Metformin therapy and assessment for vitamin B12 deficiency: is it necessary?

Abstract

AbstractMetformin therapy in type 2 diabetes mellitus (T2DM) has been recognised as a cause of vitamin B12 deficiency for at least 40 years, but routine measurement is not currently advocated in clinical guidelines. Assessment might be of particular relevance in T2DM complicated by peripheral neuropathy.This service review examined whether serum vitamin B12 levels were measured in patients with high dose (>2g/day) and long‐term (four years) metformin treatment, in particular among those with peripheral neuropathy. We also evaluated the effectiveness of vitamin B12 replacement when levels were low.Of 283 patients on high dose metformin for more than four years only, 70 (25%) had vitamin B12 levels checked. All of these 70 cases had peripheral neuropathy. Vitamin B12 deficiency (<150pg/ml) was recorded in 23 (33%). Where vitamin B12 levels were deficient, replacement vitamin B12 was documented in only two (2.9%) patients and improvement in neuropathic symptoms post treatment were documented in only four (5.7%) patients.Conclusion: vitamin B12 levels were measured infrequently in T2DM, in particular among those with peripheral neuropathy. Levels were frequently low when assessed among T2DM patients with peripheral neuropathy. A record that vitamin B12 therapy was initiated was only made in a small number of cases, so the impact on peripheral neuropathy was unclear.Recommendations: all patients with T2DM on long‐term treatment with high dose metformin should be assessed for vitamin B12 deficiency, particularly if complicated by peripheral neuropathy, and then considered for parenteral vitamin B12 replacement if deficient. Copyright © 2011 John Wiley & Sons.