Why is this medication prescribed?
Guanfacine tablets (Tenex) are used alone or in combination with other medications to treat high blood pressure. Guanfacine extended-release (long-acting) tablets (Intuniv) are used as part of a treatment program to control symptoms of attention deficit hyperactivity disorder (ADHD; more difficulty focusing, controlling actions, and remaining still or quiet than other people who are the same age) in children. Guanfacine is in a class of medications called centrally acting alpha2A-adrenergic receptor agonists. Guanfacine treats high blood pressure by decreasing heart rate and relaxing the blood vessels so that blood can flow more easily through the body. Guanfacine extended-release tablets may treat ADHD by affecting the part of the brain that controls attention and impulsivity.
High blood pressure is a common condition and when not treated, can cause damage to the brain, heart, blood vessels, kidneys and other parts of the body. Damage to these organs may cause heart disease, a heart attack, heart failure, stroke, kidney failure, loss of vision, and other problems. In addition to taking medication, making lifestyle changes will also help to control your blood pressure. These changes include eating a diet that is low in fat and salt, maintaining a healthy weight, exercising at least 30 minutes most days, not smoking, and using alcohol in moderation.
How should this medicine be used?
Guanfacine comes as a tablet and as an extended-release tablet to take by mouth. The tablet is usually taken once a day at bedtime. The extended-release tablet is usually taken once a day and should not be taken with a high fat meal. Take guanfacine at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take guanfacine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
Swallow the extended-release tablets whole with a small amount of water or another liquid; do not break, chew, or crush them.
Your doctor will probably start you on a low dose of guanfacine and may gradually increase your dose, not more often than once a week if you are taking the extended-release tablets, and not more often than once every 3-4 weeks if you are taking the tablets.
Guanfacine may control your condition, but will not cure it. It may take 2 weeks before you feel the full benefit of guanfacine extended-release tablets. Continue to take guanfacine even if you feel well. Do not stop taking guanfacine without talking to your doctor. If you suddenly stop taking guanfacine, your blood pressure may increase and you may become nervous or anxious. Your doctor will probably decrease your dose gradually.
Other uses for this medicine
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.
What special precautions should I follow?
Before taking guanfacine,
- tell your doctor and pharmacist if you are allergic to guanfacine, any other medications, or any of the ingredients in guanfacine tablets or extended-release tablets. Ask your pharmacist for a list of the ingredients.
- you should know that guanfacine is the active ingredient in guanfacine tablets and guanfacine extended-release tablets. Do not take both of these products at the same time.
- tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take. Be sure to mention any of the following: antidepressants; antihistamines; barbiturates such as phenobarbital (Luminal); carbamazepine (Carbatrol, Epitol, Equetro, Tegretol); clarithromycin (Biaxin, in PrevPac); indinavir (Crixivan); itraconazole (Onmel, Sporanox); ketoconazole (Nizoral); medications for anxiety, high blood pressure, mental illness, nausea, or seizures; nefazodone; nelfinavir (Viracept); phenytoin (Dilantin, Phenytek); pioglitazone (Actos, in Actoplus Met, in Duetact, in Oseni); rifabutin (Mycobutin); rifampin (Rifadin, in Rifamate, in Rifater, Rimactane); ritonavir (Norvir, in Kaletra); sedatives; sleeping pills; tranquilizers; and valproic acid (Depakene). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- tell your doctor what herbal products you are taking, especially St. John's wort.
- tell your doctor if you have ever fainted, or if you have recently had a heart attack; and if you have or have ever had a stroke; low blood pressure; a slow heart rate; bipolar disorder (manic depressive disorder; a disease that causes episodes of depression, episodes of mania, and other abnormal moods); or heart, kidney or liver disease.
- tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking guanfacine, call your doctor.
- if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking guanfacine.
- you should know that guanfacine may make you drowsy or dizzy. Do not drive a car or operate machinery until you know how this medication affects you.
- ask your doctor about the safe use of alcoholic beverages while you are taking guanfacine. Alcohol can make the side effects from guanfacine worse.
- you should know that guanfacine may cause dizziness, lightheadedness, and fainting when you get up too quickly from a lying position. This is more common when you first start taking guanfacine. To avoid this problem, get out of bed slowly, resting your feet on the floor for a few minutes before standing up.
- you should know that you may faint if you become dehydrated or overheated during your treatment with guanfacine. Be sure to drink plenty of liquids and stay cool while you are taking this medication.
- you should know that guanfacine should be used as part of a total treatment program for ADHD, which may include counseling and special education. Make sure to follow all of your doctor's and/or therapist's instructions.
What special dietary instructions should I follow?
Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.
What should I do if I forget a dose?
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are taking guanfacine extended-release tablets, and miss two or more doses in a row, call your doctor.
What side effects can this medication cause?
Guanfacine may cause side effects. Tell your doctor if any of these symptoms or those listed in the SPECIAL PRECAUTIONS section are severe or do not go away:
- dry mouth
- decreased sexual ability
- decreased appetite
- stomach pain
Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:
- blurred vision
- slow heart rate
Guanfacine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.
If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at http://www.fda.gov/Safety/MedWatch] or by phone [1-800-332-1088].
What should I know about storage and disposal of this medication?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.
In case of emergency/overdose
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.
Symptoms of overdose may include:
- lack of energy
- slow heart rate
- blurred vision
- smaller pupils (black circles in the middle of the eyes)
What other information should I know?
Keep all appointments with your doctor. Your blood pressure and heart rate should be checked regularly to determine your response to guanfacine.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.