Influence of pH on release of phenytoin sodium from slow-release dosage forms

Physicochemical factors influencing the release of phenytoin sodium from slow-release dosage forms were studied. Some of these factors were solubility and intrinsic dissolution rate as functions of pH, type of dosage form, pH of dissolution medium used, and conversion of the sodium salt to free acid (phenytoin). The innovator's product, Extended Phenytoin Sodium Capsule (Dilantin Kapseal, 100 mg, Parke-Davis), and two experimental formulations (one nondisintegrating tablet containing polymeric materials and the other a solid dispersion in an erodible matrix) served as the slow-release dosage forms. The sodium salt converts to practically insoluble phenytoin in the gastrointestinal pH range of 1 to 8. Due to such a conversion inside or at the surface of slow-release dosage forms, the release of drug in this pH range was incomplete. The extent of drug release also varied with the type of formulation used. In contrast, complete dissolution could be obtained in water because the pH of the medium gradually rose from approximately 6 to approximately 9.2 where the drug solubility was higher. Although several phenytoin sodium products might have similar dissolution rates in water, the extents of drug release under gastrointestinal pH conditions (pH 1-8) could differ greatly, thus supporting the Food and Drug Administration recognition that the similarity in dissolution profiles in water does not assure that the products are bioequivalent. The reported lower steady-state level of phenytoin in human plasma following oral administration of a slow-release dosage form may be related to incomplete drug release.     

In vivo and in vitro responses to poly(ethylene terephthalate-co-diethylene glycol terephthalate) and polyethylene oxide blends

Although biocompatible polymeric compounds are generally nontoxic, nonimmunogenic, and chemically inert, implants made from these materials may trigger acute and chronic inflammatory responses. These inflammatory reactions may induce degeneration of implanted biopolymer. Interactions between implanted biomaterial and inflammatory cells are mediated by many cellular events involving cellular adhesion and activation. We studied the inflammatory responses in vivo and in vitro to samples of biopolymers composed of poly(ethylene terephthalate-co-diethylene glycol terephthalate) plus 0, 5, 25% of polyethylene oxide. We observed that these biopolymers did not induce inflammatory responses when implanted in the peritoneal cavity of mice for 28 days. However we observed deposition of hyaluronic acid at the surface of implanted biomaterial, suggesting that tolerance to biomaterial occurred after surgical implantation. No significant adhesion of inflammatory cells such as mononuclear phagocytes and peripheral leukocytes were observed in vitro, when poly(ethylene terephthalate-co-diethylene glycol terephthalate) blends were used as substratum to cellular adhesion. These results suggest that blends composed of poly(ethylene terephthalate-co-diethylene glycol terephthalate) induce low inflammatory cell adhesion, since no rejection of biopolymer was observed when implanted in experimental animal models.     

Crystallization of free aspartate aminotransferases from polyethylene glycol solution

Human papillomavirus (HPV) is associated with benign cutaneous or mucosal lesions and with malignant tumours, but none of the HPV types has so far been related to skin tags. Skin biopsy specimens from 49 Caucasian patients suffering from the presence of multiple soft fibromas were analysed by means of dot blot hybridization and by polymerase chain reaction assays aimed at detecting all known HPV types. The results revealed the presence of HPV DNA type 6/11 in 88% of the skin tags examined. This result supports the hypothesis that HPV plays a part in the progression of cutaneous soft fibromas, as previously reported for laryngeal papillomas.     

In vitro reconstitution of neurotransmitter release

Photon activation is a radiotherapy technique in which an element is added to the absorbing medium to raise the probability that a photoelectric interaction will occur, thus causing an increase in the absorption of ionizing radiation. Binding energies of key elements within an absorbing medium are closely matched with the incident photon energies to maximize the production of free electrons and subsequent absorption of their kinetic energies. The purpose of this research was to quantify potential dose enhancement using a silver tetraphenyl sulfonato porphyrin (AgTPPS4) in tumors as a photon activator for use with interstitial 125I brachytherapy. A three-dimensional Monte Carlo dosimetry model was developed using the EGS4 coding system. The photon source was modeled using spectral gamma emissions from models 6702 or 6711 brachytherapy seeds for comparison. Absorbed dose within the tumor volume was calculated for AgTPPS4 concentrations ranging between 0 and 20 mmol/kg tumor weight. These theoretical studies demonstrated linear increases in dose absorbed by the tumor with corresponding increases in AgTPPS4 concentration. The required AgTPPS4 concentration (RSC) to achieve at least a ten percent absorbed dose increase is approximately 6.5 mmol/kg tumor weight for model 6702 seeds. In vivo biodistribution and in vitro toxicity studies were conducted to determine if the theoretically derived RSC could be achieved biologically. Cell toxicity studies showed that TPPS4 porphyrin derivatives were cytotoxic at concentrations required to provide significant brachytherapy dose enhancement. Reverse phase HPLC confirmed that toxicity was due to intrinsic properties of the TPPS4 molecule, not the presence of free silver, drug impurities, or metabolites. Further research is necessary to develop a nontoxic molecular carrier for delivering silver to the DNA of tumor cells.     

Sustained-release dosage form of phenylpropanolamine hydrochloride. Part II: Formulation and in vitro release kinetics from tableted microcapsules

This work was planned to prepare sustained-action preparations of phenylpropanolamine hydrochloride by microencapsulation and by tableted microcapsules. Dissolution from both suspended microcapsules and the tablets was studied using the USP XXII basket method in simulated gastric and intestinal fluid without enzyme. The results were applied to zero-order, first-order, Hixson Crowell, RRSBW, Q/square root of t, (Bt)a and Higuchi kinetic models. Dissolution of PPA.HCl was found to be governed by the core:wall ratio, drug particle size, media pH and type of disintegrating agent. Dissolution kinetics were studied and evaluated.     

Transbuccal delivery of acyclovir: I. In vitro determination of routes of buccal transport

PURPOSE: To determine the major routes of buccal transport of acyclovir and to examine the effects of pH and permeation enhancer on drug permeation. METHODS: Permeation of acyclovir across porcine buccal mucosa was studied by using side-by-side through diffusion cells at 37 degrees C. The permeability of acyclovir was determined at pH range of 3.3 to 8.8. Permeability of different ionic species was calculated by fitting the permeation of data to a mathematical model. Acyclovir was quantified using HPLC. RESULTS: Higher steady state fluxes were observed at pH 3.3 and 8.8. The partition coefficient (1-octanol/buffer) and the solubility of acyclovir showed the same pH dependent profile as that of drug permeation. In the presence of sodium glycocholate (NaGC) (2-100 mM), the permeability of acyclovir across buccal mucosa was increased 2 to 9 times. This enhancement was independent of pH and reached a plateau above the critical micelle concentration of NaGC. The permeabilities of anionic, cationic, and zwitterionic species were 3.83 X 10-5, 4.33 X 10-5, and 6.24 x 10-6 cm/sec, respectively. CONCLUSIONS: The in vitro permeability of acyclovir across porcine buccal mucosa and the octanol-water partitioning of the drug were pH dependent. A model of the paracellular permeation of the anionic, cationic, and zwitterionic forms of acyclovir is consistent with these data. The paracellular route was the primary route of buccal transport of acyclovir, and the enhancement of transbuccal transport of acyclovir by sodium glycocholate (NaGC) appeared to operate via this paracellular route.     

In vivo evaluation of dosage forms: application of gamma scintigraphy to non-enteral routes of administration

The trend to deliver drugs to defined areas of the body involves sophisticated carriers systems. In addition to the in vitro drug release profile one must be aware of the in vivo behaviour of the dosage form and the drug. Gamma scintigraphy is an elegant way to gain insights of the actual in vivo distribution pattern of dosage forms. This technique relies on the use of radioactive tracers included into the medicament and selected so as to enable an optimum detection by a gamma ray camera. The choice of a convenient label enables the in vivo determination of the targeting of the formulation administered through a large number of routes. The present paper reviews applications of gamma scintigraphy for the evaluation of dosage forms administered by the parenteral, rectal, buccal, nasal, pulmonary, and ophthalmic routes.     

Erosion and controlled release properties of semisolid vesicular phospholipid dispersions

Single adult guinea-pig and rat ventricular cardiac myocytes were used to study the effects of two members of the omega3 class of polyunsaturated fatty acids, docosahexaenoic acid and eicosapentaenoic acid, on the electrical and mechanical activity of cardiac muscle. Docosahexaenoic acid and eicosapentaenoic acid reduced the electrical excitability of both guinea-pig and rat cells in a dose-dependent manner. Both agents produced a dose-dependent negative inotropic response in guinea-pig cells but in the rat cells there was first a dose-dependent positive inotropic effect at low concentrations (< 10 microM) followed by a negative inotropic effect at higher concentrations (> 10 microM). Possible mechanisms by which these agents affect contraction were studied using conventional electrophysiological techniques. The polyunsaturated fatty acids reduced the action potential duration and the plateau potential of the guinea-pig cells in a simple, dose-dependent manner. In contrast, the effect on the rat action potential mirrored the inotropic effect. At low concentrations (< 10 microM) there was a concentration-dependent increase in action potential duration followed by a concentration-dependent decrease at higher concentrations (> 10 microM). Both polyunsaturated fatty acids decreased the fast Na+ current and the L-type Ca2+ current in a concentration-dependent but not use-dependent manner in cells from both species. In the rat cells these agents inhibited the transient outward current resulting in an increase in the duration of the rat action potential. The effects of polyunsaturated fatty acids on the Ca2+, Na+ and K+ currents underlie these changes in the action potentials in guinea-pig and rat heart cells. The effects on the L-type Ca2+ current and action potential duration can also explain both the simple negative inotropic effects of the agents on the guinea-pig cells and the more complex effects on the rat cells. These effects of polyunsaturated fatty acids on membrane currents may account for their anti-arrhythmic properties.     

Oral solid controlled release dosage forms: role of GI-mechanical destructive forces and colonic release in drug absorption under fasted and fed conditions in humans

PURPOSE: This study was undertaken to examine the effects of mechanical destructive forces on drug release from controlled release (CR) dosage forms in vitro and in vivo and their colonic release, using two CR tablets of acetaminophen A and B, showing slower and faster erosion rates, respectively. METHODS: In vitro release rates were determined by several official methods. Tablets were administered to healthy volunteers under fasting and fed conditions. RESULTS: Both tablets showed similar release rates under mild destructive conditions (e.g., paddle method at 10 rpm) but CR-B showed faster release under highly destructive conditions (e.g., rotating basket method at 150 rpm), where the tablet was eroded. The in vivo release from CR-B was faster than from CR-A, possibly because of enhanced erosion. The variable in vivo release from CR-B indicated large inter-subject differences in destructive GI forces. The fastest in vivo release from CR-B among individuals was approximated by the in vitro dissolution determined by destructive methods such as the rotating basket at 150 rpm. The slowest in vivo release from tablets A and B was lower than the dissolution by the paddle method at 10 rpm. The release from both tablets was markedly reduced at 3-4 hrs after dosing irrespective of feeding conditions which can be attributed to release inhibition in the colon. CONCLUSIONS: Effects of GI destructive forces on the tablet erosion and the release inhibition in the colon must be considered in the development of CR dosage forms.     

In vitro cultivation of Trypanosoma acomys: production of insect stages and bloodstream forms

When Trypanosoma acomys bloodstream forms were cultivated at 37 degrees C in Schneider's Drosophila medium supplemented with 20% (v/v) heat-inactivated foetal calf serum (FCS), with Microtus agrestis embryonic fibroblasts in RPMI 1640 medium supplemented with 20% FCS or in Baltz's medium supplemented with 10% FCS, the parasites transformed and largely remained as epimastigotes. Epimastigotes were also usually the commonest stage observed when the parasites were co-cultivated with a mosquito cell line at 27 degrees C. However, if these cultures were initiated with the supernatant suspensions from fibroblast cultures that had been cryopreserved, trypomastigotes, including bloodstream-like forms, were the predominant stage for the first 4 days of culture. It is suggested that the glycerol supplement or the temperature changes stimulated this unusual morphogenesis. At 27 degrees C, T. acomys was incapable of multiplying and died when cultured in fresh Schneider's Drosophila medium supplemented with 20% FCS, but co-cultivation with the mosquito cell lines or cultivation in cell-free supernatants from 1-week-old mosquito cell cultures was successful at this temperature; most of the parasites multiplied as epimastigotes.     

In vitro investigations of drug release and penetration--enhancing effect of ultrasound on transmembrane transport of flufenamic acid

Percutaneous absorption studies are performed in various in vitro models to determine the rate of drug absorption via the skin. We designed an phonophoretic drug delivery system to investigate the influence of ultrasound on transmembrane transport of different drugs. Phonophoresis is defined as the migration of drug molecules, contained in a contact agent, through the skin under the influence of ultrasound. We investigated the absorption of flufenamic acid in a buffer medium in dependence of ultrasound energy and application time. For evaluating membrane penetration of flufenamic acid, the concentration range of buffer solution was measured. Flufenamic acid was determined by using a fluorimetric method. Ultrasound energy was supplied for between 5 and 30 min at a range of intensities (0; 0.3; 0.6; 0.9; 1.2; 1.5 W/cm2). energy levels commonly used for therapeutic purpose. The pronounced effect of ultrasound on the transmembrane absorption of the drug was observed at all ultrasound energy level studied. The time of application was found to play an important role in delivery and transport of drug. Dependent on time, we observed an arise of temperature up to 4.5 degrees. It appears that there was no difference between an intensity of 0.3 and 1.5 W/cm2 and the measured drug concentrations in solution. The highest penetration was observed at an intensity of 1.0 W/cm2 after 30 min. These results were not significantly different from concentration in measurements after 30 min and 0.5 and 1.5 W/cm2. It seems that the arise of drug concentration is caused by effects of temperature and by variation of membrane delivery in dependence of temperature.     

Concentration and purification of mycobacteriophages with polyethylene glycol 6000

Experiments were performed to concentrate and purify mycobacteriophages with polyethylene glycol 6000; 6, 9, and 8 per cent polyethylene glycol 6,000 proved to be optimal concentrations for precipitating phages of Mycobacterium phlei, Mycobacterium smegmatis strain butyricum, and mycobacterium smegmatis strain Rabinowitz, respectively. Preparative polyethylene glycol reverse gradients were constructed for further concentration and purification of the precipitated phages. With the method described, large amounts of crude phage lysates can be concentrated and purified rapidly.     

Radioimmunoassay of gastrin--dextran-coated charcoal method and polyethylene glycol method

Experiments were performed to determine whether the luteotropic effect of decidual tissue (DT) in the rat is attributable to the secretion of progesterone by DT, and the effects of ligation on utero-ovarian connections. No marked differences in progesterone levels in the uterine and jugular vein blood on Days 8 and 10 of pseudopregnancy in DT-bearing rats were voted. Pseudopregnant, DT-bearing rats receiving an injection of 2-Br-alpha-ergocryptine (CB-154) on Day 9 had markedly higher peripheral serum progesterone levels than in similarly treated hysterectomized pseudopregnant rats. The luteotropic action of DT was not altered by ligation and severing of the oviducts and/or the uterine-ovarian vasculature, or by the presence of 1 DT-bearing uterine horn contralateral to 1 remaining ovary. The findings support the notion of a luteotropic action of DT that is most likely exerted via hormonal pathways.     

In vitro release characteristics of bioactive molecules from dextran dialdehyde cross-linked gelatin hydrogel films

Vinyl chloride monomer (VCM) is a human carcinogen. However, the exact mechanism of carcinogenesis remains unclear. VCM may be metabolized by cytochrome P450 2E1 (CYP2E1), aldehyde dehydrogenase 2 (ALDH2) and glutathione S-transferases (GSTs). Thus workers with inherited variant metabolic enzyme activities may have an altered risk of genotoxicity. This study was designed to investigate which risk factors might affect sister chromatid exchange (SCE) frequency in polyvinyl chloride (PVC) workers. Study subjects were 44 male workers from three PVC factories. Questionnaires were administered to obtain detailed histories of cigarette smoking, alcohol consumption, occupations, and medications. SCE frequency in peripheral lymphocytes was determined using a standardized method, and CYP2E1, GSTM1, GSTT1 and ALDH2 genotypes were identified by the polymerase chain reaction (PCR). Analysis revealed that smoking status and exposure to VCM were significantly associated with increased SCE frequency. The presence of ALDH2 1-2/2-2 genotypes was also significantly associated with an elevation of SCE frequency (9. 5 vs. 8.1, p<0.01). However, CYP2E1, GSTM1 or GSTT1 genotypes were not significantly associated with SCE frequency. When various genotypes were considered together, combination of CYP2E1 c1c2/c2c2 with ALDH2 1-2/2-2 showed an additive effect on SCE frequency. Similar results were also found for the combination of smoking with CYP2E1, or smoking with ALDH2. These results suggest that VCM workers with ALDH2 1-2/2-2 genotypes, who also smoke, may have increased risk of DNA damage.     

High-performance liquid chromatographic analysis of isoniazid and its dosage forms

A high-performance liquid chromatographic analysis is described for isoniazid as a drug entity and in its tablet and injectable dosage forms. After incorporation of the drug or dosage form in a solvent mixture and addition of an internal standard, tribenzylamine, an aliquot is chromatographed using a pellicular silica gel medium followed by UV spectrophotometric detection at 254 nm. The response of the chromatographic system was linear over a concentration range corresponding to 20-200% of the labelled amount of isoniazid. Comparison of the results with those obtained by the official USP XIX method indicates similar accuracy and precision. The advantages of the proposed method are its simplicity and rapidity, its potential for automation, and its specificity. The specificity was demonstrated in the presence of potential degradation products of isoniazid, other drugs used with isoniazid in combination dosage forms, and an adduct formed by the reaction of isoniazid with lactose in the tablet.     

In vitro IL-1 beta and TNF-alpha release from THP-1 monocytes in response to metal ions

OBJECTIVES: Previous studies have shown that biomaterials can activate macrophages to produce cytokines and promote an inflammatory response. Although the toxicity of many metal ions has been extensively investigated, little is known about the ability of these ions to alter cytokine release from macrophages. Yet the release of these ions from biomaterials has been well documented. Previous studies indicated that alterations in cytokine release might be expected because metal ions alter protein production in macrophages at sub-toxic concentrations. Thus, the hypothesis of this study was that metal ions can alter the secretion of cytokines from macrophages at sub-toxic concentrations. METHODS: The release of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) from macrophages was investigated when the macrophages were exposed to metal ions, with or without lipopolysaccharide (LPS), a component of dental plaque. Human THP-1 macrophages were exposed to ions of Ag, Au, Cu, Hg, and Ni for 24 h. In half of the cultures, LPS was added for the last 4 h. The release of IL-1 beta and TNF-alpha into the medium was measured using enzyme-linked immunosorbent assays. ANOVA and Tukey multiple comparison intervals were used to compare the various experimental conditions. RESULTS: None of the metal ions elevated the IL-1 beta or TNF-alpha levels after 24 h, but Ni ions significantly elevated the IL-1 beta and TNF-alpha levels after 72 h. With LPS added, Ag, Cu, and Ni significantly amplified the LPS-induced production of IL-1 beta but only Ni amplified the TNF-alpha response. These alterations in cytokine response occurred with metal ion concentrations which have been previously shown to be released from dental alloys in vitro and in vivo. SIGNIFICANCE: It appeared plausible that macrophage-cytokine mediated inflammatory responses may be altered by the presence of some metal ions in tissues, particularly Ni.     

聚醇化合物在熟料-铝酸钠溶液体系中的吸附和分布

通过研究聚醇化合物在熟料-铝酸钠溶液体系中的吸附规律,发现其为饱和吸附,达到吸附饱和的时间为20 min,饱和吸附量为2.21 mg·g-1;聚醇化合物在熟料上的吸附行为属"S"型等温线,用D-R 方程线性拟合发现为多分子物理吸附为主.同时,考察了聚醇化合物在熟料溶出过程中液固分离时的分布走势.结果表明,用含有30～240 mg·L-1聚醇化合物的铝酸钠溶液溶出熟料时,66.67%～77.22%的聚醇化合物吸附在固相上,被赤泥带出系统,残留在铝酸钠溶液中的量较少.     

In vitro release of 5-fluorouracil with cyclic core dendritic polymer

This paper describes the first synthesis of a series of dendritic polymers with a core of 1,4,7,10-tetraazacyclododecane. This core was allowed to react with methyl acrylate through a Michael addition and was then amidated with ethylenediamine. Repeating the two steps led to controlled molecular weight increasing and branching on the molecular level and produced four direction poly(amide-amine) dendrimers. We successfully synthesized dendrimers from generation 0. 5 to generation 5.5. Each generation was analyzed by Fourier- transform infrared (FT-IR) spectroscopy, 1H NMR and elemental analysis. Titrimetry was also used to determine the number of -NH2 of each full generation (2.0, 3.0, 4.0, 5.0). SEC (size exclusion chromatography) was performed to test the purity of G-3.0, G-4.0 and G-5.0. Parts of the outer layer -NH2 groups of the dendrimers generation 4 and generation 5 were acylated by acetic anhydride. The solubility in water of the dendrimer was thus greatly enhanced. The acetylated dendrimers were then reacted with 1-bromoacetyl-5-fluorouracil to form dendrimer-5FU conjugates. Hydrolysis of the conjugates in a phosphate buffer solution (pH 7.4) at 37 degreesC will release free 5FU. Different generation of dendrimer-5FU conjugates exert marking influence on the amount of 5FU released. The dendritic polymer seems to be a promising carrier for the controlled release of antitumor drugs.