The World Health Organization has declared childhood obesity to be "one of the most serious public health challenges of the 21st century," (http://www.who.int/dietphysicalactivity/childhood). Given that obese children are generally excluded from clinical trials, little to no information exists regarding the impact of obesity on drug disposition and drug action, creating a gap in physicians' knowledge on how to appropriately select the dose of many critical medications (e.g., anticancer agents), so as to prevent toxicity associated with overdosing, while avoiding the harms of under-treatment. The proposed study will examine the effect of obesity on the metabolism of a commonly used medication, the proton pump inhibitor pantoprazole, by exploring the relationships between age, obesity, basal metabolic rate and genetic control of the enzyme primarily responsible for pantoprazole metabolism. We will also validate a simple breath test that can be used to predict pantoprazole dose requirement for obese children.