Filtration of crushed tablet suspensions has potential to reduce infection incidence in people who inject drugs

Introduction and Aims: The medical complications of injecting preparations from crushed tablets can be severe, and most can be attributed to the injection of insoluble particles and micro-organisms. Previously we have shown that most of the particles can be removed by filtration, but it was not known whether bacteria could also be filtered in the presence of a high particle load. This study aims to determine the feasibility of filtration to remove bacteria from injections prepared from tablets.

Design and Methods: Injections were prepared from crushed slow-release morphine tablets, in mixed bacterial suspensions of Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa. The injection suspensions were passed through syringe filters of porosity 0.45 or 0.20 μm, or combined 0.8 then 0.2 μm, and the bacterial load was counted.

Results: Bacterial concentrations in unfiltered injections were 2.5-4.3 × 10⁶ colony forming units mL^-1. Both the 0.20 and 0.45 μm filters blocked unless a prefilter (cigarette filter) was used first. The 0.2 μm filter and the combined 0.8/0.2 μm filter reduced the bacteria to the limit of detection (10 colony forming units mL^-1) or below. Filtration through a 0.45 μm filter was slightly less effective.

Discussion and Conclusions: Use of a 0.2 μm filter, together with other injection hygiene measures, offers the prospect of greatly reducing the medical complications of injecting crushed tablets and should be considered as a highly effective harm reduction method. It is very likely that these benefits would also apply to other illicit drug injections, although validation studies are needed.