Rx ending in -ex

Yesterday before my eye exam, the doctor's assistant reviewed my Rx list, and got to the meds for migraines. "Still taking I****-ex?" she asked. (Unlike the ads during the national news each evening, I have no desire to spew names of drugs here.) In fact I was now taking a newer drug, beginning in R and ending in -ex, but I only could come up with the one in the middle that we'd briefly tried, and that one began with an N.

But I must've had my mind on church as usual, because I said, "Now I take Narthex." Silence. "I'm not familiar with that one," she said. Then I realized what I'd said. There was no way to back out of it. The funny thing is, I know that she's active at a church. But some of us so immersed in church language can forget that words which naturally spring into our minds don't make sense to others, even if, in some cases, they should.