Help with Collapsing and Reshaping Data Frame

You should provide a reproducible example so that it is easier to provide you with an answer.

But anyway, I assume that it looks like this with the first column being a row number?

df <- tibble::tribble(
  ~row, ~transplantid, ~drugcode, ~monthcode,
    1L,           76L,       "P",  "Initial",
    2L,           76L,       "V",  "Initial",
    3L,           76L,       "X",  "Initial",
    4L,           76L,       "P",    "3 Mth",
    5L,           76L,       "V",    "3 Mth",
    6L,           76L,       "X",    "3 Mth",
    7L,           77L,       "P",  "Initial"

But then how do you get from here to the second bit? Where does VXU come from?