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

<p><strong>Introduction and Aims:</strong> 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.</p> <p><strong>Design and Methods:</strong> Injections were prepared from crushed slow-release morphine tablets, in mixed bacterial suspensions of <i>Staphylococcus aureus</i>, <i>Streptococcus pyogenes</i> and <i>Pseudomonas aeruginosa</i>. 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.</p> <p><strong>Results:</strong> 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.</p> <p><strong>Discussion and Conclusions:</strong> 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.</p>