Fig. 6. Simulation study. The effect of variations in opioids-antagonist-related model parameters on 100 μg naloxone reversal at t = 55 min on 0.3 mg morphine-6-glucuronide (M6G)-induced respiratory depression at t = 0. The red line is the simulation with the parameter value = 20% of the typical population value for M6G (table 4), green line = 50%, blue line = 100%, purple line = 200%, and yellow line = 500%. (A ) Naloxone t½ke0, (B ) naloxone C50, and (C ) parameter γ. C50= concentration naloxone causing 50% effect (reversal); γ= a shape parameter; t½ke0= blood-effect-site equilibration half-life.