The clinical outcome of duodenal ulcer treated with proton pump inhibitor (PPI)-based, anti-Helicobacter pylori (H.p.) regimens varies according to cytochrome P450 2C19 (CYP2C19) genotype. CYP2C19 genotypes differ markedly in peoples of Pacific Rim descent compared with another ethnicity. The authors sought to determine the specific impact that these factors have on the cost-effectiveness of duodenal ulcer management. Their model consisted of two patient cohorts with Helicobacter pylori and duodenal ulcer, trichotomized into CYP2C19 homozygous extensive metabolizers (EMs), heterozygous EMs, and poor metabolizers (PMs), altering the anti-H.p. regimen in the genotyped cohort only. The authors took the perspective of a third-party payer, and the denominator was ulcer episode prevented. In the reference case, the use of CYP2C19 genotyping prior to initiating anti-H.p. therapy was dominant (costs were saved with each ulcer episode prevented) in all geographic regions of the United States. The subsequent break-even analysis showed a range of 89.20 dollars to 118.96 dollars--from Hawaii to the Midwest, respectively--required to eliminate the cost-savings from each genotype test performed. Using probabilities most unfavorable to genotyping, the variation of peoples with Pacific Rim origins from 0% to 100% altered the cost-effectiveness from 495 dollars to 2125 dollars per ulcer event prevented, respectively. The results suggest that treatment decisions for H.p. infection that are based on a patient's CYP2C19 genotype decreases expenses for health plans implementing testing. This analysis provides an economic basis to support recent calls to expand this technology into routine clinical care to prevent toxicity of narrow therapeutic index drugs.