Why Is It Important Not to Switch Manufacturers of Theophylline

Why is it important not to switch manufacturers of theophylline once a patient has established a good drug response to it?

A) The additives from the various manufacturers have shown to increase hypersensitivity to the drug.
B) The bioavailability differs from manufacturer to manufacturer.
C) The coloring used by different manufacturers has shown to increase side effects in some patients.
D) The half-life for theophylline varies greatly from manufacturer to manufacturer,so dosing may need to be adjusted.