Re: Is this ok?

The kefir will not interfere. And make sure the kefir and bitters are taken at different times. The flora are acid sensitive so you don't want to raise stomach acid significantly when taking the kefir. And some of the herbs commonly found in bitters can also kill the flora.

The bitters will not directly interfere with the medications. But cleansing the liver can cause medications to metabolize faster, so doses may need to be adjusted.