Maternal plasma concentration of pyridoxal phosphate during pregnancy: adequacy of vitamin B6 supplementation during isoniazid therapy.

Vitamin B6 is an important supplement both for pregnant patients and for those receiving isoniazid. Therefore, we decided to monitor pyridoxal phosphate (PLP) concentrations in 12 pregnant patients who were receiving isoniazid to be certain that supplementation was adequate. Patients were given a prenatal vitamin preparation and 50 mg of pyridoxine hydrochloride daily. At 1 month 10 of the 12 patients had adequate PLP concentrations. Seven of these 10 patients had elevated PLP concentrations and 3 had normal concentrations. Supplementation with 52 to 60 mg per day of Vitamin B6 produces adequate PLP concentrations in pregnant patients who are also taking isoniazid.