Rx amounts (7)
'rx amounts' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for doses that I've seen before include "Quanitites of medicine" , "Administers medicine to (someone)" , "Gives medicine to" , "Prescribed amounts of medication" , "Potion portions" .)
(Another definition for dosages that I've seen is " measures".)