Anticipation of drug-drug interactions (DDIs) in the paediatric population are merely based on data generated in adults. Hence decision on avoiding certain combinations or attempts to adjust and manage the doses under combination-therapy are mainly speculative from the knowledge of what occurs in adults. However, due to developmental changes in elimination pathways from birth to adolescents, the assumption of DDIs being similar in adults and children might not be correct. This thesis firstly identifies and quantitatively compares the reported DDIs in paediatric and adult populations through a systematic literature review of DDIs reported in paediatric subjects. The study highlights the clear paucity of the data in children younger than 2 years. Therefore, the logical approach to test this hypothesis has been through modelling and simulation and incorporation of the biological knowledge on ontogeny of various enzymes and other elimination routes. The magnitude of any metabolic DDI depends on fractional importance of inhibited pathway which may not necessarily be the same in young children when compared to adults. To show this disparity between rate of ontogeny for metabolic pathways, the ontogeny pattern of CYP enzymes and renal function were analysed systematically. Bootstrap methodology was used to account for variability, and to define the age range over which a statistical difference is likely between each pair of specific pathways. A number of DDIs were simulated for virtual compounds to highlight the possibility that the magnitude of DDI can be influenced by age. Depending on the extent of contribution of metabolic pathways, neonates could be more sensitive to DDI than adults in certain scenarios or vice versa. Thus, extrapolation from adult DDI data may not be applicable across paediatric age groups. The uncertainty around the ontogeny functions based on in vitro information led us to carry out comprehensive performance verification for in vivo data on probe substrates of CYP1A2, -2C9 and 3A4 and assess the predictions of clearance (CL) by monitoring AUC. Although the evaluation showed that in most cases predictions were within two fold of observed data in adult and paediatric studies, the outcome suggests that the current ontogeny profiles result in under-prediction of CL values compared to clinical studies in infants and children and there is a need for better ontogeny models. Therefore, we derived novel ontogeny functions for CYP1A2 and CYP3A based on caffeine-theophylline and midazolam in vivo data. Age related CL data for caffeine, theophylline and midazolam were reconstructed back to intrinsic CL values per milligram of microsomal protein and best fit ontogeny models for CYP1A2 and CYP3A were derived from these data. The function for CYP1A2 describes an increase in relative intrinsic metabolic CL from birth to 3 years followed by a decrease to adult values. The function for CYP3A4 describes a continuous rise in relative intrinsic metabolic CL, reaching the adult value at about 2 years of age. The new models were validated by showing improved predictions of the systemic CL of ropivacaine (major CYP1A2 substrate; minor CYP3A4 substrate) and alfentanil (major CYP3A4 substrate) compared to those using a previous ontogeny function based on in vitro data. When implementing enzyme ontogeny functions it is important to consider potential confounding factors related to disease, anaesthesia and surgery that may affect the prediction of net in vivo CL. Finally, we demonstrated the application of paediatric physiologically-based pharmacokinetic (p-PBPK) models for calculation of sample size in paediatric clinical pharmacokinetic (PK) studies in a methodology suggested by Wang et al., based on desired precision for a PK parameter of interest. We obtained estimates of variability for CL, volume of distribution and area under the plasma concentration-time curve for 5 different drugs from (i) adult and paediatric classic clinical PK studies, and (ii) p-PBPK combined with in vitro-in vivo extrapolation. The estimates were applied to the sample size calculation proposal methodology for non-compartmental analysis. There were clear and drug dependent differences in calculated sample size based on various estimates of variability and overall, there was no consistent discrepancy in the sample size calculated according to the source of variability used for sample size calculations. The results are discussed in terms of their potential impact on the clinical PK studies in children. In general, considering the sensitivity of paediatric clinical PK studies and paucity of data in this group of patients, the use of p-PBPK models may offer an interim solution to uncovering age bands with potential higher vulnerability to DDI. However, these models require further refinements and testing before widely used in clinical practice with confidence.

Introduction This study describes the disease burden, clinical characteristics, antibiotic management, impact of multidrug resistance and outcome of Pseudomonas aeruginosa bloodstream infection (PABSI) among children admitted to a tertiary referral hospital for children in Cape Town, South Africa. Methods A retrospective descriptive study was conducted at a paediatric referral hospital in Cape Town, South Africa. Demographic and clinical details, antibiotic management and patient outcome information were extracted from medical and laboratory records. Antibiotic susceptibility results of identified organisms were obtained from the National Health Laboratory Service database. Results The overall incidence risk of PABSI was 5.4 PABSI episodes / 10,000 hospital admissions and the most common presenting feature was respiratory distress, 34/91 (37%). Overall, 69/91 (76%) of the PA isolates were susceptible to all antipseudomonal antibiotic classes evaluated. Fifty (55%) of the PABSI episodes were treated with appropriate empiric antibiotic therapy. The mortality rate was 24% and in multivariable analysis, empiric antibiotic therapy to which PA isolate was not susceptible to, infections present on admission, and not being in the intensive care unit at the time that PABSI was diagnosed were significantly associated with 14-day mortality. Conclusion The study provided insight into factors associated with PABSI in a tertiary hospital in SubSaharan Africa. Empiric antipseudomonal antibiotic therapy was associated with a decrease in 14-day mortality.

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Brain tumours are the second most common malignancy in children(1) (2), and despite some advancements being made over the last 2 decades, patient outcomes in general remain poor when compared with other childhood cancers. Optimal treatment of children with brain tumours is challenging and expertise and resources are not widely available in South Africa. This is important because the outcomes of children with brain tumours depend critically on the expertise and resources of a multidisciplinary team tasked with their treatment. Despite the importance of paediatric brain tumours though, little is known about childhood brain tumours in South Africa as limited data have been published and there have been no funded studies to support research in this area. In addition, we know very little about the resources available across the country to treat these children. In international centres of excellence the best outcomes are achieved by combining good epidemiological data, strong multidisciplinary teams, centralization or regionalization of services, available resources, and a research foundation. To start, we need to know more about the patients presenting to us with brain tumours. PURPOSE The overall aim of this project was to collect epidemiological data for childhood brain tumours at a tertiary paediatric hospital in South Africa with a dedicated multidisciplinary team. METHODS Study design: A retrospective review of records of patients diagnosed with a primary brain tumour and who presented to Red Cross Children’s Hospital (RCCH) system from 1 January 1996 to 31 December 2017. 2 Patient selection & data collection: Patients were identified by combining databases and admission logs from paediatric neurosurgery, oncology, radiotherapy, histopathology and radiology. Data collected included: age at diagnosis, sex, province of referral, tumour site and diagnosis. RESULTS A total of 554 paediatric patients with primary brain tumours were identified over the study period. Tumours were more common among males (55.4%) and were located in the supratentorial compartment in 52%. The median age at diagnosis was 5.92 years. The commonest tumours were astrocytomas (n=114 patients; 20.3%), followed by medulloblastomas (incl. PNETs) (n=107 patients; 19.1%), and craniopharyngiomas (n=55; 9.8%). As expected, most patients referred and seen at RCCH/GSH were from the expected drainage area in the Western Cape (73%), but a significant number of referrals (27%) were from outside the province referrals, especially in the last 10 years. CONCLUSION Our findings were largely consistent with the published literature in terms of histological diagnosis, sex profile and age ranges for children diagnosed with brain tumours with some small differences possibly related to referral bias. More patients than expected were referred from outside of the province, which emphasizes the need for establishing an ongoing tumour database registry and co-ordinating patient care across institutions. A follow-up study to assess patient management and outcomes is of critical importance to assess resource availability and patient outcomes.

There are currently more than 30 0 000 children under the age of 15 living with HIV in South Africa (SA). Due to a combination of recent success in preventing new vertical infections and success of paediatric antiretroviral treatment (ART) programmes in improving life-expectancy in perinatally HIV-infected (PHIV) children, the burden of paediatric HIV in SA has changed to older children. An increasing population of PHIV children on ART is reaching adolescence, yet information on long-term treatment outcomes in this group is lacking. There is very limited published data on treatment outcomes in PHIV children after ≥10 years on ART in high income countries (HIC), and none in low- and middle-income countries (LMIC). We conducted a retrospective cohort study of PHIV adolescents on ART for ≥ 10 years at a single ART facility. The main objective of the study was to describe long-term clinical, growth, immunologic and virologic outcomes in the cohort. Part A, the protocol, as submitted for departmental and ethical approval, details the purpose and methodology of the study. Part B, the literature review, discusses what is known about long-term treatment outcomes in PHIV children on ART to date. It compares findings between HIC and LMIC. Long-term growth, immunologic and virologic outcomes, as well as factors associated with viral failure are described. The paucity of long-term data is demonstrated, indicating the need for further research on the topic. Part C, the journal-ready manuscript, details the methodology, results and interpretation of the longitudinal analysis of long-term treatment outcomes among 127 PHIV-infected adolescents and young adults on ART for ≥10 years. After median follow-up of 12 years since ART initiation, 80% of the cohort were virally suppressed and 79% had optimal immunologic status (CD4 >500 cells/μl). These results are favourable overall, but >40% of adolescents were on 2nd-line ART with poorer immunologic outcomes than those on 1st-line ART, and approximately one in three children experienced viral failure during adolescence. This highlights the vulnerability of this group, which requires careful further management. Appendices include all supporting documentation necessary for the above parts of the mini-dissertation.

Introduction: Bloodstream infection (BSI) is an important cause of morbidity and mortality in children (1). There are few descriptions of Escherichia coli (E. coli) BSI in children, particularly in Africa, yet E. coli is increasing in importance as a cause of antibiotic-resistant infection in paediatric settings. Methods: In this retrospective, descriptive study aspects of E. coli BSI epidemiology are described over a 10-year period including incidence risk, risk factors for extended spectrum β-lactamase (ESBL)- producing E. coli BSI, antibiotic susceptibility of the bacterial isolates and outcome including risk factors for severe disease. Results: There were 583 new E. coli BSI episodes among 217,483 admissions, an overall incidence risk of 2.7 events/1,000 hospital admissions. Of 455 of these E. coli BSI episodes that were analysed, 136 (29.9%) were caused by ESBL-producing isolates. Risk factors for ESBL-producing E. coli BSI included hospitalization in the 28-day period preceding E. coli BSI episodes and having an underlying chronic illness other than HIV infection at the time of the E. coli BSI. None of the E. coli isolates were resistant to carbapenems or colistin. The mortality rate was 5.9% and admission to the intensive care unit was required in 12.3% of BSI episodes. Predictors of severe disease included age less than 1 month, hospitalization in the 28-day period preceding E. coli BSI and BSI without a definable focus. Conclusions: These findings extend our understanding of E. coli BSI in a sub-Saharan African setting, provide useful information that can guide empiric treatment choices for community- and hospitalacquired BSI and help inform prevention strategies.

Aim: The study describes the population (and care needs) of children admitted to the facility, the experiences of their primary caregivers and the health care workers caring for them. Methodology: This was a descriptive study that utilised elements of both prospective and crosssectional design. The health records of 25 patients were reviewed and matched caregivers partook in a three-part questionnaire. Focus group discussions were conducted with 15 health care workers at a single point during the study. Results: The majority (48%) of patients were referred to the facility for transitional care, the average length of stay was calculated at 97 days and pain was identified as the most prevalent symptom. Despite significant degrees of worry, most primary caregivers derived emotional strength and spiritual meaning from the experience of caring for their child. Health care workers valued access to training, appropriate resources, and support to meet the challenge of caring for children and families with specific care needs. Conclusion/Recommendations: These results conclude that children living with LL or LTC's and their families have complex holistic care needs that require a comprehensive approach. In order to best meet these needs, at ICF level, health care workers need to be assured access to a range of skills, resources and support.

Background: Red Cross Children's Hospital treats an average of 2 000 children per annum with thermal injuries. Five hundred of these are new injuries and 60 patients have a total body surface area burn (TBSAB) that exceeds 20%. There is substantial evidence in adult burn literature that suggests that early enteral feeding (EEF) compared to initial starvation has a profound impact on the hormonal response, metabolic rate and gastrointestinal maintenance post thermal injury. However, research addressing these issues in the burned child (birth to 13 years old), are limited. Aim: To compare EEF, to delayed or late enteral feeding (LEF), and to evaluate whether the practice is beneficial in paediatric burned patients. Criteria: The criteria for the patients were (a) a burn less than 24 hours old and a TBSAB more than or equal to 20%, (b) an age of less than 13 years and (c) admission to the Red Cross Children's Hospital Burns Unit. Objectives: The objectives were to compare the effect of EEF and LEF on (1) the concentrations of insulin, insulin-like growth factor-1 (IGF1), glucagon, cortisol and growth hormone (GH), (2) the estimated energy expenditure (EEE) and calculated energy expenditure, (3) the respiratory quotient (RQ), (4) the intestinal permeability and (5) the clinical outcome. Methods: The children were assigned to either the EEF or LEF group. Nine patients in each study group completed the study successfully, with similar median ages (4.5 yr.), body weights (14 kg) and TBSAB (30%). The EEF group was enterally fed via a nasojejunal feeding tube within a median time of 10.75 hours post burn, whereas the LEF group fasted for a median of 54 hours, after which enteral feeds were introduced. This study is unique in that enteral feeds were used as part of the resuscitation regime in the EEF group. The EEF group received their full resuscitation volumes from the enteral feed at a median time of 16 hours from initiation. Venous blood samples were taken daily between 7h00 and 8h00, before breakfast, for the hormone measurements. The REE and RQ were measured by indirect calorimetry and compared to the recommended dietary allowances (RDA), Galveston and Solomon's equations, which estimate energy requirements. Small bowel permeability was measured by the sugar-absorption-test (SAT), and expressed as lactulose:rhamnose ratios.

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Introduction - Gastrointestinal tonometry has been widely used in adult practice for the early detection of shock and multi-organ failure. Its application in paediatrics has been limited by unsuitably large tonometers and doubt about the accuracy of measurements when saline is used as a tonometric fluid / vehicle for carbon dioxide (CO₂) equilibration. Objective - To evaluate the accuracy and reliability of the newly developed saline 5 French (5F) neonatal gastric tonometer. Study Design - (a) Direct in-vivo comparison of the 5F 0.9%saline tonometer (NST) with the recirculating gas tonometer (RGT) [the current reference standard in adult practice] in 10 Paediatric intensive care unit (PICU) patients, measuring tonometric PCO₂ (PtCO₂) and gastric intramucosal PCO₂ (PiCO₂). (b) In-vivo comparison of PiCO₂ measurements from two 5F tonometers in 10 PICU patients in unfed and fed state. (c) In-vitro comparison of reference PCO₂ to PtCO₂ values obtained using 0.9%saline and phosphate buffered saline in SF tonometers, and the RGT. Results - (a) Comparing the SF NST to RGT in 50 paired simultaneous measurements over PtCO₂ range 3.0 - 9.7kPa, the mean bias was -1.44kPa; limits of agreements (LOA) ±1.45kPa. The mean values of PtCO₂- derived gastric intramucosal pH (pHi) and PiCO₂-PaCO₂ difference differed significantly by -.11 and + 1.1kPa respectively (p<0.0001). (b) 100 paired 5F NST measurements (50 fed/ 50 unfed) over PtCO₂ range 2.48-11.1kPa were assessed. No significant difference was observed in PtCO₂: mean difference (standard deviation) - unfed 0.05kPa (0.36) (p=0.36); fed 0.05kPa (0.42) (p=0.43). (c) 20 consecutive measurements of PtCO₂ were obtained from the 5F NST, 5F phosphate buffered saline tonometer (PBST) and RGT at constant reference PCOi's of 2.5, 5.0, 7.5, 10.0kPa. The 5F NST underestimated the reference PCO₂ by a mean bias of 58% (LOA ±20%); the 5F PBST by 6% (LOA ±26%); while the RGT performed best with a mean bias of 5.7% and tight LOA ±1.5%. Conclusion - There are inherent problems in the methodology of the saline tonometry utilised in the 5F neonatal gastric tonometer. The use of the saline SF neonatal gastric tonometer to monitor gut perfusion in neonates and children should be interpreted with caution. Recirculating gas tonometry is the most accurate method of tonometry studied.