Haven't tried it but they keep just chucking these selective serotonin 5-HT3 receptor antagonists at it and quoting a "good responder rate" as the major positive. In other words, it ain't no cure!
Something a bit different I saw aimed at IBS-D is xyloglucan (e.g. Gelsectan). This is a film-forming protein based mucoprotectant (water-soluble, polysaccharide hemicellulose that is extracted from the seeds of the tamarind tree) which is not broken down by digestive enzymes. The barrier over the intestinal mucosa helps to reduce the effect of pathogens and to improve the function of the intestinal barrier. It is often combined with gelatin (tannate) to prolong its availability within the intestine.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4628347/
Products containing this aren't widely available though, only in Europe at the moment by the looks.