase the effects of medicines used to treat this condition

• Fever—Guanethidine effects may be increased

• Recent heart attack or stroke or
• Heart or blood vessel disease—Lowering blood pressure may worsen problems from these conditions

• Kidney disease—Guanethidine may worsen this condition. Additionally, effects of guanethidine may be increased due to slower removal from the body

• Liver disease—Effects of guanethidine may be increased due to slower removal from the body

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

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

More common

• Swelling of feet or lower legs

Less common or rare

• Chest pain
• shortness of breath

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

• Diarrhea or increase in bowel movements
• dizziness, lightheadedness, or fainting, especially when getting up from a lying or sitting position
• sexual problems in males
• slow heartbeat
• stuffy nose
• unusual tiredness or weakness

Less common or rare

• Blurred vision
• drooping eyelids
• dryness of mouth
• headache
• loss of hair on scalp
• muscle pain or tremors
• nausea or vomiting
• nighttime urination
• skin rash

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

In the U.S.

• Ismelin

Pharmacologic Class: Adrenergic Blocker

In addition to the use of the medicine your doctor has prescribed, treatment for your high blood pressure may include weight control and care in the types of foods you eat, especially foods high in sodium. Your doctor will tell you which of these are most important for you. You should check with your doctor before changing your diet.

Many patients who have high blood pressure will not notice any signs of the problem. In fact, many may feel normal. It is very important that you take your medicine exactly as directed and that you keep your appointments with your doctor even if you feel well.

Remember that guanethidine will not cure your high blood pressure but it does help control it. Therefore, you must continue to take it as directed if you expect to lower your blood pressure and keep it down. You may have to take high blood pressure medicine for the rest of your life. If high blood pressure is not treated, it can cause serious problems such as heart failure, blood vessel disease, stroke, or kidney disease.

To help you remember to take your medicine, try to get into the habit of taking it at the same time each day.

Dosing

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

• For oral dosage form (tablets): For high blood pressure: Adults—At first, 10 or 12.5 milligrams (mg) once a day. Then, your doctor may increase your dose to 25 to 50 mg once a day. Children—The dose is based on body weight and must be determined by your doctor. The usual dose is 200 micrograms (mcg) per kilogram (kg) (90.9 mcg per pound) of body weight a day. Then, your doctor may increase your dose as needed.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.