Cost-effectiveness of low-dose amitriptyline for irritable bowel syndrome in primary care

Objective

General practitioners may not prescribe amitriptyline for irritable bowel syndrome (IBS) despite using it for other chronic conditions. The Amitriptyline at Low-Dose and Titrated for Irritable Bowel Syndrome as Second-Line Treatment (ATLANTIS) trial found low-dose titrated amitriptyline was a safe and clinically effective second-line treatment for IBS in primary care. We undertook a prespecified cost-effectiveness analysis of ATLANTIS trial data.

Design/method

Complete case (CC) and a full population (FP) analysis using multiply imputed data with analyses at 6 (365 participants CC, 463 participants FP) and 12 (224 participants CC, 291 participants FP) months. As the trial was not fully randomised between 6 and 12 months, we adopted inverse probability weighting to mitigate potential impact of participants choosing to continue trial medication.

Results

At a 6-month time horizon, CC analysis demonstrated low-dose amitriptyline was more likely to be cost-effective than not (incremental net health benefit (NHB) 0.0029 quality-adjusted life years (QALYs)/person, low-dose amitriptyline dominant, 67.3% probability cost-effective), but not FP analysis. At 12 months, all analyses demonstrated low-dose amitriptyline was more likely to be cost-effective than not (CC: incremental NHB 0.00757 QALYs/person, low-dose amitriptyline dominant, 81.7% probability cost-effective; FP: incremental NHB 0.00388 QALYs/person, low-dose amitriptyline dominant, 68.7% probability cost-effective).

Conclusion

In addition to the clinical benefit, safety and acceptability of low-dose amitriptyline in patients with IBS found in the ATLANTIS trial, these results indicate this inexpensive medication is likely to be cost-effective as a second-line treatment for IBS in primary care over 12 months. This strengthens amitriptyline as a treatment option for people with ongoing IBS symptoms.