Twenty-four prescribing cascades worth recognising by name

Design

population level retrospective cohort with prescription sequence symmetry analysis

Population

2,297,942 community-dwelling adults aged 66 and over in Ontario, Canada

Primary outcome

prevalence, incidence and adjusted sequence ratio for 65 candidate prescribing cascades

Effect

24 cascades met all three criteria; highest incidence iron to laxative 11.9% (11.7-12.1); strongest sequence ratio corticosteroid to antipsychotic 2.55 (2.47-2.64)

Sixty-five potentially inappropriate prescribing cascades, agreed by an international Delphi panel, were tested against health administrative data on 2,297,942 community-dwelling adults aged 66 and over in Ontario. Each was assessed on three things: how common the initiating drug is, how often the pair actually occurs, and whether the second drug follows the first more often than it precedes it, measured as an adjusted sequence ratio. Twenty-four cascades met all three thresholds.

The most frequent were mundane: iron supplement to laxative (incidence 11.9%), statin to analgesic (10.9%), cholinesterase inhibitor to sleep agent (10.3%). The strongest temporal signals were corticosteroid to antipsychotic (adjusted sequence ratio 2.55, 95% CI 2.47 to 2.64), laxative to antidiarrhoeal (2.53, 2.43 to 2.65) and cholinesterase inhibitor to antiemetic (2.24, 1.90 to 2.65). Cardiovascular drugs were the commonest class starting a cascade. One cascade differed by sex - SSRI or SNRI to an overactive bladder drug was seen in men (1.21, 1.10 to 1.33) but not women (1.02, 0.96 to 1.09).

The value of a named list is that recognition is the whole intervention. A patient started on donepezil who reports insomnia and leaves with a hypnotic is a decision nobody experiences as a mistake; the same decision, recognised as the tenth-commonest cascade in a two-million-person population, is one you pause over. Read the list once and it will find you patients this week.

• Before adding a drug for a new symptom, check what was started in the preceding three months
• Learn the three commonest by heart: iron to laxative, statin to analgesic, cholinesterase inhibitor to hypnotic
• Treat a new antipsychotic in someone recently started on corticosteroids as a cascade until shown otherwise
• Consider dose reduction or an alternative for the initiating drug before prescribing for its effect
• Flag the sequence in the notes so the next prescriber does not repeat it

Why it matters

It converts prescribing cascades from a concept clinicians agree with in principle into a short list of specific pairs they will meet this week.

Don't overread it

Administrative data show sequence, not causation - some of these pairs will be appropriate treatment of coincident illness.

The statistics, in plain English

An adjusted sequence ratio above 1 means the second drug follows the first more often than it precedes it, which is evidence of a causal ordering that a simple co-prescription count cannot give you. A ratio of 2.55 for corticosteroid to antipsychotic means that pairing is two and a half times more likely in that order than the reverse. It is still administrative data: it shows sequence, not that the first drug caused the symptom, and some pairs will be appropriate treatment of coincident disease. The prioritisation is designed to find where to look, not to label individual prescriptions as errors.

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