Therapeutic monitoring of warfarin: the appropriate response marker

Effect of Daridorexant on the Pharmacokinetics of Midazolam, and on the Pharmacokinetics and Pharmacodynamics of Warfarin in Healthy Male Subjects

BACKGROUND AND OBJECTIVES

Daridorexant, a dual orexin receptor antagonist was recently approved for the treatment of insomnia at doses up to 50 mg once per night. This study investigated the effect of single-dose and multiple-dose daridorexant 50 mg at steady state on the pharmacokinetics (PK) of the cytochrome P450 (CYP) 3A4-sensitive substrate midazolam, and the effect of single-dose daridorexant 50 mg on the PK and pharmacodynamics (PD) of the CYP2C9-sensitive substrate warfarin.

METHODS

In this prospective, single-center, open-label, fixed-sequence, phase I, drug-drug interaction study, 18 healthy male subjects sequentially received Treatment A, B, and C in three periods. Treatment A consisted of a single oral concomitant administration of midazolam 2 mg and warfarin 25 mg on day 1 of the first period. Treatment B consisted of one oral administration of daridorexant 50 mg followed 1 h later by a single oral dose of midazolam 2 mg concomitantly with a single oral dose of warfarin 25 mg on day 1 and a once-daily oral administration of daridorexant 50 mg for 6 days of the second period. Treatment C consisted of a single oral administration of daridorexant 50 mg at steady state followed 1 h later by a single oral administration of midazolam 2 mg on day 1 of the third period. Blood samples were assessed for midazolam and S-warfarin PK, and PD (international normalized ratio and factor VII). Noncompartmental  PK parameters and PD variables were evaluated with geometric mean ratios and 90% confidence intervals of Treatment B/A versus C/A for midazolam, and treatment B/A for warfarin. Safety and tolerability of each treatment were also assessed.

RESULTS

Midazolam maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from 0 to 24 h (AUC0-24) were 1.13- and 1.42-fold higher, respectively, after single-dose administration of daridorexant 50 mg compared to administration of midazolam alone, while Cmax and AUC0-24 were 1.12- and 1.35-fold higher, respectively, after administration of daridorexant 50 mg once daily at steady state. Terminal half-life and time to maximum plasma concentration were comparable between treatments. Daridorexant had no influence on the PK and PD of warfarin. All treatments were safe and well tolerated.

CONCLUSIONS

Daridorexant at 50 mg is classified as a weak CYP3A4 inhibitor after single- and multiple-dose administration once daily at steady state. Daridorexant 50 mg did not induce CYP3A4 activity or inhibit CYP2C9 activity.

CLINICAL TRIAL REGISTRATION

This trial (NCT05480488) was registered on 29 July, 2022.

A Novel LC-MS/MS Assay for Quantification of Des-carboxy Prothrombin and Characterization of Warfarin-Induced Changes

Warfarin is a narrow therapeutic index anticoagulant drug and its use is associated with infrequent but significant adverse bleeding events. The international normalized ratio (INR) is the most commonly used biomarker to monitor and titrate warfarin therapy. However, INR is derived from a functional assay, which determines clotting efficiency at the time of measurement and is susceptible to technical variability. Protein induced by vitamin K antagonist-II (PIVKA-II) has been suggested as a biomarker of long-term vitamin K status, providing mechanistic insights about variation in the functional assay. However, the currently available antibody-based PIVKA-II assay does not inform on the position and number of des-carboxylation sites in prothrombin. The assay presented in this paper provides simultaneous quantification of carboxy and des-carboxy prothrombin that are essential for monitoring early changes in INR and, thus, serves as the superior tool for managing warfarin therapy. Additionally, this assay permits the quantification of total prothrombin level, which is affected by warfarin treatment. Prothrombin recovery from plasma was 95% and the liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was linear (r²  = 0.98) with a dynamic range of 1-100 µg/mL. The assay interday precision was within 20%. A des-carboxy peptide of prothrombin (GNLER) was negatively correlated with active prothrombin (Pearson r = 0.99, P < 0.0001), whereas its association was positively linked with INR values (Pearson r = 0.75, P < 0.015). This novel LC-MS/MS assay for active and inactive prothrombin quantification can be applied to titrate anticoagulant therapy and to monitor the impact of diseases, such as hepatocellular carcinoma on clotting physiology.

Clinical pharmacokinetics and pharmacodynamics of the endothelin receptor antagonist macitentan

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vascular system, which leads to right-sided heart failure and ultimately death if untreated. Treatments to regulate the pulmonary vascular pressure target the prostacyclin, nitric oxide, and endothelin (ET) pathways. Macitentan, an oral, once-daily, dual ET_A and ET_B receptor antagonist with high affinity and sustained receptor binding is the first ET receptor antagonist to show significant reduction of the risk of morbidity and mortality in PAH patients in a large-scale phase III study with a long-term outcome. Here we present a review of the available clinical pharmacokinetic, pharmacodynamic, pharmacokinetic/pharmacodynamic relationship, and drug–drug interaction data of macitentan in healthy subjects, patients with PAH, and in special populations.

Investigation of the effect of macitentan on the pharmacokinetics and pharmacodynamics of warfarin in healthy male subjects

BACKGROUND AND OBJECTIVES

Macitentan is a novel dual endothelin receptor antagonist recently approved for the treatment of pulmonary arterial hypertension (PAH). Warfarin, an anticoagulant often prescribed to patients with PAH, has a narrow therapeutic index and is prone to potential interactions with drugs. This study assessed the effects of macitentan on the pharmacokinetics and pharmacodynamics of single-dose warfarin in healthy subjects.

METHODS

This was a randomised, open-label, single-centre, two-way crossover (treatment A followed by treatment B, or vice versa), phase I study in 14 healthy male subjects. Treatment A was a loading dose of macitentan 30 mg on Day 1 followed by 10 mg once daily for 8 days, with a single 25 mg dose of warfarin on Day 4. Treatment B was a single dose of warfarin on Day 1. Blood samples were assessed for warfarin pharmacokinetics (R- and S-warfarin) and pharmacodynamics [international normalised ratio (INR) and factor VII]. Plasma trough concentrations of macitentan and its active metabolite (ACT-132577) and the safety and tolerability of each treatment were also assessed.

RESULTS

Plasma concentrations of R- and S-warfarin were similar in both treatment periods. Warfarin did not affect the mean trough plasma concentrations of macitentan or ACT-132577. Macitentan did not affect the pharmacodynamics of warfarin; the mean INR and factor VII activity versus time profiles were similar with and without macitentan.

CONCLUSIONS

The absence of effect of macitentan on the pharmacokinetics and pharmacodynamics of a single dose of warfarin suggests that both drugs can be concomitantly administered without need for dose adjustment.

Efficacy and tolerability of the switch from a branded to a generic warfarin sodium product: an observer-blinded, randomized, crossover study

BACKGROUND

Anticoagulation is an essential part of the management of numerous cardiovascular conditions. Although warfarin sodium has been in clinical use for >40 years, only 1 proprietary warfarin preparation was in use for long-term anticoagulation in Taiwan until 2001, when the Taiwan Food and Drug Administration approved a new generic formulation.

OBJECTIVE

This study evaluated the efficacy and tolerability of switching from an established dose of the branded warfarin sodium product (in mg/wk) to the same dose of the generic product.

METHODS

This was a randomized, observer-blinded,crossover study in Taiwanese patients who received a mechanical heart valve to replace an original valve or a previously implanted mechanical valve from March 2003 to August 2004 and had received branded warfarin therapy for >/=2 months postoperatively, with a mean baseline international normalized ratio (INR) in the range from 1.7 to 3.0 in the 8- to 12-week run-in period. Patients were randomized to 1 of 2 treatment sequences, each involving three 28-day periods: the generic product for 1 period followed by the branded product for 2 periods, or the branded product for 1 period followed by the generic product for 2 periods. Prothrombin time and INR were measured, and anticoagulant activity was compared. At each visit, treatment-emergent adverse events were recorded and evaluated by the blinded observer, an internal medicine physician who was not involved in patients' care.

RESULTS

Thirty-five patients were enrolled (25 men, 10 women; mean age, 52.4 years [range, 34.5-74.4 years]). All but 2 of the patients had received a replacement for a natural heart valve. Thirty-four patients (16 who received the generic product initially, 18 who received the branded product initially) completed the study without a dose change and were >/=75% compliant with therapy. There was no difference in pooled mean (SE) INR between the 2 products (2.28 [0.06] and 2.27 [0.06], respectively). The 90% CI for the difference was 96.4 to 104.9, well within the range for bioequivalence (80-120). There were no differences in the adverse-event profiles of the 2 formulations.

CONCLUSIONS

No therapeutic inequivalence was demonstrated in this small, single-blind study, suggesting that the generic and branded warfarin products studied were equally effective in maintaining anticoagulation in patients with mechanical prosthetic heart valves. The 2 products had similar safety profiles.