Compositions include highly-concentrated Alpha-1 Proteinase Inhibitor (A1PI) in a concentration greater than or equal to 100 mg/ml. Pharmaceutical compositions can be prepared from these compositions. The pharmaceutical compositions can be suitable for subcutaneous administration. The highly-concentrated A1PI solutions can be obtained by single-pass tangential flow filtration (SPTFF).組合物包括濃度大於或等於100 mg/ml的高濃度α-1蛋白酶抑制劑(A1PI)。可由此等組合物來製備藥物組合物。藥物組合物可適用於皮下投與。高濃度A1PI溶液可藉由單程切向流過濾(SPTFF)獲得。