Effect of filtration on morphine and particle content of injections prepared from slow-release oral morphine tablets

When a tablet of slow-release morphine (MS Contin®) is crushed and mixed with water, the resulting mixture contains millions of particles, of sizes from less than 5 μm to greater than 400 μm. These particles will cause great harm if injected into the bloodstream. The number of particles can be greatly reduced by filtration. A low-porosity syringe filter (0.45 or 0.22 μm) is most effective, but is likely to block unless a coarser filter is used first. Little of the morphine is lost in filtration if the filters are rinsed. Hot extraction does not significantly increase extraction of morphine, and carries the risk of filtering a warm mixture which allows wax to pass through the filter, producing particles when it cools and solidifies. In practice, it is uncommon for solutions to be left for long before filtration and injection, producing the potential for a substantially greater level of filtrate contamination with wax than identified in the current study. It is not possible to prepare an injection of pharmaceutical standard without clean facilities, as some particles will remain even after filtration through a syringe filter, and the injection will not be sterile. Note: a plain language summary of this study is available