Acute drug-toxicity presentations involving polydrug use to Euro-DEN Plus sentinel hospitals in Europe from 2014 to 2022

Background

Polydrug use is a Public Health concern, but there are limited data on polydrug use patterns in acute drug toxicity presentations to hospital emergency services. This study aimed to identify substances that were commonly reported to have been used together in acute drug toxicity presentations to European emergency departments. 

Methods

We analysed 71,455 presentations from 48 sentinel centres in 32 countries reported to the Euro-DEN Plus network between 1/1/2014 and 31/12/2022. We used the apriori algorithm to identify all pairs substances (A and B) reported together (minimum of 30 occurrences). We derived a set of specific statistics for each pair of associated substances, in particular: support (share of all presentations that the pair occurs in), confidence (share of occurrences of substance A in which substance B was also reported) and lift (ratio of confidence and support, and a measure of strength of the association). We identified the most common pairs (highest support) and those with the strongest association (highest lift).

Results

Overall, the most frequently reported substances were cocaine (23% of all presentations), cannabis (22%), heroin (18%), GHB/GBL (12%), amphetamine (9%), MDMA (8%) and methamphetamine (5%). 46,107 (65%) presentations involved more than one substance. The two most common pairs of substances reported together (associations with the highest support) were cocaine/cannabis (4% of all presentations), and cocaine/heroin (3%). However, confidence in these associations is low: only in 17% of cocaine presentations was cannabis also reported (even though 22% of all presentations involved cannabis) and only in 11% of cocaine presentations was heroin also reported (even though 18% of all presentations involved heroin). This is reflected in the lift for both associations that is below 1 (0.77 for cocaine/cannabis, 0.63 for cocaine/heroin), i.e. a presentation with cocaine is less likely to involve cannabis or heroin than other presentations in this dataset. Conversely, the association between methamphetamine and GHB/GBL has a relatively strong support (occurs in 2% of all presentations) but is much stronger in terms of both lift (3.4) and confidence: in 41% of methamphetamine presentations, GHB/GBL was also reported, even though only 12% of all presentations involved GHB/GBL i.e. presentations with methamphetamine are more likely to involve GHB/GBL than other presentations in this dataset.

Conclusions

We were able to identify common pairs of substances reported together and distinguish between pairs of substances that were common just because the individual substances are very frequently used and pairs of substances that appear to be reported more often than expected. This can contribute to identifying patterns of polydrug use, to support public health responses, to identify particularly harmful combinations, and to support clinical management of these presentations.