Choosing a first-in-human starting dose when the toxicology margin was thin
Situation
A novel small molecule entered first-in-human planning with a narrow gap between the exposure expected to be pharmacologically active and the exposure at the nonclinical no-observed-adverse-effect level. A conventional NOAEL-based starting dose, divided by a standard safety factor, risked landing well below any informative exposure — while a more aggressive start was hard to defend.
Approach
Both anchors were built in parallel: a NOAEL-based maximum recommended starting dose and a MABEL estimate from in-vitro potency and receptor-occupancy modeling, translated to human exposure with predicted PK. The escalation scheme used sentinel dosing, exposure-triggered stopping rules, and cohort spacing tied to emerging half-life rather than fixed calendar intervals.
Decision & outcome
The MABEL-anchored dose was selected as the start, with the NOAEL ceiling kept as a hard cap for escalation. The single-ascending-dose study reached pharmacologically relevant exposures without dose-limiting findings, and the observed PK matched predictions closely enough that the multiple-dose design needed no structural changes.