We give IV Phenergan all the time. I've never diluted it, but I always give in with a wide open running IV and I push it slowly. I've never had anyone have a bad reaction to it in 16 years of nursing. I have, however, had several people become anxious, nasty, restless, shouting, etc... several times with Reglan. We give Benadryl, and the symptoms go away. I personally think Phenergan and Zofran work the best for nausea. That's been my experience anyway.