Influence of remifentanil on the pharmacokinetics and pharmacodynamics of remimazolam in healthy volunteers

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Background: Synergistic effects between opioids and remimazolam on bispectral index (BIS) and modified observer’s assessment of alertness and/or sedation (MOAAS) score were previously described. This study aimed to characterize the influence of remifentanil on the sedative properties of remimazolam as measured by MOAAS, BIS, tolerance to laryngoscopy or tetanic stimulation (TOL or TOTS) and to determine target concentrations that maximize MOAAS 2/3. Methods: A three-period, cross-over, dose-ranging clinical trial was performed in 24 healthy volunteers. In all periods, remimazolam was administered using a step-up and step-down TCI protocol (50 – 2000 ng/mL). Stable remifentanil target concentrations of 0.5 ng/mL and 0.1 to 4.0 ng/mL were maintained in periods 2 and 3, respectively. Remifentanil, remimazolam and CNS7054 (metabolite) concentrations and, MOAAS, BIS, TOL and TOTS were collected in each step of the TCI protocol. Data were analyzed using non-linear mixed-effects models, where p≤0.01 was considered significant. Results: Remifentanil reduced the apparent clearance of CNS7054 with a half-maximum inhibition at 8.0 ng/mL (95% CI 5.5 to 13.4 ng/mL). A pharmacodynamic interaction was detected on all endpoints. Simulations indicate that the probability of observing a MOAAS 2/3 is highest at remimazolam target concentration of 275, 250 or 200 ng/mL combined with 0, 0.1, or 0.5 ng/mL remifentanil resulting in probabilities of 45%, 45% and 44%, respectively. Additionally, simulations indicate that the highest probability of observing TOTS and TOL was 93.3% and 85.5%, respectively, at the highest studied target concentrations. Conclusions: A pharmacokinetic and pharmacodynamic drug-drug interaction between remimazolam and remifentanil was quantified in this clinical trial. Appropriate target concentrations for MOAAS and BIS could be estimated, but, for TOL and TOTS, the trial design did not allow to fully characterize the exposure-response relationship.