Malabsorption of vitamin B12 in diabetic patients treated with phenformin: a comparison with metformin.

An investigation into B(12) absorption in diabetic patients on long-term phenformin therapy was undertaken and the results were compared to a similar investigation previously reported in diabetics on long-term metformin. Forty-six per cent of patients were found to have B(12) malabsorption as shown by abnormal results of Schilling tests.The mechanism of B(12) malabsorption is unknown but it is suggested that all patients on long-term phenformin therapy should, like the patients on metformin, have annual serum B(12) estimations until the results of a longer follow-up series are known.