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
If 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.
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 The manufacturer recommends that guanethidine be gradually withdrawn over at least two weeks prior to administration of general anesthetics to avoid cardiovascular collapse during induction.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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