OTC drug treatments
Drug treatment for IBS is usually directed at the most predominant symptom. Patients mainly experiencing constipation may be treated with laxatives, and patients mainly experiencing cramping pains with antispasmodics.
The research into IBS provides limited evidence. This is because drug trials are usually short, rarely more than 12 weeks in length, and there is often a strong placebo response so differences between active treatment and placebo may be small. It is important to explain to patients that they may need to try various therapies until they find those that suit them best. Click on the treatments below to read more.
Traditionally, patients with IBS were advised to eat a diet high in fibre, and raw wheat bran was often recommended as a way of increasing the fibre intake. However, bran, which is an insoluble fibre, is no longer recommended as it has been shown to aggravate symptoms.
Oats and oat bran are more soluble than wheat bran and are better tolerated. Bulk-forming laxatives containing soluble fibre, such as ispaghula husk or sterculia, act by retaining fluid within the stool and increasing faecal mass, stimulating peristalsis and also have stool-softening properties. It may take a few weeks of experimentation to find a dose that suits the individual patient. Remind the patient to increase fluid intake to account for the additional fibre intake.
Osmotic and stimulant laxatives are sometimes used, but these may aggravate the condition and evidence in IBS is poor. Ideally their use should be under medical supervision. Lactulose is generally avoided as it can cause bloating.
In August 2020, the MHRA introduced new restrictions regarding the supply of laxatives. Find out more in TM’s module on managing constipation.
Antispasmodics
Antispasmodics are the mainstay of over-the-counter (OTC) treatment of IBS, and research trials show some improvement in abdominal pain and cramps. The smooth muscle relaxants alverine, peppermint oil and mebeverine and the antimuscarinic hyoscine are available OTC. They work by a direct effect on the smooth muscle of the gut, causing relaxation and thus reducing abdominal pain.
If these are to be tried for the first time, the patient should see an improvement within a few days and should be asked to return in a week or so to monitor progress. It may be worth trying a different antispasmodic if the first has not worked.
Patients who complain of diarrhoea may describe a frequent urge to pass stools that may be loose and poorly formed rather than watery. The main drug used for these symptoms is the anti-motility drug loperamide, which can be used on an occasional, short-term basis to reduce diarrhoea or urgency of defaecation. For use in IBS, it is licensed for people aged 18 years and over, only where a doctor has already made a diagnosis of IBS.
An important caution is to advise the person not to exceed the recommended daily dose or duration as cardiac arrhythmia has been reported in association with overdose.