Background and Importance Prescribing cascades occur when an unrecognised adverse drug reaction (ADR) leads to the initiation of additional medication, contributing to polypharmacy. It remains unclear whether prescribing cascades are initiated by physicians from specialties other than the initial prescriber. This study focuses on amiodarone and lithium, two medications exclusively initiated in hospitals, while the ADR thyroid dysfunction occurs in primary care (median: after two years).

Aim and Objectives To assess whether the specialty of the physician initiating amiodarone or lithium differs from the specialty of the physician initiating the thyroid medication.

Material and Methods A retrospective study was conducted (two teaching hospitals and 22 community pharmacies). Patients initiating amiodarone or lithium (index) and subsequently receiving thyroid medication (marker) within 24 months were included. The primary outcome was the proportion of different specialties initiating the index and marker medication. Secondary outcomes included the recognition of prescribing cascades in hospitals, communication of the ADR to general practitioners (GPs) through discharge letters, and the knowledge of these cascades among community pharmacists, as well as their preferences for addressing them (interviews). Descriptive analysis was used.

Results The study comprised 100 amiodarone and 17 lithium users who subsequently received thyroid medication. Different specialties were involved for amiodarone (62%) and lithium (71%). For amiodarone (initiated by cardiologists), internists initiated 48% of the marker medication, and GPs initiated 11%. For lithium (initiated by psychiatrists), GPs (47%) and internists (24%) initiated the marker medication.

In 75% (n=59) of hospital cases, the medical specialist initiating marker and/or index medication recognised the cascades as such and informed GPs in 89% of these cases. In the remaining 25% of unrecognised cases, the thyroid medication was primarily initiated by another specialty (93%). Interviews with community pharmacists revealed limited awareness of these prescribing cascades and they expressed the need for a clinical decision support system.

Conclusion and Relevance This study demonstrated that various physicians can be involved in prescribing cascades within the continuum of care. GPs are not consistently informed about managing ADRs, and community pharmacists lack awareness of these prescribing cascades. Hospital pharmacists could play a crucial role in recognising and managing these cascades in collaboration with community pharmacists.

Conflict of Interest No conflict of interest.