As per the Institute of Medicine, “Normally, the major excretory product is 4-PA, which accounts for about half the B6 compounds in urine (Shultz and Leklem, 1981). Other forms of the vitamin are also found in urine. With large doses of B6, the proportion of the other forms of the vitamin increases. At very high doses of PN, much of the dose is excreted unchanged in the urine.” ….
Read more: Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline.