Anti-Xa stability of diluted enoxaparin for use in pediatrics

The use of enoxaparin in low-weight pediatric patients is becoming common practice. Anti-Xa stability of unit-dose syringes prepared after dilution beyond one day is presently unknown.

To evaluate the anti-Xa stability of diluted enoxaparin stored in glass vials and tuberculin syringes.

Four separate batches of enoxaparin were diluted with sterile water to a final concentration of 20 mg/mL (2000 IU/mL) and aliquoted into plastic 1-mL syringes containing 6 mg (0.3 mL) or maintained in the glass vial. Syringes were stored at room temperature or under refrigeration. The glass vial used for diluting was stored at room temperature. The anti-Xa activity was measured on the date of preparation to 4 weeks. Statistical comparisons determined whether differences in anti-Xa activity in diluted enoxaparin are affected by the storage medium or temperature. A paired t-test was used to determine any significant differences between the anti-Xa activity on date of preparation (baseline) and subsequent time periods, with p < 0.05 considered statistically significant.

The mean baseline anti-Xa activity was 2607 IU/mL (95% CI 2300 to 2914). No measurable decrease occurred in diluted enoxaparin anti-Xa activity in the glass vial maintained over the 4-week period. Compared with the glass vial, room temperature and refrigerated syringe samples had trending decreases of anti-Xa activity at weeks 3 and 4, but did not reach statistical significance.

A nonsignificant decrease in anti-Xa activity occurred starting at day 22 for the diluted enoxaparin in tuberculin syringes, regardless of storage temperature. Storage up to 4 weeks of diluted enoxaparin in glass or prefilled syringes does not result in a statistically significant loss of anticoagulant potential, as measured by anti-Xa activity.