(M1530-03-21) Predicting the Relative in Vivo performance of Nanoformed and Crystalline Bulk Piroxicam Solid Suspensions from in Vitro Flux Measurements

Purpose: The formulation of APIs as solid nanosuspensions to overcome the issues presented by challenging solubility and dissolution properties has become a popular formulation pathway in recent years. Nanocrystalline API produced by a unique technology, Controlled Expansion of Supercritical Solution (CESS^®), reduces the size of API particles while maintaining tight control of system thermodynamics and, consequently, surface properties. The technique involves dissolving and extracting API particles from supercritical carbon dioxide (scCO2). The method is also called “nanoforming” and material produced by CESS® is termed “nanoformed” material. Here, we demonstrate the correlation of in vitro flux results to the outcomes of a pre-clinical rat study and explore the prediction of in vivo absorption and pharmacokinetic (PK) behaviour in humans from in vitro dissolution/permeability data, using the example of piroxicam (PRX) prepared by CESS^® technology. The absorption model employed is based on the gastrointestinal unified theoretical (GUT) framework¹. The results of this study illustrate the predictive capability of in vitro flux assays with regards to rat and human pharmacokinetics.

Methods: Two PRX solid suspensions, a “bulk” material, prepared with untreated piroxicam, and nanoformed™ material produced by CESS^®, each with identical API loading of 100 mg/ml and excipient content (1%HPMC and 1% Tween) were prepared for dissolution/permeability testing and the conduct of an in vivo pharmacokinetic study in rats with an oral administration of 20mg/kg API. Flux assays were carried out in quadruplicate using the MicroFLUX^TM two-compartment dissolution/permeability testing apparatus (Pion Inc., Billerica, MA, USA). Quantitation of the API was performed by a Rainbow R6 FO spectrometer. Predictions of human in vivo mass absorbed were generated using the fraction absorbed calculation by the Pion Predictor^TM (v1.0) software package. In vivo C_max and T_max were estimated from mass absorbed vs. time plots exported from Predictor and published pharmacokinetic data2 (V_d, K_el).

Results: The appearance rate of PRX in the acceptor vessel of the microFLUX^TM apparatus was 1.86 times greater for the nanosuspension as opposed to the bulk, whereas the AUC ratio between the appearance profiles exhibited a 2.16-fold improvement for the nanoformed™ product. Replicates showed consistent results (Figure 1). The Predictor software was used to convert the flux appearance profiles into plots of absolute mass absorbed (Figure 2), from which the human in vivo C_max and T_max values were estimated. In the human pharmacokinetic study, a dose of 20 mg administered as a tablet showed a T_max of 1.75 hours and a C_max of 2.23 µg/mL. The in vivo predictions of the nanoformed™ material provided close estimates of T_max, (1.43 hours) and C_max (2.01 µg/mL). The results of the in vivo preclinical rat study demonstrated that a 20 mg/kg oral dose of nanoformed™ piroxicam possessed superior pharmacokinetic properties compared with piroxicam bulk, with a faster T_max by 6 times, higher C_max by 1.55 times and larger AUC by 1.86 times within the first 8 hours. By comparison, in vitro flux assays exhibited a 2.16-fold improvement in the acceptor vessel AUC, showing a reasonable correlation in the relative increase in drug exposure between the formulations. When tested at 5 mg/kg, suspension with nanoformed™ material demonstrated a dose dependency showing reduced AUC by 3.85 times respectively in comparison to 20 mg/kg dose of nanoformed™ piroxicam.

Conclusion: The data presented illustrates the applicability of in vitro flux assays in conjunction with predictive modelling software for the prediction of the relative in vivo performance resulting from alterations to the design of a formulation, in this case, the nanoforming of PRX to reduce the particle size of the drug. The boost in the exposure of nanoformed™ API as opposed to untreated API at equivalent dose is also demonstrated clearly in rats, equating to a 6-fold increase in T_max and 1.55-fold increase in the C_max of plasma profiles. In this case, flux assay results alone exhibit the capacity to rank order the relative performance improvement from nanoforming based on the observed acceptor vessel AUC. We will further investigate whether it is possible to properly predict the in vivo rat data by using the generated in vitro flux and an in silico rat model.

References: 1. Sugano K. Fraction of a dose absorbed estimation for structurally diverse low solubility compounds. Int J Pharm. 2011 Feb 28;405(1-2):79-89
2. Drugs@FDA Database, https://www.accessdata.fda.gov/drugsatfda_docs/label/2006/018147s029lbl.pdf

Average acceptor appearance profiles for PRX nanosuspension and PRX bulk suspension.

Calculated absolute mass absorbed over a human intestinal residence time of 210 minutes using Predictor v1.0.

Piroxicam plasma levels in rats after 20 mg/kg and 5 mg/kg PRX administration.