Effects of the antibiotic component on in-vitro bacterial killing, physico-chemical properties, aerosolization and dissolution of a ternary-combinational inhalation powder formulation of antibiotics for pan-drug resistant Gram-negative lung infections

Abstract

Combinational antibiotic formulations have emerged as an important strategy to combat antibiotic resistance. The main objective of this study was to examine effects of individual components on the antimicrobial activity, physico-chemical properties, aerosolization and dissolution of powder aerosol formulations when three synergistic drugs were co-spray dried. A ternary dry powder formulation consisting of meropenem (75.5 %w/w), colistin (15.1 %w/w) and rifampicin (9.4 %w/w) at the selected ratio was produced by spray drying. The ternary formulation was characterized for in-vitro antibacterial activity, physico-chemical properties, surface composition, aerosol performance and dissolution. All of the formulations demonstrated excellent aerosolization behavior achieving a fine particle fraction of >70%, which was substantially higher than those for the Meropenem-SD and Colistin-Meropenem formulations. The results indicated that rifampicin controlled the surface morphology of the ternary and binary combination formulations resulting in the formation of highly corrugated particles. Advanced characterization of surface composition by XPS supported the hypothesis that rifampicin was enriched on the surface of the combination powder formulations. All spray-dried formulations were amorphous and absorbed substantial amount of water at the elevated humidity. Storage at the elevated humidity caused a substantial decline in aerosolization performance for the Meropenem-SD and Colistin-Meropenem, which was attributed to increased inter-particulate capillary forces or particle fusion. In contrast, the ternary combination and binary Meropenem-Rifampicin formulations showed no change in aerosol performance at the elevated storage humidity conditions; attributable to the enriched hydrophobicity of rifampicin on the particle surface that acted as a barrier against moisture condensation and particle fusion. Interestingly, in the ternary formulation rifampicin enrichment on the surface did not interfere with the dissolution of other two components (i.e. meropenem and colistin). Our study provides an insight on the impact of each component on the performance of co-spray dried combinational formulations.

Keywords: Aerosol performance; Dissolution; Dry powder inhaler; Solubility; Spray drying; Ternary combination.

Appendix A1:

Aerosol deposition profiles of the different spray dried formulations (A) Meropenem-SD, (B) Colistin-Meropenem, (C) Meropenem-Rifampicin, and (D) Colistin-Meropenem-Rifampicin. The data are presented as mean ± SD (n=4).

Appendix A2:

In-vitro dissolution profile of ternary antibiotic formulation. The data are presented as mean ± SD (n=4).

Figure 1.

Time-kill kinetics of colistin (8 mg/L), meropenem (40 mg/L) and rifampicin (5 mg/L) mono-drug and combinations as well as the spray dried ternary formulations against (A) P. aeruginosa 20143 n/m and (B) A. baumannii 03–149.2.

Figure 2.

Representative scanning electron microscopy images of (A) Meropenem-SD, (B) Colistin-Meropenem, (C) Meropenem-Rifampicin, and (D) Colistin-Meropenem-Rifampicin formulations.

Figure 3.

Dynamic vapor sorption behavior of the spray dried powder formulations.

Figure 4.

X-ray diffraction patterns of (A) raw materials and spray dried powder formulations, (B) formulations stored at 55% RH for a week, (C) formulations stored at 75% RH for a week.

Figure 5.

Fine Particle Fraction of the spray-dried formulations stored in the desiccated chamber. The data are presented as mean ± SD (n=4).

Figure 6.

Fine particle fraction (% FPF) of the spray-dried formulations stored under 55% and 75% RH for a week: (A) Meropenem-SD formulation, (B) Meropenem-Colistin, (C) Meropenem-Rifampicin formulation, and (D) Colistin-Meropenem-Rifampicin formulation. The data are presented as mean ± SD (n=4).

Figure 7.

Representative scanning electron microscopy images of the spray-dried formulations after storage at 75% RH for 1-week: (A) Meropenem-SD, (B) Colistin-Meropenem, (C) Meropenem-Rifampicin, and (D) Colistin-Meropenem-Rifampicin.

Figure 8.

In-vitro dissolution of meropenem (A), colistin (B) and rifampicin (C) from the composite formulations. The data are presented as mean ± SD (n=4).