CLINICAL PHARMACOLOGY
General
Tenecteplase is a modified form of human tissue plasminogen activator (tPA) that binds to fibrin
and converts plasminogen to plasmin. In the presence of fibrin, in vitro studies demonstrate that
Tenecteplase conversion of plasminogen to plasmin is increased relative to its conversion in the
absence of fibrin. This fibrin specificity decreases systemic activation of plasminogen and the
resulting degradation of circulating fibrinogen as compared to a molecule lacking this property.
Following administration of 30, 40, or 50 mg of TNKase, there are decreases in circulating
fibrinogen (4%–15%) and plasminogen (11% - 24%). The clinical significance of fibrinspecificity
on safety (e.g., bleeding) or efficacy has not been established. Biological potency is
determined by an in vitro clot lysis assay and is expressed in Tenecteplase-specific units. The
specific activity of Tenecteplase has been defined as 200 units/mg.
Pharmacokinetics
In patients with acute myocardial infarction (AMI), TNKase administered as a single bolus
exhibits a biphasic disposition from the plasma. Tenecteplase was cleared from the plasma with
an initial half-life of 20 to 24 minutes. The terminal phase half-life of Tenecteplase was 90 to
130 minutes. In 99 of 104 patients treated with Tenecteplase, mean plasma clearance ranged
from 99 to 119 mL/min.
The initial volume of distribution is weight related and approximates plasma volume. Liver
metabolism is the major clearance mechanism for Tenecteplase.
Clinical Studies
ASSENT-2 was an international, randomized, double-blind trial that compared 30-day mortality
rates in 16,949 patients assigned to receive an IV bolus dose of TNKase or an accelerated
infusion of Activase® (Alteplase).1 Eligibility criteria included onset of chest pain within 6 hours
of randomization and ST-segment elevation or left bundle branch block on
electrocardiogram (ECG). Patients were to be excluded from the trial if they received
GP IIb/IIIa inhibitors within the previous 12 hours. TNKase was dosed using actual or estimated
weight in a weight-tiered fashion as described in DOSAGE AND ADMINISTRATION. All
patients were to receive 150–325 mg of aspirin administered as soon as possible, followed by
150–325 mg daily. Intravenous heparin was to be administered as soon as possible: for patients
weighing ≤ 67 kg, heparin was administered as a 4000 unit IV bolus followed by infusion at
800 U/hr; for patients weighing > 67 kg, heparin was administered as a 5000 unit IV bolus
followed by infusion at 1000 U/hr. Heparin was continued for 48 to 72 hours with infusion
adjusted to maintain aPTT at 50–75 seconds. The use of GP IIb/IIIa inhibitors was discouraged
for the first 24 hours following randomization. The results of the primary endpoint (30-day
mortality rates with non-parametric adjustment for the covariates of age, Killip class, heart rate,
systolic blood pressure and infarct location) along with selected other 30-day endpoints are
shown in Table 1.
Table 1
ASSENT-2
Mortality, Stroke, and Combined Outcome of Death or Stroke
Measured at Thirty Days
30-Day Events |
TNKase
(n = 8461) |
Accelerated
Activase
(n = 8488) |
Relative Risk
TNKase/Activase
(95% CI) |
Mortality |
6.2% |
6.2% |
1.00
(0.89, 1.12) |
Intracranial Hemorrhage (ICH) |
0.9% |
0.9% |
0.99
(0.73, 1.35) |
Any Stroke |
1.8% |
1.7% |
1.07
(0.86, 1.35) |
Death or Nonfatal Stroke |
7.1% |
7.0% |
1.01
(0.91, 1.13) |
Rates of mortality and the combined endpoint of death or stroke among pre-specified subgroups,
including age, gender, time to treatment, infarct location, and history of previous myocardial
infarction, demonstrate consistent relative risks across these subgroups. There was insufficient
enrollment of non-Caucasian patients to draw any conclusions regarding relative efficacy in
racial subsets.
Rates of in-hospital procedures, including percutaneous transluminal coronary angioplasty
(PTCA), stent placement, intra-aortic balloon pump (IABP) use, and coronary artery bypass graft
(CABG) surgery, were similar between the TNKase and Activase® (Alteplase) groups.
TIMI 10B was an open-label, controlled, randomized, dose-ranging, angiography study which
utilized a blinded core laboratory for review of coronary arteriograms.2 Patients (n = 837)
presenting within 12 hours of symptom onset were treated with fixed doses of 30, 40, or 50 mg
of TNKase or the accelerated infusion of Activase and underwent coronary arteriography at
90 minutes. The results showed that the 40 mg and 50 mg doses were similar to accelerated
infusion of Activase in restoring patency. TIMI Grade 3 flow and TIMI Grade 2/3 flow at
90 minutes are shown in Table 2. The exact relationship between coronary artery patency and
clinical activity has not been established.
Table 2
TIMI 10B Patency Rates TIMI Grade Flow at 90 Minutes
|
Activase ≤100 mg
(n=311) |
TNKase 30 mg
(n=302) |
TNKase 40 mg
(n=148) |
TNKase 50 mg
(n=76) |
TIMI Grade 3 Flow |
63% |
54% |
63% |
66% |
TIMI Grade 2/3 Flow |
82% |
77% |
79% |
88% |
95% CI
(TIMI 2/3 Flow) |
(77%,86%) |
(72%,81%) |
(72%,85%) |
(79%,94%) |
The angiographic results from TIMI 10B and the safety data from ASSENT-1, an additional
uncontrolled safety study of 3,235 TNKase-treated patients, provided the framework to develop a
weight-tiered TNKase dose regimen.3 Exploratory analyses suggested that a weight-adjusted
dose of 0.5 mg/kg to 0.6 mg/kg of TNKase resulted in a better patency to bleeding relationship
than fixed doses of TNKase across a broad range of patient weights.
The Assessment of the Safety and Efficacy of a New Treatment Strategy with Percutaneous
Coronary Intervention (ASSENT 4 PCI) was a Phase IIIb/IV study designed to assess the safety
and effectiveness of a strategy of administering full dose TNKase with a single bolus of 4000 U
of unfractionated heparin in patients with ST segment elevation AMI, in whom primary
percutaneous coronary intervention (PCI) was planned, but in whom a delay of 1-3 hours was
anticipated before PCI. The trial was prematurely terminated with 1667 randomized patients (75
of whom were treated in the United States) due to a numerically higher mortality in the patients
receiving TNKase prior to primary PCI versus PCI without TNKase (median time from
randomization to balloon of 115 minutes). The incidence of the 90-day primary endpoint, a
composite of death or cardiogenic shock or congestive heart failure (CHF) within 90 days, was
18.6% in patients treated with TNKase plus PCI versus 13.4% in those treated with PCI alone
(p = 0.0055; OR 1.39 (95% C.I. 1.11 - 1.74)).
There were trends toward worse outcomes in the individual components of the primary endpoint
between TNKase plus PCI versus PCI alone (mortality 6.7% vs. 5.0%, respectively; cardiogenic
shock 6.1% vs. 4.8%, respectively; and CHF 12.1% vs. 9.4%, respectively). In addition, there
were trends towards worse outcomes in recurrent MI (6.1% vs. 3.5%, respectively; p = 0.03) and
repeat target vessel revascularization (6.6% vs. 3.6%, respectively; p = 0.005) in patients
receiving TNKase plus PCI versus PCI alone.
There was no difference in in-hospital major bleeding between the two groups (5.6% vs. 4.4%
for TNKase plus PCI vs. PCI alone, respectively). For patients treated with TNKase plus PCI,
in-hospital rates of intracranial hemorrhage and total stroke were similar to those observed in
previous trials (0.97% and 1.8%, respectively); however, none of the patients treated with PCI
alone experienced a stroke (ischemic, hemorrhagic or other).
REFERENCES
1. ASSENT-2 Investigators. Single-bolus tenecteplase compared with front-loaded alteplase
in acute myocardial infarction: the ASSENT-2 double-blind randomised trial.
Lancet 1999;354:716 - 22.
2. Cannon CP, Gibson CM, McCabe CH, Adgey AAJ, Schweiger MJ, Sequeira RF, et al.
TNK-tissue plasminogen activator compared with front-loaded alteplase in acute
myocardial infarction. Results of the TIMI 10B trial. Circulation 1998;98:2805 - 14.
3. Van de Werf F, Cannon CP, Luyten A, Houbracken K, McCabe CH, Berioli S, et al.
Safety assessment of a single bolus administration of TNK tissue-plasminogen activator in
acute myocardial infarction: the ASSENT-1 trial. Am Heart J 1999;137:786 - 91.