Table 4. Parameter Describing the Interaction Model  13 for Remifentanil and Propofol 

γ= Steepness factor determining the slope of the concentration–response relationship; U⁵⁰(0.5) = potency of the drug combination at ratio 0.5 relative to the normalized potency of each drug by itself. Values less than 1 indicate synergy; C⁵⁰= concentration associated with 50% of the maximum effect.