Vitamin B6 in Health Supplements and Neuropathy: Case Series Assessment of Spontaneously Reported Cases

Florence van Hunsel, Sonja van de Koppel, Eugène van Puijenbroek, Agnes Kant

In the literature, vitamin B6 has been linked to the development of polyneuropathy. Most often, these complaints were seen when taking high doses of vitamin B6 for a long time. Evidence as to whether a lower dosage range of vitamin B6 (< 50 mg/day) can also induce neuropathy is scarce. We aim to comprehensively describe the cases of neuropathy associated with vitamin B6 received by the Netherlands Pharmacovigilance Centre Lareb and to assess the case series concerning the use of vitamin B6 and neuropathic complaints. We describe the number and nature of the reported cases, including suspect product, dosage, duration of use, and vitamin B6 serum levels. In addition, we describe the causality for the individual cases (Naranjo Probability Scale) and for the entire case series (Bradford Hill criteria). In total, 90 reports on products containing vitamin B6 included at least one adverse drug reaction in the standardized Medical Dictionary for Regulatory Activities (MedDRA®) query (SMQ; broad) 'peripheral neuropathy'. The amount of vitamin B6 in the products varied between 1.4 and 100 mg per tablet. The serum vitamin B6 level was known in 36 cases (88-4338 nmol/l), and the mean serum vitamin B6 level was 907 nmol/l. However, no statistical correlation between dosage and vitamin B6 blood levels was found. Causality assessment of the case series of 90 reports to Lareb shows it is plausible for the vitamin B6 supplements to have caused complaints such as neuropathies. This is especially the case with higher dosages and prolonged use, but dosages < 50 mg/day also cannot be excluded.