How much ephedrine can one give before a patient gets tachyphylaxis?

lets just consider a normal outpatient person, not some depleted ICU patient who's on a bunch of drips for 2 weeks in ICU.

I gave my patient 10mg of ephedrine for low bp. it works. pressure goes down again few mins later, i go to give more ephedrine (heart rate around 70 i think) - new doc stops me and says, give phenylephrine. "haven't you ever heard of tachyphylaxis???"

I said, sure, but not after a one time 10mg hit of ephedrine. He says 'you've depleted your stores, blah blah'.

i've given repeated doses of ephedrine in OB (up to 50 mg total - maybe 5-10mg at a time) and its worked each time.

I tried google with no avail. are there studies showing approx how much ephedrine can be given before it is worthless?