Rifaximin

What this does, mechanistically

Rifaximin is a non-absorbable rifamycin. It binds bacterial RNA polymerase and blocks transcription. Because almost none of it crosses the intestinal wall, the pharmacologic effect stays in the lumen. The result is a short-window reduction in small-intestinal bacterial density.

Where it fits in the Host Capacity Model

Rifaximin acts on the microbiome axis. It also, secondarily, lowers barrier-side immune activation by reducing the antigenic load the barrier is seeing. It does nothing for the upstream lesion in recurrent SIBO, which sits at the colonocyte bioenergetics layer: a colonocyte that cannot keep the lumen anaerobic permits the same overgrowth as soon as antimicrobial pressure lifts.

Common patterns of response

• Symptom relief within 7–14 days, then full relapse within 2–6 months. The dominant pattern in recurrent SIBO. It is what the data predict.
• Partial response, residual methane. Archaea are not the rifaximin target. Methane-dominant patterns often need a second agent or, more productively, a different question about the host.
• No response at all. Usually means the breath test was reading a pattern that was not actually bacterial fermentation in the small bowel (fast transit, oral contamination, sulfur-reducer pattern).

When it can backfire

Rifaximin used repeatedly as a stand-alone strategy stalls the case. Each round buys less time than the last, because the host condition has not moved. Patients arrive in their fourth or fifth round convinced the drug has stopped working. The drug has not stopped working. The host has not changed.

What to run alongside it

The rifaximin window is the time to do the host work that prevents the next overgrowth. That means butyrate substrate for the colonocyte, oxygen-gradient restoration, and prokinetic support if motility is the dominant axis. If you do not use the window, you are just buying a few months.

How it interacts with related items

• Butyrate during and after rifaximin gives the colonocyte the substrate it needs to resume β-oxidation and re-establish the oxygen gradient that keeps the lumen anaerobic.
• Prokinetics (low-dose erythromycin, prucalopride) extend the symptom-free window when motility is part of the picture.
• LDN has no direct antimicrobial effect but, in patients where neuroimmune tone is part of the relapse mechanism, can shift the host condition that permitted the original overgrowth.