Doctoral Degrees (Clinical Pharmacology)
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- ItemDevelopment of a direct ADR reporting tool for patients to address under-reporting of ADRs to the National Pharmacovigilance Unit in South Africa(Stellenbosch : Stellenbosch University, 2022-12) Maluleke, Tirhani Lineth; Page, Carine; Allen, Elizabeth; Reuter, Helmuth; Faculty of Medicine and Health Sciences. Dept. of Medicine. Division of Clinical Pharmacology.ENGLISH ABSTRACT: High standards of public health can be achieved through efficient and safe utilisation of healthcare products and the continuous monitoring thereof. Pharmacovigilance (PV), defined as the science and activities relating to the monitoring of adverse reactions associated with all medicines, is however hampered by the global under-reporting of adverse drug reactions (ADRs) by healthcare professionals. Several countries have successfully incorporated direct patient reporting into their PV system as a means of addressing the under-reporting challenge. Innovative ADR reporting tools have the potential to enable PV systems through increasing signal detection, assessment, understanding and prevention of adverse effects. Whilst the proof-of-concept of such tools have been promising, the use thereof by patients and consumers with access to the South African healthcare system has not been tested. The aim of the current study is to develop an ADR reporting tool for use by consumers in reporting ADRs to address under-reporting in South Africa. The design of the current study and the development of a patient/consumer ADR reporting tool precedes the adoption and implementation of the Med Safety Mobile Application as an online Adverse Event Following Immunisation (AEFI) reporting tool by the South African Health Products Regulatory Authority (SAHPRA) in 2021. If it had not been for the outbreak of the COVID-19 pandemic in 2020 and the immediate need for AEFI reporting tools following the global roll-out of immunisation programmes shortly thereafter by the World Health Organisation (WHO), National Health Departments and Regulators around the globe, this study would have been one of the first to have investigated direct consumer reporting on a larger scale in South Africa. The standard South African Health Products Regulatory Authority (SAHPRA) Yellow Form was used as a frame reference for designing an online-based consumer ADR reporting tool, which is compatible with a mobile application and a paper-based version. Validation and reliability testing of the tool was carried out in two stages: A content validation by healthcare professionals determined whether the content of the tool is appropriate and relevant for the designed purpose of ADR reporting by consumers/patients and face validation by consumers evaluated the usability of the tool in terms of readability, how clear/easy to follow the instructions and/or provide the required information. The developed and tested ADR reporting tool consists of five main elements: consumer’s details, consumer’s medical history, ADR details, suspected medicine(s), and reporter details. All items included received a majority inter-agreement rating of over 80% each as relevant to include in the tool, except for the reporter initials, the batch number and expiry date of the suspected medicine. Using the McNemar Chi-square test, the test and re-test responses of face validation showed no significant difference in responses across all items in the ADR reporting tool. Feasibility testing to assess the ease with which the ADR reporting tool could be used, how practical it is to access the tool and submit the report through it was carried out over a period of 1 year and 3 months. Participants were recruited from twelve healthcare centres and through social media, and they have completed and submitted ADR reports via online tool. A total of 348 reports were received with female consumers contributing 58.3% most of which were from those aged 31- 40 years (22.5%). These were associated with birth control medicines, the fourth highest suspected medicines reported (13.5%) with all reported ADRs listed as expected in the respective package inserts. Hydrochlorothiazide (52.17%) and enalapril (27.54%) were the most frequently suspected medicines within the antihypertensive class. All suspected medicines had well-established safety profiles, except for a lamivudine, tenofovir disoproxil fumarate and dolutegravir fixed-dose combination, nine reports related to investigational medicinal products and twenty-three suspected medicines which could not be identified. Expectedness of reported ADRs was confirmed in 73.9% of the suspected medicines, with dose reduction in 3.4%, treatment changed in 1.8% and treatment stopped in 6.9% of the consumers. A total of 5.3% of suspected medicines could not be verified as the names could not be recognised. Only two reports were received from healthcare professionals with the completeness and terminology used being similar to those of non-healthcare professionals. Reported terms produced 63.4% ‘exact matches’ from the MedDRA search, 8.7% were from ‘contains search’ results and terms used from ‘lexicant variant’ results amounted to 2.5%. Over 25% of the reported terms could not be found in the MedDRA database and therefore an alternative term was used. The high response rate in this study as well as the manner in which the consumers completed the ADR reports demonstrates their understanding and feasibility of using the tool to consistently submit ADR reports whose information would enable causality assessment over time, which will also boost the local PV system. However, the use of English only in the study limited participation of consumers who cannot use and/or understand the language. There was also no measure on the readability index conducted and causality assessment was not carried out. With consumer reporting being relatively new in South Africa, this study can be used as a basis to assess and improve on the newly introduced SAHPRA ADR reporting tools. Further studies are needed to assess the interest, understanding and factors influencing consumers to report ADRs.
- ItemDrug repurposing and optimisation to improve tuberculosis treatment(Stellenbosch : Stellenbosch University, 2021-03) Abulfathi, Ahmed Aliyu; Svensson, Elin M.; Reuter, Helmuth; Diacon, Andreas H.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine: Clinical Pharmacology.ENGLISH ABSTRACT: Tuberculosis, a leading infectious cause of mortality, morbidity, and reduced quality of life with loss of income, remains a huge public health burden particularly in resource-limited settings. The golden thread throughout this dissertation, was improving tuberculosis treatment through repurposing and optimisation of existing medicines. For that purpose, we sought to improve our understanding of the pharmacokinetics and pharmacodynamics of selected anti-tuberculosis drugs.
- ItemIntravitreal Bevacizumab as anti-vascular endothelial growth factor in the management of complications of diabetic retinopathy(Stellenbosch : Stellenbosch University, 2018-12) Arevalo, J. Fernando; Meyer, David; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine: Clinical Pharmacology.ENGLISH ABSTRACT: Bevacizumab is a complete full-length humanized antibody that binds to all subtypes of vascular endothelial growth factor (VEGF) and is used successfully in tumor therapy as a systemic drug. Recent studies have demonstrated the usefulness of an intravitreal injection of bevacizumab (IVB) in the reduction of macular edema secondary to central retinal vein occlusion, and choroidal neovascularization secondary to age-related macular degeneration (AMD). The drug is extremely cost-effective compared to similar anti-VEGF drugs on the market, hence the need to examine its effect in diabetic eye disease (the ever-growing global health epidemic challenge) for application in middle to low income countries. The purpose of the current research is to determine if intravitreal bevacizumab (IVB) as anti-VEGF is helpful in the management of complications of diabetic retinopathy. We conducted several multicenter retrospective studies of eyes with complications from diabetic retinopathy treated with off-label IVB. Ten previously published studies (one prospective), and one unpublished prospective study are included here on the management of diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR). We progressively reported over the years our experienced as we followed patients with DME treated with IVB at 6 months, 12 months, and 24 months of follow up. In addition, 5 year follow up data was added later on. We found that primary IVB at doses of 1.25 to 2.5 mg seem to provide stability or improvement in best correct visual acuity (BCVA), optical coherence tomography (OCT), and fluorescein angiography (FA) in diffuse DME at 24 months. The results show no evident difference between IVB at doses of 1.25 or 2.5 mg. However, the early visual gains due to IVB were not maintained 5 years after treatment. Later, we provide evidence to support the use of primary IVB with or without grid laser photocoagulation (GLP) as treatment of diffuse DME. Primary IVB without GLP seems to be superior to GLP alone to provide stability or improvement in best-corrected visual acuity in patients with diffuse diabetic macular edema at 24 months. We showed first that IVB resulted in marked regression of retinal neovascularization (RN) in patients with PDR and previous pan retinal photocoagulation (PRP), and rapid resolution of vitreous hemorrhage in three naive eyes. Six-months results of intravitreal bevacizumab at doses of 1.25 or 2.5 mg in patients with PDR did not reveal any safety concerns. Later, we published that IVB resulted in marked regression of RN in patients with PDR and previous pan-retinal photocoagulation at 2 years. Intravitreal bevacizumab in naive eyes resulted in control or regression of 42.1% of eyes without adjunctive laser or vitrectomy during 24 months of follow-up. Meaning that a large number of patients (almost 58%) needed PRP or vitrectomy. Another one of our studies demonstrated the usefulness of using preoperative IVB during small-gauge vitreoretinal surgery in eyes with tractional retinal detachment (TRD) in PDR. This was a prospective non-comparative study and patients had significant anatomic and functional success. In addition, we reported for the first time ever that TRD may occur or progress shortly following administration of IVB in patients with severe PDR (5.2% and 3.2% in two studies). Based on our data, we now believe that extreme care must be taken in using a dose of 2.5 mg or more of bevacizumab in patients with PDR. In addition, to have more than 15 years with a diagnosis of diabetes can increase the risk of TRD. Physicians must be prepared to perform the vitrectomy preferably before 13 days after the application of IVB and to perform a vitrectomy immediately on those patients in whom a TRD occurs. We recommend less than 5 days after injection as more than 80% of the retinal detachments developed after that period of time. Finally, in our prospective randomized clinical trial, pre-operative intravitreal bevacizumab therapy as adjuvant to PPV may be helpful and beneficial for patients with TRD secondary to severe PDR. Pre-operative IVB seems to reduce intraoperative bleeding, improving surgical visual field visualization, and reducing intraoperative and postoperative complications including iatrogenic retinal breaks and postoperative hemorrhage. In summary, IVB as anti-VEGF agent is helpful in the management of complications of diabetic retinopathy to prevent blindness with a more accessible drug worldwide.
- ItemPharmacokinetic Herb-Drug Interactions involving african traditional medicines - fingerprint analysis and in vitro metabolism studies(Stellenbosch : Stellenbosch University, 2018-12) Kumar, Saneesh; Rosenkranz, Bernd; Bouic, Patrick J. D.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine: Clinical PharmacologyIntroduction Traditional, complementary and alternative medicines have been used to treat various health conditions. The use of such medicines among HIV/AIDS and TB patients in sub- Saharan Africa has increased considerably, and within this context, questions have been raised about the medical use of herbs or extracts as treatment alternatives without adequate clinical testing and without monitoring of adverse effects once on the market. Furthermore, potential herb-drug interactions (HDI) have been predicted based on the pharmacological and pharmacokinetic properties of prescription medications and the phytoconstituents within the herbs. This study investigated the potential of six popular African herbs consumed by HIV/AIDS and TB patients, viz., Withania somnifera, Glycyrrhiza glabra, Astragalus membranaceus, Inula helenium, Althaea officinalis and Ocimum basilicum, to inhibit the cytochrome P450 enzyme CYP2B6 and the esterase-mediated metabolism pathway of rifampicin and their ability to induce CYP3A4 and CYP2B6. The study was undertaken in four phases: (1) qualitative assessment of various classes of phytocompounds present in each herbal extract by biochemical phytoprofiling, (2) study of the potential inhibitory effects of the extracts on cytochrome CYP2B6 and on the metabolism pathway of rifampicin to 25-O-desacetyl rifampicin by in vitro assays using human liver microsomes (HLM), (3) analysis of the potential inducing effects of the herbal extracts on mRNA expression of CYP2B6 and CYP3A4 in HepG2 cell lines, using reverse transcription polymerase chain reaction (RT-PCR) and agarose gel electrophoresis (AGE), and (4) fingerprint analysis, identification and relative quantification of the major phytoconstituents present in each extract and prediction of compounds which may cause HDI by liquid chromatography-mass spectrometry coupled with photo diode array detection (LC-MS/PDA). Methods Dried roots of Withania somnifera, Glycyrrhiza glabra, Astragalus membranaceus, Inula helenium, Althaea officinalis and dried leaves and inflorescence of Ocimum basilicum were obtained from Pharma Germania, South Africa. Aqueous, methanol, ethanol and ethyl acetate extracts were prepared and analysed using biochemical tests to identify the presence of various classes of phytocompounds. HLM assays were conducted to evaluate the inhibitory potential of each extract on the CYP2B6-mediated metabolism of efavirenz to 8-Hydroxy efavirenz, and the biotransformation of rifampicin to 25-O-desacetyl rifampicin. The protocol included the incubation of the herbal extract, HLM, co-factors and substrates in phosphate buffer for 30 min at 37 oC, termination of reaction and HPLC analysis of the supernatant from the centrifuged assay sample (at 245 nm for efavirenz and its metabolite, and 254 nm for rifampicin and its metabolite). The half-maximal inhibitory concentrations (IC50) for the active extracts were calculated based on the percentage of remaining activity relative to the control. Time-dependent inhibition (TDI) IC50 fold-shift was evaluated using 30 min pre-incubation with NADPH, followed by incubation with substrate in buffer for another 30 min, using six concentrations (1-200 𝜇g/mL) of the herbal extract. CYP2B6 and CYP3A4 mRNA expression assays were conducted for measuring the induction potential of the extracts, where the 50% cytotoxic concentration (CTC50) of all herbal extracts was determined by screening them 1000.00- 31.25 𝜇g/mL) against HepG2 cells. The HepG2 cells were incubated for 24 h with the CTC50 concentration, for each herb. This was followed by extraction and purification of total mRNA and its expression through RT-PCR, followed by AGE. Relative sample expression levels were calculated and represented as fold-response levels of induction relative to a cell control (using rifampicin and dexamethasone as positive controls). LC-MS/PDA was used to identify and relatively quantify the potential phytochemical constituents in each extract. Results O.basilicum, G.glabra I.helenium and A.membranaceus contained most of the relevant groups of phytocompounds such as flavonoids, phenols, alkaloids, glycosides and terpenoids based on the biochemical qualitative analysis. The aqueous and methanolic extracts of O.basilicum showed reversible and time-dependent inhibition of CYP2B6 (TDI IC50s 33.35 𝜇g/mL, 4.93 𝜇g/mL, IC50 shift-fold >1.5 for both extracts), while the methanolic and ethanolic extracts inhibited the formation of 25-O-desacetyl rifampicin (IC50s 31 𝜇g/mL, 8.94 𝜇g/mL). The methanolic extract of O.basilicum showed the highest TDI with a 7.4-fold increase in the IC50. All extracts of I.helenium inhibited CYP2B6 (IC50s 63 𝜇g/mL, 89.43 𝜇g/mL) and rifampicin metabolism (IC50s 42.79 𝜇g/mL, 18.58 𝜇g/mL, 62.10 𝜇g/mL); the aqueous extract showed the highest TDI with a 3-fold increase in the IC50. Only the methanolic and ethyl acetate extracts of W.somnifera inhibited CYP2B6 (IC50 79.16 𝜇g/mL, 57.96 𝜇g/mL). TDI was mainly observed between the herbal extracts and CYP2B6. The ethanolic and methanolic extracts of A.officinalis induced CYP3A4, with 48%-foldresponse shift compared to the cell control (no inducer). The ethanolic extract of O.basilicum and G.glabra caused moderate induction of CYP3A4 and CYP2B6. The aqueous extract of A.membranaceus showed moderate and equal induction of CYP3A4 and CYP2B6 (36% fold-response increase). All extracts exhibited less than 2-fold induction (200%) response, in contrast to the positive controls, rifampicin and dexamethasone. Major phytocompounds detected in the LC-MS/PDA analysis of the extracts included flavonoids, phenols, glycosides, saponins and terpenoids. Relative amounts of the identified compounds were determined by comparison to standard calibrators, quercetin and gallic acid (expressed in mg/L equivalent units). Phenols such as rosmarinic acid (approximately 2298 mg/L in the aqueous extract) and caftaric acid were found in O.basilicum extracts along with the flavonoids salvigenin, rutin and isoquercetin and other compounds such as linalool, hydroxyjasmonic acid and eucommiol. The aqueous extract of I.helenium contained mostly polyphenols such as chlorogenic and caffeoylquinic acids, whereas other solvent extracts contained the sesquiterpenoid tanacetol A, helenin (isoalantolactone) and macrophyllilactone B. The methanolic and ethyl acetate extracts of W.somnifera comprised of withaperuvin, isopelletierine, salvigenin, withanolides and withaferin A (approximately 1117 mg/L in the ethyl acetate extract), and the extracts of A.membranaceus contained mainly calycosin, formononetin, astragalosides I and IV. The extracts of A.officinalis mainly comprised of quinic acid and altheahexacosanyl lactone derivatives (approximately 3874 mg/L in the methanol extract), d-galacturonic acid monohydrate, phloretin along with the fatty acid trihydroxy-octadecenoic acid, and the G.glabra extract mainly consisted of glabridin, liquiritin apioside, liquiritigenin and licochalcones. Conclusion A.membranaceus, I.helenium, O.basilicum and W.somnifera have been shown to contain astragalosides, alantolactones, phenolic acids and withanolides that may inhibit drug metabolising enzymes such as CYP2B6, CYP3A4 and the enzymes responsible for metabolism of rifampicin (including B-esterases). A.officinalis and G.glabra can cause moderate induction of CYP3A4 due to the higher concentration of lactones and chalcones present in their extracts. These in vitro findings may be relevant for clinical use of these herbs together with conventional medicines metabolised by these enzymes, if sufficient hepatic concentrations are attained in humans. The results of this study will help to guide planning and designing of clinical trials to confirm the potential relevance of HDI in patients.
- ItemImmunoactive, Antibacterial and Drug-Carrying properties of selective surfactants(Stellenbosch : Stellenbosch University, 2018-03) Van Rensburg, Lyne; Van Zyl, Johann Martin; Smith, Johan; Van Zyl, Johann Martin; Smith, Johan; Stellenbosch University. Faculty of medicine of Health Sciences. Dept. Medicine: Clinical Pharmacology.ENGLISH ABSTRACT: Surfactant replacement therapy is used the treatment of neonatal respiratory distress syndrome as surfactant’s biophysical behaviour helps to maintain proper lung function and reduces the work associated with breathing. Secondly, surfactant associated proteins are important role players in the innate immune response within the pulmonary environment and therefore assist in pulmonary host defence. However, natural and synthetic exogenous surfactants have gained much interest in other areas of therapy such as possibly aiding in dual-drug delivery systems for infectious or inflammatory pulmonary conditions. Both types have been studied extensively in animal models and in clinical trials and have elicited positive and negative effects on lung function. This thesis aims to determine whether a synthetic peptide containing surfactant, Synsurf®, may have potential immunomodulatory effects compared to the naturally derived surfactants, Curosurf® and Liposurf®. Two formulations of Synsurf®, combined with the antibiotic linezolid were tested for its efficacy as a respirable compound in a pressurised metered dose inhaler. The outcome of these experiments revealed the prospect of Synsurf®’s adaptability as a pulmonary drug carrier. Furthermore, the tuberculosis isolates H37Rv and MDR-X51 displayed enhanced susceptibility to surfactant-drug micro-particle combinations. The main findings of this study show that the natural surfactants Curosurf® and Liposurf® as well as Synsurf® inhibit secretion of pro-inflammatory cytokines and influence the production of reactive oxygen species in NR8383 alveolar macrophages and therefore influence cell viability. The inhibitory effects on cytokine secretion was displayed in a dose-dependent manner as well as a threshold effect that was seen for all three surfactants. This may result from unique mechanisms of decreasing cell signalling or up-regulating anti-inflammatory activity that was further elucidated by the employment of proteomics. The findings in this thesis on the comparison of the two natural and one synthetic surfactant led to the following main conclusions: a) Different surfactant compositions modulate the anti-inflammatory activity in lipopolysaccharide stimulated alveolar macrophages via the possible involvement of different signalling pathways. The initial hypothesis regarding the protective nature that is linked to the protein content in natural surfactants is challenged and may be deemed as “not fully supported” as these new findings suggest non-specific lipid or synthetic peptide protection with alveolar macrophages as seen with Synsurf®. b) Different surfactant compositions effect cell viability and morphology in a time and dose-dependent manner revealing that the treatment of neonatal respiratory distress syndrome may depend upon the specific preparation or dose used. c) All three surfactants displayed an impact on the antibiotic activity of linezolid that holds positive ramifications for drug loaded surfactants. d) The data shows that linezolid in combination with Synsurf® can be aerosolised in desired particle ranges for optimal lung deposition for a possible non-invasive, site-specific, delivery model via pressurised metered dose inhaler.