Assessment of the interaction between a partial agonist and a full agonist of benzodiazepine receptors, based on psychomotor performance and memory, in healthy volunteers.

Potential interactions between the imidazopyridine anxiolytic alpidem and the full benzodiazepine agonist lorazepam were assessed in a randomized, double-blind, four-way cross-over, placebo-controlled study in 16 healthy young male volunteers. Each volunteer received alpidem, 50 mg, or a placebo twice daily for 8 days with a 1- week wash-out interval. The interaction between alpidem, at the steady state, and a single oral dose of lorazepam 2 mg or a placebo was assessed after concomitant administration on days 7 or 9 of each treatment period. Psycho motor performance and cognitive function were evaluated before and 2, 4, 6 and 8 h post-dose, using objective tests [critical flicker fusion threshold (CFF), choice reaction time (CRT), digit-symbol substitution (DSST), body sway and short-term memory (Sternberg memory scanning)] and self-ratings [line analogue rating scales: (LARS)]. Long-term memory (delayed free recall and recognition of pictures) was assessed before the dose and 2 and 4 h post-dose. Pharmacodynamic interactions were evaluated by applying repeated measures ANOVA to a 2 x 2 factorial interaction model. Alpidem, 50 mg twice daily at the steady state, was free of any clinically relevant detrimental effects on skilled performance, information processing or memory. In contrast, a single 2 mg dose of lorazepam induced marked impairment of psychomotor performance and cognitive function (significant reductions in CFF and DSST and increases in CRT and body sway), as well as subjective sedation from 2 to 8 h post-dose, depending on the test used. In addition, lorazepam induced anterograde amnesia, characterized by a decrease in delayed free recall and recognition, and a deficit in short-term memory. Finally, alpidem 50 mg did not potentiate the detrimental effects of lorazepam 2 mg. On the contrary, alpidem significantly antagonized the lorazepam-induced CRT increase and anterograde amnesia, and produced similar trends on most of the other cognitive parameters; thus, the results obtained with the combination of alpidem and lorazepam consistently indicated less impairment than those measured after lorazepam alone. These results are consistent with the suggested partial agonsist properties of alpidem at the benzodiazepine receptor and indicate that such properties can be assessed in humans based on antagonism of the effects of a full agonist.