Impact of the MHRA safety update on vitamin B12 testing and coding in metformin users: a retrospective primary care analysis
Abstract
BACKGROUND: Metformin is the most commonly prescribed oral treatment for type 2 diabetes mellitus (T2DM) in the UK. Long-term therapy has been linked to vitamin B12 deficiency, a concern recognised for decades but not consistently addressed. In June 2022, the UK Medicines and Healthcare products Regulatory Agency (MHRA) classified low vitamin B12 levels as a common adverse effect of metformin and advised clinicians to consider periodic testing in at-risk patients. Translating such regulatory advice into practice can be challenging, and the extent to which the guidance has influenced testing and diagnostic coding for vitamin B12 deficiency remains unclear. This study evaluated trends in vitamin B12 testing and deficiency coding in metformin-treated patients compared with the general population before and after the 2022 MHRA Drug Safety Update.
METHODS: A retrospective quantitative analysis was conducted using Read code data from 148,000 electronic medical records across three Primary Care Networks (PCNs) in the Southwest of England. Vitamin B12 testing and deficiency coding rates were compared in patients prescribed metformin and the general population across two periods: pre-guidance (2017-2021) and post-guidance (2022-2024). Welch's t-tests were used to determine statistical significance, with p < 0.05 considered significant.
RESULTS: Among patients prescribed metformin, vitamin B12 testing rates rose from 34.5% (SD = 1.8) pre-guidance to 38.2% (SD = 0.4) post-guidance (p =…
How strong is the evidence?
Evidence Hub reads this as a cohort study, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence.
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