A dose standardisation experiment: Application to monoclonal antibodies
During reorganisation of the system by which the preparation of Monoclonal Antibodies (MAs) is handled by the pharmacy department, it was decided that we should round off the doses to be prepared using the concept of ‘dose banding’. This decision was motivated by the practice common among doctors of rounding up or down doses to the nearest flask, and by our wish to reduce the number of different doses prepared in order to make it easier to manage non-administered treatments.
The purpose of this study is to identify a method for determining the appropriate policy for rounding off doses.
For each MA, determination of the rounded dose and the boundaries of each band was based upon two criteria:
- the technical feasibility of the preparation, taking into account the smallest volume which can be withdrawn, depending upon the type of syringe used,
- remaining within a margin of 5% difference between the theoretical dose (TD) prescribed and the proposed rounded dose.
The volumes to be withdrawn allow for rounding off to multiples of 0.5 or 1ml. For each TD, the maximum permissible error is calculated with reference to the different possible rounded doses. These correspond to multiples of concentration of the parent solutions which are, respectively, 5, 10, 20, 21 and 25m mg/ml for cetuximab (C), rituximab (R), panitumumab (P), trastuzumab (T) and bevacizumab (B). The TD band should be as wide as possible, in order to limit the number of doses to be prepared.
The rounding-off figures retained were 25mg for B (hence to the nearest ml, max discrepancy: 3.2%), 50mg for C (nearest 10ml, max discrepancy: 3.9%), 20mg for P (nearest ml, max discrepancy: 3%), 50mg for R (nearest 5ml, max discrepancy: 4.1%), and 42mg for T (nearest 2ml, max discrepancy: 5%).
After more than 3 months of MA preparations, we received no negative feedback on the new ‘dose banding’ policy. We now round off our measurements during prescription validation in the pharmacy. We are currently investigating the possibility of extending this policy to cytotoxics, on the condition that the rounded doses are decided automatically.