Cost-effectiveness analysis of antiretroviral drugs for treatment-naive HIV infection in China.

INTRODUCTION: Dolutegravir (DTG)-based regimen was included in the expanded formulary of China's National Free Antiretroviral Treatment Program at the end of 2021. Yet high price of DTG and lack of health economic evaluation in China present barriers for implementation of the regimen. The study aims to investigate the lifetime cost-effectiveness of DTG-based regimen for treatment-naive HIV infection in China. METHODS: A decision-analytic Markov model was used to obtain the costs and effectiveness of four regimens: Arm A, efavirenz (EFV)-based regimen; Arm B, DTG-based regimen; Arm C, elvitegravir/cobicistat/tenofovir alafenamide/emtricitabine (EVG/c/FTC/TAF) regimen; Arm D, abacavir/lamivudine/dolutegravir (ABC/3TC/DTG) regimen. The potential impact of national centralized drug procurement policy was assessed in scenario analysis. The results were further validated through sensitivity analysis. RESULTS: Compared with other three regimens, DTG-based regimen led to the fewest cumulative adverse reactions, opportunistic infections and deaths. Compared with EFV-based regimen, the base-case ICERs for DTG-based regimen were 13,357 (USD/QALY) and 13,424 (USD/QALY) from the healthcare system and societal perspective respectively. In the policy scenario analysis with the procurement price of DTG equal to that of LPV/r, DTG-based regimen would be dominant. The model results remained robust in sensitivity analyses. CONCLUSIONS: DTG-based regimen for treatment-naive patients is likely to be cost-effective and deserve wider implementation in China. This study strongly suggests the centralized procurement of DTG to minimize cost and maximize cost-effectiveness.

Effectiveness, Safety, and Costs of Dolutegravir/Abacavir/Lamivudine Single-Tablet Regimen in a Real-Life Cohort of HIV-1 Adult Infected Patients.

Background: Real-life data on single-tablet regimen (STR) dolutegravir/abacavir/lamivudine (DTG/ABC/3TC) is scarce, and concerns about DTG neuropsychiatric adverse events (NP-AEs) have recently arisen. Objective: To explore the effectiveness and safety, in particular NP-AEs, of DTG/ABC/3TC in a cohort of HIV-1 adult infected patients. Pill burden, adherence to this STR, and the impact of switching on costs were also evaluated. Methods: This was an observational, retrospective study. The study population included antiretroviral therapy (ART)-naive and treatment-experienced (TE) patients who started DTG/ABC/3TC between February 1, 2016, and October 31, 2016. Effectiveness and safety were analyzed at week 48 (W48) by intention-to-treat analysis. The Cox regression model was used to investigate predictors of DTG/ABC/3TC discontinuation. Results: A total of 253 patients were included (44 ART naïve, 209 TE). At W48, the proportion of patients with virological suppression was 72.7% (95% CI = 58.4-87.0) in ART-naive patients, 85.6% (95% CI = 80.3-90.9) in previously suppressed TE patients, and 86.4% (95% CI = 65.1-97.1) in previously not suppressed TE patients. The rate of protocol-defined virological failure was 4.3%. The incidence of AEs was higher in the subgroup of ART-naive patients (56.1% vs 39.0%), with a rate of interruptions for this reason of 13.6% and 7.6%, respectively. The incidence of NP-AEs was 20.6%, with 3.9% of patients requiring discontinuation. Patients who had switched from a raltegravir-containing regimen discontinued DTG/ABC/3TC because of AEs more frequently (relative risk = 2.83; 95% CI = 1.04-7.72; P = 0.041) in the multivariate analysis. After switching to DTG/ABC/3TC, the median pill burden was reduced from 3 to 1 and the proportion of patients with an adherence <90%, from 20.1% to 12.0%. The annual per-patient ART costs increased by €48 (0.6% increase). Conclusion and Relevance: DTG/ABC/3TC is an effective strategy as first-line and switching ART. Our data suggest a worse tolerance in ART-naive patients, although the rate of discontinuation resulting from NP-AEs was relatively low. In the short-term, the adherence was slightly improved without significant changes in costs.

Alternative switching strategies based on regimens with a low genetic barrier: do clinicians have a choice nowadays?

Clinicians sometimes use switching strategies based on regimens such as RAL + ABC/3TC or RPV + ABC/3TC in order to resolve tolerability or safety issues associated with conventional recommended first-line strategies. Despite the low genetic barrier of these regimens, high safety and efficacy rates have been reported in retrospective studies.

Critical assessment of approaches for molecular docking to elucidate associations of HLA alleles with adverse drug reactions.

Adverse drug reactions have been linked with genetic polymorphisms in HLA genes in numerous different studies. HLA proteins have an essential role in the presentation of self and non-self peptides, as part of the adaptive immune response. Amongst the associated drugs-allele combinations, anti-HIV drug Abacavir has been shown to be associated with the HLA-B*57:01 allele, and anti-epilepsy drug Carbamazepine with B*15:02, in both cases likely following the altered peptide repertoire model of interaction. Under this model, the drug binds directly to the antigen presentation region, causing different self peptides to be presented, which trigger an unwanted immune response. There is growing interest in searching for evidence supporting this model for other ADRs using bioinformatics techniques. In this study, in silico docking was used to assess the utility and reliability of well-known docking programs when addressing these challenging HLA-drug situations. The overall aim was to address the uncertainty of docking programs giving different results by completing a detailed comparative study of docking software, grounded in the MHC-ligand experimental structural data - for Abacavir and to a lesser extent Carbamazepine - in order to assess their performance. Four docking programs: SwissDock, ROSIE, AutoDock Vina and AutoDockFR, were used to investigate if each software could accurately dock the Abacavir back into the crystal structure for the protein arising from the known risk allele, and if they were able to distinguish between the HLA-associated and non-HLA-associated (control) alleles. The impact of using homology models on the docking performance and how using different parameters, such as including receptor flexibility, affected the docking performance were also investigated to simulate the approach where a crystal structure for a given HLA allele may be unavailable. The programs that were best able to predict the binding position of Abacavir were then used to recreate the docking seen for Carbamazepine with B*15:02 and controls alleles. It was found that the programs investigated were sometimes able to correctly predict the binding mode of Abacavir with B*57:01 but not always. Each of the software packages that were assessed could predict the binding of Abacavir and Carbamazepine within the correct sub-pocket and, with the exception of ROSIE, was able to correctly distinguish between risk and control alleles. We found that docking to homology models could produce poorer quality predictions, especially when sequence differences impact the architecture of predicted binding pockets. Caution must therefore be used as inaccurate structures may lead to erroneous docking predictions. Incorporating receptor flexibility was found to negatively affect the docking performance for the examples investigated. Taken together, our findings help characterise the potential but also the limitations of computational prediction of drug-HLA interactions. These docking techniques should therefore always be used with care and alongside other methods of investigation, in order to be able to draw strong conclusions from the given results.

Cost-effectiveness of dolutegravir/abacavir/lamivudine in HIV-1 treatment-Naive (TN) patients in France.

BACKGROUND: To evaluate the cost-effectiveness of an integrase inhibitor (INI), dolutegravir (DTG), in combination with abacavir (ABC)/lamivudine (3TC) in France, in treatment-naive (TN) HIV adult patients. METHODS: The ARAMIS microsimulation Markov model, evaluates costs and effects of DTG vs. first-line ARVs options including INIs (raltegravir, elvitegravir/c), protease inhibitors (PIs) (darunavir/r, atazanavir/r, lopinavir/r), non-nucleoside reverse transcriptase inhibitors (efavirenz and rilpivirine). Efficacy and safety data were derived from phase III studies and network meta-analysis. Treatment algorithms were based on French guidelines and experts opinion. Costs included routine HIV and opportunistic infection care, and death. RESULTS: The model showed the fixed-dose combination DTG/ABC/3TC was more effective than all other recommended regimens: patients stayed longer on first-line, and lived longer and healthier. With the exception of EFV, DTG/ABC/3TC was more efficacious and less costly compared to all strategies. The cost per QALY gained (ICER) for DTG compared to EFV was €6,939. DTG/ABC/3TC was more efficacious and less costly compared to INIs and PIs in all deterministic sensitivity analyses. CONCLUSION: DTG/ABC/3TC was cost-effective in the management of HIV TN patients in France. These results are mainly explained by its lower price compared to other INIs and PIs, DTG's superior efficacy and high barrier to resistance.

An update on HLA alleles associated with adverse drug reactions.

Adverse drug reactions (ADRs) are considered as an important cause of morbidity and mortality. The hypersensitivity reactions are immune-mediated ADRs, which are dose-independent, unpredictable and have been associated with several HLA alleles. The present review aimed to describe HLA alleles that have been associated with different ADRs in populations worldwide, the recommendations of regulatory agencies and pharmacoeconomic information and databases for the study of HLA alleles in pharmacogenetics. A systematic search was performed in June 2016 of articles relevant to this issue in indexed journals and in scientific databases (PubMed and PharmGKB). The information of 95 association studies found was summarized. Several HLA alleles and haplotypes have been associated with ADRs induced mainly by carbamazepine, allopurinol, abacavir and nevirapine, among other drugs. Years with the highest numbers of publications were 2013 and 2014. The majority of the reports have been performed on Asians and Caucasians, and carbamazepine was the most studied ADR drug inducer. Two HLA alleles' databases are described, as well as the recommendations of the U.S. Food and Drug Administration, the European Medicine Agency and the Clinical Pharmacogenetics Implementation Consortium. Pharmacoeconomic studies on this issue are also mentioned. The strongest associations remain for HLA-B*58:01, HLA-B*57:01, HLA-B*15:02 and HLA-A*31:01 but only in certain populations; therefore, studies on different ethnic groups would be useful. Due to the improvement of drug therapy and the economic benefit that HLA screening represents, investigations on HLA alleles associated with ADR should continue.

Assessment of pharmacogenetic tests: presenting measures of clinical validity and potential population impact in association studies.

The progressing discovery of genetic variants associated with drug-related adverse events has raised expectations for pharmacogenetic tests to improve drug efficacy and safety. To further the use of pharmacogenetics in health care, tests with sufficient potential to improve efficacy and safety, as reflected by good clinical validity and population impact, need to be identified. The potential benefit of pharmacogenetic tests is often concluded from the strength of the association between the variant and the adverse event; measures of clinical validity are generally not reported. This paper describes measures of clinical validity and potential population health impact that can be calculated from association studies. We explain how these measures are influenced by the strength of the association and by the frequencies of the variant and the adverse event. The measures are illustrated using examples of testing for HLA-B*5701 associated with abacavir-induced hypersensitivity and SLCO1B1 c.521T>C (*5) associated with simvastatin-induced adverse events.

Effectiveness and safety of generic version of abacavir/lamivudine and efavirenz in treatment naïve HIV-infected patients: a nonrandomized, open-label, phase IV study in Cali-Colombia, 2011-2012.

BACKGROUND: Generic drug policies are often associated with concerns about the quality and effectiveness of these products. Phase IV clinical trials may be a suitable design to assess the effectiveness and safety of generic drugs. The objective of this study was to describe the effectiveness and the safety of the generic abacavir/lamivudine and efavirenz in treatment-naïve HIV-infected patients. METHODS: A monocentric, nonrandomized, open-label, phase IV study in treatment naïve HIV-infected patients 18 years or older with indication to receive abacavir/lamivudine and efavirenz were recruited from a program that provides comprehensive outpatient consultation and continuing care. The primary end-point was to achieve viral load <40 copies/mL at 12 months after baseline to assess effectiveness. Secondary end-point of the study were 1) to asses increasing in T-CD4 lymphocytes levels as accompaniment to asses effectiveness, and 2) to assess both gastrointestinal, skin, and central nervous system symptoms, and lipid profile, cardiovascular risk, renal, and hepatic function as safety profile. Data were determined at baseline, 3, 6, and 12 months. Close clinical monitoring and pharmaceutical care were used for data collection. Wilcoxon matched-pairs signed-rank test was used to compare proportions or medians. RESULTS: Sixty patients were invited to participate in the study; 42 were enrolled and 33 completed the follow-up. Of the nine patients excluded from the study, only one was withdrawn due to adverse events. At 12 months, 31 of 42 patients (73.8 % in intention-to-treat analysis) achieved a viral load of HIV1 RNA <40 copies/mL. There was a significant increase (172 cells/mm3) in the median for CD4 T lymphocyte count. The adverse events were mild and met the safety profile for this antiretroviral regimen, mainly of central nervous system symptoms, skin rash, lipid abnormalities, and an increase of 2 % in the median of the percentage of cardiovascular risk. CONCLUSIONS: The clinical outcomes of generic version of abacavir/lamivudine and efavirenz in HIV treatment naïve patients showed the expected safety and effectiveness profile of proprietary ARV drugs. TRIAL REGISTRATION: Registro Público Cubano de Ensayos Clínicos (RPCEC) ID: RPCEC00000202 . Registered 19 November 2015.

HLA-B*57: 01 genotyping in the prevention of hypersensitivity to abacavir: 5 years of experience.

INTRODUCTION: Most of the cost-effectiveness analyses are based on estimations to make decisions on the future implementation of a test. However, the model should be verified with real data to prove that previous estimations have been successfully fulfilled. OBJECTIVE: To study the economic impact of the systematic HLA-B*57:01 genotyping in preventing hypersensitivity reactions (HSRs) in the patient population of a tertiary-care hospital treated with abacavir (ABC) using retrospective data of 5 years of experience. METHODS: A retrospective study was carried out with two cohorts including 780 and 473 patients before and after the implementation of the systematic HLA-B*57:01 genotyping before ABC treatment. Cost-effectiveness analysis was carried out by the parameter 'cost per HSR avoided'. The clinical utility of the test was verified by evaluating the differences in HSR incidence between both cohorts. Finally, a sensitivity analysis including all variables was carried out. RESULTS: In the population studied, systematic genotyping represents an additional cost of &OV0556;306 per HSR avoided. In the sensitivity analysis, pharmacological therapy cost is the major influencing factor found in the estimation of the 'cost per HSR avoided'. In terms of clinical utility, the incidence ratio was 0.040 (95% confidence interval 0.0009-0.2399) and statistically significant differences were found between both groups (P=1.40×10). CONCLUSION: Retrospective data from 5 years of experience have confirmed the cost-effectiveness of the systematic genotyping in candidate patients for ABC therapy, and have shown that cost-effectiveness is a dynamic parameter closely linked to allele prevalence and pharmacological therapy costs.

A Phase II Study of 3'-Deoxy-3'-18F-Fluorothymidine PET in the Assessment of Early Response of Breast Cancer to Neoadjuvant Chemotherapy: Results from ACRIN 6688.

UNLABELLED: Our objective was to determine whether early change in standardized uptake values (SUVs) of 3'deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) using PET with CT could predict pathologic complete response (pCR) of primary breast cancer to neoadjuvant chemotherapy (NAC). The key secondary objective was to correlate SUV with the proliferation marker Ki-67 at baseline and after NAC. METHODS: This prospective, multicenter phase II study did not specify the therapeutic regimen, thus, NAC varied among centers. All evaluable patients underwent (18)F-FLT PET/CT at baseline (FLT1) and after 1 cycle of NAC (FLT2); 43 patients were imaged at FLT1, FLT2, and after NAC completion (FLT3). The percentage change in maximum SUV (%ΔSUVmax) between FLT1 and FLT2 and FLT3 was calculated for the primary tumors. The predictive value of ΔSUVmax for pCR was determined using receiver-operating-characteristic curve analysis. The correlation between SUVmax and Ki-67 was also assessed. RESULTS: Fifty-one of 90 recruited patients (median age, 54 y; stage IIA-IIIC) met the eligibility criteria for the primary objective analysis, with an additional 22 patients totaling 73 patients for secondary analyses. A pCR in the primary breast cancer was achieved in 9 of 51 patients. NAC resulted in a significant reduction in %SUVmax (mean Δ, 39%; 95% confidence interval, 31-46). There was a marginal difference in %ΔSUVmax_FLT1-FLT2 between pCR and no-pCR patient groups (Wilcoxon 1-sided P = 0.050). The area under the curve for ΔSUVmax in the prediction of pCR was 0.68 (90% confidence interval, 0.50-0.83; Delong 1-sided P = 0.05), with slightly better predictive value for percentage mean SUV (P = 0.02) and similar prediction for peak SUV (P = 0.04). There was a weak correlation with pretherapy SUVmax and Ki-67 (r = 0.29, P = 0.04), but the correlation between SUVmax and Ki-67 after completion of NAC was stronger (r = 0.68, P < 0.0001). CONCLUSION: (18)F-FLT PET imaging of breast cancer after 1 cycle of NAC weakly predicted pCR in the setting of variable NAC regimens. Posttherapy (18)F-FLT uptake correlated with Ki-67 on surgical specimens. These results suggest some efficacy of (18)F-FLT as an indicator of early therapeutic response of breast cancer to NAC and support future multicenter studies to test (18)F-FLT PET in a more uniformly treated patient population.

Cost-effectiveness of DTG + ABC/3TC versus EFV/TDF/FTC for first-line treatment of HIV-1 in the United States.

OBJECTIVE: Data from the SINGLE trial demonstrated that 88% of treatment-naïve HIV-1 patients treated with dolutegravir and abacavir/lamivudine (DTG + ABC/3TC) achieved viral suppression at 48 weeks compared with 81% of patients treated with efavirenz/tenofovir disoproxil fumarate/emtricitabine (EFV/TDF/FTC). It is unclear how this difference in short-term efficacy impacts long-term cost-effectiveness of these regimens. This study sought to evaluate long-term cost-effectiveness of DTG + ABC/3TC vs EFV/TDF/FTC from a US payer perspective. METHODS: This study is an individual discrete-event simulation which tracked the disease status and treatment pathway of HIV-1 patients. The model simulated treatment over a lifetime horizon by tracking change in patients' CD4 count, clinical events occurrence (opportunistic infections, cancer, and cardiovascular events), treatment switch, and death. The model included up to four lines of treatment. Baseline patient characteristics, efficacy, and safety of DTG + ABC/3TC and EFV/TDF/FTC were informed by data from the SINGLE trial. The efficacy of subsequent treatment lines, clinical event risks, mortality, cost, and utility inputs were based on literature and expert opinion. Outcomes were lifetime discounted medical costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratio (ICER). RESULTS: Compared with EFV/TDF/FTC, DTG + ABC/3TC increased lifetime costs by $19,153 and per person survival by 0.12 QALYs, resulting in an ICER of $158,890/QALY. ICERs comparing DTG + ABC/3TC to EFV/TDF/FTC remained above the traditional, US willingness-to-pay threshold of $50,000/QALY gained in all scenarios, and above $100,000 or $150,000/QALY gained in most scenarios. LIMITATIONS: Due to data limitations, the treatment patterns, CD4 count during viral rebound and treatment switch, viral rebound after trial end, and long-term adverse event-related treatment discontinuation were based on assumptions, presented to and approved by clinical experts. CONCLUSIONS: Compared with EFV/TDF/FTC, DTG + ABC/3TC resulted in higher cost and only slightly increased QALYs over a lifetime, with an ICER that exceeded the standard cost-effectiveness threshold. This indicates that the incremental benefit in effectiveness associated with DTG + ABC/3TC may not be worth the incremental increase in costs.

Economic efficiency of genetic screening to inform the use of abacavir sulfate in the treatment of HIV.

BACKGROUND: Abacavir sulfate (abacavir) is associated with a hypersensitivity reaction (HSR) that affects 5-8% of patients. While serious complications are rare, failure to identify it, or abacavir re-challenge following HSR, can be fatal. Genetic screening for HLA-B*5701 can identify patients who are likely to experience an HSR and reduces the incidence of the reaction. OBJECTIVE: We assessed the intrinsic and practical value, from the US healthcare system perspective, of prospective HLA-B*5701 screening among a population of antiretroviral-naive patients without elevated risk factors for cardiovascular disease, plasma HIV RNA >100,000 copies/mL, or pre-existing renal insufficiency. METHODS: Two approaches were used to evaluate the costs and benefits of prospective screening. First, the efficiency of HLA-B*5701 screening compared with no screening prior to abacavir initiation (intrinsic value of screening) was evaluated using a 60-day decision-tree model. Next, the practical value of screening was assessed using a lifetime discrete-event simulation model that compared HLA-B*5701 screening prior to abacavir use versus initiation with a tenofovir-containing regimen. Screening-effectiveness parameters were taken from an open-label trial that incorporated screening prior to abacavir initiation and other published studies. Treatment efficacy was derived from clinical trials. Modelling assumptions, costs ($US, year 2007 values) and other parameters were derived from published sources, primary data analysis and expert opinion. Multiple one-way sensitivity and scenario analyses were performed to assess parameter uncertainty. The primary outcome measure for the short-term screening versus no screening analysis was cost per patient. For the long-term analysis, outcomes were presented as QALYs. Costs and effects were discounted at 3% per year. RESULTS: Over the first 60 days of treatment, prospective screening prior to abacavir initiation cost an additional $US17 per patient and avoided 537 HSRs per 10,000 patients. The per-patient cost of screening was sensitive to the cost of the genetic test, HSR costs and screening performance. In the lifetime model, screening-informed abacavir use was more effective and less costly than initiation with a tenofovir-containing regimen in the base case and in sensitivity analyses. CONCLUSIONS: Our results suggest that prospective HLA-B*5701 screening prior to abacavir initiation produces cost savings and should become a standard component of HIV care.

Cost impact of prospective HLA-B*5701-screening prior to abacavir/lamivudine fixed dose combination use in Germany.

OBJECTIVE: Avoiding abacavir in HIV-infected patients tested positive for HLA-B*5701 reduces the risk of abacavir hypersensitivity reaction (ABC-HSR). Our aim was to assess the costs of clinically suspected HSR and to estimate potential cost savings of implementing prospective HLA-B*5701-screening for HIV-infected patients initiating abacavir/lamivudine fixed-dose combination (ABC/3TC FDC) compared to initiating respective treatment without screening. METHODS: Employing a decision tree model the expected HSR-related costs of screening vs. no screening were estimated from the societal and healthcare payer perspective (reference year 2007). A retrospective standardized assessment of all clinically suspected ABC-HSR cases without screening at 5 German HIV-centres was performed to measure resource consumption. In- and outpatient care, discarded ABC/3TC FDC and concomitant medication were considered. Direct resource utilization was valued using German fees (EBM, G-DRGs). Indirect costs were measured with the human capital approach. Estimates for the HLA-B*5701-prevalence, HSR-incidence, and hospitalization rate were based on clinical trials and cohorts and it was assumed that screening reduces the incidence of clinically suspected ABC-HSR from 10% to 0.5%. RESULTS: Thirty-two ABC-HSR cases were identified from 1998 to 2007. Mean direct and total costs per clinically suspected HSR case were Euro 1,362 and Euro 2,235, respectively. Hospital costs contributed 63.3% to direct costs. Potential cost savings when implementing genetic screening were estimated at Euro 44 and Euro 127 per screened patient, from a healthcare payer or societal perspective. CONCLUSION: HLA-B*5701 screening prior to ABC/3TC FDC initiation prevents significant HSR-related costs per screened patient and is likely to lead to overall net savings.

Cost-effectiveness analysis of HLA-B*5701 typing in the prevention of hypersensitivity to abacavir in HIV+ patients in Spain.

INTRODUCTION: Approximately 4% to 8% of patients with HIV-1 treated with abacavir present a hypersensitivity reaction (HSR). Various studies have shown a direct association between human leukocyte antigen (HLA)-B*5701 and HSR to abacavir. The objective of this study was to analyze whether systematic HLA-B*5701 testing to prevent HSR in patients treated with abacavir is a cost-effective option for the Spanish National Health System. METHODS: An analytical decision-making model was constructed as a decision tree model for a simulated cohort of 1000 HIV patients to evaluate whether HLA-B*5701 testing to prevent HSR to abacavir was cost effective compared with not performing the test. The parameters included in the model and the use of healthcare resources should the patient develop HSR were taken from the PREDICT-1 study and the opinion of clinical experts. The principal result obtained was the incremental cost per HSR avoided. The time horizon of the analysis was to 2 months [corrected] . All costs were expressed in 2008 Euros. RESULTS: The analysis showed that the total direct healthcare costs per patient were €1344 and €1322 with and without HLA-B*5701 testing respectively, and that 36 cases of HSR were prevented per 1000 screened patients. These results yielded a cost per HSR avoided of €630. The sensitivity analysis showed that the results were sensitive to the cost of the test, with an economic saving of €102 or a cost-effectiveness ratio of €4234. CONCLUSIONS: The model predicts that generalized use of the HLA-B*5701 test before prescribing abacavir in HIV+ patients could represent an economic saving or a limited additional cost for the National Health System which may be counterbalanced by the benefits in terms of a lower incidence of HSR.

Successful implementation of a national HLA-B*5701 genetic testing service in Canada.

Abacavir is a nucleoside reverse transcriptase inhibitor (NRTI) that is used in combination antiretroviral therapy in HIV-infected patients. It is currently recommended as a preferred or an alternative NRTI in antiretroviral-naïve patients. The major toxicity of abacavir is a hypersensitivity reaction (HSR), which occurs in approximately 5% of treated patients. There is a strong association between the human leukocyte antigen (HLA)-B*5701 allele and abacavir HSR, which has allowed for rapid acceptance of genetic screening for HLA-B*5701 in clinical use. Canadian clinicians working in hospital centers with HLA typing capacity opted to launch a pilot project in 2006 to offer the screening test as standard of care to HIV-infected patients. Currently, more than 11,000 HLA-B*5701 tests have been performed, among which 6.3% are positive. Continued efforts have been made to ensure that testing is available to all HIV-infected patients to widen the patients' therapeutic options. HLA-B*5701 screening shows clinical use and preliminary data suggest cost-effectiveness.

The medical and economic roles of pipeline pharmacogenetics: Alzheimer's disease as a model of efficacy and HLA-B(*)5701 as a model of safety.

Pharmacogenetics (PGX) is the study of drug response as a function of an individual's DNA. PGX is often viewed as an extension of disease association genetics, and although this information may be related, it is not the study of drug response. Although medicines are used to treat diseases, the value of strategies that identify and incorporate DNA biomarkers associated with clinical efficacy, or DNA biomarkers for untoward clinical responses, can be applied directly to pharmaceutical pipelines. The growth of adverse event PGX studies involving marketed medicines generally uses relatively large numbers of affected patients, but has been productive. However, the two critical strategies for pipeline genetics must make use of fewer patients: (1) the early identification of efficacy signals so that they can be applied early in development for targeted therapies and (2) identification of safety signals that can subsequently be validated prospectively during development using the least number of patients with adverse responses. Assumptions are often made that large numbers of patients are necessary to recognize PGX hypotheses and to validate DNA biomarkers. In some ways, pipeline pharmacogenetics may be viewed as the opposite of current genome-wide scanning designs. The goal is to obtain PGX signals in as few patients as possible, and then validate PGX hypotheses for specificity and sensitivity as development trials go forward--not using hundreds of thousand of markers to detect strong linkage disequilibrium signals in thousands of patients and their controls. Drug development takes 5-7 years for a drug candidate to traverse to registration--and this is similar to the timeframe for validating genetic biomarkers using sequential clinical trials. Two important examples are discussed, the association of APOE genotypes to the demonstration of actionable efficacy signals for the use of rosiglitazone for Alzheimer's disease; and the identification of HLA-B(*)5701 as a highly sensitive and specific predictive marker for abacavir treated patients who will develop hypersensitivity syndrome (HSS). The rosiglitazone study prevented pipeline attrition by changing the interpretation of a critical Phase IIB proof of concept study (2005) from a failed study, to a positive efficacy response in a genetically predictable proportion of patients. Now, three years later, a Phase III program of clinical trials using pharmacogenetic designs is months away from completion (late08). If successfully registered (early09), millions of patients could benefit, and efficacy PGX would have achieved its first prospective block-buster. The use of safety candidate gene association genetics in patients who received abacavir therapy and developed HSS starting in 1998 culminated in a double blind clinical trial that determined sensitivity > 97% and specificity >99% in 2007. Clinical consensus panels rapidly recommended abacavir as the preferred therapy along with HLA-B(*)5701 pre-testing, immediately increasing the market share of abacavir with respect to other reverse transcriptases that are associated with there own adverse events. Targeting of medicines during drug development is now possible, practical, and profitable.