Barriers and enablers to switching from a solid to a liquid formulation of Parkinson's medication: a theory-based mixed methods investigation

Background: Swallowing tablets/capsules can become difficult and dangerous for People with Parkinson’s (PwP) who develop oropharyngeal dysphagia. Switching to a liquid delays the need for progressing to last line patches/injections. However, liquids are rarely used therefore a change in prescribing practice is warranted but, as with any change in behaviour, may be met with resistance. Aim: To characterise PwPs and carers’ barriers and enablers (determinants) of switching from solid to liquid Parkinson’s medication formulations. Method: Underpinned by the Theoretical Domains Framework, focus groups with PwPs and carers were convened to identify determinants of switching, which were then used to develop a questionnaire distributed across the UK. Determinants were prioritised if ≥ 50% of respondents agreed/strongly agreed that they were important to their decision to switch to a liquid formulation. Percentage precisions were reported as 95% confidence intervals. Results: From three focus groups and 131 questionnaires responses, PwPs and carers prioritised nine determinants. Three enablers had almost unanimous agreement: liquids’ flexibility for incremental dosing (72% ± 8); decline in Parkinson’s control (72% ± 8); prescriber’s endorsement to switch (70% ± 8). The barriers: perception that tablets/capsules are easier to dose than liquids (72% ± 8); and prescriber’s opposition to switching (70% ± 8), attracted similarly high agreement. Conclusion: There is a desire to switch to liquids when Parkinson’s progresses and for their use beyond this to offer flexibility in dosing, a previously unrecognised indication for switching. The only notable resistance to switching may be addressed by innovations from the pharmaceutical industry to make liquids easier to measure.