See Dehydrating Event.
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https://www.ncbi.nlm.nih.gov/books/NBK114313/
NCBI Bookshelf on Vitamin B6. Excretion section. “Normally, the major excretory product is 4-PA, which accounts for about half the B6 compounds in the 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.
With dehydration, our body conserves water by holding on to urine. We are not urinating out the very large doses of PN.