A double-dissociation of behavioural and event-related potential effects of two benzodiazepines with similar potencies

This study was designed to explore the role of benzodiazepine affinity to b enzodiazepine binding site on acute psychomotor, subjective and memory effe cts, as well as auditory Event Related Potential (ERP) latencies, in health y volunteers. Two benzodiazepines with similar affinity to benzodiazepine b inding sites, or potency, were compared: the atypical compound lorazepam (2 .0 mg), which has been reported to impair priming, and a standard benzodiaz epine, flunitrazepam (0.6 mg, 0.8 mg, 1.0 mg). The study followed a placebo -controlled, double-blind, parallel-group design. Sixty subjects completed a test battery before treatment and at theoretical peak plasma concentratio n of drugs. Lorazepam and 1.0 mg of flunitrazepam led to comparable alterat ions on psychomotor, subjective and auditory episodic memory measures. A do uble-dissociation was found for lorazepam and the equipotent dose of flunit razepam (1.0 mg): lorazepam was more deleterious than flunitrazepam in time taken to identify fragmented shapes. Lorazepam also impaired direct and in direct stem-completion in comparison to placebo, but this effect was abolis hed when time to identify shapes was used as a covariate. By contrast, 1.0 mg of flunitrazepam prolonged auditory ERP latencies to a greater extent th an lorazepam. High affinity to the benzodiazepine binding sites does not se em to explain the consistent lorazepam-induced impairment of indirect stem- completion. Differences in impairment profile between the benzodiazepines e mployed may relate to the modality (visual or not) of the tasks used.