Abstract: The invention concerns a method determining an optimum drug dosing regimen to treat a patient efficiently against drug-sensitive pathogenic agents. From relevant patient-related data and the drug concentration measured at a random time in the patients body, the method estimates the drug concentration time-course based on a Bayesian model. The residual concentration (Cr) and an efficiency pharmacokinetic parameter (PPE) adapted to said drug and patient are computed from the estimated concentration. A dosing regimen is then determined by comparing the PPE to an efficiency target (CE) for efficiency purposes. The method further may further take into account toxicity constraints by comparing the residual drug concentration (Cr) to at least a toxic concentration (Ctox). A concentration of said drug is determined (E13) based on the result the above comparisons to provide a proposed dose for said optimum dosing regimen.