Allopurinol pharmacogenetics: assessment of potential clinical usefulness

Response to the FDA Decision Regarding DPYD Testing Prior to Fluoropyrimidine Chemotherapy

Fluoropyrimidine (FP) chemotherapy is associated with severe, life-threatening toxicities, particularly among patients who carry deleterious germline variants in the DPYD gene. Pretreatment DPYD testing is standard of care throughout most of Europe; however, it has not been recommended in clinical practice guidelines in the United States. Due to increased risk of severe toxicity, a Citizen's Petition asked the US Food and Drug Administration (FDA) to update language in FP drug labels to recommend DPYD testing as part of a boxed warning and recommend FP dose reduction in patients carrying deleterious germline variants. In response, the FDA updated the capecitabine package insert to inform patients about the toxicity risk and test availability and consider DPYD testing. However, the FDA did not include a testing recommendation or requirement, or a boxed warning. Additionally, the FDA did not recommend FP dose adjustment in DPYD variant carriers. This review provides a critical assessment of the DPYD-FP pharmacogenetic association using the FDA's previously published Pharmacogenetic Pyramid, demonstrating that the evidence is compelling for recommending DPYD testing prior to FP treatment. Additionally, the FDA's stated concerns about recommending DPYD testing and DPYD-guided FP dose adjustment are addressed and discussed in the context of the FDA's other genetic testing and dose adjustment recommendations. We call on the FDA to follow our European counterparts in recommending DPYD testing and genotype-based dose adjustment to ensure patients with cancer receive safe and effective FP chemotherapy.

Predominant HLA Alleles and Haplotypes in Mild Adverse Drug Reactions Caused by Allopurinol in Vietnamese Patients with Gout

Allopurinol (ALP) is commonly used as a drug for gout treatment. However, ALP is known to cause cutaneous adverse reactions (CARs) in patients. The HLA-B^*58:01 allele is considered a biomarker of severe CAR (SCAR) in patients with gout, with symptoms of Stevens Johnson syndrome, and with toxic epidermal necrolysis. However, in patients with gout and mild cutaneous adverse drug reactions (MCARs), the role of HLA-allele polymorphisms has not been thoroughly investigated. In this study, 50 samples from ALP-tolerant patients and ALP-induced MCARs patients were genotyped in order to examine the polymorphisms of their HLA-A and HLA-B alleles. Our results showed that the frequencies of HLA-A^*02:01/HLA-A^*24:02 and HLA-A^*02:01/HLA-A^*29:01, the dual haplotypes in HLA-A, in patients with ALP-induced MCARs were relatively high, at 33.3% (7/21), which was HLA-B^*58:01-independent, while the frequency of these dual haplotypes in the HLA-A locus in ALP-tolerant patients was only 3.45% (1/29). The HLA-B^*58:01 allele was detected in 38% (8/21) of patients with ALP-induced MCARs, and in 3.45% (1/29) of ALP-tolerant patients. Notably, although HLA-B^*58:01 may be a cause for the occurrence of MCARs in patients with gout, this correlation was not as strong as that previously reported in patients with SCAR. In conclusion, in addition to the HLA-B^*58:01 allele, the presence of the dual haplotypes of HLA-A^*02:01/HLA-A^*24:02 and/or HLA-A^*02:01/HLA-A^*29:01 in the HLA-A locus may also play an important role in the appearance of ALP-induced MCARs in the Vietnamese population. The obtained primary data may contribute to the development of suitable treatments for patients with gout not only in Vietnam but also in other Asian countries.

Epidemiology and Risk Factors for Severe Delayed Drug Hypersensitivity Reactions

Severe delayed drug hypersensitivity reactions comprise different clinical entities and can involve different immune-mediated mechanisms. Common examples are severe cutaneous adverse reactions and druginduced internal organ injuries. The incidence of such reactions is overall low but seems to be on the rise reaching numbers as high as 9 per million individuals-years in the case of SJS/TEN and DRESS. Such conditions carry an important associated morbidity, and mortality can attain 40% in SJS/TEN patients, making these hypersensitivity reactions important targets when implementing preventive measures. Several risk factors have been identified for reaction severity; some are transverse, such as older age and underlying chronic diseases. The recent advances in pharmacogenetics allowed the identification of specific populations with higher risk and permitted strategic avoidance of certain drugs being HLA-B*57:01 screening in patients initiating abacavir the best successful example. In this work, we reviewed the epidemiology of SCARs and liver/kidney/lung drug-induced immune-mediated reactions. We focus on particular aspects such as prevalence and incidence, drugs involved, mortality and risk factors.

Heart disease and the risk of allopurinol-associated severe cutaneous adverse reactions: a general population-based cohort study

BACKGROUND

Allopurinol is commonly prescribed for gout, and its clinical use may expand with ongoing trials assessing its potential cardiorenal benefits. Because heart disease has been suggested to be a risk factor for allopurinol-associated severe cutaneous adverse reactions, we sought to confirm this association in a Canadian general population cohort.

METHODS

We used population data from British Columbia, Canada, to identify all incident allopurinol users between 1997 and 2015. We examined the association between heart disease (ischemic heart disease and heart failure) and the risk of hospital admission for severe cutaneous adverse reactions, adjusting for known and purported risk factors. We also evaluated the joint effects of combined clinical and demographic risk factors.

RESULTS

Among 130 325 allopurinol initiators, 109 hospital admissions occurred for allopurinol-associated severe cutaneous adverse reactions. The multivariable relative risk among those with heart disease was 1.55 (95% confidence interval 1.01-2.37). Patients with heart disease and chronic kidney disease who were started on an allopurinol dosage of greater than 100 mg/d had an 11-fold higher risk. Allopurinol initiation at a lower dosage among patients with heart disease and chronic kidney disease resulted in a fivefold reduction in risk. Older women with heart disease from regions with large Asian populations had a 23-fold higher risk of allopurinol-associated severe cutaneous adverse reactions than younger men without heart disease from other regions.

INTERPRETATION

Heart disease is independently associated with risk of allopurinol-associated severe cutaneous adverse reactions, similar to chronic kidney disease, and low-dosage allopurinol initiation may substantially mitigate this risk. Risk factors for these rare but serious reactions should be considered when initiating allopurinol.

A retrospective investigation of HLA-B*5801 in hyperuricemia patients in a Han population of China

BACKGROUND

Hyperuricemia and gout have become increasingly prevalent in China. Allopurinol is an effective urate-lowering therapy, but it has severe side effects. HLA-B*5801 is highly associated with the allopurinol-induced toxic epidermal necrolysis and Stevens-Johnson syndrome.

PATIENTS AND METHODS

In this retrospective report, we had genotyped HLA-B*5801 in 253 cases of hyperuricemia and gout patients in a Han population in Shenzhen and analyzed the clinical management of medications.

RESULTS

We found 30 carriers of the HLA-B*5801 allele in 253 cases of hyperuricemia or gout patients in the population (11.9%). Allopurinol was prescribed in both HLA-B*5801-positive and HLA-B*5801-negative groups. The evaluation of four models with or without genetic screening and management of allopurinol or febuxostat indicated that the HLA-B*5801 screening had significant cost benefit for clinical management.

CONCLUSION

For appropriate management and cost-effectiveness, the HLA-B*5801 allele should be screened in all patients with hyperuricemia and gout in the Chinese population.

Pharmacogenetic Labeling of FDA-Approved Drugs: A Regulatory Retrospective

The U.S. Food and Drug Administration recently marked 10 years since first updating the labeling for warfarin (often referred to as the “poster child” of pharmacogenomics) to include information regarding the potential impact of CYP2C9 and VKORC1 genetic variation on warfarin dosing requirements and risks. Herein, we opine on the experience updating the warfarin labeling, highlighting more generally the enabling factors and challenges encountered when considering incorporation of pharmacogenomic information into the prescribing recommendations for already approved drugs. We also provide a historical perspective of implemented changes in regulatory policies related to personalized medicine.

Racial/ethnic variation and risk factors for allopurinol-associated severe cutaneous adverse reactions: a cohort study

OBJECTIVES

To examine associations of race/ethnicity and purported risk factors with hospitalised allopurinol-associated severe cutaneous adverse reactions (AASCARs).

METHODS

We used US Medicaid data to identify incident allopurinol users between 1999 and 2012. We examined the risk of hospitalised AASCARs according to race/ethnicity and purported key risk factors and calculated relative risks (RR).

RESULTS

Among 400 401 allopurinol initiators, we documented 203 hospitalised AASCAR cases (1 in 1972 initiators). The average AASCAR hospitalisation was 9.6 days and 43 individuals (21%) died. The multivariable-adjusted RRs for AASCARs among blacks, Asians and Native Hawaiians/Pacific Islanders compared with whites or Hispanics were 3.00 (95% CI 2.18 to 4.14), 3.03 (95% CI 1.72 to 5.34) and 6.68 (95% CI 4.37 to 10.22), respectively. Female sex, older age (≥60 years), chronic kidney disease and initial allopurinol dose (>100 mg/day) were independently associated with a 2.5-fold, 1.7-fold, 2.3-fold and 1.9-fold higher risk of AASCAR, respectively. In our combined demographic analysis, older women (≥60 years) of a high-risk race/ethnicity (blacks, Asians or Native Hawaiians/Pacific Islanders) had over a 12-fold higher risk of hospitalised AASCARs than younger men of a low-risk race/ethnicity (whites or Hispanics) (multivariable-adjusted RR, 12.25; 95% CI 6.46 to 23.25).

CONCLUSIONS

This racially diverse (yet mostly white) cohort study indicates that the risk of hospitalised AASCAR is rare overall, although blacks, Asians and Native Hawaiians/Pacific-Islanders have a substantially higher risk of hospitalised AASCARs, particularly among older women. These data also support the practice of initiating allopurinol at a low dose (eg, ≤100 mg/day).

Impact of HLA-B*58:01 allele and allopurinol-induced cutaneous adverse drug reactions: evidence from 21 pharmacogenetic studies

Allopurinol is widely used for hyperuricemia and gouty arthritis, but is associated with cutaneous adverse drug reactions (CADRs). Recently, HLA-B*58:01 allele was identified as a strong genetic marker for allopurinol-induced CADRs in Han Chinese. However, the magnitude of association and diagnosis value of HLA-B*58:01 in allopurinol-induced CADRs remain inconclusive. To investigate this inconsistency, we conducted a meta-analysis of 21 pharmacogenetic studies, including 551 patients with allopurinol-induced CADRs, and 2,370 allopurinol-tolerant controls as well as 9,592 healthy volunteers. The summary OR for allopurinol-induced CADRs among HLA-B*58:01 carriers was 82.77 (95% CI: 41.63 – 164.58, P < 10⁻⁵) and 100.87 (95% CI: 63.91 – 159.21, P < 10⁻⁵) in matched and population based studies, respectively. Significant results were also observed when stratified by outcomes and ethnicity. Furthermore, the summary estimates for quantitative analysis of HLA-B*58:01 allele carriers in allopurinol-induced CADRs screening were as follows: sensitivity, 0.93 (95% CI: 0.85 – 0.97); specificity, 0.89 (95% CI: 0.87 – 0.91); positive likelihood ratio, 8.24 (95% CI: 6.92 – 9.81); negative likelihood ratio, 0.084 (95% CI: 0.039 – 0.179); and diagnostic odds ratio, 98.59 (95% CI: 43.31 – 224.41). The AUSROC was 0.92 (95% CI: 0.89–0.94), indicating the high diagnostic performance. Our results indicated that allopurinol–SCAR is strongly associated with HLA-B*58:01, and HLA-B*58:01 is a highly specific and effective genetic marker for the detection allopurinol-induced CADRs, especially for Asian descents.

Applications of pharmacogenomics in regulatory science: a product life cycle review

With rapid developments of pharmacogenomics (PGx) and regulatory science, it is important to understand the current PGx integration in product life cycle, impact on clinical practice thus far and opportunities ahead. We conducted a cross-sectional review on PGx-related regulatory documents and implementation guidelines in the United States and Europe. Our review found that although PGx-related guidance in both markets span across the entire product life cycle, the scope of implementation guidelines varies across two continents. Approximately one-third of Food and Drug Administration (FDA)-approved drugs with PGx information in drug labels and half of the European labels posted on PharmGKB website contain recommendations on genetic testing. The drugs affected 19 and 15 World Health Organization Anatomical Therapeutic Chemical drug classes (fourth level) in the United States and Europe, respectively, with protein kinase inhibitors (13 drugs in the United States and 16 drugs in Europe) being most prevalent. Topics of emerging interest were novel technologies, adaptive design in clinical trial and sample collection.

Tailoring of recommendations to reduce serious cutaneous adverse drug reactions: a pharmacogenomics approach

The Health Sciences Authority launched a pharmacogenetics initiative in 2008 to facilitate evaluation of pharmacogenetics associations pertinent for Chinese, Malays and Indians in Singapore. The aim was to reduce the incidence and unpredictability of serious adverse drug reactions, with a focus on serious skin adverse drug reactions. This paper describes the gathering of evidence and weighing of factors that led to different genotyping recommendations for HLA-B*15:02 with carbamazepine and HLA-B*58:01 with allopurinol, despite both having strong genetic associations. Translation of pharmacogenomics at a national level requires careful deliberation of the prevalence of at-risk allele, strength of genetic associations, positive predictive value, cost-effectiveness and availability of alternative therapies. Our experience provides a perspective on translating genomic discoveries in advancing drug safety.

Cost-effectiveness Analysis for Genotyping before Allopurinol Treatment to Prevent Severe Cutaneous Adverse Drug Reactions

OBJECTIVE

Patients with an HLA-B*58:01 allele have an increased risk of developing severe cutaneous adverse drug reactions (SCAR) when treated with allopurinol. Although one-off pharmacogenetic testing may prevent life-threatening adverse drug reactions, testing prior to allopurinol initiation incurs additional costs. The study objective was to evaluate the cost-effectiveness of HLA-B*58:01 screening compared with using other available urate-lowering agents (ULA).

METHODS

A decision-analytical model was used to compare direct medical costs and effectiveness [including lifetime saved, quality-adjusted life-yrs (QALY) gained] in treating new patients with the following options: (1) genetic screening followed by allopurinol prescribing for noncarriers of HLA-B*58:01, (2) prescribing benzbromarone without screening, (3) prescribing febuxostat without screening, and (4) prescribing allopurinol without screening. A 1-year time frame and third-party payer perspective were modeled for both the entire cohort (base-case) and for the subgroup of patients with chronic kidney disease (CKD).

RESULTS

The incremental cost-effectiveness ratio of genetic screening prior to ULA therapy was estimated as New Taiwan (NT) $234,610 (US$7508) per QALY gained in the base-case cohort. For patients with CKD, it was estimated as NT$230,925 (US$7390) per QALY. The study results were sensitive to the probability of benzbromarone/febuxostat-related hypersensitivity, and a negative predicted value of genotyping.

CONCLUSION

HLA-B*58:01 screening gave good value for money in preventing allopurinol-induced SCAR in patients indicated for ULA therapy. In addition to the costs of genotyping, it is important to monitor ULA safety closely in adopting HLA-B*58:01 screening in practice.

The cost-effectiveness of HLA-B*5801 screening to guide initial urate-lowering therapy for gout in the United States

OBJECTIVE

Positive HLA-B*5801 carriers are at greater risk of experiencing rare but severe allopurinol hypersensitivity syndrome (AHS) [i.e., Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN)]; however, HLA-B*5801 prevalence and AHS risk vary by race/ethnicity. We evaluated the cost-effectiveness of HLA-B*5801 testing according to race/ethnicity in the United States.

METHODS

We determined the cost-effectiveness of universal testing for HLA-B*5801 compared to no testing prior to the initiation of allopurinol per US major race/ethnicity groups. Using US-specific data, SJS/TEN risks and HLA-B*5801 prevalences were modeled per race/ethnicity (i.e., 1/3846 and 0.7% among Caucasians and Hispanics, 1/735 and 3.8% among African Americans, and 1/336 and 7.4% among Asians, respectively). Those who tested positive for HLA-B*5801 received febuxostat. Costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) were estimated over a lifetime.

RESULTS

Compared to no testing, universal testing for HLA-B*5801 costs more and was more effective for all races/ethnicities. The ICERs varied substantially across racial/ethnic groups, following their HLA-B*5801 prevalences. HLA-B*5801 testing was cost-effective for African Americans (ICER $83,450) and Asians (ICER $64,190), but not for Caucasians or Hispanics (ICER $183,720), using accepted US willingness-to-pay threshold ($109,000/QALY). Results were robust in sensitivity analyses, except that reducing the risk of SJS/TEN by a half made testing not cost-effective for all races/ethnicities.

CONCLUSION

Testing for HLA-B*5801 prior to allopurinol initiation is cost-effective for Asians and African Americans, but not for Caucasians or Hispanics in the United States. Reducing AHS risk by other predictive measures could make HLA-B*5801 testing not cost-effective even among Asians and Blacks.

Measuring High-Risk Patients' Preferences for Pharmacogenetic Testing to Reduce Severe Adverse Drug Reaction: A Discrete Choice Experiment

OBJECTIVES

To investigate patient preferences and willingness to pay (WTP) for a genetic test that can reduce the risk of life-threatening adverse drug reactions (ADRs). We hypothesize that test features (risk of developing the adverse reaction with and without testing, test cost, and treatment cost) and the choice context (physician recommendation and the most common choice made by peer patients) will influence choices.

METHODS

A discrete choice experiment was conducted in which 189 patients at high risk for gout were asked to choose between treatment options that varied along key attributes. A latent class logit model was used to analyze the choice data and test the hypotheses.

RESULTS

We identified two classes of patients: the risk-averse class and the cost-conscious class. The WTP to reduce the risk of life-threatening ADRs from 1 out of 600 to 1 out of 1 million was SGD1215 in the risk-averse class. In contrast, in the cost-conscious class, the WTP was insensitive to the extent of risk reduction. Overall, the predicted take-up rate for the test is 65% at a price of SGD400. If the test was recommended by a physician or was chosen by most of the patients, the take-up rate for the test would increase by 8.5 and 1.5 percentage points, respectively.

CONCLUSIONS

There is a potentially large demand for genetic tests that could reduce the risk of life-threatening ADRs. Physician recommendations and providing information on the choices of others are powerful influences on demand, even more so than moderate price reductions.

Racial disparities in the risk of Stevens-Johnson Syndrome and toxic epidermal necrolysis as urate-lowering drug adverse events in the United States

OBJECTIVES

HLA-B*5801 allele carriage (a strong determinant of allopurinol hypersensitivity syndrome) varies substantially among races, which may lead to racial disparities in the risk of Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN) in the context of urate-lowering drug adverse events (ULDAEs). We examined this hypothesis in a large, racially diverse, and generalizable setting.

METHODS

Using a database representative of US hospitalizations (2009-2013), we investigated the racial distribution of hospitalized SJS/TEN (principal discharge diagnosis) as ULDAEs (ICD-9-CM Classification of External Causes). Our reference groups included the US Census population, US allopurinol users, and ULDAE hospitalizations without SJS/TEN.

RESULTS

We identified 606 cases hospitalized for SJS/TEN as ULDAEs (mean age = 68 years; 44% male), among which there was an overrepresentation of Asians (27%) and Blacks (26%), and an underrepresentation of Whites (29%) and Hispanics (% too-low-to-report), compared with the US Census population (5%, 12%, 67%, and 15%, respectively). The hospitalization rate ratios for SJS/TEN among Asians, Blacks, and Whites were 11.9, 5.0, and 1.0 (referent), respectively. These associations persisted using other national referents. According to the NHANES 2009-2012, allopurinol constituted 96.8% of urate-lowering drug use, followed by probenecid (2.1%).

CONCLUSIONS

These national data indicate that Asians and Blacks have a substantially higher risk of SJS/TEN as ULDAEs than Whites (or Hispanics), correlating well with corresponding frequencies of HLA-B*5801 in the US population (i.e., 7.4%, 4%, 1%, and 1%, respectively). Given its market dominance and established association with SJS/TEN, our findings support the use of vigilance in these minorities when considering allopurinol.

Cost-effectiveness analysis of genotyping for HLA-B*5801 and an enhanced safety program in gout patients starting allopurinol in Singapore

AIMS

Allopurinol is an efficacious urate-lowering therapy (ULT), but is associated with rare serious adverse drug reactions of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), with higher risk among HLA-B*5801 carriers. We assessed the cost-effectiveness of HLA-B*5801 testing, an enhanced safety program or strategies with both components.

METHODS

The analysis adopted a health systems perspective and considered Singaporean patients with chronic gout, over a lifetime horizon, using allopurinol or probenecid. The model incorporated SJS/TEN and gout treatment outcomes, allele frequencies, drug prices and other medical costs.

RESULTS

Based on cost-effectiveness threshold of US$50,000 per quality-adjusted life year, HLA-B*5801-guided ULT selection or enhanced safety program was not cost effective. Avoidance of ULTs was the least preferred strategy as uncontrolled gout leads to lower quality-adjusted life years and higher costs.

CONCLUSION

The analysis underscores the need for biomarkers with higher positive predictive value for SJS/TEN, less expensive genetic tests or safety programs, or more effective gout drugs. .

Tag SNPs for HLA-B alleles that are associated with drug response and disease risk in the Chinese Han population

Multiple HLA-B alleles (haplotypes) are associated with drug-induced adverse responses and disease risks but are difficult to be directly genotyped. The goal of this study is to identify single nucleotide polymorphisms (SNPs) that are able to tag HLA-B alleles in the Chinese Han population. Twelve HLA-B alleles that are associated with drug adverse responses and disease risks were identified. They were sequenced initially in 880 Chinese Han subjects where high-density SNPs within the HLA-B gene were available. Performances of these SNPs to tag the HLA-B alleles were assessed primarily by sensitivity and specificity. Two HLA-B alleles can be reliably tagged by SNPs at 100% sensitivity and >95% specificity. For example, HLA-B*15:02 can be tagged by the 'C' allele of rs10484555, and HLA-B*58:01 can be tagged by the 'T' allele of rs9262570. These results were confirmed in 500 additional Chinese Han subjects. If confirmed in independent studies, these tag SNPs could be used as a reliable, simple and cost-effective alternative for genotyping a subset of HLA-B alleles.

Toxic epidermal necrolysis: the year in review

PURPOSE OF REVIEW

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening severe adverse drug reactions. Once thought to be idiosyncratic and unpredictable, there has been significant progress made in the understanding of the pathomechanism and pharmacogenetics of such reactions. These advances together with their clinical implications will be elaborated in this review.

RECENT FINDINGS

It is now known that the human leukocyte antigen (HLA) association in SJS/TEN is more than just a genetic marker and has a functional role as well. This reaction is mediated by cytotoxic T lymphocytes (CTLs) in an HLA-restricted fashion. Certain drugs may bind directly to the HLA complex and facilitate the development of self-reactivity due to drug-modified HLA-peptide repertoire. The role of the drug-specific T cells and their T-cell receptors has also been clarified. Downstream cytotoxic signals have been elucidated with granulysin, a cytotoxic protein produced by CTLs or natural killer cells deemed to be the key mediator in the reaction.

SUMMARY

Pharmacogenetic screening of HLA alleles prior to drug initiation has already been shown useful in the prevention of such reactions. The other advances in the disease mechanism will form the basis for better preventive and therapeutic strategies.

Integrating pharmacogenetic information and clinical decision support into the electronic health record

Pharmacogenetics (PG) examines gene variations for drug disposition, response, or toxicity. At the National Institutes of Health Clinical Center (NIH CC), a multidepartment Pharmacogenetics Testing Implementation Committee (PGTIC) was established to develop clinical decision support (CDS) algorithms for abacavir, carbamazepine, and allopurinol, medications for which human leukocyte antigen (HLA) variants predict severe hypersensitivity reactions. Providing PG CDS in the electronic health record (EHR) during order entry could prevent adverse drug events. Medical Logic Module (MLM) programming was used to implement PG CDS in our EHR. The MLM checks to see if an HLA sequence-based gene test is ordered. A message regarding test status (result present, absent, pending, or test not ordered) is displayed on the order form, and the MLM determines if the prescriber can place the order, place it but require an over-ride reason, or be blocked from placing the order. Since implementation, more than 725 medication orders have been placed for over 230 patients by 154 different prescribers for the three drugs included in our PG program. Prescribers commonly used an over-ride reason when placing the order mainly because patients had been receiving the drug without reaction before implementation of the CDS program. Successful incorporation of PG CDS into the NIH CC EHR required a coordinated, interdisciplinary effort to ensure smooth activation and a positive effect on patient care. Prescribers have adapted to using the CDS and have ordered PG testing as a direct result of the implementation.

Pharmacogenetic testing: Current Evidence of Clinical Utility

Over the last decade, the number of clinical pharmacogenetic tests has steadily increased as understanding of the role of genes in drug response has grown. However, uptake of these tests has been slow, due in large part to the lack of robust evidence demonstrating clinical utility. We review the evidence behind four pharmacogenetic tests and discuss the barriers and facilitators to uptake: 1) warfarin (drug safety and efficacy); 2) clopidogrel (drug efficacy); 3) codeine (drug efficacy); and 4) abacavir (drug safety). Future efforts should be directed toward addressing these issues and considering additional approaches to generating evidence basis to support clinical use of pharmacogenetic tests.

Clinical Pharmacogenetics Implementation Consortium guidelines for human leukocyte antigen-B genotype and allopurinol dosing

Allopurinol is the most commonly used drug for the treatment of hyperuricemia and gout. However, allopurinol is also one of the most common causes of severe cutaneous adverse reactions (SCARs), which include drug hypersensitivity syndrome, Stevens–Johnson syndrome, and toxic epidermal necrolysis. A variant allele of the human leukocyte antigen (HLA)-B, HLA-B*58:01, associates strongly with allopurinolinduced SCAR. We have summarized the evidence from the published literature and developed peer-reviewed guidelines for allopurinol use based on HLA-B genotype.