LAUSR

Novel inhalable and synergistic combination powder formulations of phage PEV20 and ciprofloxacin were recently developed to treat Pseudomonas aeruginosa respiratory infections. In the present study, we investigated the storage stability of these powders which comprised ciprofloxacin, lactose and L-leucine in mass ratios of 1:1:1 (Formulation A) or ciprofloxacin and L-leucine in 2:1 without lactose (Formulation B). These powders were produced by spray drying, collected in polypropylene tubes and packed inside aluminium pouches which were heat-sealed at <20% relative humidity (RH), then stored at 4 °C or 25 °C. The phage viability, aerosol performance and solid-state properties of the powders were examined over 12 months. The biological activity and aerosol performance of both formulations showed no significant change over 12 months of storage at 4 °C. However, after four months of storage at 25 °C, a significant titer loss of 2.2 log10 (p<0.01) was observed in Formulation B, but the loss in Formulation A was much less (0.5 log10 (p<0.05)). In contrast, the fine particle fraction (FPF, wt. % particles ≤ 5 µm) of Formulation A was significantly reduced by 11% (p < 0.05) after four months of storage at 25 °C, whereas the aerosol performance of Formulation B remained stable over 12 months. The results showed that ciprofloxacin can sufficiently stabilize phage through vitrification and/or hydrogen bonding at 4 °C. The presence of lactose was beneficial to preserve the phage at 25 °C. In conclusion, spray dried PEV20-ciprofloxacin combination powders were biologically and physico-chemically stable even without lactose as a stabilising excipient, when stored below 20% RH at 4 °C for 12 months.