Differences in clot lysis among patients demonstrated in vitro with three thrombolytic agents (tissue-type plasminogen activator, streptokinase and urokinase)

Factors influencing the efficacy of recombinant tissue plasminogen activator: Implications for ischemic stroke treatment

Intravenous thrombolysis with a recombinant tissue plasminogen activator (rt-PA) is the first-line treatment of acute ischemic stroke. However, successful recanalization is relatively low and the underlying processes are not completely understood. The goal was to provide insights into clinically important factors potentially limiting rt-PA efficacy such as clot size, rt-PA concentration, clot age and also rt-PA in combination with heparin anticoagulant. We established a static in vitro thrombolytic model based on red blood cell (RBC) dominant clots prepared using spontaneous clotting from the blood of healthy donors. Thrombolysis was determined by clot mass loss and by RBC release. The rt-PA became increasingly less efficient for clots larger than 50 μl at a clinically relevant concentration of 1.3 mg/l. A tenfold decrease or increase in concentration induced only a 2-fold decrease or increase in clot degradation. Clot age did not affect rt-PA-induced thrombolysis but 2-hours-old clots were degraded more readily due to higher activity of spontaneous thrombolysis, as compared to 5-hours-old clots. Finally, heparin (50 and 100 IU/ml) did not influence the rt-PA-induced thrombolysis. Our study provided in vitro evidence for a clot size threshold: clots larger than 50 μl are hard to degrade by rt-PA. Increasing rt-PA concentration provided limited thrombolytic efficacy improvement, whereas heparin addition had no effect. However, the higher susceptibility of younger clots to thrombolysis may prompt a shortened time from the onset of stroke to rt-PA treatment.

Comparative fibrinolytic activity of front-loaded alteplase and the single-bolus mutants tenecteplase and lanoteplase during treatment of acute myocardial infarction

BACKGROUND

Quantification of fibrinolytic activity (FAct) in clinical practice has been abandoned because of the complexity of existing assays. The relationship between thrombolytic drug concentration and FAct is complex. FAct profiles of currently used thrombolytic drugs were not characterized.

METHODS

By use of a system that quantifies FAct by shortening of clot lysis onset time (LOT), we measured LOT in vitro with incremented concentrations of alteplase (t-PA) and tenecteplase (TNK-tPA) and ex vivo in patients with acute myocardial infarction who were receiving front-loaded t-PA (n = 31), 30 to 40 mg TNK-tPA (n = 19), and 120 kU/kg lanoteplase ([n-PA] n = 23).

RESULTS

In vitro, FAct depended on drug concentration by means of a double exponential model revealing 2 distinct activity zones (weak/strong). Ex vivo, no FAct was detected before agent administration (LOT > 1200 seconds). Ten minutes after a bolus was given, FAct was sharply increased in all patients, but it increased more with TNK-tPA than with t-PA or n-PA (mean LOT of 109, 125, and 130 seconds, respectively, P <.05). At 90 minutes, accelerated infusion of t-PA resulted in FAct that remained stronger than that observed for TNK-tPA (P <.0001) or n-PA (P =.011). At 180-minutes, significant FAct (LOT <600 seconds) was only observed in patients who received n-PA.

CONCLUSION

This study provides the first direct comparison of FAct between t-PA, TNK-tPA, and n-PA by use of the LOT test, the results of which are reliably related to drug concentration. The ideal FAct profile would combine an immediate strong FAct of relatively short duration, as seen with TNK-tPA, that may contribute to its better efficacy/safety profile in the Assessment of Safety and Efficacy of a New Thrombolytic Agent-2 (ASSENT-2) trial. Prolonged FAct after n-PA may contribute to increased hemorrhagic complications, as seen in the Intravenous n-PA for Treatment of Infarcting Myocardium Early-2 (InTIME-2) trial. Thus, characterizing FAct profiles might provide insights in developing more efficient thrombolytic regimens.

Pharmacokinetics of tissue plasminogen activator in an isolated extracorporeal circuit

PURPOSE

The aim of this study was to investigate the pharmacokinetics of tissue plasminogen activator (tPA) under the conditions of an isolated extracorporeal circuit.

METHODS

Plasma levels of tPA were measured in the perfusion solution and in central venous blood before, during, and after the perfusion in seven patients undergoing regional hyperthermic fibrinolytic perfusion with tPA in addition to surgical thrombectomy for extended deep venous thrombosis.

RESULTS

After 15 minutes of fibrinolytic perfusion, the level of tPA in the perfusion solution was 10,427 +/- 4432 ng/mL, and after 30 minutes the maximum level of 19,726 +/- 5630 ng/mL was reached. After 60 minutes when the perfusion was discontinued, tPA concentrations dropped to 15,931 +/- 4818 ng/mL. In central venous blood, tPA levels increased to a maximum of 230.7 +/- 89.6 ng/mL after 60 minutes of perfusion, which represented 1.4% of the concentration measured in the perfusion solution at the same time. With disconnection of the extracorporeal circuit, the tPA levels in central venous blood decreased rapidly and reached a level of 24.1 +/- 8.7 ng/mL after 120 minutes.

CONCLUSION

The use of regional hyperthermic fibrinolytic perfusion in the treatment of extended deep venous thrombosis makes it possible to achieve extremely high concentrations of tPA in the perfusion solution. At the same time, the entry of the fibrinolytic agent into the systemic circulation is minimized.

Influence of time to treatment on early infarct-related artery patency after different thrombolytic regimens. ALKK-Study Group

BACKGROUND

In an in vitro model, recombinant tissue-type plasminogen activator was significantly more effective than streptokinase in dissolving 24-hour-old human blood clots. Therefore there might be a difference in the effect of time to treatment on the efficacy of these fibrinolytics with different fibrin specificity in patients with acute myocardial infarction.

METHODS AND RESULTS

The effect of the interval between symptom onset and initiation of therapy on the efficacy of 6 different thrombolytic regimens was studied in a retrospective analysis of 6 angiographic trials with similar design. The patency of the infarct-related artery was assessed by angiography 90 minutes after initiation of thrombolysis in patients who were seen within 6 hours after symptom onset. Patency rates of patients with an interval of </=3 hours and >3 hours between symptom onset and start of therapy were compared. There was no difference for Thrombolysis in Myocardial Infarction (TIMI) grade 3 perfusion after front-loaded alteplase (72.5% vs 76. 3%) and reteplase (63.6% vs 63.2% ) between the 2 groups. In contrast, in patients treated with streptokinase (36.8% vs 27.6%, P =.09), anisoylated plasminogen streptokinase activator complex (59. 5% vs 34.8%, P =.004), and urokinase (62.3% vs 41.7%, P =.03), TIMI 3 patency decreased with the increasing interval between symptom onset and initiation of therapy.

CONCLUSIONS

We conclude from our data that the thrombolytic efficacy of recombinant tissue-type plasminogen activator and reteplase does not decrease with the increasing interval between symptom onset and initiation of therapy. In contrast, after anisoylated plasminogen streptokinase activator complex, streptokinase, and urokinase treatment, a decrease in patency, especially TIMI-3 patency in patients treated after >3 hours after symptom onset, was observed. These results may influence the choice of the thrombolytic agent in patients who are seen >3 hours after symptom onset.

Point-of-care fibrinolytic tests: the other side of blood coagulation

Point-of-care (POC) coagulation tests with paramagnetic iron oxide particles have provided alternatives to testing previously done only in the laboratory. With this technology, POC fibrinolytic tests have followed quietly the trail blazed by POC clotting tests and have found specific applications. These include rapid verification of in vivo thrombolytic drug action by in vitro testing with subsequent quantitative drug monitoring of the systemic lytic state, and also the determination of in vitro thrombolytic drug response before the drug is actually administered, to individualize therapy by selection of the most appropriate drug. Other applications include POC coagulation factor assays associated with fibrinolysis, and most recently the POC screening of patients with fibrinolytic defects. In this latter application, plasma from cardiac catheterization (n = 19) and venous thrombosis (n = 47) patient groups were tested. Controls consisted of two independent donor pools (n = 10, n = 21) as negatives and two plasma samples with known genetic defects in the fibrinogen molecule (Aα554 Arg → Cys) as positives.

Impairment of fibrinolysis by streptokinase, urokinase and recombinant tissue-type plasminogen activator in the presence of radiographic contrast agents

OBJECTIVES

The purpose of this study was to determine whether an adverse interaction exists between radiographic contrast agents and thrombolytic drugs.

BACKGROUND

Coronary thrombosis may occur in the setting of unstable angina and after coronary angioplasty. However, the use of thrombolytic drugs in the setting of unstable angina has not been beneficial and, in one large trial of angioplasty in patients with unstable angina, was associated with an increased incidence of ischemic complications and abrupt closure. The reasons for these results are not clear. Coronary arteriography was performed in many of these trials, and it is known that fibrin structure and assembly are altered by radiographic contrast agents.

METHODS

Blood samples were obtained from patients before (n = 25) and after (n = 20) angiography using iohexol. Blood samples obtained before angiography were tested for response to streptokinase (10 and 100 IU/ml), urokinase (100, 200 and 500 IU/ml) and recombinant tissue-type plasminogen activator (rt-PA) (100 and 1,000 IU/ml) and the results measured. Iohexol, diatrizoate or ioxaglate (4% by volume) was added to separate aliquots of the baseline sample, and the test was repeated. Blood samples obtained after angiography were tested in a similar manner.

RESULTS

The onset of lysis at baseline by rt-PA at 1,000 IU/ml occurred at 72 +/- 8.2 s (mean +/- SD) and was markedly delayed in the presence of diatrizoate (527 +/- 181.7 s, p < 0.001) or iohexol (460 +/- 197.0 s, p < 0.001) but not ioxaglate. At 100 IU/ml, there was no lysis detected with rt-PA after the addition of any contrast agent. The addition of a contrast agent caused similar delays in the onset of lysis by urokinase and streptokinase; similar to rt-PA, the effect was smaller at higher concentrations of drug. In vivo blood samples obtained from the patient after angiography showed delays in the onset of lysis by rt-PA and urokinase but not streptokinase.

CONCLUSIONS

These data demonstrate that radiographic contrast agents impede fibrinolysis. This previously undescribed interaction was demonstrated using an in vitro test system, but these findings may have clinical relevance when thrombolytic drugs are used at the time of angiography.