Influence of the composition of glycerides on the solid-state behaviour and the dissolution profiles of solid lipid extrudates

Development and characterization of solid lipid-based formulations (sLBFs) of ritonavir utilizing a lipolysis and permeation assay

As a high number of active pharmaceutical ingredients (APIs) under development belong to BCS classes II and IV, the need for improving bioavailability is critical. A powerful approach is the use of lipid-based formulations (LBFs) that usually consist of a combination of liquid lipids, cosolvents, and surfactants. In this study, ritonavir loaded solid LBFs (sLBFs) were prepared using solid lipid excipients to investigate whether sLBFs are also capable of improving solubility and permeability. Additionally, the influence of polymeric precipitation inhibitors (PVP-VA and HPMC-AS) on lipolysis triggered supersaturation and precipitation was investigated. One step intestinal digestion and bicompartmental permeation studies using an artificial lecithin-in-dodecane (LiDo) membrane were performed for each formulation. All formulations presented significantly higher solubility (5 to >20-fold higher) during lipolysis and permeation studies compared to pure ritonavir. In the combined lipolysis-permeation studies, the formulated ritonavir concentration increased 15-fold in the donor compartment and the flux increased up to 71 % as compared to non-formulated ritonavir. The formulation with the highest surfactant concentration showed significantly higher ritonavir solubility compared to the formulation with the highest amount of lipids. However, the precipitation rates were comparable. The addition of precipitation inhibitors did not influence the lipolytic process and showed no significant benefit over the initial formulations with regards to precipitation. While all tested sLBFs increased the permeation rate, no statistically significant difference was noted between the formulations regardless of composition. To conclude, the different release profiles of the formulations were not correlated to the resulting flux through a permeation membrane, further supporting the importance of making use of combined lipolysis-permeation assays when exploring LBFs.

Control of API release with matrix polymorphism in tristearin microspheres

Glycerides are widely employed as solid matrices in a range of pharmaceutical intermediates and dosage forms. Diffusion-based mechanisms are responsible for drug release, with both chemical and crystal polymorph differences in the solid lipid matrix cited as controlling factors in drug release rates. This work uses model formulations composed of crystalline caffeine embedded in tristearin to study the impacts to drug release from the two primary polymorphic states of tristearin and dependencies on the conversion routes between them. Using contact angles and NMR diffusometry, this work finds that drug release from the meta-stable α-polymorph is rate limited by a diffusive mechanism relating to its porosity and tortuosity, but initial burst release occurs due to ease of initial wetting. Poor wettability resulting from surface blooming can be rate limiting for the β-polymorph, resulting in slower initial drug release relative to the α-polymorph. The route to achieve the β-polymorph strongly impacts the bulk release profile due to differences in crystallite size and packing efficiency. API loading enhances the effective porosity, leading to enhanced drug release at high loadings. These findings offer generalizable principles to guide formulators on the types of impacts to drug release rates that one may expect due to triglyceride polymorphism.

Liquid Lipids Act as Polymorphic Modifiers of Tristearin-Based Formulations Produced by Melting Technologies

Despite the growing interest in lipid-based formulations, their polymorphism is still a challenge in the pharmaceutical industry. Understanding and controlling the polymorphic behavior of lipids is a key element for achieving the quality and preventing stability issues. This study aims to evaluate the impact of different oral-approved liquid lipids (LL) on the polymorphism, phase transitions and structure of solid lipid-based formulations and explore their influence on drug release. The LL investigated were isopropyl myristate, ethyl oleate, oleic acid, medium chain trigycerides, vitamin E acetate, glyceryl monooleate, lecithin and sorbitane monooleate. Spray-congealing was selected as an example of a melting-based solvent-free manufacturing method to produce microparticles (MPs) of tristearin (Dynasan^®118). During the production process, tristearin MPs crystallized in the metastable α-form. Stability studied evidenced a slow phase transition to the stable β-polymorph overtime, with the presence of the α-form still detected after 60 days of storage at 25 °C. The addition of 10% w/w of LL promoted the transition of tristearin from the α-form to the stable β-form with a kinetic varying from few minutes to days, depending on the specific LL. The combination of various techniques (DSC, X-ray diffraction analysis, Hot-stage polarized light microscopy, SEM) showed that the addition of LL significantly modified the crystal structure of tristearin-based formulations at different length scales. Both the polymorphic form and the LL addition had a strong influence on the release behavior of a model hydrophilic drug (caffeine). Overall, the addition of LL can be considered an interesting approach to control triglyceride crystallization in the β-form. From the industrial viewpoint, this approach might be advantageous as any polymorphic change will be complete before storage, hence enabling the production of stable lipid formulations.

New insights into process understanding of solid lipid extrusion (SLE) of extruded lipid implants for sustained protein delivery

The aim of this work is a better understanding of solid lipid extrusion (SLE) for protein depot production using a lab-scale twin-screw (tsc)-extruder. In this context, little is known about the relationship of process parameters such as extrusion temperature, screw speed, or formulation on implant characteristics. It is difficult to attribute release characteristics to only one parameter, since the release will always be influenced by a combination of parameters. In this study, we describe the use of an online pressure measurement tool which allows to characterize pressure profiles during an extrusion run. We systematically investigated the impact of various process parameters on implant properties as well as release patterns using a monoclonal antibody (mAb). Solid lipid implants (SLIs) were produced by tsc-extrusion using the low melting triglyceride H12 and the high melting triglyceride Dynasan® D118. A mAb available in a freeze-dried matrix containing hydroxypropyl-β-cyclodextrine (HP-β-CD) was used as incorporated active pharmaceutical ingredient. Extrusion temperature (33-37 °C), screw speed (40-80 rpm) and the lipid composition (30-70% of each triglyceride) were modified. Additionally, freshly extruded SLIs were ground and extruded again as a preparation technique to optimize properties of SLIs. Using the pressure monitoring tool, four characteristic phases were defined for an extrusion run. We found that both, sufficient pressure and adequately molten material, is needed to form a suitable implant. Using the double extrusion technique, release rates could substantially be slowed down without changing formulation.

Impact of change of matrix crystallinity and polymorphism on ovalbumin release from lipid-based implants

The objectives of this study were to prepare lipid-based implants by hot melt extrusion (HME) for the prolonged release of ovalbumin (OVA), and to relate protein release to crystallinity and polymorphic changes of the lipid matrix. Two lipids, glycerol tristearate and hydrogenated palm oil, with different composition and degree of crystallinity were studied. Solid OVA was dispersed within the lipid matrixes, which preserved its stability during extrusion. This was partially attributed to a protective effect of the lipidic matrix. The incorporation of OVA decreased the mechanical strength of the implants prepared with the more crystalline matrix, glycerol tristearate, whereas it remained comparable for the hydrogenated palm oil because of stronger physical and non-covalent interactions between the protein and this lipid. This was also the reason for the faster release of OVA from the glycerol tristearate matrix when compared to the hydrogenated palm oil (8 vs. 28 weeks). Curing induced and increased crystallinity, and changes in the release rate, especially for the more crystalline matrix. In this case, both an increase and a decrease in release, were observed depending on the tempering condition. Curing at higher temperatures induced a melt-mediated crystallization and solid state transformation of the glycerol tristearate matrix and led to rearrangements of the inner structure with the formation of larger pores, which accelerated the release. In contrast, changes in the hydrogenated palm oil under the same curing conditions were less noticeable leading to a more robust formulation, because of less polymorphic changes over time. This study helps to understand the effect of lipid matrix composition and crystallinity degree on the performance of protein-loaded implants, and to establish criteria for the selection of a lipid carrier depending on the release profile desired.

Long-term release and stability of pharmaceutical proteins delivered from solid lipid implants

Solid lipid implants (SLIs) prepared by twin-screw (tsc) extrusion represent a promising technology platform for the sustained release of pharmaceutical proteins. In this work, we report on two aspects, long-term release and stability of released protein. First, SLIs were produced by tsc-extrusion containing the low melting triglyceride H12 and the high melting triglyceride Dynasan D118. Two different proteins available in a freeze-dried matrix containing hydroxypropyl-β-cyclodextrine (HP-β-CD) were incorporated into the lipid matrix: a monoclonal antibody (mAb) from the IgG₁ class and the f_ab-fragment Ranibizumab (Lucentis®). SLIs, composed of 10% protein lyophilizate and both triglycerides, were extruded at 35°C and 40rpm. Sustained release of both proteins was observed in a sustained manner for approximately 120days. Protein load per implant was increased by three different approaches resulting in a protein load of 3.00mg per implant without affecting the release profiles. The incubation medium containing the released protein was collected, concentrated and analyzed including liquid chromatography (SE-HPLC, IEX, HIC), electrophoresis (SDS-PAGE, on-chip gel electrophoresis) and FT-IR spectroscopy. The mAb showed a monomer loss of up to 7% (SE-HPLC) and IEX analysis revealed the formation of 16% acidic subspecies after 18weeks. FT-IR spectra of mAb indicated the formation of random coil structures towards the end of the release study. Ranibizumab was mainly released in its monomeric form (>95%), and approximately 5% hydrophobic subspecies were formed after 18weeks of release. FT-IR analysis revealed no changes in secondary structure. The release and stability profiles of both proteins underline the potential of SLIs as a delivery system. SLIs provide a promising platform for applications where really long-term release is needed, for example for intraocular delivery of anti-vascular endothelial growth factor (VEGF) drugs for age related macular degeneration (AMD).

Solvent-free melting techniques for the preparation of lipid-based solid oral formulations

Lipid excipients are applied for numerous purposes such as taste masking, controlled release, improvement of swallowability and moisture protection. Several melting techniques have evolved in the last decades. Common examples are melt coating, melt granulation and melt extrusion. The required equipment ranges from ordinary glass beakers for lab scale up to large machines such as fluid bed coaters, spray dryers or extruders. This allows for upscaling to pilot or production scale. Solvent free melt processing provides a cost-effective, time-saving and eco-friendly method for the food and pharmaceutical industries. This review intends to give a critical overview of the published literature on experiences, formulations and challenges and to show possibilities for future developments in this promising field. Moreover, it should serve as a guide for selecting the best excipients and manufacturing techniques for the development of a product with specific properties using solvent free melt processing.

Preparation of lipid aspirin sustained-release pellets by solvent-free extrusion/spheronization and an investigation of their stability

A novel solvent-free extrusion/spheronization technique was investigated for preparing stable aspirin sustained-release pellets. Lipids as binders and the matrix in this technique were extruded below their melting points, and spheronized in a thermomechanical process. Four types of lipids (adeps solidus, Compritol(®) 888 ATO, Precirol(®) ATO5 and Compritol(®) HD5 ATO) and their admixture in different ratios were used to obtain spherical and extended-release pellets. Pellets containing 80% aspirin, 15% adeps solidus and 5% Compritol(®) 888 ATO had the best spherical geometry and met the dissolution requirements of aspirin extended-release tablets in USP 31. Storage stability studies showed that the content of free salicylic acid increased sharply in the traditional pellets produced by wet extrusion/spheronization, from 1.91 to 7.84%, whereas there was little increase in the lipid pellets (from 0.48 to 1.08%). The dissolution rate from the optimal pellets (F11) stored at 26°C did not change, but became faster at 40°C/RH75% after 5 months. Powder X-ray diffraction, scanning electron microscopy (SEM) and differential scanning calorimetry were used to investigate the physical properties of the pellets during stability testing. The increase in the rate of drug release from aged pellets (40°C/RH75%) may result from the partially melted adeps solidus observed in SEM photographs. This study suggests that it is possible to prepare sustained-release pellets by solvent-free extrusion/spheronization using an appropriate mixture of lipids with high stability. In particular, this novel technique is excellent for hygroscopic drugs.

Development of novel sustained release matrix pellets of betahistine dihydrochloride: effect of lipophilic surfactants and co-surfactants

Sustained release matrix pellets of the freely water soluble drug, betahistine dihydrochloride (BH), were prepared using freeze pelletization technique. Different waxes and lipids (cetyl alcohol, beeswax, glyceryl tripalmitate (GTP) and glyceryl tristearate) were evaluated for the preparation of matrix pellets. A D-optimal design was employed for the optimization and to explore the effect of drug loading (X(1)), concentration of lipophilic surfactant (X(2)), concentration of co-surfactant (X(3)) and wax type (X(4)) on the release extent of the drug from matrix pellets. The entrapment efficiency (Y(1)), pellet diameter (Y(2)), and the percentage drug released at given times were selected as dependent variables. Results revealed a significant impact of all independent variables on drug release from the formulated pellets. The lipophilic surfactant significantly increased both the entrapment efficiency and the in vitro drug release and significantly decreased the pellet size. The optimized BH-loaded pellets were composed of 19.95% drug loading, 9.95% Span(®) 80 (surfactant), 0.25% Capmul(®) (co-surfactant) using glyceryl tripalmitate as a matrix former. The release profiles of the drug from hard gelatin capsule containing optimized pellets equivalent to 32 mg BH was similar to that of target release model for once-daily administration based on similarity factor. It could be concluded that a promising once-daily capsule containing sustained release pellets of BH was successfully designed.

Design and characterization of sustained release ketoprofen entrapped carnauba wax microparticles

CONTEXT

Ketoprofen is a non-steroid anti-inflammatory drug (NSAID) used in the treatment of rheumatic diseases and in mild to moderate pain. Ketoprofen has a short biological half-life and the commercially available conventional release formulations require dosages to be administered at least 2-3 times a day. Due to these characteristics, ketoprofen is a good candidate for the preparation of controlled release formulations.

OBJECTIVES

In this work, a multiparticulate-sustained release dosage form containing ketoprofen in a carnauba wax matrix was developed.

METHODS

Particles were prepared by an emulsion congealing technique. System variables were optimized using fractional factorial and response surface experimental design. Characterization of the particles included size and morphology, flow rate, drug loading and in vitro drug release.

RESULTS

Spherical particles were obtained with high drug load and sustained drug release profile. The optimized particles had an average diameter of approximately 200 µm, 50% (w/w) drug load, good flow properties and prolonged ketoprofen release for more than 24 h.

CONCLUSIONS

Carnauba wax microspheres prepared in this work represent a new multiparticulate-sustained release system for the NSAID ketoprofen, exhibiting good potential for application in further pharmaceutical processes.

Investigating the principles of recrystallization from glyceride melts

Different lipids were melted and resolidified as model systems to gain deeper insight into the principles of recrystallization processes in lipid-based dosage forms. Solid-state characterization was performed on the samples with differential scanning calorimetry and X-ray powder diffraction. Several recrystallization processes could be identified during storage of the lipid layers. Pure triglycerides that generally crystallize to the metastable alpha-form from the melt followed by a recrystallization process to the stable beta-form with time showed a chain-length-dependent behavior during storage. With increasing chain length, the recrystallization to the stable beta-form was decelerated. Partial glycerides exhibited a more complex recrystallization behavior due to the fact that these substances are less homogenous. Mixtures of a long-chain triglyceride and a partial glyceride showed evidence of some interaction between the two components as the partial glyceride hindered the recrystallization of the triglyceride to the stable beta-form. In addition, the extent of this phenomenon depended on the amount of partial glyceride in the mixture. Based on these results, changes in solid dosage forms based on glycerides during processing and storage can be better understood.