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Guanfacine (Guanfacine Hydrochloride) - Side Effects and Adverse Reactions

 
 



ADVERSE REACTIONS

Adverse reactions noted with guanfacine 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. 2

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, the frequency of the most commonly observed adverse reactions showed a dose relationship from 0.5 to 3 mg as follows: CLINICAL PHARMACOLOGY

  Adverse   Placebo   0.5 mg   1 mg   2 mg   3 mg
  Reaction   n=59   n=60   n=61   n=60   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%  13%  7%  5%  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.

    Placebo   0.5 mg   1 mg   2 mg   3 mg
 Percent dropouts  0%  2%  5%  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:

    Placebo   0.5 mg   1 mg   2 mg   3 mg
  Adverse Reaction   n = 73   n = 72   n = 72   n = 72   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 (1%)  1 (0%)  0 (0%)  1 (1%)  3 (4%)
 Constipation  0 (0%)  0 (0%)  0 (0%)  1 (1%)  1 (1%)
 Fatigue  3 (3%)  2 (3%)  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, the most common adverse reactions noted were as follows: CLINICAL PHARMACOLOGY

    Guanfacine   Clonidine
  Adverse Reactions   (n=279)   (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 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.

  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).

An open-label postmarketing study involving 21,718 patients was conducted to assess the safety of guanfacine (as the 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. Postmarketing Experience:

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

MUSCULOSKELETAL 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.



REPORTS OF SUSPECTED GUANFACINE SIDE EFFECTS / ADVERSE REACTIONS

Below is a sample of reports where side effects / adverse reactions may be related to Guanfacine. The information is not vetted and should not be considered as verified clinical evidence.

Possible Guanfacine side effects / adverse reactions in 10 year old female

Reported by a consumer/non-health professional from United States on 2011-10-31

Patient: 10 year old female

Reactions: Confusional State, Swelling Face, Dyspepsia, Swollen Tongue, Coordination Abnormal, Blood Pressure Decreased, Complex Partial Seizures

Suspect drug(s):
Guanfacine
    Administration route: Oral
    Indication: Abnormal Behaviour
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01



Possible Guanfacine side effects / adverse reactions in 10 year old female

Reported by a consumer/non-health professional from United States on 2011-11-17

Patient: 10 year old female

Reactions: Confusional State, Swelling Face, Swollen Tongue, Dyspepsia, Sedation, Coordination Abnormal, Complex Partial Seizures, Blood Pressure Decreased

Suspect drug(s):
Guanfacine
    Administration route: Oral
    Indication: Abnormal Behaviour
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01



Possible Guanfacine side effects / adverse reactions in 10 year old female

Reported by a consumer/non-health professional from United States on 2011-12-02

Patient: 10 year old female

Reactions: Confusional State, LIP Swelling, Chest Discomfort, Swelling Face, Dyspnoea, Swollen Tongue, Fatigue, Syncope, Dyspepsia, Sedation, Dizziness, Coordination Abnormal, Complex Partial Seizures, Blood Pressure Decreased

Suspect drug(s):
Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01

Guanfacine
    Administration route: Oral
    Indication: Abnormal Behaviour
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Administration route: Oral
    Indication: Autism
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Administration route: Oral
    Indication: Aggression
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01

Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01

Guanfacine
    Administration route: Oral
    Indication: Autism Spectrum Disorder
    Start date: 2009-11-13
    End date: 2009-12-14

Guanfacine
    Dosage: 1/2 tablet 3 times daily
    Administration route: Oral
    Start date: 2009-12-15
    End date: 2010-02-01



See index of all Guanfacine side effect reports >>

Drug label data at the top of this Page last updated: 2013-01-30

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