。
The medicine didn't work at all.
Literal
Medicine [subj-が] at-all didn't-take-effect.
The adverb まったく (also written 全く) paired with a negative predicate is a fixed intensifier meaning 'not at all.' Similar pairings: ぜんぜん~ない, ちっとも~ない, 全く~ない — all negative-polarity intensifiers. まったく by itself with a positive predicate means something different ('completely, truly').