The invention provides methods of determining a therapeutically effective dose of an agent that targets a metabolic pathway based on measured levels of a metabolite in the pathway. The methods, which may include providing the agent in a therapeutically effective dose, are useful for treating disorders, such as cancer, in a subject. The invention also provides methods for assessing the impact of a therapeutic agent on a tumor in a subject by monitoring, in real time, metabolism of a molecule in the tumor, oxygenation of the tumor, or both. The invention further provides devices that determine a therapeutically effective dose of an agent that targets a metabolic pathway based on measured levels of a metabolite in the pathway and notify a subject to administer the dose.
