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Discontinued Warning IconPlease Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

Ismelin Patient Information including If I Miss a Dose

What happens if I miss a dose (Ismelin)?

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 (Ismelin)?

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 (Ismelin)?

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.

What other drugs will affect guanethidine (Ismelin)?

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:

  • haloperidol (Haldol);
  • methylphenidate (Ritalin);
  • minoxidil (Loniten);
  • thiothixene (Navane);
  • 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.

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.

Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2009 Cerner Multum, Inc. Version: 5.02. Revision date: 2/13/04.

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Side Effects Centers

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.


Get tips on handling your hypertension.