Background: Injections of mixtures prepared from crushed tablets contain insoluble particles
which can cause embolisms and other complications. Although many particles can be removed by
filtration, many injecting drug users do not filter due to availability, cost or performance of filters,
and also due to concerns that some of the dose will be lost.
Methods: Injection solutions were prepared from slow-release morphine tablets (MS Contin®)
replicating methods used by injecting drug users. Contaminating particles were counted by
microscopy and morphine content analysed by liquid chromatography before and after filtration.
Results: Unfiltered tablet extracts contained tens of millions of particles with a range in sizes from
< 5 μm to > 400 μm. Cigarette filters removed most of the larger particles (> 50 μm) but the
smaller particles remained.

Commercial syringe filters (0.45 and 0.22 μm) produced a dramatic
reduction in particles but tended to block unless used after a cigarette filter. Morphine was retained
by all filters but could be recovered by following the filtration with one or two 1 ml washes.

The combined use of a cigarette filter then 0.22 μm filter, with rinses, enabled recovery of 90% of the
extracted morphine in a solution which was essentially free of tablet-derived particles.
Conclusions: Apart from overdose and addiction itself, the harmful consequences of injecting
morphine tablets come from the insoluble particles from the tablets and microbial contamination.
These harmful components can be substantially reduced by passing the injection through a
sterilizing (0.22 μm) filter. To prevent the filter from blocking, a preliminary coarse filter (such as
a cigarette filter) should be used first. The filters retain some of the dose, but this can be recovered
by following filtration with one or two rinses with 1 ml water.

Although filtration can reduce the
non-pharmacological harmful consequences of injecting tablets, this remains an unsafe practice due
to skin and environmental contamination by particles and microorganisms, and the risks of bloodborne
infections from sharing injecting equipment.

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