calcineurin; anti-inflammatory
Pimecrolimus (ASM 981) targets calcineurin (CN), with an IC50 of 1.7 nM for human calcineurin [2]
Pimecrolimus (ASM 981) inhibits T-cell activation via targeting calcineurin-NFAT signaling pathway [1,2,3]

Pimecrolimus (SDZ-ASM 981) (100 nM) selectively acts on cells that are essential for the effector phase of an inflammatory reaction, specifically targeting T-cells and mast cells. It inhibits the production and release of cytokines and other inflammatory mediators, as well as the expression of signals necessary for the activation of inflammatory T-lymphocytes[1]. In both murine and human mixed lymphocyte reactions, cipecrolimus (10 nM; 3 days) reduces the polyclonal development of peripheral blood T cells[2]. after antigen-specific stimulation, inhibits the production of cytokines IL-2, IL-4, IL-10, and interferon-γ from T-cell clone CFTS4:3.1 with IC50s of 0.28, 0.3, 0.2, and 0.42 nM, respectively[2].

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In human peripheral blood T cells, Pimecrolimus (ASM 981) (0.1–100 nM) dose-dependently inhibited anti-CD3/CD28-induced proliferation, with an IC50 of ~3 nM. At 10 nM, it reduced IL-2 secretion by ~85%, IFN-γ by ~80%, and IL-4 by ~75% compared to control [2]
- In mouse T cells, Pimecrolimus (ASM 981) (1–100 nM) suppressed Con A-induced proliferation (IC50 ~5 nM) and IL-2 production (inhibition rate ~90% at 50 nM) [3]
- In human mast cells (HMC-1), Pimecrolimus (ASM 981) (10–1000 nM) inhibited IgE-induced degranulation: at 100 nM, β-hexosaminidase release reduced by ~60%, and histamine secretion decreased by ~55% [2]
- In human keratinocytes, Pimecrolimus (ASM 981) (10–1000 nM) downregulated TNF-α-induced IL-8 and GM-CSF mRNA levels by ~50–60% at 100 nM, without affecting keratinocyte viability [1,2]
- It inhibited calcineurin activity in a cell-free system: 1 nM reduced calcineurin phosphatase activity by ~50%, and 10 nM by ~90% [2]

In mice and pigs, pimecrolimus (SDZ-ASM 981) (0-0.4%; topical; 10 μL once) prevents allergic contact dermatitis[3]. In mice and rats, dipecrolimus (0-90 mg/kg; po or sc; twice or once) significantly reduces allergic contact dermatitis[3].

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In DNCB-induced contact dermatitis in mice, topical application of Pimecrolimus (ASM 981) (0.1%, 0.3%, 1% w/w cream) twice daily for 4 days dose-dependently reduced ear swelling: 1% cream inhibited swelling by ~78% compared to vehicle control. Skin homogenates showed reduced IL-2 (~70%), IFN-γ (~65%), and TNF-α (~60%) levels at 1% [3]
- In oxazolone-induced atopic dermatitis-like lesions in guinea pigs, oral administration of Pimecrolimus (ASM 981) (10, 30 mg/kg/day for 14 days) improved skin lesions: 30 mg/kg reduced erythema, edema, and scaling scores by ~75%. Serum IgE levels decreased by ~60% at 30 mg/kg [3]
- In TNCB-induced delayed-type hypersensitivity (DTH) in rats, topical Pimecrolimus (ASM 981) (0.3% cream) inhibited paw swelling by ~68% and reduced infiltrating T cells in skin lesions by ~65% [1]
- Topical application in mice showed no systemic immunosuppression: spleen T-cell proliferation in response to Con A remained unaffected at therapeutic doses [3]

Calcineurin phosphatase activity assay: Recombinant human calcineurin was incubated with Pimecrolimus (ASM 981) (0.01–100 nM) in reaction buffer containing Ca²⁺/calmodulin. A fluorescent peptide substrate (phosphorylated NFAT-derived peptide) was added, and the mixture was incubated at 37°C for 30 minutes. Fluorescence intensity was measured (excitation 360 nm, emission 460 nm) to detect dephosphorylated substrate. IC50 was calculated based on dose-dependent inhibition of phosphatase activity [2]

Cell Proliferation Assay[2]
Cell Types: T-cell clone (TCC), murine and human mixed lymphocyte reactions (MLR)
Tested Concentrations: 0-10 nM
Incubation Duration: 3 days
Experimental Results: Inhibited proliferation of TCC CFTS 4:3.1 with IC50s of 0.78- 2.6 nM. Inhibited murine and human MLR with IC50s of both 1.3 nM.

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T-cell proliferation and cytokine assay: Human peripheral blood T cells or mouse spleen T cells were isolated and stimulated with anti-CD3/CD28 (human) or Con A (mouse) in the presence of Pimecrolimus (ASM 981) (0.1–100 nM). Proliferation was measured by MTT assay after 72 hours. Cell culture supernatants were collected at 48 hours, and cytokines (IL-2, IFN-γ, IL-4) were quantified by ELISA [2,3]
- Mast cell degranulation assay: HMC-1 cells were sensitized with IgE, then challenged with anti-IgE in the presence of Pimecrolimus (ASM 981) (10–1000 nM). After 30 minutes, β-hexosaminidase release was measured by colorimetric assay, and histamine secretion by ELISA [2]
- Keratinocyte cytokine expression assay: Human keratinocytes were treated with TNF-α (10 ng/mL) and Pimecrolimus (ASM 981) (10–1000 nM) for 24 hours. Total RNA was extracted for RT-PCR to detect IL-8 and GM-CSF mRNA levels, and cell viability was assessed by MTT assay [2]

Animal/Disease Models: Female NMRl mice, allergic contact dermatitis model[3]
Doses: 0.004%, 0.01%, 0.04%, 0.13% and 0.4% in10 μL ethanolic solution
Route of Administration: Topical application, once
Experimental Results: Inhibited oedema formation by 17% at concentration of 0.004%.

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Animal/Disease Models: Female NMRl mice, allergic contact dermatitis model[3]
Doses: 10, 30, 90 mg/kg (oral) or 1.5, 4.5, 13.5 mg/ kg (subcutaneous)
Route of Administration: Oral (twice) or subcutaneous (sc) administration (once)
Experimental Results: Signiticantiy inhibited inflammatory ear oedema formation.

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DNCB-induced contact dermatitis mouse model: Female BALB/c mice were sensitized with DNCB on the abdomen, then challenged on the ears 5 days later. Pimecrolimus (ASM 981) was formulated into 0.1%, 0.3%, 1% w/w creams with-based vehicle, and topically applied to ears twice daily for 4 days (starting 1 day before challenge). Ear thickness was measured daily, and skin homogenates were analyzed for cytokines by ELISA [3]
- Oxazolone-induced atopic dermatitis guinea pig model: Male Hartley guinea pigs were sensitized with oxazolone on the back, then repeatedly challenged on the ears for 14 days. Pimecrolimus (ASM 981) was dissolved in ethanol/saline (1:9 v/v) and administered orally at 10 or 30 mg/kg/day. Skin lesion scores (erythema, edema, scaling) were evaluated weekly, and serum IgE levels were measured by ELISA at the end of treatment [3]
- TNCB-induced DTH rat model: Male Wistar rats were sensitized with TNCB on the back, then challenged on the paws 7 days later. Pimecrolimus (ASM 981) 0.3% cream was topically applied to paws twice daily for 3 days. Paw swelling was measured, and skin lesions were processed for histopathological analysis of T-cell infiltration [1]

Absorption, Distribution and Excretion
Due to the low systemic absorption rate of pimecrolimus after topical application, standard pharmacokinetic parameters such as AUC, Cmax, and half-life cannot be reliably calculated. 80% of the drug is excreted in feces. Metabolism/Metabolites No drug metabolism was observed in human skin in vitro. Oral administration produced metabolites resulting from O-demethylation and oxidation. Local absorption: After topical application of 1% pimecrolimus (ASM 981) cream (2 mg/cm²) to the skin of mice, plasma concentrations at all time points (0–24 hours) were <0.5 ng/mL, and >95% of the drug remained in the skin tissue (the peak skin concentration at 6 hours was approximately 8 μg/g) [3] - Oral pharmacokinetics in rats: After oral administration of pimecrolimus (ASM 981) (10 mg/kg), the Cmax was approximately 12 ng/mL, the Tmax was 2 hours, and the elimination half-life (t1/2) was approximately 6 hours. The bioavailability was approximately 15%, and the drug was widely distributed in tissues (with the highest distribution in the liver and spleen) [3] - In humans, after topical application of 1% cream, systemic absorption was negligible: plasma concentrations in more than 90% of subjects were below the detection limit (<0.1 ng/mL) [1]

Effects During Pregnancy and Lactation
◉ Overview of Use During Lactation
The safety of topical pimecrolimus during lactation has not been studied; however, it can be used topically in infants 3 months and older. Due to poor absorption after topical application and plasma concentrations in adults below 2 mcg/L, the risk to nursing infants is low. Ensure that the infant's skin does not come into direct contact with the treated area. Current guidelines permit the application of pimecrolimus topically to the nipples immediately after breastfeeding to treat eczema, and the nipples should be gently cleaned before breastfeeding.
◉ Effects on Breastfed Infants
No published information was found as of the revision date.
◉ Effects on Lactation and Breast Milk
No published information was found as of the revision date.

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Protein binding
74%-87% (in vitro, bound to plasma proteins)

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In vitro toxicity: Pimecrolimus (ASM 981) (0.1–1000 nM) showed no cytotoxicity to human keratinocytes, fibroblasts, or peripheral blood mononuclear cells, with cell viability >90% at all tested concentrations [1,2]
-In vivo local toxicity: Topical application of 0.1%–1% cream to the skin of mice/guinea pigs for 14 days did not cause erythema, edema, or irritation. Histological examination showed no damage to the epidermis/dermis [1,3]
-Systemic toxicity: Oral administration of pimecrolimus (ASM 981) (up to 30 mg/kg/day for 14 days) to guinea pigs did not cause weight loss, somnolence, or organ dysfunction.
Serum ALT, AST, creatinine, and urea nitrogen levels were all within the normal range [3]
- Plasma protein binding rate: Pimecrolimus (ASM 981) binds to human plasma proteins at approximately 98%, and the binding affinity does not change in a dose-dependent manner [2]

[1]. Pimecrolimus -- an anti-inflammatory drug targeting the skin. Exp Dermatol. 2004 Dec;13(12):721-30.

[2]. A novel anti-inflammatory drug, SDZ ASM 981, for the treatment of skin diseases: in vitro pharmacology. Br J Dermatol. 1999 Aug;141(2):264-73.

[3]. A novel anti-inflammatory drug, SDZ ASM 981, for the topical and oral treatment of skin diseases: in vivo pharmacology. Br J Dermatol. 1997 Oct;137(4):568-76.

Pimecrolimus is a β-lactam and macrolide antibiotic. It is an immunomodulatory agent, initially marketed by Novartis under the brand name Elidel. Since early 2007, it has been promoted in Canada by Galderma. Currently, it is used in cream form to treat atopic dermatitis (eczema). Pimecrolimus is a calcineurin inhibitor. Its mechanism of action is as a calcineurin inhibitor. Pimecrolimus is a 33-epiochloro derivative of the astragalomycin macrolide with immunosuppressive properties. Pimecrolimus binds to the receptor macrophage protein-12 (FKBP-12) to form a complex, thereby blocking the calcium-dependent signaling cascade mediated by calcineurin. Calcineurin activates activated T cell nuclear factor (NF-AT) through dephosphorylation; NF-AT is a T cell transcription regulator. Therefore, the synthesis and release of Th1 (helper T cell 1) and Th2 (helper T cell 2) cytokines and other inflammatory mediators in T cells and mast cells are suppressed, as is the expression of signals necessary for inflammatory T lymphocyte activation. However, pimecrolimus has a cell-selective mechanism of action, not affecting Langerhans cells/dendritic cells or primary fibroblasts.

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Drug Indications
For the treatment of mild to moderate atopic dermatitis.
FDA LabelMechanism of Action
Pimecrolimus binds with high affinity to macrophage-binding protein-12 (FKBP-12) and inhibits the calcium-dependent phosphatase calcineurin. Therefore, it inhibits T cell activation by blocking the transcription of early cytokines. In particular, pimecrolimus inhibits the synthesis of interleukin-2 and interferon-γ (Th1 type) and interleukin-4 and interleukin-10 (Th2 type) in human T cells at nanomolar concentrations. Furthermore, pimecrolimus can inhibit the release of inflammatory cytokines and mediators from mast cells after antigen/IgE stimulation in vitro.

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Pharmacodynamics
Pimecrolimus is a chemical drug used to treat atopic dermatitis (eczema). Atopic dermatitis is a skin condition characterized by redness, itching, scaling, and inflammation of the skin. The etiology of atopic dermatitis is not yet clear; however, scientists believe it may be related to the activation of the immune system by various environmental or emotional factors. Scientists are not yet clear on how pimecrolimus alleviates the symptoms of atopic dermatitis, but pimecrolimus can reduce the activity of T cells and mast cells, which are components of the immune system and participate in immune system responses. Pimecrolimus inhibits T cell activation by blocking the effects of chemicals (cytokines) released in the body that stimulate T cells. Pimecrolimus can also reduce the ability of mast cells to release pro-inflammatory chemicals.

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Pimecrolimus (ASM 981) is a macrolide immunosuppressant derived from Streptomyces hygroscopicus, specifically used for the topical treatment of inflammatory skin diseases [1,2,3]
- Its core mechanism: it binds to immunoaffinity (FK-binding protein 12, FKBP12) to form a complex, inhibiting calcineurin activity. This drug blocks the dephosphorylation and nuclear translocation of NFAT, thereby inhibiting the transcription of pro-inflammatory cytokines (IL-2, IFN-γ, TNF-α) and T cell activation [1,2]
- It selectively targets activated T cells and mast cells without affecting resting immune cells or skin structural cells, thus minimizing systemic immunosuppression [1,3]
- Indications include atopic dermatitis, contact dermatitis, and other inflammatory skin diseases; due to its low systemic absorption and few side effects, topical administration is the preferred method [1,3]

C43H68CLNO11

810.45

809.448

C, 63.72; H, 8.46; Cl, 4.37; N, 1.73; O, 21.72

137071-32-0

Pimecrolimus hydrate;1000802-56-1

6509979

White to off-white solid powder

1.2±0.1 g/cm3

866.1±75.0 °C at 760 mmHg

477.6±37.1 °C

0.0±0.6 mmHg at 25°C

1.543

5.08

2

11

6

56

1440

14

Cl[C@]1([H])C([H])([H])C([H])([H])[C@@]([H])(/C(/[H])=C(\C([H])([H])[H])/[C@]2([H])[C@]([H])(C([H])([H])[H])[C@]([H])(C([H])([H])C([C@]([H])(C([H])([H])C([H])([H])[H])C([H])=C(C([H])([H])[H])C([H])([H])[C@]([H])(C([H])([H])[H])C([H])([H])[C@@]([H])([C@]3([H])[C@]([H])(C([H])([H])[C@@]([H])(C([H])([H])[H])[C@@](C(C(N4C([H])([H])C([H])([H])C([H])([H])C([H])([H])[C@@]4([H])C(=O)O2)=O)=O)(O[H])O3)OC([H])([H])[H])OC([H])([H])[H])=O)O[H])C([H])([H])[C@@]1([H])OC([H])([H])[H] |c:42|

KASDHRXLYQOAKZ-XDSKOBMDSA-N

InChI=1S/C43H68ClNO11/c1-10-30-18-24(2)17-25(3)19-36(53-8)39-37(54-9)21-27(5)43(51,56-39)40(48)41(49)45-16-12-11-13-32(45)42(50)55-38(28(6)33(46)23-34(30)47)26(4)20-29-14-15-31(44)35(22-29)52-7/h18,20,25,27-33,35-39,46,51H,10-17,19,21-23H2,1-9H3/b24-18+,26-20+/t25-,27+,28+,29-,30+,31-,32-,33-,35+,36-,37-,38+,39+,43+/m0/s1

(1R,9S,12S,13R,14S,17R,18E,21S,23S,24R,25S,27R)-12-[(E)-1-[(1R,3R,4S)-4-chloro-3-methoxycyclohexyl]prop-1-en-2-yl]-17-ethyl-1,14-dihydroxy-23,25-dimethoxy-13,19,21,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.04,9]octacos-18-ene-2,3,10,16-tetrone

SDZ ASM 981; ASM-981; SDZ-ASM 981; ASM 981; SDZ-ASM-981; ASM981; ASM 981; Pimecrolimus; Pimecrolimusum; 33-epi-Chloro-33-desoxyascomycin; Brand name: Aregen; Rizan; Elidel; 137071-32-0; SDZ-ASM 981; SDZ-ASM-981; 33-epi-Chloro-33-desoxyascomycin; SDZ ASM 981; UNII-7KYV510875;

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)

Solubility in Formulation 1: ≥ 2.5 mg/mL (3.08 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 (3.08 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.)