Use of adsorbents in enhancement of drug dissolution. II

Nanocomposite Hydrogels: Advances in Nanofillers Used for Nanomedicine

The ongoing progress in the development of hydrogel technology has led to the emergence of materials with unique features and applications in medicine. The innovations behind the invention of nanocomposite hydrogels include new approaches towards synthesizing and modifying the hydrogels using diverse nanofillers synergistically with conventional polymeric hydrogel matrices. The present review focuses on the unique features of various important nanofillers used to develop nanocomposite hydrogels and the ongoing development of newly hydrogel systems designed using these nanofillers. This article gives an insight in the advancement of nanocomposite hydrogels for nanomedicine.

Supersaturation Potential of Ordered Mesoporous Silica Delivery Systems. Part 1: Dissolution Performance and Drug Membrane Transport Rates

Ordered mesoporous silica materials have shown great potential as oral drug delivery systems for poorly soluble drugs. However, the ability of these delivery systems to generate drug supersaturation has not been widely investigated, and the recently noted phenomenon of incomplete drug release is not well understood. Therefore, the aim of this study was to comprehensively evaluate the release of hydrophobic drug molecules into solution from ordered mesoporous silica, focusing on the extent and duration of drug supersaturation. The dissolution and supersaturation behavior of ritonavir, following loading into mesoporous SBA-15 silica particles, was investigated by undertaking simple in vitro dissolution studies in phosphate buffer pH 6.8 and fasted state simulated intestinal fluid, as well as membrane flux studies using a side-by-side diffusion cell apparatus. It was found that supersaturated ritonavir solutions were generated from ritonavir-loaded mesoporous SBA-15 particles; however, drug release was always incomplete, even under sink conditions. In addition, the percentage drug release was observed to decrease significantly as the theoretical supersaturation ratio and dose of ritonavir-loaded SBA-15 formulation increased. The data obtained suggest an equilibrium exists between drug adsorbed to the SBA-15 silica surface and free drug present in solution. The findings described herein are highly significant in aiding our understanding of ordered mesoporous silica as a supersaturating drug delivery system for bioavailability enhancement.

Enhanced dissolution and stability of Tanshinone IIA base by solid dispersion system with nano-hydroxyapatite

Background:

Tanshinone IIA (TSIIA) exhibits a variety of cardiovascular effects; however, it has low solubility in water. The preparation of poorly soluble drugs for oral delivery is one of the greatest challenges in the field of formulation research. Among the approaches available, solid dispersion (SD) technique has proven to be one of the most commonly used these methods for improving dissolution and bioavailability of drugs, because of its relative simplicity and economy in terms of both preparation and evaluation.

Objective:

This study was aimed at investigating the dissolution behavior and physical stability of SDs of TSIIA by employing nano-hydroxyapatite (n-HAp).

Materials and Methods:

The TSIIA SDs was prepared to use a spray-drying method. First, an in vitro dissolution test was performed to assess dissolution characteristics. Next, a set of complementary techniques (differential scanning calorimetry, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy) was used to monitor the physicochemical properties of the SDs. The SDs was stored at 40°C/75% relative humidity for 6 months, after which their stability was assessed.

Results:

TSIIA dissolution remarkably improved because of the formulation of the SDs with n-HAp particles. Comparisons with the corresponding physical mixtures revealed changes in the SDs and explained the formation of the amorphous phase. In the stability test, virtually no time-dependent decrease was observed in either in vitro drug dissolution or drug content.

Conclusion:

SD formulation with n-HAp may be a promising approach for enhancing the dissolution and stability of TSIIA.

An attempt to stabilize tanshinone IIA solid dispersion by the use of ternary systems with nano-CaCO3 and poloxamer 188

Background:

Tanshinone IIA (TSIIA) on solid dispersions (SDs) has thermodynamical instability of amorphous drug. Ternary solid dispersions (tSDs) can extend the stability of the amorphous form of drug. Poloxamer 188 was used as a SD carrier. Nano-CaCO₃ played an important role in adsorption of biomolecules and is being developed for a host of biotechnological applications.

Objective:

The aim of the present study was to investigate the dissolution behavior and accelerated stability of TSIIA on solid dispersions (SDs) by the use of ternary systems with nano-CaCO₃ and poloxamer 188.

Materials and Methods:

The TSIIA tSDs were prepared by a spray-drying method. First, the effect of combination of poloxamer 188 and nano-CaCO₃ on TSIIA dissolution was studied. Subsequently, a set of complementary techniques (DSC, XRPD, SEM and FTIR) was used to monitor the physical changes of TSIIA in the SDs. Finally, stability test was carried out under the conditions 40°C/75% RH for 6 months.

Results:

The characterization of tSDs by differential scanning calorimetry analysis (DSC) and X-ray powder diffraction (XRPD) showed that TSIIA was present in its amorphous form. Fourier transforms infrared spectroscopy (FTIR) suggested the presence of interactions between TSIIA and carriers in tSDs. Improvement in the dissolution rate was observed for all SDs. The stability study conducted on SDs with nano-CaCO₃ showed stable drug content and dissolution behavior, over the period of 6 months as compared with freshly prepared SDs.

Conclusion:

SDs preparation with nano-CaCO₃ and poloxamer 188 may be a promising approach to enhance the dissolution and stability of TSIIA.

Preparation, characterization, and in vivo evaluation of tanshinone IIA solid dispersions with silica nanoparticles

We prepared solid dispersions (SDs) of tanshinone IIA (TSIIA) with silica nanoparticles, which function as dispersing carriers, using a spray-drying method and evaluated their in vitro dissolution and in vivo performance. The extent of TSIIA dissolution in the silica nanoparticles/TSIIA system (weight ratio, 5:1) was approximately 92% higher than that of the pure drug after 60 minutes. However, increasing the content of silica nanoparticles from 5:1 to 7:1 in this system did not significantly increase the rate or extent of TSIIA dissolution. The physicochemical properties of SDs were investigated using scanning electron microscopy, differential scanning calorimetry, X-ray powder diffraction, and Fourier transforms infrared spectroscopy. Studying the stability of the SDs of TSIIA revealed that the drug content of the formulation and dissolution behavior was unchanged under the applied storage conditions. In vivo tests showed that SDs of the silica nanoparticles/TSIIA had a significantly larger area under the concentration-time curve, which was 1.27 times more than that of TSIIA (P < 0.01). Additionally, the values of maximum plasma concentration and the time to reach maximum plasma concentration of the SDs were higher than those of TSIIA and the physical mixing system. Based on these results, we conclude that the silica nanoparticle based SDs achieved complete dissolution, increased absorption rate, maintained drug stability, and showed improved oral bioavailability compared to TSIIA alone.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Characterization and Stability of Tanshinone IIA Solid Dispersions with Hydroxyapatite

Solid dispersions of tanshinone IIA (TanIIA) using hydroxyapatite (HAp) as the dispersing carrier (TanIIA-HAp SDs) were prepared by the solvent evaporation method. The formed solid dispersions were characterized by scanning electron microscopy (SEM), differential scanning calorimetry analysis (DSC), X-ray powder diffraction (XRPD) and Fourier transforms infrared (FTIR) spectroscopy. The in vitro dissolution rate and the stability of TanIIA-HAp SDs were also evaluated. DSC and XRPD showed that TanIIA was changed from a crystalline to an amorphous form. FTIR suggested the presence of interactions between TanIIA and HAp in solid dispersions. The result of an in vitro dissolution study showed that the dissolution rate of TanIIA-HAp SDs was nearly 7.11-folds faster than free TanIIA. Data from stability studies for over one year of TanIIA-HAp SDs performed under room temperature revealed no significant differences in drug content and dissolution behavior. All these results indicated that HAp may be a promising carrier for improving the oral absorption of TanIIA.

Controlled-release approaches towards the chemotherapy of tuberculosis

Tuberculosis (TB), caused by the bacteria Mycobacterium tuberculosis, is notorious for its lethality to humans. Despite technological advances, the tubercle bacillus continues to threaten humans. According to the World Health Organization’s 2011 global report on TB, 8.8 million cases of TB were reported in 2010, with a loss of 1.7 million human lives. As drug-susceptible TB requires long-term treatment of between 6 and 9 months, patient noncompliance remains the most important reason for treatment failure. For multidrug-resistant TB, patients must take second-line anti-TB drugs for 18–24 months and many adverse effects are associated with these drugs. Drug-delivery systems (DDSs) seem to be the most promising option for advancement in the treatment of TB. DDSs reduce the adverse effects of drugs and their dosing frequency as well as shorten the treatment period, and hence improve patient compliance. Further advantages of these systems are that they target the disease area, release the drugs in a sustained manner, and are biocompatible. In addition, targeted delivery systems may be useful in dealing with extensively drug-resistant TB because many side effects are associated with the drugs used to cure the disease. In this paper, we discuss the DDSs developed for the targeted and slow delivery of anti-TB drugs and their possible advantages and disadvantages.

Influence of adsorbents in transdermal matrix patches on the release and the physical state of ethinyl estradiol and levonorgestrel

The drug release from medium molecular weight polyisobutene patches containing adsorbates (drug content: 0.2% ethinyl estradiol, 1.0% levonorgestrel; adsorbent content: 20%, w/w) increased in the order of no adsorbent<titanium dioxide<MCC<crospovidone. This was attributed to differences in drug crystallinity which increased in the order of crospovidone (crystal free)<MCC<titanium dioxide<no adsorbent and the water uptake which increased in the order of no adsorbent (0.1%)=titanium dioxide (0.1%)<MCC (1.6%)<crospovidone (4.8%) at 90% rh. Patches containing adsorbates onto crospovidone were investigated in detail. Increasing the adsorbate's drug loading increased the drug release up to a crospovidone content of 15% (w/w). Patches were crystal free for crospovidone contents ≥ 10% (w/w), which corresponds to a drug loading of crospovidone of 12% (w/w). In conclusion, the incorporation of drug adsorbates onto crospovidone into patches based on polyisobutene significantly increased the drug release (approximately 9.1 times for ethinyl estradiol and 15.4 times for levonorgestrel) and prevented drug recrystallization.

Solid State and Dissolution Rate Characterization of Co-Ground Mixtures of Nifedipine and Hydrophilic Carriers

Co-ground powders of the poorly water-soluble drug nifedipine and a hydrophilic carrier, [partially hydrolyzed gelatin (PHG), polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS), hydroxypropyl methylcellulose (HPMC), polyethylene glycol (PEG), urea or Pluronic F108] were prepared in order to improve the dissolution rate of nifedipine. The effects of type of grinding equipment, grinding time, and type of hydrophilic carrier on the crystallinity of nifedipine (x-ray diffraction and differential scanning calorimetry) on the interaction between drug and carriers (differential scanning calorimetry), on the particle size and appearance (scanning electron microscopy), on the wettability (contact angle measurements), and on the drug release were investigated. Grinding nifedipine together with these carriers improved the dissolution rate. PHG-ground mixtures resulted in the fastest dissolution rate followed by PVP, SDS, HPMC, Pluronic, urea, and PEG. This effect was not only due to particle size reduction, which increased in the order PHG<PEG=SDS<Pluronic<drug<urea<HPMC<PVP, but also resulted from the ability of some carriers (PVP and HPMC) to prevent reaggregation of the finely divided drug particles. PVP, HPMC, and PHG formed a powder with amorphous drug. The carriers improved the wettability of the ground products in the order HPMC<drug<urea<PVP<SDS<PHG<PEG<Pluronic. Differential scanning calorimetry (DSC) measurements gave valuable information about the nature of drug crystallinity and the interactions with the carriers within the ground mixtures.

Dissolution-rate enhancement of fenofibrate by adsorption onto silica using supercritical carbon dioxide

Dissolution rate of a poorly water-soluble drug, fenofibrate, is increased by adsorbing the drug onto silica. The adsorption is achieved by first dissolving the drug in supercritical carbon dioxide and then depressurizing the solution onto silica. Loadings of up to 27.5 wt.% drug onto silica are obtained. Since solvents are not used in the loading process, the fenofibrate/silica formulation is free of any residual solvent, and carbon dioxide is freely removed upon depressurization. The formulation is characterized using infrared spectroscopy, ultraviolet spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. Based on in vitro dissolution study, a significant increase in the dissolution rate (approximately 80% drug release in 20 min) of drug-silica formulation is observed as compared to micronized fenofibrate (approximately 20% drug release in 20 min), which can be attributed to increase in the surface area and decrease in the crystallinity of drug after adsorption onto silica. Two different formulations are compared: (A) amorphous fenofibrate/silica and (B) slightly crystalline fenofibrate/silica. The second formulation is found to be more stable on storage.

Investigation of drug-porous adsorbent interactions in drug mixtures with selected porous adsorbents

The adsorption of drugs onto porous substrates may prove to be a convenient method by which to enhance the dissolution rate of certain poorly water-soluble drugs in body fluids. The purpose of this research is to provide a better understanding of the type of interactions occurring between drugs and certain pharmaceutically acceptable porous adsorbents that leads to enhanced drug dissolution rates. The interactions between ibuprofen (acidic drug), acetaminophen (acidic drug), dipyridamole (basic drug), and the porous adsorbents used (calcium silicate and silica gel) were investigated using differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier Transform infrared spectroscopy (FTIR). DSC and PXRD results indicated a significant loss of crystallinity of both ibuprofen and acetaminophen but not dipyridamole. In the case of ibuprofen, FTIR results indicated the ionization of the carboxylic group based on the shift in the FTIR carboxylic band. Dissolution of ibuprofen from its mixtures with porous adsorbents was found to be significantly higher compared to the neat drug, whereas dipyridamole dissolution from its mixtures with porous adsorbents was not significantly different from that of the neat drug.

Inclusion of ketoprofen with skimmed milk by freeze-drying

Ketoprofen is a non-steroidal anti-inflammatory drug which is not soluble in water and creates gastrointestinal problems. In order to improve the solubility of the drug in water and enhance its dissolution rate, physical mixture (PM) and inclusion (IC) of ketoprofen with skimmed milk (SM) were prepared and investigated. Enhancement of solubility of ketoprofen was obtained by preparing its IC with SM which can be used because of its amino acid and surface active agents content and can also be used for treatment of gastric disturbance. Lyophilization technique was used to prepare the IC. Results obtained showed that the solubility of IC of ketoprofen with SM was almost four times greater than the solubility of the plain drug. Data from the dissolution rate determination have also indicated that IC of ketoprofen with SM significantly improved the dissolution rate of the drug compared with PM and the plain form. Differential scanning calorimetry (DSC), X-ray powder diffraction and scanning electron microscopic (SEM) analysis revealed the formation of IC of ketoprofen with SM.

Effect of protective colloids on the induction of polymorphic changes in indomethacin agglomerates after solvent evaporation from o/w emulsions

Indomethacin (IMC) agglomerates were prepared by the solvent evaporation process from o/w emulsions containing different protective colloids in the external aqueous solution. The types of protective colloids inducing the polymorphic transformation of IMC in the agglomerates without wall material were investigated. The composition and its polymorphs were evaluated from the X-ray diffraction patterns, IR spectra and DSC thermograms. The results indicate that when pectin, beta-cyclodextrin, sodium alginate or sodium dodecyl supphase acted as a protective colloid, the respective IMC agglomerates consisted only of the alpha form of IMC. When gelatin or hydroxypropyl methylcellulose was used as a protective colloid, the amorphous, alpha and gamma forms as well as methylene chloride solvates of IMC were found in the IMC agglomerates. There was only methylene chloride solvate of IMC with a small amount of amorphous form in the IMC agglomerates prepared from albumin as a protective colloid, while IMC agglomerates prepared from methylcellulose, polyvinyl alcohol or biosoluble polymer consisted of the mixture of amorphous and alpha forms, and methylene chloride solvate of IMC. When polyvinyl pyrrolidone was applied to act as a protective colloid, the mixture of methylene chloride solvate and gamma form of IMC with less quantity of amorphous form was found in its IMC agglomerates. This strongly suggests that the composition of IMC agglomerates prepared from the solvent evaporation process was significantly influenced by the type of protective colloids used.

Enhancement of the dissolution rate of a poorly water-soluble drug (tolbutamide) by a spray-drying solvent deposition method and disintegrants

The dissolution rate of a poorly water-soluble drug, tolbutamide, was improved by spray-drying a diluted ammonia solution of the drug containing either a low-substituted hydroxypropylcellulose (L-HPC) or partly pregelatinized corn starch (PCS) as disintegrants. With L-HPC the resultant particles were agglomerates of disintegrant with drug on the surface and within the particles, while particles formed with PCS were composed of a single core of PCS on which the drug was deposited. The deposited drug crystals were very fine because the rapid solvent evaporation restricted crystal growth. The spray-dried particles prepared with PCS had a structure similar to that of an ordered mix. The drug dissolution rate from the spray-dried particles was more rapid than that of the powdered drug alone or with disintegrant and could be attributed to separation of the layer of fine drug crystals from the surface of the particles by swelling of disintegrant. PCS enhanced the drug dissolution rate compared with systems using corn starch. The dissolution rate also depended on the drug content of the particles which was higher than that in ordered mixtures or conventional solvent deposition systems. This system described also had the advantage of avoiding the use of organic solvents.

Application of differential scanning calorimetry to the study of solid drug dispersions

The present study describes the application of differential scanning calorimetry (DSC) to ascertain the crystalline state of a drug with a melting point of approximately 53 degrees C after dispersion on hydrophilic carriers by either simple mixing or by fusion. The carriers examined include polyethylene glycol 6000 and colloidal silicon dioxides. The most interesting of the systems investigated, in which the drug is gradually transformed from the crystalline to the amorphous state at room temperature, are physical mixtures of the drug and colloidal silicon dioxides. The crystalline transformation is manifested by the gradual decrease in the endothermic transition energy of the physical mixture with time. The crystalline transformation is characteristically biphasic with initially fast first-order kinetics, followed by a slow conversion process. The rate of transformation is dependent on the drug-silicon dioxide ratio, temperature, and certain physical properties of the silicon dioxides. An inverse relationship exists between transition energy and the in vitro dissolution rate of the drug in the physical mixtures with silicon dioxide. This suggests that DSC may provide a useful method for evaluating the effects of formulation variables upon dissolution rate.

Solid dispersion of morphine-tristearin with reduced presystemic inactivation in rats

Solid dispersions of morphine in tristearin, beta-sitosterol, and cholesterol were prepared by evaporation of their ethanol solutions. Weight ratios of morphine-lipid of 1:1, 1:3, and 1:4.5 were prepared. Dissolution studies of the solid dispersions and morphine were conducted in a simulated GI medium at 37 degrees. The release rates of morphine from the tristearin dispersions were the slowest. The 1:1 morphine-tristearin dispersion was administered orally to rats. Free and total morphine levels in rat urine were determined by spectrofluorometric and enzymatic immunoassay procedures, respectively. The morphine-tristearin dispersion yielded a higher percentage of free morphine after 24 and 48 hr as compared with morphine and its sulfate.

Fenoprofen: drug form selection and preformulation stability studies

Several fenoprofen salts were prepared to obtain the most acceptable form for an oral dosage formulation. Thermal analysis techniques were used to compare stabilities of the water of hydration in different salt forms and to assess the effects of the water of hydration on compatibility with propoxyphene and codeine salts. Photodegradation products of fenoprofen were isolated and identified, and their relevance to product formulation was evaluated.

Solvent deposition method for enhancement of dissolution rate: importance of drug-to-excipient ratio

Dissolution rates and particle sizes of phenylbutazone solvent deposited on lactose, starch, and silicon dioxide, separately, and of norethindrone and digoxin deposited on lactose were investigated. Microparticulate dispersed drugs on the surface of excipients result when drug-to-excipient ratios are low. Fast dissolution rates are observed for such systems. This effect can be extended to higher ratios when silicon dioxide is used as the excipient. Because of adsorption, however, the release from silicon dioxide is more or less limited.