title: Indirect estimation of the comparative treatment effect in pharmacogenomic subgroups.
abstract: Evidence of clinical utility is a key issue in translating pharmacogenomics into clinical practice. Appropriately designed randomized controlled trials generally provide the most robust evidence of the clinical utility, but often only data from a pharmacogenomic association study are available. This paper details a method for reframing the results of pharmacogenomic association studies in terms of the comparative treatment effect for a pharmacogenomic subgroup to provide greater insight into the likely clinical utility of a pharmacogenomic marker, its' likely cost effectiveness, and the value of undertaking the further (often expensive) research required for translation into clinical practice. The method is based on the law of total probability, which relates marginal and conditional probability. It takes as inputs: the prevalence of the pharmacogenomic marker in the patient group of interest, prognostic effect of the pharmacogenomic marker based on observational association studies, and the unstratified comparative treatment effect based on one or more conventional randomized controlled trials. The critical assumption is that of exchangeability across the included studies. The method is demonstrated using a case study of cytochrome P450 (CYP) 2C19 genotype and the anti-platelet agent clopidogrel. Indirect subgroup analysis provided insight into relationship between the clinical utility of genotyping CYP2C19 and the risk ratio of cardiovascular outcomes between CYP2C19 genotypes for individuals using clopidogrel. In this case study the indirect and direct estimates of the treatment effect for the cytochrome P450 2C19 subgroups were similar. In general, however, indirect estimates are likely to have substantially greater risk of bias than an equivalent direct estimate.
authors.affiliation: School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia ; School of Medicine, Flinders University, Adelaide, South Australia, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sorich
authors.forename: Michael
authors.initials: M
authors.lastname: Coory
authors.forename: Brita A K
authors.initials: BA
authors.lastname: Pekarsky
mesh_terms: D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D002318:Cardiovascular Diseases / Q000139:chemically induced / Q000235:genetics; D000077144:Clopidogrel; D003362:Cost-Benefit Analysis; D065731:Cytochrome P-450 CYP2C19; D056726:Genetic Association Studies / Q000379:methods*; D006801:Humans; D015233:Models, Statistical; D010597:Pharmacogenetics; D010975:Platelet Aggregation Inhibitors / Q000009:adverse effects / Q000627:therapeutic use; D016032:Randomized Controlled Trials as Topic; D013988:Ticlopidine / Q000009:adverse effects / Q000031:analogs & derivatives / Q000627:therapeutic use; D016896:Treatment Outcome
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D013988:Ticlopidine