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A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Medicine 2015 / The dissertation aims to discuss the disulphide and thiol chemistry for use in drug delivery. In particular it focuses on the use of the modified native ovalbumin polymer as a vehicle for the thiol containing captopril. The binding capabilities of thiols expand the area in which peptides and proteins can be used as potential therapeutic drug carriers. It is important that drug delivery systems enhance drug storage stability and in vivo particle stability while delivering the drug efficiently. As part of the developing novel drug delivery systems, thiol-based chemical reactions are distinctive role players in stabilizing disulphide bioconjugated nanostructures for use as efficient drug carrier vehicles in vivo. A review of the current approaches for designing, optimizing and functionalizing nanostructures and conjugates by thiol chemistry modifications was explored. Captopril (Cp) is an Angiotensin-Converting Enzyme (ACE) inhibitor, which acts as an anti-hypertensive, structurally contains a free reactive thiol that binds variably via the thiol/disulphide reaction. A single dose of captopril can regulate hypertension for up to eight hours and the duration of the antihypertensive action of a single dose of 35-75 mg would be taken at 8 hour intervals for 24 hours. Hence the necessities in developing a sustained controlled release ovalbumin carrier system to maintain relatively constant blood pressure levels for 24 hours. The research focused on the construction, characterization and optimization of the thiol conjugated complex for sustained oral drug delivery. The thiol/disulphide-functionalized captopril-ovalbumin conjugate complex was assessed in terms of the structural characteristics and the thiol-disulphide covalent substitution reaction. For analysis of the conjugation complex, the Fourier Transmission IR-spectroscopy (FTIR), H+ NMR and Differential Scanning Calorimetry (DSC) was performed and used to confirm conjugation. Preliminary studies focused on a comparative study of sodium alginate, polyvinyl alcohol and hydroxypropylmethylcellulose hydrogel formulations for the release testing and drug entrapment of the ovalbumin-captopril conjugate complex. Utilizing this data, a series of process variables were used to achieve an optimized formulation through a Box- Behnken statistical design. Furthermore the drug release profiles of the optimised formulation were then analyzed in vitro and in vivo. The captopril released from the formulation was high with a cumulative release of 82%. In vivo analysis was the final testing to verify the validity of the ovalbumin-captopril conjugate complex encapsulated in sodium alginate and utilized a pig model. Ultra Performance Liquid Chromatography (UPLC) blood analysis revealed increased blood levels of captopril (Cmax Cp=33.2ng/mL) in relation to conventional dosage forms validating prolonged (24 hour) site-specific release and increased bioavailability. In conclusion, our validated method was successfully applied to the pharmacokinetic studies of captopril in the blood plasma samples.

Hydrogels are three dimensional networks of hydrophilic homopolymers or copolymers generally covalently or ionically crosslinked. They interact with aqueous media by swelling to some equilibrium value by retaining the aqueous media in their structures. This study concerns the investigation of the swelling and the controlled drug release behaviour of hydrogels synthesized via the photopolymerisation process. The study of hydrogels in this project was oriented towards their biomedical applications as controlled drug delivery devices. It is a known fact that the complete conversion of monomers to polymers may not be achieved in the polymerisation process thus there is always a certain component of unreacted toxic monomers still remained in the polymer matrix. These monomers have the tendency to leach out of the polymer matrices when the polymers are in contact with an aqueous medium thus rendering the hydrogel to be nonbiocompatable. The polymers synthesized in this work were washed thoroughly in milli-Q-water and then evaluated in vitro for any possible toxic effect on human keratinocyte (HaCaT)v cells using a 3-[4,5-dimethylthiazol-2-yl]-2,5-diaphenyl tetrazolium bromide (MTT) cell proliferation assay. The cytotoxicity results indicated that the hydrogels understudy sustained and allowed a positive growth of the HaCat cells in the duration of the cytotoxicity experiment, thus proving to be satisfactorily compatible. / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 86-92).

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Titles called 1,2,3, and 4. Includes bibliographical references (leaves 276-286). Also available on the World Wide Web.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Chemistry." Includes bibliographical references.

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There exists a demand to re-engineer pre-existing pharmaceuticals to provide improved drug delivery, new dosage forms and increased drug safety and efficacy. Furthermore, the development of novel methods and formulations allows for the patent life of pre-existing drugs to be extended, which has obvious economic benefits for pharmaceutical companies. Dense gas technology provides a means to achieve these aims and to overcome the distinct limitations of traditional technologies. A novel formulation of the antifungal drug itraconazole has been developed using gas antisolvent processes. The new itraconazole-polymer formulation displayed a significant improvement in dissolution rate achieving 89.8 % dissolution compared to 52.5 % for the commercial formulation. The results of this study demonstrate the great opportunity to use dense gases for the creation of novel drug-polymer composite formulations with improved dissolution properties. The impregnation of an active ingredient into a polymer matrix is another method that can be used to improve the dissolution of poorly water soluble drugs. Dense gas technology has been incorporated into traditional methods for the formation of porous polymer matrices decreasing process residence times. However, some issues still need to be overcome including high operating temperatures and the use of class 3 solvents. A novel dense gas process for the formation of a porous polymer hydrogel matrix has been developed to improve upon current methodologies; Dense Gas Solvent Exchange Process (DGSEP). The Dense Gas Solvent Exchange Process was used to create a porous chitosan hydrogel impregnated with a stable amorphous form of the drug griseofulvin. Furthermore, the process was extended to include a hydrophilic polymer into the matrix. The resulting formulation had a dramatically improved dissolution rate achieving complete dissolution within 70 minutes compared with the commercial formulation which achieved less than 40 %dissolution in the same time. There is great potential for DGSEP to be applied to the formation of a variety of polymer hydrogels impregnated with active ingredients and incorporating polymers and other compounds. The significance of these results is that a simple and effective processing method has been developed to produce hydrogel systems that are suitable for the development of a diverse range of drug delivery systems.