Objective Tinzaparine is used in paediatric intensive care (PICU) following cardiac surgery as a bridge to oral anticoagulation. Low Molecular Weight Heparins (LMWH), such as Tinzaparin are thought to lead to immediate anticoagulation with adequate anti-Xa levels 2–4 hours after the first dose. Dosing following international guidelines, is age dependent and guided by anti-Xa levels. However, little is known about LMWH dosing in PICU patients. We conducted a retrospective study to evaluate tinzaparin dosing.

Methods We retrospectively analysed Tinzaparin doses and anti-Xa levels from all children admitted to PICU (January 2012–December 2013). Hospital policy is to determine the first aXa level after 3–4 doses and 4 h post dose, targeting 0.5–1.5 IU/ml.

Results There were 31 episodes of newly started Tinzaparin in 28 children. Mean age was 57 (SD±62) months. First anti-Xa levels were determined at 3.45 (SD±1.9; range 1–12) days after the first dose and were sub therapeutic in 25 of 31 (81%): mean 0.33 (SD± 0.15) IU/ml. Tinzarin dose was increased in 12/25 (48%) patients and further anti-Xa levels were determined. In 15 patients further levels were not available due to transition to vit K antagonists or PICU discharge. Therapeutic anti-Xa levels (0.69 (SD± 0.27) IU/ml), were eventually reached in PICU in 16 patients after a mean of 8.8 (SD± 7.1 range 3–30) days.

Conclusion Tinzaparin dosing in PICU patients only leads to target anti-Xa levels after more than 8 days. Levels need to be determined after the first dose so that doses can be adequately increased.