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.