Investigating antihistamine-related misuse and mortality in England

King’s College London

New research has found that the proportion of drug-related deaths where first-generation antihistamines were detected ‘significantly increased’ between 1999 and 2019.

Antihistamines commonly feature in home first aid kits, being routinely taken for the control of allergic reactions or sedation for the induction of sleep. There are, however, growing concerns regarding the misuse of antihistamines with sedative properties.

A team of researchers led by Dr Caroline Copeland, Lecturer in Pharmaceutical Medicine from the School of Cancer & Pharmaceutical Sciences and Director of the National Programme on Substance Abuse Deaths (NPSAD), have recommended an urgent review of how first-generation sedating antihistamines are currently supplied.

By studying cases reported to the NPSAD in England between 1999 and 2019, they identified 1,666 antihistamine detections at post-mortem from 1,537 cases, with antihistamines available for purchase from pharmacies without a prescription detected in 85% of these cases. Promethazine was identified as a specific concern.

The research goes on to highlight that in 95% of the cases, the drugs had been taken alongside another central nervous system depressant, with opioids co-detected in 74% of cases – providing potential evidence that opioid users are specifically seeking the effects of the drug combination.

Co-administration of ‘more dangerous’ central nervous system depressants may be causing the contribution of sedating antihistamines to be overlooked. The global focus on opioids, whilst essential, might be distracting from a more holistic assessment.– Dr Caroline Copeland, School of Cancer & Pharmaceutical Sciences

An urgent review of sedating antihistamines currently assigned under the ‘pharmacy-only’ classification with special attention to promethazine, is needed to achieve antihistamine harm reduction. This depends upon the assessed risk versus benefit profile of individual antihistamines. The researchers suggested that options include: reclassification to prescription-only medicine, limitations on quantity per pack, prominent warning labels or the requirement of a formal pharmacist consultation before access to these compounds is granted.

It is clear than an urgent review of how sedating antihistamines are supplied is needed. Careful consideration will be required to ensure accessibility for those who legitimately use them, whilst restricting use in those deliberately seeking their abuse.– Dr Caroline Copeland, School of Cancer & Pharmaceutical Sciences

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