Heparin activity, assay curve

Figure 6. APTT heparin activity assay curve. Key 9, control heparinized plasma (units mL plasma) calibration APTT and O, derivatized heparin (at known weight concentrations, mg/mL plasma) APTT.

A pharmacokinetic comparison of both product generations, and their formulation buffers was conducted in partially heparinized Sprague-Dawley rats using a monoclonal antibody capture/activity assay. The two rFVIII concentrates exhibited a high degree of similarity in half-life, area under the curve (AUC), clearance rate, and mean retention time, predicting biological activity of rAHF-PFM in humans similar to that of rAHF. 

When anti-factor Xa activity is used to monitor LMWH therapy, the sample should be drawn approximately 4 hours after the subcutaneous injection, during the peak period of anti-factor Xa activity. A calibrated LMWH heparin should be used to establish the standard curve for the assay. The therapeutic range for anti-factor Xa activity is not well defined and to date has not been correlated clearly with efficacy or the risk of bleeding. Eor the treatment of VTE, an acceptable target range is 0.5 to 1.0 unit/mL. Specific algorithms for dosing adjustments based on anti-factor Xa activity are not available at the present time. 

---