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Brimonidine (UK 14304 and AGN190342) is a highly potent and selective α-adrenergic receptor agonist with EC50 of 0.45 nM for the α2A adrenoreceptor, and used to treat open-angle glaucoma or ocular hypertension. Brimonidine reduces the progressive loss of ganglion cells to 26% and 15% at doses of 0.5 mg/kg and 1 mg/kg, respectively. In order to stop additional ganglion cell loss, brimonidine therapy is started 10 days following an increase in IOP. In ocular hypertensive retinas, brimonidine reduces the rise in GFAP immunoreactivity.
Physicochemical Properties
| Molecular Formula | C11H10BRN5 | |
| Molecular Weight | 292.14 | |
| Exact Mass | 291.011 | |
| Elemental Analysis | C, 45.23; H, 3.45; Br, 27.35; N, 23.97 | |
| CAS # | 59803-98-4 | |
| Related CAS # | Brimonidine tartrate; 70359-46-5; Brimonidine-d4; 1184971-51-4; 59803-98-4 | |
| PubChem CID | 2435 | |
| Appearance | Light yellow to yellow solid powder | |
| Density | 1.8±0.1 g/cm3 | |
| Boiling Point | 432.6±55.0 °C at 760 mmHg | |
| Melting Point | 207.5 °C | |
| Flash Point | 215.4±31.5 °C | |
| Vapour Pressure | 0.0±1.0 mmHg at 25°C | |
| Index of Refraction | 1.798 | |
| LogP | 0.96 | |
| Hydrogen Bond Donor Count | 2 | |
| Hydrogen Bond Acceptor Count | 3 | |
| Rotatable Bond Count | 2 | |
| Heavy Atom Count | 17 | |
| Complexity | 308 | |
| Defined Atom Stereocenter Count | 0 | |
| SMILES | BrC1C2C(C([H])=C([H])C=1N([H])C1=NC([H])([H])C([H])([H])N1[H])=NC([H])=C([H])N=2 |
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| InChi Key | XYLJNLCSTIOKRM-UHFFFAOYSA-N | |
| InChi Code | InChI=1S/C11H10BrN5/c12-9-7(17-11-15-5-6-16-11)1-2-8-10(9)14-4-3-13-8/h1-4H,5-6H2,(H2,15,16,17) | |
| Chemical Name | 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)quinoxalin-6-amine | |
| Synonyms |
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| HS Tariff Code | 2934.99.9001 | |
| Storage |
Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month |
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| Shipping Condition | Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs) |
Biological Activity
| Targets | α adrenergic receptor | ||
| ln Vitro |
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| ln Vivo |
Brimonidine (1 mg/kg) dramatically shields RGCs from elevated IOP-induced cell death in adult rats. In adult Sprague-Dawley rats, brimonidine (0.0001%) BMD possesses no discernible neuroprotective effects and causes the loss of roughly 37% of the retinal ganglion cell (RGC) population. RGC mortality is completely avoided in the first seven days following ischemia in adult Sprague-Dawley rats when brimonidine (0.001% or 0.01%) is used. This results in the survival of 76 or 90%, respectively, of the RGC population. In the control eyes injected with saline, BDNF was present in a minority of the RGCs. Two days after Brimonidine injection, the number of BDNF-positive RGCs was increased from 55% to 166%, depending on brimonidine concentrations, when compared with those in the controls. In addition, the BDNF signal intensities in individual RGCs were elevated 50% in brimonidine-injected eyes compared with control eyes. Northern blot revealed a 28% increase of BDNF expression in the brimonidine group compared with the controls (P <.003). No significant difference was observed in BDNF receptor, trk B, expression between brimonidine, or BSS control groups. Conclusions: A single dose of a low concentration of intravitreal Brimonidine is sufficient to significantly increase endogenous BDNF expression in RGCs. These results suggest that brimonidine neuroprotection may be mediated through up-regulation of BDNF in the RGCs. The BDNF should be further investigated regarding its role in the neuroprotective effects reported with brimonidine. Clinical relevance: Brimonidine may be (potentially) used clinically as a neuroprotective agent in optic neuropathy, including glaucoma, and ischemic and traumatic optic neuropathy[4]. |
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| Enzyme Assay |
[3H]A complete agonist at alpha 2-adrenergic receptors is rimonidine (UK 14304). [3H] In the human brain, brimonidine (UK 14304) labels at least two distinct binding sites that share traits with alpha 2-adrenergic binding sites. At these two sites, GTP inhibits agonist binding, albeit to varying degrees depending on the site. [3H]UK 14,034 is a full agonist at alpha 2-adrenergic receptors. Although the characteristics of the binding of the partial alpha 2-adrenergic agonists in postmortem human brain were known, the binding of [3H]UK 14,304 had not been studied in this tissue. Multi-site binding of this radiolabel had been reported in other tissues and guanosine triphosphate (GTP) had been shown to reduce [3H]UK 14,304 binding. We now report that [3H]UK 14,304 labels at least 2 specific binding sites in human brain that both have the characteristics of an alpha 2-adrenergic binding site. GTP decreases agonist binding at both of these sites, but with different potencies at each site[2]. |
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| Animal Protocol |
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| ADME/Pharmacokinetics |
Absorption, Distribution and Excretion Brimonidine readily penetrates the cornea following ocular administration to reach pharmacologically active concentrations in the aqueous humor and ciliary body, the putative sites of its IOP-lowering activity. Following ocular administration of 0.2% brimonidine solution, the peak plasma concentrations were achieved within 1 to 4 hours. In a clinical study of adult subjects with facial erythema of rosacea, brimonidine was cutaneously applied on facial skin in a repeated manner. While there was no drug accumulation in plasma, the highest peak plasma concentrations (Cmax) and AUC were 46 ± 62 pg/mL and 417 ± 264 pgxhr/mL, respectively. Brimonidine and its metabolites are predominantly eliminated via urinary excretion, with 74% of the total dose being found in the urine. The volume of distribution of brimonidine has not been established. In animal studies, brimonidine was shown to cross the placenta and enter into the fetal circulation to a limited extent. As its lipophilicity is relatively low, brimonidine is not reported to easily cross the blood-brain barrier. The apparent clearance has not been studied. However, the systemic clearance of brimonidine is reported to be rapid. Approximately 87% of the total radioactive dose of brimonidine was shown to be eliminated within 120 hours following oral administration. Metabolism / Metabolites Brimonidine is reported to be metabolized in the cornea. Brominidine that reaches the systemic circulation upon topical administration undergoes extensive hepatic metabolism mediated by hepatic aldehyde oxidases. Metabolized primarily by the liver. Route of Elimination: Urinary excretion is the major route of elimination of the drug and its metabolites. Half Life: 2 hours [ophthalmic solution] Biological Half-Life Following ocular administration of 0.2% brimonidine solution, the systemic half-life was approximately 3 hours. |
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| Toxicity/Toxicokinetics |
Toxicity Summary Brimonidine is an alpha adrenergic receptor agonist (primarily alpha-2). It has a peak ocular hypotensive effect occurring at two hours post-dosing. Fluorophotometric studies in animals and humans suggest that Brimonidine has a dual mechanism of action by reducing aqueous humor production and increasing uveoscleral outflow. The topical gel reduces erythema through direct vasocontriction. Effects During Pregnancy and Lactation ◉ Summary of Use during Lactation Limited information indicates that maternal use of brimonidine 0.2% ophthalmic drops do not adversely affect their nursing infants. However, some authors warn of possible CNS depression, apnea, lethargy, bradycardia with brimonidine and recommend against its use during breastfeeding. To substantially diminish the amount of drug that reaches the breastmilk after using eye drops, place pressure over the tear duct by the corner of the eye for 1 minute or more, then remove the excess solution with an absorbent tissue. Topical brimonidine gel used to treat rosacea has not been studied during breastfeeding. It is unlikely that the topical gel would affect the breastfed infant, but the manufacturer states that it should not be used during nursing. Until more data are available, an alternative topical agent might be preferred ◉ Effects in Breastfed Infants A woman used brimonidine 0.2%, timolol gel-forming solution 0.5%, dipivefrin 0.2%, and dorzolamide 0.5% drops for glaucoma while nursing a newborn. The frequency of medication use and extent of nursing were not stated. All medications were given immediately after nursing with punctal occlusion of the tear duct. The infant's vital signs were closely monitored with no signs of bradycardia or apnea. A woman was using ophthalmic drops containing 0.5% timolol and 0.2% brimonidine twice daily in the right eye for 6 months. During this time, she breastfed her infant (extent not stated) apparently without harm to her infant. ◉ Effects on Lactation and Breastmilk Relevant published information was not found as of the revision date. Protein Binding The protein binding of brimonidine has not been studied. Toxicity Data LD50: 50 mg/kg (oral, mice) LD50: 100 mg/kg (oral, rat) |
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| References |
[1]. Specific [3H]UK 14,304 binding in human cortex occurs at multiple high affinity states with alpha 2-adrenergic selectivity and differing affinities for GTP. Life Sci, 1988. 43(22): p. 1805-12. [2]. UK-14,304, a potent and selective alpha2-agonist for the characterisation of alpha-adrenoceptor subtypes. Eur J Pharmacol, 1981. 72(4): p. 413-5. [3]. Effects of alpha-2 adrenoceptor agonists and antagonists on circling behavior in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway. J Pharmacol Exp Ther, 1999. 288(2): p. 798-804. [4].Up-regulation of brain-derived neurotrophic factor expression by brimonidine in rat retinal ganglion cells. Arch Ophthalmol. 2002 Jun;120(6):797-803. |
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| Additional Infomation |
Pharmacodynamics Brimonidine is a highly selective alpha-2 adrenergic receptor agonist that is 1000-fold more selective for the alpha2-adrenergic receptor than the alpha1-adrenergic receptor. This characteristic gives the drug some therapeutic advantages, since it reduces the risk of systemic side effects, such as systemic hypotension, bradycardia, and sedation. In addition, there is a reduction in the risk for developing alpha-1 mediated ocular unwanted effects, such as conjunctival blanching, mydriasis, and eyelid retraction. However, despite high alpha-2 receptor specificity, brimonidine may still produce alpha-1 adrenoceptor-mediated ocular effects, such as conjunctival vasoconstriction. Brimonidine has a peak ocular hypotensive effect occurring at two hours post-dosing. In a randomized, double-blind clinical study, ocular administration of 0.2% brimonidine in healthy volunteers resulted in a 23% reduction of mean intraocular pressure from baseline at 3 hours following administration. In comparative studies consisting of patients with open-angle glaucoma or ocular hypertension, the ocular hypotensive effect of brimonidine was maintained during treatment periods of up to 1 year. Brimonidine mediates vasoconstrictive effects and it was shown to exhibit anti-inflammatory properties in _ex vivo_ human skin model and _in vivo_ inflammation models. In a clinial trials consisting of adults with moderate to severe facial erythema of rosacea, brimonidine was shown to improve the extent of redness at 3 hours after application, compared to placebo. It was shown to be a potent vasoconstrictor of human subcutaneous vessels with a diameter of less than 200 µm. In _in vivo_ mouse inflammation models, brimonidine displayed anti-inflammatory properties by inhibiting edema. In a randomized, double-blind study, brimonidine reduced erythema for the 12 hours of the study in a dose-dependent manner. When adminsitered systemically, brimonidine was shown to cause cardiovascular effects by decreasing blood pressure, decreasing heart and respiratory rate, and prolonging the PR interval in the electrocardiogram. This is due to the targeting of adrenoceptors by the drug. Although the clinical significance has not been established, there is evidence that brimonidine exhibits neuroprotective activity in experimental models of cerebral ischemia and optic nerve injury. _In vitro_ studies show that brimonidine mediated protective effects on neuronal cells from kainate acid insult and on cultured retinal ganglion cells from glutamate-induced cytotoxicity, which is a possible mediator of secondary neuronal degeneration in human glaucoma. Neuroprotective actions of brimonidine were also demonstrated in rat models of acute retinal ischemia and chronic IOP elevation. It has been proposed that brimonidine may exert neuroprotective effects on the retina and optic nerve by enhancing intrinsic retinal ganglion cell survival mechanisms and/or induction of neuronal survival factors, such as bFGF. However, further investigations are needed to conclude on these possible therapeutic benefits of the drug. |
Solubility Data
| Solubility (In Vitro) |
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| Solubility (In Vivo) |
Solubility in Formulation 1: ≥ 2.5 mg/mL (8.56 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. Solubility in Formulation 2: ≥ 2.5 mg/mL (8.56 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 saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 3: 2.5 mg/mL (8.56 mM) 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. (Please use freshly prepared in vivo formulations for optimal results.) |
| Preparing Stock Solutions | 1 mg | 5 mg | 10 mg | |
| 1 mM | 3.4230 mL | 17.1151 mL | 34.2302 mL | |
| 5 mM | 0.6846 mL | 3.4230 mL | 6.8460 mL | |
| 10 mM | 0.3423 mL | 1.7115 mL | 3.4230 mL |