AI Precision Dosing and Pharmacokinetics

Pharmacokinetics summarizes a drug's behavior with a few parameters. Clearance (CL) is the volume of blood cleared of drug per unit of time. Volume of distribution (V) describes how widely the drug spreads. Half-life follows from both. For vancomycin, the exposure that best predicts efficacy is the area under the concentration-time curve over 24 hours (AUC24). At steady state, AUC24 equals the daily dose divided by clearance. In 2020, a revised consensus guideline from ASHP, IDSA, PIDS and SIDP recommended AUC-guided dosing for serious MRSA infections. It set a target AUC/MIC of 400 to 600, assuming an MIC of 1 mg/L, and preferred Bayesian software. This replaced the older practice of aiming for troughs of 15 to 20 mg/L. The change was made because trough levels predict AUC poorly and high troughs were linked to kidney injury. Older methods used nomograms or first-order equations with two levels drawn at steady state within the same dosing interval. Bayesian methods start from a population model developed in published studies, which gives typical parameter values, how they change with weight, kidney function and age, and how much patients vary. The software then updates those values with the patient's measured levels. It can work with a single level, with levels not at steady state, and with irregular dosing. Commercial examples include DoseMeRx, InsightRx and PrecisePK. A common misconception is that these tools are mysterious AI. Most are built on established pharmacometric methods, known as model-informed precision dosing. Machine learning is now being added for choosing or averaging models and for predicting clearance from EHR data. Another misconception is that software removes the need for judgment. If a patient differs sharply from the population used to build the model, for example with extreme obesity, dialysis or rapidly changing kidney function, the model's starting assumptions may mislead.