Potential cost effectiveness of tissue plasminogen activator among patients previously treated with streptokinase

BACKGROUND: A major limitation of streptokinase is the development and pers istence of problematic neutralizing antibodies that have the potential to l imit the effectiveness of repeat streptokinase therapy. Accordingly, tissue -type plasminogen activator (t-PA) is frequently administered to patients w ith recurrent infarction presenting more than four days from previous treat ment with streptokinase. OBJECTIVE: To explore the marginal cost effectiveness of the use of t-PA am ong patients with resistance to streptokinase. MATERIALS AND METHODS: A model was developed incorporating short term (five - to six-week) costs and mortality data for various thrombolytic strategies . It was assumed that streptokinase would be clinically ineffective when ad ministered to streptokinase-resistant patients. Sensitivity analyses were p erformed varying the baseline mortality, the proportion of patients resista nt to streptokinase and the absolute survival benefit of t-PA compared with streptokinase. RESULTS: In the absence of streptokinase resistance, streptokinase is a cos t effective strategy for patients with suspected myocardial infarction, eve n when the expected mortality is low. In the presence of streptokinase resi stance, the combination of streptokinase and acetylsalicylic acid is most c ost effective when rates of resistance are low ($16,389 per shore run survi vor with 5% resistance versus $21,306 with 50% resistance). t-PA is a cost effective alternative when rates of resistance are high ($54,158 per short run survivor with 50% resistance) assuming a 1% absolute risk reduction in mortality. As the level of resistance decreases, however, t-PA becomes a le ss cost effective choice ($203,092 per short run survivor with 5% resistanc e). However, t-PA is always more cost effective in the presence of any stre ptokinase resistance than when it is administered for an index myocardial i nfarction. CONCLUSIONS: This analysis shows that using t-PA in patients previously tre ated with streptokinase is a cost effective strategy, t-PA becomes less cos t effective as the percentage of patients with streptokinase resistance dec reases, particularly when the absolute risk reduction favouring t-PA over s treptokinase is small. Nevertheless, if the early mortality advantage is su stained, very favourable cost effectiveness ratios are attained with t-PA e ven when the risk of resistance is low, t-PA used in the presence of strept okinase resistance is always more cost effective than when it is used for a first myocardial infarction.