Determination of a weight-adjusted dose of TNK-tissue plasminogen activator

TNK-tissue plasminogen activator (TNK-tPA) is a potent new thrombolytic agent for treatment of acute myocardial infarction. TNK-tPA was evaluated in 4214 patients in two dose-ranging trials (Thrombolysis in Myocardial Infarction [TIMI] 10B and Assessment of the Safety and Efficacy of a New Thrombolytic Agent [ASSENT] I). This article describes the rationale for the weight-adjusted dosing regimen of TNK-tPA that was selected for evaluation in the large phase III clinical trial ASSENT II.

Weight-based analyses were conducted with data from both the angiographic TIMI 10B trial, which compared TNK-tPA in doses of 30 mg, 40 mg, and 50 mg with the accelerated regimen of tPA in 889 patients, and the ASSENT I trial, which evaluated the safety of TNK-tPA in doses of 30 mg, 40 mg, and 50 mg in 3301 patients. Graphic and statistical analytic methods were used to assess relationships between weight and efficacy or safety measurements.

The plasma clearance, initial plasma concentrations, and plasma steady-state volume of distribution all increased with decreasing body weight (all P<.001). The corrected TIMI frame count decreased (flow was faster) (P =.001) and the TIMI grade 3 flow increased with an increasing weight-standardized dose of TNK-tPA (P<.008). Mortality was inversely related to dose, but this relationship was not statistically significant. There was no clear relationship between intracranial hemorrhage and dose and weight. Serious bleeding events increased with increasing weight-standardized dose (P<.02).

On the basis of these analyses, a weight-adjusted dosing regimen was devised for TNK-tPA that included five dosing increments and was based on a target weight-standardized dose of 0.53 mg/kg.