Guanethidine Side Effects
Some side effects of guanethidine may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.
For the Consumer
Applies to guanethidine: oral tablet
Along with its needed effects, guanethidine 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 while taking guanethidine:More common
- Swelling of feet or lower legs
- Chest pain
- shortness of breath
Some side effects of guanethidine 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
- Blurred vision
- drooping eyelids
- dryness of mouth
- loss of hair on scalp
- muscle pain or tremors
- nausea or vomiting
- nighttime urination
- skin rash
For Healthcare Professionals
Applies to guanethidine: oral tablet
The risk of orthostatic hypotension, sometimes followed by syncope, is greatest within the first 10 minutes after dosing, early in the morning, and in hypovolemic patients. It is accentuated by alcohol, hot weather, or exercise--all of which are associated with peripheral vasodilation. The manufacturer recommends that guanethidine be gradually withdrawn over at least two weeks prior to administration of general anesthetics to avoid cardiovascular collapse during induction.
Cardiovascular side effects can result from excessive sympathetic blockade or a relative increase in parasympathetic tone. Orthostatic hypotension is reported in approximately 15% of patients, some of whom experience syncope.
Unopposed or excessive parasympathetic tone can cause excessive bradycardia in rare cases. This may cause serious problems in patients with underlying sinus node dysfunction.
Guanethidine can cause generalized edema in 10% to 15% of patients. Some patients with preexisting congestive heart failure do not tolerate this, and require concomitant diuretic therapy.
Gastrointestinal side effects are also related to increased parasympathetic tone. Diarrhea is reported in 11% of patients, some of whom discontinued therapy because of it. Dry mouth or parotid tenderness are reported in approximately 5% of patients.
There is evidence that guanethidine may interfere with ejaculation by inhibiting contraction of the seminal vesicle, ampula and ductus deferens.
Large studies report sexual impotence as a relatively uncommon genitourinary complaint, occurring in only approximately 2% of male patients. Smaller studies, where specific questions were asked of male patients reveal an incidence of impotence as high as 60%. Delayed or retrograde ejaculation and decreased sperm counts are reported. Impotence appears to be reversible upon discontinuation of therapy or reduction in dosage.
A relatively common respiratory system complaint, nasal stuffiness in up to 30% of patients, is related to increased parasympathetic tone. Rare reports of dyspnea or exertion unaccompanied by other signs or symptoms of congestive heart failure are associated with guanethidine.
In one study, 58% of patients with or without preexisting elevated BUN developed an increase in the BUN during guanethidine therapy. The study did not, however, quantify the rise in BUN, attempt to make an association with the degree of blood pressure control, or attempt to measure other parameters of renal function.
Because guanethidine does not affect the central nervous system, neurologic side effects are notably either absent or infrequent. Insomnia and weakness are occasionally reported more often with guanethidine than with placebo.
Hypersensitivity reactions are not associated with guanethidine.
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