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Like other antihypertensive agents, guanfacine should be used with caution in patients with severe coronary insufficiency, recent myocardial infarction, cerebrovascular disease or chronic renal or hepatic failure.
Guanfacine, like other orally active central a2 adrenergic agonists, causes sedation or drowsiness, especially when beginning therapy. These symptoms are dose-related (see ADVERSE REACTIONS). When guanfacine is used with other centrally active depressants (such as phenothiazines, barbiturates, or benzodiazepines), the potential for additive sedative effects should be considered.
Abrupt cessation of therapy with orally active central a2 adrenergic agonists may be associated with increases (from depressed on-therapy levels) in plasma and urinary catecholamines, symptoms of "nervousness and anxiety" and, less commonly, increases in blood pressure to levels significantly greater than those prior to therapy.
In clinical trials, no clinically relevant laboratory test abnormalities were identified as causally related to drug during short-term treatment with guanfacine.
Drug/Laboratory Test Interactions
No laboratory test abnormalities related to the use of guanfacine have been identified.
Carcinogenesis, Mutagenesis, Impairment of Fertility
No carcinogenic effect was observed in studies of 78 weeks in mice at doses more than 150 times the maximum recommended human dose and 102 weeks in rats at doses more than 100 times the maximum recommended human dose. In a variety of test models, guanfacine was not mutagenic.
No adverse effects were observed in fertility studies in male and female rats.
Pregnancy Category B
Administration of guanfacine to rats at 70 times the maximum recommended human dose and to rabbits at 20 times the maximum recommended human dose resulted in no evidence of harm to the fetus. Higher doses (100 and 200 times the maximum recommended human dose in rabbits and rats respectively) were associated with reduced fetal survival and maternal toxicity. Rat experiments have shown that guanfacine crosses the placenta.
There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Labor and Delivery
Guanfacine is not recommended in the treatment of acute hypertension associated with toxemia of pregnancy. There is no information available on the effects of guanfacine on the course of labor and delivery.
It is not known whether guanfacine is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when guanfacine hydrochloride is administered to a nursing woman. Experiments with rats have shown that guanfacine is excreted in the milk.
Safety and effectiveness in pediatric patients under 12 years of age have not been demonstrated. Therefore, the use of guanfacine in this age group is not recommended. There have been spontaneous postmarketing reports of mania and aggressive behavioral changes in pediatric patients with attention-deficit hyperactivity disorder (ADHD) receiving guanfacine. The reported cases were from a single center. All patients had medical or family risk factors for bipolar disorder. All patients recovered upon discontinuation of guanfacine HCl.
Clinical studies of guanfacine did not include sufficient numbers of subjects aged 65 and over to determine whether they responded differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients.
In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy (see CLINICAL PHARMACOLOGY, Pharmacokinetics).This monograph has been modified to include the generic and brand name in many instances.
Last reviewed on RxList: 12/6/2007
Additional Guanfacine Hydrochloride Information
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