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.