Mechanism of Action
AGGRASTAT is a reversible antagonist of fibrinogen binding to the GP lIb/lIla
receptor, the major platelet surface receptor involved in platelet aggregation.
When administered intravenously, AGGRASTAT inhibits ex vivo platelet
aggregation in a dose- and concentration-dependent manner.
When given according to the recommended regimen, >90% inhibition is attained
by the end of the 30-minute infusion. Platelet aggregation inhibition is reversible
following cessation of the infusion of AGGRASTAT.
Pharmacokinetics
Tirofiban has a half-life of approximately 2 hours. It is cleared from the
plasma largely by renal excretion, with about 65% of an administered dose appearing
in urine and about 25% in feces, both largely as unchanged tirofiban. Metabolism
appears to be limited.
Tirofiban is not highly bound to plasma proteins and protein binding is concentration
independent over the range of 0.01 to 25 mcg/mL. Unbound fraction in human plasma
is 35%. The steady state volume of distribution of tirofiban ranges from 22
to 42 liters.
In healthy subjects, the plasma clearance of tirofiban ranges from 213 to 314
mL/min. Renal clearance accounts for 39 to 69% of plasma clearance. The recommended
regimen of a loading infusion followed by a maintenance infusion produces a
peak tirofiban plasma concentration that is similar to the steady state concentration
during the infusion. In patients with coronary artery disease, the plasma clearance
of tirofiban ranges from 152 to 267 mL/min; renal clearance accounts for 39%
of plasma clearance.
Special Populations
Gender
Plasma clearance of tirofiban in patients with coronary artery disease is similar
in males and females.
Elderly
Plasma clearance of tirofiban is about 19 to 26% lower in elderly (>65 years)
patients with coronary artery disease than in younger (≤ 65 years) patients.
Race
No difference in plasma clearance was detected in patients of different races.
Hepatic Insufficiency
In patients with mild to moderate hepatic insufficiency, plasma clearance of
tirofiban is not significantly different from clearance in healthy subjects.
Renal Insufficiency
Plasma clearance of tirofiban is significantly decreased (>50%) in patients
with creatinine clearance <30 mL/min, including patients requiring hemodialysis
(see DOSAGE AND ADMINISTRATION, Recommended
Dosage). Tirofiban is removed by hemodialysis.
Pharmacodynamics
AGGRASTAT inhibits platelet function, as demonstrated by its ability to inhibit
ex vivo adenosine phosphate (ADP)-induced platelet aggregation and prolong
bleeding time in healthy subjects and patients with coronary artery disease.
The time course of inhibition parallels the plasma concentration profile of
the drug.
Following discontinuation of an infusion of AGGRASTAT, 0.10 mcg/kg/min, ex
vivo platelet aggregation returns to near baseline in approximately 90%
of patients with coronary artery disease in 4 to 8 hours. The addition of heparin
to this regimen does not significantly alter the percentage of subjects with
>70% inhibition of platelet aggregation (IPA), but does increase the average
bleeding time, as well as the number of patients with bleeding times prolonged
to >30 minutes.
In patients with unstable angina, a two-staged intravenous infusion regimen
of AGGRASTAT (loading infusion of 0.4 mcg/kg/min for 30 minutes followed by
0.1 mcg/kg/min for up to 48 hours in the presence of heparin and aspirin), produces
approximately 90% inhibition of ex vivo ADP-induced platelet aggregation
with a 2.9-fold prolongation of bleeding time during the loading infusion. Inhibition
persists over the duration of the maintenance infusion.
Clinical Trials
Three large-scale clinical studies were conducted to study the efficacy and
safety of AGGRASTAT in the management of patients with Acute Coronary Syndrome (unstable angina/ non-Q-wave myocardial infarction). Acute Coronary Syndrome
is characterized by prolonged (≥10 minutes) or repetitive symptoms of cardiac ischemia occurring at rest or with minimal exertion, associated with either
ischemic ST-T wave changes on electrocardiogram (ECG) or elevated cardiac enzymes.
The definition includes ”unstable angina“ and ”non-Q-wave
myocardial infarction“ but excludes myocardial infarction that is associated
with Q-waves or non-transient ST-segment elevation. The three studies examined
AGGRASTAT alone and as an addition to heparin, prior to and after angioplasty
(if indicated) (PRISM-PLUS), in comparison to heparin in a similar population
(PRISM), and in addition to heparin in patients undergoing percutaneous transluminal
coronary angioplasty (PTCA) or atherectomy (RESTORE). These trials are discussed
in detail below.
PRISM-PLUS (Platelet Receptor Inhibition for lschemic Syndrome Management
- Patients Limited by Unstable Signs and Symptoms)
In the multi-center, randomized, parallel, double-blind PRISM-PLUS trial, the
use of AGGRASTAT in combination with heparin (n=773) was compared to heparin
alone (n=797) in patients with documented unstable angina/non-Q-wave myocardial
infarction within 12 hours of entry into the study and initiation of treatment.
All patients with unstable angina/non-Q-wave myocardial infarction had cardiac
ischemia documented by ECG or had elevated cardiac enzymes. Patients who were
medically managed or who subsequently underwent revascularization procedures
were studied. The mean age of the population was 63 years; 32% of patients were
female and approximately half of the population presented with non- Q-wave myocardial
infarction. Exclusions included contraindications to anticoagulation (see CONTRAINDICATIONS),
decompensated heart failure, platelet count <150,000/mm³, and creatinine
>2.5 mg/dL. In this study, patients were randomized to either AGGRASTAT (30
minute loading infusion of 0.4 mcg/kg/min followed by a maintenance infusion
of 0.10 mcg/kg/min) and heparin (bolus of 5,000 units (U) followed by an infusion
of 1,000 U/hr titrated to maintain an activated partial thromboplastin time
(APTT) of approximately 2 times control), or heparin alone (bolus of 5,000 U
followed by an infusion of 1,000 U/hr titrated to maintain an APTT of approximately
2 times control). All patients received concomitant aspirin unless contraindicated.
Patients underwent 48 hours of medical stabilization on study drug therapy, and they were to undergo angiography before 96 hours (and, if indicated, angioplasty/atherectomy,
while continuing on AGGRASTAT and heparin for 12-24 hours after the procedure).
Some patients went on to coronary artery bypass grafting (CABG) after cessation
of drug therapy. AGGRASTAT and heparin could be continued for up to 108 hours.
On average, patients received AGGRASTAT for 71.3 hours. A third group of patients
was initially randomized to AGGRASTAT alone (no heparin). This arm was stopped
when the group was found, at an interim look, to have greater mortality than
the other two groups. Note, however, that a direct comparison of heparin and
tirofiban alone in the PRISM study (see below) did not show excess mortality.
The primary endpoint of the study was a composite of refractory ischemia, new
myocardial infarction and death at 7 days after initiation of AGGRASTAT and
heparin. At the primary endpoint, there was a 32% risk reduction in the overall
composite. The components of the composite were examined separately (they total
more than the composite because a patient could have more than one, e.g., by
dying after having a new infarction). There was a 47% risk reduction in myocardial
infarction and a 30% risk reduction in refractory ischemia. The results are
shown in Table 1.
Table 1: Cardiac Ischemia Events (7 days)
| Endpoint |
AGGRASTAT+ Heparin (n=773) |
Heparin (n=797) |
Risk Reduction |
p-value |
| Composite Endpoint |
12.9% |
17.9% |
32% |
0.004 |
| Components |
| Myocardial Infarction and Death |
4.9% |
8.3% |
43% |
0.006 |
| Myocardial Infarction |
3.9% |
7.0% |
47% |
0.006 |
| Death |
1.9% |
1.9% |
- |
- |
| Refractory Ischemia |
9.3% |
12.7% |
30% |
0.023 |
The benefit seen at 7 days was maintained over time. At 30 days, the risk of
the composite endpoint was reduced by 22% (p=0.029) and there was a 30% reduction
in the composite of myocardial infarction and death (p=0.027). At 6 months,
the risk of the composite endpoint was reduced by 19% (p=0.024). The risk reduction
in the composite endpoint at 30 days and 6 months is shown in the Kaplan-Meier
curve below.
PRISM-PLUS was not designed to provide definitive results in subsets of the
overall population. Nonetheless, results were examined for demographic (age,
gender, race) subsets and for people who did and did not receive PTCA, atherectomy,
or CABG.
In PRISM-PLUS, there was a consistent treatment effect in patients either greater
or less than 65 years old, and in men and women. Too few non-Caucasians were
enrolled to make a definite statement about racial differences in treatment
effect.
Approximately 90% of patients in the PRISM-PLUS study underwent coronary angiography
and 30% underwent angioplasty/atherectomy during the first 30 days of the study.
The majority of these patients continued on study drug throughout these procedures.
AGGRASTAT was continued for 12-24 hours (average 15 hours) after angioplasty/atherectomy.
The effects of AGGRASTAT at Day 30 did not appear to differ among the sub-populations
that did or did not receive PTCA or CABG, both prior to and after the procedure.
A sub-study in PRISM-PLUS of angiograms after 48 to 96 hours found that there
was a significant decrease in the extent of angiographically apparent thrombus
in patients treated with AGGRASTAT in combination with heparin compared to heparin
alone. In addition, flow in the affected coronary artery was significantly improved.
PRISM (Platelet Receptor Inhibition for Ischemic Syndrome Management)
In the PRISM study, a randomized, parallel, double-blind, active control study,
AGGRASTAT alone (n=1616) was compared to heparin (n=1616) alone as medical management
in patients with unstable angina/non-Q-wave myocardial infarction. In this study,
the drug was started within 24 hours of the time the patient experienced chest pain. The mean age of the population was 62 years; 32% of the population was
female and 25% had non-Q-wave myocardial infarction on presentation. Thirty
percent had no ECG evidence of cardiac ischemia. Exclusion criteria were similar
to PRISM-PLUS. The primary, prospectively identified endpoint was the composite
endpoint of refractory ischemia, myocardial infarction or death after a 48-hour
drug infusion with AGGRASTAT. The results are shown in Table 2.
Table 2: Cardiac Ischemia Events
| Composite Endpoint |
AGGRASTAT (n=1616) |
Heparinm (n=1616) |
Risk Reduction |
p-value |
| 2 Days |
3.8% |
5.6% |
33% |
0.015 |
| 7 Days |
10.3% |
11.3% |
10% |
0.33 |
| 30 Days |
15.9% |
17.1% |
8% |
0.34 |
In the PRISM study, no adverse effect of AGGRASTAT on mortality at either 7
or 30 days was detected. This result is in conflict with the PRISM-PLUS study,
where the arm that included AGGRASTAT without heparin (n=345) was dropped at
an interim analysis by the Data Safety Monitoring Committee due to increased
mortality at 7 days. A pooled analysis of the data from these two trials (PRISM
and PRISM-PLUS) demonstrated that the effect of AGGRASTAT alone on mortality
(at 7 and 30 days) was comparable to that of heparin alone.
RESTORE (Randomized Efficacy Study of Tirofiban for Outcomes and Restenosis)
The RESTORE study (n=2141) was a randomized, controlled comparison of AGGRASTAT
and placebo, each added to heparin, in patients undergoing PTCA or atherectomy
within 72 hours of presentation with unstable angina or acute myocardial infarction.
The mean age of the population was 59 years; 27% were female. Two-thirds of
patients underwent angioplasty for unstable angina and the remainder in association
with acute myocardial infarction. Exclusions included anatomy not amenable to
angioplasty, contraindications to anticoagulation (see CONTRAINDICATIONS),
platelet count <150,000/mm³, and creatinine >2.0 mg/dL. AGGRASTAT
(with heparin) was initiated immediately prior to the angioplasty/ atherectomy
at a dose of 10 mcg/kg bolus (over 3 minutes) followed by an infusion of 0.15
mcg/kg/min along with a heparin bolus (bolus of 10,000 U, or 150 U/kg for patients
<70 kg). The infusion dose of AGGRASTAT is 50% higher than the dose used
in the PRISM-PLUS trial. AGGRASTAT was administered for a total of 36 hours.
In general, heparin was to be discontinued at the conclusion of the angioplasty/atherectomy.
Reasons for continued heparin included: imperfect outcome (e.g., large tear,
intraluminal filling defect, or residual stenosis >40%), large thrombus load,
continuing rest angina through the procedure, abrupt closure or very active
artery during the procedure, or side branch occlusion. The primary endpoint
was the composite of all deaths, non-fatal myocardial infarctions, and all repeat
revascularization procedures at 30 days. For results see Table 3. A sub-study
in RESTORE of angiograms after approximately 6 months found that AGGRASTAT had
no significant effect on the extent of coronary artery restenosis following
angioplasty.
Table 3: Cardiac Ischemia Events
| Composite Endpoint |
AGGRASTAT (n=1071) |
Heparin (n=1070) |
Risk Reduction |
p-value |
| 2 Days |
5.4% |
8.7% |
38% |
0.004 |
| 7 Days |
7.6% |
10.4% |
28% |
0.023 |
| 30 Days |
10.3% |
12.2% |
17% |
0.17 |
The risk reduction in the composite endpoint at 180 days is shown in the Kaplan-Meier
curve below.
Last updated on RxList: 6/13/2008