The Suitability of End Point Designs for Health Technology Assessment in Chronic Pain Studies

To identify the pain instruments and study end points most commonly used in clinical trial settings and to provide insight into the extent to which outcome measures in clinical studies are meeting payer needs.

A literature review was conducted to identify published clinical studies and ongoing/recently completed registered trials in chronic pain. Inclusion criteria were interventional study, chronic pain in adults, and pain measured within the primary end point.

Of 1256 PubMed citations and 3006 clinical trial registry entries, 356 reported large clinical studies in pain populations (e.g., malignant, neuropathic, functional, and musculoskeletal). Studies were designed for superiority in 28% of PubMed citations and 8% of registry entries. The primary end points of most studies were single-dimension pain instruments, such as the numerical rating scale (n = 131) and the visual analogue scale (n = 69). In cases in which multidimensional pain end points were used, this was most commonly the Brief Pain Inventory (n = 37). Payer-relevant end points were typically limited to secondary end points, and were limited and/or reported inconsistently in published studies and ongoing/recently completed studies: preference-weighted quality of life (36% and 42%), resource use (2% and 8%), physical function (28% and 39%), and psychological function (25% and 24%).

Most pain trials were not designed to show superiority to an active comparator, and they used single-dimension pain scales as their primary end point in combination with a broader selection of secondary end points. The inclusion of payer-relevant end points among clinical trials was inconsistent.