Box 2ADQs

Average Daily Quantities (ADQ) is a measure of prescribing volume based upon prescribing behaviour in England. It represents the assumed average maintenance dose per day for a drug used for its main indication in adults. The ADQ is not a recommended dose but an analytical unit to compare prescribing activity. Defined Daily Doses (DDDs) have been defined by the World Health Organization (WHO) based on international prescribing habits. Work done by the Prescribing Support Unit has demonstrated that the prescribing of general practitioners (GPs) in England can differ from the international standard. To allow comparison of prescribing within England the PSU set about implementing a measure which more accurately reflects GPs prescribing. Hence ADQs were developed by an expert group convened by the PSU.

The following information is considered when defining an Average Daily Quantity:

  • The Defined Daily Dose (if one is available)

The World Health Organization Advisory Group have much experience in this area and have access to a variety of data sources when defining values. However, it should be noted that DDDs are an international compromise and do not necessarily accurately reflect prescribing patterns in England.

  • The Prescribed Daily Dose (PDD) (if available)

When calculated on a large enough sample of items, this should also be considered, as it reflects the actual usage by GPs. However, it may well be that the single value Prescribed Daily Dose hides a wide variation in prescribing practice, again stressing the nature of the Prescribed Daily Dose and the subsequent ADQs as being analytical units.

  • Prescription Pricing Division of the Business Services Authority (PPDBSA) data

This gives the number of items prescribed by particular quantities of each drug preparation. This information source has the advantage of being based on every prescription dispensed in England but the disadvantage of not including the intended duration for the item, making the calculation of an accurate Prescribed Daily Dose impossible.

  • British National Formulary (BNF) information

Regarding dosage, particularly for maintenance doses.

  • Whenever possible, therapeutic equivalence between drugs of the same therapeutic type is sought

However, where there is a discrepancy between actual usage as suggested by the PDD, PPDBSA and BNF data sources and equivalence data from clinical research, then the actual usage is given priority. The expert group stresses that these discrepancies should be kept to a minimum and that when they occur, should be noted in any disseminated information regarding the ADQs.

An ADQ is set only with the agreement of all members of the expert group, and are reviewed on a regular basis, thus reflecting any changes in drug utilisation and the introduction of new drugs.

Source: PSU, (Anon 2007b)

From: Appendix D, Details of the NSAID/COX-2 inhibitor health economic model

Cover of Osteoarthritis
Osteoarthritis: National Clinical Guideline for Care and Management in Adults.
NICE Clinical Guidelines, No. 59.
National Collaborating Centre for Chronic Conditions (UK).
Copyright © 2008, Royal College of Physicians of London.

All rights reserved. No part of this publication may be reproduced in any form (including photocopying or storing it in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright owner. Applications for the copyright owner’s written permission to reproduce any part of this publication should be addressed to the publisher.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.