Supplementary Material for: Empirically Reduced Dosages of Tinzaparin in Patients with Moderate-to-Severe Renal Insufficiency Lead to Inadequate Anti-Xa Levels

Background: Due to the higher molecular weight of tinzaparin, the low molecular weight heparin (LMWH) is less dependent on renal excretion than other LMWH preparations. However, several international guidelines recommend the same preemptive dosage reduction for all therapeutic dose LMWHs prescribed in renal insufficient patients, to ensure that there is no accumulation of anticoagulant activity and increased risk of bleeding. This study is aimed at assessing whether a preemptive dosage reduction of tinzaparin in all renal insufficient patients (comprising 25% reduction in patients with Modification of Diet in Renal Disease - estimated glomerular filtration rate (MDRD-eGFR) 30-60 mL/min/1.73 m2 and 50% reduction in patients with MDRD-eGFR <30 mL/min/1.73 m2) leads to adequate anti-Xa levels. Methods: We selected the anti-Xa levels of in-hospital patients (≥18 years) with moderate-to-severe renal insufficiency (MDRD-eGFR <60 mL/min/1.73 m2), on therapeutic dosages of tinzaparin. Anti-Xa levels were measured using a chromogenic assay. Results: Preemptive dosage reduction resulted in a median anti-Xa activity of 0.50 IU/mL (interquartile range [IQR] 0.38-0.60). In 92.3% of patients the anti-Xa level was below the target anti-Xa level of >0.85 IU/mL for therapeutic indications. Unadjusted dosages led to a median anti-Xa activity of 0.74 IU/mL (IQR 0.56-0.92). The preemptive dosage reduction was significantly associated with anti-Xa activity below therapeutic range (p = 0.007). No difference in anti-Xa activity was observed between patients with moderate (0.71 IU/mL, IQR 0.61-0.95) versus severe (0.65 IU/mL, IQR 0.41-1.06) renal insufficiency in whom an unadjusted dose had been administered (p = 0.77). None of the anti-Xa levels were above the upper margin of the presumed therapeutic range of 2.0 IU/mL. Conclusion: In renal insufficient patients, the preemptive dosage reduction of tinzaparin leads to inadequate anti-Xa levels.