Pharmacokinetic behaviors and oral bioavailability of oridonin in rat plasma

AIM: To study the intravenous and oral pharmacokinetic behavior of oridonin and its extent of absolute oral bioavailability in rats. METHODS: Oridonin was administered to rats via iv (5, 10 and 15 mg/kg), po (20, 40 and 80 mg/kg) or ip administration (10 mg/kg). The concentrations of oridonin in rat plasma were determined by a high performance liquid chromatography with electrospray ionization mass spectrometric detection (HPLC/ESI-MS) method and the pharmacokinetic parameters were determined by non-compartmental analysis. RESULTS: The plasma concentration of oridonin after intravenous administration decreased polyexponentially, and the pharmacokinetic parameters of oridonin were dose-independent within the examined range. Oridonin was absorbed rapidly after oral gavage with a t(max) of less than 15 min; the extent of absolute bioavailability of oridonin following oral administration was 4.32%, 4.58% and 10.8%. The extent of absolute bioavailability of oridonin following intraperitoneal administration was 12.6%. CONCLUSION: First order rate pharmacokinetics were observed for oridonin within the range of iv doses, while the extent of absolute oral bioavailability was rather low and dose- dependent. The low and dose-dependent extent of oral bioavailability may be due to the saturation of first-pass effects.     

Use of compressed gas precipitation to enhance the dissolution behavior of a poorly water-soluble drug: generation of drug microparticles and drug-polymer solid dispersions

The classical anticonvulsant drug phenytoin (5,5-diphenyl hydantoin, C(15)H(12)N(2)O(2)) has been used as a model compound to investigate the possibility of enhancing the dissolution rate of poorly water-soluble drugs using dense gas antisolvent techniques. In a first step, microcrystals of neat phenytoin have been generated using the gas antisolvent (GAS) and precipitation with compressed antisolvent (PCA) processes, thereby assessing process performances and elucidating similarities and differences between the two techniques. In a second step, the PCA process has been used to generate solid dispersions of phenytoin in the hydrophilic polymer poly(vinyl-pyrrolidone)-K30 (PVP). In vitro dissolution results reveal a substantially better performance of the PCA-processed co-formulations compared to unprocessed phenytoin and to GAS- and PCA-precipitates of neat drug crystals. A comparison of the product quality of phenytoin-PVP co-formulations with solid dispersions obtained by spray drying convincingly underlines the potential of dense gas antisolvent techniques for the production of pharmaceutical formulations with enhanced oral bioavailability.     

Evaluation of molecular pharmaceutical and in‐vivo properties of spray‐dried isolated andrographolide—PVP

Objectives Andrographolide, a natural lipophilic molecule, has a wide range of pharmacological actions. However, due to low aqueous solubility, it has low oral bioavailability. The purpose of the study was to increase the solubility and dissolution rate of isolated andrographolide by formulating its solid dispersion. Method Solid dispersions were obtained by a spray‐drying technique using different ratios of drug to polyvinylpyrrolidine (PVP K‐30). Solid dispersions in compression with isolated drug and corresponding physical mixtures were characterized for various molecular pharmaceutical properties and subjected to stability study for up to 3 months. Key findings A five‐fold increase in saturation solubility of andrographolide with higher values of Q_5min (cumulative percentage release in 5 min) and lower values of t_75% (time required for 75% w/w drug release) for solid dispersion was observed in different dissolution mediums. This was attributed to the formation of amorphous nature and intermolecular hydrogen bonding between drug and PVP K‐30. The stability study showed there to be no significant change in molecular pharmaceutical properties and dissolution profile over the period of 3 months. Moreover, the in‐vivo study in Wistar albino rats also justified improvement in the therapeutic efficacy of andrographolide after solid dispersion. Conclusions This study demonstrates the utility of solid dispersion to improve primary and secondary pharmaceutical properties of andrographolide using PVP K‐30 as a carrier.     

Dissolution behaviour of nalidixic acid solid dispersions using water soluble dispersion carriers

The oral bioavailability of nalidixic acid (NA) is low due to its poor solubility and slow dissolution. Solid dispersions of NA containing varying concentrations of polyvinylpyrrolidone (PVP), beta-cyclodextrin (BCD) and sodium starch glycolate (SSG) were prepared by solvent evaporation technique in an attempt to improve dissolution rate of NA. Physical characterization of NA, physical mixtures (PM) and solid dispersions were investigated by a variety of analytical methods including scanning electron microscopy (SEM), infrared (IR) spectroscopy and powder X-ray diffraction (XRD). SEM was useful in the verification of possible nalidixic acid inclusion in the dispersion system by studying its surface and shape characteristics of different samples. IR analysis demonstrated no strong interaction between the drug and the carrier exists in the solid dispersions. The degree of crystallinity of nalidixic acid decreased and also differed with the dispersion systems of different carriers. Disolution studies indicated that the dissolution rate and percent dissolution efficiency (DE) were significantly increased in the solid dispersions compared with drug alone. The relative potency of the carriers to enhance the dissolution rate of nalidixic acid was in the order: BCD > PVP > SSG. The dissolution rate of the drug in the solid dispersions was faster when the ration of the drug to carrier was smaller. F-test suggests that first order model may be used for explaining the kinetics of drug release from all the solid dispersion systems.     

Studies on Flash Evaporation for Preparation of Porous Solid Dispersions Using Piroxicam as a Model Drug

An amalgamation of solid dispersion and capillarity has been attempted in present study for enhancement of dissolution rate of poorly soluble drugs. Flash evaporation technique was utilized for enhancement of the dissolution rate of piroxicam. One of the major problems with this drug is its very low solubility in biological fluids, which results in poor bioavailability after oral administration. An attempt was made to enhance the dissolution rate of piroxicam by converting it into porous solid dispersion by flash evaporation method using polyvinylpyrrolidone (PVP) 40,000 as a water-soluble carrier. The resulting solid dispersions were characterized by DSC, FTIR, and X-ray diffraction. In vitro dissolution study revealed significant improvement of dissolution profile of piroxicam. The release of drug from porous solid dispersions containing PVP was superior to those of marketed product, conventional nonporous solid dispersion prepared by solvent evaporation method and drug alone. The steep increase in dissolution rate of porous form is attributable to combined effect of solid dispersion and capillarity.     

Poly(2-Ethyl-2-Oxazoline) as an Alternative to Poly(Vinylpyrrolidone) in Solid Dispersions for Solubility and Dissolution Rate Enhancement of Drugs

Poly(2-ethyl-2-oxazoline) (PEOX), a biocompatible polymer considered as pseudopolypeptide, was introduced as a potential alternative to the commonly used polymer, poly(vinylpyrrolidone) (PVP) for the preparation of solid dispersion with a poorly soluble drug. Glipizide (GPZ), a Biopharmaceutical Classification System class II model drug, was selected for solubility and dissolution rate study. GPZ-polymer solid dispersions and physical mixtures were characterized and investigated by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy, and FTIR spectroscopy. The impact of polymers on crystal nucleation kinetics was studied, and PEOX exhibited strong inhibitory effect compared with PVP. Solubility and dissolution behavior of the prepared solid dispersions and their physical blends were in vitro examined and evaluated. A significant enhancement in GPZ solubility was obtained with PEOX compared with the pure drug and solid dispersion with PVP. A big improvement in the intrinsic dissolution rate (45 times) and dissolved amount of GPZ (58 times) was achieved with PEOX in fasted state simulated intestinal fluid, against comparable enhancement observed with PEOX and PVP in phosphate buffer at pH 6.8. Lower molecular weight of PEOX-5K (5000 g/mol) was found to be superior to higher molecular weight PEOX-50K (50,000 g/mol) in the improvement of dissolution behavior. The findings of this study with GPZ as a model drug introduce lower molecular weight PEOX as a promising polymeric carrier toward better oral bioavailability of poorly soluble drugs.     

丹参酮ⅡA固体分散体制备工艺研究

目的研究减压干燥法制备丹参酮ⅡA-聚乙烯吡咯烷酮K30（PVPK30）固体分散体的最佳工艺。方法采用减压干燥法制备,正交试验优化,以丹参酮ⅡA为检测指标,用高效液相色谱法进行体外溶出度的测定。结果制备丹参酮ⅡA-PVPK30固体分散体的最佳工艺为用5倍量的载体、4倍量的粮食酒精溶解,减压干燥1h。丹参酮ⅡA的体外溶出百分比为60.1%。结论用减压干燥法成功制备了丹参酮ⅡA-PVPK30固体分散体,该固体分散体对丹参酮ⅡA有很好的增溶效果。     

Formulation and delivery of improved amorphous fenofibrate solid dispersions prepared by thin film freezing

The objective of this study was to prepare amorphous fenofibrate (FB) solid dispersions using thin film freezing (TFF) and to incorporate the solid dispersions into pharmaceutically acceptable dosage forms. FB solid dispersions prepared with optimized drug/polymer ratios were characterized by modulated differential scanning calorimetry (MDSC), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area measurements, Fourier-transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), and supersaturation dissolution testing. Furthermore, a dry granulation technique was used to encapsulate the TFF compositions for in vitro dissolution and in vivo animal pharmacokinetic studies. The results showed that the TFF process produced amorphous, porous, microstructured, and stable solid dispersions with high surface areas. Development of solid oral dosage forms revealed that the performance of the FB containing solid dispersions was not affected by the formulation process, which was confirmed by DSC and XRD. Moreover, an in vivo pharmacokinetic study in rats revealed a significant increase in FB absorption compared to bulk FB. We confirmed that amorphous solid dispersions with large surface areas produced by the TFF process displayed superior dissolution rates and corresponding enhanced bioavailability of the poorly water-soluble drug, FB.     

Development of raloxifene-solid dispersion with improved oral bioavailability via spray-drying technique

The purpose of this study was to develop a raloxifene-loaded solid dispersion with enhanced dissolution rate and bioavailability via spray-drying technique. Solid dispersions of raloxifene (RXF) were prepared with PVP K30 at weight ratios of 1:4, 1:6 and 1:8 using a spray-drying method, and characterized by differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and solubility and dissolution tests. The bioavailability of the solid dispersion in rats was also evaluated compared to those of RXF powder and commercial product. Results showed that the RXF-loaded solid dispersion was in amorphous form with increased solubility and dissolution rate. The absorption of RXF from solid dispersion resulted in approximately 2.6-fold enhanced bioavailability compared to pure drug. Moreover, RXF-loaded solid dispersion gave similar AUC, C_max and T_max values to the commercial product, suggesting that it was bioequivalent to the commercial product in rats. These findings suggest that an amorphous solid dispersion of RXF could be a viable option for enhancing the oral bioavailability of RXF.     

盐酸溴己新缓释片的制备及体外释放度研究

目的制备盐酸溴已新（Bromhexine hydrochloride．BH）缓释片。方法以聚乙烯毗咯烷酮（PVP）为载体。将盐酸溴己新制成固体分散体．再以羟丙甲基纤维素（HPMC）为骨架材料,采用湿法制粒压片制备盐酸溴己新缓释片,并进行体外释放度试验。结果所制备的缓释片12h内呈现良好的缓释特性,符合Higuchi方程。结论盐酸澳己新缓释片体外释药缓慢、平稳,符合设计要求。     

Preparation of a solid dispersion of felodipine using a solvent wetting method.

A straightforward solvent wetting method was used to prepare felodipine solid dispersions in the presence of various carriers. Dichloromethane is not needed when HPMC solid dispersions were produced using the solvent wetting method. The amount of ethanol used to prepare solid dispersions did not have a significant effect on the dissolution rate of felodipine. The results of X-ray diffraction and thermal analysis indicated that the drug was in the amorphous state when PVP, HPMC, and poloxamer were used as carriers. The dissolution rates of felodipine in PVP, HPMC, or poloxamer solid dispersions were much faster than those for the corresponding physical mixtures. However, dissolution profiles were found to depend on the carrier used; the dissolution rate of felodipine increased slowly for solid dispersions prepared using HPMC, whereas rapid initial dissolution rates were observed for solid dispersions prepared using PVP or poloxamer. Increases in dissolution rates were partly dependent on the ratios of felodipine to carrier. No significant changes in crystal form were observed by X-ray diffraction or thermal analysis, and no significant changes in dissolution rate were observed when sorbitol and mannitol were used as carriers.     

Physicochemical characterization and dissolution study of solid dispersions of Lovastatin with polyethylene glycol 4000 and polyvinylpyrrolidone K30

Solid dispersions in water-soluble carriers have attracted considerable interest as a means of improving the dissolution rate, and hence possibly bioavailability, of a range of hydrophobic drugs. The aim of the present study was to improve the solubility and dissolution rate of a poorly water-soluble drug, Lovastatin, by a solid dispersion technique. Solid dispersions were prepared by using polyethylene glycol 4000 (PEG 4000) and polyvinylpyrrolidone K30 (PVP K30) in different drug-to-carrier ratios. Dispersions with PEG 4000 were prepared by fusion-cooling and solvent evaporation, whereas dispersions containing PVP K30 were prepared by solvent evaporation technique. These new formulations were characterized in the liquid state by phase solubility studies and in the solid state by differential scanning calorimetry, X-ray powder diffraction, and FT-IR spectroscopy. The aqueous solubility of Lovastatin was favored by the presence of both polymers. The negative values of the Gibbs free energy and enthalpy of transfer explained the spontaneous transfer from pure water to the aqueous polymer environment. Solid-state characterization indicated Lovastatin was present as amorphous material and entrapped in polymer matrix. In contrast to the very slow dissolution rate of pure Lovastatin, the dispersion of the drug in the polymers considerably enhanced the dissolution rate. This can be attributed to improved wettability and dispersibility, as well as decrease of the crystalline and increase of the amorphous fraction of the drug. Solid dispersion prepared with PVP showed the highest improvement in wettability and dissolution rate of Lovastatin. Even physical mixture of Lovastatin prepared with both polymers also showed better dissolution profile than that of pure Lovastatin. Tablets containing solid dispersion prepared with PEG and PVP showed significant improvement in the release profile Lovastatin compared with tablets containing Lovastatin without PEG or PVP.     

Physicochemical Characterization and Dissolution Study of Solid Dispersions of Lovastatin with Polyethylene Glycol 4000 and Polyvinylpyrrolidone K30

Solid dispersions in water-soluble carriers have attracted considerable interest as a means of improving the dissolution rate, and hence possibly bioavailability, of a range of hydrophobic drugs. The aim of the present study was to improve the solubility and dissolution rate of a poorly water-soluble drug, Lovastatin, by a solid dispersion technique. Solid dispersions were prepared by using polyethylene glycol 4000 (PEG 4000) and polyvinylpyrrolidone K30 (PVP K30) in different drug-to‐carrier ratios. Dispersions with PEG 4000 were prepared by fusion-cooling and solvent evaporation, whereas dispersions containing PVP K30 were prepared by solvent evaporation technique. These new formulations were characterized in the liquid state by phase solubility studies and in the solid state by differential scanning calorimetry, X-ray powder diffraction, and FT-IR spectroscopy. The aqueous solubility of Lovastatin was favored by the presence of both polymers. The negative values of the Gibbs free energy and enthalpy of transfer explained the spontaneous transfer from pure water to the aqueous polymer environment. Solid-state characterization indicated Lovastatin was present as amorphous material and entrapped in polymer matrix. In contrast to the very slow dissolution rate of pure Lovastatin, the dispersion of the drug in the polymers considerably enhanced the dissolution rate. This can be attributed to improved wettability and dispersibility, as well as decrease of the crystalline and increase of the amorphous fraction of the drug. Solid dispersion prepared with PVP showed the highest improvement in wettability and dissolution rate of Lovastatin. Even physical mixture of Lovastatin prepared with both polymers also showed better dissolution profile than that of pure Lovastatin. Tablets containing solid dispersion prepared with PEG and PVP showed significant improvement in the release profile of Lovastatin compared with tablets containing Lovastatin without PEG or PVP.     

The characterization and dissolution performances of spray dried solid dispersion of ketoprofen in hydrophilic carriers

Solid dispersion is one of the most promising strategies to improve oral bioavailability of poorly soluble API. However, there are inconsistent dissolution performances of solid dispersion reported which entails further investigation. In this study, solid dispersions of ketoprofen in three hydrophilic carriers, i.e. PVP K30, PVPVA 6:4 and PVA were prepared and characterized. Physical characterization of the physical mixture of ketoprofen and carriers shows certain extent of amorphization of the API. This result is coinciding to evaluation of drug–polymer interaction using ATR-FTIR whereby higher amorphization was seen in samples with higher drug–polymer interaction. XRPD scanning confirms that fully amorphous solid dispersion was obtained for SD KTP PVP K30 and PVPVA system whereas partially crystalline system was obtained for SD KTP PVA. Interestingly, dissolution profiles of the solid dispersion had shown that degree of amorphization of KTP was not directly proportional to the dissolution rate enhancement of the solid dispersion system. Thus, it is concluded that complete amorphization does not guarantee dissolution enhancement of an amorphous solid dispersion system.     

Solid dispersion of carbamazepine in PVP K30 by conventional solvent evaporation and supercritical methods

This study compares the physicochemical properties of carbamazepine (CBZ) solid dispersions prepared by either a conventional solvent evaporation versus a supercritical fluid process. Solid dispersions of carbamazepine in polyvinylpyrrolidone (PVP) K30 with either Gelucire 44/14 or Vitamin E TPGS, NF (d-alpha-tocopheryl polyethylene glycol 1000 succinate) were prepared and characterized by intrinsic dissolution, differential scanning calorimetry, powder X-ray diffraction and Fourier transform infrared spectroscopy. CBZ/PVP K30 and CBZ/PVP K30/TPGS solid dispersions showed increased dissolution rate. The best intrinsic dissolution rate (IDR) was obtained for supercritically processed CBZ/PVP K30 that was four-fold higher than pure CBZ. Thermograms of various solid dispersions did not show the melting peak of CBZ, indicating that CBZ was in amorphous form inside the carrier system. This was further confirmed by X-ray diffraction studies. Infrared spectroscopic studies showed interaction between CBZ and PVP K30 in solid dispersions. The amorphous state of CBZ coupled with presence of interaction between drug and PVP K30 suggests fewer, if any, stability problems. Because the supercritical-based process produced solid dispersions with IDR better than conventional solid dispersions augmented with amphiphilic carriers, stability issues associated with lipid carriers do not apply, which, in turn, implies easier scale up under current Good Manufacturing Practice for this technique.     

Anomalous properties of spray dried solid dispersions

The use of solid dispersions for oral dosage forms can increase the dissolution rate of poorly soluble drugs. Spray drying is one process that can be used to prepare solid dispersions. Spray dried solid dispersions of griseofulvin, poly[N-(2-hydroxypropyl)methacrylate] (PHPMA) and polyvinylpyrrolidone (PVP) were prepared from acetone and water. When methanol was substituted for water, the morphology, stability and dissolution properties of the solid dispersion changed dramatically. The glass transition temperature for the ternary solid dispersion (GF, PHPMA, and PVP) shifted from 83°C (acetone/water) to 103°C for the acetone/methanol system. These differences in the dispersions are thought to derive from conformational variations of the polymers in solution prior to spray drying. Both PHPMA and PVP formed globules in solution of a size range between 16 and 33 nm. The effect of drug and polymer concentration in solution (before spray drying) on the properties of the solid dispersion was studied. It was found that solid dispersions that were prepared using lower concentrations of drug and polymers in solutions resulted in the formation of particles that display a lower relaxation rate. This result supports the hypothesis that the polymer conformation may significantly change the properties of the solid dispersion. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4724–4737, 2009     

Development and evaluation of nitrendipine loaded solid lipid nanoparticles: influence of wax and glyceride lipids on plasma pharmacokinetics

Nitrendipine is an antihypertensive drug with poor oral bioavailability ranging from 10 to 20% due to the first pass metabolism. For improving the oral bioavailability of nitrendipine, nitrendipine loaded solid lipid nanoparticles have been developed using triglyceride (tripalmitin), monoglyceride (glyceryl monostearate) and wax (cetyl palmitate). Poloxamer 188 was used as surfactant. Hot homogenization of melted lipids and aqueous phase followed by ultrasonication at temperature above the melting point of lipid was used to prepare SLN dispersions. SLN were characterized for particle size, zeta potential, entrapment efficiency and crystallinity of lipid and drug. In vitro release studies were performed in phosphate buffer of pH 6.8 using Franz diffusion cell. Pharmacokinetics of nitrendipine loaded solid lipid nanoparticles after intraduodenal administration to conscious male Wistar rats was studied. Bioavailability of nitrendipine was increased three- to four-fold after intraduodenal administration compared to that of nitrendipine suspension. The obtained results are indicative of solid lipid nanoparticles as carriers for improving the bioavailability of lipophilic drugs such as nitrendipine by minimizing first pass metabolism.     

Processing of carbamazepine-PEG 4000 solid dispersions with supercritical carbon dioxide: preparation, characterisation, and in vitro dissolution

The purpose of this study was to apply the attractive technique of the supercritical fluid to the preparation of solvent-free solid dispersions. In particular, the gas antisolvent crystallisation technique (GAS), using supercritical carbon dioxide as processing medium, has been considered to prepare an enhanced release dosage form for of the poorly soluble carbamazepine, employing PEG 4000 as a hydrophilic carrier. The physical characterisation of the systems using laser granulometer, powder X-ray diffraction, thermal analyses, and scanning electron microscopy was carried out in order to understand the influence of this technological process on the physical status of the drug. The results of the physical characterisation attested a substantial correspondence of the solid state of the drug before and after treatment with GAS technique, whereas a pronounced change in size and morphology of the drug crystals was noticed. The dramatic reduction of the dimensions and the better crystal shape, together with the presence of the hydrophilic polymer determined a remarkable enhancement of the in vitro drug dissolution rate.     

Application of quartz crystal microbalance to study the impact of pH and ionic strength on protein-silicone oil interactions

The effect of adding a third polymer to immiscible binary solid dispersions was investigated. The model actives griseofulvin (GF), progesterone (PG) and phenindione (PD) were selected because they exemplify a key property of many poorly soluble molecules of having at least one hydrogen bonding acceptor moiety while not having any hydrogen bond donating moieties. Ternary solid dispersions of the drug, PVP (polyvinylpyrrolidone) (proton acceptor) and PHPMA (poly[2-hydroxypropyl methacrylate]) (proton acceptor and donor) were prepared by spray drying. Stability results showed that binary solid dispersions (API and PVP) of GF and PVP crystallized quickly while the amorphous form was not possible to prepare for PG and PD. The amorphous form was prolonged upon the incorporation of PHPMA in the solid dispersion (API, PHPMA and PVP). Based on measuring the melting points, the energy of mixing the drug with the polymer was calculated using the Flory-Huggins theory. The results showed that GF had the lowest free energy followed by PG and finally PD which agreed well with the stability results. These results suggest that the addition of a third polymer to immiscible binary solid dispersions can significantly improve the stability of the amorphous form.     

Properties of solid dispersions of piroxicam in polyvinylpyrrolidone.

Solid dispersions of piroxicam were prepared with polyvinylpyrrolidone (PVP) K-17 PF and PVP K-90 by solvent method. The physical state and drug:PVP interaction of solid dispersions and physical mixtures were characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). FTIR analysis demonstrated the presence of intermolecular hydrogen bonding between piroxicam and PVP in solid dispersions. These interactions reflected the changes in crystalline structures of piroxicam. The amorphousness within the PVP moeity might be predicted in piroxicam dispersions by the disappearance of N-H or O-H peak of piroxicam. Dissolution studies indicated a significant increase in dissolution of piroxicam when dispersed in PVP. The better results were obtained with the lower molecular weight PVP K-17 than with higher molecular weight PVP K-90. The non-amorphous solid dispersions in PVP K-17 showed almost equally fast dissolution rates to amorphous dispersions in PVP K-90. The mechanism of dissolution of solid dispersion in PVP K-90 is predominantly diffusion-controlled due to the very high viscosity of PVP K-90. Dissolution was maximum with the amorphous solid dispersions containing drug:PVP K-17 1:5 and 1:6 which showed a 40-fold increase in dissolution in 5 min as compared with pure drug. Copyright