Secondary vitamin B6 deficiency most often results from Protein-energy undernutrition Malabsorption Alcohol use disorder Use of pyridoxine - inactivating drugs (eg, antiseizure drugs, isoniazid, cycloserine, hydralazine, corticosteroids, penicillamine) Excessive loss during hemodialysis Rarely, secondary deficiency results from increased metabolic demand (eg, in hyperthyroidism).