Selection of outcome measurement instruments for a core outcome set for trials aimed at improving appropriate polypharmacy in older people in primary care: a Delphi consensus study.

Background: Despite developing a polypharmacy core outcome set (COS) in primary care, it is not clear how these outcomes should be measured.

Aim: To select outcome measurement instruments (OMIs) for a COS targeting appropriate polypharmacy in older patients in primary care.

Method: Following the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) guideline, OMIs were identified from a Cochrane review focusing on appropriate polypharmacy. The quality of OMIs was assessed using a published checklist. Subsequently, two rounds of Delphi questionnaires were conducted via the SoGoSurvey^® platform, engaging stakeholders (researchers, clinicians and journal editors specialising in geriatric primary care) to achieve consensus on OMIs using a scale encompassing "agree", "disagree", or "unsure". Consensus was achieved if 70% or more participants chose "agree" and 15% or fewer chose "disagree."

Results: The quality of 20 OMIs identified from the Cochrane review was evaluated. Seven OMIs were selected based on meeting the COSMIN guideline's minimum requirements. Out of 188 potential participants, 57 (30.3%) consented to participate. Rounds 1 and 2 of Delphi exercises were completed by 50 respondents, achieving agreement on three OMIs: 'number of serious adverse drug reactions (ADRs)' (98%), 'number of deaths' (76%), and 'number of patients who fell' (70%) for measuring 'serious ADRs,' 'mortality,' and 'falls,' respectively. No agreement was reached for 'medication appropriateness,' 'medication side-effects,' 'quality of life,' and 'medication regimen complexity.'

Conclusion: OMIs were selected for a limited number of outcomes in the polypharmacy COS. Future research should identify suitable OMIs for the remaining four outcomes.