Example: The following results were obtained when the Wagner-Nelson method was used to calculate the absorption rate constant after an oral administration.

  • Time
    (hr)
    fraction remaining
    to be absorbed
  • 10.7
  • 20.5
  • 30.35
  • 50.17

Determine the order of drug absorption and calculate the absorption rate constant.

This is not a linear relationship
This is a linear relationship
slope = -ka/2.303

The absorption process is first order since the plot is linear on the semilog scale.

Slope = 0.152 hr-1

ka = 2.303 x 0.152 = 0.35 hr-1

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