Guanfacine 1 MG Oral Tablet
Generic Name: GUANFACINE
Brand Name: Guanfacine
- Substance Name(s):
- GUANFACINE HYDROCHLORIDE
DRUG INTERACTIONS
Drug Interactions The potential for increased sedation when guanfacine is given with other CNS-depressant drugs should be appreciated.
The administration of guanfacine concomitantly with a known microsomal enzyme inducer (phenobarbital or phenytoin) to two patients with renal impairment reportedly resulted in significant reductions in elimination half-life and plasma concentration.
In such cases, therefore, more frequent dosing may be required to achieve or maintain the desired hypotensive response.
Further, if guanfacine is to be discontinued in such patients, careful tapering of the dosage may be necessary in order to avoid rebound phenomena (see Rebound above).
Anticoagulants Ten patients who were stabilized on oral anticoagulants were given guanfacine, 1-2 mg/day, for 4 weeks.
No changes were observed in the degree of anticoagulation.
In several well-controlled studies, guanfacine was administered together with diuretics with no drug interactions reported.
In the long-term safety studies, guanfacine was given concomitantly with many drugs without evidence of any interactions.
The principal drugs given (number of patients in parentheses) were: cardiac glycosides (115), sedatives and hypnotics (103), coronary vasodilators (52), oral hypoglycemics (45), cough and cold preparations (45), NSAIDs (38), antihyperlipidemics (29), antigout drugs (24), oral contraceptives (18), bronchodilators (13), insulin (10), and beta blockers (10).
Drug/Laboratory Test Interactions No laboratory test abnormalities related to the use of guanfacine have been identified.
OVERDOSAGE
Signs and Symptoms: Drowsiness, lethargy, bradycardia, and hypotension have been observed following overdose with guanfacine.
A 25-year-old female intentionally ingested 60 mg.
She presented with severe drowsiness and bradycardia of 45 beats/minute.
Gastric lavage was performed and an infusion of isoproterenol (0.8 mg in 12 hours) was administered.
She recovered quickly and without sequelae.
A 28-year-old female who ingested 30-40 mg developed only lethargy, was treated with activated charcoal and a cathartic, was monitored for 24 hours, and was discharged in good health.
A 2-year-old male weighing 12 kg, who ingested up to 4 mg of guanfacine, developed lethargy.
Gastric lavage (followed by activated charcoal and sorbitol slurry via NG tube) removed some tablet fragments within 2 hours after ingestion, and vital signs were normal.
During 24-hour observation in ICU, systolic pressure was 58 and heart rate 70 at 16 hours post-ingestion.
No intervention was required, and child was discharged fully recovered the next day.
Treatment of Overdosage: Gastric lavage and supportive therapy as appropriate.
Guanfacine is not dialyzable in clinically significant amounts (2.4%).
DESCRIPTION
Guanfacine hydrochloride is a centrally acting antihypertensive with α 2 -adrenoceptor agonist properties in tablet form for oral administration.
The chemical name of guanfacine hydrochloride is N-Amidino-2-(2,6-dichlorophenyl) acetamide monohydrochloride and its molecular weight is 282.55.
Its structural formula is: Guanfacine hydrochloride is a white to off-white powder; sparingly soluble in water and alcohol and slightly soluble in acetone.
Each tablet, for oral administration, contains guanfacine hydrochloride equivalent to 1 mg or 2 mg guanfacine.
The tablets contain the following inactive ingredients: anhydrous lactose, microcrystalline cellulose, partially pregelatinized starch, magnesium stearate and talc.
The 2 mg tablet also contains D&C Yellow #10 Aluminum Lake.
Structural Formula
HOW SUPPLIED
Guanfacine Tablets USP, 1 mg are available as white, round, flat-faced beveled-edge tablets, debossed “ Є 48” on one side and plain on the other side.
These are supplied in bottles of 30, 60 and 90..
Store at 20°-25°C (68°-77°F).
[See USP controlled room temperature.] Dispense in a tight, light-resistant container.
Manufactured by: Epic Pharma, LLC Laurelton, NY 11413 Manufactured in USA Revised November 2014 MF048REV11/14 OE1126 Repackaged by: Proficient Rx LP Thousand Oaks, CA 91320
GERIATRIC USE
Geriatric Use 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 ).
INDICATIONS AND USAGE
Guanfacine hydrochloride tablets are indicated in the management of hypertension.
Guanfacine may be given alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.
PEDIATRIC USE
Pediatric Use 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.
Hallunications have been reported in pediatric patients receiving guanfacine for treatment of attention-deficit hyperactivity disorder.
PREGNANCY
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.
NUSRING MOTHERS
Nursing Mothers 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.
INFORMATION FOR PATIENTS
Information for Patients Patients who receive guanfacine should be advised to exercise caution when operating dangerous machinery or driving motor vehicles until it is determined that they do not become drowsy or dizzy from the medication.
Patients should be warned that their tolerance for alcohol and other CNS depressants may be diminished.
Patients should be advised not to discontinue therapy abruptly.
DOSAGE AND ADMINISTRATION
The recommended initial dose of guanfacine (as the hydrochloride) when given alone or in combination with another antihypertensive drug is 1 mg daily given at bedtime to minimize somnolence.
If after 3 to 4 weeks of therapy, 1 mg does not give a satisfactory result, a dose of 2 mg may be given, although most of the effect of guanfacine is seen at 1 mg (see CLINICAL PHARMACOLOGY ).
Higher daily doses have been used, but adverse reactions increase significantly with doses above 3 mg/day.
The frequency of rebound hypertension is low, but it can occur.
When rebound occurs, it does so after 2-4 days, which is delayed compared with clonidine hydrochloride.
This is consistent with the longer half-life of guanfacine.
In most cases, after abrupt withdrawal of guanfacine, blood pressure returns to pretreatment levels slowly (within 2-4 days) without ill effects.