Peter G. Milner

The First Evaluation of a Novel Vitamin K Antagonist, Tecarfarin (ATI-5923), in Patients With Atrial Fibrillation

Background— Tecarfarin (ATI-5923) is a novel oral vitamin K antagonist. Unlike warfarin, it is metabolized by esterases, escaping metabolism by the cytochrome P450 system and thereby avoiding cytochrome P450–mediated drug-drug or drug-food interactions as well as genetic variations found in the cytochrome P450 system. Both tecarfarin and warfarin can be monitored with the international normalized ratio. We hypothesized that the time in therapeutic range for tecarfarin will exceed values usually experienced with warfarin. Methods and Results— This was a 6- to 12-week open-label, multicenter, phase IIA study of 66 atrial fibrillation patients with a mild to moderate risk of stroke to determine the safety and tolerability of tecarfarin and to ascertain an optimal tecarfarin dosing regimen. Sixty-four subjects (97%) were taking warfarin at enrollment and were switched to tecarfarin. After the initial 3 weeks of tecarfarin treatment, the mean interpolated time in therapeutic range was 71.4%. Only 10.9% of patients had time in therapeutic range of <45%. Times in extreme international normalized ratio ranges of <1.5 and >4.0 were 1.2% and 1.2%, respectively. The median daily dose (for an individual patient) to maintain an international normalized ratio between 2 and 3 was 15.6 mg (range, 6 to 29 mg). Conclusions— This is the first study of tecarfarin in patients with atrial fibrillation. It appears that tecarfarin may possess advantages over the currently available standard of care, warfarin, by improving time in therapeutic range. Adequately powered prospective trials are warranted to definitively compare tecarfarin with warfarin in clinical settings for which warfarin is indicated.

Tecarfarin, a novel vitamin K reductase antagonist, is not affected by CYP2C9 and CYP3A4 inhibition following concomitant administration of fluconazole in healthy participants.

Comparative pharmacokinetics of vitamin K epoxide reductase antagonists tecarfarin and warfarin were assessed before and after coadministration for 21 days of the CYP450 inhibitor fluconazole in a randomized, open‐label, single‐center drug interaction study. Twenty healthy adult participants were randomized 1:1 to receive approximately equipotent single oral doses of tecarfarin (50 mg) or warfarin (17.5 mg). Following 7 days of baseline serial blood level collections, each participant received oral fluconazole 400 mg daily for 21 days. A second identical single oral dose of tecarfarin or warfarin was given 14 days after starting fluconazole with serial pharmacokinetic sampling. Key pharmacokinetic parameters Cmax, tmax, AUC0–168, apparent clearance, and t1/2 demonstrated no tecarfarin‐fluconazole interaction but a strong warfarin‐fluconazole interaction. The ratio of log‐transformed mean AUC0–168 with versus without fluconazole for tecarfarin was 91.2% (90% confidence interval [CI]: 83.3–99.8) and for racemic warfarin was 213% (90% CI: 202–226). The 90% CI was entirely within the standard 80% to 125% bioequivalence interval for tecarfarin but well outside the bioequivalence interval for warfarin, confirming a clinically significant pharmacokinetic interaction between warfarin and fluconazole. In contrast, tecarfarin pharmacokinetics were apparently unchanged by fluconazole.

Antithrombotic Activity of the Novel Oral Anticoagulant, Tecarfarin (Sodium 3-(4-((1,1,1,3,3,3-hexafluoro-2-methylpropan-2-yloxy) carbonyl) benzyl)-2-oxo-2H-chromen-4-olate) in Animal Models

The antithrombotic activity of tecarfarin, a novel orally active vitamin K epoxide reductase inhibitor, was assessed in canine and rabbit thrombosis models. In dogs, once-daily oral doses of 0.5mg/kg tecarfarin selectively reduced the levels of the vitamin K-dependent coagulation factors (factors II, VII, IX, and X) and prolonged the prothrombin time (PT). A 4 to 7day course of oral tecarfarin (0.05 - 0.5mg/kg) prolonged the PT by 3 to 5-fold and reduced thrombus formation in arterial and venous segments subjected to a combination of electrical injury and flow-limiting constriction. To compare the effects of tecarfarin with those of warfarin, rabbits were given once-daily oral doses of 1mg/kg tecarfarin, 1.5mg/kg warfarin, or saline for 2days. After verifying increases in the PT with tecarfarin and warfarin, blood loss from standardized ear incisions was measured to assess hemorrhagic potential. Then, after intravenous injection of (125)I-labeled rabbit fibrinogen, thrombosis was induced in an isolated jugular vein segment by a combination of balloon catheter-induced endothelial denudation and venous occlusion. Compared with the saline control, both tecarfarin and warfarin prolonged the PT, increased blood loss from the ear incisions, and attenuated thrombus formation. Thus, like warfarin, tecarfarin attenuates venous and arterial thrombus formation in animal models by reducing the levels of the vitamin K-dependent coagulation factors.

Pharmacokinetics and pharmacodynamics of tecarfarin, a novel vitamin K antagonist oral anticoagulant

Tecarfarin is a vitamin K antagonist (VKA) with reduced propensity for drug interactions. To evaluate the pharmacokinetic (PK), pharmacodynamic (PD), and safety of tecarfarin, we performed single ascending dose (SAD) (n=66), multiple ascending dose (MAD) (n=43), and tecarfarin versus warfarin (n=28) studies in human volunteers. In the SAD, tecarfarin was administered to 5 of 6 subjects (1 received placebo) in each of 11 cohorts. AUC0-∞ exhibited linearity and dose proportionality. Elimination T1/2 ranged from 87-136 hours (h) across all doses. In the MAD, tecarfarin was administered to 5 of 6 volunteers in each of 7 cohorts. The starting dose was continued until the subjects INR reached the target range (TR) of 1.7 to 2.0. Dosing was down-titrated if the TR was achieved. Elimination T1/2 ranged from 107-140 h. Doses <10 mg had insignificant effect on INR. Higher doses raised INRs and required down-titration to maintain the TR. Steady state INR dosing was 10-20 mg. INR declined promptly after discontinuation. In the comparative study, subjects received tecarfarin or warfarin and dose titrated to a TR of 1.5-2.0. Mean dose after TR was achieved was 13.9 mg (range 10.0-25.5 mg) for tecarfarin and 5.3 mg (range 2.5-9.0 mg) for warfarin. At similar INR levels, the concentration of coagulation factors II, VII, IX, and X were similar for tecarfarin and warfarin. Tecarfarin was tolerated well without serious adverse events in all three studies.

Pharmacokinetics of Tecarfarin and Warfarin in Patients with Severe Chronic Kidney Disease

Chronic kidney disease (CKD) complicates warfarin anticoagulation partially through its effect on CYP2C9 activity. Tecarfarin, a novel vitamin K antagonist, is not metabolized by CYP2C9. To evaluate the effect of CKD on their metabolism, we measured PK parameters of warfarin and tecarfarin in subjects with and without CKD. CKD subjects with estimated glomerular filtration rate < 30 mL/min not on dialysis (n = 13) were matched to healthy volunteers (HVs) (n = 10). Each subject was randomized to either warfarin 10 mg or tecarfarin 30 mg and was later crossed over to the other drug. PK parameters were measured following each drug. Mean plasma concentrations of (S)-warfarin and (R,S)-warfarin were higher (44 and 27%, respectively) in the subjects with CKD than in the healthy subjects. Both of these values fell outside of the 90% confidence interval of equivalence. For tecarfarin, the difference was less than 15% higher. Elimination half-life (t1/2) increased by 20% for (S)-warfarin and by 8% for (R,S)-warfarin and decreased by 8% for tecarfarin. The mean plasma concentration for tecarfarins inactive metabolite ATI-5900 increased by approximately eightfold. CKD increased the effect of CYP2C9 genetic variation on (S)-warfarin and (R,S)-warfarin metabolism. Tecarfarin exposure was similar between the HVs and the CKD subjects regardless of CYP2C9 genotype. There were neither serious adverse events (SAEs) nor treatment-emergent adverse events (TEAEs) for any subject in the study. CKD inhibits metabolism of (S)-warfarin and (R,S)-warfarin, but not tecarfarin. The safety of repeated dosing of tecarfarin in CKD patients remains unknown. However, if the PK findings of this single-dose study are present with repeated dosing, tecarfarin may lead to dosing that is more predictable than warfarin in CKD patients who require anticoagulation therapy.