On the science of heroin injection preparation: a response to Ciccarone and Harris

A second aim was to highlight the plausibility that prepared heroin injection acidity is an explanatory component of the hypothesis that heroin type can alter risks to physical health. The authors explain that the physiochemical properties of street heroin vary globally. This is due to differences in production methods and the chemicals used. In turn, this influences routes of administration and injection preparation processes at street level. Specifically, in this work the scientific focus is on the differences between heroin that is soluble in warm water without the need for acid to be added (as found in Philadelphia) and heroin that requires the addition of acid and heating to facilitate solubility (as found in London). The authors report that a few participants from Philadelphia who only injected heroin reported few vein problems, in contrast to participants in London who attributed vein damage and loss of peripheral access to acid use.

However we do not know for how long these people had been injecting or at what frequency. Additionally, acid type is the only identifiable factor to the lay person, out of several described below, that can affect vein irritation, so likely to be ‘blamed’ for causing vein damage. The authors clearly acknowledge the limits of drawing any conclusions from their results. They tested a small number of varying samples. This limit is explicitly discussed, as is the lack of measurement of the variables likely to influence the findings, a factor of great importance in scientific study. Many other factors are important in causing irritation to the lining of the veins, including the injection of visible and sub-visible solid particles, the osmolality of the liquid that is injected (i.e. how isotonic the liquid is) and the injection of non sterile liquids that can cause infection in the vein, particularly if already inflamed, as well as at other sites. Human factors such as the speed of injection administration are also critical. Injection speed and vein diameter (as a function of blood flow volume) dictates how quickly the body can dilute the irritating effects of acid and combat high osmolality (which bursts red blood cells and causes pain). Individual skin flora and attention to hygiene practices are also important. The authors acknowledge these factors, but it is not explicit that these will also vary with the source, type of heroin and location, hence they will vary in the samples that were pH tested in this study.

This is not a paper that gives any new evidence from which we can make clinical or practice decisions, but it does prompt consideration of the ‘science’ of heroin injection preparation and administration and how we might better deliver harm reduction advice. This paper shows us that in a small number of street heroin injectors (n = 8) recruited from two locations in one city (London), there is a tendency to produce injections that are too acidic. We cannot however assume the quantities of acid or nuances of the preparation process used by London injectors are typical of injectors across the UK or Europe. Just as we cannot assume the Philadelphia sample represent PWID from East coast USA. As the authors suggest, ascorbic acid is more ‘forgiving’ because it donates less protons (hydrogen ions, ‘acid’) per molecule than citric acid, meaning a greater quantity of ascorbic acid is needed to dissolve the heroin molecules compared to citric acid, so ascorbic acid carries a wider margin for error ( Scott, 2008). Ascorbic acid also places its own limits on how much can be added by forming a precipitate with street heroin at high concentrations ( Scott, 2008). This means PWID who add excessive amounts of ascorbic acid will see the solution going ‘cloudy’ and difficult to draw up into the syringe, a factor likely to deter excess ascorbic acid use. Citric acid in comparison is quicker and consistent in achieving the desired result (a clear solution for injecting) and excessive use will break down other plant materials present in street heroin that otherwise could be interpreted as ‘wasted drug’, with no precipitate forming. The authors make suggestions for reducing the risks from using too much citric acid or being too imprecise in the preparation process. Many of these are already emphasised in the information printed on acid sachets and in the leaflet that is intended to accompany acid supply in the UK. A film available on You Tube and distributed on DVD through UK needle and syringe programmes gives more detail: https://www.youtube.com/watch?v=e_hlxbW1v20.

But are these messages translating into practice? Reducing the sachet size of acids is a sensible suggestion, but it is my understanding that this would require investment in technology, as 100 mg is the lower limit of industry Good Manufacturing Practice sachet filling standards. Supplying a tiny scoop is worth consideration. Attempting to buffer street heroin at pH 4 to make it comparable to pharmaceutical heroin is plausible and one we have explored in our lab, but of course would not negate the other risks described above (osmolality, particulate and microbiological contaminations). In Europe this would require significant investment in product licensing, as such buffered solutions would probably come under the jurisdiction of the European Medicines Agency. Perhaps in the immediate term, we need to remind all those who work in needle and syringe programmes, including pharmacies, of the importance of encouraging PWID to be like the 57 year old London participant who was ‘a model of safer injection technique’: always use new, sterile equipment, clean hands and sites, take your time to prepare: add sterile acid in small and step wise way, always use less than half a sachet for a single hit, make injections close to 1 ml and inject slowly, never using the same vein twice in succession.