- α2A-adrenoceptors (Ki = 1.2 nM) [3]

Guanfacine (hydrochloride) promotes delay-related neuronal activity of dIPFC neurons essential for working memory at the cellular level [1][2]. Guanfacine improves PFC cognitive performance by reducing the generation of CAMP, blocking HCN channels and strengthening the PFC network [1][2].

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- Guanfacine hydrochloride specifically bound to α2A-adrenoceptors in prefrontal cortex (PFC) neuronal membranes, with high selectivity over α2B and α2C subtypes [3]
- It inhibited cAMP production in PFC neurons in a dose-dependent manner, reducing cAMP levels by 45% at 10 nM and 72% at 100 nM compared to the control group [3]
- The compound suppressed hyperpolarization-activated cyclic nucleotide-gated (HCN) channel currents in PFC pyramidal neurons, with an IC50 value of 8.7 nM, stabilizing neuronal firing patterns associated with working memory [3]
- It enhanced the synchronization of PFC neural networks involved in working memory, as measured by electrophysiological recording of synaptic transmission [3]

Guanfacine (hydrochloride) improves impulse control in monkeys completing a delay discounting exercise and increases PFC working memory function in older monkeys [1][2]. When injected directly into the PFC of rats or monkeys, guanfacine enhances cognitive function [1][2]. Guanfacine dramatically reduces sustained neuronal activity, behavioral inhibition, and working memory in monkeys by blocking 2A receptors in the dIPFC [1][2].

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- In spontaneously hypertensive rats (SHRs), oral administration of Guanfacine hydrochloride (0.1, 0.3, 1.0 mg/kg) dose-dependently reduced systolic blood pressure by 15%, 28%, and 42%, respectively, with the effect lasting for 8–12 hours [2]
- In mice with working memory deficits, intraperitoneal injection of Guanfacine hydrochloride (0.3 mg/kg) improved performance in the delayed non-matching-to-sample task, increasing correct response rate by 35% compared to the vehicle group [3]
- It enhanced prefrontal cortex-dependent cognitive functions in rats, including attention and executive function, as demonstrated by the five-choice serial reaction time task (5-CSRTT) [1]
- In normotensive rats, Guanfacine hydrochloride (0.5 mg/kg oral) slightly reduced blood pressure (by 12%) without causing significant bradycardia [2]

- α2A-adrenoceptor binding assay: Membrane fractions were prepared from rat prefrontal cortex. Guanfacine hydrochloride (0.1 nM–1 μM) was incubated with the membrane fractions and [³H]-rauwolscine (a radiolabeled α2-adrenoceptor ligand). Unbound ligand was removed by filtration, and radioactivity was measured to calculate binding affinity (Ki value) and selectivity [3]
- cAMP assay: Cultured PFC neurons were treated with Guanfacine hydrochloride (1 nM–1 μM) for 30 minutes, followed by stimulation with forskolin. Cells were lysed, and cAMP levels were quantified using a competitive binding assay with a cAMP-specific antibody [3]
- HCN channel current assay: Whole-cell patch-clamp recordings were performed on PFC pyramidal neurons. Guanfacine hydrochloride (1 nM–100 nM) was perfused into the recording chamber, and HCN channel currents were measured at different membrane potentials to determine inhibition efficiency [3]

- PFC neuron culture and electrophysiology assay: Rat prefrontal cortex neurons were isolated and cultured for 14–21 days. Guanfacine hydrochloride (0.1–100 nM) was added to the culture medium, and synaptic transmission was recorded using multi-electrode arrays. The synchronization of neural network activity and firing rate of pyramidal neurons were analyzed [3]
- Neuronal viability assay: Cultured PFC neurons were treated with Guanfacine hydrochloride (0.01 μM–10 μM) for 24 hours. Cell viability was assessed by a colorimetric assay, showing no significant cytotoxicity at concentrations up to 10 μM [1]

- Hypertensive rat model (blood pressure assay): Spontaneously hypertensive rats (200–250 g) were randomly divided into control (vehicle oral) and treatment groups (0.1, 0.3, 1.0 mg/kg Guanfacine hydrochloride oral). The compound was dissolved in distilled water and administered once daily for 7 days. Systolic blood pressure was measured using a tail-cuff plethysmograph before and after treatment [2]
- Working memory assay in mice: C57BL/6 mice (20–25 g) with scopolamine-induced working memory deficits were divided into control (saline i.p.) and treatment groups (0.3 mg/kg Guanfacine hydrochloride i.p.). The compound was administered 30 minutes before the delayed non-matching-to-sample task. Correct response rate and latency were recorded to evaluate memory function [3]
- Cognitive function assay in rats: Male Sprague-Dawley rats (250–300 g) were trained in the 5-CSRTT for 2 weeks. Rats were then treated with Guanfacine hydrochloride (0.1, 0.3 mg/kg oral) once daily for 5 days. Attention and executive function were assessed by measuring accuracy, omission rate, and response latency [1]

Absorption, Distribution and Excretion
The oral bioavailability of guanifaxine is 80%. The peak plasma concentration (Cmax) of 1 mg immediate-release oral guanifaxine is 2.5 ± 0.6 ng/mL, the time to peak concentration (Tmax) is 3.0 h, and the area under the curve (AUC) is 56 ± 15 ng/mL. The peak plasma concentration (Cmax) of 1 mg extended-release oral guanifaxine is 1.0 ± 0.3 ng/mL, the time to peak concentration (Tmax) is 6.0 h, and the AUC is 32 ± 9 ng/mL. In adults, the peak plasma concentration (Cmax) of 4 mg extended-release oral guanifaxine is 3.58 ± 1.39 ng/mL, and the time to peak concentration (Tmax) is 5.5 h; in children, the peak plasma concentration (Cmax) of 2 mg extended-release oral guanifaxine is 2.6 ± 1.03 ng/mL, and the time to peak concentration (Tmax) is 4.98 h. In adolescents, the peak plasma concentration (Cmax) of guanifaxine, obtained orally at a dose of 2 mg extended-release, was 1.7 ± 0.43 ng/mL, with a time to peak concentration (Tmax) of 4.96 hours. In patients with normal renal function, 57.0 ± 32.0% of guanifaxine was excreted in the urine. In patients with a glomerular filtration rate (GFR) of 10-30 mL/min, the urinary excretion rate was 14.0 ± 9.0%; while in patients with a GFR < 1 mL/min, the urinary excretion rate was 7.5 ± 2.4%. The volume of distribution of guanifaxine is 6.3 L/kg. In patients with normal renal function, the systemic clearance of guanifaxine was 360 ± 262 mL/min, and the renal clearance was 233 ± 245 mL/min. For patients with a glomerular filtration rate (GFR) of 10–30 mL/min, the total clearance was 308 ± 274 mL/min, and the renal clearance was 34 ± 22 mL/min. For patients with a GFR < 1 mL/min, the total clearance was 257 ± 187 mL/min, and the renal clearance was 18 ± 15 mL/min. Metabolism/Metabolites Guanifacin is oxidized by CYP3A4 to its major metabolite, 3-hydroxyguanifacin. 3-hydroxyguanifacin is subsequently glucuronidated or sulfated. Biological Half-Life Guanifacin has a half-life of 17 hours, but may be between 10 and 30 hours. The half-life is largely unaffected by renal function.

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- The oral bioavailability of guanifacin hydrochloride in humans is 70-80% [1]
- The plasma elimination half-life (t1/2) in adults is 17-20 hours [1]
- The drug is widely distributed in the body, with a volume of distribution (Vd) of 6-8 L/kg [1]
- It is mainly metabolized in the liver by cytochrome P450 enzymes (CYP3A4 and CYP2D6), producing inactive metabolites [1]
- Approximately 60% of the dose is excreted in the urine as the parent drug and its metabolites, and 30% is excreted in the feces [1]
- The plasma protein binding rate is 70-75% [1]

Hepatotoxicity
In multiple clinical trials of guanifaxine in adolescents and children with ADHD, no cases of elevated serum enzymes or clinically significant liver injury have been reported. Furthermore, although this drug is widely used to treat hypertension and ADHD, there have been no reports of clinically significant liver injury caused by guanifaxine. Therefore, serious liver injury caused by guanifaxine, even if it occurs, should be very rare. Probability Score: E (Unlikely to cause clinically significant liver injury). Pregnancy and Lactation Effects ◉ Overview of Use During Lactation Since there is currently no information on the use of guanifaxine during lactation and its potential negative effects on lactation, it is recommended to prioritize other medications, especially when breastfeeding newborns or premature infants. ◉ Effects on Breastfed Infants As of the revision date, no relevant published information was found. ◉ Effects on Lactation and Breast Milk As of the revision date, no published information was found on the effects of guanifaxine on serum prolactin or lactation in breastfeeding women. Guanfasin lowers basal serum prolactin levels in men and non-lactating women. With continuous use for at least 7 years, serum prolactin levels will continue to decline. For mothers who have established lactation, prolactin levels may not affect their ability to breastfeed.
◈ What is Guanfasin?
Gufasin is a medication approved for the treatment of high blood pressure and attention deficit hyperactivity disorder (ADHD). It has also been used to treat Tourette syndrome and opioid withdrawal symptoms. Some brand names for Guanfasin include Intuniv® and Tenex®. Sometimes, when people find out they are pregnant, they consider changing how they take the medication or stopping it completely. However, it is essential to consult your healthcare provider before changing how you take the medication. Your healthcare provider can discuss with you the benefits of treating your condition and the risks of not treating the condition during pregnancy. If you have been taking this medication regularly, you should not stop abruptly. If you do plan to stop taking it, you should do so slowly under the guidance of your healthcare provider.
◈ I am taking Guanfasin. Will taking Guanfasin affect my pregnancy?
Currently, there are no studies indicating whether guanfasine affects pregnancy. Animal studies have also not found that guanfasine affects fertility.
◈ Does taking guanfasine increase the risk of miscarriage?
Miscarriage can occur in any pregnancy. Currently, there are no studies indicating that guanfasine increases the risk of miscarriage.
◈ Does taking guanfasine increase the risk of birth defects?
There is a 3-5% risk of birth defects in each pregnancy, known as background risk. Research on guanfasine is insufficient. A small study of 30 pregnancies involving guanfasine did not find any birth defects. Animal studies have not shown that guanfasine increases the risk of birth defects.
◈ Does taking guanfasine during pregnancy increase the risk of other pregnancy-related problems?
Currently, there are no studies exploring whether guanfasine increases the risk of pregnancy-related problems such as preterm birth (delivery before 37 weeks of gestation) or low birth weight (birth weight less than 2500 grams). One study observed the pregnancies of 30 women who took guanfasine to treat preeclampsia. Preeclampsia is a pregnancy-related condition that can cause symptoms such as high blood pressure or fluid retention. Studies on guanfasin have not found changes in fetal heart rate during pregnancy.
◈ Will taking guanfasin during pregnancy affect a child's future behavior or learning abilities?
Currently, there are no studies exploring whether exposure to guanfasin during pregnancy leads to behavioral or learning problems in children.
◈ Breastfeeding while taking guanfasin:
No studies have been conducted on taking guanfasin while breastfeeding. Because research on this drug is insufficient, it is recommended that you discuss alternative medication options with your healthcare provider to see if there are more well-researched medications available to treat your condition while breastfeeding. If you suspect your infant is experiencing related symptoms (such as lethargy, muscle weakness, or low blood pressure), contact your child's healthcare provider. Be sure to consult your healthcare provider about all questions regarding breastfeeding.
◈ If a man takes guanfasin, will it affect his fertility (the ability to impregnate his partner) or increase the risk of birth defects in the fetus during his partner's pregnancy?
Currently, there are no studies exploring whether guanfasin affects male fertility or increases the risk of birth defects. Generally, exposure to the drug by the father or sperm donor is unlikely to increase the risk of pregnancy. For more information, see the “Paternal Exposure” information sheet on the MotherTobaby website: https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy.

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Protein Binding
Guifacin is approximately 70% protein-bound in serum.

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- Common side effects in humans include drowsiness, dizziness, dry mouth, and constipation, which are dose-related and mild to moderate in severity[1].
- No significant hepatotoxicity or nephrotoxicity was observed in clinical trials at therapeutic doses (0.5–4 mg/day)[1].
- Due to its central nervous system depressant effects, guanifacin may enhance the sedative effects of benzodiazepines and alcohol[1][2].
- In rats, the acute oral LD50 is greater than 1000 mg/kg[2].

[1]. Guanfacine for the treatment of cognitive disorders: a century of discoveries at Yale. Yale J Biol Med. 2012 Mar;85(1):45-58. Epub 2012 Mar 29.

[2]. The pharmacology of centrally acting antihypertensive drugs. Br J Clin Pharmacol. 1983; 15(Suppl 4): 455S–462S.

[3]. Alpha2A-adrenoceptors strengthen working memory networks by inhibiting cAMP-HCN channel signaling in prefrontal cortex. Cell. 2007 Apr 20;129(2):397-410.

Guanfaxine belongs to the acetamide class of drugs. Guanfaxine, also known as BS 100-141, is a selective α-A2 adrenergic receptor agonist, initially used to treat hypertension, but now available in extended-release tablets for the treatment of attention deficit hyperactivity disorder (ADHD). Guanfaxine was first documented in 1974. It was approved by the U.S. Food and Drug Administration (FDA) on October 27, 1986. Guanfaxine is a centrally acting α-2 adrenergic receptor agonist. Its mechanism of action is as an α2 adrenergic receptor agonist. Guanfaxine is a selective α-adrenergic receptor agonist used to treat hypertension and ADHD in adults and children. Guanfaxine has not caused elevated serum enzymes or acute, clinically significant liver injury during treatment. Guanfaxine is a centrally acting adrenergic agonist with non-excitatory and antihypertensive effects. Guanfacinon selectively stimulates α2-adrenergic receptors in the central nervous system, thereby inhibiting sympathetic nervous system output. Used alone or in combination with other drugs, it reduces peripheral and renal vascular resistance and lowers systolic, diastolic, and heart rate. A centrally acting antihypertensive drug with specificity for α2-adrenergic receptors. See also: Guanfacinon hydrochloride (salt form). Drug Indications Guanfacinon can be used alone or in combination with stimulants for the treatment of attention deficit hyperactivity disorder (ADHD). Intuniv is indicated for the treatment of ADHD in children and adolescents aged 6 to 17 years who are unsuitable for, intolerant of, or have had stimulants proven ineffective. Intuniv must be used as part of a comprehensive ADHD treatment regimen, which typically includes psychological, educational, and social interventions. Mechanism of Action Guanfacin is a selective α2A adrenergic receptor agonist that reduces the effects of the sympathetic nervous system on the heart and circulatory system. The link between the molecular mechanism of guanfacin and its efficacy in treating attention deficit hyperactivity disorder (ADHD) is not yet clear. Pharmacodynamics Guanfacin is a selective α2A adrenergic receptor agonist, but how it is used to treat ADHD is unclear. Due to its once-daily dosing, long duration of action, and wide therapeutic window, no fatal overdose cases have been reported in the literature. Patients should be informed of the risks of hypotension, bradycardia, and syncope.

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- Guifacin hydrochloride is a selective α2A adrenergic receptor agonist with central nervous system and antihypertensive effects[1][2][3]
- Its cognitive enhancement mechanism involves binding to α2A adrenergic receptors in the prefrontal cortex, inhibiting cAMP-HCN channel signaling, and enhancing working memory neural networks[3]
- The drug was initially used to treat hypertension and was later approved for the treatment of attention deficit hyperactivity disorder (ADHD) and cognitive impairment associated with aging or neurological disorders[1]
- The drug has good pharmacokinetic characteristics and is suitable for long-term use when administered once daily[1]
- Its antihypertensive effect is achieved by inhibiting central sympathetic output and reducing peripheral vascular resistance without causing significant reflex tachycardia[2]

C9H9CL2N3O

246.0933

280.988

29110-48-3

Guanfacine;29110-47-2;Guanfacine-d2 hydrochloride;1398065-88-7

3519

White to off-white solid powder

213 °C

3.538

2

1

2

15

256

0

INJOMKTZOLKMBF-UHFFFAOYSA-N

InChI=1S/C9H9Cl2N3O/c10-6-2-1-3-7(11)5(6)4-8(15)14-9(12)13/h1-3H,4H2,(H4,12,13,14,15)

N-(diaminomethylidene)-2-(2,6-dichlorophenyl)acetamide

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 30 mg/mL (~106.18 mM)
H2O : ~20 mg/mL (~70.78 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.85 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (8.85 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (8.85 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)