Flow-through Cell Method Research Articles

<i>In vitro</i> Evaluation of Trimethoprim and Sulfamethoxazole from Fixed-Dose Combination Generic Drugs using Spectrophotometry: Comparison of Flow-Through Cell and USP Paddle Methods

Purpose: To develop a first-order derivative spectrophotometric method for the determination of trimethoprim (TMP) and sulfamethoxazole (SMX) from fixed-dose combination generic products using a flow-through cell technique. Methods: Absorbance measurement was achieved at 247.8 and 257.9 nm for trimethoprim and sulfamethoxazole, respectively. USP Apparatus 4 with 22.6 mm cells, laminar flow at 16 ml/min, and 0.1 N HCl at 37 °C as dissolution medium, were used. Dissolution profiles were compared with modeldependent and independent methods. Results: All the products met the pharmacopeial dissolution criterion (Q ≥ 70 %, at 60 min), except SMX in two products (SC 400 mg and SB1 800 mg) using the flow-through cell (53.62 and 49.74 % dissolved, respectively). Using both USP apparatuses, significant differences in mean dissolution time and dissolution efficiency values were found (p < 0.05). All products were in line with Weibull’s kinetics and significant differences in derived parameters (Td) values were found (p < 0.05). Conclusion: Determination of TMP and SMX by derivative spectrophotometry can easily be employed for dissolution studies using the flow-through cell technique. However, it would be necessary to determine correlation with in-vivo test results in order to assure safe interchangeability. Keywords: Trimethoprim, Sulfamethoxazole, Flow-through cell method, First-order derivative spectrophotometry, Fixed-dose combination generic drugs

Liposome, gel and lipogelosome formulations containing sodium hyaluronate

The moisture-imparting effect of sodium hyaluronate (Na-HA) was investigated in liposome, gel and lipogelosome topical formulations. Sixteen liposome formulations were prepared with or without Na-HA (45 kDa) using various ratios of dimyristoylphosphatidylcholine, 1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol, dipalmitoylphosphatidylcholine and phospholipon 100H. The liposomes were characterized in terms of their structure, composition, zeta potential, Na-HA-entrapment capacity and stability. In particular, scanning electron microscopy, polarized light microscopy, dynamic light scattering and atomic force microscopy were utilized to probe appearance, size and size distribution and lamellarity. The work was then extended to gels using the gelling agents poloxamer (PXM 188 or 407) and Carbopol or Ultrez 21 (U-21), yielding liposome-loaded gel formulations (i.e. lipogelosomes). The in vitro release kinetics of Na-HA from liposomes, lipogelosomes and commercial Na-HA reference formulations were studied via a flow-through cell method. Among the liposomal formulations tested, L6, comprising of Na-HA-loaded phospholipon 100H:stearylamine:cholesterol (7:1:2), displayed optimal traits. The mean particle size, zeta potential and entrapment capacity of L6 were determined as 1900 nm, −20.9 mV and 15.0%. The optimum lipogelosome, LG4, was obtained by incorporating liposome L6 into a U-21 gel at a ratio of 1:1 (w/w). In clinical trials, in-house formulations were applied twice daily to 15 female volunteers. The two-week benefits were assessed against a commercial product; and in all cases, changes of skin humidity, sebum content, pH and wrinkle depth were promising. In particular, the LG4 lipogelosome-based formulation had significantly improved skin hydration and compliance, as evidenced by a moisture content gain of 30.4%.

Evaluation of in vitro absorption, decontamination and desorption of organophosphorous compounds from skin and synthetic membranes

Chemical warfare agents, such as soman, and pesticides, such as chlorpyrifos, dichlorvos or malathion, are toxic organophosphorous compounds (OPCs) that are readily absorbed by the skin. Decontamination using solvents or surfactants may modify the cornified layer – the skin's main barrier against xenobiotic penetration. Thus, effective skin decontamination with fewer side effects is desired. We determined the membrane absorption, decontamination and desorption of toxic OPCs using human skin and synthetic membrane (cuprophane, cellulose acetate, methyl ethyl cellulose, acetophane and nylon) models, and estimated the efficacy of adsorptive powders (bentonite and magnesium trisilicate) at inhibiting this transfer. Using validated flow-through and static diffusion cell and HPLC methods, we found that the transfer of OPCs depends on their membrane affinity. The chlorpyrifos transfer decreased with a decrease in the membrane hydrophilicity, and that of malathion across hydrophilic membranes was less than half of that across hydrophobic membranes. We reliably modeled the toxicant transfer through the skin and synthetic membranes as first-order kinetic and/or square root law transfer processes, suggesting a potential application of synthetic membranes for predicting percutaneous absorption of OPCs. All tested adsorptive powders, applied either alone or as mixtures, significantly reduced the toxicant amount transferred across all membrane models, suggesting a potential therapeutic application with fewer later undesired effects on intact skin.

Comparison of Flow-Through Cell and Paddle Methods for Testing Vaginal Tablets Containing a Poorly Water-Soluble Drug

Purpose: To evaluate the usefulness of the flow-through cell apparatus for testing commercial vaginal tablets containing poorly water-soluble clotrimazole. Methods: The effect of experimental conditions (type of dissolution medium, flow rate and positioning of the tablet) on the dissolution profile of clotrimazole were examined and optimal parameters for conducting the experiments were determined. The amount of drug released was analyzed by high performance chromatography (HPLC) at 210 nm. The usefulness of the flow-through cell apparatus was compared to FDA recommended paddle apparatus. Results: Using acetate buffer pH 5.2 containing 1 % SDS, both methods gave different dissolution profiles. The paddle apparatus tended to give faster rate of dissolution (approx. 88.5 % during the first 20 min of the experiment), which was probably caused by higher agitation and greater surface area of the drug-dissolution medium in a vessel. In the flow-through cell method, total drug release was definitely slower and was observed after 2 to 5 h; at a flow rate of 16 ml/min, more than 80 % of the drug dissolved after 30 min of the test. It was noticed that raising the flow rate of the dissolution medium caused significantly higher drug release. Conclusion: The results demonstrate that the flow-through cell method is reproducible and can be successfully used for evaluating in vitro dissolution of clotrimazole from non-modified release tablets. The slower rate of dissolution obtained in the flow-through cell method would help to distinguish between different formulations.

Preparation of Tetracycline-containing Acrylic Polymer Microparticles by an In-liquid Drying Process from an Oil-in-oil System

This paper describes the production and characterization of polyacrylic polymer microparticles by using an oil-in-oil system. Microparticles were designed for oral administration of tetracycline. Eudragit L 100, Eudragit S 100 and Eudragit RS 100 microparticles were produced by an oil-in-oil-based in-liquid drying process using as external phase light mineral oil. Microparticle morphology was characterized by optical and electron microscopy. The release kinetics of the antibiotic from microspheres were determined by using two different experimental approaches, a flow-through cell method and a dialysis method. The oil-in-oil method here described allows the production of microparticles with a high encapsulation efficiency and appropriate dimensional and morphological characteristics for oral administration. Release profile data indicate that tetracycline is released from microparticles with a rate adequate for a sustained enteric delivery. In addition the release pattern of the drug is influenced by the type of Eudragit used for microparticle production. Our results suggest that tetracycline-containing microparticles represent an interesting system for the sustained release of orally administered tetracycline.

Flow-Through Cell Method and IVIVR for Poorly Soluble Drugs

The percentage of poorly soluble compounds in drug discovery and development increases steadily. A variety of possibilities exists f or increasing solubility and bioavailability; among them is the formation of salts. For the characterization of poorly soluble active pharmaceutical ingredients (API), it is necessary to develop appropriate analytical methods to determine relevant physicochemical properties. One important physicochemical parameter is the dissolution rate. As the flow-through cell (FTC) offers various advantages, such as operating with pH gradients and in sink conditions or applying unlimited amount of media, the FTC is particularly suitable for poorly soluble compounds. When developing an FTC method it is important to consider the physiological circumstances. By choosing the appropriate conditions for media, volume, flow rate, and so forth, it is possible to predict in vivo behavior. The focus of this work was to develop a small-scale FTC method for poorly soluble compounds designed for determining dissolution kinetics in the early development phase, where only limited amount of drug is available. The predictive power of the presented system could be demonstrated by an in vitro–in vivo relationship (IVIVR) study.

Flow-Through Cell Apparatus (USP Apparatus 4): Operation and Features

INTRODUCTION Dissolution testing plays an important role in several areas during drug development. It can be used as a quality control tool to monitor batch-to-batch consistency of drug release from a dosage form and as an in vitro surrogate for in vivo performance that can guide formulation development and ascertain the need for bioequivalence tests. Several apparatus (compendial and noncompendial) are used for the study of dissolution of compounds and dosage forms. The flow-through cell method for the study of dissolution first appeared in 1957 as a flowing medium dissolution apparatus developed by FDA (1). The method was adapted by USP, the European Pharmacopoeia (Ph. Eur.), and the Japanese Pharmacopoiea (JP), and the flowthrough cell became an official apparatus (Apparatus 4 for the USP and Ph. Eur., Apparatus 3 for JP). Specifications and methodology are described in the relevant chapters of the pharmacopeias—USP Chapter Dissolution (2), Ph. Eur. 2.9.3 (3), and JP XV, 6.10 Dissolution Test (4)—and there is good harmonization among them.

In vitro–in vivo correlation for wet-milled tablet of poorly water-soluble cilostazol

The purpose of the present study was to investigate oral bioavailability of an immediate release tablet containing wet-milled crystals of a poorly water-soluble drug, cilostazol, and to establish in vitro–in vivo correlation. Sub-micron sized cilostazol (median diameter: 0.26 μm) was successfully prepared using a beads-mill in water in the presence of a hydrophilic polymer and an anionic surfactant. The milled suspension was solidified with a sugar alcohol as a water-soluble carrier by spray-drying method. The co-precipitate was compressed into an immediate release tablet with common excipients. Oral bioavailability of the wet-milled cilostazol tablet in male beagle dogs was 13-fold higher than the hammer-milled commercial tablet in fasted condition. Food did not increase the oral bioavailability of the wet-milled tablet, while 4-fold increase was found for the commercial tablet. Irrespective to the bioavailability enhancement, in vitro dissolution rate of the wet-milled tablet was even slower than the commercial tablet by the compendial method (USP Apparatus 2). On the other hand, a good correlation was found between the dissolution profiles obtained by a flow-through cell method (USP Apparatus 4, closed-loop system without outlet filter) using a large volume of water and sodium lauryl sulfate (SLS) solution at the concentration lower than the critical micellar concentration (cmc) as dissolution media corresponding to the fasted and fed conditions, respectively.

Development of a vessel-simulating flow-through cell method for the in vitro evaluation of release and distribution from drug-eluting stents

A novel in vitro dissolution test for drug-eluting stents (DES) based on the compendial flow-through cell was developed. The model contains an additional compartment simulating the vessel wall enabling the examination of drug release and distribution. The compartment consists of alginate hydrogel containing a central aperture forming the lumen for stent placement and media flow. The method was tested utilizing stents coated with hydrophilic (fluorescein sodium) and hydrophobic (triamterene) fluorescent model substances as well as the cytostatic drug doxorubicin hydrochloride and compared to standard dissolution methods. The results show the suitability of the developed method to observe drug release and distribution. The determination of model substance content in the compartments media, hydrogel and stent yielded differing distribution patterns for the model compounds and enabled the observation of redistribution processes. The dissolution profiles differed from the results of compendial dissolution testing. Besides lower endpoints and slower rises of media concentrations due to distribution into the hydrogel, the release rates from the stent coatings were altered. These findings emphasize the necessity to adapt dissolution testing for DES to the unique conditions influencing delivery to the vessel wall to learn more about local distribution and to anticipate the in vivo performance of DES.

Slow Release of Tetracycline from a Mucoadhesive Complex with Sucralfate for Eradication of Helicobacter pylori

Treatment composed of a gastric mucoadhesive antibiotic with slow release drug delivery is expected to be effective for the eradication of Helicobacter pylori (H. pylori). In this study, we evaluated the slow release property of the tetracycline-sucralfate acidic complex. Tetracycline was the antibiotic selected because of its complexation capacity with sucralfate. Sustained release was tested using two different dissolution test methods: paddle and flow-through cell. The adhesive paste formed from the acidic complex displayed a longer sustained release profile of tetracycline using flow-through cell method. The milder conditions of the flow-through cell method better mimicked the fasted state of the stomach, suggesting that the oral administration with fasting is appropriate for the acidic complex. Furthermore, the paste formation protected the tetracycline from decomposition under an acidic condition, which apparently contributes to long-term release. Change in the zeta potential of the acidic complex particles was helpful in clarifying the release mechanisms of the tetracycline. The data indicated that the immediate release of tetracycline in the early stage of the test was indispensable to the subsequent paste formation that enables slow release. If administrated orally with fasting, the acidic complex rapidly adheres to the gastric mucosa and sustains long-term release of the tetracycline to the gastric lumen or mucus layer. This antibiotic delivery mechanism, which requires only a minimum dosage, may be effective for efficient eradication of H. pylori.

Influence of aluminum tristearate and sucrose stearate as the dispersing agents on physical properties and release characteristics of Eudragit RS microspheres.

The purpose of this research was to investigate the effects of different concentrations of polymer and sucrose stearate, aluminum tristearate as dispersing agents on microsphere properties and performance. The yield values of microspheres were over the 78%, and the encapsulation efficiencies were found to be ∼735. Particle sizes of microspheres prepared with aluminum tristearate were between 76 and 448 μm, while that of the microspheres containing sucrose stearate were between 521 and 2000 μm. Morphological and physicochemical properties of microspheres were investigated by scanning electron micrography and differential scanning calorimetry (DSC). DSC analysis indicated that verapamil hydrochloride formed a solid solution with acrylic polymers. In vitro release studies were performed using the flow-through cell method. While ∼80% of drug was released from the microspheres containing aluminum tristearate in 480 minutes, the same amount of drug was released from microspheres containing sucrose stearate in only 60 minutes. Chemical structures and concentrations of the dispersing agents were clearly effective on the physical properties of microspheres and their drug-release characteristics.

Dissolution tests for self-setting calcium phosphate cement-containing nifedipine.

Nifedipine-containing calcium phosphate cement (CPC) was prepared, and nifedipine (NF) release from this preparation was evaluated by the shaking method (SK), Japanese Pharmacopoeia XIV (JPXIV) paddle method (PD), and JPXIV flow-through cell method (FT). The release of NF from the CPC preparation continued for 7 d or longer by all these methods. This suggests that the release of NF can be controlled by preparing NF-containing CPC. The release pattern of NF from CPC in these tests was found to follow the Higuchi equation. However, the Higuchi constant differed among the three dissolution tests, probably because the apparent tortuosity of capillary system (tau) varied.

Performance of USP calibrator tablets in flow-through cell apparatus

USP dissolution calibrator tablets were analysed by the flow-through cell method with the intention of examining its applicability for the flow-through cell apparatus suitability test. Test was performed with Dissotest CE-6 apparatus, (Sotax, Switzerland) in flow-through cells for tablets and capsules: smaller cells of 12 mm diameter and larger ones of 22.6 mm diameter. Analyses were performed with laminar and turbulent flow of dissolution medium. The flow rates were 16 and 8 ml/min for laminar flow and only 16 ml/min for turbulent flow. From the results it can be concluded that both salicylic acid tablets and prednisone tablets could be used for apparatus suitability test also for the flow-through cell under the conditions of laminar flows of 16 and 8 ml/min in cells φ 12 and 22.6 mm. As regards the turbulent flow of 16 ml/min, without a holder, cells φ 12 mm could be used for salicylic acid tablets and both cells (φ 12 and 22.6 mm) for prednisone tablets.

Studies of Floating Dosage Forms of Furosemide: In Vitro and In Vivo Evaluations of Bilayer Tablet Formulations

For the purpose of enhancement the bioavailability of furosemide (FR), a floating dosage form with controlled release of FR was designed in this study. Because of the lower solubility of active material in the gastric medium, it was first enhanced by preparing an inclusion complex of FR with beta-cyclodextrin (β-CD) in a 1:1 proportion using the kneading method. Following the design of dosage form, bilayer floating tablets were prepared. After dissolution rate studies were performed using the continuous flow-through cell method, the formulation that provided delivery of active material near the target profile was given to six healthy male volunteer subjects, and in vivo tests were performed. It was determined by radiographs that floating tablets prepared by adding BaSO4 stayed in the stomach for 6 hr. Further, values of the area under the plasma concentration-time curve (AUC) obtained with the floating dosage form were about 1.8 times those of the conventional FR tablet in blood analyses; maximum and minimum plasma concentrations were also found to be between the desired limits. In urine analyses, the peak diuretic effect seen in classical preparations was decreased and prolonged in floating dosage forms. Also, a considerably significant correlation was detected between in vivo results and in vitro data of the dissolution rate, and it was concluded that the modified continuous flow-through cell method is usable for in vitro dissolution rate tests of floating dosage forms.

Influence of Swelling Degree on Release of Nicardipine Hydrochloride from Acrylic Microspheres Prepared by Solvent Evaporation Method

ABSTRACTThe purpose of this study was to prepare and evaluate an enteric coated dosage form of nicardipine hydrochloride (NCH)-loaded microspheres for delivery over a 12-hr period. Microspheres containing Eudragit RS and L with different ratios were prepared by solvent evaporation method and the effect of swelling on the release rate and characteristics was investigated. The change in the diameters of microspheres with time in simulated intestinal fluid (pH 7.5) at 37°C has been studied. Drug release was determined using the flow-through cell method, and related to the degree of swelling (Q) of the microspheres. Q values in turn depended on the ratio of Eudragit RS-L used. Release of NCH from microspheres increased with Eudragit L amount, but no controlled-release pattern was observed. Q values ≥18.88 caused a slow initial release followed by an accelerated release. Microspheres with an Eudragit RS-L ratio of 1:5.7, Q value of 38.71, and drug release rate of 0.155% min−1 exhibited a remarkable delayed time for erosion to begin (120 min). Thus, microspheres prepared from this formulation may provide an effective enteric dosage form, releasing NCH at a predetermined rate.

A collaborative study of the in vitro dissolution of acetylsalicylic acid gastro-resistant capsules comparing the flow-through cell method with the USP paddle method

A collaborative in vitro dissolution study was performed comparing the Flow-through cell (FTC) method with the USP Paddle method. The objective was to compare the two methods regarding their suitability for changing the pH of a dissolution medium and for measuring the in vitro dissolution of a gastro-resistant dosage form. Aspirin, a gastro-irritant substance in an enteric-coated, multiple-unit dosage form, was used as the test material. The results show that the FTC method gives comparable results compared with the Paddle method. The FTC method is also more convenient to use for shifting the pH from an acidic condition at pH 1.2 to a pH of 6.8. The effect of different ionic strengths of the dissolution media on dissolution rate results was observed for the test product by using the FTC method.

Dissolution testing of artemisinin solid oral dosage forms

Dissolution can best be described as a tool that can provide valuable information about the bioavailability of a drug product. But to obtain a good overall correlation with in vivo data, the presence of sink conditions is an essential requirement in the dissolution tests. The flow-through cell method has been recommended to be a dissolution method that most satisfactorily fulfils this requirement for poorly water soluble drugs. The present article demonstrates that in case of artemisinin, a hydrophobic compound used in high dose per tablet or capsule, even the flow-through cell method does not guarantee the presence of sink conditions during the total duration of the experiments.

In vitro dissolution tests corresponding to the in vivo dissolution of clarithromycin tablets in the stomach and intestine.

The correlation between in vivo and in vitro dissolution of clarithromycin (CAM) tablets was examined. In vivo dissolution rate constants in the stomach and the intestine were obtained from analysis of the urinary excretion data of CAM following oral administration to humans in the fasting or postprandial state using a pharmacokinetic model including gastrointestinal transit. In the present study, the flow-through cell method with moderate agitation was used, as the in vitro dissolution test related to the in vivo dissolution rate constants. Both the effects of pH of the dissolution medium and the volumetric solvent flow rate on the dissolution rate in the flow-through cell method were examined. The pH of the dissolution medium and the flow rate were related to the in vitro dissolution rate. Therefore, the conditions of the flow-through cell method in correlation with the in vivo dissolution rates in the stomach and intestine were determined by controlling the flow rate at pH 3.0 and 6.8 dissolution medium. The urinary excretion of CAM, simulated by substituting the in vitro dissolution rate constants into the equation, were consistent with the in vivo data. The in vitro tests corresponding to the in vivo dissolution in the stomach and intestine following a single oral administration in the fasting or postprandial state for a CAM tablet were established.

Gelatin microspheres as a new approach for the controlled delivery of synthetic oligonucleotides and PCR-generated DNA fragments

The present paper reports the preparation and characterization of gelatin microspheres containing (a) a 44-mer single-stranded synthetic oligonucleotide, complementary to the HLA-DRA gene (ssDNA-44) and (b) a double-stranded fragment, 144 bp in length, prepared by the polymerase chain reaction (PCR) mimicking a region of the HIV-1 LTR (dsDNA-144). Spherical gelatin microspheres were obtained by a coacervation method, showing a high percentage of encapsulation yields (over 85%). Size distribution analysis of the microspheres produced resulted in an average diameter of 22 μm. In order to analyse the release profiles of both ssDNA-44 and dSDNA-144 from microspheres, in vitro studies were carried out by using a flow-through cell method. The chemical stability of dsDNA-144 to the encapsulation procedure steps was in addition demonstrated by PCR amplication of the DNA eluted from the gelatin microspheres. The reported results indicate that gelatin-based microspheres offer excellent potential as carrier systems for the in vivo administration of both single- and double-stranded DNA molecules.

Controlled-release coevaporates of dipyridamole prepared with acrylic polymers

The objective of this study was to obtain Controlled-release dosage forms of dipyridamole chosen as a model drug practically insoluble above pH 5. The coevaporates were prepared by the solvent method using enteric and insoluble acrylic polymers as well as their mixtures in different proportions. The in vitro dissolution test results were determined by the USP XXII paddle method at different pH values during a period of 8 h. These results showed that the progressive pH-dependent release of dipyridamole could only be achieved by blending enteric and insoluble polymers. To overcome the difficulty in maintaining sink conditions with the paddle method, the dissolution profiles of some of the formulations were investigated using the open flow-through cell method.