Developing an in vitro lipolysis model for real-time analysis of drug concentrations during digestion of lipid-based formulations

Co-milling of glass forming ability class III drugs: Comparing the impact of low and high glass transition temperatures

With an increasing focus on sustainable technologies in the pharmaceutical industry, milling provides a solvent-free approach to improve drug dissolution. Milling of drugs with an excipient offers additional opportunities to achieve supersaturation kinetics. Therefore, this work aims to present insights of co-milling fenofibrate and apremilast, two good glass formers with low and high glass transition temperatures (Tgs) respectively. Drugs were co-milled with croscarmellose sodium for various process durations followed by thermal analysis, investigation of crystallinity, surface area and dissolution. The dissolution enhancement of the low-Tg glass former fenofibrate highly correlated with the process-induced increase in surface area of co-milled systems (R2 = 0.96). In contrast, the high-Tg glass former apremilast lost its crystalline order gradually after ≥ 10 min of co-milling, and favourable supersaturation kinetics during biorelevant dissolution testing were observed. Interestingly, the melting point of co-milled apremilast decreased and linearly correlated with the highest measured drug concentration (cmax) during in vitro dissolution (onset temperature R2 = 0.98; peak temperature R2 = 0.96). The melting point depression remained stable after 90 days for apremilast, whereas fenofibrate co-milled for 20 min or more showed an increase in melting point upon storage. This study demonstrated that co-milling with croscarmellose sodium is ideally suited to good glass formers with a high Tg. The melting point depression is thereby proposed as an easily accessible critical quality attribute to estimate likely dissolution performance of drugs in dry co-milled formulations.

Exploring supersaturated type IV lipid-based formulations: Impact of supersaturation, digestion and precipitation wInhibition on cinnarizine absorption

Building up on previous publications for type I, II, IIIa, and IIIb Lipid-based formulations (LBFs), the supersaturation potential for cinnarizine in type IV LBFs and the effect of supersaturation, lipid digestion, and precipitation inhibition in vivo was investigated. The supersaturation potential for cinnarizine-loaded type IV LBFs was high and this was investigated in vivo in rats. Supersaturated LBFs tended to show higher drug exposures in vivo than their non-supersaturated counterparts (22 - 92 % increase in AUC0-24h, not dose-normalized), but this was only statistically significant for the formulation containing a precipitation inhibitor under lipase-inhibited conditions, so the overall impact was limited. Soluplus® as a precipitation inhibitor did not increase drug exposure in general, even though the administered cinnarizine dose was higher for the supersaturated formulations. Lipase inhibition had no impact on cinnarizine absorption, indicating no increased precipitation during digestion. The results were in line with previous findings from type IIIb LBFs that revealed that the digestion process was less important for drug absorption from hydrophilic types of LBFs as opposed to the more lipophilic type I- and II systems.

Intraluminal enzymatic hydrolysis of API and lipid or polymeric excipients

The role of intraluminal enzymes for the hydrolysis of active pharmaceutical ingredients (API), prodrugs and pharmaceutical excipients will be reviewed. Carboxylesterases may hydrolyze ester-based API, prodrugs and ester-bond containing polymer excipients, whereas lipases digest lipid formulation excipients, such as mono-, di- and triglycerides. To clarify the conditions that should be mimicked when designing in vitro studies, we briefly review the upper gastrointestinal physiology and provide new data on the inter-individual variability of enzyme activities in human intestinal fluids. Afterwards, the methodology for studying enzymatic hydrolysis of API, prodrugs, lipid and polymeric excipients, as well as the main results that have been obtained, are summarized. In vitro digestion models used to characterize lipid formulations are well described, but data about the hydrolysis of lipid excipients (including surfactants) has been scarce and contradictory. Data on API and prodrug hydrolysis by esterases is available; however, inconsistent use of enzyme types and concentrations limits structure-stability relationships. Hydrolysis of polymer excipients in the lumen has not been significantly explored, with only qualitative data available for cellulose derivates, polyesters, starches, etc. Harmonization of the methodology is required in order to curate larger enzymatic hydrolysis datasets, which will enable mechanistic understanding and theoretical prediction.

Predictions of biorelevant solubility change during dispersion and digestion of lipid-based formulations

Computational approaches are increasingly explored in development of drug products, including the development of lipid-based formulations (LBFs), to assess their feasibility for achieving adequate oral absorption at an early stage. This study investigated the use of computational pharmaceutics approaches to predict solubility changes of poorly soluble drugs during dispersion and digestion in biorelevant media. Concentrations of 30 poorly water-soluble drugs were determined pre- and post-digestion with in-line UV probes using the MicroDISS Profiler™. Generally, cationic drugs displayed higher drug concentrations post-digestion, whereas for non-ionized drugs there was no discernible trend between drug concentration in dispersed and digested phase. In the case of anionic drugs there tended to be a decrease or no change in the drug concentration post-digestion. Partial least squares modelling was used to identify the molecular descriptors and drug properties which predict changes in solubility ratio in long-chain LBF pre-digestion (R2 of calibration = 0.80, Q2 of validation = 0.64) and post-digestion (R2 of calibration = 0.76, Q2 of validation = 0.72). Furthermore, multiple linear regression equations were developed to facilitate prediction of the solubility ratio pre- and post-digestion. Applying three molecular descriptors (melting point, LogD, and number of aromatic rings) these equations showed good predictivity (pre-digestion R2 = 0.70, and post-digestion R2 = 0.68). The model developed will support a computationally guided LBF strategy for emerging poorly water-soluble drugs by predicting biorelevant solubility changes during dispersion and digestion. This facilitates a more data-informed developability decision making and subsequently facilitates a more efficient use of formulation screening resources.

Development of lipid-based SEDDS using digestion products of long-chain triglyceride for high drug solubility: Formulation and dispersion testing

A self-emulsifying drug delivery system (SEDDS) containing long chain lipid digestion products (LDP) and surfactants was developed to increase solubility of two model weakly basic drugs, cinnarizine and ritonavir, in the formulation. A 1:1.2 w/w mixture of glyceryl monooleate (Capmul GMO-50; Abitec) and oleic acid was used as the digestion product, and a 1:1 w/w mixture of Tween 80 and Cremophor EL was the surfactant used. The ratio between LDP and surfactant was 1:1 w/w. Since the commercially available Capmul GMO-50 is not pure monoglyceride and contained di-and-triglycerides, the digestion product used would provide 1:2 stoichiometric molar ratio of monoglyceride and fatty acid after complete digestion in gastrointestinal fluid. Both cinnarizine and ritonavir had much higher solubility in oleic acid (536 and 72 mg/g, respectively) than that in glyceryl monooleate and glyceryl trioleate. Therefore, by incorporating oleic acid in place of glyceryl trioleate in the formulation, the solubility of cinnarizine and ritonavir could be increased by 5-fold and 3.5-fold, respectively, as compared to a formulation without the fatty acid. The formulation dispersed readily in aqueous media, and adding 3 mM sodium taurocholate, which is generally present in GI fluid, remarkably improved the dispersibility of SEDDS and reduced particle size of dispersions. Thus, the use of digestion products of long-chain triglycerides as components of SEDDS can enhance the drug loading of weakly basic compounds and increase dispersibility in GI fluids.