Guanfacine

INDICATIONS AND USAGE Guanfacine Tablets, USP are indicated in the management of hypertension. Guanfacine hydrochloride may be given alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.

DOSAGE AND ADMINISTRATION The recommended initial dose of guanfacine 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 hydrochloride 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.

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 hydrochloride could not be established, should a rash occur, guanfacine hydrochloride 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=60 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 to 3 mg as follows: Adeverse 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 (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 pateints 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 Reactions 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 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. Adverse Reaction Incidence of adverse reactions at any time during the study n = 580 Incidence of adversed reactions at end of the one year 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 hydrochloride 1 mg/day given at bedtime for 28 days. Guanfacine hydrochloride 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 hydrochloride-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 BILLIARY SYSTEM abnormal liver function tests MUSCULO­ SKELETAL SYSTEM arthralgia, leg cramps, leg pain, myalgia PSYCHIATRIC agitation, anxiety, confusion, depression, insomnia, nervousness RREPRODUCTIVE 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 hydrochloride 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.

Drug Interactions The potential for increased sedation when guanfacine hydrochloride 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 hydrochloride 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 hydrochloride have been identified.

HOW SUPPLIED Guanfacine Tablets, USP are available in the following dosing strengths (expressed in equivalent amounts of guanfacine): 1 mg—white round tablets, debossed “i3” on one side and “18” on the other side in bottles of 100 (NDC 73141-018-04). 2 mg—White round tablets, debossed “i3” on one side and “19” on the other side in bottles of 100 (NDC 73141-019-04). Store at controlled temperature, between 20°C and 25°C (68°F and 77°F). Dispense in a tight, light-resistant container. Distributed by: A2A Integrated Pharmaceuticals Franklin, KY 42134 PI0019-02 R02/25 Revised: February 2025