Combination of co-crystal and nanocrystal techniques to improve the solubility and dissolution rate of poorly soluble drugs.

PURPOSE: Solubility and dissolution rate are essential for the oral absorption and bioavailability of poorly soluble drugs. The aim of this study was to prepare nano-co-crystals by combination of nanocrystal and co-crystal technologies, and investigate its effect, in situ, on increased kinetic solubility and dissolution rate. METHODS: Co-crystals of itraconazole-fumaric acid, itraconazole-succinic acid, indomethacin-saccharin and indomethacin-nicotinamide were prepared and nano-sized by wet milling. The particle size and solid state of the co-crystals were characterized by optical microscope, LD, PCS, DSC and XRPD before and after milling. RESULTS: 300-450 nm sized nano-co-crystals with a stable physical solid state were successfully prepared. Nano-co-crystals exhibited a lower crystallinity reduction than nanocrystals after wet milling. The particle size effect on the kinetic solubility of co-crystals was analysed for macro-, micro- and nano-co-crystals with in situ kinetic solubility studies. The maximum kinetic solubility of nano-co-crystals increased with excess conditions until a plateau. The highest increase was obtained with itraconazole-succinic acid nano-co-crystals with a kinetic solubility of 263.5 ± 3.9 µg/mL which was 51.5 and 6.6 times higher than the solubility of raw itraconazole and itraconazole-succinic acid co-crystal. CONCLUSIONS: The synergistic effect of nanocrystals and co-crystals with regard to increased kinetic solubility and dissolution rate was proven. The combination of the advantages of nanocrystals and co-crystals is a promising formulation strategy to increase both the solubility and dissolution rate of poorly soluble drugs.

Incorporation of itraconazole nano-co-crystals into multiparticulate oral dosage forms.

Limited research has been performed on the downstream processing of nano-co-crystal suspensions into solid oral dosage forms. The objectives of this study were to evaluate the impact of three downstream processes (wet granulation, spray granulation and bead layering) on the performance of itraconazole-succinic acid (ITZ-SUC) nano-co-crystal suspension. An optimized ITZ-SUC nano-co-crystal suspension mixed with HPMC E5 was utilized for the downstream processing. The suspension was converted in the solid state either by wet or spray granulation (with microcrystalline cellulose or lactose as substrates) or by layering onto microcrystalline cellulose and sugar beads. The multiparticulate solid dosage forms were characterized by optical microscopy, differential scanning calorimeter (DSC), X-ray powder diffraction (XRPD) and in situ dissolution studies. Spray granulation and bead layering resulted in less particle aggregation, a faster dissolution rate, and higher kinetic solubility when compared to wet granulation. ITZ-SUC nano-co-crystals spray granulated with lactose resulted in higher kinetic solubility profiles compared to microcrystalline cellulose granules. The type of bead core had no impact on the dissolution behavior. A slower dissolution and decreased kinetic solubility were observed with increasing drug loading for sprayed granules when microcrystalline cellulose was used as substrate. All dosage forms were stable under accelerated storage conditions (40 °C/75% RH) when blistered. Nano-co-crystals incorporated in granules were less stable than layered beads under non-blistered condition. Nano-co-crystals layered sugar beads are an interesting alternative to amorphous solid dispersion; a comparable kinetic solubility but a faster drug release were achieved. This study identified bead layering as a superior downstream process approach for incorporating ITZ-SUC nano-co-crystals into an oral solid dosage form without compromising drug dissolution.

Kinetic solubility improvement and influence of polymers on controlled supersaturation of itraconazole-succinic acid nano-co-crystals.

Nano-co-crystals enhance the solubility and dissolution rate of poorly soluble drugs. The objective of this study was to obtain a better understanding of the dissolution process of nano-co-crystals and of the precipitation inhibition by various polymers. Itraconazole-succinic acid (ITZ-SUC) nano-co-crystal was chosen as model drug formulation to investigate the supersaturation and precipitation inhibition capabilities of various polymers (HPMC E5, HPMC E50, HPMCAS, HPC-SSL, PVPK30 and PVPVA64). The kinetic concentration-time profiles of nano-co-crystal were measured under non-sink conditions with in situ UV-VIS spectroscopy. HPMC E5 performed best by achieving the greatest extended supersaturation/precipitation inhibition. The precipitation inhibition capacity of HPMC E5 was proportional to its concentration. The maximum achievable supersaturation was proportional to the dissolution rate which can be modulated by the rate of supersaturation generation (i.e., addition rate or dose). Supersaturation could be prolonged significantly resulting in 2-5-fold increased area under the dissolution curves compared to nano-co-crystals alone. This effect was limited by a critical excess of undissolved particles with high specific surface area which acted as crystallization seeds resulting in faster precipitation. The study highlighted that a faster dissolution rate and the use of precipitation inhibitors were two key factors determining the extent and time of supersaturation of nano-co-crystals.

Sub-50 nm ultra-small organic drug nanosuspension prepared by cavi-precipitation and its brain targeting potential.

The purpose of this study was to show whether it is possible to prepare sub 100 nm or preferably sub-50 nm drug nanosuspension (NS) of suitable quality for intravenous administration. Furthermore, we have studied how the brain targeting potential of such small size organic NS differs from relatively bigger size NS. Two combination technologies (cavi-precipitation, H96) and a standard high-pressure homogenization (HPH) technology were used to prepare drug NS of different sizes. The cavi-precipitation process generated the smallest AmB NS, i.e., 27 nm compared to 79 nm by H96 technology and 252 nm by standard HPH technology. Dialysis of the nanosuspension in the original dispersion media was found to be the most efficient solvent removal method without negatively affecting particle size. The removal of organic solvent was found to drastically improve the stability of the formulations. The protein adsorption pattern shows that the small size NS particles obtained by the cavi-precipitation process have the potential to circulate longer in the bloodstream and have the potential to be taken up by the blood-brain barrier. The cavi-precipitation process generated ultrafine NS particles, which fulfilled the quality requirements for intravenous administration and offer a potential solution for brain targeting.

Preparation and characterization of dexamethasone lipid nanoparticles by membrane emulsification technique, use of self-emulsifying lipids as a carrier and stabilizer.

Self-emulsifying lipids (SEL) were used as a stabilizer for the preparation of dexamethasone lipid nanoparticles by membrane emulsification employing Shirasu porous glass. The effect of process and formulation parameters on the size and polydispersity and dexamethasone solubility in lipids and its release from lipid nanoparticles were investigated. Lipid phase pressure (40-80 kPa), membrane pore-size (0.1 - 0.4 µm) and agitation speed (300 - 900 rpm) did not affect the size and polydispersity of SEL. However, the size was increased with increasing lipid content and fatty acid chain of the lipid. Sizes of < 250 nm were achieved from TEGO® care:Gelucire® blend and it increased to 487 nm by adding 20% w/w of hard fat. The highest solubility of dexamethasone was found in TEGO® care 450 (29 mg/g). Release from the lipid nano-dispersions was extended with no burst effect and the absolute release was increased with increasing lipid content.

Nanocrystals for Improved Drug Delivery of Dexamethasone in Skin Investigated by EPR Spectroscopy.

Nanocrystals represent an improvement over the traditional nanocarriers for dermal application, providing the advantages of 100% drug loading, a large surface area, increased adhesion, and the potential for hair follicle targeting. To investigate their advantage for drug delivery, compared to a base cream formulation, dexamethasone (Dx), a synthetic glucocorticoid frequently used for the treatment of inflammatory skin diseases, was covalently linked with the paramagnetic probe 3-(carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) to DxPCA. To investigate the penetration efficiency between these two vehicles, electron paramagnetic resonance (EPR) spectroscopy was used, which allows the quantification of a spin-labeled drug in different skin layers and the monitoring of the drug release. The penetration behavior in excised healthy and barrier-disrupted porcine skin was monitored by EPR, and subsequently analyzed using a numerical diffusion model. As a result, diffusion constants and free energy values in the different layers of the skin were identified for both formulations. Dx-nanocrystals showed a significantly increased drug amount that penetrated into viable epidermis and dermis of intact (factor 3) and barrier-disrupted skin (factor 2.1) compared to the base cream formulation. Furthermore, the observed fast delivery of the spin-labeled drug into the skin (80% DxPCA within 30 min) and a successive release from the aggregate unit into the viable tissue makes these nanocrystals very attractive for clinical applications.

Preparation of amorphous indomethacin nanoparticles by aqueous wet bead milling and in situ measurement of their increased saturation solubility.

The aim of this study was to prepare amorphous indomethacin nanoparticles in aqueous media and to determine in situ their increased saturation solubility and dissolution rate. Drug nanosuspensions with a Z-average of ∼300 nm were prepared by wet media milling and afterwards freeze-dried. The drug solid state was analyzed by DSC, XRD and FTIR before and after the milling process. Milling of amorphous indomethacin with polyvinylpyrrolidone (PVP) as stabilizer resulted in an amorphous nanosuspension which could not be redispersed in the nanosize range after freeze-drying. The combination of PVP and poloxamer 407 resulted in crystalline nanoparticles: poloxamer 407, a polymer with high molecular weight, competed with PVP for surface coverage, and hindered the interaction between PVP and indomethacin. This indicated the importance of sufficient drug-PVP interactions on the drug particle surface for amorphous state stabilization. Redispersable amorphous indomethacin nanoparticles were obtained by combining the anti-recrystallization effect of PVP with the particle size stabilization provided by sodium dodecyl sulfate. Solubility studies were performed in situ. The solubility of crystalline micronized indomethacin of 6.7 ±â€¯1.3 µg/mL was increased up to 17.3 ±â€¯2.8 µg/mL by its amorphization, with a factor of increase of 2.6. Indomethacin amorphization increased its dissolution rate by a factor of 30. Indomethacin nanocrystals resulted in an increased solubility of 2.6 times, with a solubility of 17.2 ±â€¯0.4 µg/mL. The highest increase was obtained with amorphous indomethacin nanoparticles with a solubility of 35 ±â€¯1.6 µg/mL and 5.2 times higher than the solubility of the original indomethacin. Amorphous indomethacin nanoparticles resulted in the highest dissolution rate, which increased from 0.003 µg/(mL s) to 2.328 µg/(mL s). The synergistic effect obtained by the combination of nanosize and amorphous solid state was demonstrated.

Evaluation of a biphasic in vitro dissolution test for estimating the bioavailability of carbamazepine polymorphic forms.

The purpose of this study was to discriminate three crystal forms of carbamazepine (a BCS II drug) by in vitro dissolution testing and to correlate in vitro data with published in vivo data. A biphasic dissolution system (phosphate buffer pH6.8 and octanol) was used to evaluate the dissolution of the three polymorphic forms and to compare it with conventional single phase dissolution tests performed under sink and non-sink conditions. Similar dissolution profiles of three polymorphic forms were observed in the conventional dissolution test under sink conditions. Although a difference in dissolution was seen in the single phase dissolution test under non-sink conditions as well as in the aqueous phase of the biphasic test, little relevance for in vivo data was observed. In contrast, the biphasic dissolution system could discriminate between the different polymorphic forms in the octanol phase with a ranking of form III>form I>dihydrate form. This was in agreement with the in vivo performance. The dissolved drug available for oral absorption, which was dominated by dissolution and solution-mediated phase transformation, could be reflected in the biphasic dissolution test. Moreover, a good correlation was established between in vitro dissolution in the octanol phase of the biphasic test and in vivo pharmacokinetic data (R2=0.99). The biphasic dissolution method is a valuable tool to discriminate between different crystal forms in the formulations of poorly soluble drugs.

Development of a discriminative biphasic in vitro dissolution test and correlation with in vivo pharmacokinetic studies for differently formulated racecadotril granules.

The purpose of this study was to discriminate the release behavior from three differently formulated racecadotril (BCS II) granules and to establish an in vitro-in vivo correlation. Three granule formulations of the lipophilic drug were prepared with equivalent composition but prepared with different manufacturing processes (dry granulation, wet granulation with or without binder). In vitro release of the three granules was investigated using a biphasic dissolution system (phosphate buffer pH6.8 and octanol) and compared to the conventional single phase USP II dissolution test performed under sink and non-sink conditions. In vivo studies with each granule formulation were performed in rats. Interestingly, the granule formulations exhibited pronouncedly different behavior in the different dissolution systems depending on different wetting and dissolution conditions. Single phase USP II dissolution tests lacked discrimination. In contrast, remarkable discrimination between the granule formulations was observed in the octanol phase of biphasic dissolution system with a rank order of release from granules prepared by wet granulation with binder>wet granulation without binder>dry granulation. This release order correlated well with the wettability of these granules. An excellent correlation was also established between in vitro release in the octanol phase of the biphasic test and in vivo data (R2=0.999). Compared to conventional dissolution methods, the biphasic method provides great potential to discriminate between only minor formulation and process changes within the same dosage form for poorly soluble drugs.

In situ determination of the saturation solubility of nanocrystals of poorly soluble drugs for dermal application.

The aim of this study was to determine, in situ, the saturation solubility and dissolution rate of nanocrystals of three poorly water-soluble drugs for dermal application. The nanocrystals were prepared by wet bead milling. Their size could be controlled by various process parameters. The saturation solubility was measured in water or in the presence of surfactant at 32°C with a Sirius® inForm based on in situ UV-vis spectroscopy. The saturation solubility of nanocrystals with sizes of ∼300nm increased for each drug in comparison to non-milled drug powders, with factors of increase in the range 1.3-2.8. The tacrolimus solubility was further analyzed with excess nanocrystal amounts four and ten times higher than the drug powder solubility. The corresponding solubility increases were 2.8 and 6.6 and thus dependent on the amount of excess nanocrystals. The higher increase was due to the presence of a larger fraction of small size particles, and only crystals far below 1µm showed supersaturation. The solubility increase for nanocrystals determined in situ was remarkably lower than the one previously reported with the use of non in situ methods. Nanomilling increased the drug dissolution rates: the highest increase was obtained with ibuprofen (rate increase ∼30).

Influence of Drug Brittleness, Nanomilling Time, and Freeze-Drying on the Crystallinity of Poorly Water-Soluble Drugs and Its Implications for Solubility Enhancement.

The aim of this study was to assess whether wet bead milling of dexamethasone and tacrolimus suspensions leads to a lower degree of crystallinity of nanocrystals, and if the degree of crystallinity affects the drug solubility, in addition to particle size. Powder X-ray diffraction (XRD) was used to determine the degree of crystallinity of the particles, which decreased during milling until reaching a plateau: the particles had ∼79% degree of crystallinity after 5 h milling. Different milling times were required for the two drugs in order to reach their plateaux, 2 h for dexamethasone and 3 h for tacrolimus. These results could be explained with the brittleness of the drugs. Dexamethasone was more brittle than tacrolimus, with an apparent elastic modulus of 16 GPa compared to ∼12 GPa of tacrolimus. Freeze-drying the nanosuspensions resulted in a reduction in the degree of crystallinity to ∼35% for dexamethasone and to ∼45% for tacrolimus in comparison to non-freeze-dried particles. Solubility studies were performed with a Sirius® inForm based on in situ UV/VIS spectroscopy. The reduced degree of crystallinity of nanocrystals after milling was responsible, in addition to the nanoparticle size, for the solubility increase. Indeed, while the smallest particle size (394 nm for dexamethasone and 240 nm for tacrolimus) did not always result in the highest increase in solubility (factor of 1.04 for dexamethasone and 1.3 with tacrolimus), the smallest degree of crystallinity was always characteristic of the maximum solubility obtained (factor of 1.15 for dexamethasone and 1.7 for tacrolimus).

Effect of drug solubility and lipid carrier on drug release from lipid nanoparticles for dermal delivery.

Lipid nanoparticles have gained increased interest in the field of dermal products because of various advantages such as improved drug absorption and controlled drug release. The main objective was to investigate the influence of drug solubility and type of lipid carrier on the in vitro drug release. Drugs of different solubilities in the release medium PBS pH 7.4 (dexamethasone: 0.1mg/ml and diclofenac sodium: 5.0mg/ml) and three different lipids (in which the drugs had the highest solubility), Gelucire® 50/13 (solid lipid, mp: 50°C), Witepsol® S55 (solid lipid, mp: 33.5-35.5°C) and Capryol® 90 (liquid lipid) were chosen. The lipid nanoparticles were prepared by high shear homogenization. All nanosuspensions were in the nanometer range (up to 400nm) and the drug encapsulation efficiency was between 84% and 95%. The drug release was prolonged over 48h without an initial burst release and was dependent on the lipid carrier. Formulations containing a higher amount of solid Gelucire® 50/13 released the drugs slower due to the high affinity of the drugs to this lipid product. Inclusion of the liquid lipid Capryol® 90 resulted in a less organized lipidic structures (softer particles) and therefore a faster drug release. Despite its higher water solubility, diclofenac was released slower than dexamethasone because of its higher solubility in the lipid carriers. DSC studies indicated a partial miscibility between the solid lipids and a good miscibility between the solid and liquid lipids. Primary studies using total internal reflection fluorescence (TIRF) microscopy indicated that it is possible to detect individual fluorescently labeled dexamethasone (DXM-F) molecules dissolved in the liquid lipid Capryol® 90. These studies will allow for the precise determination of the drug distribution within the lipid carrier, and the changes upon drug release. In conclusion, lipid carrier type and drug solubility in the lipid have a large influence on the in vitro drug release from lipid nanoparticles.

Comparison of different in vitro release methods used to investigate nanocarriers intended for dermal application.

In vitro drug release measurement is one of the most important methods used to assess the quality of a nanocarrier and estimate it́s in vivo performance. Different in vitro drug release methods have been used to investigate the drug release from nanocarriers, however, little information is available with regard to a comparison of these methods (e.g. discriminative power, reproducibility). Thus, drug release from four nanocarriers (nanocrystals, lipid nanoparticles, Eudragit® RS and ethyl cellulose nanoparticles) was investigated under sink and non-sink conditions with three drug release methods: an in situ method using Sirius® inForm and two in vitro methods using dialysis bags and Franz diffusion cells. Dexamethasone was used as the model drug. The in situ measurement was a simple and fast method but not adequately discriminating because of a too rapid drug dissolution/release. Franz diffusion cells and dialysis bags were in most cases discriminative for the different nanocarriers with the drug dissolution/release being in the order of nanocrystals>Eudragit® RS nanoparticles>lipid nanoparticles>ethyl cellulose nanoparticles. Drug release experiments with Franz diffusion cells had the highest reproducibility. The Franz diffusion cells could also be easily used with semisolid dosage forms.

Surface characterization and protein interaction of a series of model poly[acrylonitrile-co-(N-vinyl pyrrolidone)] nanocarriers for drug targeting.

The surface properties of intravenously injected nanoparticles determine the acquired blood protein adsorption pattern and subsequently the organ distribution and cellular recognition. A series of poly[acrylonitrile-co-(N-vinyl pyrrolidone)] (PANcoNVP) model nanoparticles (133-181 nm) was synthesized, in which the surface properties were altered by changing the molar content of NVP (0-33.8 mol%) as the more hydrophilic repeating unit. The extent of achieved surface property variation was comprehensively characterized. The residual sodium dodecyl sulfate (SDS) content from the synthesis was in the range 0.3-1.6 µgml(-1), potentially contributing to the surface properties. Surface hydrophobicity was determined by Rose Bengal dye adsorption, hydrophobic interaction chromatography (HIC) and aqueous two-phase partitioning (TPP). Particle charge was quantified by zeta potential (ZP) measurements including ZP-pH profiles. The interaction with proteins was analyzed by ZP measurements in serum and by adsorption studies with single proteins. Compared to hydrophobic polystyrene model nanoparticles, all PANcoNVP particles were very hydrophilic. Differences in surface hydrophobicity could be detected, which did not linearly correlate with the systematically altered bulk composition of the PANcoNVP nanoparticles. This proves the high importance of a thorough surface characterization applying a full spectrum of methods, complementing predictions solely based on bulk polymer composition.