Worldwide there are an estimated 13.2 million injecting drug users . In addition to the high risk of overdose amongst this group [13, 14], drug users who choose to inject are particularly vulnerable to a range of infectious diseases, including viral infections such as HIV and hepatitis, and bacterial infections such as Group A Streptococci and Staphlococcus aureus, resulting in considerable levels of morbidity and mortality . Growing concern regarding these injecting-related health problems is reflected in recent changes in the UK law, which in 2003, sanctioned the dispensing of injecting paraphernalia reported to have harm reduction benefits, in addition to the provision of clean needles and syringes. Under these amendments, it became legal in the UK to provide citrate to injecting drug users, a substance shown to be an appropriate means by which to convert street heroin into a soluble form .
It was envisaged that the introduction of citrate would increase both the number of injectors attending SEPs and the number of visits each person made . The recently updated guidance on the commissioning and provision of treatment for adult drug users  highlights the need for the reinvigoration of harm reduction activities across all treatment tiers (drug-related interventions in England and Wales fall into a tier structure that reflects the increasing intensity of the interventions). Increasing the number of individuals in contact with SEPs and the frequency of their engagement are positive public health indicators for harm reduction development. Analysis of SEP monitoring data showed no increase between pre and post citrate periods in the number of established or new clients. Importantly however, there was no significant decrease either, showing that the introduction of citrate had not negatively affected attendance.
Monitoring data also showed no significant increase in the frequency with which heroin/crack injectors attended SEPs following citrate's introduction. The median number of visits made by established clients was three in both pre and post citrate periods while new clients made, on average, two visits within each of the two six month periods. However, matched pair analyses of longitudinal attenders of SEPs, comparing an individual's post citrate profile with their own behaviour pre citrate, showed that this cohort of injectors made significantly more visits post citrate (median = 5) than pre citrate (median = 4, P < 0.05). Further to this, matched pair analyses showed the median visits per person post citrate (median = 5) was significantly greater than the median visits for the corresponding six months in the previous year (median = 4, P < 0.005), for those injectors who were recorded in these two six month periods. We can therefore discount the possibility that the increase in visit rate between pre and post citrate was due to seasonal variation because the increased visit rate following the introduction of citrate occurred across years as well as within the year. Additionally, again using matched pair analysis, we observed no difference in the median number of visits pre and post citrate for steroid injectors (median number of visits being one in both the pre and post citrate periods). Steroid users do not use an acidifier so their behaviour should not be affected by the introduction of citrate. That no change in the behaviour of steroid injectors was observed supports the conclusion that the increased visit rate post citrate of heroin/crack injectors who attended SEPs in both pre and post citrate periods was due to the introduction of citrate. It is important to note, however, that the legal changes that permitted the distribution of citrate also sanctioned the distribution of other injecting paraphernalia (for example, spoons and water), although the distribution of other paraphernalia in SEPs in Cheshire and Merseyside occurred less consistently than the introduction of citrate. Despite this, it is possible that the distribution of other injecting paraphernalia also affected the behaviour of SEP attenders within this geographical area.
From these findings, we can conclude that the introduction of citrate did not encourage more clients to contact SEPs to collect clean injecting equipment in the first six months of its introduction, nor can we conclude that its introduction negatively affected attendance. Furthermore, we cannot conclude that overall, people visited SEPs more frequently following the introduction of citrate but that its introduction has encouraged longitudinal attenders of SEPs (i.e. those who were recorded in both the pre and post citrate six month periods) to visit more frequently. Therefore, at SEPs included in this study, the introduction of citrate has resulted in a change in service use amongst certain SEP clients, with less impact on those injectors who visit SEPs infrequently. Any increase in visit frequency should be welcomed as it provides SEP staff greater opportunity to engage with injectors to discuss a range of harm reduction measures and, where appropriate, to refer into other services. It is not clear from this study whether further changes will be observed once information about the availability of citrate at SEPs becomes universal amongst the injecting community.
With respect to the number of syringes collected per visit, no difference was evident pre versus post citrate for established SEP clients. Matched pair analysis showed comparable findings. Similarly, no difference was observed in the number of syringes collected for heroin/crack injectors post citrate compared to the corresponding six month period in the previous year or for steroid injectors pre versus post citrate. Established SEP clients are therefore continuing to receive the same number of syringes per visit and, presumably, sufficient citrate for the number of syringes dispensed. Injectors who are classified as 'longitudinal attenders' for the purpose of this study, are thus attending SEPs more frequently post citrate but collecting the same number of syringes per visit, increasing, very slightly, the total number of syringes dispensed to this cohort of injectors from 71,495 in the pre citrate six month period to 71,743 in the post citrate six month period (data not shown). In light of evidence to suggest that clean syringes are used in only 25% of injections , from a public health perspective, any increase in syringe provision is welcome.
Despite the benefits of citrate over other acidifiers , all may result in vein damage and the smallest possible amount is recommended to solubilise heroin. Consultation with injecting drug users resulted in the current practice of dispensing citrate in 100 mg sachets . This amount was deemed sufficient to dissolve the £20 of heroin normally prepared and because packaging a smaller amount would be unfeasible. Injectors liked the idea of single use sachets which were also deemed to decrease the risk of contamination from sharing whilst encouraging hygienic injecting techniques. Monitoring data showed that SEP staff dispensed significantly less syringes to new clients per visit post citrate (median = 10 per visit) than pre citrate (median = 14.5 per visit, P < 0.05). While it is important that SEP staff are aware of the potential harm excess citrate may cause, fears regarding the dispensation of too much citrate to new clients must not be allowed to impact negatively on the number of clean syringes dispensed.