Kovets Teshuvos - HaRav Sh Y Elyashiv
HaRav Yosef Shalom Elyashiv
Lactose, milk sugar, is not banned as Chalav Akum because:
A] in its finished state, as a sweetening tablet, it is not a food;
[note - although its end purpose is to be consumed as a food sweetener, its Kosher status is nevertheless determined by its present finished state]
B] whey, from which it is usually made, is not subject to the ban of Chalav Akkum. [the ban applies exclusively to milk processed for drinking, not to milk collected for cheese, butter, yoghurt etc. or even producing powdered milk]
For the same reasons it may be consumed after a meat meal.
Even if it would be considered a food, it is permitted since it is not extracted from milk but from whey and the ban against consuming whey with meat is due only to Maris Ayin which forbids eating them together when the whey is readily identifiable in the dish.