In the US, tenapanor has been licensed for IBS-C. It is a retainagogue, a new class of compounds which block sodium uptake in the gut by inhibiting the sodium-hydrogen exchanger NHE3. This results in more water remaining in the intestine, speeding up intestinal transit time with softer bowel movements. It may also reduce pain and bloating.^22,23

Rifaximin is an antibiotic which is not absorbed to any great extent from the gut. Its UK license authorisations are for traveller’s diarrhoea and for hepatic encephalopathy, but in the US it has also been approved for IBS-D. If it is going to be effective, the patient should see IBS symptom improvement within two weeks.^23,24,25