Table 6.

Chemical and clinical characteristics of drugs approved for other gastrointestinal indications and currently investigated for constipation-predominant irritable bowel syndrome

	Itopride	Neomycin/Rifaximin
Brand name	Ganaton®	Neomycin: Neo-Fradin®
		Rifaximin: Xifaxan®
Chemical structure	Benzamide derivative	Neomycin: aminoglycoside
		Rifaximin: semisynthetic antibiotic based on rifampicin
Mechanism of action	Dopamine D2 antagonist and acetylcholinesterase inhibitor	Neomycin: inhibition of protein synthesis
		Rifaximin: inhibition of bacterial RNA synthesis
Pharmacodynamic effects	Gastrokinetic;	Eradication of methane; accelerated intestinal transit (?)
	Acceleration of intestinal transit (?)
Most common adverse events	Diarrhea	Neomycin:
	Headache	Neurotoxicity
	Hyperprolactinemia	Ototoxicity
		Nephrotoxicity
		Rifaximin:
		Headache
		Nausea
		Dizziness
		Fatigue
Approval status/stage of development	Approved in Japan for functional dyspepsia;	FDA-approved for hepatic encephalopathy and traveler’s diarrhea;
	Phase 2 RCT in IBS-C completed in the United States	Phase 2 efficacy RCT in methane + IBS-C patients, comparing neomycin vs combination rifaximin and neomycin (completed)

FDA: Food and Drug Administration; IBS-C: Constipation-predominant irritable bowel syndrome; RCT: Randomized controlled trial.