Tranexamic acid quantification in human whole blood using liquid samples or volumetric absorptive microsampling devices

Tranexamic Dosing for Major Joint Arthroplasty in Adult Patients with Chronic Kidney Disease: A Pharmacokinetic Study and New Dosing Regimen

BACKGROUND

Tranexamic acid is an antifibrinolytic agent routinely used during hip and knee joint replacement surgery to minimize bleeding. Chronic kidney disease is a common chronic health problem seen among adults requiring major arthroplasty surgery. Tranexamic acid is renally cleared and may accumulate in chronic kidney disease. Optimal tranexamic acid dosing and dose adjustment for chronic kidney disease patients needing major arthroplasty is unknown. The objective of this study was to serially measure plasma tranexamic acid concentrations in patients with varied kidney function undergoing hip or knee replacement surgery for population pharmacokinetic modeling and to guide new dosing recommendations.

METHODS

A prospective cohort study enrolled 21 adults undergoing hip or knee replacement surgery between June 2020 and September 2022. Based on estimated glomerular filtration rate, the patients were stratified into good (greater than or equal to 60 ml · min -1 · 1.73 m -2 ) and poor (less than 60 ml · min -1 · 1.73 m -2 ) renal function. Serial blood samples were taken to measure plasma tranexamic acid concentration levels (primary outcome) after an intravenous tranexamic acid 20-mg/kg bolus dose after anesthesia induction. Secondary clinical outcomes included adverse events (thromboembolic events, seizures), red cell transfusion, mortality, and length of hospital stay. Analyses used curve stripping and population pharmacokinetic modeling and simulation.

RESULTS

Plasma tranexamic acid concentration levels were higher in patients with poor renal function and clearance compared to those with good renal function. Population pharmacokinetic modeling tested various tranexamic acid bolus and maintenance infusion regimens. Simulations revealed that single-bolus tranexamic acid administration leads to rapid rise and decline in plasma concentrations. This study identified that plasma tranexamic acid levels of 50 to 75 mg/l were maintained for approximately 4 h using a tranexamic acid bolus infusion of 15 mg/kg over a 15-min duration together with a maintenance infusion of 7.5 or 5 mg · kg -1 · h -1 for 2 h for the good and poor renal function groups, respectively. There was no difference in secondary outcomes.

CONCLUSIONS

Population pharmacokinetic modeling and simulation resulted in recommendations for a new dosing regimen to optimize the antifibrinolytic effect of tranexamic acid and avoid excessive dosing.

Clinical Validation of a Volumetric Absorptive Micro-Sampling Device for Pharmacokinetic Studies With Tranexamic Acid

We assessed the accuracy of tranexamic acid (TXA) concentrations measured in capillary whole blood using volumetric absorptive micro-sampling (VAMS) devices. Paired venous and VAMS capillary blood samples were collected from 15 healthy volunteers participating in a pharmacokinetic study of alternative routes (oral, IM and IV) of administering TXA. To assess accuracy across a range of concentrations, blood was drawn at different times after TXA administration. We measured TXA concentrations in plasma, whole blood from samples collected by venepuncture and whole blood from venous and capillary samples collected using VAMS devices. TXA was measured using a validated high sensitivity liquid chromatography - mass spectrometry method. We used Bland-Altman plots to describe the agreement between the TXA concentrations obtained with the different methods. In the 42 matched samples, the mean plasma TXA concentration was 14.0 mg/L (range 2.6-36.5 mg/L) whereas the corresponding whole blood TXA concentration was 7.7 mg/L (range 1.6-17.5 mg/L). When comparing TXA concentrations in VAMS samples of venous and capillary whole blood, the average bias was 0.07 mg/L (lower and upper 95% limits of agreement: -2.1 and 2.2 mg/L respectively). When comparing TXA concentrations in venous whole blood and VAMS capillary whole blood, the average bias was 0.7 mg/L (limits of agreement: -2.7 and 4.0 mg/L). Volumetric absorptive micro-sampling devices are sufficiently accurate for use in pharmacokinetic studies of tranexamic acid treatment in the range of plasma concentrations relevant for the assessment of fibrinolysis inhibition.

WOMAN-PharmacoTXA trial: Study protocol for a randomised controlled trial to assess the pharmacokinetics and pharmacodynamics of intramuscular, intravenous and oral administration of tranexamic acid in women giving birth by caesarean section

Background: Intravenous tranexamic acid (TXA) within 3 hours of birth significantly reduces death due to bleeding in women with postpartum haemorrhage (PPH). Most PPH deaths occur in the first hours after giving birth and treatment delay decreases survival.  One barrier to rapid TXA treatment is the need for intravenous injection. Intramuscular injection and oral solution of TXA would be easier and faster to administer and would require less training. However, the pharmacokinetics (PK), pharmacodynamics and safety of TXA administered by different routes in pregnant women have not been established. The main aim of this study is to ascertain whether IM and oral solution of TXA will be absorbed at levels sufficient to inhibit fibrinolysis in pregnant women.

Methods: WOMAN-PharmacoTXA is a prospective, randomised, open label trial to be conducted in Zambia and Pakistan.  Adult women undergoing caesarean section with at least one risk factor for PPH will be included.  Women will be randomised to receive one of the following about 1 hour prior to caesarean section: 1-gram TXA IV, 1-gram TXA IM, 4-grams TXA oral solution or no TXA. Randomisation will continue until 120 participants with at least six post randomisation PK samples are included. TXA concentration in maternal blood samples will be measured at baseline and at different time points during 24 hours after receipt of intervention. Blood TXA concentration will be measured from the umbilical cord and neonate.

The primary endpoint is maternal blood TXA concentrations over time. Secondary outcomes include umbilical cord and neonate TXA concentration D-dimer concentration, blood loss and clinical diagnosis of PPH, injection site reactions and maternal and neonate adverse events.

Discussion: The WOMAN-PharmacoTXA trial will provide important data on pharmacokinetics, pharmacodynamics and safety of TXA after IV, intramuscular and oral administration in women giving birth by caesarean section.

Trial registration: ClincalTrials.gov, NCT04274335 (18/02/2020).