There are different ways to solve this problem:
[label]
Kill *
If Item has dropped : X
Get Drop: X
goto: label
or you can
Kill for Item: X; 48
Kill *
Get Drop: X
Kill *
Get Drop: X
or you can merge them if you item doesnt have a 100% drop:
[label]
kill for item: X; 48
kill *
If Item has dropped : X
Get Drop: X
if item isnt in inventory: X; 50
goto: label
I suggest using grimoire 3.8+, as it has better if statements.
Because 2 and 3 combines get drop and whitelist, I suggest 1 if you have d/c issues. Good Luck.