What is Guanfacine?
Guanfacine is a prescription medication that acts as a selective alpha-2A adrenergic receptor agonist, affecting norepinephrine signaling in the brain. It is available in two forms: immediate-release (IR, brand name Tenex), historically used for hypertension, and extended-release (ER, brand name Intuniv), approved for ADHD.
FDA-Approved Uses
Attention Deficit Hyperactivity Disorder (ADHD)
Guanfacine ER is FDA-approved for treating ADHD in children and adolescents aged 6 to 17. It can be used alone or with stimulant medications. By enhancing signaling in the prefrontal cortex, guanfacine helps improve attention, impulse control, and emotional regulation. As a non-stimulant option, it can benefit patients who do not tolerate stimulants or have conditions like anxiety or tic disorders.
High Blood Pressure (Hypertension)
Guanfacine IR is approved for treating high blood pressure in adults. It lowers blood pressure by relaxing blood vessels and reducing heart rate. However, it is not a first-line treatment due to potential side effects like sedation and dizziness.
Off-Label and Investigational Uses
Guanfacine is also used off-label for conditions such as Tourette's Syndrome, Oppositional Defiant Disorder (ODD), Post-Traumatic Stress Disorder (PTSD), and adult ADHD.
Dosage and Administration
Guanfacine dosage depends on the form and condition. Treatment typically begins with a low dose and is gradually increased.
Key Administration Guidelines:
- For ADHD (ER tablets): Take once daily at the same time. Swallow tablets whole and avoid high-fat meals.
- For Hypertension (IR tablets): Usually taken at bedtime.
- Tapering: Do not stop guanfacine abruptly due to the risk of rebound hypertension and withdrawal symptoms. Discontinuation must be supervised by a healthcare provider.
Important Warnings and Precautions
Patients should be aware of potential side effects and drug interactions.
Potential Side Effects
Common side effects include drowsiness, dizziness, dry mouth, and constipation. Guanfacine can also affect blood pressure and heart rate, requiring monitoring, especially in patients with existing cardiovascular issues. Abruptly stopping the medication can cause rebound hypertension.
Drug Interactions
Guanfacine can interact with CNS depressants, alcohol, and certain medications that affect liver enzymes (CYP3A4 inhibitors and inducers), potentially altering its effects or increasing side effects.
Guanfacine vs. Clonidine
Both guanfacine and clonidine are alpha-2 adrenergic receptor agonists used for ADHD, but they differ. Guanfacine is more selective for the alpha-2A subtype and is generally less sedating, with a longer duration of action. Clonidine acts on multiple alpha-2 subtypes, is associated with more sedation, and has a shorter half-life. Both require tapering upon discontinuation.
| Feature | Guanfacine (Intuniv, ER) | Clonidine (Kapvay, ER) |
|---|---|---|
| Receptor Selectivity | More selective for alpha-2A. | Acts on all three alpha-2 subtypes (A, B, C). |
| Effect on Sedation | Generally less sedating. | Higher risk of sedation. |
| Duration of Action | Longer half-life, once-daily dosing. | Shorter half-life, more frequent dosing for IR form. |
| Comorbid Conditions | May be preferred for less sedation. | Often chosen for patients with tics or anxiety. |
| Withdrawal | Tapering necessary. | Tapering necessary, potentially milder effects. |
Conclusion
Guanfacine is a valuable medication for treating ADHD (ER formulation) and high blood pressure (IR formulation) by affecting norepinephrine pathways. While effective, it has potential side effects like drowsiness and cardiovascular changes, necessitating careful monitoring and gradual discontinuation under medical supervision to avoid rebound hypertension. Consulting a healthcare provider is crucial to determine if guanfacine is appropriate. More information is available on the MedlinePlus website MedlinePlus: Guanfacine Drug Information.
Key Side Effects
- Drowsiness/Somnolence: Common, especially initially.
- Dizziness: Can occur with positional changes.
- Fatigue: A frequently reported feeling of tiredness.
- Dry Mouth: Manageable with gum or hydration.
- Bradycardia (Slow Heart Rate): Requires monitoring.
- Hypotension (Low Blood Pressure): Possible, especially with risk factors.
- Rebound Hypertension: Risk of abrupt cessation.
