Rational dosing guidelines for drugs in pediatrics are urgently needed. To develop these guidelines, we use population pharmacokinetic-pharmacodynamic (PK-PD) modeling and simulation by: (i) optimization of clinical trial designs based on preliminary data; (ii) development and internal validation of population PK-PD models using sparse data; (iii) external validation using independent data; and (iv) prospective clinical evaluation. Optimized dosing regimens for specific drugs may then serve as a basis to develop dosing guidelines for existing or newly developed drugs with similar disposition and/or effect. In addition to modeling of drug disposition (PK) pathways, we emphasize the need for modeling of effect (PD) pathways and the use of a multidisciplinary infrastructure for data-sharing.