Use of Genotyping to Prevent Allopurinol Induced SCARS
Use of Genotyping to Prevent Allopurinol Induced SCARS
Owing to the tight association between HLA-B*58:01 and life threatening SCARs induced by allopurinol, this study was approved by our institutional review board as a non-randomised study, using historical incidence as a control. We recruited patients from 15 participating hospitals throughout Taiwan (see author affiliations and web appendix). There were nine points of interaction with patients who did not have the HLA-B*58:01 allele and 10 points of interaction with HLA-B*58:01 carriers: the initial screening visit, a second clinic visit for HLA-B*58:01 carriers, and weekly telephone interviews for both groups during the two month follow-up. Recruited patients were aged between 6 months and 99 years, and had not previously taken allopurinol within three months. In accordance with clinical indications at the time of screening, these patients would have received allopurinol and thus were invited to participate in the study. The efficacy of all treatments to reduce levels of uric acid was evaluated on the basis of the guideline for gout management.
We excluded patients who had undergone a bone marrow transplant, were not of Han Chinese descent, and had a history of allopurinol induced hypersensitivity. Han Chinese descent was confirmed via a multiple choice questionnaire that asked patients to report the ethnic origin of both parents and grandparents.
We prescribed and dispensed allopurinol to all participants at the initial screen, but we asked that each person defer taking allopurinol until the HLA-B*58:01 genotyping results were finalised. Blood samples were collected and transferred to our central laboratory for HLA-B*58:01 genotyping. We reported the genotyping results to the participating physicians within three days.
Patients who tested positive for HLA-B*58:01 were asked to return to their respective hospitals within three days. We then explained their risk of allopurinol induced SCARs and recommended that they take alternative medicine. Those who tested negative for HLA B*58:01 (and who also were counselled about SCARs risk) were started on allopurinol treatment. In our previous large scale retrospective study, all patients developed SCARs during the study period within two months of starting allopurinol treatment, which was in agreement with what has been reported consistently in the literature. We therefore interviewed all participants by telephone during the two month period following initial screening (for HLA-B*58:01 negative patients) or after the second clinic visit (for HLA-B*58:01 positive patients) to monitor for symptoms of adverse drug reactions, including SCARs. If early symptoms of SCARs developed, a participant was asked to return to the clinic immediately for dermatological evaluation. We monitored all patients throughout the study's duration, apart from those who had a protocol violation or were lost during follow-up.
The study was performed in accordance with Good Clinical Practice Standards and the provisions of the Declaration of Helsinki. The research ethics committee at Academia Sinica in Taipei and the institutional review board at each participating clinic approved the study. We obtained written informed consent from all participants or from parents or guardians for participants aged 21 years or younger.
Whole blood (2 mL) was collected from each participant in a Monovette tube and stored at 4–12°C, and each sample was sent to the central lab on the day obtained. We isolated genomic DNA with the QIAamp DNA purification system (Qiagen). The presence or absence of HLA-B*58:01 was determined by the PG5801 DNA detection kit (Pharmigene). The kits are based on a real time polymerase chain reaction with sequence specific primers for HLA-B*58:01. To confirm the genotyping results, the first 900 samples were also examined in parallel with a reverse line blot using an HLA sequence oligonucleotide (Dynal Biotech); the results were consistent in each sample.
We diagnosed SCARs using code 695.1 in both ICD-9 (international classification of diseases, 9th revision) and ICD-9-CM (clinical modification), which are commonly used in studies of adverse drug reactions. The ICD-9-CM 695.1 code covers all SCARs, including drug rash with eosinophilia and systemic symptoms, Stevens-Johnson syndrome, and toxic epidermal necrolysis. The number of participants with this code was determined from the National Health Insurance research database, as provided by the National Health Insurance administration of Taiwan.
The National Health Insurance research database is reliable and applies to nationwide studies in Taiwan, and was established by the Taiwanese government when the National Health Insurance system was launched in 1995. The database is a single payer health insurance plan managed by the Taiwanese government, and provides healthcare for nearly all the Taiwanese population (enrolment was 99.5% in 2008). More than 92% of Taiwanese healthcare facilities have been contracted by the National Health Insurance system. Data obtained from the National Health Insurance research database are therefore comprehensive.
We estimated the annual incidence of allopurinol induced SCARs in Taiwan as the annual number of SCARs cases caused by allopurinol divided by the annual number of new allopurinol users. In 2005, we published an article stating the potential of HLA-B*58:01 as a biomarker for preventing allopurinol-induced SCARs. After this, some physicians began to genotype HLA-B region before allopurinol treatment. This measure could confound our analysis. Therefore, to obtain a suitable control group, we adopted the most recent, non-confounded data (that is, 2001–04 data) from the National Health Insurance research database.
The prevalence of the HLA-B*58:01 allele in the Han Chinese population residing in Taiwan has been calculated to be 20%. Therefore, 2169 people would provide a power of 86% (using the two sided, one sample binomial test) to detect a reduction in the incidence of allopurinol induced SCARs from 0.30% per year (95% confidence interval 0.28% to 0.31%; that is, 30 cases per 10 000 new recipients) to 0.03%. We used the two sided, one sample binomial test to compare the rate of allopurinol induced SCARs in the prospective screening population with historical incidence. All P values are two tailed, and P<0.05 was considered to be significant.
No patients were involved in setting the research question or the outcome measures, nor were they involved in the design and implementation of the study. There are no plans to involve patients in dissemination.
Methods
Study Design
Owing to the tight association between HLA-B*58:01 and life threatening SCARs induced by allopurinol, this study was approved by our institutional review board as a non-randomised study, using historical incidence as a control. We recruited patients from 15 participating hospitals throughout Taiwan (see author affiliations and web appendix). There were nine points of interaction with patients who did not have the HLA-B*58:01 allele and 10 points of interaction with HLA-B*58:01 carriers: the initial screening visit, a second clinic visit for HLA-B*58:01 carriers, and weekly telephone interviews for both groups during the two month follow-up. Recruited patients were aged between 6 months and 99 years, and had not previously taken allopurinol within three months. In accordance with clinical indications at the time of screening, these patients would have received allopurinol and thus were invited to participate in the study. The efficacy of all treatments to reduce levels of uric acid was evaluated on the basis of the guideline for gout management.
We excluded patients who had undergone a bone marrow transplant, were not of Han Chinese descent, and had a history of allopurinol induced hypersensitivity. Han Chinese descent was confirmed via a multiple choice questionnaire that asked patients to report the ethnic origin of both parents and grandparents.
We prescribed and dispensed allopurinol to all participants at the initial screen, but we asked that each person defer taking allopurinol until the HLA-B*58:01 genotyping results were finalised. Blood samples were collected and transferred to our central laboratory for HLA-B*58:01 genotyping. We reported the genotyping results to the participating physicians within three days.
Patients who tested positive for HLA-B*58:01 were asked to return to their respective hospitals within three days. We then explained their risk of allopurinol induced SCARs and recommended that they take alternative medicine. Those who tested negative for HLA B*58:01 (and who also were counselled about SCARs risk) were started on allopurinol treatment. In our previous large scale retrospective study, all patients developed SCARs during the study period within two months of starting allopurinol treatment, which was in agreement with what has been reported consistently in the literature. We therefore interviewed all participants by telephone during the two month period following initial screening (for HLA-B*58:01 negative patients) or after the second clinic visit (for HLA-B*58:01 positive patients) to monitor for symptoms of adverse drug reactions, including SCARs. If early symptoms of SCARs developed, a participant was asked to return to the clinic immediately for dermatological evaluation. We monitored all patients throughout the study's duration, apart from those who had a protocol violation or were lost during follow-up.
The study was performed in accordance with Good Clinical Practice Standards and the provisions of the Declaration of Helsinki. The research ethics committee at Academia Sinica in Taipei and the institutional review board at each participating clinic approved the study. We obtained written informed consent from all participants or from parents or guardians for participants aged 21 years or younger.
Genotyping of HLA-B*58:01
Whole blood (2 mL) was collected from each participant in a Monovette tube and stored at 4–12°C, and each sample was sent to the central lab on the day obtained. We isolated genomic DNA with the QIAamp DNA purification system (Qiagen). The presence or absence of HLA-B*58:01 was determined by the PG5801 DNA detection kit (Pharmigene). The kits are based on a real time polymerase chain reaction with sequence specific primers for HLA-B*58:01. To confirm the genotyping results, the first 900 samples were also examined in parallel with a reverse line blot using an HLA sequence oligonucleotide (Dynal Biotech); the results were consistent in each sample.
Annual Incidence
We diagnosed SCARs using code 695.1 in both ICD-9 (international classification of diseases, 9th revision) and ICD-9-CM (clinical modification), which are commonly used in studies of adverse drug reactions. The ICD-9-CM 695.1 code covers all SCARs, including drug rash with eosinophilia and systemic symptoms, Stevens-Johnson syndrome, and toxic epidermal necrolysis. The number of participants with this code was determined from the National Health Insurance research database, as provided by the National Health Insurance administration of Taiwan.
The National Health Insurance research database is reliable and applies to nationwide studies in Taiwan, and was established by the Taiwanese government when the National Health Insurance system was launched in 1995. The database is a single payer health insurance plan managed by the Taiwanese government, and provides healthcare for nearly all the Taiwanese population (enrolment was 99.5% in 2008). More than 92% of Taiwanese healthcare facilities have been contracted by the National Health Insurance system. Data obtained from the National Health Insurance research database are therefore comprehensive.
We estimated the annual incidence of allopurinol induced SCARs in Taiwan as the annual number of SCARs cases caused by allopurinol divided by the annual number of new allopurinol users. In 2005, we published an article stating the potential of HLA-B*58:01 as a biomarker for preventing allopurinol-induced SCARs. After this, some physicians began to genotype HLA-B region before allopurinol treatment. This measure could confound our analysis. Therefore, to obtain a suitable control group, we adopted the most recent, non-confounded data (that is, 2001–04 data) from the National Health Insurance research database.
Statistical Analysis
The prevalence of the HLA-B*58:01 allele in the Han Chinese population residing in Taiwan has been calculated to be 20%. Therefore, 2169 people would provide a power of 86% (using the two sided, one sample binomial test) to detect a reduction in the incidence of allopurinol induced SCARs from 0.30% per year (95% confidence interval 0.28% to 0.31%; that is, 30 cases per 10 000 new recipients) to 0.03%. We used the two sided, one sample binomial test to compare the rate of allopurinol induced SCARs in the prospective screening population with historical incidence. All P values are two tailed, and P<0.05 was considered to be significant.
Patient Involvement
No patients were involved in setting the research question or the outcome measures, nor were they involved in the design and implementation of the study. There are no plans to involve patients in dissemination.
