Association between benzodiazepine coprescription and mortality in people on opioid replacement therapy: a population-based cohort study.

OBJECTIVE: To investigate the association between opioid replacement therapy (ORT) and benzodiazepine (BZD) coprescription and all-cause mortality compared with the prescription of ORT alone. DESIGN: Population-based cohort study. SETTING: Scotland, UK. PARTICIPANTS: Participants were people prescribed ORT between January 2010 and end of December 2020 aged 18 years or above. MAIN OUTCOME MEASURES: All-cause mortality, drug-related deaths and non-drug related deaths. SECONDARY OUTCOME: ORT continuous treatment duration. ANALYSIS: Cox regression with time-varying covariates. RESULTS: During follow-up, 5776 of 46 899 participants died: 1398 while on coprescription and 4378 while on ORT only. The mortality per 100 person years was 3.11 during coprescription and 2.34 on ORT only. The adjusted HR for all-cause mortality was 1.17 (1.10 to 1.24). The adjusted HR for drug-related death was 1.14 (95% CI, 1.04 to 1.24) and the hazard for death not classified as drug-related was 1.19 (95% CI, 1.09 to 1.30). CONCLUSION: Coprescription of BZDs in ORT was associated with an increased risk of all-cause mortality, although with a small effect size than the international literature. Coprescribing was also associated with longer retention in treatment. Risk from BZD coprescription needs to be balanced against the risk from illicit BZDs and unplanned treatment discontinuation. A randomised controlled trial is urgently needed to provide a clear clinical direction. TRIAL REGISTRATION NUMBER: NCT04622995.

Development of an intervention to manage benzodiazepine dependence and high-risk use in the context of escalating drug related deaths in Scotland: an application of the MRC framework.

BACKGROUND: Scotland has the highest rate of drug related deaths (DRD) in Europe. These are deaths in people who use drugs such as heroin, cocaine, benzodiazepines and gabapentinoids. It is a feature of deaths in Scotland that people use combinations of drugs which increases the chance of a DRD. Many deaths involve 'street' benzodiazepines, especially a drug called etizolam. Many of the 'street' benzodiazepines are not licensed in the UK so come from illegal sources. People who use opiates can be prescribed a safer replacement medication (e.g., methadone). While guidance on management of benzodiazepines use highlights that there is little evidence to support replacement prescribing, practice and evidence are emerging. AIM: To develop an intervention to address 'street' benzodiazepines use in people who also use opiates. METHODS: The MRC Framework for Complex Interventions was used to inform research design. Co-production of the intervention was achieved through three online workshops with clinicians, academics working in the area of substance use, and people with lived experience (PWLE). Each workshop was followed by a PWLE group meeting. Outputs from workshops were discussed and refined by the PWLE group and then further explored at the next workshop. RESULTS: After these six sessions, a finalised logic model for the intervention was successfully achieved that was acceptable to clinicians and PWLE. Key components of the intervention were: prescribing of diazepam; anxiety management, sleep, and pain; and harm reduction resources (locked box and a range of tips), personal safety conversations, as well as a virtual learning environment. CONCLUSION: A co-produced intervention was developed for next stage clinical feasibility testing.

Feasibility and Acceptability of an Overdose Prevention Intervention Delivered by Community Pharmacists for Patients Prescribed Opioids for Chronic Non-Cancer Pain.

There have been increases in prescriptions of high strength opioids for chronic non-cancer pain (CNCP), but CNCP patients perceive themselves as being at low risk of opioid overdose and generally have limited overdose awareness. This study examined how an overdose prevention intervention (opioid safety education, naloxone training, and take-home naloxone (THN)) delivered by community pharmacists for patients prescribed high-strength opioids for CNCP would work in practice in Scotland. Twelve patients received the intervention. CNCP patients and Community Pharmacists were interviewed about their experiences of the intervention and perceptions of its acceptability and feasibility. CNCP patients did not initially perceive themselves as being at risk of overdose but, through the intervention, developed insight into opioid-related risk and the value of naloxone. Pharmacists also identified patients' low risk perceptions and low overdose awareness. While pharmacists had positive attitudes towards the intervention, they outlined challenges in delivering it under time and resource pressures and during the COVID-19 pandemic. Overdose prevention interventions are required in the CNCP population as this group has elevated risk factors for overdose but are commonly overlooked. Customised overdose prevention interventions for CNCP patients attend to gaps in overdose awareness and risk perceptions in this population.

Making community pharmacies psychologically informed environments (PIE): a feasibility study to improve engagement with people using drug services in Scotland.

AIM: This developmental study tested the feasibility of training pharmacy staff on the psychologically informed environments (PIE) approach to improve the delivery of care. BACKGROUND: Community pharmacies provide key services to people who use drugs (PWUD) through needle exchange services, medication-assisted treatment and naloxone distribution. PWUD often have trauma backgrounds, and an approach that has been demonstrated to work well in the homeless sector is PIEs. METHODS: Bespoke training was provided by clinical psychologists and assessed by questionnaire. Staff interviews explored changes made following PIE training to adapt the delivery of care. Changes in attitude of staff following training were assessed by questionnaire. Peer researchers interviewed patient/client on observed changes and experiences in participating pharmacies. Staff interviews were conducted six months after training to determine what changes, if any, staff had implemented. Normalisation process theory (NPT) provided a framework for assessing change. FINDINGS: Three pharmacies (16 staff) participated. Training evaluation was positive; all participants rated training structure and delivery as 'very good' or 'excellent'. There was no statistically significant change in attitudes. COVID-19 lockdowns restricted follow-up data collection. Staff interviews revealed training had encouraged staff to reflect on their practice and communication and consider potentially discriminatory practice. PIE informed communication skills were applied to manage COVID-19 changes. Staff across pharmacies noted mental health challenges for patients. Five patients were interviewed but COVID-19 delays in data collection meant changes in delivery of care were difficult to recall. However, they did reflect on interactions with pharmacy staff generally. Across staff and patient interviews, there was possible conflation of practice changes due to COVID-19 and the training. However, the study found that training pharmacy teams in PIE was feasible, well received, and further development is recommended. There was evidence of the four NPT domains to support change (coherence, cognitive participation, collective action and reflexive monitoring).

Patient, family members and community pharmacists' views of a proposed overdose prevention intervention delivered in community pharmacies for patients prescribed high-strength opioids for chronic non-cancer pain: An explorative intervention development study.

INTRODUCTION: Despite opioid prescribing for chronic non-cancer pain (CNCP) having limited therapeutic benefits, recent evidence indicates significant increases in the prescribing of high-strength opioids for individuals with CNCP. Patients prescribed opioids for CNCP have overdose risk factors but generally have low opioid overdose awareness and low perceptions of risk related to prescribed opioids. Currently, there are few bespoke overdose prevention resources for this group. METHODS: This qualitative study investigated views on a naloxone intervention for people prescribed high-strength opioids for CNCP delivered via community pharmacies. The intervention included overdose risk awareness and naloxone training and provision. Interviews were conducted with eight patients, four family members and two community pharmacists. Participants were convenience sampled and recruited through networks within the Scottish pain community. The Framework approach was used to analyse findings. RESULTS: All participants had positive attitudes towards the intervention, but patients and family members considered risk of overdose to be very low. Three themes were identified: potential advantages of the intervention; potential barriers to the intervention; and additional suggestions and feedback about the intervention. Advantages included the intervention providing essential overdose information for CNCP patients. Barriers included resource and time pressures within community pharmacies. DISCUSSION AND CONCLUSION: While patients had low overdose knowledge and did not see themselves as being at risk of opioid overdose, they were receptive to naloxone use and positive about the proposed intervention. A feasibility trial is merited to further investigate how the intervention would be experienced within community pharmacy settings.

Negotiating an Illicit Economy in the Time of COVID-19: Selling and Buying Dilemmas in the Lives of People Who Use Drugs in Scotland.

The impact of COVID-19 itself and societal responses to it have affected people who use drugs and the illicit drug economy. This paper is part of a project investigating the health impacts of COVID-19 related control measures on people who use drugs in Scotland. It examines their roles and decisions as economically situated actors. It does this within a moral economy perspective that places economic decisions and calculations within a context of the network of social obligations and moral decisions. The paper uses a mixed methods approach, reporting on a drug trend survey and in-depth interviews with people who use drugs. It finds they were affected by restrictions in the drug consumption context and changes in the supply context, both in terms of what was supplied and changes in the relationship between sellers and buyers. Face to face selling became more fraught. Participants in more economically precarious circumstances were faced with dilemmas about whether to move into drug selling. The double impact of loss of income and reduced access to support networks were particularly difficult for them. Despite the perception that the pandemic had increased the power of sellers in relation to their customers, many full-time sellers were reported to be keeping their prices stable in order to maintain their relationships with customers, instead extending credit or adulterating their products. The effect of spatial controls on movement during the pandemic also meant that the digital divide became more apparent. People with good access to digital markets and easy drug delivery through apps were in a better position to manage disruption to drug sales contexts. We make recommendations in relation to how policy can respond to the interests of people who use drugs in a pandemic.

A Realist Review of How Community-Based Drug Checking Services Could Be Designed and Implemented to Promote Engagement of People Who Use Drugs.

With rising numbers of drug-related deaths in the UK and globally, exploration of interventions that seek to reduce drug-related harm is essential. Drug checking services (DCS) allow people to submit drug samples for chemical analysis and receive feedback about the sample, as well as harm reduction advice. The use of DCS is often linked to festival and/or nightlife settings and to so-called 'recreational' drug use, but research has also shown the potential of community-based DCS as an intervention serving more varied demographics of people who use drugs, including more marginalised individuals and those experiencing drug dependence. Whilst there is a growing evidence base on the effectiveness of drug checking as a harm reduction intervention, there is still limited evidence of the underlying mechanisms and processes within DCS which may aid implementation and subsequent engagement of people who use drugs. This presents a challenge to understanding why engagement differs across types of DCS, and how best to develop and deliver services across different contexts and for different populations. To explore the contexts and mechanisms which impact engagement in community-based DCS, a realist review was undertaken to synthesise the international evidence for the delivery and implementation of DCS. There were 133 sources included in the review. From these sources the underlying contexts, mechanisms, and outcomes relating to DCS implementation and engagement were developed and refined into seven programme theories. The findings of this review are theoretically novel and hold practical relevance for the design of DCS, with implications for optimisation, tailoring, and implementing services to reach individuals in different settings.

Long-acting depot buprenorphine in people who are homeless: Views and experiences.

INTRODUCTION: People experiencing homelessness often experience intersecting mental and physical health problems, alongside problem substance use and a range of overlapping challenges, including access to appropriate treatment. New long-acting opioid replacement therapies (ORT) offer potential benefits for this group. This study explored the views of people who are homeless and dependent on prescribed or illicit opiates/opioids on the range of ORT delivery options, including long-acting buprenorphine (LAB) depot injection, methadone liquid, and sublingual/wafer buprenorphine. METHODS: The research team conducted three focus groups (n = 9 participants) and individual interviews (n = 20) with people living in Scotland and Wales. We sought to explore participants' experiences and views on a range of ORT options, and to explore experiences and perceptions of the acceptability and utility of LAB for this group. RESULTS: Twenty-nine people participated (8 women, 21 men) and described experiences of poor mental health and interaction with the criminal justice system, including prison. All had experience of ORT and some had a preference for the "comfort" of methadone while others liked the clear headedness of buprenorphine. Participants saw LAB as a valuable addition to the treatment options. Potential benefits included freedom from the challenges associated with daily dispensing and the freedom to be able to attend to their priorities and regain control over their day-to-day lives. LAB naïve participants required reassurance regarding the duration of effect and wanted information and evidence from both their health care providers and their peers. CONCLUSION: Participants generally recognized the potential of LAB. The research team identified crucial themes for those experiencing homelessness: emotions, trust, and time. A move to LAB represents a shift in the locus of control to the individual, which, for some is exciting, but for others is daunting. Providers should address this shift in control, and it must to be central to joint decision-making on whether someone is ready for LAB, the information they require to help them decide, and the support they will require during treatment.

The impact of COVID-19 on access to harm reduction, substance use treatment and recovery services in Scotland: a qualitative study.

INTRODUCTION: People who use drugs (PWUD) are considered vulnerable to COVID-19 exposure and the sequelae of infection due to their social circumstances, health conditions, drug purchasing, and substance use. They can depend on access to services that provide harm reduction, substance use treatment, recovery and support, and general healthcare. Social distancing measures and service restrictions posed significant challenges to the health and wellbeing of PWUD. METHODS: Ethical approvals were secured. PWUD were recruited from voluntary sector homeless and housing, harm reduction, and recovery organisations across central Scotland. Data was collected via semi-structured interviews and analysed using the Framework Method. RESULTS: Twenty nine PWUD participated and reported mixed experiences of the impacts of COVID-19 lockdown. Several benefitted from policy and practice developments designed to sustain or increase access to harm reduction services. Some PWUD reported improved access to substitute prescribing and/or appreciated being trusted to manage multiple take-home doses. Others noted the loss of regular in-person contact with treatment providers and dispensers. Access to recovery support was challenging for many, especially those unable to access or uncomfortable with online provision who experienced greater isolation. Lack of access to general healthcare services was common, and especially problematic for PWUD with chronic physical and mental health conditions. CONCLUSIONS: This qualitative research describes the impacts of COVID-19 social and service restrictions on PWUD in Scotland. These impacts were anticipated by policy makers and service providers. Effective and acceptable developments were shown to maintain and even increase service provision for PWUD. Developments were geographically dependent and significant challenges remained for many people. The learning generated can inform responses to increase service access and uptake in post-pandemic times.

Assessing the feasibility, acceptability and accessibility of a peer-delivered intervention to reduce harm and improve the well-being of people who experience homelessness with problem substance use: the SHARPS study.

BACKGROUND: For people experiencing homelessness and problem substance use, access to appropriate services can be challenging. There is evidence that the development of trusting relationships with non-judgemental staff can facilitate service engagement. Peer-delivered approaches show particular promise, but the evidence base is still developing. METHODS: The study used mixed methods to assess the feasibility, acceptability and accessibility of a peer-delivered, relational intervention to reduce harms and improve health/well-being, quality of life and social functioning, for people experiencing homelessness and problem substance use. Four Peer Navigators were employed to support individuals (n = 68 total, intervention participants). They were based in outreach services and hostels in Scotland and England. Qualitative interviews were conducted with intervention participants, Peer Navigators and staff in services, and observations were conducted in all settings. Quantitative outcomes relating to participants' substance use, physical and mental health, and quality of the Peer Navigator relationship, were measured via a 'holistic health check' with six questionnaires completed at two time-points. RESULTS: The intervention was found to be acceptable to, and feasible and accessible for, participants, Peer Navigators, and service staff. Participants reported improvements to service engagement, and feeling more equipped to access services independently. The lived experience of the Peer Navigators was highlighted as particularly helpful, enabling trusting, authentic, and meaningful relationships to be developed. Some challenges were experienced in relation to the 'fit' of the intervention within some settings. Among participants there were reductions in drug use and risky injecting practices. There were increases in the number of participants receiving opioid substitution therapy. Overall, the intervention was positively received, with collective recognition that the intervention was unique and highly valuable. While most of the measures chosen for the holistic health check were found to be suitable for this population, they should be streamlined to avoid duplication and participant burden. CONCLUSIONS: The study established that a peer-delivered, relational harm reduction intervention is acceptable to, and feasible and accessible for, people experiencing homelessness and problem substance use. While the study was not outcomes-focused, participants did experience a range of positive outcomes. A full randomised controlled trial is now required to assess intervention effectiveness. TRIAL REGISTRATION: Study registered with ISRCTN: 15900054.

Why are drug-related deaths among women increasing in Scotland? A mixed-methods analysis of possible explanations.

Drug-related deaths have increased significantly in Scotland in recent years, with a much greater percentage increase in deaths among women than among men. We undertook a mixed-methods project to identify explanations for this trend, comprising three parallel methodological strands: (i) an analysis of available routine data, including drug treatment data, death registrations, and surveys of people using needle exchanges; (ii) thematic analysis of interviews and focus groups with professional stakeholders and (iii) secondary analysis of interviews with women who use drugs. Results indicated that the observed trend is likely to reflect multiple, interacting causes. Potential contributors identified were: ageing; changing patterns of substance use; increasing prevalence of physical and mental health co-morbidities; changing relationships and parenting roles; changes to treatment services and wider health and social care provision; unintended consequences or poor implementation of recovery-oriented practice; and changes in the social security system. Policy responses to rising drug-related death rates require a gender-informed approach, recognising the commonalities and differences between men and women who use drugs; the diversity of experiences within each gender; and the intersections between gender and other forms of inequality, such as poverty.

A systematic review and meta-analysis of the prevalence of take-home naloxone (THN) ownership and carriage.

BACKGROUND: Drug-related deaths globally are increasing year on year, with the largest proportion of these being opioid-related. The opioid antagonist naloxone distributed for take-home use ('Take-Home Naloxone (THN)') has been championed as one method of tackling this public health crisis, however to be effective it must be available at an opioid overdose. Ownership and carriage are therefore fundamental to THN success. This study aimed to assess the prevalence of ownership and carriage of THN internationally among people who use drugs (PWUD). METHODS: NHS Scotland Journals, AMED, EMBASE, HMIC, MEDLINE, PsycINFO, CINAHL Complete, PubMed, Cochrane Library, PROSPERO and grey literature were searched for articles which measured prevalence of THN ownership or carriage between 1996 and 2020. Ownership was defined as report of a personal supply of THN. Carriage was defined as the participant carrying THN on their person at time of data collection or reporting a frequency of how often they carry THN. Risk of bias was evaluated using the Joanna Briggs Checklist for Prevalence Studies. RESULTS: Systematic search yielded 6363 papers, with ten eligible papers identified. Eight articles were included in ownership prevalence and five articles included for carriage prevalence, with an overlap of three studies between both measures. Pooled prevalence indicated moderate ownership levels (57%, CI 47-67%) but lower carriage levels (20%, CI 12-31%). Analysis was complicated by the limited number of available studies and lack of standardised terminology and measurement. CONCLUSION: Understanding naloxone ownership and carriage globally is hampered by limited evidence and heterogeneity across studies. From the available data, prevalence of THN carriage overall appears low, despite moderate ownership. Given the variation across studies, future research should seek to utilise more standardised terminology and methods of measurement. Furthermore, services distributing THN must ensure the importance of regular carriage of naloxone is consistently emphasised.

Quantifying prescribed high dose opioids in the community and risk of overdose.

BACKGROUND: Opioid prescribing for a range of health issues is increasing globally. The risk of fatal and non-fatal overdose is increased among people prescribed strong opioids: in high doses in the context of polypharmacy (the use of multiple medications at the same time), especially with other sedatives; and among people with multiple morbidities including cardiorespiratory, hepatic and renal conditions. This study described and quantified the prescribing of strong opioids, comorbidities and other overdose risk factors among those prescribed strong opioids, and factors associated with high/very high opioid dosage in a regional health authority in Scotland as part of a wider service improvement exercise. METHODS: Participating practices ran searches to identify patients prescribed strong opioids and their characteristics, polypharmacy, and other overdose risk factors. Data were anonymised before being analysed at practice and patient-level. Morphine Equivalent Doses were calculated for patients based on drug/dose information and classed as Low/Medium/High/Very High. Descriptive statistics were generated on the strong opioid patient population and overdose risk factors. The relationship between the prescribing of strong opioids and practice/patient-level factors was investigated using linear and logistic regression models. RESULTS: Eighty-five percent (46/54) of GP practices participated. 12.4% (42,382/341,240) of individuals in participating practices were prescribed opioids and, of these, one third (14,079/42,382) were prescribed strong opioids. The most common comorbidities and overdose risk factors among strong opioid recipients were pain (67.2%), cardiovascular disease (43.2%), and mental health problems (39.3%). There was a positive significant relationship between level of social deprivation among practice caseload and level of strong opioid prescribing (p < 0.001). People prescribed strong opioids tended to be older (mean 59.7 years) and female (8638, 61.4%) and, among a subset of patients, age, gender and opioid drug class were significantly associated with prescribing of High/Very High doses. CONCLUSIONS: Our findings have identified a large population at potential risk of prescription opioid overdose. There is a need to explore pragmatic models of tailored interventions which may reduce the risk of overdose within this group and clinical practice may need to be tightened to minimise overdose risk for individuals prescribed high dose opioids.

HIV diagnosis in older adults.

It is recognised that those diagnosed with HIV infection over the age of 50 have higher rates of morbidity and mortality. Little is known about how clinical presentation at diagnosis of HIV varies within this group. We sought to compare clinical presentation and markers of outcome among those diagnosed with HIV aged 60 and over vs. those diagnosed aged 50-59, over a ten-year period. The results showed that 84/111 were diagnosed with HIV aged 50-59 and 27/111 aged ≥60. Ethnicity and HIV risk factors were similar between groups, and most infections were sexually acquired with 7.4% of those aged ≥60 suspected to have a recent infection. Median CD4 cell count at presentation was significantly lower in the ≥60 age group (111 vs. 249; p < 0.001), and the proportion with a CD4 cell count <50 was also significantly lower in this population (33% vs. 15%; p = 0.04). In keeping with this, the frequency of AIDS-defining illness at diagnosis was higher in the ≥60 group (38% vs. 4%; p < 0.001). Co-morbidities were found in both groups, and 38% of those aged ≥60 at diagnosis were known to have since died compared to 4% of those aged 50-59 at diagnosis ( p ≤ 0.01). Those aged ≥60 had lower CD4 cell counts at diagnosis and more AIDS-defining illnesses, highlighting the increased risk of poor outcomes in this group. The majority of infections were sexually acquired. More work is needed to understand survival in adults diagnosed with HIV at an older age and to consider those over 60 as a specific population worthy of further research.

Conception, realization and qualification of a radioactive clean room lab facility dedicated to the synthesis of radiolabeled API for human ADME studies.

The human absorption, distribution, metabolism and elimination study administering radiolabeled drugs to human volunteers is an important clinical study in the development program of new drug candidates. The manufacture of radiolabeled Active Pharmaceutical Ingredients is covered by national drug laws and may come within the scope of regulatory GMP requirements. Additionally, authorities may request an appropriate environmental zoning to minimize the risk of microbiological contaminations particularly during the synthesis of radiolabeled Active Pharmaceutical Ingredients intended for parenteral application. Thus, a radioactive clean room lab facility in line with both GMP and radiation safety regulations was installed and the environmental zoning validated by appropriate testing of technical parameters and microbial and particle monitoring. The considerations detailed in this paper cover only GMP aspects related to the synthesis of radioactive drug substance. The subsequent, final formulation step in the overall process for manufacturing of radioactive drug product for any kind of administration is not within the scope of this paper. Under these qualified and controlled environmental conditions, we are now in a position to provide radiolabeled drug substances for all kinds of drug administration including both po and iv.

The prevalence of hepatitis C virus among people of South Asian origin in Glasgow - results from a community based survey and laboratory surveillance.

BACKGROUND: South Asians often present late with HCV or HBV related liver disease which could have been avoided with early diagnosis and subsequent treatment; however the prevalence of HCV/HBV among South Asians in Glasgow is not known. Accordingly, to inform the need for case finding among this group we aimed to examine the prevalence of Hepatitis C virus (HCV) among South Asians living in Glasgow. METHODS: A community-based survey recruited individuals at six mosques and four community centres serving the South Asian community during 2009-2010; participants had predominantly never been HCV tested. Laboratory surveillance data involving all individuals tested for HCV during 1993-2009 were examined and South Asians were identified using Nam Pehchan software. RESULTS: In the community-based survey, 2.6% of 1288 participants tested HCV-antibody positive; the prevalence ranged from 0.6% among those born in the UK to 3.1% among those born in Pakistan. The odds of testing HCV-antibody positive were significantly raised among those who had surgery in South Asia (aOR: 5.0, 95% CI: 2.0-12.3) and had either medical/dental treatment or an injection in South Asia (aOR: 2.2, 95% CI: 1.0-5.0). Of 6404 South Asians identified from laboratory surveillance data, 9.3% tested HCV positive. An estimated 38% (330/870) of HCV-infected South Asians living in Glasgow remain undiagnosed. CONCLUSIONS: South Asians living in Glasgow, particularly those born outside the UK are at greater risk of HCV infection than the general population. Efforts to increase awareness and testing in this population are warranted.

An improved method for specific and quantitative determination of the clopidogrel active metabolite isomers in human plasma.

Pharmacokinetic analyses of clopidogrel are hampered by the existence of multiple active metabolite isomers (H1 to H4) and their instability in blood. We sought to retest the pharmacodynamic activities of the four individual active metabolite isomers in vitro, with the ultimate aim of determining the isomers responsible for clopidogrel activity in vivo. In vitro activity was evaluated by measuring binding of [³³P]-2-methylthio-ADP on P2Y12-expressing Chinese hamster ovary (CHO) cells and human platelets in platelet-rich plasma (PRP). A stereoselective method that used reverse-phase ultra high-performance liquid chromatography (UHPLC) and tandem mass spectrometry (MS) was developed to measure individual concentrations of the stable 3'-methoxyacetophenone (MP) derivatives of H1-H4. The new method was used to analyze plasma samples from clopidogrel-treated subjects enrolled in a phase I clinical trial. In vitro binding assays confirmed the previously observed biological activity of H4 (IC50: CHO-P2Y12: 0.12 µM; PRP: 0.97 µM) and inactivity of H3, and demonstrated that H1 was also inactive. Furthermore, H2 demonstrated approximately half of the biological activity in vitro compared with H4. Optimisation of UHPLC conditions and MS collision parameters allowed the resolution and detection of the four derivatised active metabolite isomers (MP-H1 to MP-H4). The stereoselective assay was extensively validated, and was accurate and precise over the concentration range 0.5-250 ng/ml. Only MP-H3 and MP-H4 were quantifiable in incurred clinical samples. Based on in vitro pharmacodynamic data and found concentrations, the active metabolite isomer H4 is the only diastereoisomer of clinical relevance for documenting the pharmacokinetic profile of the active metabolite of clopidogrel.