Guanfacine Hydrochloride
Brand Name: Tenex, Intuniv
Generic Available
Common Dosage Forms:
Tablets, immediate-release: 1 mg, 2 mg
Tablets, extended-release (Intuniv): 1 mg, 2 mg, 3 mg, 4 mg
FDA Indications/Dosages:
For the treatment of hypertension, alone or in combination with other antihypertensives, especially thiazide-type diuretics: 1 mg given at bedtime is recommended. Up to 3 mg may be given. Use a divided dose if the patient shows a rise in pressure toward the end of the dosing interval.
For the treatment of Attention-Deficit Hyperactivity DIsorder (ADHD) as monotherapy and as adjunctive therapy to stimulant medications: Begin with 1 mg once daily. Increase weekly to reach the target dose of 1 mg to 4 mg daily.
Pharmacology/Pharmacokinetics: Guanfacine stimulates central alpha-2-adrenergic receptors thereby reducing sympathetic nerve transmission from the vasomotor center in the CNS to the heart and blood vessels. This results in a decreased peripheral resistance and a reduction in the heart rate. Its exact mechanism of action in ADHD is not known. Peak plasma concentrations occur in 1-4 hours (IR) or 5 hours (ER). Average half-life approaches 17 hours. Excreted primarily in the urine, 50% unchanged and the remaining as conjugates. 70% is bound to plasma proteins.
Drug Interactions: Strong CYP3A4/5 inhibitors (ketoconazole) may increase plasma levels. Rifampin may decrease serum levels. Additive sedative effects are seen with antihypertensives and CNS depressants. May increase plasma concentrations of valproic acid.
Contraindications/Precautions: Use with caution in patients with severe coronary insufficiency, recent myocardial infarction, cerebrovascular disease, or chronic renal or hepatic failure. Drowsiness is pronounced during initiation of therapy. Pregnancy Category B.
Adverse Effects: Dry mouth, drowsiness, weakness, dizziness, constipation, headache, insomnia, and impotence.
Patient Consultation:
Do not take extended-release tablets with a high-fat meal.
Swallow extended-release tablets whole, do not chew, crush, or split.
Do not discontinue therapy abruptly.
May cause drowsiness. Use care when operating machinery or when alertness is required.
Avoid alcohol while taking this medication, tolerance may be diminished.
If a dose is missed, take it as soon as possible. If it is closer to the time of your next dose than the time of the dose you missed, skip the missed dose and return to your dosing schedule. Do not double doses.
Contact a physician if the above side effects are severe or persistent.