The current study assessed the bioavailability of slower desorbing sediment-associated permethrin by manipulating the desorption properties of two sediments with an absorbent, Amberlite XAD-4. The two sediments differed in OC content and the size of the rapidly desorbing pool and rate constants were smaller in the higher OC sediment. Manipulation decreased desorption rate constants in the treated sediments compared to the untreated sediments. Greater activity of permethrin in the pore water was observed in the lower OC sediment compared to the higher OC sediment, and in the untreated sediment compared to the treated sediment. The higher occurrence of permethrin in the pore water was attributable to the larger pool of rapidly desorbing compound. Based on BAF calculations, bioaccumulation of permethrin by all three species was lower in the higher OC sediment compared to the lower OC sediment, and bioaccumulation was also lower in the treated sediments compared to the untreated sediments for Lumbriculus variegatus and Hexagenia sp., suggesting that bioavailability was reduced for those organisms. Desorption rate constants suggest that a reduction in desorption was the cause. However, bioaccumulation was not reduced for Hyalella azteca whose body residues were not significantly different between the two treatments and so BAF values did not reflect a reduction in bioavailability. The results for H. azteca do not match with typical observations, where bioaccumulation decreases with decreased desorption; suggesting that an important exposure pathway for those organisms was not influenced heavily by the sediment desorption properties. Therefore, the role of ingestion was investigated as a route of uptake. Synthetic digestive fluid extractions increased desorption compared to water; indicating that ingestion increased desorption, and thus bioavailability of sediment-associated permethrin. Estimated pore water and feeding contributions suggested that more than one route of exposure contributed to the uptake of permethrin, and that neither exposure route was responsible for uptake alone. The contribution from feeding was estimated to be greater than the contribution from pore water for WBS sediment for all three species, and for the treated sediments compared to the untreated sediments; indicating that as desorption decreases, the role of ingestion in uptake increases. Therefore, pore water may be more important to the contribution of uptake for faster desorbing compound, and ingestion may be more important to the contribution of uptake for slower desorbing compound.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O perfil farmacocinÃtico de duas diferentes formulaÃÃes de norfloxacino - comprimido revestido de 400 mg - como formulaÃÃo teste versus a formulaÃÃo referÃncia, Floxacin comprimido revestido de 400 mg (Merck Sharp & Dohme) foi avaliado em 32 voluntÃrios saudÃveis de ambos os sexos. A pesquisa consistiu de um estudo aberto, aleatorizado, cruzado, com 2 tratamentos, 2 perÃodos (duas sequÃncias) com intervalo mÃnimo de sete dias entre os internamentos. Amostras de sangue foram coletas em intervalos regulares para construÃÃo das curvas de concentraÃÃo plasmÃtica versus tempo. As concentraÃÃes de norfloxacino foram analisadas por Cromatografia LÃquida de Alta EficiÃncia acoplada à Espectrometria de Massa (LC-MS/MS). A mÃdia geomÃtrica do Norfloxacino teste/Norfloxacino referÃncia e o intervalo de confianÃa (IC) de 90% para Cmax e ASCo-t Ãltimo foram 103,9020% (89,5247-120,5881%) e 99,3030% (87,8186-112,2892%) respectivamente. Considerando que as formulaÃÃes estudadas apresentaram razÃo entre as mÃdias de Cmax e ASC0-tÃltimo entre 80 e 125%, e considerando um intervalo de confianÃa de 90% como proposto pelo Food and Drug Administration e ANVISA, conclui-se que as duas formulaÃÃes de norfloxacino apresentaram biodisponibilidades semelhantes tanto na taxa quanto na extensÃo de absorÃÃo. / The pharmacokinetic profile of two different formulations of Norfloxacin tablets - 400 mg; as test formulation versus FloxacinÂ, Norfloxacin reference formulation (- 400 mg; Merck Sharp & Dohme) was evaluated in 32 healthy volunteers of both sexes. The research was consisted of an open, randomized, crossover study, designed with two treatments, two periods (two sequences) with a minimum interval of seven days (washout) between the admissions. Blood samples were collected at regular intervals to construct the plasma concentration versus time curves. The concentrations of Norfloxacin were analyzed by High Performance Liquid Chromatography coupled to Mass Spectrometry (HPLC-MS/MS). The geometric mean of test Norfloxacin / reference Norfloxacin and confidence interval (CI) of 90% for Cmax and AUC0-t last were 103.9020% (89.5247 to 120.5881%) and 99.3030% (87.8186 - 112.2892%) respectively. Whereas the studied formulations showed the ratio between the mean Cmax and AUC0-t last between 80 and 125%, considering a confidence interval of 90%, as proposed by the Food and Drug Administration and ANVISA, it appears that the two formulations of Norfloxacin showed similar bioavailability in rate and in extent of absorption.

Erythromycin, a macrolide antibiotic isolated from Streptomyces erythreus, was first introduced into clinical medicine in 1952. It is active against most gram-positive bacteria, some gram-negative bacteria and is currently the agent of choice for Legionella pneumophila. Erythromycin is an acid-labile compound rapidly degrading in acidic solutions such as the acid environment of the stomach. As such, erythromycin absorption following oral administration of solid dosage forms is relatively poor. Accordingly there have been various approaches used to protect the drug against gastric inactivation. These precautions include enteric-coating of tablets, capsules or pellets of erythromycin base, the synthesis of acid stable 2' esters of erythromycin (ethylsuccinate and propionate) and salts of these esters (erythromycin estolate), and more recently, the synthesis of a range of new acid-stable, semi-synthetic macrolide antibiotics. The 2' esters are antimicrobially inactive or much less active than the parent compound and must be converted to the free erythromycin base in vivo in order to exhibit antibacterial activity. Intrinsic dissolution rates determined on raw material can provide extremely useful information relating to the gastrointestinal absorption of drugs from solid dosage forms. The large inter- and intrasubject variability associated with erythromycin base has, to date, mainly been attributed to gastric acid inactivation of the drug. However, changes in duodenal pH resulting in altered solubility and intrinsic dissolution rates may account for the observed variability. Thus, the intrinsic dissolution rates of erythromycin base at pH 6.0, 6.5, 7.0, 7.5 and 8.0 were compared in order to investigate the possible effects of pH changes which may occur in the duodenal contents, on the in vivo dissolution and subsequent absorption of this compound. The standard intrinsic dissolution rate test procedure employing a rotating disc of pure erythromycin base powder which only allows for dissolution from a constant surface area, was adapted and the drug quantitatively determined by reversed phase high performance liquid chromatography (HPLC) using ultraviolet detection. Results of intrinsic dissolution studies at both 22°C and 37°C indicate that the solubility, and therefore the rate of dissolution of erythromycin base is pH dependent, being more soluble at pH 6.0 than pH 8.0 (an approximate 800 times and 1000 times reduction in the amount dissolved after 30 minutes, at 22°C and 37°C respectively, when the pH of the medium was increased from 6 to 8). Although the stability of erythromycin and its ester derivatives in aqueous acidic solutions has been well documented, very little has been reported on the compound's stability in organic solvents. Methanol is recommended by official drug compendia (U.S.P. and B.P.) for use in erythromycin identification tests as well as in the sample preparation steps during assay procedures. Thus, the effect of methanol and acetonitrile, organic solvents of similar polarities and densities, on the stability of erythromycin base, erythromycin ethylsuccinate, propionyl erythromycin and erythromycin estolate at room temperature (22°C ± 0.5°C), using HPLC with electrochemical detection, was investigated. Erythromycin base is relatively stable in both methanol and acetonitrile, remaining intact for over 168 hours in acetonitrile and showing less than 5% degradation in methanol over the same period. Erythromycin ethylsuccinate in acetonitrile shows less than 5% degradation over 168 hours whereas in methanol, rapid hydrolysis occurs resulting in almost total conversion to base within 40 hours. Approximately 87% of erythromycin propionyl ester remained intact after 168 hours in acetonitrile whilst methanol caused rapid hydrolysis to erythromycin base (35% remaining after 28 hours). Erythromycin estolate appeared to be unstable in both acetonitrile and methanol. In acetonitrile, only 13% of the estolate remained intact after 168 hours, whereas in methanol, the reaction was much more rapid with 35% of the estolate remaining after 28 hours. The use of methanol as a solvent for erythromycin estolate reference standards is thus contraindicated. A number of conflicting reports on the half- life as well as the body compartment model that best describes erythromycin base serum concentration-time profiles (lBCM generally used to describe orally administered erythromycin, whilst a 2BCM has been used to describe erythromycin administered intravenously), appear in the literature. These differences may be largely attributed to the sampling period (between 6 and 12 hours) used in the repective studies. The objective of this study was to determine the body compartment model that best describes erythromycin base serum concentration-time curves by increasing the sampling time to 24 hours. In addition, the effect of chronic dosing of erythromycin on erythromycin pharmacokinetics, in the same group of subjects, was investigated. The single and multiple oral dose pharmacokinetics of erythromycin enteric coated base pellets within a gelatin capsule (250mg), were studied in 6 healthy, normal volunteers (19.5 ± 0.76 years, 71.5 ± 8.18 kg, 180.33 ± 5.99 cm). Furthermore, steady state concentrations were predicted using the pharmacokinetic parameters obtained from the single dose study, and compared with those obtained in the multiple dose study. Plasma concentrations were determined using a sensitive high-performance liquid chromatographic method with electrochemical detection. For the single dose study, after a tlag of 2.5 ± 0.71 hr, Cmax (1.12 ± 0.47 μ/ml) was reached at a tmax of 4.08 ± 0.93 hr post dose, with serum concentrations ranging from 0.31 - 1.62 μ/ml. The half-life was found to be 5.42 ± 1.31 hr. On multiple dosing (250mg six hourly), serum concentrations for the fifth, ninth and thirteenth dosing intervals ranged from 0.67 - 2.92 μ/ml, 1.69 - 3.65 μ/ml and 0.61 - 3.01 μ/ml, occurring at 3.75 ± 0.69 hr, 3.17 ± 1.03 hr and 3.17 ± 1.03 hr post dose with a Cmax of 1.89 ± 0.68 μ/ml, 2.35 ± 0.70 μ/ml and 1.94 ± 0.74 μ/ml, respectively. The area under the serum concentration- time curve for the single dose study (AUC₀₋∞) was 4.67 ± 0.88 hr.μ/ml, whilst the AUC₀₋τ. for the fifth, ninth and thirteenth dosing intervals of the multiple dose study were 5.77 ± 1.76 hr.μ/ml, 6.46 ± 1.33 hr.μ/ml and 5.97 ± 2.36 hr.μ/ml respectively, indicating an approximately 33% increase in AUC on chronic dosing of erythromycin. The observed increase in AUC may be a result of increased bioavailability or a decrease in clearance on chronic dosing.

The investigations detailed herein have been conducted to address various aspects of the biopharmaceutics and pharmacokinetics of josamycin which to-date, have received little or no attention in the literature. Areas of investigation have included the selective determination of josamycin in serum and urine samples, the stability of josamycin in stored biological samples, intrinsic dissolution rates, solubility, acid and alkali stability and bioavailability and pharmacokinetics after dosing with a solution, powder and tablets. High performance liquid chromatography (HPLC) was used as the main analytical tool throughout these studies and proved to be highly versatile for the determination of josamycin in a number of different media. HPLC analysis afforded simple yet accurate determination of josamycin in samples from dissolution, solubility, tablet content and stability studies. Furthermore, the specificity afforded by HPLC was particularly useful for the separation of josamycin from degradation products formed in acid and alkali media. Since metabolites of josamycin are microbiologically active, microbiological assays do not determine the concentration solely of josamycin. An analytical method capable of the selective determination of josamycin in serum and urine samples is therefore required for the procurement of reliable bioavailability and pharmacokinetic data. HPLC affords this selectivity and a method for the selective determination of josamycin in serum and urine was successfully developed. The assay was simple yet precise, accurate and sensitive. Furthermore, it was well suited to the determination of josamycin in a large number of biological samples. Its success was largely due to the use of a solid phase extraction step using C₁₈ extraction columns, with a highly specific wash sequence followed by a phase separation step after elution from the extraction column. Chromatography was performed on a C₁₈ reversed-phase analytical column with UV detection of josamycin and internal standard at 231 nm and at 204 nm respectively using a programmable multi-wavelength detector. Only slight modification of the assay described should enable the selective determination of the metabolites of josamycin. This assay, therefore, lays the groundwork for future investigations into the pharmacokinetics of these metabolites. The re-usability of extraction columns was assessed in an attempt to reduce the cost of sample analysis. It was found that extraction columns could be used twice for the extraction of serum samples and up to four times for the extraction of urine samples. The difference between the re-usability of extraction columns for serum and urine samples was ascribed to various differences in the composition of the sample matrix. The stability of josamycin in stored serum and urine samples was also assessed.

Nanoscale zero-valent iron (NZVI) particles and iron cross-linked alginate (FCA) beads were successfully used for the first time for phosphate removal and recovery. NZVI was successfully used for phosphate removal and recovery. Batch studies indicated a removal of ~96 to 100% phosphate in 30 min (1, 5, and 10 mg PO43--P/L with 400 mg NZVI/L). Phosphate removal efficiency by NZVI was 13.9 times higher compared to Microscale ZVI (MZVI) particles. The successful rapid removal of phosphate by NZVI from aqueous solution is expected to have great ramification for cleaning up nutrient rich waters. The presence of sulfate, nitrate, and humic substances and the change in ionic strength in the water marginally affected phosphate removal by NZVI. A maximum phosphate recovery of ~78% was achieved in 30 min at pH 12. Novel iron cross-linked alginate (FCA) beads were synthesized, characterized and used for phosphate removal. The beads removed up to 37-100% phosphate from aqueous solution in 24 h. Freundlich isotherm was found to most closely fit with experimental data and the maximum adsorption capacity was found to be 14.77 mg/g of dry beads. The presence of chloride, bicarbonate, sulfate, nitrate, and natural organic matters in aqueous solution did not interfere in phosphate removal by FCA beads. The phosphate removal efficacy FCA beads was not affected due to change in pH (4-9). Nanosacle zero-valent iron (NZVI) and iron cross-linked alginate beads were also tested for phosphate removal using actual wastewater treatment plant effluent and animal feedlot runoff. The FCA beads could remove ~63% and ~77% phosphate from wastewater and feedlot runoff in 15 min, respectively. Bioavailability of phosphate was examined using algae and higher plants. Phosphate and iron bioavailability of the NZVI sorbed phosphate was examined by supplying spent particles (NZVI with sorbed phosphate) to Tyee Spinach (Spinacia oleracea) and algae (Selenastrum capricornutum). Results revealed that the phosphate was bioavailable for both the algae and spinach. Also, presence of the nanoparticles enhanced the algae growth and plant growth and increases in biomass and plant length were observed. Iron (from spent NZVI) was found to be bioavailable for spinach.

Mercury (Hg) is a global pollutant and potent neurotoxin that is detrimental to the environment and human health. (MeHg). All forms of Hg are toxic, but methylmercury (MeHg) can biomagnify through food webs and become concentrated in food staples such as fish and rice, creating an exposure risk to people. The conversion of Hg to MeHg is mediated by anaerobic microbes, particularly sulfate and iron-reducing bacteria and methanogenic archaea. However, Hg methylation is an intracellular process, and MeHg production is dependent on the bioavailability of inorganic Hg to these microbes. One outstanding knowledge gap in understanding Hg methylation is the nature of bioavailability of inorganic divalent Hg (HgII). Much research has gone into developing a framework describing how microbes take up Hg for methylation. Still, the framework describing Hg bioavailability processes is not fully developed. The overall objective of my thesis is to address these mechanisms governing HgII bioavailability to anaerobic microbes. HgII bioavailability is determined by its speciation; these are all the different forms and compounds of HgII. To address the bioavailability of various HgII species, I used microbial Hg-biosensors. Hg-biosensors are bacterial cells that emit a quantifiable signal when HgII enters them and let me observe HgII bioavailability in real-time. The biosensors I developed are the first Hg-biosensors that function without oxygen and let me explore HgII species and their bioavailability under conditions conducive to methylation. HgII speciation is spatially and temporally dynamic moving from oxic to anoxic conditions and under various biogeochemical controls. I follow HgII speciation and bioavailability in my thesis as it transgresses through these conditions. Understanding HgII bioavailability to complex microbial communities across redox gradients and through dynamic ligand interactions is a missing key component to understanding and predicting MeHg formation. My results show how altering HgII speciation can identify novel bioavailability pathways or make it completely inaccessible. My results highlight how microbes can control HgII bioavailability and the importance of microbial community structure on metal acquisition. First, I resolve pathways for charged inorganic HgII species through the cell membrane and demonstrate novel pathways for previously unconsidered charged species. Using dissolved organic matter (DOM) originating from various algal species, I show how algae can uniquely control HgII bioavailability to other organisms. I demonstrate how DOM has emergent properties that can control HgII bioavailability. Next, I investigated the compounds microbes use to scavenge metals such as iron and copper. I reveal how they could inadvertently interact with HgII and form new bioavailability pathways. Lastly, I demonstrate how the diffusion of biogenic hydrogen sulfide from an isolated system can make an otherwise non-bioavailable HgII species rapidly available for microbial uptake. Overall, my thesis expands the framework describing HgII bioavailability to microbes and potential drivers of Hg methylation in the environment.

No description available.

The dissolution profiles of eight lots of paracetamol tablets representing seven different tablet brands are determined in a USP rotating basket assembly and a stationary basket-rotating paddle apparatus. The in vitro data are expressed in terms of dissolution parameters and inter-tablet differences are assessed statistically using analysis of variance (ANOVA) and the Scheffe test. Highly significant differences are observed between a number of the tablets at the 95% confidence level. Representative tablets from the dissolution rate study and a control dose of paracetamol dissolved in water are subsequently investigated in a 4 x 4 latin square design bioavailability trial. Serum and urine samples are collected and assayed for paracetamol alone (serum) and together with its metabolites (urine) by means of high pressure liquid chromatography. The in vivo data are expressed in terms of bioavailability parameters and differences between the test doses are assessed by means of ANOVA. No significant differences are observed between the dosage forms at the 95% confidence level.

No description available.

Under conditions of phosphate starvation Escherichia coli can solubilize mineral phosphates, such as dicalcium phosphate, to orthophosphate which is then available for uptake and cell growth processes. lac operon fusions were created using MudX phage, and mineral phosphate solubilization (Mps) mutants were identified by their inability to solubilize mineral phosphate on plate assays. Four of these mutants have been mapped on the E. coli chromosome via Hfr matings and are located at two distinct portions of the chromosome; between 23 and 50 minutes and between 60 and 90 minutes. One mutant in each region has phosphate starvation inducible (Psi) promoter activity. One of these mutants (DB1047) was mapped to between 69 and 75 minutes via F' matings, and fine structure mapped to 75 minutes by hybridization with λ clones from a genomic library of Escherichia coli. DB1047 was characterized more closely and found to exhibit pleiotropy with regard to several membrane related traits. Evidence that this is a single insertional event comes from the simultaneous loss of all traits tested in spontaneous revertants. Additionally, a Tn5 mutant was identified that was identical for these traits. Our data strongly support the hypothesis that the mutation carried by DB1047 is in the ompB locus. This locus consists of the two regulatory cotranscribed genes, ompR and envZ. This locus is involved in regulation of transcription of the ompC and ompF genes for outer membrane porin proteins, and is located at 75 minutes on the chromosome as is the DB1047 mutation. DB1047 lacks the outer membrane porin OmpF, a phenotype previously attributed to envZ mutants. However, the ompR321 mutant resembles DB1047 in reduced ability to solubilize phosphate. Additional supporting evidence for the DB1047 mutation belonging to the ompB locus comes from the most recent report that mutations in the himA gene, which I found to be deficient in the ability to solubilize phosphate, also affect the regulation of production of the outer membrane porin OmpF.