A Pilot Dose-Escalation Safety Study of Tenecteplase in Acute Ischemic Stroke
Background and Purpose— Recombinant tissue-type plasminogen activator (rtPA) is the only approved treatment in acute ischemic stroke. However, intracerebral hemorrhage (ICH) occurs in 6.4% of patients treated with rtPA and limits its use. Tenecteplase (TNK) is a modified form of rtPA, with longer half-life and greater fibrin specificity. Patients after myocardial infarction had fewer systemic hemorrhages when treated with TNK compared with rtPA. This open-label, dose-escalation safety study was conducted to develop initial experience with TNK in the treatment of ischemic stroke.
Methods— Eligible patients were treated with an intravenous bolus infusion of TNK within 3 hours of stroke onset. The dose escalation was conducted in tiers of 25 patients, starting at 0.1 mg/kg, to a planned maximum of 0.6 mg/kg. The primary endpoint was symptomatic intracranial hemorrhage within 36 hours of treatment. All patients were followed-up for 3 months.
Results— Eighty-eight (88) patients were treated in 4 dosing tiers. In the first 3 tiers (0.1, 0.2, 0.4 mg/kg) of 25 patients each, no symptomatic and 2 (8%), 8 (32%), and 7 (28%) asymptomatic ICHs occurred. Enrollment into the fourth tier at 0.5 mg/kg was closed after 2 of 13 patients (15%) had symptomatic and 3 (23%) had asymptomatic ICHs. Overall, modified Rankin scores at 3 months were similar to those of historical controls treated with rtPA and not significantly different between treatment groups.
Conclusions— TNK doses of 0.1 to 0.4 mg/kg are safe in ischemic stroke. Future trials are needed to compare the effect of TNK on neurological outcome and safety as compared with rtPA.
Ischemic stroke remains a major public health problem in the United States and the world.1 Despite approval of recombinant tissue-type plasminogen activator (rtPA) for treatment of patients with acute ischemic stroke within 3 hours of onset, use of this therapy remains limited, even among patients who reach medical attention within the time window, largely because of concerns regarding associated hemorrhagic complications.2 Moreover, even with timely treatment, up to 40% of patients may remain severely disabled or die,3 leaving substantial room for improvement.
Tenecteplase (TNK) is a genetically engineered mutant tissue plasminogen activator that has a longer half-life, is more fibrin-specific, and is more resistant to plasminogen activator-1 than rtPA.4 In patients with myocardial infarction, doses of ≈0.5 mg/kg administered as an intravenous bolus resulted in similar mortality rates but with less systemic bleeding than in patients treated with front-loaded rtPA.5 Symptomatic intracranial hemorrhage rates were similar in the 2 groups. These findings led to Food and Drug Administration approval of TNK for treatment of patients with acute myocardial infarction. In animal models of acute ischemic stroke, hemorrhagic conversion of experimental infarcts was less frequent with TNK than equipotent doses of rtPA, although the differences did not reach statistical significance.6,7 Peripheral bleeding was less with TNK.
In December1999, an initial pilot dose-escalation safety study of TNK in patients with acute ischemic stroke was funded. This open-label, single-arm trial was designed to test the hypothesis that TNK could be administered safely to patients with acute ischemic stroke within 3 hours of onset at doses that may be associated with improvement in clinical neurological outcome.
Patient Selection and Study Design
The inclusion and exclusion criteria for this study are summarized in Table 1 and were designed to be nearly identical to those used for the National Institutes of Neurological Disorders and Stroke (NINDS) rtPA Stroke Trial.3 All patients underwent pretreatment head computerized tomography (CT) scanning to exclude hemorrhage. The protocol and consent form used for this study were reviewed and approved by each participating hospital’s institutional review board. Eligible patients were offered alternative treatment with intravenous rtPA in every case.
The initial dose of TNK chosen for study was 0.1 mg/kg to be administered as a bolus. This dose was chosen to be bio-equivalent to the approved dose of rtPA used for acute ischemic stroke based on lytic bio-equivalence studies conducted in a rabbit embolic stroke model.6 The planned number of patients to be enrolled in each dosage tier was 25. This number was chosen to provide 80% power of observing at least 1 symptomatic intracranial hemorrhage if the true symptomatic intracranial hemorrhage rate for TNK was 6.4% (the rate reported for rtPA in the NINDS rtPA Stroke Trial) or greater. No patient in any dosage tier was to receive more than that dose calculated for a 100-kg person. At the outset of the study, the maximum dose planned to be studied was 0.6 mg/kg, because doses above that level were associated with excessive bleeding in patients with myocardial infarction.8
After informed consent was obtained, a baseline National Institutes of Health Stroke Scale (NIH Stroke Scale) examination9 was performed, and patients were treated with TNK at the assigned dose calculated for their estimated body weight. After treatment, patients were monitored closely in either an intensive care unit or an acute stroke care and monitoring unit where frequent blood pressure and neurological checks could be performed. Post-treatment elevations in blood pressure were managed as per guidelines developed in the NINDS rtPA Stroke Trial.10 Antiplatelet and anticoagulant therapy were prohibited for 24 hours after treatment.
Patients were closely monitored for adverse events, particularly bleeding. Minor systemic bleeding (eg, gum bleeding, bleeding from shaving cuts or venipuncture sites) not requiring treatment beyond direct compression were distinguished from major bleeding (ie, causing hypotension, resulting in surgery, or requiring blood transfusion). Intracranial bleeding was classified as either asymptomatic or symptomatic (ie, associated with neurological worsening judged to be caused by the hemorrhage). All patients with clinically important neurological worsening underwent emergency head CT scanning and repeat NIH Stroke Scale examination. Additionally, all patients, whether they had neurological worsening, underwent follow-up head CT scanning at 48±6 hours after treatment to detect asymptomatic bleeding. All baseline and head CT scans were read by a central neuroradiologist, and hemorrhages were classified as either asymptomatic or symptomatic by consensus of the investigators (E.C.H. and P.D.L.) and an independent National Institutes of Health Data and Safety Monitoring Board (NIH DSMB).
Fibrinogen levels were obtained at baseline before treatment and at 2 and 24 hours. The assays were performed locally and are reported here as a percent change from baseline. Additionally, a TNK blood level was obtained at 1 hour after treatment. These specimens were immediately spun, separated, and frozen for shipment on ice to Genentech, Inc, where the assays were performed.
NIH Stroke Scale examinations were performed at baseline, 24 hours after stroke onset, at 7 to 10 days, and at 3 months. The Barthel Index,11 modified Rankin Scale,12 and Glasgow Outcome Scale13 were performed at 7 to 10 days and at 3 months. Ischemic stroke subtype, using the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) criteria,14 was assessed at day 7 to 10 using all clinical diagnostic studies available to date. Additionally, major neurological improvement, defined prospectively as an improvement of ≥8 points or a score of 0 on the NIH Stroke Scale at 24 hours, was monitored as a surrogate for drug activity.15
The cumulative safety experience from each dosage tier, including each case in which hemorrhage was detected on a follow-up head CT scan, was reviewed with the NIH DSMB before escalation to the next highest dose. The primary outcome of the study was the occurrence of symptomatic intracranial hemorrhage within 36 hours of treatment. Sequential alerting rules were in place to halt enrollment if observed symptomatic intracranial hemorrhage rates were inconsistent with a true rate of ≤6.4%.
From July 8, 2000 to April 16, 2003, 88 patients were treated in 4 escalating dosage tiers: 0.1 mg/kg, 0.2 mg/kg, 0.4 mg/kg, and 0.5 mg/kg. The study was closed when 2 of 13 patients in the fourth tier sustained symptomatic intracranial hemorrhages within 36 hours of treatment.
Table 2 displays the baseline characteristics and day 7 to 10 ischemic stroke subtypes of the enrolled patients. The median baseline NIH Stroke Scale score varied from 8 to 14 across dosage tiers, and most patients were treated between 91 and 180 minutes from stroke onset.
Table 3 summarizes the bleeding complications encountered in the trial. No symptomatic intracranial hemorrhages were observed within 36 hours of treatment among any of the first 75 patients treated with 0.1 mg/kg, 0.2 mg/kg, or 0.4 mg/kg. As noted, 2 patients among the first 13 treated with 0.5 mg/kg sustained symptomatic hemorrhagic conversions (Figure) of their large cerebral infarctions within 36 hours of treatment. Both patients subsequently died; one after support was withdrawn per his pre-expressed wishes, and the other from presumed aspiration pneumonia at a local nursing home. The rate of asymptomatic intracranial hemorrhage detected on the protocol-required head CT scan at 48 hours ranged from 8% to 32%. Whereas the 8% were observed with the lowest dose, no dose–response trend was observed across the remaining dose tiers for asymptomatic hemorrhage alone. Many of the asymptomatic hemorrhagic changes noted were trivial (Figure). None occurred outside the area of the clinically relevant infarct. One patient treated with 0.1 mg/kg and who had an asymptomatic hemorrhage noted on the 48-hour scan had a transient neurological worsening on day 5 after treatment. A repeat head CT scan at that time showed a small amount of subarachnoid extension of the blood into the insular cistern not present on the 48-hour scan. The relationship of the subarachnoid extension seen on the follow-up scan to the transient neurological worsening was not clear, nor was the extension clearly attributable to TNK treatment. When the incidence of symptomatic and asymptomatic intracranial hemorrhage within 48 hours is combined (ie, all intracranial hemorrhage), a trend toward increasing intracranial hemorrhage with increasing dose is noted. This trend was not seen with minor systemic bleeding. No major systemic bleeding was reported.
Fifteen patients (17%) died during the 3-month follow-up period of the study. Except for the 2 patients in tier 4 who died after their symptomatic intracranial hemorrhages, none of the deaths was attributable to TNK administration.
Serious adverse events (life-threatening or resulting in prolonged or recurrent hospitalization) were reported at rates similar to those of other ischemic stroke populations.16 Aside from the 2 symptomatic intracranial hemorrhages reported, only 1 additional serious adverse event was attributable to TNK administration. Serious oral–lingual angioedema developed requiring endotracheal intubation for airway protection within 1 hour of treatment with 0.5 mg/kg of TNK. The swelling subsided within 4 hours, and the patient was safely extubated without sequellae. This was presumed to be reaction to the medication. Most of the observed serious adverse events were events commonly seen in an ischemic stroke population.16
Table 4 summarizes the fibrinogen data and TNK blood levels. Because the measurements were made at the individual sites, as opposed to a central laboratory, the results are expressed as a percent change from baseline. Negative percent changes represent a decrease from baseline, whereas positive percentages represent an increase. The data suggest a modest reduction of fibrinogen concentration at 2 hours that largely recovered by 24 hours. The mean percent decrease in 2-hour fibrinogen level increased with increasing dose and peaked at 16±17% in the 0.4-mg/kg dose. Severe hypofibrinogenemia defined by a fibrinogen <100 mg/dL did not develop. TNK blood levels at 1 hour after treatment ranged from a mean of 359±146 ng/mL with 0.1 mg/kg to 1647±732 ng/mL with 0.5 mg/kg. The 2 patients with symptomatic intracranial hemorrhage in tier 4 had 1-hour blood levels of 2000 and 2010 ng/mL, respectively.
Table 5 summarizes early major neurological improvement measured by the NIH Stroke Scale at 24 hours, as well as the 3-month clinical outcomes as measured by the modified Rankin Scale. No patients were lost to follow-up. In terms of early activity, there did not appear to be a dose response with major neurological improvement within 24 hours of treatment. The best results were observed with the 0.1-mg/kg dose (36%). In general, the 3-month outcomes followed the same trends as the early neurological improvement data, ie, that the best outcomes were observed with the 0.1-mg/kg dose, although none of the distributions was statistically significantly different across the 5-fold dose escalation. The Glasgow Outcome Scale, Barthel Index, and NIH Stroke Scale scores at 3 months showed similar trends (Appendix 1, available online only at http://www.strokeaha.org).
This pilot dose-escalation safety study of TNK in patients with acute ischemic stroke demonstrated safety and tolerability of TNK at several doses. No symptomatic intracranial hemorrhages were observed among any of the 75 patients treated with 0.1 mg/kg, 0.2 mg/kg, or 0.4 mg/kg TNK, a 4-fold range of doses begun with a dose calculated to be bio-equivalent to the approved dose of rtPA for stroke. Whereas the upper bound of the 95% confidence interval surrounding 0 of 25 still includes 11%, the observed experience provides encouragement that TNK treatment of acute ischemic stroke at these doses may be safer than rtPA.
Enrollment in the study was stopped after 2 of 13 (15%) patients treated with 0.5 mg/kg sustained symptomatic intracranial hemorrhages within 36 hours of treatment. The decision to stop the study was not based solely on statistical grounds, although 2 of 12 hemorrhages would have crossed 1 of the prespecified statistical boundaries used as a guideline to potentially halt the study. There was concern with the apparent trend toward increasing intracranial hemorrhage (all intracranial hemorrhage) with increasing dose, and it was noted that increasing doses were not clearly associated with increasing clinical benefit, measured either by major neurological improvement at 24 hours or by 3-month outcome. Moreover, further uncontrolled observations at the 0.5-mg/kg dose up to a total of 25 patients would have little likelihood of providing evidence of a safety advantage over rtPA and would potentially put more patients at risk if the true hemorrhage rate was close to the observed rate.
The incidence of asymptomatic intracranial hemorrhage observed in this study was higher than that reported in the NINDS rtPA Stroke Trial.3 Two factors may help explain the apparent discrepancy. First, the CT scans checking for asymptomatic bleeding in the TNK study were obtained at 48 hours instead of 24 hours, as in the NINDS study. Previous studies of hemorrhagic conversion in infarction without thrombolysis have demonstrated that the incidence of CT-detectable hemorrhagic change increases over the first 7 to 10 days after the infarct, and may approach 40% if patients are followed-up long enough.17 Second, this study included so-called hyperdense cerebral infarction (ie, CT findings of a region of intermediate density between gray matter and blood within an area of infarction), as defined by the NINDS Study Group,18 with frank hemorrhagic changes. The rates from this study are thus more comparable to ECASS19 than to NINDS.
In terms of clinical benefit, this was an uncontrolled pilot safety study, so inferences regarding potential benefits of treatment compared with rtPA are necessarily limited. Table 5 summarizes reference results from the NINDS rtPA Stroke Trial, parts 1 and 2 combined, in patients treated from 91 to 180 minutes from onset. The results observed with TNK are comparable to those reported in the rtPA group and are generally better than those in the placebo group. These comparisons should be made cautiously, however, because there may be differences in the baseline characteristics of the patients in the 2 studies that may confound any comparisons. Nevertheless, the results from the TNK experience suggest, but do not prove, that doses from 0.1 mg/kg to 0.4 mg/kg may be equally or more effective than rtPA (particularly in reducing combined severe disability and death) and may be safer. A safer alternative to rtPA would be a welcome addition to the clinical armamentarium and would represent a significant medical advance, even within the 3-hour time window. Further studies comparing TNK to rtPA in patients with acute stroke are planned.
The following persons and institutions participated in the Pilot Study of TNK in Acute Stroke (TNK-S):
Clinical Centers–University of California, San Diego
P. Lyden, K. Rapp, K. Norris, J. Werner, T. Hemmen, C. Jackson, N. Kelly, T. McClean, B. Meyer, L. Al-Khoury, Y. Cheng.
Affiliated sites: Grossmont Hospital, S. Braheny, E.-K. Gao, P. Delaney, E. Perkins; Scripps Memorial Hospital, La Jolla, J. Schim, T. Chippendale, E. Diamond, B. Frishberg, M. Lobatz, F. Martin, J. Nelson, A. Pagdan, M. Sadoff, D. Silver; Scripps Mercy Hospital, J. Licht, J. Grisolia; Sharp Memorial Hospital, D. Stein, M. Ellington; Tri-City Medical Center–Oceanside, G. Sahagian, G. Wochaski;
University of Virginia: E. Haley, G. Kongable, M. Davis, K. Johnston, B. Worrall, N. Solenski, B. Nathan, D. Kindler, J. Provencio, G. Lopez, D. Brown, T. Smith, S. Bassin, C. Winter, M. TeKrony, M. Goldman, A. Wittmann, R. Cavaliere.
Clinical Coordinating Center–University of Virginia: E. Haley (Principal Investigator), K. Johnston, J. van Wingerden, C. Phillips; D. Wagner.
Data Management Center–INC Research: W. Alves, R. Bichard, R. Holladay, L. Truskowski; J. Shultz.
NINDS Data and Safety Monitoring Board: M. Walker (Chair), J. Hallenbeck, D. Stump.
NINDS Project Officer: B. Radziszewska
Supported by a grant (NS37666) from the National Institute for Neurological Disorders and Stroke–National Institutes of Health. Genentech, Inc supplied tenecteplase and performed the tenecteplase blood level assays for this study. This work was presented, in part, at the 28th International Stroke Conference, February 13 to 15, 2003, Phoenix, Arizona.
↵* See Appendix 2 online at http://www.strokeaha.org for list of participating investigators.
- Received August 11, 2004.
- Revision received October 25, 2004.
- Accepted November 10, 2004.
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