<p>Cefuroxime is a renally eliminated antibiotic used against a variety of different bacterial infections. The pharmacokinetics (PK) for cefuroxime was studied in 97 hospitalized patients using population analysis. To be able to measure cefuroxime in human serum a new sensitive analytical method was developed using mass spectrometry detection. The method was validated and shown to be sensitive and selective. Cystatin C was found to be a better covariate for cefuroxime clearance compared to the traditionally used creatinine clearance (CLcr). This relation might be useful when designing dosing strategies for cefuroxime and other renally eliminated drugs. </p><p>The time-courses of the biomarkers C-reactive protein (CRP), serum amyloid A (SAA), interleukin-6 (IL-6) and body temperature were studied for the first 72 hours of cefuroxime treatment and was related to the duration of illness previous treatment with cefuroxime and to time to step-down of treatment. When duration of illness was short, CRP and SAA were showed increasing levels. None of the biomarkers could be used to differentiate between early or late step-down of therapy.</p><p>By use of known PK and pharmacodynamic (PD) principles, dosing strategies based on CLcr for cefuroxime were estimated using minimization of a risk function. The risk function was constructed with the aim to expose patients to cefuroxime concentration above minimum inhibitory concentration (MIC) for 50 % of the dosing interval and to minimize the amount of drug administered in excess to reach the aim. Based on evaluation using wild type MIC distributions for <i>Escherichia coli</i> and <i>Streptococcus pneumoniae</i> improved dosing strategies were selected.</p><p>In vitro experiments were performed exposing <i>Streptococcus pyogenes</i> to constant concentration of benzylpenicillin, cefuroxime, erythromycin, moxifloxacin or vancomycin. A semi-mechanistic PK/PD model characterizing the time-course of the antibacterial effect was developed using all data simultaneously. Internal validation showed the model being predictive and robust. </p>

<p>The pharmacokinetics and pharmacodynamics of oxycodone and morphine was investigated and related to the transport across the blood-brain barrier (BBB) in rats. The influence of a P-glycoprotein (P-gp) inhibitor on the plasma pharmacokinetics and pharmacodynamics of oxycodone was evaluated. Microdialysis experiments were conducted to evaluate the unbound pharmacokinetics, including the rate and extent of transport across the BBB, of oxycodone and morphine. Mathematical models were used to assess the pharmacokinetics and also the relationship between pharmacokinetics and pharmacodynamics of the drugs.</p><p>Oxycodone clearance, volume of distribution at steady-state, half-life, total brain tissue concentrations and tail-flick latency were all unaffected when a P-gp inhibitor was co-administered with oxycodone as compared to a control group. The lack of differences between the groups indicates that oxycodone BBB transport is not affected by P-gp inhibition. Investigating the unbound concentrations of oxycodone in brain and blood using microdialysis revealed an exciting finding. At steady-state, the unbound concentration in brain was 3 times higher than in blood (i.e. a K_p,uu of 3), indicating that active influx is involved in the BBB transport of oxycodone. In contrast, the K_p,uu of morphine was estimated to 0.56, which is an indication that active efflux mechanisms are involved in the BBB transport of morphine. This means that based on the same unbound concentration in blood, an approximately 6-fold higher unbound concentration of oxycodone compared to morphine will be reached in the brain. Using pharmacokinetic-pharmacodynamic modelling, the unbound brain concentrations of oxycodone and morphine were correlated to the tail-flick latency in vivo. The relative potency of the drugs was found to be concentration dependent with an infliction point of 55 nM.</p><p>In summary, this thesis emphasise the importance of taking the local brain pharmacokinetics into consideration when investigating the pharmacokinetics and the pharmacokinetic-pharmacodynamic relationships of centrally acting drugs.</p>

<p>Enzyme induction is a process whereby a molecule enhances the expression of enzymes. If the affected enzymes are involved in the elimination of a drug, this may result in a drug interaction. Induction is therefore of major concern during drug development and in clinical practice. </p><p>The induction process depends on the half-life of the induced enzyme, the pharmacokinetics of the inducing agent, and the relationship between the inducer’s concentration and the induction stimulus. The aim of the conducted research was to investigate these key aspects of enzyme induction and the consequences that induction has for substrate elimination.</p><p>Successful investigations of the induction process presuppose the existence of appropriate methods for the estimation of the metabolic activity. Enzyme activity measurements can be conducted in tissues with low enzyme content using the analytical method presented here. </p><p>A model was developed describing the changes in the pharmacokinetics of clomethiazole and its metabolite NLA-715, that are attributable to carbamazepine induction. The consequences of the induction was explained using a mechanistic approach, acknowledging food-induced changes in the blood flow to the liver, and interpreting in vitro generated metabolic information.</p><p>The time course of the induction process was examined in two investigations. In the first of these, the pharmacokinetics of the autoinducing drug phenobarbital and its effect on several enzymes were described in rats. This was accomplished by integrating the bidirectional interaction between drug and enzymes in a mechanistic manner. In the final investigation, the time course of the increase and cessation in enzyme activity was studied in healthy volunteers treated with carbamazepine. This investigation allowed the half-lives of CYP3A and CYP1A2 to be estimated. </p><p>The key aspects of the enzyme induction process have been examined using mechanistic induction models. These novel models improve the understanding of the induction process and its consequences for substrate elimination.</p>

Cetirizine, an H1-antihistamine, is prescribed for allergic disorders. It exists as a racemic mixture, with levocetirizine being the active enantiomer. The central nervous system side-effects of H1-antihistamines are caused by their penetration into the brain. In this thesis the plasma pharmacokinetics, transport across the blood-brain barrier (BBB) and H1 receptor occupancy of cetirizine enantiomers was investigated in vivo in guinea pigs. The transport across the BBB was quantified using the microdialysis technique. Stereoselective brain distribution was investigated by measuring both unbound and total concentrations in plasma and brain. The time aspects of the H1 receptor occupancy of levocetirizine was studied in the brain and the periphery. The plasma pharmacokinetics of cetirizine was stereoselective with clearance and volume of distribution of levocetirizine being approximately half that of dextrocetirizine. This was mainly due to the differences in plasma protein binding of the enantiomers. The stereoselectivity in brain distribution indicated by the partition coefficient Kp (total AUC ratio brain to plasma) was caused by stereoselective plasma protein binding. The transport across the BBB measured in this thesis by the unbound partition coefficient Kp,uu (unbound AUC ratio brain to plasma) was the same for the two enantiomers. Binding within the brain was also not significantly different. The H1 receptor occupancy of levocetirizine in brain lagged behind the plasma concentrations whereas it was not delayed with respect to the brain concentrations. This indicates that the delayed brain H1 receptor occupancy of levocetirizine is caused by a slow transport across the BBB. In summary, the results of this thesis emphasize the importance of measuring both the unbound and total concentrations in blood and brain to characterize stereoselective brain distribution. The thesis also emphasize the importance of taking local brain pharmacokinetics into consideration in understanding pharmacokinetic-pharmacodynamic relationships of drugs with central activity.

The pharmacokinetics and pharmacodynamics of oxycodone and morphine was investigated and related to the transport across the blood-brain barrier (BBB) in rats. The influence of a P-glycoprotein (P-gp) inhibitor on the plasma pharmacokinetics and pharmacodynamics of oxycodone was evaluated. Microdialysis experiments were conducted to evaluate the unbound pharmacokinetics, including the rate and extent of transport across the BBB, of oxycodone and morphine. Mathematical models were used to assess the pharmacokinetics and also the relationship between pharmacokinetics and pharmacodynamics of the drugs. Oxycodone clearance, volume of distribution at steady-state, half-life, total brain tissue concentrations and tail-flick latency were all unaffected when a P-gp inhibitor was co-administered with oxycodone as compared to a control group. The lack of differences between the groups indicates that oxycodone BBB transport is not affected by P-gp inhibition. Investigating the unbound concentrations of oxycodone in brain and blood using microdialysis revealed an exciting finding. At steady-state, the unbound concentration in brain was 3 times higher than in blood (i.e. a Kp,uu of 3), indicating that active influx is involved in the BBB transport of oxycodone. In contrast, the Kp,uu of morphine was estimated to 0.56, which is an indication that active efflux mechanisms are involved in the BBB transport of morphine. This means that based on the same unbound concentration in blood, an approximately 6-fold higher unbound concentration of oxycodone compared to morphine will be reached in the brain. Using pharmacokinetic-pharmacodynamic modelling, the unbound brain concentrations of oxycodone and morphine were correlated to the tail-flick latency in vivo. The relative potency of the drugs was found to be concentration dependent with an infliction point of 55 nM. In summary, this thesis emphasise the importance of taking the local brain pharmacokinetics into consideration when investigating the pharmacokinetics and the pharmacokinetic-pharmacodynamic relationships of centrally acting drugs.

Enzyme induction is a process whereby a molecule enhances the expression of enzymes. If the affected enzymes are involved in the elimination of a drug, this may result in a drug interaction. Induction is therefore of major concern during drug development and in clinical practice. The induction process depends on the half-life of the induced enzyme, the pharmacokinetics of the inducing agent, and the relationship between the inducer’s concentration and the induction stimulus. The aim of the conducted research was to investigate these key aspects of enzyme induction and the consequences that induction has for substrate elimination. Successful investigations of the induction process presuppose the existence of appropriate methods for the estimation of the metabolic activity. Enzyme activity measurements can be conducted in tissues with low enzyme content using the analytical method presented here. A model was developed describing the changes in the pharmacokinetics of clomethiazole and its metabolite NLA-715, that are attributable to carbamazepine induction. The consequences of the induction was explained using a mechanistic approach, acknowledging food-induced changes in the blood flow to the liver, and interpreting in vitro generated metabolic information. The time course of the induction process was examined in two investigations. In the first of these, the pharmacokinetics of the autoinducing drug phenobarbital and its effect on several enzymes were described in rats. This was accomplished by integrating the bidirectional interaction between drug and enzymes in a mechanistic manner. In the final investigation, the time course of the increase and cessation in enzyme activity was studied in healthy volunteers treated with carbamazepine. This investigation allowed the half-lives of CYP3A and CYP1A2 to be estimated. The key aspects of the enzyme induction process have been examined using mechanistic induction models. These novel models improve the understanding of the induction process and its consequences for substrate elimination.

Overexpression of the epidermal growth factor receptor (EGFR), a member of the ErbB family, and its closest homologue HER2, have been associated with aggressive tumour progression and reduced sensitivity to DNA-damaging agents. In order to block the proliferation of refractory tumors overexpressing EGFR, a novel strategy has been developed that sought to design molecules capable of not only blocking EGFR-TK, but also damaging DNA. These molecules, termed combi-molecules (CMs), have been shown to degrade under physical conditions to release another inhibitor of EGFR, and to be potent against tumor cells of various origins including breast, prostate and carcinoma of the vulva. However, despite their potency, their growth inhibitory IC50 values were still in the high micromolar range. In order to augment the potency of the CMs, here they were re-designed to contain two quinazoline moieties and a central N,N-bis(2-aminoethyl)methylamine spacer which, following degradation, could yield higher concentrations of free inhibitors and a more cytotoxic bifunctional DNA damaging species. Here, we describe the mechanism of action of the first prototype of this approach, JDE52, which we now classify as a double-arm CM, in comparison with ZRBA1, its closest single-arm counterpart. The results indicated that JDE52 was capable of inducing significant blockade of EGFR, DNA single-strand breaks and inter-strand cross-links. ZRBA1, its single-arm counterpart, was capable of only forming DNA single-strand breaks. The fluorescent property of FD105, the secondary inhibitor that both JDE52 and ZRBA1 are capable of releasing, has permitted the analysis of its levels in tumor cells by UV flowcytometry. It was found that JDE52 was indeed capable of significantly releasing higher levels of fluorescence (p&lt;0.05) in human tumor cells, compared with levels of fluorescence released by ZRBA1. More importantly, JDE52 induced higher levels of apoptosis and cell killing than ZRBA1. Apoptosis was triggered by JDE52 at a faster rate than ZRBA1. The results in toto suggest that the superior potency of JDE52, when compared with ZRBA1, may be imputed to mechanisms associated with the generation of higher levels of FD105 intracellularly, and the induction of DNA cross-links, which are known to be more cytotoxic. These combined mechanisms (blockade of EGFR-TK and formation of cross-links) contributed to an accelerated rate of apoptosis in cells treated with JDE52. This study conclusively demonstrated that designing molecules as prodrugs of high levels of quinazoline inhibitors of EGFR and bifunctional DNA cross-linking species is a valid strategy to enhance the potency of CMs against refractory tumors.

Cefuroxime is a renally eliminated antibiotic used against a variety of different bacterial infections. The pharmacokinetics (PK) for cefuroxime was studied in 97 hospitalized patients using population analysis. To be able to measure cefuroxime in human serum a new sensitive analytical method was developed using mass spectrometry detection. The method was validated and shown to be sensitive and selective. Cystatin C was found to be a better covariate for cefuroxime clearance compared to the traditionally used creatinine clearance (CLcr). This relation might be useful when designing dosing strategies for cefuroxime and other renally eliminated drugs. The time-courses of the biomarkers C-reactive protein (CRP), serum amyloid A (SAA), interleukin-6 (IL-6) and body temperature were studied for the first 72 hours of cefuroxime treatment and was related to the duration of illness previous treatment with cefuroxime and to time to step-down of treatment. When duration of illness was short, CRP and SAA were showed increasing levels. None of the biomarkers could be used to differentiate between early or late step-down of therapy. By use of known PK and pharmacodynamic (PD) principles, dosing strategies based on CLcr for cefuroxime were estimated using minimization of a risk function. The risk function was constructed with the aim to expose patients to cefuroxime concentration above minimum inhibitory concentration (MIC) for 50 % of the dosing interval and to minimize the amount of drug administered in excess to reach the aim. Based on evaluation using wild type MIC distributions for Escherichia coli and Streptococcus pneumoniae improved dosing strategies were selected. In vitro experiments were performed exposing Streptococcus pyogenes to constant concentration of benzylpenicillin, cefuroxime, erythromycin, moxifloxacin or vancomycin. A semi-mechanistic PK/PD model characterizing the time-course of the antibacterial effect was developed using all data simultaneously. Internal validation showed the model being predictive and robust.

Paclitaxel (Taxol®) is now widely used against breast, ovarian and non-small-cell lung cancer. Anticancer agents generally have narrow therapeutic indices, often with myelosuppression (mainly neutropenia) as dose-limiting side effect. A further complicating factor is that paclitaxel when given as Taxol® has a nonlinear pharmacokinetic (PK) behaviour in plasma. Identifying risk groups more sensitive to chemotherapy due to either a PK or pharmacodynamic (PD) interindividual variability is of importance. The aim of the thesis was to develop predictive mechanism-based PK and PD models applicable for paclitaxel. PK and PK/PD models were developed for patient data from studies with relatively frequent sampling or sparse sampling schedules. Population analyses were performed using the software NONMEM. A pharmacokinetic model describing unbound, total plasma and blood concentrations of paclitaxel from known binding mechanisms was developed and validated. The nonlinear PK in plasma could to a large extent be explained by the micelle forming vehicle Cremophor EL (CrEL) and the unbound drug showed linear PK. Besides a binding component directly proportional to concentrations of CrEL, the model included both linear and nonlinear binding components in plasma and blood. Further, relations between the PK parameters and different demographic factors, including polymorphisms in the cytochrome P450s involved in paclitaxel metabolism, were investigated. A semi-physiological PD model for chemotherapy-induced myelosuppression was developed and applied to different anticancer drugs. The model included a self-renewal for proliferating cells, transit compartments describing the delay in observed myelosuppression and a feedback parameter reflecting the effect on the bone marrow from growth factors that can result in an overshoot in white blood cells. The system-related parameters estimated showed consistency across drugs and the difference in the drug-related parameter reflected the relative bone marrow toxicity of the drugs. Relations between demographic factors and the PD parameters were identified. The developed mechanism-based models promote a better understanding of paclitaxel PK and PD and may be used as tools in dosing individualisation and in development of dosing strategies for new administration forms and new drugs in the same area.

[Truncated abstract] Malaria is the most important parasitic disease of man. Of the five species known to infect humans, Plasmodium falciparum causes most deaths and illness, especially when it affects children and pregnant women living in highly endemic areas of the rural tropics. Pharmacological therapies for malaria must be optimised for these groups and must be practical for administration in critically ill patients in remote settings. The clinical studies in this thesis evaluated the clinical pharmacology of modern antimalarial treatments in a Melanesian population exposed to highly endemic malaria. The clinical studies were conducted between March 2001 and June 2007, with final data analysis completed by mid-2008. They aimed to evaluate key pharmacokinetic, parasitological, host genetic and socio-cultural determinants of treatment effectiveness in children with uncomplicated and severe malaria and in pregnant women. A multi-centre study of children with uncomplicated malaria evaluated the efficacy of four treatment regimens, including three artemisinin combination treatments. PCR corrected recrudescence rates by day 42 were 81.5%, 85.4%, 88.0% and 95.2% for chloroquine + sulphadoxine-pyrimethamine, artesunate + sulphadoxine-pyrimethamine, dihydroartemisinin-piperaquine (DHA-PQ) and artemether-lumefantrine (AL), respectively. Determinants of efficacy in the DHA-PQ group included day 7 piperaquine (PQ) levels and baseline parasitaemia. Therefore, the worse than expected efficacy in this group may have been partly due to the high parasitaemias commonly seen in this population. ... Preliminary data suggested a protective effect of the erythrocyte polymorphism caused by the glycophorin C mutation against cerebral malaria. These studies also evaluated key pharmacokinetic, host genetic and socio-cultural determinants of the likely effectiveness of a novel pharmaceutical approach using artesunate suppositories for severe malaria. These demonstrated favourable absorption characteristics, clinical efficacy, safety and patient/community acceptability. Contrary to previous data, no evidence was found to suggest that the pharmacokinetic profiles or efficacy of artemisinin derivatives are likely to be compromised by a high prevalence of thalassaemia in this population. However, their highly variable bioavailability raises questions regarding the consistency of therapeutic response. Given the favourable efficacy and socio-cultural acceptability of rectal artesunate demonstrated in these studies, the PNG Ministry of Health has decided to add artesunate suppositories to its national pharmacopoeia and incorporate them into standard treatment recommendations. A final study compared the pharmacokinetics of chloroquine, sulphadoxine and pyrimethamine in pregnant, versus non-pregnant women. This demonstrated significantly lower concentrations of all three drugs and active metabolites in the pregnant group, due to a combination of effects on either volume of distribution, clearance and elimination half-life. It suggests that significant dosage alterations are necessary to optimise therapy in pregnant women.