Background and Importance A 3-month-old infant (3kg) was admitted in the paediatric intensive care unit for extracorporeal membrane oxygenation (ECMO) after a pulmonary lobectomy.

Anticoagulant treatment was performed with unfractionated heparin (UFH).

During treatment with UFH, the patient had a sustained decrease in platelet count (>50% of basal) and inferior cava deep venous thrombosis (DVT). Once ECMO was finished, anticoagulant treatment was modified to enoxaparin.

Due to persistent thrombocytopenia and DVT, heparin-induced thrombocytopenia was suspected. Anticoagulant was replaced to fondaparinux, whose recommended dose in paediatrics is 0.1mg/kg/day.

Aim and Objectives To show the need to redose fondaparinux in paediatrics, as registered presentations don’t allow fractionation: they are single-dose pre-filled syringes based on two concentrations: 5mg/ml and 12.5mg/ml.

To verify the stability of the preparation through the study of the pharmacotherapeutic effect, indirectly measured by plasma levels of anti-Xa factor (antiXa).

Material and Methods Subcutaneous fondaparinux was started at a dose of 0.3mg/day (0.06mL).To facilitate administration, the preparation was initially diluted 1mg/mL in normal saline under sterile conditions. The dose was packaged in 1ml dead space free syringe with a purged needle. According to the datasheet, the preparation is stable for 24h at room temperature.

AntiXa was monitored 3 hours after administrations. The dose was adjusted according to Table 1 until the target level (0.5mg/l) was reached.

Subsequently, as the dose increase allowed, the undiluted dose (0.4mg/0.08ml) was fractionated from commercial presentation. Stability of 7 days in the refrigerator was defined according to the risk matrix (low risk) of the Good Pharmaceutical Practices for the preparation of sterile drugs.

Results The dose was adjusted according to antiXa (Table 2). The monitoring of antiX, necessary for the clinical follow-up, allowed us to obtain indirect data on the stability of the fractionated drug, maintaining correct levels throughout treatment, as shown in graph.

After fondaparinux initiation, the platelet count increased to normal values. Anticoagulation therapy was discontinued after three months, upon confirmation of DVT resolution.

Conclusion and Relevance Individualised dosing of fondaparinux by dilution or fractionation has allowed DVT treatment, using a commercial presentation unsuitable for paediatric s.

We verify stability of the fractionated dose with the therapeutic effect.

Conflict of Interest No conflict of interest