What are some examples of successful mathematical attempts in clinical setting, specifically at the patient-disease-drug level?

To clarify, by patient-disease-drug level, I mean the mathematical work is approved to be used as part of a decision making process to prescribe a specific treatment for a specific patient?

I do not mean general modeling attempts that study and simulate on a more or less theoretical level.

Additionally, are these mathematical work have to be approved by the regulators like the FDA or a national board of physicians?