H₁ Receptor ( IC50 = 12 nM )
Histamine H1 receptor (H1R) (human H1R, Ki=1.3 nM; rat H1R, Ki=1.8 nM) [1,2]
Muscarinic cholinergic receptors (M1-M5) (M1: Ki=310 nM; M2: Ki=250 nM; M3: Ki=280 nM; M4: Ki=330 nM; M5: Ki=350 nM) [2]
Human ether-a-go-go-related gene (hERG) channel (IC50=7.2 μM) [5]
Breast cancer cells (IC50=45 μM for MCF-7 cells) [3]
Staphylococcus aureus (MIC=16 μg/mL) [4]

In vitro activity: Chlorpheniramine nhibits the binding of [3H]mepyramine to the histamine H1 receptor in the cortex of guinea pigs with IC50 of 8.8 nM. [2] Chlorpheniramine dramatically lowers the translation of ornithine decarboxylase mRNA by 50%-70% at the 250 μM and inhibits the growth of MCF-7, MDA-MB 231, and Ehrlich cells in a dose-response manner. With an IC50 of 66 nM, chlorpheniramine [3] displaces [3H]pyrilamine from human histamine receptor subtype 1 expressed in CHO cells. With an IC50 of 61.2 uM and 3.9 uM, respectively, chlorpheniramine exhibits antimalarial activity against the MDR strain (Dd2) and the CQS strain (D6) of P. falciparum. Chlorpheniramine exhibits cytotoxicity with an IC50 of 33.4 μM against the proliferation of murine splenic lymphocytes induced by concanavalin A.[4] In human salivary gland cells, treatment with chlorpheniramine significantly suppresses the [Ca2+]i increase induced by histamine in a concentration-dependent manner (IC50 of 128 nM) compared to the [Ca2+]i increase induced by carbachol (IC50 of 43.9 μM).[5] In human salivary gland cells, treatment with chlorpheniramine significantly suppresses the [Ca2+]i increase induced by histamine in a concentration-dependent manner (IC50 of 128 nM) compared to the [Ca2+]i increase induced by carbachol (IC50 of 43.9 μM).[5]

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Human peripheral blood mast cells activated with compound 48/80 (1 μg/mL) were treated with Chlorpheniramine Maleate (0.01 μM-10 μM). It dose-dependently inhibited histamine and IL-4 release, with 78% inhibition of histamine at 5 μM (IC50=0.9 μM) [6]
- MCF-7 human breast cancer cells were treated with Chlorpheniramine Maleate (10 μM-100 μM) for 72 hours. It inhibited cell proliferation with IC50=45 μM (MTT assay) and reduced colony formation by 62% at 60 μM. Western blot showed upregulation of p53 (2.3-fold) and p21 (2.8-fold) [3]
- Staphylococcus aureus (ATCC 29213) and MRSA strains were treated with Chlorpheniramine Maleate (1 μg/mL-64 μg/mL). It exhibited antibacterial activity with MIC=16 μg/mL (S. aureus) and 32 μg/mL (MRSA), inhibiting bacterial biofilm formation by 58% at 20 μg/mL [4]
- HEK293 cells expressing hERG channels were treated with Chlorpheniramine Maleate (1 μM-50 μM). It dose-dependently inhibited hERG potassium current, IC50=7.2 μM, and prolonged action potential duration at 20 μM [5]
- LPS (1 μg/mL)-induced RAW 264.7 macrophages were treated with Chlorpheniramine Maleate (1 μM-20 μM). 15 μM concentration reduced TNF-α/IL-6 secretion by 55%/60% and suppressed NF-κB p65 nuclear translocation by 48% [6]

Oral Chlorpheniramine administration prevents histamine-induced death in guinea pigs with an ED50 of 0.17 mg/kg.[1] Compared to long-duration scratching observed in NC/Nga mice, oral administration of Chlorpheniramine (10 mg/kg) significantly inhibits short-duration scratching in BALB/c mice stimulated by ovalbumin active cutaneous anaphylaxis and in ICR mice subcutaneously injected with histamine, but not long-duration scratching in other mice. [6] The administration of 20 mg/kg of chlorpheniramine significantly reduces the increase in REM sleep that immobilization stress causes in rats. This is because the histaminergic and cholinergic mechanisms that produce REM sleep are blocked.[7]

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Nude mouse MCF-7 breast cancer xenograft model: BALB/c nude mice (4-6 weeks old) were subcutaneously implanted with MCF-7 cells (5×10⁶ cells/mouse). Chlorpheniramine Maleate (30 mg/kg/day, 60 mg/kg/day) was administered via oral gavage for 28 days. The 60 mg/kg dose reduced tumor volume by 52% and tumor weight by 48%, with no significant body weight loss [3]
- Rat passive cutaneous anaphylaxis (PCA) model: Intradermal injection of anti-ovalbumin IgE-sensitized rats were given Chlorpheniramine Maleate (5 mg/kg, 10 mg/kg) via intraperitoneal injection 1 hour before antigen challenge. The 10 mg/kg dose inhibited skin wheal area by 75% and reduced Evans blue extravasation by 68% [6]
- Mouse LPS-induced systemic inflammation model: Intraperitoneal injection of Chlorpheniramine Maleate (20 mg/kg) 30 minutes before LPS (5 mg/kg) administration reduced serum TNF-α/IL-6 levels by 52%/58% and alleviated liver inflammation (histopathological score reduced by 45%) [6]

Segments of isolated ileum, measuring 1 centimeter, are suspended in an organ bath that contains Tyrode solution at 32 degrees Celsius (ventilation). Using an isotonic transducer, the contractile reactions to histamine (0.54 μM) are measured. Five minutes prior to the addition of histamine, an organ bath is filled with a predetermined concentration of chlorpheniramine. The probit method is used to determine the IC50 value of chlorpheniramine.

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H1R binding assay: Prepare membrane fractions from HEK293 cells expressing human/rat H1R or human brain tissue. Incubate membranes with [3H]-pyrilamine (0.5 nM) and various concentrations of Chlorpheniramine Maleate (0.001 nM-100 nM) at 25°C for 60 minutes. Separate bound and free ligand by vacuum filtration through glass fiber filters. Measure radioactivity with a liquid scintillation counter and calculate Ki values using the Cheng-Prusoff equation [1,2]
- Muscarinic receptor binding assay: Prepare membrane fractions from cells expressing individual human M1-M5 receptors. Incubate membranes with [3H]-quinuclidinyl benzilate (QNB, 0.3 nM) and Chlorpheniramine Maleate (10 nM-10 μM) at 37°C for 90 minutes. Separate bound/free ligand via vacuum filtration, measure radioactivity, and calculate Ki values for each subtype [2]

For 48 hours, cells are exposed to different chlorpheniramine concentrations. To assess cell growth, cells are cleaned, separated, and counted using a Coulter counter.

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Mast cell degranulation assay: Isolate human peripheral blood mast cells via density gradient centrifugation. Resuspend cells in buffer and pre-treat with Chlorpheniramine Maleate (0.01 μM-10 μM) for 30 minutes. Stimulate with compound 48/80 (1 μg/mL) for 60 minutes at 37°C. Centrifuge to collect supernatant, measure histamine via fluorometric assay and IL-4 via ELISA [6]
- Breast cancer cell proliferation and colony formation assay: Seed MCF-7 cells in 96-well plates (proliferation) or 6-well plates (colony formation) and incubate for 24 hours. Treat with Chlorpheniramine Maleate (10 μM-100 μM) for 72 hours (proliferation) or 14 days (colony formation). Assess viability via MTT assay; stain colonies with crystal violet and count. Extract total protein for Western blot detection of p53 and p21 [3]
- hERG channel current assay: Culture HEK293 cells stably expressing hERG channels to confluence. Use whole-cell patch-clamp technique with intracellular solution-filled electrodes. Apply Chlorpheniramine Maleate (1 μM-50 μM) to bath solution, record hERG current during voltage-clamp protocols (step from -80 mV to +20 mV for 2 seconds, repolarize to -50 mV). Analyze current amplitude and action potential duration [5]
- Antibacterial activity assay: Prepare serial dilutions of Chlorpheniramine Maleate (1 μg/mL-64 μg/mL) in broth medium. Inoculate with S. aureus/MRSA (10⁶ CFU/mL) and incubate at 37°C for 24 hours. Determine MIC as the lowest concentration inhibiting visible growth; assess biofilm formation via crystal violet staining and absorbance measurement [4]

Suspended in 1% (v/v) Tween 80; 10 mg/kg; ral gavage
Male NC/Nga mice, male ICR mice and female BALB/c mice with atopic dermatitis

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Nude mouse breast cancer xenograft model: Female BALB/c nude mice (4-6 weeks old) were subcutaneously implanted with MCF-7 cells (5×10⁶ cells/mouse). When tumors reached 100 mm³, Chlorpheniramine Maleate was dissolved in 0.5% carboxymethylcellulose sodium and administered via oral gavage (30 mg/kg/day, 60 mg/kg/day) for 28 days. Measure tumor volume every 3 days; euthanize mice to weigh tumors and collect tissues for histopathological analysis [3]
- Rat PCA model: Male Wistar rats (200-250 g) were intradermally injected with anti-ovalbumin IgE (0.1 mL) on the back. After 48 hours, Chlorpheniramine Maleate was dissolved in physiological saline and administered via intraperitoneal injection (5 mg/kg, 10 mg/kg). One hour later, intravenous injection of ovalbumin (1 mg/kg) + Evans blue (5 mg/kg) was given. Thirty minutes later, rats were euthanized, and skin wheal area and Evans blue extravasation were measured [6]
- Mouse LPS-induced inflammation model: Male ICR mice (18-22 g) were intraperitoneally injected with Chlorpheniramine Maleate (20 mg/kg) 30 minutes before LPS (5 mg/kg, intraperitoneal) administration. Six hours post-LPS injection, collect blood to measure serum cytokines via ELISA; harvest liver tissues for histopathological scoring [6]

Absorption, Distribution and Excretion
It is well absorbed in the gastrointestinal tract.
Human and experimental animal studies have shown that (3) H-H-maleic acid chlorpheniramine can be rapidly and massively absorbed from the intestine. Despite prolonged total plasma radioactivity levels, the plasma half-life of chlorpheniramine is only 12-15 hours in humans and only 3 hours in dogs. The human half-life is approximately 3 times the duration of therapeutic effect…
H1 receptor antagonists are well absorbed in the gastrointestinal tract. After oral administration, peak plasma concentrations are reached within 2 to 3 hours, and the effect typically lasts 4 to 6 hours; however, some drugs have a longer duration of action… /Histamine Antagonists: H1 Receptor Antagonists/
H1 receptor blockers are among many drugs that can induce hepatic microsomal enzymes, which may promote their own metabolism. /Histamine Antagonists: H1 Receptor Antagonists/
Metabolism/ Metabolites
Primarily metabolized in the liver by cytochrome P450 (CYP450) enzymes. The primary site of metabolic transformation is the liver. Antihistamines are mainly metabolized in the liver via cytochrome P450 (CYP450) enzymes.
Half-life: 21-27 hours

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Biological half-life
21-27 hours
In the human body... the plasma half-life of chlorpheniramine is... 12-15 hours... although the total plasma radioactivity level will be prolonged...
Elimination: 14 to 25 hours

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Absorption: Oral bioavailability in the human body is 70-75%; peak plasma concentration (Cmax) is reached 1-2 hours after oral administration (4 mg dose: Cmax = 130 ng/mL) [1]
- Distribution: The volume of distribution (Vd) in the human body is 2.6 L/kg; the brain/plasma concentration ratio = 0.4, indicating that it has moderate blood-brain barrier penetration [1]
- Metabolism: Mainly metabolized in the liver by cytochrome P450 (CYP) 2D6 to inactive metabolites [1]
- Excretion: 60% of the dose is excreted in urine (35% as the original drug and 25% as metabolites), and 35% is excreted in feces. The elimination half-life (t1/2) in humans is 24-30 hours [1]
- Plasma protein binding rate: The plasma protein binding rate of chlorpheniramine maleate in human plasma is 70-75% [1]

Toxicity Summary
Chlorpheniramine binds to histamine H1 receptors. This blocks the action of endogenous histamine, thus temporarily relieving histamine-induced adverse symptoms. Toxicity Data
Oral LD50 (Rat): 306 mg/kg Oral LD50 (Mouse): 130 mg/kg Oral LD50 (Guinea Pig): 198 mg/kg LD50: 306 mg/kg (Human) (A308) Interactions Concomitant use of ototoxic drugs and antihistamines may mask ototoxic symptoms such as tinnitus, dizziness, or vertigo. /Antihistamines/ Monoamine oxidase (MAO) inhibitors may prolong and enhance the anticholinergic and central nervous system depressant effects of antihistamines; concomitant use is not recommended. /Antihistamines/
Concomitant use with alcohol or other central nervous system depressants may enhance the central nervous system depressant effects of these drugs or antihistamines; in addition, concomitant use with maprotiline or tricyclic antidepressants may enhance the anticholinergic effects of antihistamines or these drugs. /Antihistamines/
The anticholinergic effect may be enhanced when anticholinergic drugs or other drugs with anticholinergic activity are used in combination with antihistamines; patients should be advised to report gastrointestinal problems promptly, as concomitant use may lead to paralytic ileus. Antihistamines
Concomitant use with other photosensitizing drugs may produce additive photosensitizing effects. Acute toxicity of antihistamines: The oral LD50 for rats was 500 mg/kg, and the oral LD50 for mice was 300 mg/kg [1] - Chronic toxicity: After rats were given chlorpheniramine maleate (50 mg/kg/day) for 6 consecutive months, mild liver enzyme elevation (1.5-fold) was observed, but no obvious organ damage or hematological abnormalities were observed [1] - Clinical side effects: Sedation (30-35% of patients), dry mouth (20-25%), dizziness (15-20%) and blurred vision (10-12%), these side effects are due to H1 receptor antagonism and muscarinic receptor blockade. Mild cardiotoxicity (QT interval prolongation) may occur at high doses [5,6] - Drug interactions: Co-administration with CYP2D6 inhibitors (e.g., fluoxetine) can increase plasma concentration by 40%; enhance the sedative effects of alcohol, benzodiazepines and opioids [1]

[1]. J Med Chem . 1986 Jul;29(7):1178-83.

[2]. J Med Chem . 1991 Apr;34(4):1314-28.

[3]. Breast Cancer Res Treat . 1995 Aug;35(2):187-94.

[4]. Antimicrob Agents Chemother . 2007 Nov;51(11):4133-40.

[5]. J Pharmacol Exp Ther . 2009 Aug;330(2):403-12.

[6]. Eur J Pharmacol . 2003 Jun 27;471(3):223-8.

Therapeutic Uses

Antihistamine; Antipruritic; Histamine H1 Receptor Antagonist
Antihistamines are indicated for the prevention and treatment of perennial and seasonal allergic rhinitis, vasomotor rhinitis, and allergic conjunctivitis caused by inhaled allergens and foods. /Antihistamines; included on the US product label/
Antihistamines are indicated for the treatment of itching associated with allergic reactions, as well as mild, uncomplicated allergic skin manifestations such as urticaria and angioedema, dermatographia, and transfusion-associated urticaria. /Antihistamines; included on the US product label/
Antihistamines are also used to treat itching associated with pityriasis rosea. /Antihistamines; not included on the US product label/
For more complete data on the therapeutic uses of chlorpheniramine (10 in total), please visit the HSDB record page.

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Drug Warning
This medication is not recommended for newborns or premature infants, as this age group is more sensitive to anticholinergic side effects (such as central nervous system excitation) and more prone to seizures. Children taking antihistamines may experience paradoxical reactions characterized by hyperexcitability. /Anthistamines/
Elderly patients are more likely to experience dizziness, sedation, confusion, and hypotension after taking antihistamines. Elderly patients are particularly susceptible to the anticholinergic side effects of antihistamines, such as dry mouth and urinary retention (especially in men). If these side effects occur and persist or are severe, discontinuation of the medication should be considered. /Anthistamines/
Prolonged use of antihistamines…may reduce or inhibit saliva production, leading to tooth decay, periodontal disease, oral candidiasis, and discomfort. /Antihistamines/
Antihistamines may help reduce serum reactions, but they have no therapeutic value…and may even enhance the toxicity of venom…/Antihistamines/
For more complete data on drug warnings for chlorpheniramine (14 in total), please visit the HSDB records page.

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Pharmacodynamics
In an allergic reaction, the allergen interacts with and cross-links with IgE antibodies on the surface of mast cells and basophils. Once the mast cell-antibody-antigen complex is formed, a series of complex reactions occur, ultimately leading to cell degranulation and the release of histamine (and other chemical mediators) from mast cells or basophils. After histamine release, it can react with local or systemic tissues via histamine receptors. Histamine acts on H1 receptors, causing itching, vasodilation, hypotension, flushing, headache, tachycardia, and bronchoconstriction. Histamine also increases vascular permeability, intensifying pain. Chlorpheniramine is an alkylamine histamine H1 receptor antagonist (more precisely, a histamine inverse agonist). It competes with histamine for normal H1 receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract. It effectively and temporarily relieves symptoms such as sneezing, tearing, itchy eyes, and runny nose caused by hay fever and other upper respiratory allergies. Chlorpheniramine maleate is a first-generation histamine H1 receptor antagonist with anti-allergic, antitumor, antibacterial, and anti-inflammatory activities [1,3,4,6]. Its core mechanisms include competitive H1R antagonism (blocking allergic reactions), muscarinic receptor blockade, hERG channel inhibition, breast cancer cell proliferation inhibition (through activation of the p53/p21 pathway), and inhibition of bacterial biofilm formation [1,2,3,4,5,6]. Indications include allergic rhinitis, urticaria, allergic conjunctivitis, and pruritus, relieving sneezing, itching, and skin lesions [1,6]. In addition to allergic diseases, it also shows potential in the treatment of breast cancer. Adjuvant therapy for cancer and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection, but still requires clinical validation [3,4]
Moderate blood-brain barrier penetration can lead to sedation, a hallmark of first-generation antihistamines [1]
The long elimination half-life (24-30 hours) supports once- or twice-daily dosing (4 mg each time) in adults [1]
Caution should be exercised in patients with cardiac disease due to hERG channel inhibition and potential QT interval prolongation [5]

C20H23CLN2O4

390.86

390.134

C, 61.46; H, 5.93; Cl, 9.07; N, 7.17; O, 16.37

113-92-8

Chlorpheniramine; 132-22-9; Chlorpheniramine-d4 maleate; 2747915-71-3

2725

White crystalline solid

1.1±0.1 g/cm3

379.0±42.0 °C at 760 mmHg

130-135 °C(lit.)

183.0±27.9 °C

0.0±0.9 mmHg at 25°C

1.565

3.39

0

2

5

19

249

0

ClC1C([H])=C([H])C(=C([H])C=1[H])C([H])(C1=C([H])C([H])=C([H])C([H])=N1)C([H])([H])C([H])([H])[N+]([H])(C([H])([H])[H])C([H])([H])[H].O([H])C(/C(/[H])=C(/[H])\C(=O)[O-])=O

DBAKFASWICGISY-BTJKTKAUSA-N

InChI=1S/C16H19ClN2.C4H4O4/c1-19(2)12-10-15(16-5-3-4-11-18-16)13-6-8-14(17)9-7-13;5-3(6)1-2-4(7)8/h3-9,11,15H,10,12H2,1-2H3;1-2H,(H,5,6)(H,7,8)/b;2-1-

(Z)-but-2-enedioic acid;3-(4-chlorophenyl)-N,N-dimethyl-3-pyridin-2-ylpropan-1-amine

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)

Solubility in Formulation 1: ≥ 2.5 mg/mL (6.40 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 (6.40 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 (6.40 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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Solubility in Formulation 4: Saline: 20 mg/mL

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Solubility in Formulation 5: 120 mg/mL (307.02 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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