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Erythromycin is a macrolide antibiotic with a spectrum similar to penicillin and is used mainly in the treatment of infections caused by gram-positive organisms. Since its discovery in 1952, erythromycin has achieved wide-spread clinical use. Susceptibility of erythromycin base to inactivation by acid results in decreased availability following exposure to acidic gastric fluids. Formulation of acid resistant dosage forms and the preparation of acid stable chemical derivatives have been attempted to improve absorption and subsequent clinical efficacy . Two of the most commonly used erythromycin derivatives are the stearic acid salt (erythromycin stearate) and the lauryl sulphate salt of the propionyl ester (erythromycin estolate). Although it has been known for many years that erythromycin is susceptible to acid degradation, very few reports on the stability of erythromycin in aqueous solutions appear in the literature. In this study, a high-performance liquid chromatographic system using electrochemical detection was employed for a kinetic study of erythromycin degradation. The effect of varying acid pH on the degradation rate of both erythromycin base and erythromycin stearate, and the effect on the hydrolysis rate of erythromycin estolate is presented. In addition, the effect of temperature on erythromycin degradation was also investigated. Until recently, the majority of pharmacokinetic and bioavailability studies have utilized relatively non-specific microbiological assay procedures. However, in this study a solid phase extraction, followed by the use of a high-performance liquid chromatographic system using electrochemical coulometric detection was employed for the determination of erythromycin in biological fluids. Human volunteers each received enteric coated erythromycin base pellets in capsule dosage form and also film coated erythromycin stearate tablets on separate occasions. Results from the clinical trials revealed the enteric coated erythromycin base pellets had a greater bioavailability than the film coated erythromycin stearate tablets. Computer fitting of data revealed no intra-volunteer variability in elimination rate constants, suggesting differences in serum levels following administration of both dosage forms are due to variation in absorption. Results from the clinical trials were also compared with those obtained from a further trial, during which the same volunteers received erythromycin estolate

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Nitrile biocatalysts are of use in the chemical and pharmaceutical industries for the synthesis of carboxyamides and carboxylic acids. In particular, the application of biocatalysts in the synthesis of single enantiomer compounds is of increasing interest, but requires novel substrate specific highly stereoselective biocatalysts. Addition to the limited toolbox of known nitrile biocatalysts requires definitive characterisation of the biocatalysts through accurate determination of the substrate profiles and quantification of activity. The accurate quantification of stereoisomers chiral mixtures to determine biocatalyst stereoselectivity remains a significant challenge due to the difficulty in separating stereoisomers by physical methods. The known nitrile metabolising organism, Rhodococcus rhodochrous ATCC BAA-870, was grown in a defined medium and harvested, providing whole cell biocatalyst. Additional biomass was disrupted to provide a cell free enzyme extract, which was put through an enzyme purification protocol to provide a solution with specific activity of 351 U.mg⁻¹. A portion of the enzyme was self immobilised using the SphereZyme™ technique. The nitrile hydratase SphereZymes™ (1.2 U.mg⁻¹ initial activity) that were prepared had pH and temperature optima of 6 and 30°C respectively, and could be recovered by repeated washing. The particles retained activity in the presence of the organic solvents isooctane and n-hexadecane saturated with 50 mM phosphate buffer (pH 7.5). An initial analytical system was devised for quantification of the nitrile hydratase activity using the non-chiral substrate benzonitrile. An improved reversed phase high performance liquid chromatography method was developed to separate and quantify benzamide, benzoic acid and benzonitrile. The mobile phase consisting of 0.1% trifluoroacetic acid in H₂O and acetonitrile (70:30, %v/v), at a flow rate of 0.5 ml.ml⁻¹, 25°C, resolved all three analytes in 3.5 minutes on a Waters X-Terra MS C18 3.5μm column. UV detection was carried out at 210 nm. Analytical methods to determine activity and enantioselectivity of the whole cell biocatalyst were subsequently developed for both β-amino nitriles and β-hydroxy nitrile substrates and hydrolysis products.

The aim of this diploma thesis was to develop and validate a high performance liquid chromatography (HPLC) method for purity and stability evaluation of fesoterodine. The HPLC method development was carried out using design of experiments (DOE), which allows to find optimal separation conditions within small number of experimental analysis. Design was done by using L18 linear model. Chromatographic system of the developed method consisted of a C8 stationary phase (SF) XBridge BEH - C8 (100 x 4.6 mm, 2.5 µm), a binary mobile phase (MF) consisting of 10mM borate buffer pH 9.2 and MeOH in various ratios according to the gradient program. Flow rate was 0.7 ml/min, column temperature 35 řC and a diode-array detector (DAD) was applied for the detection at 227 nm. Analysis time was 22 min. The optimized method was validated and the forced degradation study was performed. Studied effects were: the effect of elevated temperature (60 řC), humidity (10 and 75% relative humidity), acidic and basic conditions, oxidation and light. Peak purity of fesoterodine was evaluated for all experiments of forced degradation study. Additionally, the sensitivity of the active substance to hydrolysis was determined within the pH range of 2-10.

Background: Moxifloxacin is a new fourth-generation 8-methoxy fluoroquinolone developed primarily for the treatment of community-acquired pneumonia and upper respiratory tract infections. The aim of the study was to investigate the plasma pharmacokinetics characteristic of moxifloxacin in calves, after intravenous, intramuscular and subcutaneous administration of a single dose. Meanwhile, plasma protein binding and bioavailability of moxifloxacin were also estimated. Methods: Plasma concentrations of moxifloxacin were measured using a modified HPLC method, and the extent of plasma protein binding was determined in vitro using ultrafiltration. Results: Following intravenous administration, the half life of elimination, the volume of distribution at steady state and the area under the curve were 3.29 h, 0.94 l/kg and 24.72 μg·h/ml, respectively. After intramuscular and subcutaneous administration of moxifloxacin at the same dose, the peak plasma concentrations were 2.41 and 2.20 μg/ml and were obtained at 1.54 and 1.59 h, respectively. The systemic bioavailabilities were 87.19 and 75.94%, respectively. The in vitro plasma protein binding of moxifloxacin in plasma of calves was 27%. Conclusion: A high peak plasma concentration, area under the curve, rapid absorption and bioavailability following intramuscular and subcutaneous administration characterize the pharmacokinetics of moxifloxacin in calves.

Organochlorines are ubiquitous pollutants of the marine environment. These lipid-soluble and highly persistent compounds are found in detectable amounts in almost all marine organisms, and accumulate in the lipid tissues of marine animals. This bioaccumulation leads to biomagnification of these contaminants in higher trophic levels. Near the top of many marine food chains are found the marine mammals, in whose blubber high levels of organochlorine residues have been measured. The most commonly occurring of these pollutants in these animals are the polychlorinated biphenyls (PCB's) and p,p-DDE, a metabolite of the insecticide DDT. These substances have been shown to cause disruptions in the endocrine, immune, and reproductive systems, and are passed from mother to offspring through the placenta and by lactation. Presence and levels of residues of these compounds are, therefore, monitored in marine mammals to provide an indication of the health of a given population and the environment in which they live. Such monitoring is generally done with the use of gas chromatography (GC). High performance liquid chromatography (HPLC) is little used due to the poor ultraviolet (UV) absorbance properties of many of the organochlorines. PCB's and p,p-DDE do absorb UV well enough at concentrations usually encountered in marine mammals to permit the use of HPLC for detection and semiquantification of these substances. A method was developed for the screening of blubber of marine mammals for total PCB's and p,p-DDE using HPLC. The method was applied to the detection and approximation of levels of these two organochlorines in marine mammals from the east and west coasts of the United States. Geographical differences in levels of the two pollutants were found, indicating differences in primary feeding ranges. Evidence of placental transfer of these two organochlorines was also found. Especially high residue levels were found in the blubber of stranded killer whales, indicating that acquisition of high pollutant burdens is still a problem in these top predators. It was concluded that HPLC can be used to screen marine mammals for PCB's and p,p-DDE, and that residue levels determined can be useful in investigating species range, pollutant burdens, and health of populations.

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