The initiators of the amiodarone-induced and lithium-induced hypothyroidism prescribing cascades: Recognizing it and how physicians communicate this

Abstract

Background: not recognising prescribing cascades can be harmful to the patient. One of the potential complication factors in recognising a cascade can be incomplete or too little information transfer between physicians about (new) drug treatments of a patient and its potential adverse drug events (ADEs). The prescribing cascades of amiodarone and lithium were studied to investigate this further. Both amiodarone and lithium can cause hypothyroidism as a side-effect, for which levothyroxine can be prescribed and this initiates the cascade. Amiodarone can also cause hyperthyroidism, which is treated with a thyrostatic drug. Objective: to determine the specialism of the physician who initiates the prescribing cascades of lithium and amiodarone. Secondly, the proportion of the physicians involved in the prescribing cascades who were aware of the cascade and whether they communicated it to the general physician (GP) involved in the patient’s treatment was also determined. Methods: the main inclusion criteria of this retrospective follow-up study were if patients started with amiodarone or lithium (index) after 1-1-2019 and also received either levothyroxine or one of the thyrostatic drugs propylthiouracil, carbimazole or thiamazole (markers). The main exclusion criterion was whether they received the marker before the index drug. The patient follow-up period was two years. Data were retrieved from the electronic patient database Epic with an SQL query, and patient selection was made with R. To determine whether a cascade was recognised and what form of communication there was between physicians, discharge letters and notes around the initiation of index and marker drug were studied. The primary outcome was the percentage of cascades initiated by a different prescriber than that of the index drug. The secondary outcomes were the percentage of recognised cascades and whether the cascade was communicated towards the GP, also put in percentages. Results: 59 patients with the amiodarone-induced hypothyroidism (AIH) cascade were included. Zero lithium patients were included. The index prescriber was a cardiologist in 100% of the AIH cases. In 48% of these cases, the cascade initiator was a different prescriber. 75% of the cascades were recognised, and of the 25% that were not recognised, 93% were initiated by a different prescriber. Regarding communication, two cardiologists warned the GP about the potential AIH cascade at the start of amiodarone, and 89% of the specialists who recognised the cascade communicated this towards the GP. Conclusions: approximately half of the AIH cascade cases were not initiated by a cardiologist. When amiodarone was not recognised as the cause of hypothyroidism, the initiator was mainly a different prescriber. Since 93% of the cascades that were not recognised were prescribed by a different prescriber, warning other physicians that are involved in a patient’s treatment for a potential prescribing cascade at the start of a new drug treatment might prevent the initiation of a cascade. Further research is needed to pinpoint more complicating factors of not recognising a prescribing cascade and to find resolutions for them.