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Displacement value presentation in monographs - October 2016
As monographs are updated, the way displacement values1 are displayed in Medusa monographs
will change.
Background
A national survey undertaken in 2015 found the use of displacement values in paediatrics is
commonplace in the UK. Standardising displacement value information in Medusa monographs was
viewed as ‘very useful’ or ‘preferred’ by 95% of respondents; reasons for this preference were risk
reduction due to errors or misinterpretation (1).
A second study assessed the option of using average displacement values and the potential
impact of this on doses of IV medicines for paediatric and neonatal patients. It concluded that for
the majority of drugs an average displacement value results in a dose difference below 5% and
can be used safely (2).
In view of this Medusa in collaboration with the Neonatal and Paediatric Pharmacist Group has
made the decision to display average displacement values for drugs when the resulting dose
difference is below 5% (see example below). Detailed brand specific displacement value
information will be available through a link embedded in the monograph.
How displacement values will be displayed
The example below for flucloxacillin shows how average displacement values will be shown for
those medicines requiring reconstitution
INSTRUCTIONS FOR RECONSTITUTION
USING THE AVERAGE DISPLACEMENT VALUE
Reconstitute with water for injections (WFI) taking the average displacement value into account. Using the average
displacement value is acceptable as the difference in final concentration achieved is minimal for brands covered in this
monograph.
250mg vial: Average displacement value 0.2mL. Reconstitute with 4.8mL WFI to give 50mg in 1mL (250mg in 5mL)
500mg vial: Average displacement value 0.4ml. Reconstitute with 9.6mL WFI to give 50mg in 1mL (500mg in 10mL)
1gram vial: Average displacement value is 0.6ml. Reconstitute with 19.4mL WFI to give 50mg in 1mL (1gram in 20mL)
USING BRAND SPECIFIC DISPLACEMENT VALUES
If local policy is to use brand specific displacement information follow the reconstitution instructions in the 'linked' table
below.
Table with brand specific
displacement values provided.
Reconstitution instructions to use when use of 'brand specific' displacement values is local practice
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1. N Christiansen, Z Kehk, S Keeling, B Dean A national survey to identify how displacement value
information is used and presented to clinical staff in NHS hospitals Arch Dis Child 2016;101:9 e2
2. N Christiansen, A Lo, H Bhatti The appropriateness of using average displacement values for paediatric
intravenous drug administration Arch Dis Child 2016;101:9 e2
1
When the diluent is added to a powder during reconstitution, the resulting volume of the solution may be greater than the
volume of the diluent added because of the increase in volume caused by the displacement volume of the powder. This
volume is called the displacement value.The ‘displacement value’ is only significant when the dose to be administered to the
patient is only part of the reconstituted vial and is brand specific.