Use of prescribing indicators as a means of identifying variation in the prevalence of valproate prescribing between health communities: a cross-sectional study.

Objective: To determine the appropriateness of valproate prescribing indicators in England and Wales as a means of identifying variation in the prevalence of valproate use among women and girls of childbearing potential between health communities.

Methods and analysis: Cross-sectional study using an ecological design using routinely published, publicly available valproate prescribing data for the period January to March 2019 and 2018 mid-year population estimates.

Results: In England and Wales, 87.7 people in every 1000 people prescribed valproate were women or girls aged 14-45 years (range 60.4-133.2). The prevalence of valproate use among all women and girls of childbearing age was 1.49 cases per 1000 women and girls aged 14-45 years (range 0.47-3.13). Considerable variation in prevalence was observed depending on which of two measures was used. The relative risk of exposure between health communities increased from 2.2 to 6.6 depending on the measure used, leading to the identification of different health communities being a priority for action. Wide variation was observed in the prevalence of valproate use among individuals other than women and girls aged 14-45 years (mean prevalence 3.89 cases per 1000 population, range 2.42-7.78). The prevalence of valproate use in all Clinical Commissioning Groups and Local Health Boards was lower in the at-risk population than in the rest of the population (p=0.046) with a strong positive correlation observed between the prevalence of valproate use in these two groups (p<0.001).

Conclusion: Current indicators may lead to a failure to systematically review women and girls of childbearing age prescribed valproate. Urgent consideration should be given to changing the indicators used in England and Wales.