dmethyl1 = {
      {0, 0},
      {.25, 1},
      {.5, 7},
      {1, 26},
      {1.5, 40},
      {2, 45},
      {2.5, 45},
      {3, 44},
      {3.5, 44},
      {4, 43},
      {4.5, 41},
      {5, 39},
      {6, 38},
      {7, 37},
      {8, 35},
      {9, 33},
      {10, 32},
      {11, 29},
      {12, 24},
      {24, 13},
      {48, 4},
      {60, 2},
      {72, 0}
     }

cmaxd = Interpolation[dmethyl1, InterpolationOrder -> 3]

Gives the interpolation function. I need to translate this into a crude multi dose model. I need work out how to write a function that works like: