Background: Metronidazole is often administered to patients with irritable bowel syndrome with an erroneous diagnosis of 'chronic amebiasis'.
Aims: To assess how patients with irritable bowel syndrome respond to metronidazole in the absence of amebae in their stools.
Methods: We randomly allocated 45 patients (35 men; aged 15-59 years) with irritable bowel syndrome to receive isapghul (10 g bid x 60 days), metronidazole (400 mg tid X 10 days, followed by placebo x 50 days), or placebo (1 capsule bid x 60 days). Symptoms were evaluated and scored on days 0, 15, 30, 45 and 60. Rectosigmoid manometry was performed in 5 of 15 patients in each group on days 0 and 60.
Results: There was a significant time effect and treatment effect on the symptom scores in all groups (isapghul > metronidazole > placebo); total score decreased from mean 25.8, 24.0 and 24.6 on day 0 to 7.2, 10.9 and 18.1 on day 60, respectively. Severity, duration and frequency of pain; and mucus in stool were all significantly reduced in all treatment groups (p < 0.001 for each). Treatment with isapghul increased the mean amplitude of propagated activity from 26.2 mmHg to 30.1 mmHg at 20 cm (p < 0.025) and from 23.1 mmHg to 27.4 mmHg at 10 cm (p < 0.05) from the anal verge, as well as the total duration of propagated activity at both sites (p < 0.05), with decrease in number of propagated contractions per 10 min (p < 0.025). Metronidazole and placebo had no effect on manometric findings.
Conclusions: Metronidazole provides symptom relief in irritable bowel syndrome, without affecting rectosigmoid motility. This symptom response may be misinterpreted as supporting a diagnosis of 'chronic amebiasis'.