As with recombinant human TPO (rhTPO), avatrombopag (E5501; AKR-501) specifically binds the TPO receptor and induces megakaryopoiesis throughout megakaryocyte development and maturation [1]. In a concentration-dependent way, avatrombopag (0-100 nM) promotes the growth of Ba/F3 cells that express TPO receptors. Similar to rhTPO, avatrombopag (0-3 μM) causes tyrosine phosphorylation of STAT3 and STAT5, as well as threonine phosphorylation of ERK, in cells [1]. In human CD34+ cells, avatrombopag stimulates the development of megakaryocyte colonies in a concentration-dependent way. Avatrombopag has a 25 nM EC50 and a maximal activity that is comparable to rhTPO [1].

As with recombinant human TPO (rhTPO), avatrombopag (E5501; AKR-501) specifically binds the TPO receptor and induces megakaryopoiesis throughout megakaryocyte development and maturation [1]. In a concentration-dependent way, avatrombopag (0-100 nM) promotes the growth of Ba/F3 cells that express TPO receptors. Similar to rhTPO, avatrombopag (0-3 μM) causes tyrosine phosphorylation of STAT3 and STAT5, as well as threonine phosphorylation of ERK, in cells [1]. In human CD34+ cells, avatrombopag stimulates the development of megakaryocyte colonies in a concentration-dependent way. Avatrombopag has a 25 nM EC50 and a maximal activity that is comparable to rhTPO [1].

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Avatrombopag metabolism is mediated by cytochrome P450 (CYP) 3A4 and CYP2C9. In vitro data using the relative activity factor in human liver microsomes and recombinant CYP enzymes suggested that CYP2C9 and CYP3A contribute equally to the formation of the 4-hydroxy metabolite. [3]

NOD/SCID mice transplanted with human FL CD34+ cells have higher human platelet counts when administered with avatrombopag (0.3-3 mg/kg; oral; daily for 14 days) [1].

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In a three-part, open-label clinical study in healthy subjects, coadministration of a single 20-mg dose of avatrombopag with the dual CYP2C9/CYP3A inhibitor fluconazole (400 mg once daily) resulted in a 2.16-fold increase in AUC, a prolonged terminal elimination half-life (from 19.7 h to 39.9 h), and a clinically significant 1.66-fold increase in maximum platelet count. The mean difference in Emax was 21.19 × 10⁹/L. [3]
Coadministration of avatrombopag with the strong CYP3A inhibitor itraconazole (200 mg twice daily on Day 1, then 200 mg once daily) resulted in a milder increase in AUC (1.37-fold), a prolonged half-life (from 19.6 h to 28.0 h), but no statistically significant impact on the maximum platelet count. [3]
Coadministration of avatrombopag with the dual inducer rifampicin (600 mg once daily) caused a 0.5-fold decrease in AUC and a shortened half-life (from 20.3 h to 9.77 h), with no significant impact on the maximum platelet count. However, the area under the effect curve for platelet count over 28 days [AUEC(0-28d)] was reduced approximately 5-fold. [3]
The study suggests that CYP2C9 plays a more predominant role than CYP3A in the metabolic clearance of avatrombopag. [3]

An in vitro study using human liver microsomes and recombinant CYP enzymes was conducted to assess the relative percentage contribution of CYP2C9 and CYP3A to the CYP-dependent metabolism of avatrombopag. The data suggested that these two enzymes contribute equally to the formation of the primary 4-hydroxy metabolite. [3]

Cell proliferation assay [1]
Cell Types: Ba/F3 cells
Tested Concentrations: 0.003 μM, 0.03 μM, 0.3 μM, 3 μM
Incubation Duration:
Experimental Results: Increased proliferation of Ba/F3 cells expressing TPO receptor in a concentration-dependent manner.

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Western Blot Analysis [1]
Cell Types: Ba/F3 cells
Tested Concentrations: 0.003 μM, 0.03 μM, 0.3 μM, 3 μM
Incubation Duration: 15 minutes
Experimental Results: Induction of intracellular tyrosine phosphorylation of STAT3 and STAT5 and threonine of ERK Acid phosphorylation.

Animal/Disease Models: NOD/SCID (severe combined immunodeficient) mouse (transplanted with human FL CD34+ cells) [1]
Doses: 0.3, 1, and 3 mg/kg
Route of Administration: Po; one time/day for 14 days
Experimental Results: Human platelet counts were dose-dependent The increase was approximately 2.7-fold at 1 mg/kg/d and approximately 3.0-fold at 3 mg/kg/d on day 14 after initiation of administration.

Absorption, Distribution and Excretion
Following a single dose in both fasting and fed conditions, the mean peak concentrations in Japanese and Caucasian subjects occurred at 5–8 hours, with a half-life of 16–18 hours. Co-administration with food did not affect the rate or extent of avatrombopag absorption, but significantly reduced pharmacokinetic variability compared to fasting. The pharmacokinetics of avatrombopag are dose-proportional after a single dose, ranging from 10 mg (0.25 times the lowest approved dose) to 80 mg (1.3 times the highest recommended dose). In healthy subjects, after a 40 mg dose of avatrombopag, the geometric mean (%CV) maximum concentration (Cmax) was 166 (84%) ng/mL, and the area under the time-concentration curve (extrapolated to infinity) was 4198 (83%) ng·hr/mL. The pharmacokinetics of avatrombopag were similar in healthy subjects and individuals with chronic liver disease.
88% of the administered dose is excreted in feces, of which 34% is excreted unchanged as avatrobappa. Only 6% of the administered dose is detected in urine.
The mean volume of distribution of avatrobappa is estimated to be 180 L (%CV) (25%).
The mean clearance of avatrobappa is estimated to be 6.9 L/hr (%CV) (29%).
Metabolites
Avatrobappa is primarily metabolized by CYP2C9 and CYP3A4.
Biological half-life
The mean plasma elimination half-life (%CV) of avatrobappa is approximately 19 hours (19%).
In healthy subjects, avatrobappa exhibits linear pharmacokinetic characteristics in the dose range of 20 mg to 60 mg. [3]
The mean peak plasma concentration (Cmax) occurs 6–8 hours after a single dose in a fed state. [3]
In healthy subjects, the terminal elimination half-life is 16–19 hours. [3]
Food does not alter the rate or extent of absorption, but may reduce pharmacokinetic variability compared to fasting. It is recommended to take with food. [3]
The primary route of excretion of avatrobappa and its metabolites is feces, accounting for approximately 88% of the administered dose. The major metabolite, a 4-hydroxy derivative, is detected only in feces, accounting for 44% of the administered dose. No metabolites have been detected in plasma. [3]
The metabolism of avatrobappa is mediated by CYP3A4 and CYP2C9. In vitro studies have shown that the relative contributions of these two enzymes are equal. [3]
In a clinical drug interaction study of a single dose of 20 mg avatrobappa, the arithmetic mean (standard deviation) of the pooled data (if any) of the pharmacokinetic parameters were: Cmax: approximately 10³–10⁶ µg/L; AUC(0-inf): approximately 3170–3380 µg·h/L; t¹/²: approximately 19.7–20.3 h. [3]

Effects During Pregnancy and Lactation
◉ Overview of use during lactation There is currently no information available regarding the use of avatrobappa during lactation. The manufacturer recommends avoiding breastfeeding during avatrobappa use and for at least 2 weeks after the last dose. ◉ 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. Protein binding Avatrobappa binds to human plasma proteins at a rate greater than 96%. In clinical drug interaction studies, avatrobappa in combination with fluconazole, itraconazole, or rifampin was generally safe and well-tolerated. [3] The incidence of adverse events was similar in the avatrobappa monotherapy group and the combination therapy group. All adverse events that occurred during treatment were mild or moderate. No clinically significant changes in vital signs or significant electrocardiographic abnormalities were observed. [3]
Drug interactions may occur when avatrobappa is used in combination with CYP2C9 and CYP3A inhibitors or inducers. Combination with dual inhibitors such as fluconazole significantly increases avatrobappa exposure and platelet count, potentially increasing the risk of thrombosis. Combination with potent inducers such as rifampin significantly reduces exposure and the duration of platelet response. [3]
Dose adjustments are recommended when avatrobappa is used in combination with CYP3A and CYP2C9 inhibitors. Concomitant use of potent inducers is currently not recommended for patients with chronic liver disease scheduled for surgery. [3]
One study showed that subjects with the CYP2C9 3/3 genotype had the highest avatrobappa exposure, but due to the limited sample size, a clear relationship between CYP2C9 or CYP3A5 genotype and the pharmacokinetics of avatrobappa has not been established. [3]

[1]. AKR-501 (YM477) a novel orally-active thrombopoietin receptor agonist. Eur J Haematol. 2009;82(4):247-254.

[2]. Avatrombopag for the treatment of thrombocytopenia in patients with chronic liver disease. Expert Rev Clin Pharmacol. 2019 Sep;12(9):859-865.

[3]. Pharmacokinetic/pharmacodynamic drug-drug interactions of avatrombopag when coadministered with dual or selective CYP2C9 and CYP3A interacting drugs. Br J Clin Pharmacol. 2018;84(5):952-960.

Avatrombopag (brand name: Dopril) is an oral, small-molecule thrombopoietin receptor (c-MPl) agonist that increases platelet count without increasing platelet activation, thus reducing the need for transfusions. Patients with thrombocytopenia and chronic liver disease often require platelet transfusions before surgery to reduce the risk of bleeding. Thrombocytopenia is a common complication in patients with chronic liver disease, and it can occur either from the liver disease itself or as a consequence of interferon-based antiviral therapy. Avatrombopag was first approved by the U.S. Food and Drug Administration (FDA) in May 2018 for adult patients with chronic liver disease scheduled for surgery. It is administered orally in the form of Avatrombopag maleate. Dopril (Avatrombopag) was the first oral medication for the treatment of chronic liver disease that can raise platelet counts to optimal levels (≥50,000/μL), thus allowing many patients to avoid platelet transfusions before surgery.
Avatrobappa is an orally effective thrombopoietin receptor (TPOR; MPL) agonist with potential megakaryocyte-stimulating activity. Upon administration, avatrobappa binds to TPOR and stimulates its activity, thereby promoting the proliferation and differentiation of bone marrow progenitor cells into megakaryocytes. This can increase platelet production and may prevent chemotherapy-induced thrombocytopenia (CIT). TPOR is a cytokine receptor belonging to the hematopoietic factor receptor superfamily.
See also: Avatrobappa maleate (active ingredient).
Indications

For the treatment of thrombocytopenia in adult patients with chronic liver disease who are scheduled for surgery. Also indicated for adult patients with chronic immune thrombocytopenia who have had an inadequate response to prior therapy.
FDA Label
Doppler is indicated for the treatment of severe thrombocytopenia in adult patients with chronic liver disease who are scheduled for invasive surgery. Doppler is indicated for the treatment of primary chronic immune thrombocytopenic purpura (ITP) in adults who are unresponsive to other treatments, such as corticosteroids and immunoglobulins.
Treatment of chemotherapy-induced thrombocytopenia

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Mechanism of Action
Avatrombopag is an orally bioavailable small molecule thrombopoietin (TPO) receptor agonist that stimulates the proliferation and differentiation of bone marrow progenitor cells into megakaryocytes, thereby increasing platelet production. Avatrombopag does not compete with thrombopoietin for binding to TPO receptors and has an additive pharmacological effect with TPO on platelet production. Avatrombopag is a thrombopoietin receptor (TPOR; MPL) agonist and may have activity that stimulates megakaryocyte production. After administration, avatrombopag binds to and stimulates the activity of the thrombopoietin receptor (TPOR), thereby promoting the proliferation and differentiation of bone marrow progenitor cells into megakaryocytes. This process increases platelet production and helps prevent chemotherapy-induced thrombocytopenia (CIT). TPOR belongs to the cytokine receptor family and is a member of the hematopoietic factor receptor superfamily.

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Pharmacodynamics
In a efficacy study, avatrobappa increased platelet count in adults in a dose- and exposure-dependent manner. The increase in platelet count was observed within 3 to 5 days after the start of a 5-day course of treatment and reached its peak after 10 to 13 days. Thereafter, the platelet count gradually decreased and returned to near baseline levels by 35 days. Increased platelet activation can lead to increased blood coagulation, which may cause various complications. Avatrobappa does not cause increased platelet activation.

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Avatrobappa is a thrombopoietin receptor agonist and is currently being investigated as an alternative to platelet transfusion in patients with chronic liver disease and thrombocytopenia undergoing elective interventional procedures. It has also been evaluated in patients with immune thrombocytopenic purpura. [3]
The drug increases platelet count in a dose-dependent manner. An increase in platelet count can be observed 3-5 days after administration, and reaches its peak around 6-10 days after administration. [3]
This study is a three-part, open-label, fixed-sequence drug interaction study conducted in healthy subjects to evaluate the effects of steady-state administration of CYP2C9/CYP3A inhibitors (fluconazole, itraconazole) and inducers (rifampin) on the pharmacokinetics, pharmacodynamics (platelet count) and safety of avatrobappa at a single dose. [3]

C29H34CL2N6O3S2

649.65

648.151

570406-98-3

Avatrombopag hydrochloride;570403-17-7;Avatrombopag maleate;677007-74-8

9852519

White to off-white solid powder

1.4±0.1 g/cm3

1.671

6.82

2

10

7

42

935

0

OFZJKCQENFPZBH-UHFFFAOYSA-N

InChI=1S/C29H34Cl2N6O3S2/c30-20-15-23(41-17-20)24-27(37-12-10-35(11-13-37)21-4-2-1-3-5-21)42-29(33-24)34-26(38)19-14-22(31)25(32-16-19)36-8-6-18(7-9-36)28(39)40/h14-18,21H,1-13H2,(H,39,40)(H,33,34,38)

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)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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