Guanfacine Side Effects

Brand Names: Intuniv

Please note - some side effects for Guanfacine may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

Side Effects of Guanfacine - for the Consumer

Guanfacine

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Guanfacine:

Constipation; dizziness; drowsiness; dry mouth; tiredness.

Seek medical attention right away if any of these SEVERE side effects occur when using Guanfacine:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); changes in heartbeat; inability to have sex; pounding in the chest.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. To report side effects to the appropriate agency, please read the Guide to Reporting Problems to FDA.

Guanfacine Extended-Release Tablets

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Guanfacine Extended-Release Tablets:

Constipation; decreased appetite; dizziness; drowsiness; dry mouth; headache; irritability; nausea; sluggishness; stomach pain; tiredness; vomiting.

Seek medical attention right away if any of these SEVERE side effects occur when using Guanfacine Extended-Release Tablets:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); fainting; severe or persistent dizziness, drowsiness, or weakness; slow or irregular heartbeat.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. To report side effects to the appropriate agency, please read the Guide to Reporting Problems to FDA.

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Guanfacine Side Effects - for the Professional

Guanfacine

Adverse reactions noted with Guanfacine are similar to those of other drugs of the central α2-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:

Adverse Reaction	Placebo n=59	0.5 mg n=60	1 mg n=61	2 mg n=60	3 mg n=59
Dry Mouth	0%	10%	10%	42%	54%
Somnolence	8%	5%	10%	13%	39%
Asthenia	0%	2%	3%	7%	3%
Dizziness	8%	12%	2%	8%	15%
Headache	8%	8%	13%	7%	3%
Impotence	0%	0%	0%	7%	3%
Constipation	0%	2%	0%	5%	15%
Fatigue	2%	2%	5%	8%	10%

The percent of patients who dropped out because of adverse reactions are shown below for each dosage group.

Dose	Placebo	0.5 mg	1 mg	2 mg	3 mg
Percent Dropouts	0%	2.0%	5.0%	13%	32%

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:

Adverse Reactions	Placebo n=73	0.5 mg n=72	1 mg n=72	2 mg n=72	3 mg n=72
Dry Mouth	5 (7%)	4 (5%)	6 (8%)	8 (11%)	20 (28%)
Somnolence	1 (1%)	3 (4%)	0 (0%)	1 (1%)	10 (14%)
Asthenia	0 (0%)	2 (3%)	0 (0%)	2 (2%)	7 (10%)
Dizziness	2 (2%)	1 (1%)	3 (4%)	6 (8%)	3 (4%)
Headache	3 (4%)	4 (3%)	3 (4%)	1 (1%)	2 (2%)
Impotence	1 (0%)	1 (0%)	0 (0%)	1 (1%)	3 (4%)
Constipation	0 (0%)	1 (0%)	0 (0%)	1 (1%)	1 (1%)
Fatigue	3 (3%)	0 (0%)	2 (3%)	5 (6%)	3 (4%)

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:

Dose	Placebo	0.5 mg	1 mg	2 mg	3 mg
Percent Dropouts	6.9%	4.2%	3.2%	6.9%	8.3%

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 Reaction	Guanfacine (n=279)	Clonidine (n=278)
Dry Mouth	30 %	37%
Somnolence	21%	35%
Dizziness	11%	8%
Constipation	10%	5%
Fatigue	9%	8%
Headache	4%	4%
Insomnia	4%	3%

Adverse reactions occurring in 3% or less of patients in the three controlled trials of Guanfacine 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 incontinuence

• 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.

Adverse Reaction	Incidence of adverse reactions at any time during the study	Incidence of adverse reactions at end of one year
	n=580	n=580
Dry Mouth	60%	15%
Drowsiness	33%	6%
Dizziness	15%	1%
Constipation	14%	3%
Weakness	5%	1%
Headache	4%	0.2%
Insomnia	5%	0%

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 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 post-marketing 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.

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Side Effects by Body System - for Healthcare Professionals

General

Guanfacine is generally well-tolerated. In a study of 580 hypertensive patients, only 7% withdrew due to adverse side effects. In addition, most side effects were mild, dose-related, and resolved over time.

Nervous system

Nervous system side effects have included fatigue or a sedative effect and dizziness in 33% and 15% of patients, respectively. After one year of therapy, the incidence of these side effects falls to 6% and 1%, respectively. Headaches occur in less than 5% of patients. Nervous system side effects associated with the extended-release formulation have included somnolence (38%), fatigue (14%), headache (24%), lethargy (6%), dizziness (6%), and postural dizziness (less than 2%).

Gastrointestinal

Gastrointestinal side effects have included dry mouth in up to 60% of patients. Constipation has been associated with the use of this drug in 14% of patients. After one year of therapy the incidence of dry mouth and constipation averages 15% and 3%, respectively. Gastrointestinal side effects associated with the extended-release formulation have included dry mouth (4%), upper abdominal pain (10%), nausea (6%), and dyspepsia (less than 2%).

Cardiovascular

Cardiovascular side effects have included orthostatic hypotension and palpitations, each of which is rare. There is limited, indirect (ECG) evidence of left ventricular hypertrophy resolution after guanfacine therapy. Cardiovascular side effects associated with the extended-release formulation have included hypotension/decreased blood pressure (6%), atrioventricular block (less than 2%), bradycardia (less than 2%), and sinus arrhythmia (less than 2%) .

Genitourinary

Genitourinary complaints in male patients are limited to impotence, which is associated with higher doses (daily doses of 3 mg or more).

Metabolic

Metabolic side effects associated with the extended-release formulation have included decreased appetite (5%), and constipation (3%).

Psychiatric

Psychiatric side effects associated with the extended-release formulation have included irritability (6%)

Respiratory

Respiratory side effects associated with the extended-release formulation have included asthma (less than 2%).

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