Biopharmaceutics and pharmacokinetics of the macrolide antibiotic Josamycin
- Authors: Skinner, Michael Fredrick
- Date: 1992
- Subjects: Antibiotics -- Bioavailability , Antibiotics -- Pharmacokinetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3791 , http://hdl.handle.net/10962/d1003269
- Description: 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.
- Full Text:
- Date Issued: 1992
- Authors: Skinner, Michael Fredrick
- Date: 1992
- Subjects: Antibiotics -- Bioavailability , Antibiotics -- Pharmacokinetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3791 , http://hdl.handle.net/10962/d1003269
- Description: 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.
- Full Text:
- Date Issued: 1992
Neuropharmacological interactions in the rat pineal gland a study of antidepressant drugs
- Authors: Banoo, Shabir
- Date: 1992
- Subjects: Antidepressants -- Research , Pineal gland -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3744 , http://hdl.handle.net/10962/d1003222 , Antidepressants -- Research , Pineal gland -- Research
- Description: The rat pineal gland provides a convenient model for investigating nor adrenergic receptor neurotransmission and the effects of various drugs on these processes in health and disease. The effect of a variety of antidepressant drugs on rat pineal gland function following acute and chronic administration is described. Antidepressants from several different classes increase melatonin synthesis in rat pineal gland cultures when administered acutely. This effect appears to be mediated by noradrenaline acting on postsynaptic β-adrenoceptors. Activation of these receptors, in turn, activates the enzyme serotonin N-acetyltransferase via a cyclic adenosine monophosphate (cAMP) second messenger system. Serotonin N-acetyltransferase catalyses the rate-limiting conversion of serotonin to melatonin. Blockade of postsynaptic β-adrenoceptors prevents the antidepressant-induced increase in melatonin synthesis. The possibility that atypical antidepressants as well as those that selectively inhibit serotonin reuptake may increase melatonin synthesis via a β-adrenoceptor mechanism is discussed. In contrast, however, antidepressants from different classes have variable effects on rat pineal gland function when administered repeatedly. Chronic treatment with antidepressants that selectively inhibit noradrenaline reuptake appear to down-regulate the β-adrenoceptor system while, simultaneously, increasing melatonin output. Atypical antidepressants and those that selectively inhibit serotonin reuptake appear to be without these effects when administered repeatedly. The pineal gland of normal rats may therefore not represent a suitable model for evaluating the biochemical effects of chronic antidepressant treatment. In an attempt to investigatc pineal gland function in rats with "model depression" , antidepressants were administered to chronically reserpinized rats. Treatment with reserpine produced an increase in the density of pineal β-adrenoceptors. In addition, pineal cyclic AMP accumulation and N-acetyltransferase activity were increased in reserpinized rats following exogenous catecholamine stimulation. Reserpine, by depleting intraneuronal catecholamine stores, prevented the nocturnal induction of N-acetyltransferase activity and reduced the synthesis of melatonin in pineal gland cultures. A variety of antidepressants, irrespective of their acute pharmacological actions, reversed these effects when administered chronically to resepinized rats. Acute antidepressant administration was not associated with a reversal of the reserpine-induced effects. These findings provide additional evidence against the hypothesis that antidepressant drugs act by reducing noradrenergic neurotransmission and casts doubt on the importance of β-adrenoceptor down-regulation in the mechanism of antidepressant action. The possibility that the pineal gland of the reserpinized rat may represent an alternative model for evaluating antidepressant therapies is discussed.
- Full Text:
- Date Issued: 1992
- Authors: Banoo, Shabir
- Date: 1992
- Subjects: Antidepressants -- Research , Pineal gland -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3744 , http://hdl.handle.net/10962/d1003222 , Antidepressants -- Research , Pineal gland -- Research
- Description: The rat pineal gland provides a convenient model for investigating nor adrenergic receptor neurotransmission and the effects of various drugs on these processes in health and disease. The effect of a variety of antidepressant drugs on rat pineal gland function following acute and chronic administration is described. Antidepressants from several different classes increase melatonin synthesis in rat pineal gland cultures when administered acutely. This effect appears to be mediated by noradrenaline acting on postsynaptic β-adrenoceptors. Activation of these receptors, in turn, activates the enzyme serotonin N-acetyltransferase via a cyclic adenosine monophosphate (cAMP) second messenger system. Serotonin N-acetyltransferase catalyses the rate-limiting conversion of serotonin to melatonin. Blockade of postsynaptic β-adrenoceptors prevents the antidepressant-induced increase in melatonin synthesis. The possibility that atypical antidepressants as well as those that selectively inhibit serotonin reuptake may increase melatonin synthesis via a β-adrenoceptor mechanism is discussed. In contrast, however, antidepressants from different classes have variable effects on rat pineal gland function when administered repeatedly. Chronic treatment with antidepressants that selectively inhibit noradrenaline reuptake appear to down-regulate the β-adrenoceptor system while, simultaneously, increasing melatonin output. Atypical antidepressants and those that selectively inhibit serotonin reuptake appear to be without these effects when administered repeatedly. The pineal gland of normal rats may therefore not represent a suitable model for evaluating the biochemical effects of chronic antidepressant treatment. In an attempt to investigatc pineal gland function in rats with "model depression" , antidepressants were administered to chronically reserpinized rats. Treatment with reserpine produced an increase in the density of pineal β-adrenoceptors. In addition, pineal cyclic AMP accumulation and N-acetyltransferase activity were increased in reserpinized rats following exogenous catecholamine stimulation. Reserpine, by depleting intraneuronal catecholamine stores, prevented the nocturnal induction of N-acetyltransferase activity and reduced the synthesis of melatonin in pineal gland cultures. A variety of antidepressants, irrespective of their acute pharmacological actions, reversed these effects when administered chronically to resepinized rats. Acute antidepressant administration was not associated with a reversal of the reserpine-induced effects. These findings provide additional evidence against the hypothesis that antidepressant drugs act by reducing noradrenergic neurotransmission and casts doubt on the importance of β-adrenoceptor down-regulation in the mechanism of antidepressant action. The possibility that the pineal gland of the reserpinized rat may represent an alternative model for evaluating antidepressant therapies is discussed.
- Full Text:
- Date Issued: 1992
Structural analysis of some Escherichia coli capsular antigens
- Authors: Hackland, Peter Linton
- Date: 1992
- Subjects: Antigens , Enterobacteriaceae , Escherichia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3758 , http://hdl.handle.net/10962/d1003236 , Antigens , Enterobacteriaceae , Escherichia
- Description: The work presented in this thesis forms part of a collaborative effort to determine the chemical structures of the surface antigens of bacteria which belong to the Enterobacteriaceae. These antigens are largely polysaccharides and occur as lipopolysaccharides and capsular polysaccharides which give rise to the somatic or 0 antigens and the capsular or K antigens, respectively. In recent years interest has mostly been focused on the extracellular polysaccharide antigens expressed by the genus Escherichia coli because of the effect they exert on normal immunological processes and their structural relatedness to the surface antigens of other more pathogenic bacteria. Therefore the molecular structures of the capsular polysaccharides (Kantigens)produced by E. coli 09:K35(AI04a) and 09:K38(A262a) have been determined by novel enzymic, chemical and spectroscopic procedures. These investigations show that the structures of these polysaccharides can be determined by a combination of chemical and spectroscopic procedures , or almost entirely by n.m.r. spectroscopy alone. The in vitro bacteriophage mediated depolymerisation of the native E. coli K35 polysaccharide demonstrates the value of this method for the isolation of oligosaccharides representing the repeating- unit and multiples thereof. Finally E. coli K37 and K38 capsular polysaccharides were used as model compounds for the evaluation of partial and selective reductive cleavage as methods of generating oligosaccharide for further structural analysis. The products of these reactions were analysed largely by a combination of mass spectrometric procedures.
- Full Text:
- Date Issued: 1992
- Authors: Hackland, Peter Linton
- Date: 1992
- Subjects: Antigens , Enterobacteriaceae , Escherichia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3758 , http://hdl.handle.net/10962/d1003236 , Antigens , Enterobacteriaceae , Escherichia
- Description: The work presented in this thesis forms part of a collaborative effort to determine the chemical structures of the surface antigens of bacteria which belong to the Enterobacteriaceae. These antigens are largely polysaccharides and occur as lipopolysaccharides and capsular polysaccharides which give rise to the somatic or 0 antigens and the capsular or K antigens, respectively. In recent years interest has mostly been focused on the extracellular polysaccharide antigens expressed by the genus Escherichia coli because of the effect they exert on normal immunological processes and their structural relatedness to the surface antigens of other more pathogenic bacteria. Therefore the molecular structures of the capsular polysaccharides (Kantigens)produced by E. coli 09:K35(AI04a) and 09:K38(A262a) have been determined by novel enzymic, chemical and spectroscopic procedures. These investigations show that the structures of these polysaccharides can be determined by a combination of chemical and spectroscopic procedures , or almost entirely by n.m.r. spectroscopy alone. The in vitro bacteriophage mediated depolymerisation of the native E. coli K35 polysaccharide demonstrates the value of this method for the isolation of oligosaccharides representing the repeating- unit and multiples thereof. Finally E. coli K37 and K38 capsular polysaccharides were used as model compounds for the evaluation of partial and selective reductive cleavage as methods of generating oligosaccharide for further structural analysis. The products of these reactions were analysed largely by a combination of mass spectrometric procedures.
- Full Text:
- Date Issued: 1992
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