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Guanfacine
Overview
What is Guanfacine Hydrochloride?
Guanfacine hydrochloride, USP is a centrally acting antihypertensive with α
-adrenoceptor agonist properties in tablet form for oral administration.
The chemical name of guanfacine hydrochloride, USP is N-amidino-2-(2,6-dichlorophenyl) acetamide hydrochloride and its molecular weight is 282.56. Its structural formula is:
Guanfacine hydrochloride, USP 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, USP equivalent to 1 mg or 2 mg guanfacine. In addition, each tablet contains the following inactive ingredients: microcrystalline cellulose, pregelatinized starch, and stearic acid.
What does Guanfacine Hydrochloride look like?
What are the available doses of Guanfacine Hydrochloride?
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What should I talk to my health care provider before I take Guanfacine Hydrochloride?
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How should I use Guanfacine Hydrochloride?
Guanfacine tablets, USP are indicated in the management of hypertension. Guanfacine may be given alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.
The recommended initial dose of guanfacine tablets, USP 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
). 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 to 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 to 4 days) without ill effects.
What interacts with Guanfacine Hydrochloride?
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What are the warnings of Guanfacine Hydrochloride?
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What are the precautions of Guanfacine Hydrochloride?
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What are the side effects of Guanfacine Hydrochloride?
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What should I look out for while using Guanfacine Hydrochloride?
Guanfacine tablets, USP are contraindicated in patients with known hypersensitivity to guanfacine hydrochloride, USP.
What might happen if I take too much Guanfacine Hydrochloride?
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 to 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%).
How should I store and handle Guanfacine Hydrochloride?
Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK Guanfacine tablets, USP are available in 2 tablet strengths of guanfacine (as the hydrochloride salt) as follows:1 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “711” on the other side. 2 mg: white, oval, flat-faced, beveled-edge tablet with “AN” on one side and “713” on the other side. NDC 50268-374-15 (10 tablets per card, 5 cards per carton). Dispensed in Unit Dose Package. For Institutional Use Only. Store at 20º to 25 ºC (68 ºF to 77 ºF) [see USP Controlled Room Temperature]. Manufactured for: AvKARE, Inc. Pulaski, TN 38478 Mfg. Rev. 11-2015-00 AV 05/17 (P) AvPAK
Clinical Information
Chemical Structure
No Image foundClinical Pharmacology
Guanfacine hydrochloride is an orally active antihypertensive agent whose principal mechanism of action appears to be stimulation of central α
-adrenergic receptors. By stimulating these receptors, guanfacine reduces sympathetic nerve impulses from the vasomotor center to the heart and blood vessels. This results in a decrease in peripheral vascular resistance and a reduction in heart rate.
The dose-response relationship for blood pressure and adverse effects of guanfacine given once a day as monotherapy has been evaluated in patients with mild to moderate hypertension. In this study patients were randomized to placebo or to 0.5 mg, 1 mg, 2 mg, 3 mg or 5 mg of guanfacine. Results are shown in the following table. A useful effect was not observed overall until doses of 2 mg were reached, although responses in white patients were seen at 1 mg; 24 hour effectiveness of 1 mg to 3 mg doses was documented using 24 hour ambulatory monitoring. While the 5 mg dose added an increment of effectiveness, it caused an unacceptable increase in adverse reactions.
Controlled clinical trials in patients with mild to moderate hypertension who were receiving a thiazide-type diuretic have defined the dose-response relationship for blood pressure response and adverse reactions of guanfacine given at bedtime and have shown that the blood pressure response to guanfacine can persist for 24 hours after a single dose. In the 12-week placebo-controlled dose-response study, patients were randomized to placebo or to doses of 0.5, 1, 2 and 3 mg of guanfacine, in addition to 25 mg chlorthalidone, each given at bedtime. The observed mean changes from baseline, tabulated below, indicate the similarity of response for placebo and the 0.5 mg dose. Doses of 1, 2 and 3 mg resulted in decreased blood pressure in the sitting position with no real differences among the three doses. In the standing position, there was some increase in response with dose.
While most of the effectiveness of guanfacine in combination (and as monotherapy in white patients) was present at 1 mg, adverse reactions at this dose were not clearly distinguishable from those associated with placebo. Adverse reactions were clearly present at 2 and 3 mg (see
).
In a second 12-week placebo-controlled study of 1, 2 or 3 mg of guanfacine hydrochloride administered with 25 mg of chlorthalidone once daily, a significant decrease in blood pressure was maintained for a full 24 hours after dosing. While there was no significant difference between the 12 and 24 hour blood pressure readings, the fall in blood pressure at 24 hours was numerically smaller, suggesting possible escape of blood pressure in some patients and the need for individualization of therapy.
In a double-blind, randomized trial, either guanfacine or clonidine was given at recommended doses with 25 mg chlorthalidone for 24 weeks and then abruptly discontinued. Results showed equal degrees of blood pressure reduction with the two drugs and there was no tendency for blood pressures to increase despite maintenance of the same daily dose of the two drugs. Signs and symptoms of rebound phenomena were infrequent upon discontinuation of either drug. Abrupt withdrawal of clonidine produced a rapid return of diastolic and especially systolic blood pressure to approximately pretreatment levels, with occasional values significantly greater than baseline, whereas guanfacine withdrawal produced a more gradual increase to pretreatment levels, but also with occasional values significantly greater than baseline.
Pharmacodynamics
Hemodynamic studies in man showed that the decrease in blood pressure observed after singledose or long-term oral treatment with guanfacine was accompanied by a significant decrease in peripheral resistance and a slight reduction in heart rate (5 beats/min). Cardiac output under conditions of rest or exercise was not altered by guanfacine.
Guanfacine hydrochloride lowered elevated plasma renin activity and plasma catecholamine levels in hypertensive patients, but this does not correlate with individual blood-pressure responses.
Growth hormone secretion was stimulated with single oral doses of 2 and 4 mg of guanfacine. Long-term use of guanfacine had no effect on growth hormone levels.
Guanfacine had no effect on plasma aldosterone. A slight but insignificant decrease in plasma volume occurred after one month of guanfacine therapy. There were no changes in mean body weight or electrolytes.
Non-Clinical Toxicology
Guanfacine tablets, USP are contraindicated in patients with known hypersensitivity to guanfacine hydrochloride, USP.Like other antihypertensive agents, guanfacine hydrochloride should be used with caution in patients with severe coronary insufficiency, recent myocardial infarction, cerebrovascular disease, or chronic renal or hepatic failure.
Sedation
Guanfacine, like other orally active central α -adrenergic agonists, causes sedation or drowsiness, especially when beginning therapy. These symptoms are dose-related (see ). When guanfacine is used with other centrally active depressants (such as phenothiazines, barbiturates, or benzodiazepines), the potential for additive sedative effects should be considered.
Adverse reactions noted with guanfacine hydrochloride are similar to those of other drugs of the central α -adrenoreceptor agonist class: dry mouth, sedation (somnolence), weakness (asthenia), dizziness, constipation, and impotence. While the reactions are common, most are mild and tend to disappear on continued dosing.
Skin rash with exfoliation has been reported in a few cases; although clear cause and effect relationships to guanfacine could not be established, should a rash occur, guanfacine should be discontinued and the patient monitored appropriately.
In the dose-response monotherapy study described under CLINICAL PHARMACOLOGY, the frequency of the most commonly observed adverse reactions showed a dose relationship from 0.5 to 3 mg as follows:
The percent of patients who dropped out because of adverse reactions are shown below for each dosage group.
The most common reasons for dropouts among patients who received guanfacine were dry mouth, somnolence, dizziness, fatigue, weakness and constipation.
In the 12-week, placebo-controlled, dose-response study of guanfacine administered with 25 mg chlorthalidone at bedtime, the frequency of the most commonly observed adverse reactions showed a clear dose relationship from 0.5 to 3 mg as follows:
There were 41 premature terminations because of adverse reactions in this study. The percent of patients who dropped out and the dose at which the dropout occurred were as follows:
Reasons for dropouts among patients who received guanfacine were: somnolence, headache, weakness, dry mouth, dizziness, impotence, insomnia, constipation, syncope, urinary incontinence, conjunctivitis, paresthesia and dermatitis.
In a second 12-week placebo-controlled combination therapy study in which the dose could be adjusted upward to 3 mg per day in 1 mg increments at 3-week intervals, i.e., a setting more similar to ordinary clinical use, the most commonly recorded reactions were: dry mouth, 47%; constipation, 16%; fatigue, 12%; somnolence, 10%; asthenia, 6%; dizziness, 6%; headache, 4%; and insomnia, 4%.
Reasons for dropouts among patients who received guanfacine were: somnolence, dry mouth, dizziness, impotence, constipation, confusion, depression and palpitations.
In the clonidine/guanfacine comparison described in CLINICAL PHARMACOLOGY, the most common adverse reactions noted were as follows:
Adverse reactions occurring in 3% or less of patients in the three controlled trials of guanfacine hydrochloride with a diuretic were:
• Cardiovascular: bradycardia, palpitations, substernal pain
• Gastrointestinal: abdominal pain, diarrhea, dyspepsia, dysphagia, nausea
• CNS: amnesia, confusion, depression, insomnia, libido decrease
• ENT disorders: rhinitis, taste perversion, tinnitus
• Eye disorders: conjunctivitis, iritis, vision disturbance
• Musculoskeletal: leg cramps, hypokinesia
• Respiratory: dyspnea
• Dermatologic: dermatitis, pruritus, purpura, sweating
• Urogenital: testicular disorder, urinary incontinence
• Other: malaise, paresthesia, paresis
Adverse reaction reports tend to decrease over time. In an open-label trial of one year’s duration, 580 hypertensive subjects were given guanfacine, titrated to achieve goal blood pressure, alone (51%), with diuretic (38%), with beta blocker (3%), with diuretic plus beta blocker (6%), or with diuretic plus vasodilator (2%). The mean daily dose of guanfacine reached was 4.7 mg.
There were 52 (8.9%) dropouts due to adverse effects in this 1-year trial. The causes were: dry mouth (n = 20), weakness (n = 12), constipation (n = 7), somnolence (n = 3), nausea (n = 3), orthostatic hypotension (n = 2), insomnia (n = 1), rash (n = 1), nightmares (n = 1), headache (n = 1) and depression (n = 1).
Postmarketing Experience
An open-label postmarketing study involving 21,718 patients was conducted to assess the safety of guanfacine hydrochloride 1 mg/day given at bedtime for 28 days. Guanfacine was administered with or without other antihypertensive agents. Adverse events reported in the postmarketing study at an incidence greater than 1% included dry mouth, dizziness, somnolence, fatigue, headache and nausea. The most commonly reported adverse events in this study were the same as those observed in controlled clinical trials.
Less frequent, possibly guanfacine-related events observed in the postmarketing study and/or reported spontaneously include:
• Body as a Whole: asthenia, chest pain, edema, malaise, tremor
• Cardiovascular: bradycardia, palpitations, syncope, tachycardia
• Central Nervous System: paresthesias, vertigo
• Eye Disorders: blurred vision
• Gastrointestinal System: abdominal pain, constipation, diarrhea, dyspepsia
• Liver and Biliary System: abnormal liver function tests
• Musculo-Skeletal System: arthralgia, leg cramps, leg pain, myalgia
• Psychiatric: agitation, anxiety, confusion, depression, insomnia, nervousness
• Reproductive System, Male: impotence
• Respiratory System: dyspnea
• Skin and Appendages: alopecia, dermatitis, exfoliative dermatitis, pruritus, rash
• Special Senses: alterations in taste
• Urinary System: nocturia, urinary frequency
Rare, serious disorders with no definitive cause and effect relationship to guanfacine have been reported spontaneously and/or in the postmarketing study. These events include acute renal failure, cardiac fibrillation, cerebrovascular accident, congestive heart failure, heart block, and myocardial infarction.
Reference
This information is obtained from the National Institute of Health's Standard Packaging Label drug database.
"https://dailymed.nlm.nih.gov/dailymed/"
While we update our database periodically, we cannot guarantee it is always updated to the latest version.
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