The pharmacokinetics of recombinant double-chain t-PA (duteplase): effects of bolus injection, infusions, and administration by weight in patients with myocardial infarction

Endogenous tissue plasminogen activator enhances fibrinolysis and limits thrombus formation in a clinical model of thrombosis

OBJECTIVE

Using a clinical model of deep arterial injury, we assessed the ability of exogenous and endogenous tissue plasminogen activator (t-PA) to limit acute in situ thrombus formation.

APPROACH AND RESULTS

Ex vivo thrombus formation was assessed in the Badimon chamber at low and high shear rates in 2 double-blind randomized cross-over studies of 20 healthy volunteers during extracorporeal administration of recombinant t-PA (0, 40, 200, and 1000 ng/mL) or during endogenous t-PA release stimulated by intra-arterial bradykinin infusion in the presence or absence of oral enalapril. Recombinant t-PA caused a dose-dependent reduction in thrombus area under low and high shear conditions (P<0.001 for all). Intra-arterial bradykinin increased plasma t-PA concentrations in the chamber effluent (P<0.01 for all versus saline) that was quadrupled in the presence of enalapril (P<0.0001 versus placebo). These increases were accompanied by an increase in plasma D-dimer concentration (P<0.005 for all versus saline) and, in the presence of enalapril, a reduction in thrombus area in the low shear (16±5; P=0.03) and a trend toward a reduction in the high shear chamber (13±7%; P=0.07).

CONCLUSIONS

Using a well-characterized clinical model of coronary arterial injury, we demonstrate that endogenous t-PA released from the vascular endothelium enhances fibrinolysis and limits in situ thrombus propagation. These data support a crucial role for the endogenous fibrinolytic system in vivo and suggest that continued exploration and manipulation of its therapeutic potential are warranted.

Alteplase at 0.6 mg/kg for Acute Ischemic Stroke Within 3 Hours of Onset

BACKGROUND AND PURPOSE

Based on previous studies comparing different recombinant tissue plasminogen activator (rt-PA) doses, we performed a clinical trial with 0.6 mg/kg, which is lower than the internationally approved dosage of 0.9 mg/kg, aiming to assess the efficacy and safety of alteplase in acute ischemic stroke for the Japanese.

METHODS

Our prospective, multicenter, single-arm, open-label trial was designed with a target sample size of 100 patients. The primary end points were the proportion of patients with a modified Rankin Scale (mRS) score of 0 to 1 at 3 months and the incidence of symptomatic intracranial hemorrhage (sICH) within 36 hours. Thresholds for these end points were determined by calculating 90% CIs of weighted averages derived from published reports. The protocol was defined according to the National Institute of Neurological Disorders and Stroke (NINDS) rt-PA stroke study with slight modifications.

RESULTS

Among the 103 patients enrolled, 38 had an mRS of 0 to 1 at 3 months; this proportion (36.9%) exceeded the predetermined threshold of 33.9%. sICH within 36 hours occurred in 6 patients; this incidence (5.8%) was lower than the threshold of 9.6%.

CONCLUSIONS

In patients receiving 0.6 mg/kg alteplase, the outcome and the incidence of sICH were comparable to published data for 0.9 mg/kg. These findings indicate that alteplase, when administered at 0.6 mg/kg to Japanese patients, might offer a clinical efficacy and safety that are compatible with data reported in North America and the European Union for a 0.9 mg/kg dose.

Comparison of pharmacokinetics of lanoteplase and alteplase during acute myocardial infarction

OBJECTIVE

Lanoteplase is a rationally designed variant of tissue plasminogen activator. The aim of this study was to examine the pharmacokinetics and functional activity of a single intravenous bolus dose of lanoteplase with those of a bolus plus two-step infusion of alteplase.

DESIGN

Seven-centre substudy of the InTIME-I angiographic trial in patients presenting within 6 hours of onset of suspected acute myocardial infarction.

PATIENTS AND PARTICIPANTS

A total of 31 patients (28 males, 3 females) enrolled in this substudy [mean age 59 (range 26 to 76) years].

METHODS

Twenty-three patients randomised to lanoteplase received single bolus doses of 15 kU/kg (n = 5), 30 kU/kg (n = 3), 60 kU/kg (n = 9), or 120 kU/kg (n = 6). Eight patients received alteplase <or=100mg as a bolus followed by a two-stage 90 min infusion. Blood samples were analysed for antigen concentration and plasminogen activator (PA) activity.

RESULTS

The distribution plasma half-life of approximately 35 min for lanoteplase was at least five times longer than that of alteplase. Lanoteplase plasma clearance averaged 3 L/h (50 ml/min), whereas the mean plasma clearance of approximately 24 L/h (400 ml/min) for alteplase approaches hepatic blood flow following acute myocardial infarction. PA activity after lanoteplase 120 kU/kg remained for 6 hours, compared with less than 4 hours after alteplase 100mg.

CONCLUSIONS

The longer antigen and activity half-lives, slower clearance and less complicated administration of lanoteplase compared with alteplase suggest that it may offer advantages for use as a single intravenous bolus to achieve reperfusion after myocardial infarction.

Marked bradykinin-induced tissue plasminogen activator release in patients with heart failure maintained on long-term angiotensin-converting enzyme inhibitor therapy

OBJECTIVES

The aim of the present study was to assess the contribution of angiotensin-converting enzyme (ACE) inhibitor therapy to bradykinin-induced tissue-type plasminogen activator (t-PA) release in patients with heart failure (HF) secondary to ischemic heart disease.

BACKGROUND

Bradykinin is a potent endothelial cell stimulant that causes vasodilatation and t-PA release. In large-scale clinical trials, ACE inhibitor therapy prevents ischemic events.

METHODS

Nine patients with symptomatic HF were evaluated on two occasions: during and following seven-day withdrawal of long-term ACE inhibitor therapy. Forearm blood flow was measured using bilateral venous occlusion plethysmography. Intrabrachial bradykinin (30 to 300 pmol/min), substance P (2 to 8 pmol/min), and sodium nitroprusside (1 to 4 pmol/min) were infused, and venous blood samples were withdrawn from both forearms for estimation of fibrinolytic variables.

RESULTS

On both study days, bradykinin and substance P caused dose-dependent vasodilatation and release of t-PA from the infused forearm (p < 0.05 by analysis of variance [ANOVA]). Long-term ACE inhibitor therapy caused an increase in forearm vasodilatation (p < 0.05 by ANOVA) and t-PA release (p < 0.001 by ANOVA) during bradykinin, but not substance P, infusion. Maximal local plasma t-PA activity concentrations approached 100 IU/ml, and maximal forearm protein release was approximately 4.5 microg/min.

CONCLUSIONS

Long-term ACE inhibitor therapy augments bradykinin-induced peripheral vasodilatation and local t-PA release in patients with HF due to ischemic heart disease. Local plasma t-PA activity concentrations approached those seen during systemic thrombolytic therapy for acute myocardial infarction. This may contribute to the primary mechanism of the anti-ischemic effects associated with long-term ACE inhibitor therapy.

Effects of liver blood flow on the pharmacokinetics of tissue-type plasminogen activator (alteplase) during thrombolysis in patients with acute myocardial infarction

BACKGROUND

The removal of recombinant tissue-type plasminogen activator (rt-PA; alteplase) by the liver is so rapid that liver blood flow becomes rate determining for its clearance. In patients with myocardial infarction changes in liver blood flow may result from impaired cardiac performance or drug treatment.

OBJECTIVE

To estimate the effect of variations in liver blood flow on t-PA plasma concentrations during thrombolytic therapy.

METHODS

Fifteen patients with acute myocardial infarction were investigated in an open single-center study at the coronary care unit of University Hospital Leiden. Patients received thrombolytic treatment with 100 mg rt-PA over 3 hours. Liver blood flow was estimated by indocyanine green clearance and by Doppler echocardiography. Concentrations of t-PA antigen, t-PA activity, indocyanine green, alpha 2-antiplasmin, fibrinogen, and fibrin and fibrinogen degradation products were measured.

RESULTS

Indocyanine green clearance and clearance of both t-PA antigen (r = 0.78; p < 0:01) and t-PA activity (r = 0.54; p < 0.05) were significantly related. Significant associations between t-PA antigen and fibrin and fibrinogen degradation products and between t-PA antigen and alpha 2-antiplasmin were also found.

CONCLUSIONS

The liver blood flow of patients with myocardial infarction is inversely correlated with plasma concentrations of t-PA. In patients with severely impaired liver blood flow and heart failure, high t-PA plasma concentrations may occur if standard doses are given. This finding could contribute to optimization of the dosage of t-PA in certain patient groups.

Clearance of tissue plasminogen activator (TPA) and TPA/plasminogen activator inhibitor type 1 (PAI-1) complex: relationship to elevated TPA antigen in patients with high PAI-1 activity levels

BACKGROUND

To evaluate the effect of plasminogen activator inhibitor type 1 (PAI-1) levels on the clearance of total tissue plasminogen activator (TPA) antigen, we studied the clearance of active TPA and TPA/PAI-1 complex in subjects with low (181+/-109 pmol/L; n=7) and high (1166+/-322 pmol/L; n=4) baseline active PAI-1.

METHODS AND RESULTS

A 5-microg/kg bolus of TPA was infused over a 15-second period followed by measurement of TPA activity, TPA antigen, TPA/PAI-1, TPA/C1 inhibitor, PAI-1 activity, and PAI-1 antigen over a 4-hour period. alpha-Phase clearance of total TPA antigen was faster in subjects with low PAI-1 (t(1/2) of 3.5+/-0.7 minutes) versus high PAI-1 (t(1/2) of 5.3+/-0.9 minutes) (P=.006). Clearance of all factors was best fit by a two-compartment pharmacokinetic model based on a computer-simulated human circulatory system. The average hepatic clearance fraction in the two-compartment model was greater for active TPA (89+/-10%, t(1/2) of 2.4+/-0.3 minutes) than for TPA/PAI-1 complex (48+/-17%, t(1/2) of 5.0+/-1.8 minutes) (P=.0006).

CONCLUSIONS

Plasma clearance of active TPA was faster than clearance of TPA/PAI-1 complex. High levels of active PAI-1 converted more TPA into TPA/PAI-1 complex, effectively slowing the clearance of total TPA antigen and explaining in part why high levels of PAI-1 activity are associated with increases in total TPA antigen.

Effects of increased liver blood flow on the kinetics and dynamics of recombinant tissue-type plasminogen activator

OBJECTIVE

To investigate the influence of increased liver blood flow on the pharmacokinetics and pharmacodynamics of recombinant tissue-type plasminogen activator (rt-PA) and to study the changes in endogenous urokinase-type plasminogen activator (u-PA).

METHODS

This open, randomized, crossover trial was carried out in a clinical research unit. Eight healthy, nonsmoking volunteers received linear infusions of 24 mg rt-PA and 92 mg indocyanine green over 160 minutes. Sixty minutes after the infusions were started, the subjects consumed a standardized meal to increase liver blood flow on one occasion and abstained from taking food on the other occasion. Plasma concentrations of indocyanine green, tissue-type plasminogen activator (t-PA) antigen, t-PA activity, total u-PA antigen, plasmin-activatable single-chain u-PA (scu-PA), active two-chain u-PA (tcu-PA), fibrinogen, total fibrin, and fibrinogen/fibrin degradation products (TDP), and alpha 2-antiplasmin were measured.

RESULTS

After the consumption of the meal, the area under the curve (AUC) was 35% (95% confidence interval [CI]: 25%, 43%) lower for indocyanine green, 15% (CI: 6%, 24%) lower for t-PA antigen, and 11% (CI: 2%, 19%) lower for t-PA activity compared to the AUC after subjects abstained from food. No changes were observed in fibrinogen, TDP, or alpha 2-antiplasmin concentrations that were attributable to the intake of food. The infusion of rt-PA caused a fivefold increase in the concentration of active tcu-PA and a concomitant decrease in scu-PA concentrations by more than 50%.

CONCLUSIONS

Increased liver blood flow results in an increase in t-PA clearance. The conversion of the inactive zymogen scu-PA to the active tcu-PA is increased by an infusion of rt-PA, but total u-PA antigen concentrations remain unchanged.

Cardiovascular drugs

Since the category of cardiovascular drugs comprises a considerable number of pharmacotherapeutic groups, an overview of future developments must necessarily be limited to those areas in which innovations are most likely to occur. Further extension of our knowledge of thrombolytic therapy may eventually lead to new choices of primary drugs. In the area of antiarrhythmic therapy, the clinical use of a number of drugs has been hampered by the pro-arrhythmogenic actions of these agents. The development of new class III anti-arrhythmics will continue, probably giving rise to new therapeutic options. In the vascular area a new group of drugs, the renin inhibitors, is likely to emerge for the treatment of hypertension. Moreover, exciting discoveries in vascular pharmacology should eventually translate into new pharmacotherapeutic approaches. Finally, the large-scale availability of blood fractions (coagulation factors) prepared by recombinant technology may help solve current shortages of products derived from donated blood.