Lack of influence of pretreatment antistreptokinase antibody on efficacy in a multicenter patency comparison of intravenous streptokinase and anistreplase in acute myocardial infarction

Proinflammatory cytokines in the prefrontal cortex of teenage suicide victims

Teenage suicide is a major public health concern, but its neurobiology is not well understood. Proinflammatory cytokines play an important role in stress and in the pathophysiology of depression-two major risk factors for suicide. Cytokines are increased in the serum of patients with depression and suicidal behavior; however, it is not clear if similar abnormality in cytokines occurs in brains of suicide victims. We therefore measured the gene and protein expression levels of proinflammatory cytokines interleukin (IL)-1β, IL-6, and tissue necrosis factor (TNF)-α in the prefrontal cortex (PFC) of 24 teenage suicide victims and 24 matched normal control subjects. Our results show that the mRNA and protein expression levels of IL-1β, IL-6, and TNF-α were significantly increased in Brodmann area 10 (BA-10) of suicide victims compared with normal control subjects. These results suggest an important role for IL-1β, IL-6, and TNF-α in the pathophysiology of suicidal behavior and that proinflammatory cytokines may be an appropriate target for developing therapeutic agents.

A rapid agglutination assay to detect anti-streptokinase antibodies

BACKGROUND

Streptokinase resistance may cause suboptimal thrombolytic therapy.

AIM

To develop a rapid latex-bead assay to detect streptokinase antibodies.

METHODS

Sera were obtained from 16 patients presenting with acute myocardial infarction (MI) before treatment with streptokinase and 1 and 6 months post treatment, and from 100 controls. Sera were assayed for anti-streptokinase antibodies using a functional streptokinase-neutralising assay.

RESULTS

Streptokinase-neutralising activity was low in controls (54 +/- 5U/ml) and patients prior to treatment (101 +/- 18), increasing to 2,110 +/- 823 and 1,017 +/- 169 at 1 and 6 months (mean +/- SEM). The latex assay had a sensitivity of 94% and a specificity of 93% for detecting individuals with > 350U/ml of streptokinase resistance, which is sufficient to neutralise the drug clinically.

CONCLUSIONS

Estimation of streptokinase resistance using an enzyme immunoassay and a latex bead assay correlated well with serum neutralising activity. This assay can rapidly identify patients who have a high level of streptokinase-neutralising activity.

Clinical usefulness of a functional test of neutralising streptokinase antibodies for the prediction of the thrombolytic effect of streptokinase in acute myocardial infarction

We investigated whether the occurrence of neutralising streptokinase (SK) antibodies, as assessed by a new bedside test, was related to the effect of SK in acute myocardial infarction (AMI), assessed with continuous vectorcardiography (VCG). Twenty-eight patients with ST elevation, admitted </= 6 h after the onset of symptoms, treated with 1.5 MIU SK were included. The level of SK antibodies was assessed by the TAS Streptokinase Test Panel, measuring the lysis time of clotted fibrin in the sample. Clot lysis time was negatively correlated to ST vector magnitude (ST-VM) recovery at 90 min (r(S) = -0.40, p = 0.03), and clot lysis time was positively correlated to time to reperfusion, (r(S) = 0.42, p = 0.03). The predictive values of the test, however, were low. In conclusion, as the prediction of reperfusion in AMI after SK by the new test was poor, we cannot recommend it for clinical decision-making prior to the choice of the thrombolytic agent.

Antistreptokinase platelet-activating antibodies are common and heterogeneous

BACKGROUND

Platelet activation by antistreptokinase (SK) antibodies could impair the clinical effect of SK administration.

OBJECTIVE

To better describe anti-SK antibodies with particular emphasis on procoagulant activities as a result of platelet activation.

PATIENTS AND METHODS

Sera were collected from 146 patients with coronary artery disease: non-SK-treated, 95 from mainland France, 31 from French Polynesia; 20 patients from mainland in year 2 after SK treatment. Serum-induced SK-dependent platelet activation resulting in procoagulant activities was assessed with washed platelets from five donors representative of the known patterns of reactivities to IgG.

RESULTS

Concentrations (2-5252 microg mL(-1)) and fibrinolytic neutralization titres (< 10 to > 1280) were found in the expected wide range and correlated (rho = 0.66, P < 0.0001). Platelet activation was detected with 145 samples, but varied in intensity and pattern (depending on the donors), although there was no systematic hierarchy; it was presumably due to IgG (inhibited by an IgG Fc receptor-blocking antibody and recovered in the IgG fraction) and only partially affected by aspirin. Marked platelet activation could be detected in samples with concentration as low as 2 microg mL(-1), and/or no detectable neutralizing titers. The way of immunization to SK was not found to influence the functional profile of antibodies.

CONCLUSION

Anti-SK platelet-activating antibodies are widespread, heterogeneous, poorly predictable on the basis of their antifibrinolytic effect and strong enough to trigger procoagulant activities. Their clinical relevance should be formally assessed, using patients' own platelets for detection owing to the variation of platelet reactivity.

Effect of intrapleural streptokinase administration on antistreptokinase antibody level in patients with loculated pleural effusions

BACKGROUND

Streptokinase is widely used IV for the treatment of myocardial infarction and intrapleurally for the treatment of loculated pleural effusions. IV administration of streptokinase is known to cause the production of antistreptokinase antibodies.

OBJECTIVE

The aim of this study was to evaluate whether the intrapleural administration of streptokinase results in a similar elevation of the serum antistreptokinase antibody level.

METHODS

During 1 year, venous blood samples were taken from 16 consecutive patients (10 men and 6 women; age range, 22 to 60 years) requiring intrapleural streptokinase administration (250,000 IU once a day, for 2 to 6 days). Blood samples were taken before treatment, on day 5, and day 14. Antistreptokinase antibodies were measured using enzyme-linked immunosorbent assay (ELISA) and were expressed in arbitrary ELISA units. Four patients with myocardial infarction treated with IV streptokinase (1,500,000 IU) were included as control subjects for the method.

RESULTS

Before treatment, the median antistreptokinase antibody level in patients with loculated pleural effusions was 729 ELISA units (range, 196 to 13,529 ELISA units) and increased to 9,240 ELISA units (range, 1,456 to 77,389 ELISA units) by day 14 (p < 0.0001). In the control group, the median pretreatment level was 119 ELISA units, and by day 14 it had increased to 20,495 ELISA units. Four patients who developed an elevated body temperature after intrapleural administration of streptokinase had a significantly higher pretreatment antistreptokinase antibody level compared to other patients.

CONCLUSIONS

The intrapleural administration of streptokinase results in the elevation of the serum antistreptokinase antibody level, which is similar to the case with IV administration. An increased pretreatment antistreptokinase antibody level does not influence the result of intrapleural fibrinolysis but can cause an elevation of body temperature after the administration of streptokinase.

Platelet activity and antibody titers after exposure to streptokinase or streptococcal infection

INTRODUCTION

Streptokinase use, in acute myocardial infarction, is hindered by failure to reperfuse (60%) and early reocclusion (16%). This phenomenon may, among other causes, be due to systemic inactivation of streptokinase, as well as streptokinase-induced platelet aggregation and clot propagation from antibodies to streptokinase produced after streptokinase administration or streptococcal infections. The purpose of this study was to determine the incidence of streptokinase-induced, antibody-mediated, platelet activation and aggregation after administration of SK or development of a streptococcal infection.

MATERIALS AND METHODS

We included 45 normal volunteers (Control group), as well as 45 patients who had received streptokinase (Streptokinase group) and 13 who had suffered a severe streptococcal infection (Streptococcal infection group) within the past 3 years. Extent of streptokinase-induced, antibody-mediated, platelet activation and aggregation, as well as anti-streptokinase antibody and streptokinase resistance titers (lowest streptokinase concentration to cause clot lysis within 10 min) were measured.

RESULTS

Whereas streptokinase-induced, antibody-mediated, platelet activation was observed in 49% of streptokinase patients and in only 17% and 15% of streptococcal infection patients and normal volunteers (p<0.05 Streptokinase vs. Control and Streptokinase vs. Streptococcal infection), streptokinase-induced platelet aggregation was observed in 23% of streptokinase patients and streptococcal infection patients, and in none of the control patients (p<0.05).

CONCLUSIONS

Streptokinase-induced, antibody-mediated, platelet activation and aggregation occur in patients with high titers of anti-streptokinase antibody and may play a role in failure of streptokinase therapy. Streptococcal infection patients behave like streptokinase patients in terms of the reactivity of their platelets to subsequent streptokinase dose in vitro.

C-reactive protein levels on admission are associated with response to thrombolysis and prognosis after ST-segment elevation acute myocardial infarction

BACKGROUND

Several studies have shown the independent association of high plasma C-reactive protein (CRP) levels with an adverse prognosis in patients with acute myocardial infarction. However, the possible association of plasma CRP levels with response to thrombolysis and short- and long-term cardiac mortality has not been investigated. The aim of this study was to evaluate these possible associations.

METHODS

Three hundred nineteen consecutive patients who received intravenous thrombolysis because of ST-segment elevation acute myocardial infarction were prospectively studied. Patients were classified according to tertiles of plasma CRP levels on admission.

RESULTS

Patients at the top tertile had a significantly lower incidence of complete ST-segment resolution (third vs first, P <.001, third vs second, P =.009) or Thrombolysis In Myocardial Infarction (TIMI) 3 flow in the infraction-related artery (third vs first, P <.001, third vs second, P =.02), more compromised left ventricular function (third vs first, P =.02, second vs third, P =.04), greater inhospital mortality (third vs first, P =.03, third vs second, P =.06), and greater 3-year cardiac mortality (third vs first, P =.01, third vs second, P =.07).

CONCLUSIONS

Plasma levels of CRP on admission may be a predictor of reperfusion failure and of short- and long-term prognosis in patients with ST-segment elevation acute myocardial infarction.

The effect of streptokinase neutralizing antibodies on fibrinolytic activity and reperfusion following streptokinase treatment in acute myocardial infarction

OBJECTIVES

To evaluate tissue plasminogen activator (tPA) activity as a measure of fibrinolytic response to treatment with streptokinase (SK) and to relate this to the effect of pretreatment SK antibodies and to successful reperfusion assessed by continuous computerized vectorcardiography (VCG).

SETTING

Umeå University Hospital.

SUBJECTS

A total of 104 patients with acute myocardial infarction (AMI) treated with SK and no history of previous SK treatment were studied. The tPA activity was measured 4 h after the start of treatment. The effect of pre-existing neutralizing antibodies to SK was analysed with a functional assay in pretreatment samples. Reperfusion was evaluated with VCG.

MAIN OUTCOME MEASURES

Successful reperfusion.

RESULTS

Fifty-five patients (53%) were classified as successfully reperfused. The risk for failed reperfusion was calculated in logistic regression models. In a univariate model, a borderline significant increase in the risk of failed reperfusion was observed in intermediate levels of SK neutralizing antibodies, but not in the highest levels. In a multivariate model, only high tPA activity, >25 U mL(-1), at 4 h (OR 0.17: 95% CI: 0.06-0.51) was associated with a higher rate of reperfusion whilst longer time to treatment (OR 1.17; 95% CI: 1.02-1.35) was associated with a higher risk of failed reperfusion. There was no significant correlation between neutralizing antibodies to SK and tPA activity at 4 h.

CONCLUSION

The SK treatment of AMI induced high levels of tPA activity which were associated with successful reperfusion. The effect of pre-existing SK antibodies had no significant influence on reperfusion and were not correlated to the fibrinolytic activity obtained.

Failed reperfusion after thrombolytic therapy: recognition and management

BACKGROUND

Failed reperfusion after thrombolysis occurs in as many as 30% of patients with acute myocardial infarction (MI). Furthermore, some patients have incomplete tissue perfusion despite reperfusion of the infarct-related artery. Close assessment of the efficacy of thrombolytic administration in people with evolving acute MI is necessary, particularly with regard to myocardial perfusion status, because some patients may benefit from incremental pharmacologic or invasive reperfusion strategies.

PURPOSE AND METHOD

This article reviews a number of strategies to assess infarct-related artery patency and myocardial tissue perfusion. These include coronary angiography, continuous ST-segment monitoring, serial electrocardiography, obtaining serial serum biochemical markers of myocardial necrosis, monitoring for reperfusion arrhythmias, and assessment of changes in chest pain intensity.

CONCLUSION

The early detection of failed reperfusion is critical if incremental strategies to enhance myocardial salvage are to be considered. Continuous ST-segment monitoring is a relatively inexpensive, reliable, and accurate tool for assessing real-time myocardial perfusion.

Anti-streptokinase titers and response to streptokinase treatment in Pakistani patients

In order to investigate whether anti-streptokinase (anti-SK) antibody titers have any effect on response to standard dose (1.5 million units) streptokinase (SK) therapy in patients with acute myocardial infarction, anti-SK titers in plasma were determined in 97 such patients. These patients were classified as "responders" or "non-responders" on the basis of a criteria which involved resolution of chest pain in less than 90 min after the start of thrombolysis, greater than 50% reduction of ST segment elevation in two contiguous leads showing maximum elevations in a 12-lead tracing, reperfusion arrythmias and slope of increase in creatine kinase over a 90-min period after initiation of thrombolysis. Anti-SK antibody levels in plasma were determined in these patients as well as in 50 normal healthy subjects by dissolution of clot method. Mean+/-S.D. anti-SK levels among responders, non-responders and normal healthy subjects were found to be 0.21+/-0.12, 0.25+/-0.22 and 0.21+/-0.15 million units, respectively. A comparison of these mean values by one-way ANOVA revealed no statistical difference (P=0.68). However, when compared with the reported values for a Western population, these values were found to be significantly higher (P<0.03). Whereas, compared to the reported values for an Indian population, these were significantly lower (P<0.0001). 42% of patients appeared to have responded to SK treatment, while 21% were found to be non-responders. There was no association between response to SK and anti-SK titers in these patients suggesting that the standard dose of SK (1.5 million units) may be quite appropriate for the Pakistani population requiring SK treatment for the first time.

Failed thrombolysis in myocardial infarction

Prompt treatment with thrombolytic therapy in acute myocardial infarction has been proven to reduce infarct size and mortality. However, reperfusion fails to occur in 30-50% of patients, either due to impaired epicardial artery flow or microvascular occlusion, with these patients experiencing a higher morbidity and mortality. We review the diagnosis and management of failed thrombolysis in acute myocardial infarction.

Streptokinase antibodies inhibit reperfusion during thrombolytic therapy with streptokinase in acute myocardial infarction

OBJECTIVES

To evaluate the influence of pretreatment IgG against streptokinase on the outcome of streptokinase treatment in acute myocardial infarction.

SETTING

Coronary care unit.

DESIGN

From 88 patients admitted to the coronary care unit due to chest pain, blood samples were taken for determination of the pre-existing titre of antibodies against streptokinase. The patients were treated and monitored according to standard protocols. Fifty of the patients received thrombolytic therapy with streptokinase due to acute myocardial infarction and were monitored with continuous dynamic vectorcardiography, making possible the continuous analysis of ST- and QRS-vector changes and determination of the event of reperfusion. None of these 50 patients had been given streptokinase therapy previously.

RESULTS

According to the vectorcardiographic criteria 21(42%) patients had signs of early (within 2 h) reperfusion after streptokinase therapy. These patients had lower pre-existing antibody titres than patients without signs of reperfusion (mean values 0.20 and 0.45 arbitrary units, P = 0.01). None of the patients with a titre higher than 0.50 arbitrary units (nine patients) had signs of early reperfusion. Of the 41 patients with a titre lower than 0.50 arbitrary units 52.5% had signs of early reperfusion.

CONCLUSION

The present investigation indicates that pre-existing streptokinase antibodies play an important role in reperfusion failure during thrombolytic therapy with streptokinase in acute myocardial infarction. Therefore, the determination of streptokinase antibodies may differentiate between those patients who may benefit from streptokinase treatment and those who should be treated with some other regime.

Thrombolysis: the development of unit guidelines

A challenge remains to develop guidelines for practice which facilitate safer and effective administration of thrombolytic agents following acute myocardial infarction. Clinical trials have proven that early reperfusion of ischaemic myocardium following rapid diagnosis, aspirin administration, analgesia and the instigation of an appropriate thrombolytic regime reduces mortality rates. Accordingly, as thrombolysis becomes the buzzword of the 1990s, controversy has resulted in substantial variations in practice of thrombolytic strategies within the UK (FTTCC 1994). The purpose of this review article is to consider the importance of current research and its application to current practices. Topics under discussion include thrombolytic agents, antistreptokinase antibody, time delay, eligibility for thrombolytic treatment, and clinically proven therapeutic regimes; with a suggested admission protocol that facilitates bi-directional communication minimising time delay and preventing inappropriate, cost-inefficient admissions to critical care areas. The results of this provide a logistical basis to thrombolytic therapy, and the subsequent development of effective and safe algorithmic guidelines in a busy medical intensive care unit.

Systemic lytic state is not a predictor of coronary reperfusion in acute myocardial infarction

To investigate why approximately one third of patients thrombolysed with streptokinase fail to reperfuse, we assessed the lytic status, antistreptokinase antibody and non invasive parameters of reperfusion in 95 consecutive patients with acute myocardial infarction treated with streptokinase for the first time. The lytic status was assessed by Clauss fibrinogen assay and thrombin clotting time before and 2 h after streptokinase infusion. Antistreptokinase antibody was measured prior to the infusion. Reperfusion was assessed by measurement of the 24:96 h troponin-T ratio (a ratio > 1 indicating reperfusion) and ST segment resolution 2 h post streptokinase. Ninety-two (97%) patients achieved a systemic lytic state with a fibrinogen titre of less than 1.0 g/l and thrombin clotting time ratio of > 2.5. Despite this, 27% failed to reperfuse with a mean 24:96 h troponin-T of 0.9, SD 0.6 vs. 3.4 +/- 3.2 in the reperfused group, (P < 0.0001). 83% of the reperfused group but none of the non reperfused group had ST segment resolution. No difference was observed in the levels of fibrinogen and thrombin clotting time between the reperfused 0.25 +/- 0.3 g/l; 6.9 +/- 4, and the non reperfused group 0.4 +/- 0.6 g/l; 7.9 +/- 2.6. No difference was observed in the levels of antistreptokinase antibody between the reperfused (median = 168 U/ml and the non reperfused (median = 177 U/ml). Failure to reperfuse with Streptokinase is not due to failure to achieve a lytic state. Therefore increased or accelerated dosages of streptokinase are unlikely to increase the rate of reperfusion.

Anti-streptokinase antibodies and streptokinase resistance in an Aboriginal population in northern Australia

BACKGROUND

Thrombolytic treatment with streptokinase in acute myocardial infarction has proven to be safe and effective in Caucasian populations with relatively low levels of anti-streptokinase IgG and streptokinase resistance. Higher levels of antibodies, as seen in previous recipients of streptokinase therapy, cause more adverse reactions and may result in lower efficacy.

AIMS

To examine the levels of anti-streptokinase IgG and streptokinase resistance in a population subjected to endemic streptococcal infections.

METHODS AND RESULTS

Thirty Aboriginal adults from a remote community in Northern Australia with endemic streptococcal infections and 15 non-Aboriginal adults from an urban community without endemic infections participated in this study. Aboriginal adults exhibited levels of anti-streptokinase IgG and streptokinase resistance that, respectively, were almost 20 and 15 times greater than the values of non-Aboriginal adults. At least 23% of Aboriginal adults had sufficiently high levels of streptokinase resistance to neutralise a standard 1.5 million unit dose of streptokinase.

CONCLUSIONS

Aboriginal adults from a remote community had dramatically elevated levels of anti-streptokinase IgG and in vitro streptokinase resistance. Prospective studies are needed to assess the clinical relevance of streptokinase resistance in populations from areas with endemic streptococcal infection.

Mapping the antigenic regions of streptokinase in humans before and after streptokinase therapy

Streptokinase saves lives in patients suffering a myocardial infarction. However, because nearly all humans tested show antibodies against streptokinase, allergic reactions to streptokinase are common and may be severe. In this report we have analysed antibodies purified from normal blood donors and patients, before and after streptokinase therapy, to identify antigenic regions of the streptokinase molecule. Antibody to streptokinase was seen in all subjects, but there were 20-30-fold differences between individuals in the antibody titer. These individual differences in titer persisted after SK treatment, though the titer for all patients rose an average of 7-fold 1 week after streptokinase therapy. To identify the regions of streptokinase to which the antibody bound, we employed a panel of well-characterized murine monoclonal antibodies and recombinant streptokinase truncated fragments. Antibodies to three discrete regions of streptokinase could be detected in all patients. Antibodies to two other regions, at the amino terminal and carboxyl terminus of the molecule, were found in many but not in all patients. However, antibodies to a sixth region of streptokinase were uncommon and of very low titer. Interestingly, individuals receiving streptokinase tended to show the same pattern of immunoreactivity after treatment as they had prior to streptokinase. We conclude that although individual differences exist in the titers of streptokinase antibody, certain regions of streptokinase appear to be more antigenic or immunodominant.

Pre-dosing antibody levels and efficacy of thrombolytic drugs containing streptokinase

OBJECTIVE

To evaluate the influence of pretreatment streptokinase resistance titre and the concentration of IgG antibodies to streptokinase on the efficacy of thrombolytic drugs containing streptokinase in restoring coronary patency in acute myocardial infarction.

DESIGN

Comparative observational study.

SETTING

City general hospital.

PATIENTS

One hundred and twenty four previously unexposed patients presenting within six hours of onset of acute myocardial infarction.

INTERVENTIONS

Streptokinase, 1.5 MIU as intravenous infusion over 60 minutes (60 patients), or anistreplase, 30 units as intravenous injection over five minutes (64 patients).

MAIN OUTCOME MEASURES

Pretreatment streptokinase resistance titre and concentration of IgG antibodies to streptokinase were measured in 96 and 124 patients respectively and coronary patency assessed angiographically at 90 minutes and 24 hours.

RESULTS

Pretreatment streptokinase resistance titre and concentrations of IgG antibodies to streptokinase were low and skewed towards higher values. Those patients with coronary occlusion at 24 hours had a significantly higher median streptokinase resistance titre (100 v 50 streptokinase IU ml-1, P = 0.02). There were trends towards a higher streptokinase resistance titre in those patients with coronary occlusion at 90 minutes (50 v 20 streptokinase IU ml-1, P = 0.06) and higher concentrations of IgG antibodies to streptokinase in those with coronary occlusion at both 90 minutes and 24 hours (1.53 v 0.925, P = 0.03; 1.65 v 1.04 micrograms streptokinase binding ml-1, P = 0.06). Coronary patency rates were similar in the two treatment groups.

CONCLUSIONS

In the range measured in previously unexposed patients the streptokinase resistance titre has a small, but significant, negative influence on the efficacy of streptokinase and anistreplase. This effect should be considered if retreatment with streptokinase or anistreplase is proposed.

Repeat thrombolysis

Since 20% of patients with myocardial infarction (MI) have had a previous infarction, and reinfarction within one year after infarction occurs in 9% of cases, it is important to clarify the role of repeat thrombolysis. After streptokinase (SK) administration, IgG antibodies rise to a peak at two weeks and slowly fall over the next 12 months, but 50% of patients still have antibody levels sufficient to neutralise a standard dose of SK up to four years after initial SK administration. On this evidence, SK or anistreplase should not be readministered, except perhaps in the first two to three days after initial treatment. The efficacy of tissue plasminogen activator (t-PA) and urokinase is not affected by prior treatment with SK.

Chemical derivatization of therapeutic proteins

Despite major advances in redesigning and producing proteins through recombinant DNA technology, many therapeutic proteins are still produced by extraction from biological tissues or fluids, or from nonrecombinant microorganisms. Modification of such proteins, to improve potency and bioavailability and reduce immunogenicity, can only be carried out post-translationally by chemical-derivatization methods. Genetic- and chemical-modification methods are not mutually exclusive, however, and may be combined to optimize protein-engineering strategies, because chemical modification can introduce structural changes that are not encoded by DNA into both recombinant, and nonrecombinant proteins.

Neutralizing antibodies to streptokinase four years after intravenous thrombolytic therapy

Neutralization antibodies to streptokinase increase to high levels within several days of administration. It is not known how long these high levels persist. The time course of antibody levels needs to be further characterized owing to the increasing need to readminister thrombolytic therapy, and to the possibility that these antibodies may compromise the safety and efficacy of a further dose of streptokinase or streptokinase-containing compounds. In this study, paired streptokinase neutralization titers (in vitro functional assay) and specific antistreptokinase immunoglobulin G (IgG) antibody levels were measured in 145 patients who received streptokinase between 10 and 48 months previously. Serologic evidence of recent streptococcal infection was also sought. Neutralization titers sufficient to inactivate a conventional dose of 1,500,000 units of streptokinase were still present in 50% of patients (95% confidence interval 36-64) at 24 months, 48% (34-62) at 36 months, and 51% (37-71) at 48 months after streptokinase administration. Levels of specific antistreptokinase IgG antibodies also remained constant over the 1- to 4-year period. Neutralization titers were weakly correlated with specific IgG levels (r = 0.35). Antistreptolysin titers > or = 250 and > or = 333 IU/ml were present in 30% (24-38) and 12% (8-18) of these patients, respectively. Neutralization titers were not correlated with antistreptolysin titers. Neutralizing antibodies (assessed by an in vitro functional assay) remained high in 51% of patients 4 years after intravenous streptokinase administration. It is not known whether persisting high in vitro neutralization titers affect the efficacy and safety of repeat administration of streptokinase or streptokinase-containing compounds.