Acute reversal of flunitrazepam effects by Ro 15-1788 and Ro 15-3505: inverse agonism, tolerance, and rebound.

A phase 1 double blind crossover comparison of a new benzodiazepine antagonist (Ro 15-3505) with Ro 15-1788 and placebo, in the reversal of sedative and psychophysiological effects of single IV doses of flunitrazepam (2 mg), was carried out in 12 normal volunteers. The antagonists were equally effective, leading to full reversal of all effects with a potency ratio of approximately 2.5 mg Ro 15-1788 for 1 mg Ro 15-3505. Inverse agonism, in the form of unpleasant feelings and symptoms, was reported by all subjects following Ro 15-3505 but none after Ro 15-1788. Adaptational phenomena such as acute tolerance and rebound of sedative effects of flunitrazepam were also detected and their potential implications are discussed.