Andexanet alfa

(heavy chain)
IVGGQECKDG ECPWQALLIN EENEGFCGGT ILSEFYILTA AHCLYQAKRF KVRVGDRNTE
QEEGGEAVHE VEVVIKHNRF TKETYDFDIA VLRLKTPITF RMNVAPACLP ERDWAESTLM
TQKTGIVSGF GRTHEKGRQS TRLKMLEVPY VDRNSCKLSS SFIITQNMFC AGYDTKQEDA
CQGDAGGPHV TRFKDTYFVT GIVSWGEGCA RKGKYGIYTK VTAFLKWIDR SMKTRGLPKA
KSHAPEVITS SPLK
(light chan)
ANSFLFWNKY KDGDQCETSP CQNQGKCKDG LGEYTCTCLE GFEGKNCELF TRKLCSLDNG
DCDQFCHEEQ NSVVCSCARG YTLADNGKAC IPTGPYPCGK QTLER
(Disulfide bridge: H7-H12, H27-H43, H108-L98, H156-H170, H181-H209, L16-L27, L21-L36, L38-L47, L55-L66, L62-L75, L77-L90)

Andexanet alfa

JAPAN 2022, PEPTIDE

CAS: 1262449-58-0

アンデキサネットアルファ (遺伝子組換え)

• Andexanet alfa
• r-Antidote
• rfXa Inhibitor Antidote
• PRT-4445
• PRT064445

Andexanet alfa, sold under the trade name Andexxa among others, is an antidote for the medications rivaroxaban and apixaban, when reversal of anticoagulation is needed due to uncontrolled bleeding.^[1] It has not been found to be useful for other factor Xa inhibitors.^[2] It is given by injection into a vein.^[2]

Common side effects include pneumonia and urinary tract infections.^[2] Severe side effects may include blood clots, heart attacks, strokes, or cardiac arrest.^[2] It works by binding to rivaroxaban and apixaban.^[2]

It was approved for medical use in the United States in May 2018.^[1] It was developed by Portola Pharmaceuticals.^[3]

ndexanet alfa is a recombinant human coagulation Factor Xa that promotes blood coagulation. It was developed by Portola Pharmaceuticals and was approved in in May 2018. It is marketed as Andexxa for intravenous injection or infusion and is indicated for the reversal of anticoagulation in combination with rivaroxaban and apixaban in cases of life-threatening or uncontrolled bleeding. Rivaroxaban and apixaban are Factor Xa inhibitors that promote anticoagulation in situations where blood clotting is unfavourable, such as in deep vein thrombosis and pulmonary embolism. However, the use of these agents is associated with a risk for uncontrollable bleeding episodes that can lead to can cause serious or fatal bleeding. Andexanet alfa is currently under regulatory review by the European Union and is undergoing clinical development in Japan ¹.

Andexanet alfa works by binding to Factor Xa inhibitors and prevent them from interacting with endogenous Factor Xa. It displayed high affinity (0.53–1.53 nmol/L) to apixaban, betrixaban, edoxaban and rivaroxaban ¹. However, the effectiveness of andexanet alfa on treating bleeding related to any FXa inhibitors other than apixaban and rivaroxaban was not demonstrated, thus such use is limited ⁷. Its pharmacokinetic properties are not reported to be affected by factor Xa inhibitors ¹. Andexanet alfa retains the structural similarity to that of endogenous human factor Xa, but exists in its mature functional form without the need for activation via the intrinsic or extrinsic coagulation pathways ⁵ and remains catalytically inactive due to structural modification ¹. The procoagulation potential of andexanet alfa is eliminated through the removal of a 34-residue fragment containing Gla: via this truncation, andexanet alfa is unable to bind to membrane surfaces and assemble the prothrombinase complex ⁵. It also prevents andexanet alfa from taking up space on phospholipid surface membranes, so that native FXa may bind and assemble the prothrominase complex ⁵. The amino acid residue modification from serine to alanine in the binding site of the catalytic domain allows more effective binding to FXa inhibitors and deters the andexanet alfa from converting prothrombin to thrombin ⁵.

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Structure of andexant alfa. Andexanet alfa is a modified activated human factor Xa (FXa) that binds FXa with high affinity and a 1:1 stoichiometric ratio but does not have intrinsic catalytic activity (the amino acid serine at position 419 is replaced by alanine) and lacks the membrane-binding-carboxyglutamic acid domain (Gla domain) of native FX. The Gla domains are responsible for the binding of FXa to phospholipids

Medical uses

Andexanet alfa is used to stop life threatening or uncontrollable bleeding in people who are taking rivaroxaban or apixaban.^[1]

There are no randomised clinical trials as of 2019. Studies in healthy volunteers show that the molecule binds factor Xa inhibitors and counters their anti-Xa-activity.^[4] The only published clinical trial is a prospective, open label, single group study.^[5] This study reports results on 352 people and demonstrates a reduction of anti-Xa-activity while also showing an excellent or good hemostatic efficacy in 82%. While people who were expected to die in 30 days were excluded from the study, 14% of participants died. There was no relationship between hemostatic efficacy and reduced anti-Xa-activity.^[6] The FDA has demanded a randomised clinical trial: the first results are not expected before 2023.^[7]

Adverse effects

Common side effects include pneumonia and urinary tract infections.^[2] Severe side effects may include blood clots or cardiac arrest.^[2]

Andexanet alfa has a boxed warning that it is associated with arterial and venous blood clots, ischemic events, cardiac arrest, and sudden deaths.^[1]

Pharmacology

Mechanism of action

Andexanet alfa is a biologic agent, a recombinant modified version of human activated factor X (FXa).^[8] Andexanet alfa differs from native FXa due to the removal of a 34 residue fragment that contains the Gla domain. This modification reduces andexanet alfa’s procoagulant potential. Additionally, a serine to alanine (S419A) mutation in the active site eliminates its activity as a prothrombin to thrombin catalyst, but still allows the molecule to bind to FXa inhibitors.^[9] FXa inhibitors bind to andexanet alfa with the same affinity as to natural FXa. As a consequence in the presence of andexanet alfa natural FXa is partially freed, which can lead to effective hemostasis.^[3][10] In other words, it acts as a decoy receptor. Andexanet alfa reverses effect of all anticoagulants that act directly through FXa or by binding antithrombin III. The drug is not effective against factor IIa inhibitor dabigatran.^[11]

History[edit]

It was approved in the United States in 2018 based on data from two phase III studies on reversing the anticoagulant activity of FXa inhibitors rivaroxaban and apixaban in healthy volunteers.^[4] As a condition of its accelerated approval there is a study being conducted comparing it to other currently used reversal agents (“usual care”).^[5][12]

Society and culture

Economics

Initial pricing (AWP) is $58,000 per reversal (800 mg bolus + 960 mg infusion, $3,300 per 100 mg vial) which is higher than reversal agents for other DOAC agents (idarucizumab for use in dabigatran reversal is $4,200 per reversal).^[13]

References

1. ^ Jump up to:^{a b c d e} “Andexxa- andexanet alfa injection, powder, lyophilized, for solution”. DailyMed. 21 September 2020. Retrieved 12 November 2020.
2. ^ Jump up to:^{a b c d e f g} “Andexxa Monograph for Professionals”. Drugs.com. Retrieved 19 December 2018.
3. ^ Jump up to:^a b Dolgin E (March 2013). “Antidotes edge closer to reversing effects of new blood thinners”. Nature Medicine. 19 (3): 251. doi:10.1038/nm0313-251. PMID 23467222. S2CID 13340319.
4. ^ Jump up to:^a b Siegal DM, Curnutte JT, Connolly SJ, Lu G, Conley PB, Wiens BL, Mathur VS, Castillo J, Bronson MD, Leeds JM, Mar FA, Gold A, Crowther MA (December 2015). “Andexanet Alfa for the Reversal of Factor Xa Inhibitor Activity”. New England Journal of Medicine. 373 (25): 2413–24. doi:10.1056/NEJMoa1510991. PMID 26559317.
5. ^ Jump up to:^a b Connolly SJ, Crowther M, Eikelboom JW, Gibson CM, Curnutte JT, Lawrence JH, et al. (April 2019). “Full Study Report of Andexanet Alfa for Bleeding Associated with Factor Xa Inhibitors”. New England Journal of Medicine. 380 (14): 1326–1335. doi:10.1056/NEJMoa1814051. PMC 6699827. PMID 30730782.
6. ^ Justin Morgenstern, “Andexanet Alfa: More garbage science in the New England Journal of Medicine”, First10EM blog, February 11, 2019. Available at: https://first10em.com/andexanet-alfa/.
7. ^ “A Randomized Clinical Trial of Andexanet Alfa in Acute Intracranial Hemorrhage in Patients Receiving an Oral Factor Xa Inhibitor”. 11 January 2022.
8. ^ Lu, Genmin; DeGuzman, Francis R.; Lakhotia, Sanjay; Hollenbach, Stanley J.; Phillips, David R.; Sinha, Uma (2008-11-16). “Recombinant Antidote for Reversal of Anticoagulation by Factor Xa Inhibitors”. Blood. 112 (11): 983. doi:10.1182/blood.V112.11.983.983. ISSN 0006-4971.
9. ^ Kaatz, Scott; Bhansali, Hardik; Gibbs, Joseph; Lavender, Robert; Mahan, Charles E.; Paje, David G. (2017-09-13). “Reversing factor Xa inhibitors – clinical utility of andexanet alfa”. Journal of Blood Medicine. 8: 141–149. doi:10.2147/JBM.S121550. PMC 5602457. PMID 28979172.
10. ^ Lu G, Deguzman FR, Hollenbach SJ, et al. (March 2013). “A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa”. Nature Medicine. 19 (4): 446–51. doi:10.1038/nm.3102. PMID 23455714. S2CID 11235887.
11. ^ H. Spreitzer (23 December 2013). “Neue Wirkstoffe – Andexanet Alfa”. Österreichische Apothekerzeitung (in German) (26/2013): 40.
12. ^ “Trial of Andexanet in ICH Patients Receiving an Oral FXa Inhibitor”. ClinicalTrials.gov. 11 January 2022.
13. ^ “Lexi Comp Drug Information Online”. 24 May 2018.

Further reading

• Connolly SJ, Milling TJ, Eikelboom JW, Gibson CM, Curnutte JT, Gold A, et al. (September 2016). “Andexanet Alfa for Acute Major Bleeding Associated with Factor Xa Inhibitors”. New England Journal of Medicine. 375 (12): 1131–41. doi:10.1056/NEJMoa1607887. PMC 5568772. PMID 27573206.

External links

• “Andexanet alfa”. Drug Information Portal. U.S. National Library of Medicine.
• “Ondexxya (andexanet alfa): Avoid use of andexanet prior to heparinization”. European

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