Fancy a Pharmaceutical Milkshake?
Malinda Salim,1 Gisela Ramirez,1 Andrew J. Clulow,1 Adrian Hawley2 and Ben J. Boyd1*
1Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville, VIC 3052, Australia
2SAXS/WAXS beamline, Australian Synchrotron, ANSTO, 800 Blackburn Rd, Clayton, VIC 3169, Australia
Malinda Salim is the Vice Chair of the CD&P Division
Ben Boyd is the CRS President Elect
Introduction
Milk is a source of nutrients and contains bioactive compounds that are needed for the growth and development of infants. Milk has gained interest as an oral drug delivery system and studies to enhance the solubility of lipophilic drugs by dispersing these drugs in milk have been reported.[1] However, differences in the lipid compositions in milk (that can arise from the different species, feed, and seasonal variations) can pose a challenge during development, as the rate and extent of digestion of the milk lipids and consequently drug solubilisation could vary. Additionally, the digestion of milk lipids is an important aspect often neglected in considering milk-based formulations. Hence, the effect of the digestion of milk lipids on drug solubilisation is central to the development of milk-based formulations for oral drug delivery.[2] Herein, using a novel SAXS/WAXS technique developed in collaboration with the Australian Synchrotron, the solubilisation behaviour of poorly water-soluble antimalarial drugs in milk during digestion were investigated in vitro.
Methods and results
Two antimalarial drugs used in combination, artefenomel (OZ439-mesylate) and ferroquine. The solubilisation behaviour of these drugs during digestion in milk under gastrointestinal tract conditions, was studied using in situ X-ray diffraction using the SAXS/WAXS beamline at the Australian Synchrotron (see Figure 1). The power of the synchrotron technique allows the solid state characteristics of solid drug particles present in milk to be studied dynamically during digestion, to identify potential polymorphism and trajectories of drug solubilisation through changes in the X-ray scattering profiles. The drugs (99 mg OZ439-mesylate and/or ferroquine granules equivalent to 93 mg ferroquine active pharmaceutical ingredient) were then added to 17.5 mL milk after exposure to gastric conditions and digestion was initiated at pH 6.5 by addition of pancreatic lipase. A pH-STAT controller allows tracking of digestion kinetics by titrating against fatty acids produced on digestion of milk lipids.[3,5]
The X-ray scattering patterns of OZ439-mesylate after exposure to gastric pH and small intestinal pH showed precipitation of the drug as a hydrochloride salt (OZ439-HCl) and disproportionation to a free base form (OZ439-FB 1) respectively. The OZ439-FB 1 observed was however not thermodynamically stable and could readily undergo polymorphic transformation to the more stable free base form (termed OZ439-FB 2) during digestion (fast below), upon storage of the OZ439-FB 1 powder in room temperature or with an increase in temperature (slower).[4]
As expected, OZ439-FB 1 was detected when the mesylate or hydrochloride salt forms of OZ439 were dispersed in milk near physiological pH. With continuous stirring at pH 6.5 and 37 °C, no changes in the X-ray scattering patterns were observed and the OZ439 remained as FB form 1 throughout the dispersions (Figure 3a). However, upon injection of pancreatic lipase to initiate the digestion of milk, a decrease in intensity of diffraction peaks characteristic of OZ439-FB 1 was observed and peaks characteristic of a new free base form ‘OZ439-FB 2’ appeared (Figure 3b), indicating that digestion provided the required conditions for the polymorphic transformation.[3] Figure 3c summarises the solid-state transformation of OZ439 occurring in milk at pH 6.5 following dispersion and digestion.
Although the presence of crystalline OZ439-FB 2 in milk after digestion indicated that drug solubilisation was incomplete at the drug/milk fat ratio tested, a significant reduction in drug crystals was observed compared to lipid-free medium (data shown in ref [3]). In contrast, ferroquine (a partner drug co-administered with OZ439) was highly solubilised in digesting milk.[5] Figure 4a shows that upon digestion in milk, intensity of the characteristic diffraction peak for ferroquine at approximately q=1.29 Å-1 decreased and disappeared completely within several minutes of digestion. Finally, we also showed that interestingly the kinetics of transformation of OZ439-FB 1 to OZ439-FB 2 was accelerated in the presence of ferroquine potentially due to the presence of excipients in the ferroquine granules, or the increased amount of supersaturated free OZ439 in solution due to the reduced initial drug solubilisation in the milk fat globules (Figure 4b).
Conclusion
Findings from the studies highlighted that (1) incorporation of a digestion step is critical to understanding drug solubilisation in lipid-based formulations such as milk during digestion, and (2) the influence of one drug on another during solubilisation and solid-state behaviour of drugs when used in combination treatments must be taken into consideration to understand how one drug affects the solubilisation of another and the potential polymorphic transitions occurring during digestion.
Acknowledgements
This work was funded by the Bill and Melinda Gates Foundation grant number OPP1160404 in collaboration with the Medicines for Malaria Venture (MMV). Funding is also acknowledged from the Australian Research Council under the Discovery Projects scheme DP160102906. The SAXS experiments for this work were conducted on the SAXS/WAXS beamline of the Australian Synchrotron, part of ANSTO. OZ-439 was provided by Medicines for Malaria Venture (MMV) and ferroquine was provided by Sanofi (please refer to the references in the bibliography for full details).
References
[1] MacHeras, P.E. and Reppas, C.I., 1986. Studies on Drug—Milk Freeze-Dried Formulations I: Bioavailability of Sulfamethizole and Dicumarol Formulations. Journal of pharmaceutical sciences, 75(7), pp.692-696.
[2] Boyd, B.J., Salim, M., Clulow, A.J., Ramirez, G., Pham, A.C. and Hawley, A., 2018. The impact of digestion is essential to the understanding of milk as a drug delivery system for poorly water soluble drugs. Journal of Controlled Release, 292, pp.13-17.
[3] Salim, M., Khan, J., Ramirez, G., Clulow, A.J., Hawley, A., Ramachandruni, H. and Boyd, B.J., 2018. Interactions of artefenomel (OZ439) with milk during digestion: insights into digestion-driven solubilization and polymorphic transformations. Molecular Pharmaceutics, 15(8), pp.3535-3544.
[4] Clulow, A.J., Salim, M., Hawley, A., Gilbert, E.P. and Boyd, B.J., 2018. The curious case of the OZ439 mesylate salt: An amphiphilic antimalarial drug with diverse solution and solid state structures. Molecular Pharmaceutics, 15(5), pp.2027-2035.
[5] Salim, M., Khan, J., Ramirez, G., Murshed, M., Clulow, A.J., Hawley, A., Ramachandruni, H., Beilles, S. and Boyd, B.J., 2019. Impact of ferroquine on the solubilization of artefenomel (OZ439) during in vitro lipolysis in milk and implications for oral combination therapy for malaria. Molecular Pharmaceutics, 16(4), pp.1658-1668.
