The effect of fibre, antispasmodics, and peppermint oil in the treatment of irritable bowel syndrome (IBS) has been examined in a systematic review and meta-analysis of RCTs.

From a search of Medline (1950 to April 2008), Embase (1980 to April 2008), and the Cochrane controlled trials register (2007), 38 studies were eligible for inclusion in the systematic review:

• 12 compared fibre with placebo or no treatment (n = 591)
• 22 compared antispasmodics with placebo (n = 1778)
• 4 compared peppermint oil with placebo (n = 392)

The primary outcomes assessed were efficacy compared with placebo or no treatment on global symptoms of IBS or abdominal pain after treatment. Secondary outcomes included efficacy according to specific type of fibre or antispasmodic, and adverse events as a result of treatment. The following findings were reported:

Fibre

• 155 of 300 (52%) patients assigned to fibre had persistent or unimproved symptoms after treatment compared with 168 of 291 (57%) on placebo or a low fibre diet (relative risk 0.87, 95% CI, 0.76 to 1.00, p = 0.05, NNT = 11).

• When only seven studies scoring 4 or more on the Jadad scale were considered in the analysis the treatment effect for fibre was no longer statistically significant (0.90, 0.75 to 1.08).

• Bran had no statistically significant effect on IBS compared with placebo or a low fibre diet.

• The beneficial effect of fibre seemed to be limited to ispaghula husk (0.78, 0.63 to 0.96, NNT = 6), but these findings only marginal statistical significance when only high quality studies were considered in the analysis.

• Only 4 trials provided data on total number of adverse events and as the number of reported was small, the data were not pooled.

Antispasmodics

• 350 of 905 (39%) patients assigned to antispasmodics had persistent symptoms after treatment compared with 485 of 873 (56%) allocated to placebo (0.68, 0.57 to 0.81, NNT = 5). There was however significant heterogeneity between study results and there was evidence of publication bias.

• The best evidence for an individual drug seemed to be for hyoscine (0.63, 0.51 to 0.78, NNT = 3.5).

• Thirteen studies reported a total number of adverse events in 1379 patients; overall, 101 of 704 (14%) patients on antispasmodics experienced adverse events compared with 62 of 675 (9%) on placebo. The commonest adverse events were dry mouth, dizziness, and blurred vision (relative risk of experiencing adverse events with antispasmodics vs. placebo was 1.62 (1.05 to 2.50), NNH = 17.5).

• Data were limited for many of the drugs licensed for use in the UK, such as mebeverine, dicycloverine, and alverine, therefore it is difficult to know whether this is a true class effect of antispasmodics.

Peppermint oil

• As only four RCTs were identified including fewer than 400 patients, the data were more limited than for fibre and antispasmodics.

• 52 of 197 (26%) patients randomised to peppermint oil had persistent symptoms compared with 127 of 195 (65%) receiving placebo (0.43, 0.32 to 0.59, NNT = 2.5).

• Adverse event data were not pooled as only three studies reported data on adverse events and these were few in number.

The researchers conclude from these findings that all three interventions were more effective than placebo in the treatment of IBS, and doctors should therefore consider ispaghula, antispasmodics (preferably hyoscine as first line treatment), and peppermint oil to treat this condition.

Though the best evidence of efficacy for antispasmodics was for hyoscine butylbromide, it is not widely used in primary care in the UK at present, with 10 times more prescriptions being written for mebeverine. Peppermint oil seems to be the most promising agent though there are less data on its use. Limitations of the meta-analysis include the lack of information on the subtype of IBS, drug dosage, and patterns of administration. In addition, the analysis does not provide guidance on patient selection for particular agents, which limits the implementation of the findings. The author of the editorial concludes “it may be a little premature to follow the authors’ recommendation that national guidelines should be updated to include therapeutic guidance on these agents, but the results should reawaken an interest in the pharmacotherapy of irritable bowel syndrome and stimulate further research.”

A Behind the Headlines assessment from NHS Choices discusses the study (please see the link below).