Category: Formulation and Quality
Purpose: There are approximately 1.5 - 2 million tuberculosis (TB) deaths annually, and it is a leading cause of death for those with compromised immune systems, including human immunodeficiency virus (HIV) infection. Mycobacterium tuberculosis (Mtb) is transmitted via inhalation into the lungs, where it is taken up by alveolar macrophages which unwittingly serve as the site of replication. Current first line TB treatments involving oral rifampicin, ethambutol, isoniazid, and pyrazinamide regimens require long treatment durations (at least six months) and result in systemic side effects. In addition, the incidence of multiple and extensively drug resistant TB is growing and contributes to increased transmission risks and risk of mortality. TB treatment requires further exploration of alternative treatments to reach the World Health Organization’s goal of a 90% decrease in TB incidence by 2035. An alternative approach is the use of inhaled antibiotics that could attack the bacteria at its primary site of infection in the lungs.
CPZEN-45 is a caprazamycin derivative with a unique mechanism of action against Mtb and has shown efficacy in acute and chronic in vivo models of both MDR and XDR. However, while CPZEN-45 is water soluble, it has low oral bioavailability. A portable, inhalable variation of CPZEN-45 would offer an alternative to standard TB regimens, especially considering systemic CPZEN-45 concentrations administered via inhalation have been shown to be comparable to intravenous or subcutaneous routes with aerosol delivery showing a) the highest concentration of the three in the lungs and b) a minimal toxicity, similar to aminoglycosides already approved for clinic. Here we develop a dry powder formulation of CPZEN-45 exhibiting aerodynamic characteristics suitable for inhalation toward development of contemporary solutions to TB treatment.
Methods: Batches of CPZEN-45 were spray dried using a Buchi-B290 using the standard cyclone. Percent recovery was calculated with respect to the initial CPZEN-45 mass in solution prior to spraying. Morphology (via scanning electron microscopy [SEM]), aerodynamic particle size distribution ([APSD], via next generation impaction [NGI] and laser diffraction), emitted dose (via nephele tube), in vitro delivered dose (via custom mice and guinea pig dosators), moisture content (via Karl Fischer titration [KF] and thermogravimetric analysis [TGA]), thermal stability (via differential scanning calorimetry [DSC]), and crystallinity (via X-ray powder diffraction [XRPD]) were evaluated. Powder generation as a function of power (pressure gradient × air flow) for inhalers of varying resistance was explored using four inhalers with different pressure drops (a RS-01 Cyclohaler was used as a standard for comparison).
Results: Following spray drying of CPZEN-45 (recovery percentage = 65.7 ± 3.4 %) predominantly corrugated particles with a geometric mean of 1.96 ± 0.75 µm were produced. Impaction after actuating a nominal mass of dry powder through a RS-01 Cyclohaler resulted in particles with a mass median aerodynamic diameter (MMAD) of 2.49 µm, geometric standard deviation (GSD) of 1.91, nominal fine particle fraction (FPFN = the percentage of particles collected < 4.46 µm at NGI operation for 4 s. at 60 L/min with respect to the mass of powder loaded into the inhaler capsule) of 45.1 % and a FPFED (ED = emitted dose) of 73.5 %. Laser diffraction indicated a volume median particle size (d50) of 3.20 ± 0.20 µm with a span of 1.82 ± 0.10 (d10 = 1.44 ± 0.06 µm; d90 = 7.25 ± 0.20 µm). Spray dried particles were confirmed to be amorphous via DSC and XRPD and moisture content was < 10 % as identified by KF and weight loss due to moisture from TGA. Delivery of dry powder was shown to be reproducible through custom dosator and was also impacted by inhaler power characteristics.
Conclusion: Dry powder of CPZEN-45 were manufactured in gram batches resulting in aerodynamic qualities suitable for inhalation, namely small particle size (< 5 µm) and efficient dispersibility. It is our goal to use these results as a springboard for continued development of dry powders of CPZEN-45 for planned in vivo studies regarding TB treatment.