Several pharmaceutical products are liable to 'abuse' or use outside their prescription, which frequently involves their injection. Examples are slow-release forms of morphine and oxycodone, and sublingual buprenorphine. During injection preparation, the drug is extracted into water, after crushing and heating the tablet if considered necessary. Since these products are designed for oral administration, they can contain excipients (ingredients other than the drug) which are poorly soluble, resulting in suspension of particles in the injection solution. Injected particles are able to produce medical complications such as the blockage of small blood vessels leading to ischaemia (inadequate blood flow) and tissue damage. Filtration can be used to remove particles from the suspension; including bacteria if the porosity is small enough (0.2 μm). However, filters are liable to blockage when overloaded, especially if the pore size is small. This problem can be minimised by using a larger pore size (e.g. 5-10 μm), but the resulting filtrate will contain many residual small particles. The use of two filters, coarse and fine, either sequentially or in a double membrane device, enables removal of the majority of particles as well as bacteria, although not quite meeting pharmaceutical standards for safe injection. Although not yet evaluated by a clinical trial, this highly effective filtration process would be expected to greatly reduce the risk of vascular and related complications, as well as non-viral infections. Careful technique ensures that drug is not lost by filtration, a priority for most drug consumers. Practical issues that affect acceptability of filtration by injecting drug users, including ease of use and cost, will need to be considered. However, given the laboratory evidence demonstrating the effectiveness of filters it is time to consider these tools as essential for safe injection as sterile needles/syringes for the world's approximately 16 million people who inject drugs.
