Measure volume in DDDs or ADQs

[stupidpupil]

The HSCIC's guide to Prescribing Measures says

Historically, the number of items was used as a measure of volume. However, for areas of prescribing where there is a good deal of repeat prescribing, the number of items can be misleading because different practices use a different duration of supply, i.e. some will issue a prescription monthly, others for two months or three months and so will have different numbers of items for the same amount of medication. Even within a single practice there can be differences in the duration of prescriptions. … The system of Defined Daily Doses (DDDs), developed and maintained by the World Health Organisation (WHO), attempts to overcome these limitations. In this system each drug is given a value, within its recognised dosage range, that represents the assumed average maintenance dose per day for a drug used for its main indication in adults. It is emphasised that the DDD is a unit of measurement; it is not a recommended dose and may not be a real dose. … To allow comparison of prescribing within England there is a need to have a system which more accurately reflects primary care prescribing. To meet this need Average Daily Quantities (ADQs) have been developed by an expert group convened by the PSU.

ADQs and DDDs are commonly used in prescribing measures, indicators and comparators, both public and internal. They are generally supported, to some extent, by internal prescribing measurement applications like ePACT.net (used in England) and CASPA.net (used in Wales).

For these reasons it would be useful to support ADQs and/or DDDs in OpenPrescribing.

Where can we find ADQs or DDDs?

Defined Daily Doses (DDDs) can be looked individually up online. That states "Use of all or parts of the material requires reference to the WHO Collaborating Centre for Drug Statistics Methodology. Copying and distribution for commercial purposes is not allowed. Changing or manipulating the material is not allowed." (The German Institute of Medical Documentation and Information (DIMDI) makes their own adaptation of the WHO DDDs 'freely' available.)

Average Daily Quantities (ADQs) can be found on the HSCIC website. That document states "This work remains the sole and exclusive property of [HSCIC] and may only be reproduced where there is explicit reference to the ownership of The NHS Information Centre. Permission for reproducing this material must be sought in advance from The NHS Information Centre."

As can be seen, there are some intellectual property issues that need to be at least clarified before either of these sources can be used.

How do we calculate volume in ADQs or DDDs?

There are two problems to be solved in order to calculate ADQs or DDDs:

1. Determining which, if any, ADQ/DDD applies to the Presentation.
2. Determining the amount of the Presentation in the units of the ADQ/DDD.

In the case of DDDs, the first involves mapping BNF Presentations to codes in the Anatomical Therapeutic Chemical Classification System. I am not aware of any freely available mapping. (See The Detail's report of prescribing for an example of such mappings.)

In the case of ADQs, the first seems more straightforward. The HSCIC document linked above identifies that the relevant ADQ for a presentation usually depends only on the BNF Chemical and the route of administration. Some ADQs are more specific regarding the form of the presentation (aerosol vs. solution, for example) but the small number of relevant presentations could be identified manually.

I have opened #4 to look at how the given BNF Name for a presentation might be used to extract both the route of administration and the amount in the units of the relevant ADQ.

How do we make volume in ADQs or DDDs available?

Volume in ADQs or DDDs should be made available in the user interface and the API alongside the current measures of items and spend. This is complicated by the fact that not every presentation will have an ADQ or DDD defined and, as a consequence, it won't always be possible to measure volume in ADQs or DDDs for all of any Chapter, Section or even Chemical.

[annapowellsmith]

Thanks for this, really helpful.

It sounds like the next steps are (i) to clarify the intellectual property issues (ii) to talk to our users about the priority of adding ADQs/DDDs, versus other things.

We're going to be discussing new features in the new year.

In the meantime, I'll contact the NHS IC to see if they'd object in principle to us using ADQs. I'll ask them also if they know of any open data on units etc for BNF presentation codes. Will report back here.

It sounds to me like using DDDs should be OK, since we're not commercial, and we're not changing the data.

[stupidpupil]

I've been told by Primary Care Services in NHS Wales that they hold a mapping between BNF presentation codes and their volume in ADQs (and possibly DDDs?), and that they think they can make this freely available. I've not had much in the way of details yet unfortunately.

[stupidpupil]

I've just noticed that the Welsh data now seems to include pre-calculated ADQs and DDDs for each record.

(This is something that I discussed with the NHS Wales team involved a year ago but, since they never got back to me about it, I wonder if someone else asked for it as well..)