Do be wise in the use of medicine! (6)
I believe the answer is:
dosage
'use of medicine' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'do be wise' is the wordplay.
'be wise' becomes 'sage' (similar in meaning).
'do'+'sage'='DOSAGE'
'in the' is the link.
Can you help me to learn more?
(Other definitions for dosage that I've seen before include "Correct use of a prescribed drug" , "amount of 14 [WONDER DRUG], say" , "Measured portion of medicine" , "Sea dog (anag)" , "Measured amount of medicine to be taken" .)