Hi mfrfr. We had a similar experience -- the hubby had completed 10 mo tx for babs (mepron/zith), then tx for bart (levaquin), while doing tx for Bb (bicillin, still on it). Had 2 great months, then relapsed horribly. Definitely a babs relapse in his case.He's now doing mepron/ketek again, with tinidazole for the protozoal tissue form (I believe) as well as for Bb, and bicillin. Recovering well, but not nearly up to par with the 2 months of feeling good. Both tinidazole and mepron seem to cause horrendous fatigue.
The lesson for us was -- babs is very recalcitrant, and does enormous damage. I now think that much of what we thought was Bb was babs. We're pretty sure the bart has not come back.
Have no experience with Rifampin; other options for bart that I know of are the quinolones (scary, but worked for the hubby), and gentomycin (also a little scary).
We found flagyl very hard to deal with, too. Tinidazole has been easier, but the fatigue it causes is still crushing for both of us.
Our LLMD says he hasn't had much luck with the quinine/clinda combo for babs, but I know some folks here think they kicked it with that. Several months doesn't seem enough for babs on this combo, though.
As far as backsliding while actually on the babs meds -- I dunno. Could be so many things, including a flare (since he was doing so much more physical activity), resistance, massive die off, reaction to the meds themselves...So frustrating and disheartening!
Our experience of such backsliding has been that the coinfections were insufficiently treated, and came roaring back, often re-awakening the Lyme sx. Detox (especially liver and colon), the steam sauna, and step-by-step re-treatment have been successful for us (in so far as we are successful -- we're much better than we were, and we were about as sick as you can be. We're not well yet, but much much more functional. We've been working with our current LLMD for a year).
One other possibility is, as always, yeast. We found that it was a big factor in previous episodes of nausea, fatigue, and mental weirdness.
Please let your hubby know that we've fallen into that dreadful relapse hole ourselves, and deeply sympathize. Recovery is definitely possible. And I'm sending a hug for you too -- so hard to watch someone go through this. And so frightening to revisit the vast and unmapped landscape of severe illness.
I'm very interested in the serrapeptase -- thanks for the link, C-in-P.