First-Time-in-Human Study With GSK1018921, a Selective GlyT1 Inhibitor: Relationship Between Exposure and Dizziness

Abstract

The pharmacokinetics (PK), safety, and tolerability of GSK1018921, a glycine transporter 1 (GlyT-1) inhibitor, were assessed in this first-time-in-human (FTIH) study. Single oral doses ranging from 0.5 to 280 mg and placebo were administered to 25 healthy subjects in a five-period, two-cohort, crossover study. GSK1018921 showed dose-proportional PK with a terminal half-life of ~17 h. The subjects reported dizziness with a dose-dependent frequency of 22-88% at doses of 70-280 mg. The time course of the dizziness paralleled the PK of the drug, with peak response at 2 h after the dose, consistent with time to maximum plasma concentration (T(max)). The dizziness was resolved by 10-12 h in all subjects. A Markov-chain logistic regression model was implemented in NONMEM to determine the probability of developing dizziness as a function of the plasma concentration of the compound. Frequency, onset (<1 h), and offset (4 h) were well described by the model. Exposure resulting in 80% receptor occupancy is predicted to be well tolerated.