Guanfacine: 7 things you should know
Medically reviewed by Carmen Fookes, BPharm. Last updated on Apr 8, 2020.
1. How it works
- Guanfacine reduces blood pressure by stimulating alpha2 adrenergic receptors in the brain. This stimulation reduces nerve impulses from the vasomotor center (located in the medulla oblongata of the brain) to the heart and blood vessels. As a result, the heart rate reduces and blood vessels dilate (widen), reducing how hard the heart has to work to pump blood around the body.
- Experts are not sure how guanfacine works in attention deficit hyperactivity disorder (ADHD).
- Guanfacine belongs to the class of medicines known as centrally acting alpha 2A-adrenergic receptor agonists.
- May be used in the treatment of high blood pressure (applies to the brand of guanfacine called Tenex).
- A once-daily extended-release form of guanfacine (Intuniv) is approved for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents aged 6 to 17 years.
- A generic form of Tenex is available under the name guanfacine hydrochloride. A generic form of Intuniv is available under the name of guanfacine hydrochloride extended release.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Dry mouth, sedation, dizziness, constipation, erectile dysfunction, fatigue, and weakness are the most common side effects. Most side effects resolve with continued dosing.
- Hallucinations have been reported as a side effect in children taking guanfacine for ADHD.
- May not be suitable for people with severe heart disease, a recent heart attack, history of stroke, or severe kidney or liver disease. Elderly people may be more sensitive to the side effects of guanfacine.
- Guanfacine causes drowsiness, particularly on initiation of therapy. Night-time dosing may minimize this effect; however, people should not drive or operate machinery or perform other hazardous tasks if they are affected. The sedative effect of guanfacine may be enhanced with higher dosages and when used in combination with other drugs that cause sedation, including alcohol.
- Abrupt cessation of guanfacine has been associated with symptoms of nervousness and anxiety and occasionally increased blood pressure. Guanfacine should be discontinued slowly.
- The extended-release Intuniv brand of guanfacine is more expensive than the immediate-release Tenex brand.
- May interact with a number of other drugs including those that also lower blood pressure or cause sedation. Medications that induce or inhibit liver enzymes such as phenytoin and phenobarbital may also affect levels of guanfacine.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- The usual dosage of guanfacine for high blood pressure is 1mg at bedtime. Occasionally the dosage may need increasing to 2mg at bedtime if a satisfactory response has not been seen within three to four weeks. Follow your doctor's instructions and take as directed.
- Do not drive or operate machinery or perform other hazardous tasks if guanfacine makes you drowsy. Alcohol is best avoided while taking guanfacine.
- Do not stop guanfacine suddenly. If guanfacine needs to be discontinued, your doctor will advise you how to taper the dose.
- Do not take any other medications, including those bought over the counter, without first checking with your doctor or pharmacist that these are compatible with guanfacine.
- Report any serious side effects, such as extreme sedation, hallucinations, chest pain or an irregular heartbeat, severe constipation or an excessively dry mouth to your doctor.
- If your mouth feels dry while taking guanfacine, try sucking on a piece of sugar-free hard candy, chewing sugar-free gum, chewing ice-chips, or use a saliva substitute. Having a dry mouth increases your risk of developing gum disease and cavities. Brush and floss your teeth regularly and visit your dentist every six months for a check-up.
- Drink plenty of fluids throughout the day to ensure you remain well hydrated because dehydration may increase your risk of low blood pressure (and therefore your risk of falls).
6. Response and Effectiveness
- Peak plasma concentrations occur within one to four hours of a single dose of immediate release guanfacine (average time to peak is 2.6 hours). The effect of guanfacine lasts approximately 24 hours.
Medicines that interact with guanfacine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with guanfacine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may interact with guanfacine include:
- antibiotics, such as ciprofloxacin, clarithromycin, erythromycin, fluconazole, or itraconazole
- anticonvulsants, such as carbamazepine,
- antidepressants, such as amitriptyline, clomipramine, desipramine, doxepin, escitalopram, imipramine, or nortriptyline
- antifungals, such as voriconazole
- antipsychotics, such as haloperidol, thioridazine, or ziprasidone
- antivirals, such as boceprevir
- barbiturates, such as phenobarbital
- benzodiazepines, such as diazepam, oxazepam, and temazepam
- biologics, such as imatinib
- diuretics, such as amiloride, bendroflumethiazide, or furosemide
- heart medications, such as acebutolol, amiodarone, atenolol, candesartan, diltiazem, felodipine, or sotalol
- HIV medications, such as amprenavir, atazanavir, cobicistat, efavirenz or saquinavir
- medications used to treat ADHD such as dextroamphetamine or lisdexamfetamine
- monoamine oxidase inhibitors, such as isocarboxazid, selegiline, or tranylcypromine
- opioids, such as fentanyl, oxycodone, methadone, morphine, or codeine
- Parkinson's disease medications, such as selegiline or levodopa
- sedatives, or any medication that causes sedation, such as sleeping pills, muscle relaxants, or other antidepressants
- St John's wort
- steroids, such as betamethasone, budesonide, cortisone, or dexamethasone.
Note that this list is not all-inclusive and includes only common medications that may interact with guanfacine. You should refer to the prescribing information for guanfacine for a complete list of interactions.
Guanfancine. Revised 11/2019. Drugs.com https://www.drugs.com/ppa/guanfacine.html
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use guanfacine only for the indication prescribed.
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- Drug class: antiadrenergic agents, centrally acting