The time between updates or new editions of the formulary will depend upon:

- frequency of changes in information and the importance of the new information requiring changes to the NF;

- availability of resources for review tasks, publishing and implementation.

Generally formularies undergo major revisions every 2-3 years. After 5 years it is likely that there will be a substantial amount of information in the formulary that is outdated; therefore it is important to complete reviews at least every 4-5 years. The WMF is scheduled for revision every 2 years (even years, e.g. 2004 and 2006). In countries without an EML or guidelines, the electronic release of subsequent editions of the WMF can start the NF review process, depending on availability of resources and the need for revisions.

In those countries where an EML and national treatment guidelines are regularly reviewed it is best to link the review of the NF to these events and to the release of revised editions of the WMF.

The British national formulary has an ongoing review process which results in updated editions being produced every 6 months. This short publication cycle is a based on a very well-structured and clearly defined operational process, supported by the work of the Joint Formulary Committee, the large and well-qualified editorial team and more than 50 expert clinical advisers, as well as substantial financial resources.

In many other countries with fewer resources, the NF review and production process is likely to require a significantly longer time, at least between 8 and 12 months, to publish a revised edition. This means that a biannual review should start approximately 1 year after the release of the first publication. Good planning with adequate resources can help to achieve a reasonably regular publication cycle.