Pharmacokinetic considerations for optimizing inhaled spray-dried pyrazinoic acid formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis ( Mtb ), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive development of PZA resistant Mtb . PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA , and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung, hence direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA- mutant PZA-resistant Mtb . The objectives of the current study were to i) develop novel dry powder POA formulations ii) assess their feasibility for pulmonary delivery using physicochemical characterization, iii) evaluate their pharmacokinetics (PK) in the guinea pig model and iv) develop a mechanism based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3); (ii) the highest concentration in ELF ( CmacELF : 171 nM) within 15.5 minutes, correlating with a fast transfer into ELF after pulmonary administration ( kPM : 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. * TB : tuberculosis Mtb : Mycobacterium tuberculosis PZA : pyrazinamide POA : pyrazinoic acid PK : pharmacokinetic MBM : mechanism based pharmacokinetic model ELF : epithelial lining fluid MDR-TB : multi-drug resistant TB DS-TB : drug-susceptible TB PZAse : pyrazinamidase PM : POA maltodextrin PML : POA maltodextrin and leucine PLS : POA leucine Salt TGA : thermogravimetric analysis NGI : Next Generation Impactor XRPD : X-ray powder diffraction APSD : aerodynamic particle size distribution USP : United States Pharmacopeia HPMC : hydroxypropyl methylcellulose MMAD : mass median aerodynamic diameter GSD : geometric standard deviation FPD : fine particle dose FPF : fine particle fraction IACUC : Institutional Animal Care and Use Committee JVC : Jugular vein catheter BALF : bronchoalveolar lavage fluid IV : intravenous IT : intratracheal PO : oral NCA : Non-compartmental analysis AUC : area under the concentration curve t1/2 : half-life Tmax : time to peak concentration Cmax : peak concentration ML : maximum likelihood estimation KaOral : first-order oral absorption rate FOral : oral bioavailability kIT : first-order transfer rate between intratracheal depot to ELF FIT : intratracheal bioavailability kForm : first-order transfer rate of POA formulations between inhalation depot to ELF FForm : bioavailability after pulmonary administration of POA formulations BWH : body weight of humans BWGP : body weight of guinea pig PH : Scaled PK parameter for human PGP : PK parameter for guinea pig MRT : mean residence time CLPOA : POA clearance from plasma VPOA : volume of distribution in plasma CLd : intercompartmental clearance between lung and plasma CLELF : intercompartmental clearance between ELF and lung KPLung : lung-to-plasma partition coefficient, VLung , lung tissue volume VELF : volume of the ELF MIC : minimum inhibitory concentration [1]: pending:yes