Do I need to monitor both Oseltamivir and Zanamivir?
Monitor susceptibility to both drugs if you are able to do so. Development of resistance is drug specific and therefore may arise to either oseltamivir or zanamivir independently. Samples tested against one drug cannot be assumed to be sensitive to the other. Resistance has developed more readily to oseltamivir than to zanamivir albeit infrequently and therefore if you cannot monitor both drugs, oseltamivir testing is more relevant.
