In drug discovery and development, estimating therapeutic and subtherapeutic doses is crucial for designing early-phase clinical trials, particularly first-in-human (FIH) studies. While increasing the invitro pharmacological potency (lowering Ki) of a compound to its target is expected to decrease the therapeutic dose, its benefit is not necessarily clarified. We analyzed invitro Ki, human invivo pharmacokinetics (PK) parameters, and therapeutics doses of 144 oral small-molecule drugs approved in Japan (2010-2021). The data on classic drugs were obtained from Goodman and Gilman's textbook, 9th ed. (published in 1996). Modern drugs had lower Ki (2.5 nM) and daily doses (88 μmol/day) than classic drugs (33 nM and 313 μmol/day), but 3.6-fold higher intrinsic clearance (CLint; 171 vs. 47 L/h), suggest that increasing potency over the years has not resulted in a reduction in dosage as expected. Estimating therapeutic doses using target receptor occupancy (tRO)-optimized approach improved estimation accuracy (63% within 10-fold of observed values) compared with tRO-fixed approaches. Subtherapeutic dose estimations revealed a risk of overdosing in FIH trials, indicating that these estimates are not necessarily as conservative as is generally understood. Notably, the unbound average concentration-to-Ki ratio (Cave,u/Ki) varied among drugs and correlated negatively with Ki, suggesting the possible necessity of incorporating it into dose estimation methods. This study provides insights into the relationship between invitro Ki, invivo PK parameters, and therapeutic dose of modern drugs, proposing strategies and revealing the risk for dose estimation and drug development in the era of highly potent small molecules.
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