People who inject drugs face multiple health and social risks from injection practices as well as the lifestyle of drug use and abuse [13
]. Injection practices, which include unsterile injection practices, contaminated drug paraphernalia, and drug adulterants, enhance the risk of drug overdose, infections from bacterial, fungal, and protozoal pathogens and parenterally acquired viral infections, including HIV and hepatitis [15
]. Lifestyle events, such as homelessness, poverty, mental illness, or family abandonment, as well as lifestyle behaviors, such as multiple sexual partners or criminal behavior, increase the risk of sexually transmitted infections and comorbidities. The medical cooccurring conditions are specifically prevalent in key populations, especially PWID. Estimates for the population of PWID are available for at least 130 countries with approximately 78% of the 13.2 million people who inject drugs living in developing or transitional countries [16
Forty-one countries have reported a high prevalence (>5%) of HIV infection in key populations (PWID, sex workers, and men having sex with men). Globally, PWID now account for at least 10% of all new HIV infections which are estimated at 5 million per year [17
]. In chronic HIV infection, AIDS has been reported as the leading cause of death in PWID [18
]. Epidemiological data of HIV infection show that generalized HIV epidemics can result from diffusion transmission of HIV from key populations. Thus, it is important for countries and regions, as part of the CoR-PWID, to undertake surveillance studies to identify current drug use patterns and develop the best practices for the treatment of individuals who inject and abuse illicit drugs.
Drug injection can rapidly develop into drug dependence, a chronic, relapsing neurophysiological disease resulting from the prolonged physiological effects of drug(s) acting in the brain. The neurochemical abnormalities occurring in the brain that result from chronic use and drug injection are the underlying cause of many of the observed physical and behavioral aspects of abuse and dependence. The brain abnormalities associated with addiction are wide ranging, complex, and long lasting [19
]. They can involve abnormal brain signaling pathways, psychological conditioning or stress, and social factors that result in drug cravings leading to a predisposition to relapse even months or years after drug(s) use cessation. Thus, substance abuse/dependence can be most effectively addressed in a multifaceted medical-based paradigm to address the complex changes in the brain along with other comorbidities. The medical-based paradigm comprises a comprehensive program of interventions delivered through the course of long-term treatment. Comprehensive treatment programs include behavioral, social rehabilitative components, and biological (pharmacological) components comprising a continuum of care, as shown in . Behavioral therapy interventions have been extensively researched and are critical components of the treatment of all drug addictions. Social rehabilitative components are also important as an integral element of a treatment environment and as a wrap-around service.
Elements of the continuum of care for people who use drugs, abuse, or are drug dependent.
The use of medications, as part of comprehensive substance abuse treatment, is particularly important for PWID and who abuse opioids or who are opioid dependent [12
]. Globally the most common medication used for the treatment of opioid dependence is methadone [22
]. Methadone is an opioid agonist whose use in treatment and research is controlled by international conventions. The international conventions allow for differing levels of regulation for individual countries that utilize methadone. Thus, in a highly regulated and structured environment, as in the United States, methadone is dispensed daily at Opioid Treatment Programs (OTPs). These OTPs are increasingly providing wrap-around services to address important patient needs, enhance time in treatment, and promote recovery. Alternatively, methadone can be provided to patients in treatment through prescription or through specific regulated pharmacies.
An alternative medication to methadone is buprenorphine, a partial opioid agonist. Buprenorphine, while regulated, can be prescribed in a primary health care setting even in a highly regulated and structured environment. Thus, opioid dependence treatment can be accessed and provided similar to other illnesses with the result being reduced stigma/discrimination. As part of the CoR-PWID, both medications can be a component of a substance abuse treatment programs in an effort to address the reduced quality of life as well as reduced physical and mental functioning commonly found in drug injectors and drug abuse/dependence [23
Naltrexone is a nonnarcotic prescription medication for use in relapse prevention to opioid use. Unlike methadone, there is no negative reinforcement (opioid withdrawal) upon discontinuation. Naltrexone is most effective when utilized subsequent to the medical detoxification from opioids. The effectiveness of naltrexone treatment depends upon patient motivation and a social support system that promotes medication adherence [24
Depot-naltrexone (Vivitrol) addresses the reduced medication adherence of oral naltrexone through a monthly injectable formulation. Increased medication adherence was shown in a recent Phase 3 clinical trial that confirmed Vivitrol's safety and efficacy in the prevention of relapse to heroin use in a cohort of injection drug users [25
]. Currently, studies are underway to determine the most efficacious service model(s) for the use of depot-naltrexone in the treatment of relapse prevention to heroin use and as part of the CoR for opioid users.
Until recently, the global availability and consumption of opioid agonists, such as methadone and buprenorphine, as well as opioid antagonists, such as naltrexone, have been below the levels needed for international research to demonstrate local efficacy and to develop local evidence-based best medical practices [26
]. In addition, the global availability and use of methadone has not been sufficient to implement the well-documented efficacy shown for the treatment of opioid dependence that has been developed by research over the last 40 years [27
]. However, a strong research base in Western countries has resulted in the development of evidence-based medical practices using opioid agonists in maintenance treatment regimens and opioid antagonists in relapse prevention strategies. The recognition of these evidence-based medical treatment for opioid abuse and dependence has resulted in a substantial global increase in the medical use of opioid agonists and psychotropic medications to address opioid dependence [28
]. This increase is particularly evident in the initiation of new pharmacotherapy programs in regions of Europe, North America, Africa, Asia, and Oceania. While in other regions of the world, the medical use of opioid agonists and psychotropic medications have not substantially increased; the implementation of pharmacotherapy programs have begun as part of the global effort to reduce HIV/AIDS. These HIV prevention programs have utilized medications as an element of programs that target injection drug users to reduce their risk of both acquiring and transmitting HIV infection. Thus, the recent international expansion of the use of pharmacotherapy for opioid dependence as a result of efforts to increase access and availability of evidence-based treatments for opioid dependence as well as efforts to reduce the spread of infectious diseases, such as HIV/AIDS, a life priority of PWID.
Addressing the life priorities of opioid users in the CoR-PWID is important to enhance the quality of life of the patient in treatment, promote treatment acceptance, and further develop the trusting patient-provider relationship. Life priorities for opioid users have been reported as concerns about HIV and treatment of infection with HIV, housing, money, and protection from violence [31
]. The CoR-PWID with its integrated approach to services for HIV/AIDS and injection drug use is centrally positioned to address the life priorities of opioid users.
Substance abuse is a complex medical disorder composed of multiple physiologic, social, and behavioral problems often interrelated with psychological illness. As part of the CoR-PWID, health care providers need to screen people who inject drugs for psychological illness as well as associated trauma and abuse [32
]. Although PWID may be self-medicating due to a history of trauma or abuse, an initial focus on the medical treatment of drug abuse is often necessary to create sufficient patient stability from which other treatments can begin. Patient stability is further increased with gender-based, trauma-informed care, and treatment coupled to both mental health services and substance abuse treatment, thereby enhancing the medical outcomes of treatment for other comorbidities [33
]. An effective treatment strategy for PWID is to match a comprehensive treatment plan to the individual's particular substance abuse problems and needs. Desired treatment outcomes should (a) reduce dependence on drugs of abuse, (b) reduce morbidity and mortality of and associated with drugs of abuse, and (c) maximize the patients' abilities to access services and achieve social integration.