What it means
BIW (or biw) has been read as "twice a day," which would give the drug seven times too often. ISMP lists it as error-prone.
For the nurse
Write "2 times weekly" and name the days when you can, such as "Monday and Thursday."
Dictionary · Abbreviation
BIW
An abbreviation for "twice a week" that ISMP advises against; write "2 times weekly."