Really? I always just changed it if I didn't have the strength that was asked in stock. Like prednisone 20 was on back order, we just switched to 10 without asking for a new RX... Seems like a waste of time and money to always ask if it's not a control.
Its different if you are changing the ultimate meaning and intent of the script. If you are, you need to call the dr.
Ex: dr writes a specified drug, specified dosage form, at a specified frequency, dose, and duration .. as long as you aren't changing these in a way that substantially deviates from the prescriber's order .. you don't have to call.
Like changing qty on nasal spray, topicals (sometimes) , liquids, inhalers, etc... you know the dr just wants one package or one months worth, you use your professional judgment and change it in order to dispense.
On a script that has qty 90 of one strength and you want to change it to 180 of half strength .. that seems to vary by pharmacist .. but myself and everyone else I've worked with would do this without calling first. Prescriber's medical intent and order is still being followed.
If its a script for 30 of one strength and you want to dispense 90 of the same strength, obviously you call.
On the other hand, if dr writes for one month supply of something but doesn't specify quantity.. you are allowed to just calculate the quantity . You don't have to go and ask the md office if one month x QD really meant to dispense #30 lol.