Guanfacine Side Effects

ADVERSE REACTIONS Adverse reactions noted with guanfacine hydrochloride are similar to those of other drugs of the central α 2 -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 tablets could not be established, should a rash occur, guanfacine tablets 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 mg 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 % 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 % 2.0 % 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 mg to 3 mg as follows: Adverse Reaction 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 (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 %;