The time course of drug effect is described based on the concentration-time course and the effect-time course. The concentration-time course depends on the drug's half-life. The effect is calculated based on the maximum drug effect and the plasma concentration producing 50% of the maximal effect. Consider a bolus drug dose with a 3-hour half-life and 1 ng/ml C50 value. The peak plasma concentration is 64 ng/ml at 3 hours. At 24 hours, the drug plasma concentration is below 1% of the peak concentration. This is half the value of C50, with only 33% ACE inhibition. If the concentration is above C80 the effect change is negligible despite changes in concentration, and the curve is almost flat. If the concentration is between C80 and C20, the effect curve is almost a straight line. If the concentration is below C20, the curves are almost parallel.