An apparatus includes a needle, a cutter, a medication fluid path, and a filter assembly. The needle defines a tissue receiving feature. The cutter is movable relative to the needle to sever tissue protruding into the tissue receiving feature. The medication fluid path includes a first portion and a second portion. The first portion is configured to couple with a source of medication fluid. The tissue receiving feature is in fluid communication with the medication fluid path such that the first portion is upstream of the tissue receiving feature. The filter assembly is located in the second portion of the medication fluid path. The filter assembly is configured to permit air to pass through the filter assembly. The filter assembly is further configured to prevent medication fluid from passing through the filter assembly.
