Abstract Metabolism is a major determinant of the pharmacokinetic properties of most drugs and is often behind bioavailability problems, drug-drug interactions, and metabolic idiosyncrasies. Cytochrome P450 (CYP) enzymes are a superfamily of microsomal hemoproteins catalysing the metabolic reactions of several exogenous compounds. The majority of crucial steps within drug metabolism are in connection with CYP enzymes. In the present study, in vivo, in vitro, and in silico approaches were applied and characterised to evaluate the effects of chemical entities on CYP-mediated metabolism. CYP2B6 was used as a target enzyme for these studies. For evaluation of the CYP inhibition potential of new chemical entities, a novel in vitro test system utilising the n-in-one approach was developed. This method proved to be robust and applicable to screening purposes. Validation of the n-in-one assay was done by comparing its performance to commonly used in vitro techniques using six structurally diverse drugs. All assay types yield remarkably similar results with the majority of the CYP forms tested. Several chemicals were screened in vitro and in silico in order to find potent and selective chemical inhibitors for CYP2B6. Ticlopidine, thioTEPA and 4-(4-chlorobenzylpyridine) were found to be highly effective inhibitors of CYP2B6. The selectivity of thioTEPA proved to be very high, whereas ticlopidine and 4-(4-chlorobenzylpyridine) also inhibited other CYPs. At a concentration level of 1 μM for ticlopidine and 0.1 μM for 4-(4-chlorobenzylpyridine), the inhibitory effect towards other CYPs was negligible. Due to wide clinical use and relevance, clopidogrel and ticlopidine were selected for further in vivo interaction studies. Both clopidogrel and ticlopidine significantly inhibited the CYP2B6-catalysed bupropion hydroxylation and patients receiving either clopidogrel or ticlopidine are likely to need dose adjustments when treated with drugs primarily metabolised by CYP2B6. The effect of impaired kidney function on CYP2B6 activity and on bupropion pharmacokinetics was also explored. In patients with kidney disease, the bupropion AUC and Cmax were significantly higher and the apparent oral clearance of bupropion was notably lower compared to healthy controls. The present results indicate that the in silico and in vitro methods used are helpful in predicting in vivo drug-drug interactions. The effective utilisation of these models in the early phases of drug discovery could therefore help to target the in vivo studies and to eliminate metabolically unfavourable drug candidates.

Magister Pharmaceuticae - MPharm / Many studies have reported low cure rates for multidrug-resistant tuberculosis (MDRTB) patients and MDR-TB patients co-infected with human immunodeficiency virus (HIV). However, little is known about the effect of HIV infection and antiretroviral therapy on the treatment outcomes of MDR-TB in South Africa. Therefore, the objectives of the study are: to find out whether HIV infection and interactions between ARVs and second line anti-TB drugs have an impact on the following MDR-TB treatment outcomes: cure rate and treatment failure at Brewelskloof Hospital. MDR-TB patients were treated for 18-24 months. The study was designed as a case-control retrospective study comparing MDR-TB treatment outcomes between HIV positive (cases) and HIV negative patients (controls). Patients were included in the study only if they complied with the following criteria: sensitivity to second line anti-TB drugs, MDR-TB infection, co-infection with HIV (for some of them), male and female patients, completion of treatment between 1 January 2006 and 31 December 2008. Any patients that presented with extreme drug-resistant tuberculosis (XDR-TB) were excluded from the study. Data were retrospectively collected from each patient’s medical records. There were a total of 336 patients of which 242 (72%) were MDR-TB patients and 94 (27.9%) MDRTB co-infected with HIV patients. Out of the 242 MDR-TB patients, 167 (69.2%) were males and 75 (30.7%) were females. Of the 94 patients with MDR-TB co-infected with HIV, 51 (54.2%) males and 43 (45.7%) females. Patients with multidrug-resistant tuberculosis co-infected with HIV who qualify for antiretroviral therapy were treated with stavudine, lamivudine and efavirenz while all MDR-TB patients were given kanamycin, ethionamide, ofloxacin, cycloserine and pyrazinamide. The cure rate of MDR-TB in HIV (+) patients and in HIV (-) patients is 34.5% and 30 % respectively. There is no significant difference between both artes (pvalue = 0.80). The MDR-TB cure rate in HIV (+) patients taking antiretroviral drugs and in HIV (+) patients without antiretroviral therapy is 35% and 33% respectively. The difference between both rates is not statistically significant. The study shows that 65 (28.0%) patients completed MDR-TB treatment but could not be classified as cured or failure, 29 (12.5%) patients failed, 76 (32.7%) defaulted, 18 (7.7%) were transferred out and 44 (18.9%) died. As far as treatment completed and defaulted is concerned, there is no significant statistical difference between HIV (+) and HIV (-) The number of patients who failed the MDR-TB treatment and who were transferred out is significantly higher in the HIV (-) group than in the HIV (+) group. Finally the number of MDR-TB patients who died is significantly higher in the HIV (+) group). The median (range) duration of antiretroviral therapy before starting anti-tuberculosis drugs is 10.5 (1-60) months. According to this study results, the MDR-TB treatment cure rate at Brewelkloof hospital is similar to the cure rate at the national level. The study also hows that HIV infection and antiretroviral drugs do not influence any influence on MDR-TB treatment outcomes. / South Africa

Background: A post-exposure regrowth model utilizing the well-tried Bactec radiometric system, which would simulate in vivo situations at the site of invasive disease, was developed to measure drug activity against multiplying Mycobacterium tuberculosis. Aims: The aims of this dissertation were to (a) construct a radiometric model simulating drug efficacy relating to the combined bactericidal activity and delays in regrowth due to the action of anti¬tuberculosis (TB) agents, (b) compare the killing kinetics of drugs singly and in combinations by the time-kill curve method, with the radiometrically-determined regrowth model, and (c) assess whether the Bactec radiometric regrowth model could predict likely bactericidal activities of drugs. Design and methods: Drug concentrations in the time-kill curve method were in a range of achievable drug concentrations at the site of infection and in multiples of the minimal inhibitory concentration (MIC), (1x, 2x or 3x, and 8x). Exposure times of 6h, 24h, 48h and 72h were used and these were based on pharmacokinetic data reflecting likely periods of in vivo exposure in TB lesions. Standardized inocula of approximately 106CFU/mi of actively multiplying M. tuberculosis strains were used. The same concentrations, exposure times and bacterial concentrations were used for the assessment of radiometrically-determined post-exposure regrowth times of M. tuberculosis. Growth times were recorded as the number of days required to reach a predetermined growth index (GI) level in the Bactec system, and were expressed as T400 readings in days. Simple linear regression and a mathematical logistic model were used to assess whether the radiometric post-exposure regrowth model could predict the bactericidal activity of the drugs. For drug combination studies, 1MIC of isoniazid (INH) and rifampicin (RMP) were used singly and in combination while 2MIC of ethambutol (EMB), streptomycin (SM), ofloxacin (OFL) and amikacin (AMK) were used in combinations studies. Colony counts at Oh and following 24h exposures were performed and regrowth patterns were determined using the T400 method. M. tuberculosis H37Rv was tested and subsequently resistant strains. Results: INH and RMP were highly bactericidal while EMS showed moderate activity in the time-kill curve method. The three drugs produced the best curves, showing longer regrowth times and markedly depressed rates of regrowth in the Sactec post-exposure regrowth model. Using simple linear regression, a linear relationship between bacterial survivors and the radiometric regrowth times, T400, was achieved for all drugs tested. Even better agreement was found when control-related regrowth times, (T-C) 400, were used in the analysis. Conditions compromising the linear relationsbip in the radiometric regrowth model, for OFL and less markedly EMS and AMK, were likely postantibiotic effects (PAEs) brought on by the short exposure time (6h), and drug carry-over effects due to concentrations ≥ 8 MIC for INH, RMP and 8M (10x and 20x MICs). The mathematical logistic model showed good correlation between bactericidal activity and regrowth for INH and RMP but not for EMB, SM, OFL and AMK. Drug combination effects in the two techniques depended on the criteria used to describe synergy. Generally, it was found in drug combination experiments that the drugs did not influence each other to a meaningful extent. Discussion and conclusions: For prediction of bactericidal activity, interpretation of the radiometrically-determined regrowth model needs to accommodate PAEs and the effect of subinhibitory concentrations. The validity of the mathematical logistic model is not clear. Technical aspects of future studies such as better organism dispersal, need to be improved to achieve a more reliable evaluation based on the logistic model. For drug combination studies, the radiometric regrowth model yielded findings that were difficult to interpret in relation to published data, reinforcing the need for the use of internationally standardized techniques which would give statistically reliable data. The radiometrically-determined regrowth model showed good discrimination between the standard activities of anti- TB agents, correlating with clinical efficacy. It is simple to perform and could prove to be useful for the screening of candidate anti- TB drugs. Improved technical stringency and the evaluation of poorly active control drugs, are however needed before proof of validity of the model can be established. / Dissertation (MSc (Medical Microbiology))--University of Pretoria, 2007. / Medical Microbiology / unrestricted

SFME and HD for the extraction of essential oil in Lavandula officinalis in Alice have been reported. A total of 59 compounds were identified with the major compound being 1,8-cineole, an oxygenated monoterpene, with 46.89% and 44.84% yield obtained for HD and SFME respectively. Charge transfer (CT) complexes formed between α-pinene, 1,8-cineole and camphor as electron donors with iodine as the electron acceptor have been studied spectrophotometrically in methylene chloride solution. The Benesi- Hildebrand equation has been applied to estimate the formation constant (Kf) and molecular extinction coefficient (εCT). The value of Kf is the highest in camphor-I2 complex compared to the other two complexes. Antibacterial assessment was carried out on the various reagents, determining the MIC of individual reagents and in combination. The results show an improvement, on combination of the various reagents than when tested alone.

This thesis applied a novel interdisciplinary approach for pharmacovigilance to examine the use of complementary and integrative medicine (CIM), focusing on herbal remedies, to manage pediatric attention-deficit hyperactivity disorder (ADHD). The safety and potential risk of herb-drug interactions in ADHD management were first evaluated through an assessment of available information on the safety and efficacy of natural health products (NHPs) commonly used by ADHD patients as a means of identifying knowledge gaps. A clinical questionnaire was administered to caregivers of pediatric patients with ADHD to determine the factors and related outcomes of CIM use, including adverse events. A systematic search was conducted to further identify clinical adverse events involving herbal remedies and ADHD drugs to determine causal links to herb-drug interactions. In vitro analysis of identified herbal remedies was conducted to determine their potential for pharmacokinetic interactions, specifically on carboxylesterase-1 (CES1) mediated metabolism. The presented research builds on otherwise scarce evidence of the safety of herbal remedies for ADHD, particularly with respect to herb-drug interactions and adverse events (AEs) associated with concurrent use of NHPs and ADHD prescription drugs. Beyond studies conducted on the pharmacokinetic safety of herbal remedies through the cytochrome P450 pathways that metabolize some ADHD drugs, including amphetamine, atomoxetine and guanfacine, few data were available for CES1, which metabolizes methylphenidate, the first line of drug used to manage ADHD. The clinical questionnaire revealed that 40% of patients had used CIM and confirmed the use of a variety of CIM. Moreover, the majority of CIM users were also concurrently taking ADHD medication, and eight mild adverse events were self-reported. The systematic search on the adverse event reporting system highlighted a potential NHP-drug interaction between methylphenidate and St. John’s wort, and the overall poor quality of NHP-related adverse event reports. As a follow-up from the adverse event results, various commercial St. John’s wort products showed variable inhibition of recombinant human CES1 in vitro. Although the concentration of marker phytochemicals was not correlated to inhibition, hyperforin showed stronger activity than hypericin and quercetin. The preliminary in vitro investigation revealed that the herbal remedies used by ADHD patients have the potential to interact with CES1 mediated metabolism, with Rhodiola rosea identified as the most potent inhibitor. Further investigation on various commercial products of Rhodiola rosea revealed both reversible and irreversible inhibition of recombinant CES1. However, the inhibition was not dependent on the concentration of marker phytochemicals, and rosarin, rosavin, rosin, and salidroside were not potent inhibitors of recombinant CES1. Moreover, a commercial Rhodiola rosea extract showed concentration-dependent inhibition of human liver microsome meditated metabolism of methylphenidate. Overall, results from this thesis suggest potential risk from use of NHPs concurrently with conventional medicine used to manage ADHD. Improved evidence and pharmacovigilance for the use of NHPs in a pediatric population is warranted.

In most hospitals today, plastic devices are replacing the traditional metal, glass and rubber. The increased use of polymeric materials as implanted prosthetic devices, catheters, disposable equipment and for the administration of blood, intravenous fluids and drugs has been widely accepted by the medical profession. This present study was designed to evaluate different types of plastics for potential use as large volume parenteral containers. Using several different therapeutic agents, a variety of plastic containers were examined for the possibility of the occurrence of drug-plastic interactions. The inclusion in the study of a commercially available plasticized product used for the administration of parenteral solutions was to compare the results of commercial products to non-commercial products.

Through the years, various studies (1-5) have been done regarding the prevalent practice of adding one or more drugs to parenteral fluids. The greater variety of drugs being used intravenously, plus the formulation of newer and more complex parenteral fluids, has led to an increased awareness of potential incompatibilities existing between drug and solution. Recognition of the hazards of such extemporaneous combinations has necessitated the study of drug stability in solution. The objective of this report is to determine compatibility characteristics of admixtures prepared from a series of balance intravenous electrolyte solutions and a group of commonly used therapeutic agents. Visual, spectrophotometric and microbiological assay techniques are to be used to establish the compatibility profiles of these admixtures.

Drug interactions of drugs used in thyroid diseases Author: Veronika Teťáková1 Tutor: PharmDr. Josef Malý, Ph.D.1 1 Department of Social and Clinical Pharmacy, Charles University, Faculty of Pharmacy in Hradec Králové Introduction and objectives: Drug interactions are considered to be a significant aspect of pharmacotherapy that can lead to the potentiation of toxicity and side effects of drugs. However, their identification and adequate management of the use of drug combinations hampers a number of obstacles. The aim of this thesis was to summary information about the drug interactions of drugs used in thyroid diseases (levothyroxine, propylthiouracil, thiamazole) and to formulate articles describing the management of interactions in a clinical practice including information for the dispensation of these drugs. To compare the information presented in each database and to determine the degree of conformity between these sources. Methodology: Based on the use of numerous information sources (Micromedex, UpToDate, SPC, Stockley's Drug Interactions) lists of drug interactions of drugs used in thyroid disaeses were established. Information about these interactions were completed by findings from other sources (PubMed®, scientific reports, Google Scholar). The information presented in each of these...

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Patients with human immunodeficiency virus (HIV)/AIDS live a far different life today compared with those who were infected in the 1980s and 1990s. Antiretroviral therapy has evolved from a once poorly tolerated, heavy pill burden to the availability of many once-daily single-tablet regimens. The improvements in therapy have necessitated the need to be cognizant of comorbidities as well as drug-drug interactions. Despite the tremendous advances in therapy, newer therapies are in the pipeline and continue to emerge, making care for patients burdened by HIV perhaps easier than it has ever been.