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Evolution of Emicizumab Plasma Concentrations and aPTT rratio in 183 Treated Patients with Severe Haemophilia A. A Real Life and Multi-centre Analysis

1University Hospital of Tours, Tours, France, 2University of Tours, EA 7501, Tours, France, 3University Hospital of Lyon, Lyon, France, 4Hospital of Versailles, Versailles, France, 5University Hospital of Nantes, Nantes, France, 6University Hospital of Limoges, Limoges, France, 7University Hospital of Poitiers, Poitiers, France, 8University Hospital of Lille, Lille, France, 9APHP, Hopital Cochin, Paris, France, 10APHP, Hopital Necker, Paris, France, 11University Hospital of Strasbourg, Strasbourg, France, 12University Hospital of Caen, Caen, France, 13University Hospital of Bordeaux, Bordeaux, France, 14University Hospital of Marseille, Marseille, France

Abstract Number: PB0494

Meeting: ISTH 2021 Congress

Theme: Hemophilia and Rare Bleeding Disorders » Hemophilia - Clinical

Background: Measurement of emicizumab plasma concentration is available in laboratories but usual values are not well defined as well as variations in aPTT ratio.

Aims: To evaluate emicuzumab concentrations (EmC°) and aPTT variation in a large cohort of severe hemophilia A (HA) patients.

Methods: 183 severe HA patients (whose 69 < 12 years) with (n = 57) or without (n=126) inhibitors were included in 13 centres. EmC° were assessed during (n = 67) or after the loading phase (LP) with different regimen: 1.5 mg/kg weekly (n = 92), 3.0 mg/kg biweekly (n = 21) or 6 mg/kg monthly (n=3).

Results: Median EmC° increased from 17.7 µg/ml in the first week to 50.4 µg/ml at the end of the LP (Figure). During the maintenance phase (MP), the median concentration remained stable around 50.9 µg/mL (10th-90th percentiles: 31.1 – 77.2 µg/ml, n=143). EmC° did not vary according to the regimen (50.9 µg/mL  (IQR 27.0 µg/mL ) and 53.8 µg/mL (IQR 27.8 µg/mL ) with one injection weekly (n=115) or every two weeks (n=26) respectively). The aPTT ratio shortened during the LP (0.86) and then during the MP (0.79, p < 0.0001). Interestingly, EmC° were significantly lower during MP in children than in adults/adolescents (47.4 vs 56.1 µg/ml, p = 0.036). 22 patients had bleeding events during the LP (n = 6) or the MP (n = 16), but EmC° were not significantly different than in non-bleeders (50.7 vs 49 µg/mL). Moreover, EmC° were lower than the 10th percentile in 2 of 16 bleeders during MP compared to 10/86 in those without bleeding (NS).

Evolution of emicizumab concentration during treatment

Conclusions: Our results confirm that EmC° are quite variable in treated HA patients. This variability must be taken into account for interpretating EmC° in case of suspicion of anti-drug antibody or lack of compliance.

To cite this abstract in AMA style:

Pouplard C, Nougier C, Flaujac C, Ternisien C, Auditeau C, Donnard M, Grand F, Jeanpierre E, Proulle V, Timsit S, Sattler L, Repesse Y, Ryman A, Hezard N, Lasne D, BIMHO Study Group on behlaf of GFHT . Evolution of Emicizumab Plasma Concentrations and aPTT rratio in 183 Treated Patients with Severe Haemophilia A. A Real Life and Multi-centre Analysis [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/evolution-of-emicizumab-plasma-concentrations-and-aptt-rratio-in-183-treated-patients-with-severe-haemophilia-a-a-real-life-and-multi-centre-analysis/. Accessed November 29, 2023.

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