Pharmacokinetic-guided dosing of factor VIII concentrate in a patient with haemophilia during renal transplantation

[Surgery in patients with severe or inhibitory hemophilia A under prevention injection of emicizumab]

OBJECTIVE

To determine the features of preoperative hemostatic therapy and laboratory control in patients with severe and inhibitory forms of hemophilia A under preventive treatment by FVIII.

MATERIAL AND METHODS

Four patients with severe and inhibitory forms of hemophilia A underwent surgery between 2021 and 2022. All patients received Emicizumab (the first monoclonal drug for «non-factor» therapy of hemophilia) for prevention of specific hemorrhagic signs of hemophilia.

RESULTS

Surgical intervention under preventive Emicizumab therapy was essential. Additional hemostatic therapy was not carried out or performed in reduced mode. There were no hemorrhagic, thrombotic or other complications. Thus, the so-called «non-factor» therapy is one of the variants for uncontrollable hemostasis in patients with severe and inhibitory forms of hemophilia.

CONCLUSION

Preventive injection of Emicizumab ensures certain buffer of hemostasis system and stable lower limit of coagulation potential. This is the result of stable concentration of Emicizumab when used in any of the registered forms regardless of age and other individual characteristics. The risk of acute severe hemorrhage is excluded, while the probability of thrombosis is not increased. Indeed, FVIII has higher affinity than Emicizumab and displaces Emicizumab from coagulation cascade that does not result summation of total coagulation potential.

[Acute arterial thrombosis in hemophilia with inhibitory antibodies]

The authors demonstrate an importance of personalized approach to perioperative hemostatic therapy in a 48-year-old patient with hemophilia A and inhibitory antibodies. Laparoscopic hernia repair and extraction of 15 decayed teeth were performed. Hemostatic therapy included AICC and rFVIIa. Postoperative period was complicated by acute thrombosis of splenic artery and partial spleen infarction. An essential factor in splenic artery thrombosis was increase in blood coagulation potential under rFVIIa administration and depletion of fibrinolytic system (prolongation of XIIa-dependent fibrinolysis from 25 to 75 min) and antithrombin III decrease up to 81%. Cancellation of hemostatic therapy under TEG control ensured fast regression of arterial thrombosis and preservation of spleen. Individual characteristics of patients (compensatory mechanisms of coagulation, comorbidities, clinical changes) should be considered when prescribing hemostatic therapy in hemophilia patients. Perioperative control of all possible coagulation tests (routine and integral) is required for individual selection of hemostatic therapy and decrease of the risk of hemorrhagic and thrombotic complications.

Validation of a perioperative population factor VIII pharmacokinetic model with a large cohort of pediatric hemophilia a patients

AIMS

Population pharmacokinetic (PK) models are increasingly applied to perform individualized dosing of factor VIII (FVIII) concentrates in haemophilia A patients. To guarantee accurate performance of a population PK model in dose individualization, validation studies are of importance. However, external validation of population PK models requires independent data sets and is, therefore, seldomly performed. Therefore, this study aimed to validate a previously published population PK model for FVIII concentrates administrated perioperatively.

METHODS

A previously published population PK model for FVIII concentrate during surgery was validated using independent data from 87 children with severe haemophilia A with a median (range) age of 2.6 years (0.03-15.2) and body weight of 14 kg (4-57). First, the predictive performance of the previous model was evaluated with MAP Bayesian analysis using NONMEM v7.4. Subsequently, the model parameters were (re)estimated using a combined dataset consisting of the previous modelling data and the data available for the external validation.

RESULTS

The previous model underpredicted the measured FVIII levels with a median of 0.17 IU mL^-1 . Combining the new, independent and original data, a dataset comprising 206 patients with a mean age of 7.8 years (0.03-77.6) and body weight of 30 kg (4-111) was obtained. Population PK modelling provided estimates for CL, V1, V2, and Q: 171 mL h^-1  68 kg^-1 , 2930 mL 68 kg^-1 , 1810 mL 68 kg^-1 , and 172 mL h^-1  68 kg^-1 , respectively. This model adequately described all collected FVIII levels, with a slight median overprediction of 0.02 IU mL^-1 .

CONCLUSIONS

This study emphasizes the importance of external validation of population PK models using real-life data.

Pharmacokinetic-guided dosing of factor VIII concentrate in a morbidly obese severe haemophilia A patient undergoing orthopaedic surgery

A 58-year-old morbidly obese male (body mass index: 38 kg/m²) with severe haemophilia A underwent total knee replacement surgery. Perioperatively, factor VIII (FVIII) levels were measured daily and maximum a posteriori (MAP) Bayesian estimation was used to calculate the individual pharmacokinetic (PK) parameters and doses required to obtain prescribed FVIII target levels. In the MAP Bayesian procedure, a population PK model was used in which PK parameters were normalised using body weight. In this specific case, ideal body weight was used to scale the PK parameters instead of actual body weight. Except for the preoperative FVIII level, adequate FVIII levels were achieved during the 10-day perioperative period. During follow-up visits, the knee prosthesis was reported to function adequately.

Population pharmacokinetics of factor IX in hemophilia B patients undergoing surgery

Essentials Factor IX (FIX) dosing using body weight frequently results in under and overdosing during surgery. We aimed to establish a population pharmacokinetic (PK) model describing the perioperative FIX levels. Population PK parameter values for clearance and V1 were 284 mL h-170 kg-1 and 5450 mL70 kg-1. Perioperative PK parameters differ from those during non-surgical prophylactic treatment. SUMMARY: Background Hemophilia B is a bleeding disorder characterized by a deficiency of coagulation factor IX (FIX). In the perioperative setting, patients receive FIX concentrates to ensure hemostasis. Although FIX is usually dosed according to bodyweight, under- and overdosing occurs frequently during surgery. Aim The objective was to quantify and explain the interpatient variability of perioperatively administered plasma-derived (pd) and recombinant (r) FIX concentrates. Methods Data were collected from 118 patients (median age, 40 years [range, 0.2-90]; weight, 79 kg [range, 5.3-132]) with moderate (28%) or severe hemophilia B (72%), undergoing 255 surgical procedures. Population pharmacokinetic (PK) parameters were estimated using nonlinear mixed-effect modeling in NONMEM. Results Measured perioperative FIX level vs. time profiles were adequately described using a three-compartment PK model. For a typical 34-year-old patient receiving rFIX, clearance (CL), intercompartmental clearance (Q2, Q3), distribution volume of the central compartment (V1) and peripheral compartments (V2, V3) plus interpatient variability (%CV) were: CL, 284 mL h-170 kg-1 (18%); V1, 5450 mL70 kg-1 (19%); Q2, 110 mL h-170 kg-1; V2, 4800 mL70 kg-1; Q3, 1610 mL h-170 kg-1; V3, 2040 mL70 kg-1. From 0.2 years, CL and V1 decreased 0.89% and 1.15% per year, respectively, until the age of 34 years. Patients receiving pdFIX exhibited a lower CL (11%) and V1 (17%) than patients receiving rFIX. Interpatient variability was successfully quantified and explained. Conclusions The estimated perioperative PK parameters of both pdFIX and rFIX are different from those reported for prophylactic treatment. The developed model may be used to apply PK-guided dosing of FIX concentrates during surgery.

[Thrombotic events in patients with hemophilia]

The paper describes 4 clinical cases of thrombotic events (pulmonary embolism, deep vein thrombophlebitis, acute myocardial infarction, ischemic stroke) that have occurred in patients with hemophilia. It discusses the possible causes of their development and methods for their prevention and treatment. Controlled natural hypocoagulation, in which the dose of an administered deficient factor decreases to such an extent that in order to maintain the safe level of hypocoagulation (plasma factor activity is 15-20%; activated partial thromboplastin time is 1.5-2 times normal values), is proposed as one of the treatment options.