(700g) Screening Studies of Co-Amorphous System Formation between Ritonavir and Non-Steroidal Anti-Inflammatory Drugs for Improved Aqueous Solubility

Ritonavir (RIT) and non-steroidal anti-inflammatory drugs (NSAIDs) such as naproxen (NAP), ketoprofen (KET), and flurbiprofen (FLU) are BCS (Biopharmaceutical Classification Scheme) class 2 molecules, with the bioavailability limited by the solvation rate. In this presentation, we describe the development and characterization of co-amorphous dispersions of RIT with NSAIDs. The main driver for design of these systems was to increase the solubility of RIT in the amorphous state. NSAIDs were selected for co-amorphous system formation because apart from NSAID anti-inflammatory action direct antiviral activity was reported against SARS-CoV-2 at high concentrations (Bruin et al., 2022, Int J mol Sci, 1049; Terrier et al., 2021, Molecules, 26, 2593).

In silico studies were performed using COnductor-like Screening MOdel for Real Solvents (COSMO RS) to predict RIT/NSAIDs mixtures formation feasibility and drug solubility. Powder mixtures were prepared by mixing RIT with a NSAID at a range of RIT/NSAID mol% between 10 and 90, and co-amorphous melts were prepared by heating the powder mixtures to temperatures above the melting point. The systems were characterized by Differential Scanning Calorimetry (DSC) and X-ray diffractometry (XRD). Equilibrium solubility of active pharmaceutical ingredients (APIs), powder mixtures and co-amorphous mixtures in water was determined at 500 rpm at 37 °C.

In silico studies in COSMO revealed complementarity of the proton acceptor area of RIT and proton donor area of NSAIDs in their sigma profiles, indicating the potential of hydrogen bond formation between these compounds. The enthalpy of mixing determined by COSMO showed good miscibility between RIT and NSAIDs. The lowest enthalpy of mixing was observed at 1:2 RIT/NSAID composition for all tested NSAIDs.

Mixing of RIT and NSAIDs in mortar yielded white electrostatic powder mixtures for all tested compositions. Heating of RIT/NSAID mixtures resulted in eutectic formation. The experimentally determined eutectic melting points differed from the theoretical eutectic diagram calculated by the Schröder van Laar equation implying the presence of intermolecular interactions between RIT and NSAIDs. In the subsequent heating of melted RIT/NSAID mixtures one glass transition event was observed, indicating components miscibility and formation of RIT/NSAID co-amorphous mixtures by melting and cooling of a liquidus state from temperatures above melting point. Formation of co-amorphous systems was observed for all tested RIT/KET and RIT/FLU compositions and for RIT/NAP mixtures containing up to 80 mol% of NAP. Binary mixture containing 90 mol% NAP showed different behavior, because glass transition was followed by NAP crystallization exotherm at 68.07±2.09 °C and NAP melting endotherm at 117.91±0.67 °C.

The solubility of RIT in water at 37 °C increased from 2.5±0.3 µg/ml to 4.1±1.0 µg/ml when it was converted from crystalline to amorphous form. The solubility of RIT in 1:2 and 1:1 RIT/NSAID powder mixtures did not change significantly compared with crystalline RIT. On the other hand, in RIT/NSAID 1:2 and 1:1 melts the solubility of RIT was significantly increased compared with amorphous RIT to approximately 12-14 µg/ml. RIT also had an influence on NSAID solubility in RIT/NSAID melts. The solubility of KET was reduced from 208.8±3.3 µg/ml (amorphous KET) to 106.3±8.7 µg/ml in 1:1 RIT/KET melt. The solubility of FLU was reduced from 73.5 µg/ml (crystalline FLU) to 62.9±2.9 µg/ml in 1:1 RIT/FLU melt, whereas the solubility of NAP increased from 36.7±0.5 µg/ml (crystalline NAP) to 219.4±11 µg/ml in 1:1 RIT/NAP melt. The XRD analysis of undissolved material after solubility studies showed that the RIT/NSAID melts remained amorphous except for 1:2 RIT/NAP, whereby small amount of NAP crystallized after exposure to water during solubility studies.

Funding: Part of the research was funded by the European Union's Horizon 2020 Research and Innovation program under the Marie Sklodowska-Curie grant agreement No 778051, and the Ministry of Science and Higher Education in Poland 5014/H2020-MSCARISE/2019/2.