The wealth of research on illicit substance use to date has focused on traditional street drugs, most notably including heroin, cocaine and amphetamine . However, the misuse of prescription opioid pain relievers (OPR), such as oxycodone, methadone, hydrocodone and morphine, has newly emerged as a public health emergency [2–4]. In the United States, drug overdose deaths, more than half of which involve the use of OPR, have approached—and in some jurisdictions surpassed—the number of deaths from motor vehicle crashes, the leading cause of injury death among adults . Indeed, overdose deaths attributable to OPR now surpass those related to use of heroin and cocaine combined .
Although many OPR formulations are readily injected intravenously, less is known about the prevalence of this practice or its relation to infectious disease transmission . Very little evidence exists comparing injectors of heroin and other street drugs to injectors of OPR , but there is reason to believe that these two populations may have somewhat different demographics, injection practices and overall risk profiles .
In this issue of Addiction, Bruneau and colleagues demonstrate that among a prospective cohort of injection drug users in Montreal, Canada, those who injected OPR were twice as likely to acquire hepatitis C as those who did not inject OPR . A strength of the study is that the authors directly examined the distinct population alluded to above—that is, users who inject OPR but not heroin. Such users were nearly three times as likely to acquire hepatitis C virus (HCV) as those who did not inject any OPR at all. The authors note that those who inject OPR but not heroin may be relatively ‘newer’ injectors with fewer years of injecting history, and hypothesize that they may be less informed regarding safe injecting practices than are more experienced heroin users.
The study leaves unanswered which particular injecting practices unique to OPR-only injectors may place them at higher risk for HCV transmission. Surprisingly, syringe sharing did not predict HCV acquisition independently. While this could be explained by socially desirable responding, the authors highlight ethnographic work that reveals important differences in the preparation of OPR and heroin for injection . For example, whereas the powdered form of heroin, which is readily available in many drug markets, is easily dissolved in water and subsequently injected, OPR are pills that must be crushed, dissolved and filtered prior to injection. Because used filters can contain residual opioid, they are often re-used and can be shared among users. The repeated injections often required for a single ‘hit’ of OPR also expose used filters to excess blood that can be transmitted if this filter is shared among users. Further epidemiological studies should examine carefully those practices unique to injecting OPR to determine to what extent they contribute to transmission of blood-borne pathogens over and above syringe sharing.
The elevated risk for acquiring HCV associated with OPR injection is likely to extend beyond street-based populations of drug users. OPR are widely available—in many settings, more so than heroin, cocaine and amphetamine—through mechanisms different from the traditional street-based drug economy . Diversion of OPR can occur through illegal sales of prescriptions by physicians and pharmacists, theft or forgery of prescriptions, ‘doctor-shopping’ by individuals who seek prescriptions from multiple health-care providers, misuse of leftover medication and even internet sales . Indeed, this ready availability extends to mainstream populations, as reflected in the increasingly widespread misuse of OPR among US high school seniors, with 8% in 2011 reporting non-prescription use of hydromorphone and 5% reporting use of oxycodone . What remains unclear is which subgroup of this extremely large pool of OPR users are at risk for transition to injection drug use [14,15]. Moving forward, a delicate balance will need to be struck between curbing diversion of OPR for illicit use, while simultaneously ensuring appropriate access to OPR for patients when medically indicated.
Perhaps most concerning is the likelihood for clinicians, public health officials and policy makers to be poorly equipped to provide services to this newer population of injectors. Although methadone maintenance treatment, needle exchange programs and safe injection sites have clearly been shown to prevent the harms of injection drug use [16,17], the body of research supporting their effectiveness has been conducted predominantly among largely street-based populations of heroin users. The implementation of evidence-based responses to the burgeoning epidemic of OPR use, and programming to prevent the initiation of injection drug use among OPR users, should be considered an urgent public health priority.