Subselect With Numbers

I have the following table:
CREATE TABLE ITEMS ([ITEMID] int, [itRULE] varchar(1))
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (11, 3)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (12, 3)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (21, 2)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (22, 2)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (31, 1)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (32, 1)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (41, 0)
INSERT INTO ITEMS (ITEMID, itRULE) VALUES (42, 0)

-- Those works and gives me 11,12,21,22
SELECT ITEMID FROM ITEMS WHERE itRULE IN (2,3)
SELECT ITEMID FROM ITEMS WHERE itRULE IN ('2','3')

-- This doesn't works
declare @Rule varchar(10)
set @Rule='2,3'
SELECT ITEMID FROM ITEMS WHERE itRULE IN (@Rule)
Any idea?
I don't mind to change the data type if it works.