(T1530-01-05) Development of Clofazimine Lipid-Based SEDDS with High Drug Loading Using Digestion Products of Long-Chain Triglyceride

Purpose: In a previous report from our laboratory, it has been demonstrated that the use of lipid-digestion products (long-chain fatty acid plus monoglyceride) in place of undigested lipids (long-chain triglycerides) in self-emulsifying drug delivery systems (SEDDS) can greatly increase loading of weakly basic drugs in formulations while minimizing drug precipitation in gastrointestinal fluids that is otherwise often encountered with an alternative addition of organic co-solvents in products (1). In the present study, optimal combinations of lipid-digestion products (LDP) and surfactants for the formulation of SEDDS were identified by conducting LDP-surfactant-water pseudo-ternary phase diagrams. The combination was used to develop SEDDS for clofazimine (CFZ), a poorly water-soluble drug with intrinsic solubility less than 11 ng/ml in the intestinal pH range (2). CFZ is recognized as an essential drug by WHO for use against leprosy and tuberculosis, and despite its importance and therapeutic efficacy, no commercial CFZ products are currently available; one previously marketed lipid-based product was later withdrawn due to variability in oral bioavailability. Preliminary studies in our laboratory indicated that clofazimine has a very high solubility in one of the LDP (oleic acid), and, therefore, it was explored whether an LDP-based SEDDS containing 1:1.2 w/w mixture of glyceryl monooleate (Capmul GMO-50) and oleic acid would also provide high drug solubility.

Methods: Solubility studies of CFZ were conducted in formulation components, lipids, surfactants, and their combinations. Pseudo-ternary phase diagrams were constructed with a mixture of glyceryl monooleate (GMO) and oleic acid (OA) as the lipid phase and single or combined surfactants (Kolliphor EL and Tween 80) to identify the microemulsion or fine emulsion regions in water. SEDDS formulations containing 50% lipid mixture (GMO: OA, 1:1.2 w/w) and 50% surfactant mixture (Kolliphor EL: Tween 80, 1:1 w/w) were prepared with 5% and 10% drug loading equal to ~ 80% of its equilibrium. In-vitro dispersion of the formulations was tested in various aqueous media, including acidic media (pH 2.0), phosphate buffer (pH 6.8) with and without a bile salt (sodium taurocholate), biorelevant media (FeSSIF-V2), and step-dispersion testing was also conducted by changing the pH from 2.0 to 6.8.

Results: CFZ exhibited much higher solubility in oleic acid ( ≈ 500 mg of CFZ per g of oleic acid) (3) as compared to other components (Figure 1). The pseudo-ternary phase diagrams revealed a higher microemulsion region with the combined surfactant mixture. The equilibrium solubility of CFZ in the final composition with selected ratios of the GMO-OA-surfactant mixture is ≈ 130 mg/g, which was in agreement with the solubility of CFZ in the oleic acid present in the formulation. The in-vitro dispersion studies of lipid digestion product-based SEDDS containing 50 mg and 100 mg CFZ were conducted in 250 mL of different media. At pH 2.0, rapid dispersion occurred, but the drug partially precipitated out as clofazimine hydrochloride due to the common ion effect for both 50 mg and 100 mg formulations (4). Upon filtration, the drug concentrations dropped significantly (30% for 50 mg and 15% for 100 mg), indicating crystallization of clofazimine hydrochloride (Figure 2). The higher drug loading in the 100 mg formulation led to more rapid crystallization (Figure 2C). At pH 6.8, 50 mg showed coarse emulsions that formed initially with a particle size ranging between 1.0 and 1.5 µm, but the presence of 3 mM bile salt improved dispersibility and particle size (300-500 nm), with no significant difference between filtered and unfiltered aliquots, suggesting drug solubilization in mixed micelles. A finer emulsion was formed for the 100 mg formulation, and the filtered drug concentration was ~90%, indicating better solubilization than the 50 mg formulation. As drug crystallization in the acidic pH was identified, we analyzed the formulation's step-wise pH change from pH 2.0 to pH 6.8 (mimicking gastric to intestinal transition). The initially crystallized drug from the 50 mg formulation was efficiently re-dissolved, with drug concentrations increasing to 67% (without bile salt) and 76% (with 3 mM bile salt) (Figure 3A). However, as rapid crystallization was observed with 100 mg formulation, drug concentrations after the media change were less than 50% with and without bile salt (Figure 3C).

Conclusion: The developed SEDDS using long-chain lipid digestion products (1:1.2 w/w mixture of glyceryl monooleate (Capmul GMO-50) and oleic acid successfully enhanced the drug loading and dispersibility of CFZ. Incorporating the LDPs in the SEDDS formulation helped to achieve a microemulsion formation with the use of combined surfactants. The in-vitro dispersion testing demonstrated the potential challenges posed by the pH-dependent solubility behavior of CFZ, with crystallization occurring at gastric pH and redissolution at intestinal pH facilitated by the presence of bile salts. The results of the present study show that basic drugs such as CFZ have great solubility in long-chain fatty acids. By incorporating these fatty acids in LBFs, the alternative use of organic co-solvents to increase drug loading can be minimized or eliminated for basic drugs.

References: Desai HH, T M Serajuddin A. Development of lipid-based SEDDS using digestion products of long-chain triglyceride for high drug solubility: Formulation and dispersion testing. Int J Pharm. 2024 Feb 27;654:123953.
2. Verbić TŽ, Tam KY, Veljković DŽ, Serajuddin ATM, Avdeef A. Clofazimine pKa Determination by Potentiometry and Spectrophotometry: Reverse Cosolvent Dependence as an Indicator of the Presence of Dimers in Aqueous Solutions. Mol Pharm. 2023 Jun 5;20(6):3160–9.
3. Wyttenbach N, Niederquell A, Ectors P, Kuentz M. Study and Computational Modeling of Fatty Acid Effects on Drug Solubility in Lipid-Based Systems. J Pharm Sci. 2022 Jun;111(6):1728–38.
4. Bannigan P, Verma V, Hudson SP. Overcoming the Common Ion Effect for Weakly Basic Drugs: Inhibiting the Crystallization of Clofazimine Hydrochloride in Simulated Gastrointestinal Media. Cryst Growth Des. 2019 Mar 6;19(3):1599–609.


Figure 1: Solubility of clofazimine (mg/g) in individual formulation and mixture of components.


Figure 2: Results of dispersion test of CFZ-loaded lipid-based formulation (CFZ-SEDDS) in 250 mL of pH 2.0 (0.01 M HCl). One g of SEDDS containing 50 mg and 100 mg of CFZ was added to each vessel. Figure 2A shows dispersion profiles of CFZ SEDDS 50 mg dose in pH 2.0 buffer where lines 1 and 2 represent CFZ concentrations in unfiltered and filtered dispersions, respectively. Figure 2C shows dispersion profiles of CFZ SEDDS 100 mg dose in pH 2.0 buffer where lines 1 and 2 represent CFZ concentrations in unfiltered and filtered dispersions, respectively. Particle sizes of unfiltered dispersions at pH 2.0 for 50 mg and 100 mg are given in Figure 2B and 2D, respectively.


Figure 3: Results of step dispersion test of CFZ-loaded lipid-based formulation (CFZ-SEDDS) in 250 mL of pH 2.0 and 6.8 with 3 mM sodium taurocholate. One g of SEDDS containing 50 mg and 100 mg of CFZ was added to each vessel. Figure 3A shows dispersion profiles of CFZ SEDDS 50 mg dose at pH 2.0 and 6.8 with 3 mM sodium taurocholate where lines 1 and 2 represent CFZ concentrations in unfiltered and filtered dispersions, respectively. Figure 3C shows dispersion profiles of CFZ SEDDS 100 mg dose at pH 2.0 and 6.8 with 3 mM sodium taurocholate where lines 1 and 2 represent CFZ concentrations in unfiltered and filtered dispersions, respectively. Particle sizes of unfiltered dispersions at pH 2.0 and 6.8 with 3 mM sodium taurocholate for 50 mg and 100 mg are given in Figure 3B and 3D, respectively.