Generic Name: guanethidine (gwha NETH ih deen)Brand Names: Ismelin
What is guanethidine?
Guanethidine lowers blood pressure by decreasing the levels of certain chemicals in the blood. This allows your blood vessels (veins and arteries) to relax (widen).
Guanethidine is used to treat hypertension (high blood pressure). Guanethidine is also used to treat high blood pressure in the kidneys.
Guanethidine may also be used for purposes other than those listed in this medication guide.
What is the most important information I should know about guanethidine?Use caution when driving, operating machinery, or performing other hazardous activities. Guanethidine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.
Use caution when rising from a sitting or lying position, especially first thing in the morning. Dizziness may occur while taking guanethidine and may result in a fall.Do not stop taking guanethidine suddenly without first talking to your doctor. This could cause severely high blood pressure, nervousness, and anxiety.
Before having surgery, tell your doctor or dentist that you are taking this medication.
What should I discuss with my healthcare provider before taking guanethidine?
You cannot take guanethidine if you
have congestive heart failure- or
are taking a monoamine oxidase inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate).
Before taking this medication, tell your doctor if you
have peptic ulcer disease (stomach ulcers) or another stomach disease-
have kidney disease-
have any type of heart disease-
have ulcerative colitis-
are suffering from depression (especially if you have suicidal thoughts)- or
are receiving electroconvulsive shock therapy.
You may require a dosage adjustment or special monitoring during treatment if you have any of the conditions listed above.Guanethidine is in the FDA pregnancy category C. This means that it is not known whether guanethidine will be harmful to an unborn baby. Do not take guanethidine without first talking to your doctor if you are pregnant or could become pregnant during treatment. Guanethidine passes into breast milk and may be harmful to a nursing infant. Do not take guanethidine without first talking to your doctor if you are breast-feeding a baby.
How should I take guanethidine?
Take guanethidine exactly as directed. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.Take each dose with a full glass of water. Take guanethidine with food or milk if it causes stomach upset.
It is important to take guanethidine regularly to get the most benefit.Do not stop taking guanethidine suddenly without first talking to your doctor. This could cause severely high blood pressure, nervousness, and anxiety.
Your doctor may want you to have blood pressure monitoring or other medical evaluations during treatment with guanethidine to monitor progress and side effects.Store this medication at room temperature away from moisture and heat.
What happens if I miss a dose?
Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the dose you missed and take only the next regularly scheduled dose. Do not take a double dose of this medication.
What happens if I overdose?Seek emergency medical attention if an overdose is suspected.
Symptoms of a guanethidine overdose include low blood pressure (fainting, dizziness, weakness)- a slow pulse- low body temperature- diarrhea- and slow breathing.
What should I avoid while taking guanethidine?Use caution when driving, operating machinery, or performing other hazardous activities. Guanethidine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.
Use caution when rising from a sitting or lying position, especially first thing in the morning. Dizziness may occur while taking guanethidine and may result in a fall.Avoid alcohol while taking guanethidine. It may increase drowsiness an dizziness caused by guanethidine. Use caution even with small amounts of alcohol.
Guanethidine may increase the effects of other drugs that cause drowsiness, including antidepressants, alcohol, antihistamines, pain relievers, anxiety medicines, seizure medicines, and muscle relaxants. Dangerous sedation, dizziness, or drowsiness may occur if guanethidine is taken with any of these medications. Tell your doctor about all medicines that you are taking, and do not take any medicine without first talking to your doctor.
Avoid becoming overheated in hot weather or during exercise. Also avoid standing for long periods of time and use caution if you have a fever. These situations increase the effects of guanethidine in the body and may cause dizziness.
Before having surgery, tell your doctor or dentist that you are taking this medication.
Guanethidine side effectsIf you experience any of the following serious side effects, stop taking guanethidine and seek emergency medical attention or contact your doctor immediately:
an allergic reaction (difficulty breathing- closing of the throat- swelling of the lips, tongue, or face- or hives)-
heart failure (shortness of breath, swelling of ankles or legs, sudden weight gain of 5 pounds or more)- or
Other, less serious side effects are more likely to occur. Continue to take guanethidine and talk to your doctor if you experience
unusual fatigue or drowsiness-
dizziness (avoid standing up to quickly and use caution when performing hazardous activities)-
anxiety, depression, or nightmares-
diarrhea, nausea, or vomiting (take guanethidine with food or milk if it upsets your stomach)-
stuffy nose or a dry mouth (sucking on ice chips or sugarless hard candy may relieve a dry mouth)-
weight gain- or
impotence or difficulty ejaculating.
Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.
Guanethidine Dosing Information
Usual Adult Dose for Hypertension:
Initial dose: 10 mg orally once a day (25 mg to 50 mg if hospitalized).Maintenance dose: 25 mg to 50 mg orally once a day.
Usual Adult Dose for Hypertensive Emergency:
Loading dose: 25 mg to 50 mg orally 3 times a day at 6 hour intervals over 1 to 3 days. The nighttime dose is omitted.
What other drugs will affect guanethidine?Do not take guanethidine without first talking to your doctor if you have taken a monoamine oxidase inhibitor (MAOI) such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate) in the last 14 days.
Before taking this medication, tell your doctor if you are taking any of the following medicines:
respiratory medicines such as albuterol (Ventolin, Proventil, Volmax, others), pirbuterol (Maxair), salmeterol (Serevent), and others-
phenothiazines such as chlorpromazine (Thorazine), prochlorperazine (Compazine), perphenazine (Trilafon), fluphenazine (Prolixin), thioridazine (Mellaril), and others- or
tricyclic antidepressants such as amitriptyline (Elavil, Endep), imipramine (Tofranil), doxepin (Sinequan), nortriptyline (Pamelor), and others.
You may require special monitoring or a dose adjustment if you are taking any of the medicines listed above.
Drugs other than those listed here may also interact with guanethidine or affect your condition. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including vitamins, minerals, and herbal products.
Where can I get more information?
Your pharmacist has additional information about guanethidine written for health professionals that you may read.
What does my medication look like?
Guanethidine is available with a prescription under the brand name Ismelin. Other brand or generic formulations may also be available. Ask your pharmacist any questions you have about this medication, especially if it is new to you.
Ismelin 10 mg--round, pale-yellow, scored tablets
Ismelin 25 mg--round, white, scored tablets
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
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