Multiple‐Dose Pharmacokinetics and Safety of a Potential Memory‐Enhancing Compound, CL 275,838, in Healthy Male Volunteers

The pharmacokinetics and safety of CL 275,838, a new potential memory-enhancing compound, were examined after 14 daily doses (50 and 100 mg) in 16 healthy male volunteers, age 20 to 59 years, in a randomized, double-blind, placebo-controlled, parallel group study. Trough blood samples (predose) were collected on days 2, 4, 7, 10, and 14, and further samples were drawn after the final dose (day 14) to define the multiple-dose kinetics of the parent compound and its metabolites II and IV. Intercurrent clinical events, vital functions, EEG, ECG, and cognitive tests (attention, verbal memory, and spatial memory) were considered as outcome measures of safety. Performance in cognitive tests was also studied to collect preliminary information on possible therapeutic action. Predose plasma concentrations of the parent compound and its two metabolites increased approximately in proportion to the dose, and accumulation was complete within 7 days, regardless of the dose. At steady state, mean Cmax and AUC of the parent compound and its two metabolites were dose related. Mean wash-out t1/2 was 18 to 20 hours for the parent compound, 22–23 hours for metabolite II, and 28–33 hours for metabolite IV; these elimination t1/2 are comparable for the two doses, and are similar to those observed in single-dose studies. For the 50-mg-dose group, predicted and observed average plasma concentrations (Css) of CL 275,838 and its two metabolites did not differ significantly. However, for the 100-mg-dose group, observed Css of CL 275,838 and its main metabolite, the desbenzyl derivative II, were slightly higher than those predicted from the single-dose study, indicating a deviation from linearity after repeated higher oral doses. No major adverse drug reaction was detected at either dosage, and there was no evidence of CL 275,838-induced changes in hepatic parameters. Mild headache occurred in three of the ten subjects given active treatment, without any clear relation with the dose. At 100 mg, a significant improvement of attention was observed. This is a preliminary, but encouraging, finding that indicates the usefulness of studying the safety and efficacy in an appropriate patient population.