A critical overview on ticagrelor in acute coronary syndromes

Until a few years ago, the mainstay of anti-platelet therapy in patients with acute coronary syndrome (ACS) was the combination of aspirin and clopidogrel, a P2Y12 receptor inhibitor. However, current clinical practice has now changed with the introduction of ticagrelor, a more potent cardiovascular drug than clopidogrel, without the limitations related to clopidogrel therapy. In this review, we provide a critical overview of ticagrelor in ACS, highlight the results with ticagrelor in several subgroups of patients and discuss the future trials.

Effect of rifampicin on the pharmacokinetics and pharmacodynamics of ticagrelor in healthy subjects

PURPOSE

Ticagrelor, a reversibly binding oral P2Y12 receptor antagonist, is predominantly metabolized by cytochrome P450 3A and both the parent compound and its active metabolite AR-C124910XX are substrates of P-glycoprotein. Rifampicin was used to assess the effects of CYP3A and P-glycoprotein induction on the single-dose pharmacokinetics and pharmacodynamics of ticagrelor.

METHODS

Healthy volunteers received a single 180 mg oral dose of ticagrelor on days 1 and 15, and a once-daily 600 mg dose of rifampicin on days 4-17. Ticagrelor and AR-C124910XX plasma concentrations were quantified for pharmacokinetic analysis (n = 14); inhibition of platelet aggregation (IPA) was also assessed (n = 14).

RESULTS

Compared with administration of ticagrelor alone, co-administration of ticagrelor and rifampicin significantly decreased the maximum plasma concentration (Cmax) of ticagrelor from 1091 to 297.8 ng/ml, area under the plasma concentration-time curve from time zero to infinity (AUC) of ticagrelor from 6225 to 864.0 ng.h/ml, and also decreased plasma half-life of ticagrelor from 8.4 to 2.8 h; reductions of 73 %, 86 % and 67 % respectively. With rifampicin, AR-C124910XX Cmax was unaffected, AUC was significantly decreased by 46 %, and metabolite to parent ratio for AUC increased fourfold. Although maximal IPA was unaffected, offset of ticagrelor-mediated IPA was more rapid in the presence of rifampicin; a significant reduction (27 %) in the area under the effect curve between 0 and 24 h was observed following co-administration with rifampicin.

CONCLUSION

Co-administration with rifampicin reduced ticagrelor exposure and resulted in a more rapid offset of ticagrelor-mediated IPA. Co-administration of strong CYP3A/P-glycoprotein inducers with ticagrelor should be discouraged.

Evaluation of ticagrelor pharmacodynamic interactions with reversibly binding or non-reversibly binding P2Y(12) antagonists in an ex-vivo canine model

INTRODUCTION

As ticagrelor, clopidogrel and cangrelor therapies may be used in the same clinical setting, their potential pharmacodynamic interactions are of interest. Hence, we investigated possible interactions between these agents in dogs using a variety of switching protocols.

METHODS

Six male dogs all received 7 different dosing regimens separated by 1-5week washout periods: cangrelor (1μg/kg/min, intravenous infusion); ticagrelor (0.8mg/kg, oral); clopidogrel (3mg/kg, intravenous injection); cangrelor together with ticagrelor initiated 10minutes after cangrelor infusion start or clopidogrel given 30minutes after cangrelor infusion start; ticagrelor followed by clopidogrel given 3 or 7hours after ticagrelor dosing. ADP-induced whole blood platelet aggregation was measured by impedance aggregometry.

RESULTS

Mean maximum inhibition of platelet aggregation (IPA) was 81-87% at 6minutes (cangrelor), 3hours (ticagrelor) and 4hours (clopidogrel) postdosing and platelet function recovered after 1.5hours, 12hours, and 9days, respectively. IPA at 2hours post clopidogrel was reduced to 39% when clopidogrel was given during cangrelor infusion versus 69% for clopidogrel alone. With clopidogrel dosed 3hours after ticagrelor, IPA was reduced after washout of ticagrelor to 38% at 24hrs vs. 68% for clopidogrel alone, but an interaction was not seen when clopidogrel was dosed 7hours after ticagrelor. No pharmacodynamic interaction occurred between ticagrelor and cangrelor.

CONCLUSIONS

The extent of the pharmacodynamic drug-drug interactions observed between clopidogrel and cangrelor or ticagrelor apparently depends on the level of receptor occupancy when clopidogrel is administered. Importantly, no significant pharmacodynamic interaction occurred between ticagrelor/clopidogrel when clopidogrel was given at clinical trough IPA levels with ticagrelor. No significant pharmacodynamic interaction occurred with cangrelor and ticagrelor.

Role of newly formed platelets in thrombus formation in rat after clopidogrel treatment: comparison to the reversible binding P2Y₁₂ antagonist ticagrelor

Platelet P2Y₁₂ receptors play an important role in arterial thrombosis by stimulating thrombus growth. Both irreversibly (clopidogrel) and reversibly binding (ticagrelor, AZD6140) P2Y₁₂ antagonists are clinically used for restricted periods, but possible differences in platelet function recovery after drug cessation have not been investigated. We treated WKY rats with a single, high dose of 200 mg/kg clopidogrel or 40 mg/kg ticagrelor. Blood was collected at different time points after treatment. Flow cytometry confirmed full platelet protection against ADP-induced αIIbβ₃ activation shortly after clopidogrel or ticagrelor treatment. At later time points after clopidogrel treatment, a subpopulation of juvenile platelets appeared that was fully responsive to ADP. Addition of ticagrelor to clopidogrel-treated blood reduced αIIbβ₃ activation of the unprotected platelets. In contrast, at later time points after ticagrelor treatment, all platelets gradually lost their protection against ADP activation. Perfusion experiments showed abolishment of thrombus formation shortly after clopidogrel or ticagrelor treatment. Thrombus formation on collagen was determined under high shear flow conditions. At later time points, large thrombi formed in the clopidogrel but not in the ticagrelor group, and unprotected, juvenile platelets preferentially incorporated into the formed thrombi. However, platelets from both groups were still similarly reduced in assays of whole blood aggregation. Conclusively, recovery of rat platelet function after ticagrelor differs mechanistically from that after clopidogrel. This difference is masked by conventional platelet aggregation methods, but is revealed by thrombus formation measurement under flow. Juvenile platelets formed at later time points after clopidogrel treatment promoted thrombus formation.

Pharmacokinetics, pharmacodynamics, safety and tolerability of multiple ascending doses of ticagrelor in healthy volunteers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The antiplatelet agent clopidogrel is currently the recommended treatment for acute coronary syndrome (ACS). Inhibition of platelet aggregation (IPA) with clopidogrel is insufficient, which increases the risk for recurrent ischaemic events. Therefore, there is a need for antiplatelet agents with improved IPA. Ticagrelor (AZD6140) is a new antiplatelet agent in clinical development for reduction of thrombotic events in patients with ACS.

WHAT THIS STUDY ADDS

This study assesses the optimal dosing schedule for ticagrelor in healthy volunteers and compares the degree of IPA with clopidogrel. Our findings illustrate that the pharmacokinetics of ticagrelor are predictable and are associated with consistent inhibition of platelet activity. IPA with ticagrelor was greater and better sustained at high levels with twice daily ticagrelor than once daily regimens.

AIM

To determine the pharmacokinetics, pharmacodynamics, safety and tolerability of multiple oral doses of ticagrelor, a P2Y(12) receptor antagonist, in healthy volunteers.

METHODS

This was a randomized, single-blind, placebo-controlled, ascending dose study. Thirty-two subjects received ticagrelor 50-600 mg once daily or 50-300 mg twice daily or placebo for 5 days at three dose levels in two parallel groups. Another group of 16 subjects received a clopidogrel 300 mg loading dose then 75 mg day(-1), or placebo for 14 days.

RESULTS

Ticagrelor was absorbed with median t(max) 1.5-3 h, exhibiting predictable pharmacokinetics over the 50-600 mg dose range. Mean C(max) and AUC for ticagrelor and its main metabolite, AR-C124910XX, increased approximately dose-proportionately (approximately 2.2- to 2.4-fold with a twofold dose increase) over the dose range. Inhibition of platelet aggregation (IPA) with ticagrelor was greater and better sustained at high levels with ticagrelor twice daily vs. once daily regimens. Throughout dosing, more consistent IPA was observed at doses > or = 300 mg once daily and > or = 100 mg twice daily compared with clopidogrel. Mean IPA with ticagrelor > or = 100 mg twice daily was greater and less variable (93-100%, range 65-100%) than with clopidogrel (77%, range 11-100%) at trough concentrations. No safety or tolerability issues were identified.

CONCLUSIONS

Multiple dosing provided predictable pharmacokinetics of ticagrelor and its metabolite over the dose range of 50-600 mg once daily and 50-300 mg twice daily with C(max) and AUC(0,t) increasing approximately dose-proportionally. Greater and more consistent IPA with ticagrelor at doses > or = 100 mg twice daily and > or = 300 mg once daily were observed than with clopidogrel. Ticagrelor at doses up to 600 mg day(-1) was well tolerated.

Pharmacokinetics, pharmacodynamics, tolerability and safety of single ascending doses of ticagrelor, a reversibly binding oral P2Y(12) receptor antagonist, in healthy subjects

PURPOSE

Ticagrelor (AZD6140) is the first reversibly binding oral P2Y(12) receptor antagonist in development for reduction of clinical thrombotic events in patients with acute coronary syndromes. The purpose of our studies was to determine the effect of single-ascending doses of ticagrelor in healthy subjects.

METHODS

In two randomised, double-blind, placebo-controlled single ascending dose studies, healthy subjects received oral doses of 0.1-100 mg or placebo (n = 25) and 30-400 mg or placebo (n = 13).

RESULTS

Absorption of ticagrelor was rapid [median time to peak plasma concentration (t(max)) 1.3-2 h], as was the formation of its main (active) metabolite, AR-C124910XX (t(max) 1.5-3 h). For both ticagrelor and AR-C124910XX, the peak plasma concentration (C(max)) and area under the plasma concentration-time curve from time 0 to infinity (AUC(0-infinity)) increased in an apparently dose-proportional manner over the dose range studied, indicating linear pharmacokinetics. The mean terminal-phase half-life (t(1/2)) was approximately 7-8.5 h for ticagrelor and 8.5-10 h for AR-C124910XX; AR-C124910XX exposure was approximately one third that of ticagrelor. Inhibition of platelet aggregation (IPA) was dose related and was nearly complete at 2 h (mean 88-95%; final extent, with 20 microM adenosine diphosphate ADP) at doses of 100-400 mg.

CONCLUSION

Linear and predictable pharmacokinetics of ticagrelor and AR-C124910XX were observed. A consistent and high IPA was maintained over 2-12 h, gradually decreasing with declining plasma concentration starting around 12 h post-dose, indicating that the IPA is reversible. Ticagrelor was well tolerated, with no serious or dose-related adverse events or notable changes in laboratory values observed.

Ticagrelor binds to human P2Y(12) independently from ADP but antagonizes ADP-induced receptor signaling and platelet aggregation

BACKGROUND

P2Y(12) plays an important role in regulating platelet aggregation and function. This receptor is the primary target of thienopyridine antiplatelet agents, the active metabolites of which bind irreversibly to the receptor, and of newer agents that can directly and reversibly modulate receptor activity.

OBJECTIVE

To characterize the receptor biology of the first reversibly binding oral P2Y(12) antagonist, ticagrelor (AZD6140), a member of the new cyclopentyltriazolopyrimidine (CPTP) class currently in phase III development.

METHODS

Ticagrelor displayed apparent non-competitive or insurmountable antagonism of ADP-induced aggregation in human washed platelets. This was investigated using competition binding against [(3)H]ADP, [(33)P]2MeS-ADP and the investigational CPTP compound [(125)I]AZ11931285 at recombinant human P2Y(12). Functional receptor inhibition studies were performed using a GTPgammaS-binding assay, and further binding studies were performed using membranes prepared from washed human platelets.

RESULTS

Radioligand-binding studies demonstrated that ticagrelor binds potently and reversibly to human P2Y(12) with K(on) and K(off) of (1.1 +/- 0.2) x 10(-4) nm(-1) s(-1) and (8.7 +/- 1.4) x 10(-4) s(-1), respectively. Ticagrelor does not displace [(3)H]ADP from the receptor (K(i) > 10 mum) but binds competitively with [(33)P]2MeS-ADP (K(i) = 4.3 +/- 1.3 nm) and [(125)I]AZ11931285 (K(i) = 0.33 +/- 0.04 nm), and shows apparent non-competitive inhibition of ADP-induced signaling but competitive inhibition of 2MeS-ADP-induced signaling. Binding studies on membranes prepared from human washed platelets demonstrated similar non-competitive binding for ADP and ticagrelor.

CONCLUSIONS

These data indicate that P2Y(12) is targeted by ticagrelor via a mechanism that is non-competitive with ADP, suggesting the existence of an independent receptor-binding site for CPTPs.

Developments in antiplatelet therapy for acute coronary syndromes and considerations for long-term management

OBJECTIVE

This article reviews the currently available antiplatelet therapies and emerging investigational drugs in the treatment of acutecoronary syndrome (ACS), and considerations for primary and secondary prevention in the long-term management of ACS patients undergoing percutaneous coronary intervention (PCI).

RESEARCH DESIGN AND METHODS

Primary studies and reviews in the peer-reviewed, English-language literature were identified through searches of MEDLINE (1966-2008) using the terms 'acute coronary syndrome', 'antiplatelet', 'aspirin', 'long-term management', 'P2Y(12) receptor', and 'thienopyridine'. Additional references were obtained by searching the reference lists of the identified articles. Articles were included if they were recently published and pertinent, patient-focused, and authors were recognized as leaders in the field. Current review is limited by literature search on single database.

RESULTS

Platelets play a major role in atherogenesis and the formation of thrombi, the main events in the pathogenesis of ACS. Although aspirin is an effective antiplatelet agent, efficacy and safety data from a number of randomized clinical trials on atherothrombotic disease support the use of dual antiplatelet therapies such as aspirin and thienopyridines over single antiplatelet therapy for ACS and up to 1 year following ACS. Antiplatelet agents reduce, but do not eliminate, ischemic events after ACS due, in part, to variable individual response (or resistance) in antiplatelet agents, non-compliance, progression of atherosclerosis, modest inhibition of platelet aggregation (IPA) levels and other factors. Several antiplatelet agents, including novel P2Y(12)-receptor antagonists and thrombin-receptor antagonists, are currently under investigation for ACS and primary and secondary prevention in the long-term management of patients undergoing PCI.

CONCLUSIONS

Current antiplatelet therapies have clinical benefits such as reducing immediate and long-term cardiovascular risk, but substantial residual risk remains indicating a need for new therapeutic agents. Additional large randomized trials are necessary to determine the most appropriate treatment regimens for ACS patients.

Ticagrelor: the first reversibly binding oral P2Y12 receptor antagonist

Ticagrelor (AZD6140) is the first reversibly binding oral P2Y(12) receptor antagonist that blocks ADP-induced platelet aggregation. Unlike thienopyridines, which irreversibly bind to the P2Y(12) receptor for the lifetime of the platelet, ticagrelor binds reversibly to the receptor and exhibits rapid onset and offset of effect, which closely follow drug exposure levels. Animal models indicate greater separation between antithrombotic effects and bleeding effects with ticagrelor than with thienopyridines. Unlike the thienopyridines, ticagrelor does not require metabolic activation. It is quickly absorbed and exhibits a rapid antiplatelet effect, with higher and more consistent levels of inhibition of platelet aggregation (IPA) being maintained across the dosing interval than with clopidogrel. IPA levels decline with plasma drug levels after discontinuation of dosing. In the phase II DISPERSE-2 trial of 990 patients with non-ST-elevation acute coronary syndromes (ACS), ticagrelor treatment with 90 mg and 180 mg twice daily showed comparable rates of major and minor bleeding compared with clopidogrel 75 mg while there were numerically fewer myocardial infarctions. Ticagrelor resulted in greater IPA in clopidogrel-naïve patients and produced substantial additional reductions in platelet aggregation activity in patients pretreated with clopidogrel. Ticagrelor treatment was well tolerated in DISPERSE-2, and discontinuation rates were comparable to those observed for clopidogrel. An increased risk of mild to moderate dyspnea and mostly asymptomatic ventricular pauses were observed in phase II studies. The mechanisms for these effects are currently being investigated. The efficacy and safety of ticagrelor are being further evaluated in the phase III PLATO trial, involving approximately 18,000 patients with ACS, including both ST-elevation and non-ST-elevation ACS.