Guanethidine (Systemic)

Brand name(s): Ismelin

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For guanethidine, the following should be considered:

Allergies-Tell your doctor if you have ever had any unusual or allergic reaction to guanethidine. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy-Studies on effects in pregnancy have not been done in either humans or animals.

Breast-feeding-Small amounts of guanethidine pass into breast milk. However, this medicine has not been reported to cause problems in nursing babies.

Children-Although there is no specific information comparing use of guanethidine in children with use in other age groups, this medicine is not expected to cause different side effects or problems in children than it does in adults.

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

Other medicines-Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking guanethidine, it is especially important that your health care professional knows if you are taking any of the following:

• Antidiabetics, oral (diabetes medicine you take by mouth)-Effects may be increased by guanethidine

• Loxapine (e.g., Loxitane) or
• Thioxanthenes (chlorprothixene [e.g., Taractan], thiothixene [e.g., Navane]) or
• Tricyclic antidepressants (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Pertofrane], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil]) or
• Trimeprazine (e.g., Temaril)-May decrease the effects of guanethidine on blood pressure

• Minoxidil (e.g., Loniten)-Effects on blood pressure may be greatly increased

• Monoamine oxidase (MAO) inhibitor activity (isocarboxazid [e.g., Marplan], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], selegiline [e.g., Eldepryl], tranylcypromine [e.g., Parnate])-Taking guanethidine while you are taking or within 1 week of taking MAO inhibitors may cause a severe increase in blood pressure

Other medical problems-The presence of other medical problems may affect the use of guanethidine. Make sure you tell your doctor if you have any other medical problems, especially:

• Asthma (history of) or
• Diarrhea or
• Pheochromocytoma or
• Stomach ulcer (history of)-Guanethidine may worsen these conditions

• Diabetes mellitus (sugar diabetes)-Effects of medicine used to treat this condition may be increased by guanethidine

• Fever-Effects of guanethidine may be increased

• Heart attack or stroke (recent) or
• Heart or blood vessel disease-Lowering blood pressure may make problems resulting from these conditions worse

• Kidney disease-Guanethidine may worsen this condition. Also, effects of guanethidine may be increased because of slower removal of this medicine from the body

• Liver disease-Effects of guanethidine may be increased because of slower removal from the body

Last Revised: 08/18/1998