For what it's worth, here's my routine:
Front load drinking water in the morning - get ahead of it early
Eat half of lunch, take meds, eat rest of lunch (at about noon, everyday)
After lunch, curtail water until around 2p, to let the Rx activate in my stomach. Then start up again - to get about 72 oz per day total water. I really have to work at that!
No OTC stomach meds, no grapefruit, no supplements
Fairly clean, healthy diet
Frequent exercise & active yoga
If I don't get enough water, I do get a bit of a headache.
Thanks for the encouragement - I will keep up the regimen!