Guanfacine (Intuniv)

Guanfacine (Trade name: Intuniv) is an alpha 2-adrenergic agonist most commonly used in the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD).

See also article: Introduction to Pharmacology

Absorption	Taking a high-fat meal was found to increase absorption considerably (Tmax = 5-6 hours, IR = 1-4 hours)
Distribution	6.3L/kg
Metabolism	Hepatic, oxidation (phase I) and glucuronidation (phase II)
Elimination	Excreted by both the liver and the kidney
Half-life	• 13-14 hrs in children/adolescents  • 17-18 hours in adults

See also article: Cytochrome (CYP) P450 Metabolism

Substrate of (Metabolized by)	3A4 (3A5, 2C9, and 2C19)
Induces	Does not induce any of the major CYP enzymes
Inhibits	Does not inhibit any of the major CYP enzymes

Starting
Titration
Maximum
Taper	Taper the daily dose no more than 1 mg every 3 to 7 days to reduce the risk of rebound hypertension.

Precautions advised in those with a history of bradycardia, cardiovascular disease, heart block, hypotension, and syncope

QT prolonging drugs (e.g. - quetiapine, quinidine) – since guanfacine XR may cause a decrease in heart rate, concomitant use with QT prolonging drugs is not recommended
Beta-blockers may increase risk of rebound hypertensive effect if guanfacine XR is stopped abruptly
Anticonvulsants
- Guanfacine XR may increase serum concentrations of valproic acid
- Carbamazepine, phenobarbital and phenytoin may increase serum concentrations of guanfacine XR through CYP3A4 induction
CYP3A4 inducers or inhibitors (e.g. - rifampin, fluconazole, ritonavir)
- Inducers may increase serum concentrations of guanfacine XR
- Inhibitors may decrease serum concentrations of guanfacine XR

See main article: Geriatric Pharmacology

See main article: Pediatric Pharmacology

See main article: Obstetric and Fetal Pharmacology

See main article: Psychotropic Dosing in the Medically Ill

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