Background Paediatric patients receive drug dosages based on their body weights. Consequently only part of a vial with medicine for intravenous (i.v.) administration is often required for a child, contrary to an adult, for whom one vial normally equals one dosage. This does not present a problem when preparing an i.v. drug dosage from an i.v. concentrate or solution. However the problem arises when the drug is formulated as a powder requiring reconstitution. The displacement values of the drug powders can be of negligible or significant sizes. Neglecting to take into account significant displacement values can result in under-dosing. A literature search revealed guidelines highlighting the importance of accounting for displacement values. No recent studies regarding the size of underdosing resulting from ignored displacement values were found.

Purpose To investigate whether displacement values of powders for reconstitution are taken into account in the preparation and administration guide for i.v. drugs at the paediatric ward. If not, then categorising these drugs and calculating the percentage of the resulting underdosing.

Material and methods The preparation and administration guide for i.v. drugs at the paediatric ward was studied to see whether displacement values were actually stated and to establish how the specified drug concentrations of reconstituted powders had been calculated.

For the drugs where displacement values were not stated a description of the drug type was carried out and the size of the deviation between the estimated concentration (where the displacement value was addressed) and the specified concentration was calculated.

Displacement values were obtained through a literature search and by contacting the marketing authorisation holders.

Results Displacement values were taken into account in only 1 in 7 drug powders in the guide, all of them antibiotics, resulting in potential under-dosing ranging from 4–12%.

Conclusion Ignoring displacement values of i.v. antibiotic drug powders for reconstitution can result in under-dosing of children.

References and/or acknowledgements None.

No conflict of interest.