Returning north I take second grade antimalarial (7)

I believe the answer is:

atebrin

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'antimalarial' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?

I don't understand how the rest of the clue works.

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(Other definitions for atebrin that I've seen before include "to combat malaria" , "antimalarial drug" .)

I've seen this clue in The Sunday Times and The Times.

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