Personalise vitamin D using physiologically based pharmacokinetic modelling.

Plasma concentration of vitamin D metabolite 25-hydroxyvitamin D (25(OH)D ) is variable among individuals. The objective of this study is to establish an accurate model for 25(OH)D pharmacokinetics (PKs) to support selection of a suitable dose regimen for an individual. We collated vitamin D and 25(OH)D plasma PK data from reported clinical trials and developed a physiologically-based pharmacokinetic (PBPK) model to appropriately recapitulate training data. Model predictions were then qualified with 25(OH)D plasma PKs under vitamin D and 25(OH)D dose regimens distinct from training data. From data exploration, we observed the increase in plasma 25(OH)D after repeated dosing was negatively correlated with 25(OH)D baseline levels. Our final model included a first-order vitamin D absorption, a first-order vitamin D metabolism, and a nonlinear 25(OH)D elimination function. This structure explained the apparent paradox. Remarkably, the model accurately predicted plasma 25(OH)D following repeated dosing up to 1250 μg/d in the test set. It also made sensible predictions for large single vitamin D doses up to 50,000 μg in the test set. Model predicts 10 μg/d regimen may be ineffective for achieving sufficiency (plasma 25(OH)D ≥ 75 nmol/L) for a severely deficient individual (baseline 25(OH)D = 10 nmol/L), and it might take the same person over 200 days to reach sufficiency at 20 μg/d dose. We propose to personalize vitamin D supplementation protocol with this PBPK model. It would require measuring 25(OH)D baseline levels, which is not routinely performed under the current UK public health advice. STUDY HIGHLIGHTS: WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Vitamin D PK exhibits substantial inter-individual variability. Different officially recommended daily doses are confusing. ​ WHAT QUESTION DID THIS STUDY ADDRESS? Is the UK's recommended 10 µg daily dose sufficient? Should everyone be given same dose? ​ WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? Our model accurately predicts plasma 25(OH)D under daily oral administration of vitamin D . The 10 µg daily vitamin D dose is insufficient for prophylaxis (plasma 25(OH)D at 75 nmol/L). ​ HOW MIGHT THIS CHANGE DRUG DISCOVERY, DEVELOPMENT, AND/OR THERAPEUTICS? Combining blood test to measure 25(OH)D baseline with this PBPK model will help inform dosage selection and select follow-up date to improve effectiveness of Hypovitaminosis D treatment.