Varenicline acts as a partial agonist at the α4β2 neuronal nicotinic acetylcholine receptor (nAChR).
It also has agonist activity at the α7 nAChR and the 5-HT3 receptor, but with lower potency and selectivity compared to its action at α4β2 nAChR.
This review does not provide specific IC50, Ki, or EC50 values for varenicline at its endogenous targets.

Varenicline (1 μM, 24 hours) suppresses the rate of cell proliferation in RAW 264.7 macrophages as well as LPS-induced cytokine secretion (IL-1β, IL-6, and TNF α) [1]. Human adrenal chromaffin cells derived from male and female organ donors exhibit action potentials (Aps) in the absence of ACh activation when exposed to 250 nM vannicline [3]. By inhibiting VE-cadherin protein expression, vannicline (100 μM, 4 hours) increases HUVEC migration [4].

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Varenicline activated several engineered chimeric ion channels with mutant α7 nAChR ligand-binding domains (LBDs) fused to the 5-HT3 ion pore domain in a membrane potential (MP) assay.
At the α7L131G,Q139L,Y217F-GlyR channel, varenicline exhibited an EC50MP of 1.6 ± 0.1 nM, representing a 390-fold potency increase compared to the parent α7-GlyR channel.
In HEK-293 cells expressing α7L131G,Q139L,Y217F-GlyR, varenicline acted as a strong agonist, producing sustained, slowly activating currents with a high affinity and slow off-rate.
Competition binding assays using [³H]-ASEM displacement showed a Ki of 1.3 ± 0.4 nM for varenicline at the α7L131G,Q139L,Y217F-GlyR channel, which is 475-fold lower than its reported Ki at the wild-type α7 nAChR.
Varenicline showed 160-fold agonist selectivity for the engineered channel over the α4β2 nAChR and 880-fold selectivity over the 5-HT3 receptor.

Varenicline (0.01-1 mg/kg subcutaneously, 3 days) injected subcutaneously at a dose of 0.5 mg/kg 10 minutes before to the onset of nicotine-induced suppression of conditioned place preference (CPP) [5]. Place aversion caused by vannicline (subcutaneous injection, 2.5 mg/kg, 3 days) is reliant on α5 nAChR but not β2 nAChR [5]. Subcutaneous injection of vannicline (0.1 and 0.5 mg/kg, 3 days) restores the somatic symptoms and hyperalgesia associated with nicotine withdrawal, as well as withdrawal-induced aversion, in a dose-related way [5].

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In mice with unilateral substantia nigra reticulata (SNr) neurons expressing PSAM4-GlyR (the engineered channel), intraperitoneal administration of varenicline at 0.1 mg/kg induced contralateral rotation, a behavioral readout of neuronal silencing. The effect was evident within 20 minutes and lasted approximately 4 hours, consistent with varenicline's half-life.
Oral administration of varenicline (5 µg/mL in drinking water) also elicited circling behavior in these mice.
In a rhesus monkey with PSAM4-GlyR expressed in the globus pallidus internus (GPi), subcutaneous administration of varenicline (0.1 mg/kg) significantly inhibited neuron firing rates and burst firing rates compared to pre-transduction baseline.
The effective dose for chemogenetic silencing in mice and monkey (0.1 mg/kg) was 10-fold lower in mice and 5-fold lower in monkey than doses previously reported to produce nicotine-substituting discriminative stimulus effects.

Cell proliferation assay [1]
Cell Types: RAW 264.7 mouse macrophages (treated with 4 μg/mL LPS for 24 h)
Tested Concentrations: 1 μM
Incubation Duration: 0-48 h
Experimental Results: LPS-induced cell proliferation rate diminished.

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Western Blot Analysis[4]
Cell Types: HUVEC
Tested Concentrations: 1, 10, 100 μM
Incubation Duration: 24 hrs (hours) or 30 minutes
Experimental Results: diminished VE-cadherin protein expression, activation of ERK1/2, p38 and JNK signaling.

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Membrane potential (MP) assays were performed using a panel of 41 chimeric channels with mutant α7 nAChR LBDs spliced onto the 5-HT3 ion pore domain expressed in cells. The assay measures sustained channel activation, reflected as changes in membrane potential, to generate dose-response curves (EC50MP values).
Whole-cell voltage-clamp electrophysiology was performed on HEK-293 cells and other cell lines (e.g., an immune cell line) expressing engineered channels (e.g., α7L131G,Q139L,Y217F-GlyR) to characterize agonist-induced currents, desensitization, and off-rates.
Competition binding assays were performed using the selective α7 nAChR antagonist [³H]-ASEM to determine Ki values for varenicline at the engineered receptors.

Animal/Disease Models: ICR male mice [5]
Doses: 0.01-1 mg/kg, 3 days
Route of Administration: subcutaneous injection
Experimental Results: Inhibited nicotine conditioned place preference (CPP) in a dose-dependent manner.

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For mouse behavioral assays (contralateral rotation), PSAM4-GlyR was expressed unilaterally in GABAergic neurons of the substantia nigra reticulata (SNr) via stereotaxic injection of recombinant adeno-associated virus (rAAV). Mice were administered low-dose amphetamine (3 mg/kg) to increase general activity. Varenicline was administered intraperitoneally at various doses (e.g., 0.1 mg/kg) or orally via drinking water (5 µg/mL). Rotation behavior was monitored to assess the onset and duration of neuronal silencing.
For in vivo calcium imaging in mice, PSAM4-GlyR was expressed in hippocampal CA1 pyramidal neurons via viral delivery in Thy1::GCaMP6f transgenic mice. Mice were head-fixed on a treadmill, and calcium dynamics were monitored via two-photon imaging before and after intraperitoneal injection of varenicline or uPSEMs.
For primate studies, PSAM4-GlyR was expressed in the globus pallidus internus (GPi) of a rhesus monkey via electrophysiologically guided injection of rAAV8. Neuronal firing was recorded before and after subcutaneous administration of varenicline (0.1 mg/kg).

Varnicolan exhibits excellent brain permeability and is not a substrate of the P-glycoprotein (Pgp) efflux pump. It has low binding to plasma proteins. Its elimination half-life (t₁/₂) is greater than 17 hours in monkeys and humans, approximately 1.4 hours in mice, and approximately 4 hours in rats. It is estimated that a steady-state concentration in the human brain after twice-daily administration of a 1 mg dose is higher than the concentration (10⁻¹⁶ nM) required for effective chemogenetic silencing of PSAM4-GlyR in this study, suggesting that chemogenetic application may be achievable at subtherapeutic doses (antinicotine doses).

Toxicity Summary
Identification and Use: Varenicline is used as an adjunct to smoking cessation. Human Exposure and Toxicity: The safety and efficacy of varenicline as an adjunct to smoking cessation have been demonstrated in six placebo-controlled or active-controlled studies. These studies included a total of 3,659 patients (mean age: 43 years; 79–96% white; mean smoking history: approximately 25 years) who smoked at least 10 cigarettes per day (mean approximately 21 cigarettes per day). Additionally, the safety and efficacy of varenicline were evaluated in a randomized, double-blind, placebo-controlled study. This study included 703 patients with stable, documented cardiovascular disease (excluding hypertension) who smoked at least 10 cigarettes per day. Patients receiving varenicline and those receiving placebo were comparable in baseline characteristics, including age (mean age 57 years and 55.9 years, respectively), race (80.3% and 80.8% white, respectively), sex (75.2% and 82.2% male, respectively), and mean smoking history (40 years and 39 years, respectively, and 22.1 and 22.9 cigarettes per day, respectively). A randomized, double-blind, placebo-controlled study also evaluated the safety and efficacy of varenicline, which included 460 patients with mild to moderate chronic obstructive pulmonary disease (FEV1/FVC less than 70% after bronchodilator administration, and FEV1 at least 50% of the predicted normal value) who smoked at least 10 cigarettes per day (mean age 57 years, 82-84% white, approximately 62% male, mean smoking history approximately 40 years). Post-marketing surveillance data showed that patients treated with varenicline reported severe neuropsychiatric symptoms, including mood changes (e.g., depression, mania), psychosis, hallucinations, delusions, illusions, homicidal ideation, hostility, agitation, aggression, anxiety, panic, and suicidal tendencies (e.g., suicidal ideation, attempted suicide, and suicide death). Post-marketing surveillance data also showed that patients treated with varenicline reported hypersensitivity reactions, including angioedema. The safety and efficacy of varenicline in patients under 18 years of age have not been established, therefore its use in this age group is not recommended. In vitro studies showed that varenicline was not genotoxic in human lymphocytes, regardless of metabolic activation. Animal studies: Varenicline is excreted into animal milk. Rats were administered varenicline orally by gavage (1, 5, and 15 mg/kg/day) for 2 years. In male rats (n = 65 per sex per dose group), the incidence of hibernation tumors (brown fat tumors) was increased in both the intermediate-dose group (1 tumor, 5 mg/kg/day, equivalent to 23 times the maximum recommended daily human exposure based on AUC) and the maximum-dose group (2 tumors, 15 mg/kg/day, equivalent to 67 times the maximum recommended daily human exposure based on AUC). No evidence of carcinogenicity was observed in female rats. Animal reproductive studies showed that varenicline succinate had adverse effects on the fetus. Oral administration of 30 mg/kg/day (equivalent to 50 times the human AUC) of varenicline succinate to pregnant rabbits resulted in reduced fetal weight; however, no such reduction was observed at a dose of 10 mg/kg/day (equivalent to 23 times the maximum recommended daily human exposure based on AUC). Furthermore, in the offspring of pregnant rats, decreased fertility and enhanced auditory startle response were observed at oral doses of 15 mg/kg/day (equivalent to 36 times the maximum recommended daily human exposure based on AUC). Varenicline succinate was not teratogenic in rats and rabbits at oral doses up to 15 mg/kg/day and 30 mg/kg/day (equivalent to 36 and 50 times the maximum recommended daily human exposure based on AUC, respectively). Varenicline was not genotoxic in the following tests, regardless of metabolic activation: Ames bacterial mutation assay; mammalian CHO/HGPRT assay; and in vivo cytogenetic abnormality detection in rat bone marrow.

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Effects during pregnancy and lactation
◉ Overview of use during lactation
Varenicline is a partial nicotine agonist, used orally as an aid to smoking cessation and as a nasal spray for the treatment of dry eye. One researcher noted that based on data from animal studies on nicotine, varenicline may interfere with normal lung development in infants and is therefore not recommended for use by breastfeeding women. Since there is currently no information regarding the use of varenicline during breastfeeding, alternative medications are recommended, especially for breastfed newborns or premature infants. However, the maternal drug exposure after nasal spray administration is only about 7.5% of that after oral administration, so the effect on the infant is much smaller. If the mother chooses to breastfeed while taking varenicline, the infant should be closely monitored for seizures and excessive vomiting.
◉ Effects on breastfed infants
No relevant published information found as of the revision date.
◉ Effects on lactation and breast milk
No relevant published information found as of the revision date.

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Interactions
Pharmacokinetic interactions with drugs metabolized by or affecting cytochrome P-450 (CYP) isoenzymes are unlikely. In vitro studies have shown that varenicline does not inhibit CYP isoenzymes 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, or 3A4/5 in vitro. This drug does not induce CYP isoenzymes 1A2 or 3A4. Physiological changes caused by smoking cessation (with or without varenicline) may alter the pharmacokinetics or pharmacodynamics of certain drugs (e.g., theophylline, warfarin, insulin); dose adjustments may be necessary. The manufacturer notes that clinical experience in patients receiving varenicline in combination with other drugs has not revealed clinically significant interactions. Pharmacokinetic interactions are unlikely. Patients receiving combination therapy (varenicline and transdermal nicotine replacement therapy) had a higher incidence of adverse reactions (nausea, headache, vomiting, dizziness, dyspepsia, fatigue) and a higher discontinuation rate compared to patients receiving transdermal nicotine and placebo. The safety and efficacy of varenicline in combination with other smoking cessation therapies have not been studied. Pharmacokinetic interactions are unlikely. Smoking cessation may affect the pharmacokinetics of warfarin. For more complete data on interactions of varenicline (7 drugs in total), please visit the HSDB record page. Varenicline is generally well tolerated in patients at low doses. High doses of varenicline reduced food intake in mice, a behavior that was sensitive to non-targeted 5-HT3 receptor activation, suggesting potential side effects at high concentrations.

[1]. Efficacy of varenicline combined with nicotine replacement therapy vs varenicline alone for smoking cessation: a randomized clinical trial. JAMA. 2014 Jul;312(2):155-61.

[2]. Ultrapotent chemogenetics for research and potential clinical applications. Science. 2019;364(6436):eaav5282.

[3]. Varenicline promotes endothelial cell migration by lowering vascular endothelial-cadherin levels via the activated α7 nicotinic acetylcholine receptor-mitogen activated protein kinase axis. Toxicology. 2017;390:1-9.

[4]. Countering Opioid-induced Respiratory Depression in Male Rats with Nicotinic Acetylcholine Receptor Partial Agonists Varenicline and ABT 594. Anesthesiology. 2020 May;132(5):1197-1211.

[5]. Effects of chronic varenicline treatment on nicotine, cocaine, and concurrent nicotine+cocaine self-administration. Neuropsychopharmacology. 2014 Apr;39(5):1222-31.

[6]. Varenicline has antidepressant-like activity in the forced swim test and augments sertraline's effect. Eur J Pharmacol. 2009 Mar 1;605(1-3):114-6.

Varenicline is a partial agonist of the α4β2 subtype of nicotine acetylcholine receptors (nAChR). Nicotine stimulation of the central α4β2 nAChR located at the presynaptic terminal of the nucleus accumbens leads to the release of the neurotransmitter dopamine, which may be associated with pleasure; nicotine addiction is a physiological dependence associated with the dopamine reward system. As an AChR partial agonist, varenicline can alleviate cravings and withdrawal symptoms caused by nicotine withdrawal, but it is not addictive itself. A benzozazepine derivative that acts as a partial agonist of the α4β2 nicotine receptor. It is used for smoking cessation. See also: Varenicline (note moved to).

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Therapeutic Uses
Nicotine Receptor Agonist
Varenicline is used as an adjunct to smoking cessation. In this randomized, double-blind, multicenter trial, eligible adult smokers (18-75 years old, with an average of ≥10 cigarettes per day) were randomly assigned to either varenicline 1 mg twice daily (BID) or placebo for 52 weeks. Participants were followed up weekly in outpatient clinics until week 8, then every 4 weeks until week 52, with a follow-up visit in week 53. The target quit date was the morning of the first week's outpatient follow-up. Each follow-up included a brief consultation and recording of vital signs, adverse events, and smoking status. Other laboratory parameters were collected at designated follow-up visits. A total of 251 participants were randomized to the varenicline group and 126 to the placebo group. Approximately half of the participants in both groups completed the study (53.8% in the varenicline group; 46.8% in the placebo group). During the study, adverse events were observed in 96.4% of participants in the varenicline group and 82.5% of participants in the placebo group. Common adverse events associated with varenicline included nausea (40.2%), abnormal dreams (22.7%), and insomnia (19.1%). Most adverse events were mild or moderate in severity. Adverse events leading to discontinuation of varenicline treatment included nausea (7.6%), insomnia (3.2%), and abnormal dreams (2.4%). One serious adverse event associated with varenicline, bilateral subcapsular cataract, was observed. At week 52, the 7-day withdrawal rate was 36.7% (varenicline group) and 7.9% (placebo group). Varenicline 1 mg twice daily can be safely taken for up to 1 year. Varenicline was also superior to placebo in smoking cessation throughout the study period, supporting its short-term (12 weeks) and long-term (52 weeks) efficacy.

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Drug Warning
/Black Box Warning/ Warning: Serious neuropsychiatric events.
Serious neuropsychiatric events, including but not limited to depression, suicidal ideation, suicide attempts, and suicide deaths, have been reported in patients taking CHANTIX. Some reported cases may be complicated by nicotine withdrawal symptoms in patients trying to quit smoking. Depressed mood can be a symptom of nicotine withdrawal. Smokers attempting to quit without medication have been reported to experience depressive symptoms, but in rare cases, suicidal ideation. However, some of these symptoms have also been observed in patients taking CHANTIX but continuing to smoke. All patients receiving CHANTIX should be closely monitored for neuropsychiatric symptoms, including behavioral changes, hostility, agitation, depressed mood, and suicide-related events such as suicidal ideation, suicidal behavior, and suicide attempts. Post-marketing surveillance data show that some patients taking CHANTIX to quit smoking experienced the above symptoms, as well as exacerbations of pre-existing mental illness and suicide deaths. Most symptoms occurred during CHANTIX treatment, but some occurred after discontinuation. These events occurred in both patients with and without a history of mental illness. Patients with severe mental illnesses (such as schizophrenia, bipolar disorder, and major depressive disorder) were not included in premarket studies of Chantix. Patients and their caregivers should be informed that if agitation, hostility, depressed mood, or unusual changes in behavior or thought patterns (unlike the patient's past behavior), or suicidal ideation or behavior occurs, patients should immediately stop taking Chantix and contact a healthcare provider. Postmarketing reports indicate that many patients experienced symptom relief after discontinuing Chantix, but some cases showed persistent symptoms; therefore, continued monitoring and supportive care should be provided until symptoms subside. The risks and benefits of Chantix should be weighed. Studies have shown that Chantix improves smoking cessation success rates compared to placebo, with effects lasting up to one year. The health benefits of quitting smoking are immediate and significant. The U.S. Food and Drug Administration (FDA) warns that the prescription smoking cessation drug Chantix (varenicline) may alter people's responses to alcohol. Furthermore, there have been rare reports of seizures in patients taking Chantix. We have approved a labeling change for the smoking cessation drug Chantix to highlight these risks. Patients should reduce their alcohol consumption until they understand the effects of Chantix on their alcohol tolerance. Patients experiencing seizures while taking Chantix should immediately stop taking the medication and seek medical attention. Millions of Americans suffer from serious health problems due to smoking, and quitting can alleviate these problems. Chantix is a prescription drug approved by the FDA to help adults quit smoking. In clinical trials, Chantix improved smoking cessation success rates and maintained the effects of quitting for up to one year compared to placebo (an ineffective treatment). We reviewed case series submitted by Chantix manufacturer Pfizer and cases described in the FDA Adverse Event Reporting System (FAERS) database of patients who consumed alcohol and experienced adverse reactions while taking Chantix. Some patients experienced decreased alcohol tolerance, including increased intoxication, abnormal or aggressive behavior, or no memory of what happened (see Data Summary). We also reviewed the FAERS database and medical literature¹ for cases of seizures following Chantix use and found that some patients experienced seizures while taking Chantix, either without a history of epilepsy or with well-controlled epilepsy. In most of these cases, seizures occurred within the first month of starting Chantix. We have added this risk information to the "Warnings and Precautions" section of the drug label and to the patient's medication guide. Furthermore, we updated the "Warnings and Precautions" section of the drug label to include information from several studies investigating the risk of potential neuropsychiatric side effects (including mood, behavior, or thought-related side effects) following Chantix use. These studies include observational studies^2-5 and an analysis of randomized controlled clinical trial data by Pfizer⁶. These studies did not show that Chantix use increases the risk of neuropsychiatric side effects; however, these studies do not cover all types of neuropsychiatric side effects and have some limitations that prevent us from drawing reliable conclusions. We communicated the potential for serious neuropsychiatric side effects of Chantix in 2009 and 2011, and these latest findings were discussed at the FDA Advisory Committee meeting in October 2014. Pfizer is conducting a large clinical safety trial of Chantix to investigate this risk, with results expected by the end of 2015. We will update the public as soon as new information becomes available. Varenicline is contraindicated in patients with a known history of severe allergic reactions or skin reactions to varenicline. Postmarketing surveillance data show that patients treated with varenicline have experienced serious neuropsychiatric symptoms, including mood changes (e.g., depression, mania), psychosis, hallucinations, delusions, illusions, homicidal ideation, hostility, agitation, aggression, anxiety, panic, and suicidal tendencies (e.g., suicidal ideation, attempted suicide, and suicide death). Most cases of symptoms occurred during varenicline treatment, but some cases developed after discontinuation of the drug. Some reported cases may be related to nicotine withdrawal symptoms in patients trying to quit smoking; depressed mood may also be a symptom of nicotine withdrawal, and depression (rarely accompanied by suicidal ideation) is also seen in patients attempting to quit smoking without medication. However, these symptoms have also been observed in some patients who continued to smoke despite taking varenicline. Such effects can be seen in patients with or without mental illness; there are also reports that varenicline can worsen existing mental illness. Nicotine withdrawal is also associated with the exacerbation of underlying mental illness.
For more complete data on drug warnings for varenicline (19 in total), please visit the HSDB record page.
Pharmacodynamics
Varenicline is a partial nicotine acetylcholine receptor agonist designed to partially activate this system while displacing nicotine at its site of action in the brain.
VareniclineIs an FDA-approved smoking cessation medication. Its primary mechanism of action is the partial activation of α4β2 nAChR.
This study repositioned varenicline as an agonist of the engineered chemical genetic receptor (PSAM4). Engineered PSAM4 receptors (α7L131G, Q139L, Y217F-GlyR) exhibit high sensitivity and selectivity to varenicline, with minimal activation by endogenous ligands (such as acetylcholine or choline). The combined application of PSAM4 and varenicline can achieve reversible neuronal silencing or activation in rodents and non-human primates (depending on the coupled ion-pore domain), holding potential value in basic neuroscience research and future clinical treatments (e.g., movement disorders, epilepsy, or pain).

C13H13N3

211.26

211.11

249296-44-4

Varenicline dihydrochloride;866823-63-4;Varenicline Hydrochloride;230615-23-3;Varenicline Tartrate;375815-87-5;Varenicline-d4;2183239-01-0

170361

Light yellow to yellow solid powder

1.247g/cm3

400.6ºC at 760mmHg

196.1ºC

1.25E-06mmHg at 25°C

1.667

0.01

1

3

0

16

254

0

JQSHBVHOMNKWFT-UHFFFAOYSA-N

InChI=1S/C13H13N3/c1-2-16-13-5-11-9-3-8(6-14-7-9)10(11)4-12(13)15-1/h1-2,4-5,8-9,14H,3,6-7H2

5,8,14-triazatetracyclo[10.3.1.02,11.04,9]hexadeca-2,4,6,8,10-pentaene

CP 526555; CP-526555; CP526555; CP-526555-18; CP 526555 18; CP52655518; Varenicline tartrate; Chantix; Champix

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

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

DMSO : ~20 mg/mL (~94.67 mM)
H2O : ≥ 20 mg/mL (~94.67 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (11.83 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 (11.83 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 (11.83 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.)