Pharmacokinetics and pharmacodynamics of sibrafiban (Ro 48-3657), an orally active IIb/IIIa antagonist, administered alone or in combination with heparin, aspirin, and recombinant tissue-type plasminogen activator in beagles

Long-term oral platelet glycoprotein IIb/IIIa receptor antagonism with sibrafiban after acute coronary syndromes: study design of the sibrafiban versus aspirin to yield maximum protection from ischemic heart events post-acute coronary syndromes (SYMPHONY) trial. Symphony Steering Committee

BACKGROUND

Despite progress, atherosclerotic vascular disease remains a major cause of morbidity and mortality. Intravenous therapy with platelet glycoprotein (GP) IIb/IIIa receptor antagonists improves outcome in patients with acute coronary syndromes (ACS). Whether potent long-term antiplatelet therapy with oral GP IIb/IIIa antagonists will further improve outcome at a dose that is tolerable in long-term treatment is unknown.

TRIAL DESIGN

SYMPHONY (Sibrafiban versus aspirin to Yield Maximum Protection from ischemic Heart events post-acute cOroNary syndromes) was a randomized, double-blind, aspirin-controlled trial with 2 concentration regimens of sibrafiban, an oral peptidomimetic GP IIb/IIIa antagonist, for long-term treatment instead of aspirin in patients after an ACS. Patients were eligible for SYMPHONY if they presented within 7 days of an ACS (>/=20 minutes of ischemic symptoms), had been clinically stable for at least 12 hours, and met one of the following inclusion criteria: ST-segment depression or elevation of at least 0.5 mm or new left bundle branch block with the ACS or elevated creatinine kinase MB more than the upper limit of normal and >3% of total creatine kinase or, if creatine kinase MB was not measured, an elevated level of troponin T or I. Approximately 9000 patients post ACS were randomized 1:1:1 to treatment with either aspirin (80 mg every 12 hours) or high-dose or low-dose sibrafiban every 12 hours. Assignment of tablet strength (3, 4.5, or 6 mg) within the sibrafiban arms was based on body weight and renal function to achieve a target steady-state plasma concentration. The duration of study drug therapy was 90 days. Patients who had intracoronary stenting during the course of the study initially received a blinded stent medication assignment for 2 to 4 weeks based on their initial randomization as follows: aspirin/ticlopidine 250 mg twice daily, low-dose sibrafiban/ticlopidine placebo twice daily, and high-dose sibrafiban/ticlopidine placebo twice daily. After the second interim safety assessment by the Data and Safety Monitoring Board the stent regimen for the low-dose group was modified to include ticlopidine 250 mg twice daily.

END POINTS

The primary efficacy end point of SYMPHONY was the 90-day incidence of a composite of all-cause mortality, myocardial infarction or reinfarction, and severe recurrent ischemia. A clinical events classification committee was established to determine the end points of reinfarction and severe recurrent ischemia. The primary safety end points were the incidence of major bleeding or minor bleeding and the combined incidence of major and minor bleeding. Bleeding classification was done by computer algorithm. Tolerability was assessed by the rate of study drug discontinuation from bleeding.

Sibrafiban

Sibrafiban is the orally administered, nonpeptide, double-prodrug of Ro 44-3888 which is a selective glycoprotein IIb/IIIa receptor antagonist. It is currently undergoing clinical trials for secondary prevention of cardiac events in patients stabilised after acute coronary syndromes. In a phase II dose-finding study (TIMI 12) in patients stabilised after a myocardial infarction (MI) or an episode of unstable angina, there was a dose-dependent inhibition of platelet aggregation which correlated closely with the plasma concentration of the total active drug. An ongoing phase III study (SYMPHONY) compares the effects of sibrafiban on cardiac events with that of aspirin in patients stabilised after a Q wave MI or an episode of unstable angina. This large trial uses twice daily dosage regimens to produce the plasma concentrations which were associated with less bleeding in the earlier dose-ranging trial. A long term (minimum duration 12 months) phase III study (2nd SYMPHONY) is under way to compare the effects of sibrafiban on cardiac events with those of aspirin in patients stabilised after an MI or an episode of unstable angina. The most common adverse events associated with sibrafiban include bleeding, with minor haemorrhages occurring more often than with aspirin.