In vitro to in vivo pharmacokinetic translation guidance

BackgroundPharmacokinetics (PK), exposure profiles and doses of candidate drugs in man are commonly predicted using data produced using various in vitro methods, such as hepatocytes (for intrinsic metabolic clearance (CLint)), plasma (for unbound fraction (fu)), Caco-2 (measuring apparent permeability (Papp) for prediction of in vivo fraction absorbed (fa)) and plasma water and buffers (measuring solubility (S) for prediction of in vivo fraction dissolved (fdiss)). For best possible predictions it is required that the clinical relevance of in vitro data is understood (in vitro-in vivo relationships) and that uncertainties have been investigated and considered. MethodsThe aim was to investigate in vitro-in vivo relationships for CLint, Papp vs fa and S vs fdiss and interlaboratory variability for fu, describe the clinical significance and uncertainties at certain levels of in vitro CLint, fu, Papp and S, and (based on the findings) develop a general in vitro-in vivo translation guide. Results and ConclusionIt was possible to finf data for describing how in vivo CLint, fa and fdiss distribute and varies at different levels of in vitro CLint, Papp and S and how fu varies between laboratories and methods at different fu-levels. It is apparent that there are considerable interlaboratory variabilities for CLint, fu and Papp: corresponding to up to 2500-, 700- and 35-fold variability for CLint, fu and fa, respectively. Apparently, S is a poor predictor of fdiss. Proposed S-thresholds do not seem clinically useful (overestimated). It does not seem appropriate to define in vitro CLint of 0.5-2 {micro}L/min/106 cells as good metabolic stability (rather moderate to moderately high). Results shown for CLint, Papp and fu are applicable as general guidelines when internal standard values for reference compounds are unavailable.