Guanfacine (drug): what it is, and characteristics of this drug
Guanfacine is an antihypertensive drug used for the treatment of ADHD (Attention Deficit Hyperactivity Disorder) and for cases of high blood pressure. It is a selective adrenergic receptor agonist.
In this article we will know the characteristics of this drug (format, administration, mechanism of action…), its indications, adverse effects, studies and precautions to be taken into account for its use.
Guanfacina: general characteristics
Guanfacine is an antihypertensive drug, with the trade name “Intuniv”. Chemically, it is derived from phenylacetylguanidine. Its mechanism of action is based on an adrenergic agonism (adrenaline) selective for the alpha 2A receptors (α2A).
The effects of guanfacine are to lower blood pressure. How does it do this? By activating the receptors in the brain stem and inhibiting the activity of the sympathetic system (this system is part of the autonomic nervous system (ANS) and is related to the activation and preparation of the body for fighting).
All this translates into a reduction of the nervous impulses of the heart and blood vessels; in other words, the guanfacine relaxes the latter, also reducing the blood pressure and improving the blood flow.
Mechanism of action
Thus, the mechanism of action of guanfacine consists, as we said, in producing a selective agonist effect on alpha 2A adrenergic receptors .
In the case of guanfacine administration for Attention Deficit Hyperactivity Disorder (ADHD), which we will see later, the exact mechanism that produces the therapeutic effects is unknown; however, preclinical studies suggest actions on the prefrontal cortex and basal ganglia. These actions are related to intervention on noradrenaline in the aforementioned receptors.
Guanfacine is administered orally (in tablet format) . Its recommended starting dose is usually once a day; ideally in the morning or evening. Guanfacine, like many other drugs, can be taken with or without food. On the other hand, something to emphasize is that it is not recommended to be taken with foods rich in fat, nor with grapefruit juice.
Its tablets are extended release, and correspond to the following amounts: 1 mg, 2 mg, 3 mg or 4 mg.
The indications for guanfacine include cases of high blood pressure and Attention Deficit Hyperactivity Disorder (ADHD), and it has been approved for both types of pathologies. In the case of high blood pressure, guanfacine is usually used in combination with other medications to reduce this tension.
On the other hand, in the case of ADHD, a series of specifications are established for the administration of guanfacine: will be used only in children and adolescents between the ages of 17 and 18 , and in cases where stimulants have been used previously and have not provided good results, not being tolerated or showing ineffectiveness.
Furthermore, in this second case, it should be used as part of a comprehensive treatment of ADHD that also includes psychological treatment and educational and social measures.
Considerations and precautions
The only contraindication of guanfacin is to manifest a hypersensitivity to it. As for precautions, in cases of liver failure it will sometimes be necessary to reduce the dose.
On the other hand, in relation to pregnancy and breastfeeding , it is not recommended to take guanfacine when pregnant, nor if you are a woman, are of childbearing age and do not use any contraceptive method.
It is not known exactly if guanfacin (or its metabolites) is excreted in breast milk in the nursing period, but animal studies suggest that it is. Thus, breastfeeding women should evaluate the risks and benefits of their case, and assess the best option (either stopping breastfeeding or discontinuing guanfacin treatment).
Another aspect to consider is that we should not suddenly stop taking guanfacine, as this could cause a rise in blood pressure. Finally, you should avoid taking guanfacine when you have to drive , or when you have to do any task that requires a high level of alertness.
Use in ADHD
The typical drug treatment used for Attention Deficit Hyperactivity Disorder (ADHD) is stimulants. However, guanfacine has also been used for these cases, although it is not a stimulant. It is not known exactly what the mechanism of action of guanfacine is in ADHD, but it is known that it interacts with the brain areas involved in attention and impulses .
Specifically, delayed-release (or extended-release) guanfacin has been used for this purpose, proving to be an effective and well-tolerated treatment option for patients. In fact, it is approved by the FDA for children with ADHD over 6 years. The FDA is the US government agency responsible for regulating drugs and other products (cosmetics, medical devices, biological products…).
1. Adverse effects on ADHD
The adverse effects that have been found with the administration of guanfacine for ADHD have been, from more to less frequent: drowsiness, tiredness and/or fatigue (in 40% of cases), headache (25%) and abdominal pain (less frequent, only 10% of cases).
On the other hand, the symptom of drowsiness is improved when delayed-release guanfacin is given together with some kind of stimulants, such as methylphenidate (trade name: rubifen, medikinet or concerta) or lysdexamphetamine (elvanse). Stimulant-associated guanfacine thus provides a better therapeutic response than given alone, as it alleviates the adverse effects of the stimulant.
Although guanfacine has been shown to be effective in some cases of ADHD, there is not enough research to know the effects of the use of long-term release guanfacine (used for several years), in children from 6 years old. That is why we must be cautious.
Some of the adverse reactions to guanfacine are sedation, dizziness, hypotension, nightmares, constipation, nausea, vomiting, diarrhea, emotional lability, anxiety, depression , reduced appetite or weight gain and abdominal pain.
In addition, it is known that drinking alcohol along with guanfacine intake may lead to an increase in some of these adverse reactions.
In relation to the adverse effects of guanfacine on the heart, we find: low blood pressure, slow heart rate and other alterations in heart rhythm. These effects are severe enough to require medical supervision (and monitoring).
- Charach, A., Dashti, B., Carson, P., Booker, L., Lim, C.G., Yeung, E., Ma, J., Raina, P. and Schachar, R. (2011). Attention Deficit Hyperactivity Disorder: Effectiveness of Treatment in At-Risk Preschoolers; Long-term Effectiveness in All Ages; and Variability in Prevalence, Diagnosis, and Treatment. Rockville (MD): Agency for Healthcare Research and Quality (US), 12.
- Martín Fernández-Mayoralas, D. (2017). Update on the pharmacological treatment of ADHD (III). Delayed-release guanfacin (GRX). Adverse effects. Neurology, Ruber Juan Bravo Hospital Complex, Quirón Salud.
- Vademecum. (2016). Guanfacina.