This investigation originated from a suggestion by Noristan Laboratories, Pretoria, that because Black people were using the roots of A. venosum E. MEY. ex. TUL for treating headache, the plant might contain analgesics. No previous chemical investigation has been carried out on this plant but from previous work done on other species antihypertensive agents were expected to be present

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 164-173). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 164-173). Also available on the Internet.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Thesis (M. Med. Sc.)--University of Hong Kong, 2007.

Thesis (M.Sc.)--Dalhousie University, 1999. / Includes bibliographical references.

Angiotensin-converting enzyme (ACE) inhibitors are some of the most commonly prescribed medications for hypertension. They are cited in many papers as the treatment most often recommended by guidelines and favoured over other antihypertensive drugs as first-line agents especially when other high-risk conditions are present, such as diabetic nephropathy. The development of captopril (CPT) was amongst the earliest successes of the revolutionary concept of structure-based drug design. Due to its relatively poor pharmacokinetic profile or short half-life of about 1 hour, the formulation of sustained-release microcapsule dosage form is useful to improve patient compliance and to achieve predictable and optimized therapeutic plasma concentrations. Currently, CPT is mainly administered in tablet form. One of the difficulties of CPT formulation has been reported to be its instability in aqueous solutions. CPT is characterized by a lack of a strong chromophore and, therefore, not able to absorb at the more useful UV–Vis region of the spectrum. For this reason, an accurate, simple, reproducible, and sensitive HPLC-ECD method was developed and validated for the determination of CPT in dosage forms. The method was successfully applied for the determination of CPT in commercial and developed formulations. Possible drug-excipient and excipient-excipient interactions were investigated prior to formulating CPT microcapsules because successful formulation of a stable and effective solid dosage form depends on careful selection of excipients. Nuclear magnetic resonance spectroscopy, Fourier transform infra-red spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used for the identification and purity testing of CPT and excipients. The studies revealed no thermal changes during stress testing of binary and whole mixtures which indicate absence of solid state interactions. There were no shifts, appearance and disappearance in the endothermic or exothermic peaks and on the change of other associated enthalpy values on thermal curves obtained with DSC method. Characteristic peaks for common functional groups in the FT-IR were present in all the mixtures indicating the absence of incompatibility. The techniques used in this study can be said to have been efficient in the characterization and evaluation of the drug and excipients. The technique of microencapsulation by oil-in-oil was used to prepare CPT microcapsules. The effects of polymer molecular weight, homogenizing speed on the particle size, flow properties, morphology, surface properties and release characteristics of the prepared CPT microcapsules were examined. In order to decrease the complexity of the analysis and reduce cost response surface methodology using best polynomial equations was successfully used to quantify the effect of the formulation variables and develop an optimized formulation thereby minimizing the number of experimental trials. There was a burst effect during the first stage of dissolution. Scanning electron microscopy (SEM) results indicated that the initial burst effect observed in drug release could be attributed to dissolution of CPT crystals present at the surface or embedded in the superficial layer of the matrix. During the preparation of microcapsules, the drug might have been trapped near the surface of the microcapsules and or might have diffused quickly through the porous surface. The release kinetics of CPT from most formulations followed Fickian diffusion mechanism. SEM photographs showed that diffusion took place through pores at the surface of the microcapsules. The Kopcha model diffusion and erosion terms showed predominance of diffusion relative to swelling or erosion throughout the entire test period. Drug release mechanism was also confirmed by Makoid-Banakar and Korsmeyer-Peppas models exponents which further support diffusion release mechanism in most formulations. The models postulate that the total of drug release is a summation of a couple of mechanisms; burst release, relaxation induced controlled-release and diffusional release. Inspection of the 2D contour and 3D response surfaces allowed the determination of the geometrical nature of the surfaces and further providing results about the interaction of the different variables used in central composite design (CCD). The wide variation indicated that the factor combinations resulted in different drug release rates. Lagrange, canonical and mathematical modelling were used to determine the nature of the stationery point of the models. This represented the optimal variables or stationery points where there is interaction in the experimental space. It is difficult to understand the shape of a fitted response by mere inspection of the algebraic polynomial when there are many independent variables in the model. Canonical and Lagrange analyses facilitated the interpretation of the surface plots after a mathematical transformation of the original variables into new variables. In conclusion, these results suggest the potential application of Eudragit® / Methocel® microcapsules as suitable sustained-release drug delivery system for CPT.

Conclusions: In the same number of people treated, the number of CVD events avoided for the overall risk approach is always larger than that of the blood pressure approach. The additional benefits of overall risk approach compared with the blood pressure approach decreases as the percentage of people from the total population is increased. If the current practice and hypertension guidelines in China are shifted to the overall risk approach, many more CVD events could be avoided with the same resources used. / Methods: The sample used in the analyses includes a subsample of 38,673 persons from the 2002 China National Nutrition and Health Survey, who were 30-74 years old, without previous CVD, and had data on all major CVD risk factors. CVD risks of the patients selected by each approach are predicted using suitable risk prediction equation. The RRR of anti-hypertensive drug treatment derived from meta-analyses of RCTs. The difference in the absolute effectiveness between the two approaches is used to quantify how many more CVD events can be prevented in 1000 people treated by the ORA as compared to the BPA. / Objective: To estimate and compare the number of major cardiovascular events that could be avoided by shifting the blood pressure approach to the overall risk approach if the same percentage of people in a large, representative Chinese population is treated with anti-hypertensive drugs. / Results: When 2.5%, 5.5%, 10.1%, 15.5%, 20.7%, 25.7% or 33.0% of the 38,673 subjects were treated by anti-hypertensive drugs by using the two approaches respectively, 22 (95%CI: 17∼28), 13 (11∼16), 9 (8∼10), 7 (6∼8), 6 (5∼7), 5 (4∼6), or 4 (3∼4) more CVD events could be avoided in every 1000 people treated if the blood pressure approach is shifted to the overall risk approach, which is in general a 15% to 25% increase in CVD events prevented. / Qin, Ying. / Adviser: Jin Ling Tang. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 116-121). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.