Population pharmacokinetics of sibrotuzumab, a novel therapeutic monoclonal antibody, in cancer patients.

Population pharmacokinetics of sibrotuzumab, a humanized monoclonal antibody directed against fibroblast activation protein, were determined after multiple intravenous infusions of dosages ranging from 5 mg/m(2) to an absolute dose of 100 mg, in patients with advanced or metastatic carcinoma. In total, 1844 serum concentrations from 60 patients in three Phase I and II clinical studies were analyzed. The structural model incorporated two disposition compartments and two parallel elimination pathways from the central compartment, one linear and one nonlinear. Finally estimated pharmacokinetic parameters (%RSE) were: linear clearance CLL 22.1 ml/h (9.6), central distribution volume V1 4.13l (3.7), peripheral volume V2 3.19l (8.8), inter-compartmental clearance Q 37.6 ml/h (9.6); for the nonlinear clearance Vmax was 0.0338 mg/h (25) and Km 0.219 microg/ml (57). At serum concentrations between approximately 20 ng/ml and 7 microg/ml, the effect of the nonlinear clearance on pharmacokinetics was marked. Only at >7 microg/ml did CLL dominate overall clearance. Interindividual variability was 57% for CLL, 20% for V1 and V2, and 29% for Vmax and was larger than the inter-occasional variability of 13%. Of the many investigated patient covariates, only body weight was found to contribute to the population model. It significantly affected CLL, V1, V2 and Vmax resulting in marked differences in the model-predicted concentration-time profiles after multiple dosing in patients with low and high body weights. In conclusion, a robust population pharmacokinetic model was developed and evaluated for sibrotuzumab, which identified a possible need to consider body weight when designing dosage regimen for future clinical cancer trials.

Stromal antigen targeting by a humanised monoclonal antibody: an early phase II trial of sibrotuzumab in patients with metastatic colorectal cancer.

BACKGROUND: A novel immunological approach to colon cancer therapy is the antibody targeting of the fibroblast activation protein (FAP), which is highly expressed by stroma cells of this tumour. Unconjugated sibrotuzumab (BIBH 1), which is a humanised version of the murine anti-FAP mAb F19, was investigated for its anti-tumour activity, safety and pharmacokinetics. PATIENTS AND METHODS: Patients with metastatic colorectal cancer received weekly intravenous infusions of unconjugated sibrotuzumab at a dose of 100 mg over 12 scheduled weeks. The study was implemented as an open-label, uncontrolled, multicentre trial. RESULTS: 25 patients were enrolled. Patients had one or more measurable lesions, predominantly liver lesions, at baseline. At least 8 repeated weekly infusions of sibrotuzumab in 17 evaluable patients did not result in complete or partial remission. Rather, ongoing tumour progression was noted in all patients except for 2 patients with stable disease. However, progressive disease was also observed post-study in these 2 patients who received 1 and 6 additional infusions, respectively, of sibrotuzumab. Sibrotuzumab exhibited 2-compartment pharmacokinetics with a dominant terminal phase and t1/2 beta = 5.3 +/- 2.3 days. Adverse drug reactions (rigors/chills, nausea, flushing and one incidence of bronchospasm) were observed in 5 patients. Of the 24 patients given 2 or more infusions of sibrotuzumab, antibodies against sibrotuzumab were found in 3 patients (12.5%) after 4-12 infusions. CONCLUSIONS: Sibrotuzumab was well tolerated and safe. The minimal requirement for the continuation of this exploratory trial, of at least one complete or partial remission, or equivalently, of 4 patients with stable disease, was not met.

Population pharmacokinetics of antifibroblast activation protein monoclonal antibody F19 in cancer patients.

AIMS: The population pharmacokinetics of 131I-mAbF19, a radiolabelled murine monoclonal antibody against fibroblast activation protein and a potential antitumour stroma agent, were investigated during two phase I studies in cancer patients. METHODS: 131I-mAbF19 serum concentration-time data were obtained in 16 patients from two studies involving imaging and dosimetry in colorectal carcinoma and soft tissue sarcoma. Doses of 0.2, 1 and 2 mg antibody were administered as 60 min intravenous infusions. The data were analysed by nonlinear mixed effect modelling. RESULTS: The data were described by a two-compartment model. Population mean values were 109 ml h(-1) for total serum clearance, 3.1 l for the volume of distribution of the central compartment, and 4.9 l for the volume of distribution at steady state. Mean terminal half-life was 38 h. Intersubject variability was high, but no patient covariates could be identified that further explained this variability. In particular, there was no influence of tumour type or mAbF19 dose. CONCLUSIONS: The pharmacokinetics of antistromal mAbF19 were well defined in these two studies with different solid tumour types, and were comparable with those of other murine monoclonal antibodies that do not bind to normal tissue antigens or blood cells.

Pharmacokinetics and pharmacodynamics of tenecteplase: results from a phase II study in patients with acute myocardial infarction.

Tenecteplase is a site-specific engineered tissue plasminogen activator (t-PA) variant that can be administered as a single intravenous bolus injection because of its slower plasma clearance. The objective of this study was to investigate the dose-ranging pharmacokinetics and pharmacodynamics of intravenous bolus tenecteplase compared with intravenous alteplase recombinant t-PA in patients with acute myocardial infarction. A total of 103 patients received intravenous bolus doses of 30, 40, or 50 mg tenecteplase, and 56 patients received 100 mg rt-PA as the accelerated 90-minute infusion regimen in this randomized, open-label study. Tenecteplase and r-tPA plasma concentrations were measured for 6 hours. Tenecteplase exhibited biphasic elimination from the plasma with a mean initial half-life of 22 minutes and a mean terminal half-life of 115 minutes. The mean plasma clearance was 105 mL/min and did not depend on tenecteplase dose over the dose range studied. In comparison, rt-PA has a fourfold faster plasma clearance. Pharmacokinetic-pharmacodynamic evaluation showed that a dose of approximately 0.5 mg/kg results in a plasma AUC value that provides a TIMI 3 flow at 90 minutes that is comparable to that reported with accelerated r-tPA. In conclusion, tenecteplase has a fourfold slower plasma clearance compared with rt-PA, allowing dosing as an i.v. bolus injection. Weight-adjusted dosing of tenecteplase may optimize the therapeutic regimen of tenecteplase.

Nonlinear pharmacokinetics of tissue-type plasminogen activator in three animal species: a comparison of mathematical models.

A recent study presented plasma concentrations of tissue-type plasminogen activator in three different animal species and at several different dose levels. A three-compartment mammillary model with capacity-limited elimination (of Michaelis-Menten form) was postulated to describe the data. In the present study, several alternative model structures are examined with the view of determining whether better fits can be obtained, whether linear models are significantly worse than nonlinear models, and whether all three compartments are really necessary.

Sixty-minute alteplase protocol: a new accelerated recombinant tissue-type plasminogen activator regimen for thrombolysis in acute myocardial infarction.

OBJECTIVES: Our aim was to design and evaluate a new and easily administered recombinant tissue-type plasminogen activator (rt-PA) regimen for thrombolysis in acute myocardial infarction (AMI) based on established pharmacokinetic data that improve the reperfusion success rate. BACKGROUND: Rapid restoration of Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow is a primary predictor of mortality after thrombolysis in AMI. However, TIMI grade 3 patency rates 90 min into thrombolysis of only 50% to 60% indicate an obvious need for improved thrombolytic regimens. METHODS: Pharmacokinetic simulations were performed to design a new rt-PA regimen. We aimed for a plateau tissue-type plasminogen activator (t-PA) plasma level similar to that of the first plateau of the Neuhaus regimen. These aims were achieved with a 20-mg rt-PA intravenous (i.v.) bolus followed by an 80-mg i.v. infusion over 60 min (regimen A). This regimen was tested in a consecutive comparative trial in 80 patients versus 2.25 10(6) IU of streptokinase/60 min (B), and 70 mg (C) or 100 mg (D) of rt-PA over 90 min. Subsequently, a confirmation trial of regimen A in 254 consecutive patients was performed with angiographic assessment by independent investigators of patency at 90 min. RESULTS: The comparative phase of the trial yielded, respectively, TIMI grade 3 and total patency (TIMI grades 2 and 3) of 80% and 85% (regimen A), 35% and 50% (B), 50% and 55% (C) and 60% and 70% (D). In the confirmation phase of the trial, regimen A yielded 81.1% TIMI grade 3 and 87.0% total patency. At follow-up angiography 7 (4.1%) of 169 vessels had reoccluded. In-hospital mortality rate was 1.2%. Nadir levels of fibrinogen, plasminogen and alpha2-antiplasmin were 3.6 +/- 0.8 mg/ml, 60 +/- 21% and 42 +/- 16%, respectively (mean +/- SD). Fifty-seven patients (22.4%) suffered from bleeding; 3.5% needed blood transfusions. CONCLUSIONS: The 60-min alteplase thrombolysis in AMI protocol achieved a TIMI grade 3 patency rate of 81.1% at 90 min with no indication of an increased bleeding hazard; it was associated with a 1.2% overall mortality rate. These results are substantially better than those reported from all currently utilized regimens. Head to head comparison with established thrombolytic regimens in a large-scale randomized trial is warranted.

Pharmacokinetic-pharmacodynamic and metabolite modeling with TopFit.

Two examples illustrating the ease of use and powerful data fitting and simulation techniques provided by the validated program TopFit 2.0 for the PC are presented. In the first, kinetics of parent compound and metabolite for (+) and (-) enantiomers of a racemic compound X were determined during a Phase III clinical study. Four data sets were fitted simultaneously for each patient. The model could be defined by the user without programming differential equations. The fit results indicated enantiomer specific kinetics for the metabolite but not for parent compound. In the second example, a model with nonlinear elimination and an Emax-effect function was used to simultaneously fit data from six doses of compound Y in a Phase I study. The fitted parameters predicted the feasibility of a twice-daily dose regimen despite a very short plasma half-life of the compound. In conclusion, TopFit provides rapid and cost-effective support in analysis and design of clinical trials.

TopFit: a PC-based pharmacokinetic/pharmacodynamic data analysis program.

The program TopFit was developed and validated within the European pharmaceutical industry. It provides both pharmacokinetic data analysis support for international regulatory submissions of new drugs, and sophisticated techniques for model-based kinetic/dynamic evaluation during drug development. TopFit features are: (1) non-compartmental methods; (2) standard compartment models assembled from input and disposition modules; (3) a potentially unlimited number of linear user-defined models that accommodate metabolites, effects, and absorption profiles; (4) a library of 24 non-linear models. No user programming is required. A well-defined file structure allows ready exchange of data with other programs such as SAS. TopFit version 2.0 is now commercially available, with comprehensive documentation, in the form of an MS-DOS application for the PC.

Influence of acute myocardial infarction and rt-PA therapy on circulating fibrinogen.

In 12 patients treated with 100 mg rt-PA/3 h for acute myocardial infarction (AMI), serial fibrinogen levels were measured with the Clauss clotting rate assay ("functional fibrinogen") and with a new enzyme immunoassay for immunologically intact fibrinogen ("intact fibrinogen"). Levels of functional and "intact fibrinogen" were strikingly different: functional levels were higher at baseline; showed a more pronounced breakdown during rt-PA therapy; and a rebound phenomenon which was not seen for "intact fibrinogen". The ratio of functional to "intact fibrinogen" was calculated for each individual patient and each time point. The mean ratio (n = 12) was 1.6 at baseline, 1.0 at 90 min, and increased markedly between 8 and 24 h to a maximum of 2.1 (p < 0.01), indicating that functionality of circulating fibrinogen changes during AMI and subsequent thrombolytic therapy. The increased ratio of functional to "intact fibrinogen" seems to reflect a more functional fibrinogen at baseline and following rt-PA infusion. This is in keeping with data that the relative amount of fast clotting "intact HMW fibrinogen" of total fibrinogen is increased in initial phase of AMI. The data suggest that about 20% of HMW fibrinogen are converted to partly degraded fibrinogen during rt-PA infusion. The rebound phenomenon exhibited by functional fibrinogen may result from newly synthesized fibrinogen with a high proportion of HMW fibrinogen with its known higher degree of phosphorylation. Fibrinogen- and fibrin degradation products were within normal range at baseline. Upon infusion of the thrombolytic agent, maximum median levels of 5.88 micrograms/ml and 5.28 micrograms/ml, respectively, were measured at 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombolysis using consecutive high dose bolus and infusion of alteplase in a patient with acute massive pulmonary embolism.

We describe the successful use of a novel dosage regimen of alteplase in a 77-year-old man with massive acute pulmonary embolism in the presence of a relative contraindication (recent cranial surgery). An intravenous alteplase bolus of 50 mg was administered, followed 40 min later by a 50 mg infusion over 2 h. Pulmonary arteriography showed a considerable increase in intraluminal filling of thrombotically occluded vessels as a result of alteplase administration, and was accompanied by marked clinical improvement. Peak alteplase plasma concentration after the bolus was 5.5 micrograms/ml, and the steady state concentration during infusion was 0.52 micrograms/ml. Detailed monitoring of haemostasis parameters showed elevated endogenous fibrinolytic activity at baseline, very high levels of fibrin degradation products during treatment resulting from lysis of an extensive thrombus mass, moderate fibrinogenolysis compared to fibrinolysis, long plasma half-lives of fibrin(ogen) degradation products (9.2-11.0 h), and increased thrombin generation. There were no bleeding side-effects. The regimen combines the advantages of rapid onset (bolus) and maintained potency (infusion) of thrombolytic effect in pulmonary embolism.

Pharmacokinetics and fibrin specificity of alteplase during accelerated infusions in acute myocardial infarction.

Pharmacokinetics and fibrin specificity of alteplase (recombinant tissue-type plasminogen activator) were determined in 10 patients with acute myocardial infarction undergoing an accelerated infusion regimen during the alteplase/anistreplase patency study (TAPS). Fifteen milligrams of alteplase was administered as an intravenous bolus injection, followed by infusions of 50 mg over 30 min and 35 mg over a further 60 min. Mean steady state plasma concentrations of alteplase during the initial 30 min were 3.2 +/- 0.84 micrograms/ml, measured immunochemically, and 2.1 +/- 0.23 micrograms/ml, measured using a functional activity assay. These values were 45% and 51% higher, respectively, than those during the standard infusion schedule (p less than 0.01). However, the predominant plasma half-life determined by model fitting based on either assay (3.3 to 3.5 min) was unaltered compared with the standard regimen. Maximal concentrations of fibrin and fibrinogen degradation products were 5.1 +/- 2.2 and 1.9 +/- 1.1 micrograms/ml, respectively. Plasminogen decreased to 70% and alpha 2-antiplasmin to 35% of values before infusion. The results indicate that 1) improved coronary patency rates during "front-loaded" infusions can be rationalized in terms of higher plasma concentrations of both free and immunoreactive alteplase, 2) kinetic variables are comparable with those of other dosing strategies, and 3) fibrin specificity is not diminished relative to that of the standard infusion regimen.

Studies on the functionality of fibrinogen during rt-PA therapy: results of three different methods of fibrinogen determination.

The conversion of soluble fibrinogen to insoluble fibrin is a crucial event in the process of haemostasis. In the present study three different methods were used for the determination of plasma fibrinogen levels in 12 patients with acute myocardial infarction during rt-PA therapy. Two methods were based on fibrin formation and thus measured 'functional' fibrinogen: a clotting rate assay according to the Clauss method and a photometric polymerization rate assay. Thirdly, fibrinogen antigen was measured with a new enzyme immunoassay (EIA) for immunologically intact fibrinogen. The levels of functional and intact fibrinogen were strikingly different: 4.1 g/l (Clauss) and 3.6 g/l (photometric) vs 2.6 g/l (EIA) at baseline, 2.2 g/l (54% of preinfusion value) and 2.1 g/l (59%) vs 2.1 g/l (81%) at 90 min, 5.7 g/l (146%) and 4.5 g/l (130%) vs 2.7 g/l (106%) at 72 h. The rebound phenomenon exhibited by functional fibrinogen (130-150%) was not observed for levels of intact fibrinogen. A ratio was calculated of functional (Clauss method) to intact fibrinogen (EIA) for each individual patient and each time point. The mean ratio (n = 12 patients) was 1.6 at baseline, 1.0 at 90 min, and increased markedly between 8 and 24 h to a maximum of 2.1 (P less than 0.01). Our data indicate that the 'functionality', i.e. the clotting rate per unit concentration of circulating fibrinogen, changed during acute myocardial infarction and subsequent thrombolytic therapy. This is in keeping with data from literature that the relative amount of fast clotting high molecular weight (HMW) fibrinogen of total fibrinogen was increased in the initial phase of acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and hepatic catabolism of tissue-type plasminogen activator.

Recombinant tissue-type plasminogen activator (rt-PA, alteplase, Actilyse, Activase; CAS 105857-23-6) is the most effective agent currently available for thrombolytic therapy of life-threatening diseases such as acute myocardial infarction. It acts by rapid, clot-specific lysis of pathological thrombi, with only limited effects on systemic hemostasis. Pharmacokinetics of rt-PA have been extensively characterized in animal species and man, and can be generally described by a 3-compartment model. Preferred analytical methods for rt-PA in plasma are ELISA and chromogenic activity assays. The dominant plasma half-life of rt-PA in myocardial infarction patients is short (3.6 min), which allows excellent control of plasma levels during therapy. Steady-state plasma concentrations effecting coronary thrombolysis using the current dosage regimen are 2.2 micrograms/ml. A deep compartment results in elevated rt-PA concentrations several hours after termination of infusions, which may contribute to short-term maintenance of patency of reperfused blood vessels. Clearance of rt-PA can be saturated in animals at very high plasma concentrations (Km = 12-15 micrograms/ml), however, pharmacokinetics in clinical settings are linear. Clearance occurs via hepatic receptor mediated endocytosis and intracellular degradation in liver parenchymal, endothelial and Kupffer cells. The catabolism involves coated pits, coated vesicles, endosomes, and finally degradation in lysosomes. Current evidence supports the existence of hepatic receptors recognizing carbohydrate as well as polypeptide determinants in rt-PA. In conclusion, increasing knowledge of rt-PA pharmacokinetics will contribute to the optimization of new clinical dosage regimens, such as front-loaded infusions and boluses, and to the identification of novel molecular targets for pharmacologic control of rt-PA catabolism and of circulating fibrinolytic activity.

Nonlinear pharmacokinetics of tissue-type plasminogen activator in three animal species and isolated perfused rat liver.

Tissue-type plasminogen activator (t-PA) is cleared rapidly from the circulation via hepatic catabolism, but the capacity of this process is unknown. In this study, increasing doses of human t-PA were administered to rats, rabbits and marmoset monkeys, and in an isolated perfused rat liver system. t-PA concentrations in plasma and perfusate were analyzed pharmacokinetically using procedures in which nonlinear multicompartment models with Michaelis-Menten elimination were fitted to data sets from all doses simultaneously for each species. Elimination of t-PA was saturable, with Km = 12-15 micrograms/ml and Vmax = 200-350 micrograms/ml/hr in vivo. In isolated rat liver, t-PA elimination capacity was considerably reduced, with Km = 1.5 micrograms/ml and Vmax = 3.7 micrograms/ml/hr. At nonsaturating doses, plasma clearance in vivo was 18-23 ml/min/kg and the dominant half-life was 1.1-2.4 min, compared with 8 ml/min/kg and 4.4 min, respectively, in humans; rat liver perfusate clearance was 0.29 ml/min/g. It is concluded that disposition kinetics of t-PA are very similar across species, extrahepatic clearance may be significant in vivo and clearance capacity becomes limited only at plasma concentrations far in excess of clinical therapeutic values. Nonlinearity is, however, of practical significance in liver perfusion and in animal pharmacology studies utilizing high t-PA doses.

Low incidence of antibodies to recombinant human tissue-type plasminogen activator in treated patients.

Sera from over 1,600 patients who received recombinant human tissue plasminogen activator (rt-PA) during clinical trials were assessed for the presence of antibodies to this therapeutic agent. The rt-PA was administered by a variety of dosage regimens for several different indications. Two different forms of rt-PA were used; one was predominantly two chain form, and the other was a predominantly one chain form. A sensitive radioimmunoprecipitation assay was used to measure antibodies to rt-PA in patients' serum before and after treatment. Of 932 patients tested with this assay, 929 were negative for antibodies to t-PA. Three patients developed low titers after treatment. Additional serum samples were obtained from these three patients within 2 years after rt-PA therapy and were negative for antibodies to t-PA. With the limited number of positive samples, no correlation could be found with dose or type of rt-PA, dosing regimen or clinical diagnosis. The virtual absence of antibody formation was confirmed in an additional 754 patients using a novel competitive two-site ELISA. It can be concluded that a single infusion of rt-PA was virtually unassociated with antibody formation, suggesting that repeat treatments could be given when necessary without the risk of immunologic complications as are seen with streptokinase or its derivatives.

Different receptors mediate the hepatic catabolism of tissue-type plasminogen activator and urokinase.

Tissue-type plasminogen activator (t-PA) and urokinase (u-PA) are proteins with partial structural similarity and which are of importance in the therapy of thrombotic diseases. Both are known to be cleared from the circulation in vivo by uptake in the liver. The present study investigated whether the hepatic catabolism of u-PA and t-PA is mediated by a common receptor system. Four experimental protocols of increasing complexity were used: hepatocyte plasma membranes, isolated primary hepatocytes, liver perfusion and whole animals. For t-PA, a specific high-affinity binding site to hepatocytes and plasma membranes could be defined with a mean Kd of 4 +/- 3 nM, whereas the Kd for u-PA was less than 300 nM. Binding of t-PA could not be competed for by u-PA, and vice versa. Furthermore, clearance of t-PA in isolated perfused rat livers and in rabbits in vivo was 3-fold higher than that of u-PA, and a 50-100-fold molar excess of u-PA failed to inhibit clearance of t-PA in either system, and vice versa. Taken together, the results imply that hepatic elimination of t-PA and u-PA is mediated by distinct receptor systems of differing affinity.

Absolute bioavailability of pirenzepine in intensive care patients.

The absolute bioavailability (f) of pirenzepine was determined in 27 intensive care patients receiving the drug for prophylaxis and therapy of upper gastrointestinal tract bleeding. A multiple oral and intravenous dosage regimen and the times of blood sampling were adapted to individual conditions and treatment. Mean f in the patients was 0.28, which was significantly higher than in 12 normal subjects (0.14). It showed no dependence on age (range 20-82 y), nor on the risk factors cardiac insufficiency, renal and hepatic dysfunction, gastrectomy (Billroth II) and bleeding gastrointestinal ulcers, nor on concomitant administration of metoclopramide or antacids. Due to the wide therapeutic index of pirenzepine, it is concluded that individualization of therapy is not necessary for patients in intensive care.

Current developments in thrombolytic therapy using novel plasminogen activators.

As a result of intensive recent research, the molecular mechanisms governing the human fibrinolytic system could be elucidated. Clinical trials using streptokinase and urokinase demonstrated that therapeutic thrombolysis is a valuable regimen in the treatment of patients with thromboembolic diseases. After unsuccessful attempts to increase the clot specificity of these agents, efforts were increased towards developing fibrin-specific substances with high thrombolytic potency and negligible effects on systemic hemostasis. Tissue-type plasminogen activator manufactured by recombinant DNA technology (rt-PA) is currently the most comprehensively investigated fibrin-specific thrombolytic agent with the most clearly understood mechanism of action in vivo. Pro-urokinase has also become available through biotechnology. A large number of clinical trials studying thrombolytic therapy of myocardial infarction have proved that intravenous rt-PA posesses superior efficacy compared to conventional fibrinolytic agents. Comparatively few clinical studies have been performed using pro-urokinase. At therapeutic doses, the fibrin specificities of these agents differ. So far it has not been possible to correlate the incidence of bleeding complications during fibrinolytic therapy with alterations in hemostasis parameters. For routine laboratory monitoring of thrombolysis the determination of fibrinogen and thrombin clotting time can be recommended. New developments with potential for yielding the next generation of thrombolytic agents are mutants and chimeras of t-PA and pro-urokinase, and conjugates of these substances with fibrin specific antibodies.

Single-bolus injection of recombinant tissue-type plasminogen activator in acute myocardial infarction.

Recombinant tissue-type plasminogen activator (rt-PA) has hitherto been administered in acute myocardial infarction as an intravenous infusion with an initial bolus of about 10% of the total dose, both due to its short half-life and to avoid possible early reocclusions. A single-bolus dose would simplify the therapeutic regimen. Therefore, 20 patients with symptom duration of 125 +/- 58 minutes were given a single bolus of 50 mg of rt-PA over 2 minutes. Coronary angiography 60 minutes after the rt-PA bolus revealed a patent infarct-related artery in 15 of 20 patients (patency rate 75%, 95% confidence limits 51 to 91%). In the remaining patients, reperfusion was achieved by coronary angioplasty and intracoronary fibrinolysis; in 2 patients coronary artery bypass grafting was necessary. Control angiograms at 24 hours showed reocclusions in 4 of 18 patients. One woman died due to an intracranial hemorrhage 48 hours after the rt-PA bolus injection. Circulating fibrinogen decreased from 2.7 +/- 0.5 to 1.5 +/- 0.9 g/liter after 2 to 4 hours and reached the initial value within 24 hours. Pharmacokinetic parameters were obtained in 7 patients by measuring rt-PA antigen levels in multiple plasma samples. Mean peak rt-PA concentration was 9.8 +/- 3.6 micrograms/ml, total plasma clearance 476 +/- 148 ml/min and dominant half-life 4.8 +/- 1.0 minutes. Thus, rt-PA administered as a 50-mg single bolus appears to provide similar patency rates and shows similar kinetics in comparison with the conventional infusion regimen. Assessment of the incidence of bleeding complications requires further studies.

Pharmacokinetics and systemic effects of tissue-type plasminogen activator in normal subjects.

Pharmacokinetics and systemic effects of recombinant tissue-type plasminogen activator (rt-PA) were studied in 18 healthy male volunteers after 30-minute intravenous infusions of placebo, 0.25 mg/kg rt-PA, and 0.5 mg/kg rt-PA. Highly comparable pharmacokinetic parameters were obtained after analysis of rt-PA as both an antigen and an activity. Mean clearance (antigen) was 620 +/- 70 (SD) ml/min, volume of distribution at steady state was 8.1 +/- 0.8 L, initial volume of distribution was 4.4 +/- 0.6 L, and dominant half-life was 4.4 +/- 0.3 minutes. The pharmacokinetics of rt-PA were linear, showed low interindividual variation, and are compatible with rapid hepatic elimination of the protein. Systemic plasminogen activation was minimal as assessed by hemostatic assays of plasma samples treated with anti-rt-PA Immunoglobulin G (IgG) to inhibit in vitro fibrinogenolysis. Circulating fibrinogen levels, clotting times, and coagulation factors were unchanged; plasminogen and alpha 2-antiplasmin decreased maximally to 85% and 65% of baseline values, respectively. The data are consistent with the fibrin specificity of t-PA, which is derived from its role in physiologic fibrinolysis.