Dissolution experiments were conducted on bioapatite at 4°C, 21°C and 38°C and solution pH values between 2 and 8 in a stirred tank reactor. The bioapatite was obtained from modern white-tailed deer (Odocoileus virginianus) scapulae, crushed, and cleaned in 30% hydrogen peroxide to remove organic matter. The average BET specific surface area of the 75-106 and 106-246 μm particles was 255 m2 g-1. During experiments the ratio of Ca:P released became stoichiometric at ca. 1.44. The following dissolution rate law was derived from the experimental results: R = K1(H+)ⁿ+K2 in which R is the dissolution rate (mol bioapatite m-2 s-1) based on the bioapatite stoichiometry, n = 1.01 ± 0.15, k1 = 1.84 x 10-6 ± 1.71 x 10-6 mol m-2 s-1, and k2 = 4.29 x 10-10 ± 1.15 x 10-10 mol m-2 s-1 and H+ is the hydrogen ion activity. From 2 < pH < 4, dissolution rate is dependent on pH and becomes independent of pH from 4 < pH < 8. These results for modern bone may be compared with previous investigations of igneous (FAP) and phosphorite-derived sedimentary carbonate fluorapatites (CFA)(e.g., Guidry and Mackenzie, 2003). At pH = 6, in the pHindependent region, dissolution of the modern bioapatite was ca. 7 times faster than FAP and 100 times faster than CFA. The acid transition pH of the bioapatite (pH = 4) is lower than that for FAP (pH = 6). Bioapatite dissolution rates influence fossil preservation potential, the release rate of nutrients from bone meal fertilizers, the effectiveness of bone as reactive barriers to control pollutants and nuclear waste isolation, and as a feedstock material in CO2 sequestration processes. / Geology

In Sweden, among other countries, a deep multi-barrier geological repository, KBS-3, is planned for the burial of nuclear waste. One of the barriers is identified as the grantic bedrock itself and in this environment chlorite is present at surfaces in fracture zones. This thesis is focused on characterisation of chlorite samples and studies of their dissolution and sorption behaviour, in order to verify chlorites capacity to retard possible radionuclide migration in the case of leaking canisters. Chlorite dissolution of has been studied in the pH interval 2-12, and as expected the dissolution is highest at acidic pH and at most alkaline pH, whereas dissolution is lowest at near neutral pH values. Chemical and physical properties of chlorites clearly influence the dissolution rates, and at steady-state dissolution rates in the interval 10-12 ‑ 10-13 mol g-1 s-1 was observed. Sorption studies were performed since Ni(II) is one of the important activation products in spent nuclear fuel and sorption data on minerals like chlorite are lacking. Ni(II) sorption onto chlorite was studied using batch technique as a function of; pH, concentration of Ni(II), ionic strength and solid concentrations. As expected, the sorption of Ni(II) onto chlorite was pH dependent, but not ionic strength dependent, with a sorption maximum at pH ~ 8, and with a Kd of ~ 103 cm3/g. This confirms that the Ni(II) sorption onto chlorite is primarily acting through surface complexation. The acid-base properties were determined by titrations and described by a non-electrostatical surface complexation model in FITEQL. Further, the sorption results were fit with a 2-pK NEM model and three surface complexes, Chl_OHNi2+, Chl_OHNi(OH)+ and Chl_OHNi(OH)2, gave the best fit using FITEQL. / Sverige är ett av de länder som planerar ett geologiskt slutförvar kallad KBS-3, bestående av ett antal barriärer, för placering utav det använda kärnbränslet. En av dessa barriärer är identifierad som själva berggrunden där det tilltänkta förvaret kommer att byggas och i denna miljö förekommer klorit på granitytor i sprickzoner. Denna doktorsavhandling karakteriserar kloriter och studerar deras upplösnings- och sorptionsbeetende, för att kunna bestämma huruvida kloriter är utav betydelse som naturlig barriär för eventuell radionuklidtransport från det använda kärnbränslet. Upplösning av klorit har undersökts i pH intervallet 2-12 och graden av upplösningen är som förväntat högst vid sura respektive mest basiska pH och lägst där pH är neutralt. Denna studie bekräftar att den kemiska sammansättning och de fysikaliska egenskaper hos kloriterna påverkar upplösningshastigheterna och vid steady‑state har upplösningshastighet bestämts till 10-12 ‑ 10-13 mol g-1 s-1. Sorptionsstudier genomfördes då Ni(II) är en viktig aktiveringsprodukt och data rörande Ni(II) sorption till klorit saknas. Ni(II) sorption till klorit har studerats i; varierande pH, olika initiala Ni(II) koncentrationen, olika jonstyrka och olika fastfas förhållanden där individuella satser i serie har nyttjats. Som förväntat är sorptionen av Ni(II) till klorit pH beroende men inte jonstyrkeberoende och ett sorpions maximum observerades vid pH ~ 8, med ett Kd‑värde på ~ 103 cm3/g. Från detta dras slutsatsen att sorptionen av Ni(II) till klorit sker mestadels genom ytkomplexering. Syra-bas egenskaperna hos kloriterna bestämdes genom titreringar och bekrevs med en icke‑elektrostatisk modell i FITEQL. Vidare har passning av sorptionsresultaten utförts med en 2-pK NEM-modell och tre ytkomplex, Chl_OHNi2+, Chl_OHNi(OH)+ och Chl_OHNi(OH)2, vilket gav den bästa passningen av data med FITEQL. / QC 20100819

Chromium has been widely used in many industrial applications. As a result of chromite ore processing, large amounts of chromite ore processing waste (COPW) material that can be classified as hazardous have been produced and released into the environment. Therefore, knowledge of migration behavior and leaching rates of chromium through waste materials and soils are of primary concern for environmentally sound management of land-disposal hazardous wastes. Hask&ouml / k (1998) experimentally studied leaching rates of total Cr and Cr(VI) using laboratory columns packed with chromium COPW material produced by a sodium chromite plant. Based on the experimental results of Hask&ouml / k (1998), present study aim, through mathematical modeling, to understand the dissolution kinetics of chromium during leaching of COPW material and to investigate the effectiveness of intermittent leaching involving a sequence of batch (dissolution) and leaching (mass flushing) operational modes. Obtained results show that a coupled system of two first order differential equations was able to capture the essential characteristics of leaching behavior of COPW material. In addition, the kinetics of chromium dissolution from COPW appeared to be controlled by the difference between aqueous phase concentration and a saturation concentration, by the mass fraction of dissolvable chromium remaining in the solid phase, and finally by the contribution of a constant dissolution rate manifested as a steady-state tailing behavior. As a result of performed simulations it was seen that intermittent leaching could be 65%and 35% more effective than continuous leaching for total Cr and Cr(VI), respectively.

No description available.

SiO₂ is the most abundant oxide in the earth and its properties, behaviors and interactions are of immense scientific and technological importance. Of particular importance are the interactions of silica with aqueous fluids because these fluids are present in nearly every natural setting. The dissolution of silica and glass by HF plays a very important role in technology and is widely used for the etching of silica and silicate glasses in the glass industry, in the flint industry, in surface micromachining, in etching of glass fibers for near-field optical probes, in the creation of frosted surfaces for decorative applications like frosted glass and cosmetic vials. I performed 57 batch reactor experiments in acidic fluoride solutions to measure the dissolution rate of quartz. Quartz dissolution rate data from other published studies were combined with the rate data from my experiments and these 75 data were analyzed using multiple linear regression to produce an empirical rate law for quartz r_qz = 10^-4.53 (e^-18932/RT) a_HF^1.18 a_H⁺^-0.39 where -5.13 < a_HF < 1.60, -0.28 < pH < 7.18, and 25 < T < 100 °C. Similarly, 97 amorphous silica dissolution rate data from published studies were analyzed using multiple linear regression to develop an empirical rate law for amorphous silica r_as = 10^0.48 (e^-34243/RT) a_HF^1.50 a_H⁺^-0.46 where -5.13 < a_HF < 1.60, -0.28 < pH < 7.18 and 25 < T < 70 °C. An examination of the empirical rate laws suggests that the rate-determining step in the reaction mechanism involves a coordinated attack of HF and H⁺ on the Si-O bond where the H⁺ ion, acting as a Lewis acid, attacks the bridging O atom, while the F end of a HF molecule, acting as a Lewis base, attacks the Si atom. This allows a redistribution of electrons from the Si-O bond to form a O-H and a Si-FH bond, thus "breaking" the Si-O bond. In order to quantify the effect of fluoride on the dissolution of silica, I also performed a series of 81 quartz dissolution and 20 amorphous silica dissolution experiments in batch reactors over a pH range of 0 to 7 to investigate the effect of H⁺ on silica dissolution rates. Between pH 3.5 and 7 silica dissolution rates are independent of pH, but they increase significantly below pH 3.5, so that the dissolution rate of both quartz and amorphous silica at pH 0 is more than an order magnitude faster than the dissolution rate at pH 3.5. I found that the empirical rate law for the dissolution of the"disturbed surface" of quartz in the pH range of 0 to 3.5 is r_qz,pH = 10^-0.23 (e^-59392/RT) a_H⁺^0.28 where 0 < pH < 3.5 and 25 < T < 55°C. The empirical rate law for amorphous silica dissolution in the pH range 0 to 3.5 is r_qz,pH = 10^0.56 (e^-64754/RT) a_H⁺^0.40 where 0 < pH < 3.5 and 25 < T < 55°C. Based on the empirical rate laws I suggest that the rate-determining step in the reaction mechanism involves a coordinated attack of H₃O⁺, acting as a Lewis acid reacts, on a bridging O atom and the O end of a H₂O, acting as a Lewis base, on the Si atom. This results in a redistribution of electrons from the Si-O bridging bond to form two Si-OH surface species. / Ph. D.

A cefalexina é um antibiótico semi-sintético, derivado das cefalosporinas, que exibe amplo espectro de ação, sendo largamente empregado por via oral. No Brasil é comercializado na forma de comprimido revestido, por cinco laboratórios farmacêuticos diferentes. No presente estudo foram avaliados, do ponto de vista biofarmacotécnico, 2 especialidades farmacêuticas (A e B), sob a forma de comprimidos revestidos, contendo 500 mg de cefalexina, disponíveis no mercado nacional. A análise in vitro foi realizada para dois lotes (1 e 2) de cada produto (A e B), através de ensaios físicos e físico-químicos (peso médio, dureza, umidade, teor de cefalexina, teste e perfil de dissolução), com a finalidade de verificar sua conformidade com especificações estabelecidas pelos compêndios oficiais. Estudos de cinética de dissolução foram empregados para avaliação mais precisa quanto às características biofarmacotécnicas in vitro das respectivas formulações. Os estudos de bioequivalência entre os produtos A e B (lote 2) empregaram delineamento experimental cruzado aleatório, em dois períodos, utilizando-se 24 voluntários. Os parâmetros farmacocinéticos empregados nesta avaliação foram obtidos a partir de dados de excreção urinária da cefalexina, sendo sua concentração na urina determinada por cromatografia líquida de alta eficiência, através de metodologia desenvolvida e validada no presente estudo. A bioequivalência entre os produtos foi determinada a partir da análise estatística (ANOVA) dos seguintes dados: quantidade de cefalexina acumulada excretada na urina (Du acumulado); quantidade total de cefalexina excretada na urina no tempo infinito (Du&#8734;); velocidade máxima de excreção urinária ([Ddu/dt]max). Os resultados das análises físicas e físico-químicas indicaram que ambos os produtos estudados apresentaram-se dentro das especificações farmacopéicas. Na avaliação da bioequivalência entre os mesmos, obtiveram-se intervalos de confiança dentro dos limites estabelecidos internacionalmente (80 a 125%), para todos os parâmetros avaliados, comprovando, desta forma, que os produtos A e B são bioequivalentes e, portanto, intercambiáveis. / Cephalexin is a semi-synthetic cephalosporin-derived antibiotic which has an extensive action spectrum, widely used by oral administration. In Brazil, where it is largely marketed, in a tablet coated way, five differents brands can be found. The goal of this study was to evaluate from the biopharmaceutic point of view two cephalexin 500 mg tablet brands (A and B) availables in brazilian market. In order to check its accordance with official pharmacopeial specifications, two lots (1 and 2) of each brand (A and B) were analysed in vitro through physical and physical-chemical assays in vitro tests (average weight, hardness, wet, cephalexin content, dissolution test). Both formulations were also submitted to dissolution kinetics studies to reach an accurate evaluation of their in vitro biopharmaceutics features. The bioequivalence studies between A and B brands (Iot 2) was based on an open randomized two period cross over design with twenty-four male and female healthy volunteers. Pharmacokinetics parameters used in this evaluation were obtained from cephalexin urinary excretion data; to assess urine cephalexin concentrations a high performance liquid chromatographic assay developed and validated in this study was used. Bioequivalence was confirmed using a multiway ANOVA and when the 90 % confidence interval for accumulated cephalexin amount excreted in urine (Du accumulated); total amount of cephalexín excreted in urine (Du&#8734; ) and maximum rate of urinary excretion ([dDu/dt]max), fell within the interval 80-125 %.No discrepancies between both cephalexin brands in physical-chemycal tests were found. Confidence intervals for pharmacokinetics parameters were inside the bioequivalence limits according with the international atandars (80-125%), demonstrating that A and B formulations can be considered bioequivalent and therefore interchangeable.

Formas farmacêuticas de liberação prolongada são especialmente eficazes no controle da hipertensão. A incorporação da furosemida neste tipo de sistema é adicionalmente justificável por se manter as vantagens de um diurético de alça, porém, com efeito menos intenso e mais duradouro, gerando menor desconforto ao paciente crônico e diminuição no número de administrações diárias. Considerando-se a limitada solubilidade da furosemida e as vantagens tecnológicas das ciclodextrinas (CD) e dos comprimidos matriciais hidrofílicos, procuro-se averiguar a influência da &#946;-ciclodextrina (&#946;-CD) ou hidroxipropil-&#946;--ciclodextrina (HP-&#946;-CD), incorporadas às formulações como misturas físicas ou complexadas ao fármaco, no perfil de liberação de comprimidos à base de hidroxipropilmetilcelulose (HPMC), desenvolvidos para modular adequadamente a liberação da furosemida por um período de oito horas. Para tanto, complexos de inclusão foram obtidos por liofilização e caracterizados por análise térmica e espectrofotometria. Comprimidos de 500 mg foram preparados por compressão direta. Mantiveram-se constantes nas formulações: furosemida (10%), HPMC (25%) e agente lubrificante (0,5%), variando-se a concentração do diluente. Avaliou-se, estatisticamente (ANOVA), a influência da adição de &#946;-CD ou HP-&#946;-CD ou lactose, nas eficiências de dissolução (ED) do fármaco. As ED foram calculadas a partir dos perfis de liberação, determinados após submissão dos comprimidos à dissolução, por 8 horas, utilizando-se meio tamponado pH 6,8 ou gradiente de pH. Os mecanismos de liberação foram indiretamente estimados por modelos matemáticos (ordem zero, primeira ordem ou Higuchi). A presença de ciclodextrinas nas formulações, tanto em mistura física quanto complexadas, gerou aumento significativo na velocidade e extensão de liberação da furosemida pelos comprimidos, propiciando cinética de acordo com o modelo de Higuchi. Adicionalmente, a complexação foi capaz de prover uma liberação pH-independente, representando significativa vantagem tecnológica. / Extended release dosage forms are especially effective for hypertension control. Additionally, the advantages of incorporating furosemide in such system is to keep the features of a loop diuretic, however, with a less intense and more lasting effect. Moreover, less discomfort to chronic patients and decreased number of daily administrations could be provided. Considering the limited solubility of furosemide and the technological advantages of cyclodextrins (CD) and hydrophilic matrix tablets, this work evaluates the influence of &#946;-cyclodextrin (&#946;-CD) or hydroxypropyl-&#946;-cyclodextrin (HP-&#946;-CD) on the release profile of hydroxypropylmethylcellulose (HPMC) tablets, aimed to modulate the drug release during an eight hour period The CD were incorporated to the formulations as physical mixtures or complexed with the drug. Thus, inclusion complexes were obtained by freeze-drying and characterized by thermal analysis and spectrophotometry. Tablets of 500 mg were prepared by direct compression. Furosemide (10%), HPMC (25%) and lubricant agent (0,5%) were kept constant in the formulations, varying the diluent concentration. The influence of &#946;-CD or HP-&#946;-CD or lactose addition, on the dissolution efficiency (DE) of the drug, was evaluated statistically by ANOVA. The DE were calculated performing dissolution assays of the tablets for 8 hours, using phosphate buffer at pH 6,8 or pH gradient as milieu. The release mechanisms were indirectly estimated by mathematical models (zero order, first order or Higuchi). The presence of CD in the formulations, even in physical mixture or complexed with the furosemide, demonstrated significant increase of the velocity and extension of the drug release, according to Higuchi\'s model. Nevertheless, the complexation was able to provide a pH-independent release, representing significant technological advantage.

La biodisponibilité d'un composé minéral dépend de sa solubilité in vivo contrôlée par ses propriétés physicochimiques. Cependant, les caractéristiques physicochimiques qui influencent la solubilité et la biodisponibilité des produits utilisés en nutrition animale ne sont pas clairement connues. L'oxyde de zinc (ZnO) est un additif alimentaire couramment utilisé pour satisfaire le besoin en zinc (Zn) des animaux monogastriques. L'objectif de ce projet était de caractériser plusieurs types de ZnO utilisés en nutrition animale pour mieux appréhender leur devenir dans le tractus digestif et leur biodisponibilité. Les différentes sources de ZnO ont des propriétés physicochimiques variables qui influencent leurs cinétiques de dissolution. Une quarantaine d'échantillons de ZnO collectés à travers le monde auprès d'industries de la nutrition animale ont été caractérisés en termes de densité, densité tassée, taille de particules, forme, aire spécifique et cinétiques de dissolution. Une analyse en composantes principales (ACP) a été réalisée pour identifier les caractéristiques les plus pertinentes et classer les échantillons par familles. La nature des paramètres les plus pertinents suggère un mécanisme en deux étapes : dissolution de ZnO en ions Zn2+ à la surface des particules, suivie d'une diffusion vers la solution. La vitesse de dissolution détermine probablement le devenir de ZnO dans le tractus gastro-intestinal et pourrait donc expliquer les différences de performances. Une étude in vivo de produits représentatifs de chaque famille a permis de déterminer les effets des caractéristiques physicochimiques sur la biodisponibilité. Une étude dose-réponse a été réalisée sur des poulets Cobb en croissance (8 à 23 jours d'âge) soumis à un régime de base contenant 23 ppm de zinc ou à 14 régimes supplémentés à raison de 6 ou 12 ppm de ZnO (6 sources différentes) ou de sulfate de Zn. La teneur en zinc du tibia a été utilisée pour estimer la biodisponibilité relative des différentes sources de ZnO par rapport au sulfate de Zn utilisé comme référence (100%). La biodisponibilité des différentes sources variait entre 49% à 160%. La taille des agrégats et la surface spécifique expliquent une large part de la variabilité sur la biodisponibilité. En conclusion, les propriétés physicochimiques de ZnO permettent d'expliquer partiellement la variabilité observée des biodisponibilités du zinc car la complexité des phénomènes physiologiques rend difficile une telle prédiction / The bioavailability of a trace mineral source is related to its in vivo solubility, which in turn is determined by its physicochemical properties. It is still not clear which characteristics are more relevant in affecting solubility and bioavailability of feed compounds. Zinc Oxide (ZnO) is a common feed additive used to supplement zinc in the diet of monogastrics animals. However, different sources have shown different responses in animal bioavailability. This project aims to characterize different feed grade ZnO to better clarify their fate in the digestive tract and explain differences in bioavailability. It was hypothesized that the different sources of feed grade ZnO have various physicochemical properties that lead to distinct dissolution kinetics. Over 40 samples of ZnO have been collected from the feed industry worldwide. Samples were analyzed for density, tapped density, particle size, shape, specific area and dissolution kinetics. A principal component analysis (PCA) was performed to define the most relevant characteristics and categorize the samples into groups. The results showed that there is not only one variable influencing the kinetics of dissolution. It suggests a dissolution mechanism in 2 steps, in which there is the dissolution of ZnO into Zn ions in the surface of the particle, followed by a diffusion to the bulk solution. The speed of dissolution can determine the fate of zinc oxide products in the gastrointestinal tract and therefore may explain the different results in animal performance. Representative products from each family were selected for an in vivo trial to measure the effect of their characteristics on the zinc bioavailability. Male Cobb broilers were used in a dose-response experiment from 8 to 23 days of age. Treatments consisted of a basal diet with 23 ppm of zinc and 14 diets supplemented with 6 or 12 ppm of Zn in the form of different oxides or sulfate. Bone zinc was used to determine zinc bioavailability. The bioavailability of the different sources varied from 49 to 160% considering zinc sulfate as the reference. Aggregate size and specific surface area explain a large part of the variability observed on values of bioavailability. In conclusion, physicochemical properties of ZnO can partly explain the variability observed in terms of Zn biological value. However, the complexity of physiological processes makes difficult the prediction of Zn bioavailability based only on these characteristics

This study focuses on the importance of solute dissolution kinetics for cloud droplet formation. To comprehensively account for the kinetics, a numerical model of the process was developed. Simulations of cloud droplet growth were performed for solute diffusivity, droplet growth rates, dry particle and droplet diameters relevant for ambient conditions. Simulations suggest that high ambient supersaturations and a decrease in solute diffusivity are major contributors to significant decreases in effective solute surface concentrations. The numerical simulations were incorporated into Khler theory to assess the impact of dissolution kinetics on the droplet equilibrium vapor pressure. For CCN composed of partially soluble material, a significant increase was found in the equilibrium supersaturation of CCN.

A cefalexina é um antibiótico semi-sintético, derivado das cefalosporinas, que exibe amplo espectro de ação, sendo largamente empregado por via oral. No Brasil é comercializado na forma de comprimido revestido, por cinco laboratórios farmacêuticos diferentes. No presente estudo foram avaliados, do ponto de vista biofarmacotécnico, 2 especialidades farmacêuticas (A e B), sob a forma de comprimidos revestidos, contendo 500 mg de cefalexina, disponíveis no mercado nacional. A análise in vitro foi realizada para dois lotes (1 e 2) de cada produto (A e B), através de ensaios físicos e físico-químicos (peso médio, dureza, umidade, teor de cefalexina, teste e perfil de dissolução), com a finalidade de verificar sua conformidade com especificações estabelecidas pelos compêndios oficiais. Estudos de cinética de dissolução foram empregados para avaliação mais precisa quanto às características biofarmacotécnicas in vitro das respectivas formulações. Os estudos de bioequivalência entre os produtos A e B (lote 2) empregaram delineamento experimental cruzado aleatório, em dois períodos, utilizando-se 24 voluntários. Os parâmetros farmacocinéticos empregados nesta avaliação foram obtidos a partir de dados de excreção urinária da cefalexina, sendo sua concentração na urina determinada por cromatografia líquida de alta eficiência, através de metodologia desenvolvida e validada no presente estudo. A bioequivalência entre os produtos foi determinada a partir da análise estatística (ANOVA) dos seguintes dados: quantidade de cefalexina acumulada excretada na urina (Du acumulado); quantidade total de cefalexina excretada na urina no tempo infinito (Du&#8734;); velocidade máxima de excreção urinária ([Ddu/dt]max). Os resultados das análises físicas e físico-químicas indicaram que ambos os produtos estudados apresentaram-se dentro das especificações farmacopéicas. Na avaliação da bioequivalência entre os mesmos, obtiveram-se intervalos de confiança dentro dos limites estabelecidos internacionalmente (80 a 125%), para todos os parâmetros avaliados, comprovando, desta forma, que os produtos A e B são bioequivalentes e, portanto, intercambiáveis. / Cephalexin is a semi-synthetic cephalosporin-derived antibiotic which has an extensive action spectrum, widely used by oral administration. In Brazil, where it is largely marketed, in a tablet coated way, five differents brands can be found. The goal of this study was to evaluate from the biopharmaceutic point of view two cephalexin 500 mg tablet brands (A and B) availables in brazilian market. In order to check its accordance with official pharmacopeial specifications, two lots (1 and 2) of each brand (A and B) were analysed in vitro through physical and physical-chemical assays in vitro tests (average weight, hardness, wet, cephalexin content, dissolution test). Both formulations were also submitted to dissolution kinetics studies to reach an accurate evaluation of their in vitro biopharmaceutics features. The bioequivalence studies between A and B brands (Iot 2) was based on an open randomized two period cross over design with twenty-four male and female healthy volunteers. Pharmacokinetics parameters used in this evaluation were obtained from cephalexin urinary excretion data; to assess urine cephalexin concentrations a high performance liquid chromatographic assay developed and validated in this study was used. Bioequivalence was confirmed using a multiway ANOVA and when the 90 % confidence interval for accumulated cephalexin amount excreted in urine (Du accumulated); total amount of cephalexín excreted in urine (Du&#8734; ) and maximum rate of urinary excretion ([dDu/dt]max), fell within the interval 80-125 %.No discrepancies between both cephalexin brands in physical-chemycal tests were found. Confidence intervals for pharmacokinetics parameters were inside the bioequivalence limits according with the international atandars (80-125%), demonstrating that A and B formulations can be considered bioequivalent and therefore interchangeable.