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| 3. |
- Högberg, Liselotte Diaz, et al.
(författare)
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Antibiotic use worldwide
- 2014
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Ingår i: The Lancet - Infectious diseases. - 1473-3099 .- 1474-4457. ; 14:12, s. 1179-1180
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Karvanen, Matti, 1975-, et al.
(författare)
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Colistin is Extensively Lost during Standard in Vitro Experimental Conditions
- 2017
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Ingår i: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 61:11
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Tidskriftsartikel (refereegranskat)abstract
- Colistin adheres to a range of materials, including plastics in labware. The loss caused by adhesion influences an array of methods detrimentally, including MIC assays and in vitro time-kill experiments. The aim of this study was to characterize the extent and time course of colistin loss in different types of laboratory materials during a simulated time-kill experiment without bacteria or plasma proteins present. Three types of commonly used large test tubes, i.e., soda-lime glass, polypropylene, and polystyrene, were studied, as well as two different polystyrene microplates and low-protein-binding microtubes. The tested concentration range was 0.125 to 8 mg/liter colistin base. Exponential one-phase and two-phase functions were fitted to the data, and the adsorption of colistin to the materials was modeled with the Langmuir adsorption model. In the large test tubes, the measured start concentrations ranged between 44 and 102% of the expected values, and after 24 h, the concentrations ranged between 8 and 90%. The half-lives of colistin loss were 0.9 to 12 h. The maximum binding capacities of the three materials ranged between 0.4 and 1.1 μg/cm2, and the equilibrium constants ranged between 0.10 and 0.54 ml/μg. The low-protein-binding microtubes showed start concentrations between 63 and 99% and concentrations at 24 h of between 59 and 90%. In one of the microplates, the start concentrations were below the lower limit of quantification at worst. In conclusion, to minimize the effect of colistin loss due to adsorption, our study indicates that low-protein-binding polypropylene should be used when possible for measuring colistin concentrations in experimental settings, and the results discourage the use of polystyrene. Furthermore, when diluting colistin in protein-free media, the number of dilution steps should be minimized.
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| 5. |
- Karvanen, Matti, 1975-
(författare)
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Optimization of Colistin Dosage in the Treatment of Multiresistant Gram-negative Infections
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As multidrug resistance in Gram-negative bacilli increases, the old antibiotic colistin has rapidly gained attention as one of few last line treatment options in the form of colistin methanesulfonate (CMS), which is hydrolyzed to colistin both in vitro and in vivo. There is a dearth of knowledge on fundamental aspects of colistin, including pharmacokinetics and optimal dosing regimens. The aim of this thesis was to improve the basis for optimal colistin therapy.To be able to study colistin, an LC-MS/MS assay method was developed which is sensitive, specific and useful in both in vivo and in vitro studies. Using this method we detected a significant loss of colistin during standard laboratory procedures. This loss was characterized and quantified, the hypothesis being that the loss is mainly caused by adsorption to labware.The pharmacokinetics of colistin was studied in two populations of critically ill patients, one with normal renal function and one with renal replacement therapy. Plasma concentrations were assayed with the method above, and population modeling was employed to describe the data. The results include a previously unseen, long elimination half-life of colistin. The data from the population on renal replacement therapy was described without modeling, and showed that both CMS and colistin are cleared by hemodiafiltration.Combination therapy is an approach that is often used when treating patients infected with multidrug-resistant pathogens. The thesis discusses how the joint effect of antibiotics can be measured using colistin and meropenem as a model, and proposes a method for testing antibiotic combinations. Furthermore, a PKPD model was adapted to describe the pharmacodynamics of the combination.In conclusion, a specific and sensitive method for analysis of colistin was developed and the adsorption of colistin to materials was described. The assay method has been well accepted internationally. The pharmacokinetics of colistin and CMS was described in two important patient populations, partly with surprising results that have influenced dosages of colistin worldwide. The pharmacodynamics of combination therapy was investigated and quantified, and the methods applied could be further developed into clinically useful tools for selection of antibiotic combinations.
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- Karvanen, Matti, 1975-, et al.
(författare)
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Quantification of Joint Antibacterial Effects of Colistin and Meropenem in Vitro against Pseudomonas aeruginosa and Acinetobacter baumannii
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- As multidrug resistance in Gram-negative bacilli increases, colistin has rapidly gained much attention as one of few last line treatment options. An important part of therapeutic regimens with colistin has been the use of combinations, although there are no reliable methods available for testing combinations, and that the interpretation of joint effects is lacking. In addition, results of combination tests have been varying, with some results indicating no benefit of combinations while others indicate the opposite. The aims of this study were to describe the PD of colistin and meropenem in combination using clinically relevant concentrations of the drugs, to investigate some key endpoints for measuring effect, and to propose a possible path toward testing clinical strains with regard to joint effects.Eight isolates of P. aeruginosa and A. baumannii, with and without meropenem resistance, were exposed to meropenem and colistin separately and in combination over one dosage interval in an in vitro kinetic model. The PD endpoints were initial kill rate, maximum kill, net kill and area under the bactericidal curve (AUBC). Checkerboard assays were performed for comparison.Compared to the single drug exposures, the combination increased the effect with all endpoints in three of the strains, including one resistant to meropenem. The AUBC was significantly (paired t-test, p<0.05) lowered in three of the strains.The chosen endpoints reflect different features of drug effect, and may be important to discern in some patient populations. Kill rate, maximum kill and net kill are point-based endpoints and focusing on only one of them (e.g. net kill by tradition) lead to wasting of potentially important information. AUBC reflects a compressed measure of the whole dosage interval that probably is relevant to most patients and can be used in evaluating joint effect easily and robustly by a simple t-test. The combination of meropenem and colistin is a useful option for treatment of multidrug resistant infections.
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- Khan, David D., et al.
(författare)
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A mechanism-based pharmacokinetic/pharmacodynamic model allows prediction of antibiotic killing from MIC values for WT and mutants
- 2015
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press (OUP). - 0305-7453 .- 1460-2091. ; 70:11, s. 3051-3060
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: In silico pharmacokinetic/pharmacodynamic (PK/PD) models can be developed based on data from in vitro time-kill experiments and can provide valuable information to guide dosing of antibiotics. The aim was to develop a mechanism-based in silico model that can describe in vitro time-kill experiments of Escherichia coli MG1655 WT and six isogenic mutants exposed to ciprofloxacin and to identify relationships that may be used to simplify future characterizations in a similar setting. Methods: In this study, we developed a mechanism-based PK/PD model describing killing kinetics for E. coli following exposure to ciprofloxacin. WT and six well-characterized mutants, with one to four clinically relevant resistance mutations each, were exposed to a wide range of static ciprofloxacin concentrations. Results: The developed model includes susceptible growing bacteria, less susceptible (pre-existing resistant) growing bacteria, non-susceptible non-growing bacteria and non-colony-forming non-growing bacteria. The non-colony-forming state was likely due to formation of filaments and was needed to describe data close to the MIC. A common model structure with different potency for bacterial killing (EC50) for each strain successfully characterized the time-kill curves for both WT and the six E. coli mutants. Conclusions: The model-derived mutant-specific EC50 estimates were highly correlated (r(2) = 0.99) with the experimentally determined MICs, implying that the in vitro time-kill profile of a mutant strain is reasonably well predictable by the MIC alone based on the model.
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| 9. |
- Knudsen, Jenny Dahl, et al.
(författare)
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Selection of Resistant Streptococcus pneumoniae during Penicillin Treatment In Vitro and in Three Animal Models.
- 2003
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Ingår i: Antimicrobial Agents and Chemotherapy. - 1098-6596. ; 47:8, s. 2499-2506
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Tidskriftsartikel (refereegranskat)abstract
- Pharmacokinetic (PK) and pharmacodynamic (PD) properties for the selection of resistant pneumococci were studied by using three strains of the same serotype (6B) for mixed-culture infection in time-kill experiments in vitro and in three different animal models, the mouse peritonitis, the mouse thigh, and the rabbit tissue cage models. Treatment regimens with penicillin were designed to give a wide range of T>MICs, the amounts of time for which the drug concentrations in serum were above the MIC. The mixed culture of the three pneumococcal strains, 107 CFU of strain A (MIC of penicillin, 0.016 µg/ml; erythromycin resistant)/ml, 106 CFU of strain B (MIC of penicillin, 0.25 µg/ml)/ml, and 105 CFU of strain C (MIC of penicillin, 4 µg/ml)/ml, was used in the two mouse models, and a mixture of 105 CFU of strain A/ml, 104 CFU of strain B/ml, and 103 CFU of strain C/ml was used in the rabbit tissue cage model. During the different treatment regimens, the differences in numbers of CFU between treated and control animals were calculated to measure the efficacies of the regimens. Selective media with erythromycin or different penicillin concentrations were used to quantify the strains separately. The efficacies of penicillin in vitro were similar when individual strains or mixed cultures were studied. The eradication of the bacteria, independent of the susceptibility of the strain or strains or the presence of the strains in a mixture or on their own, followed the well-known PK and PD rules for treatment with ß-lactams: a maximum efficacy was seen when the T>MIC was >40 to 50% of the observation time and the ratio of the maximum concentration of the drug in serum to the MIC was >10. It was possible in all three models to select for the less-susceptible strains by using insufficient treatments. In the rabbit tissue cage model, a regrowth of pneumococci was observed; in the mouse thigh model, the ratio between the different strains changed in favor of the less-susceptible strains; and in the mouse peritonitis model, the susceptible strain disappeared and was overgrown by the less-susceptible strains. These findings with the experimental infection models confirm the importance of eradicating all the bacteria taking part in the infectious process in order to avoid selection of resistant clones.
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| 10. |
- Komp Lindgren, Patricia, et al.
(författare)
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Pharmacodynamic studies of nitrofurantoin against common uropathogens
- 2015
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press (OUP). - 0305-7453 .- 1460-2091. ; 70:4, s. 1076-1082
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Tidskriftsartikel (refereegranskat)abstract
- Objectives To determine the pharmacokinetic/pharmacodynamic index that best correlates to nitrofurantoin's antibacterial effect, we studied nitrofurantoin activity against common causative pathogens in uncomplicated urinary tract infection (UTI).Methods Five isolates [two Escherichia coli (one isolate producing the ESBL CTX-M-15), two Enterococcus faecium (including one that was vancomycin resistant) and one Staphylococcus saprophyticus] were used. The MICs of nitrofurantoin were determined by Etest. Time–kill curves with different concentrations of nitrofurantoin (based on multiples of isolate-specific MICs) were followed over 24 h. An in vitro kinetic model was used to simulate different time–concentration profiles, exposing E. coli to nitrofurantoin for varying proportions of the dosing interval. The outcome parameters reduction in cfu 0–24 h (Δcfu0–24) and the area under the bactericidal curve (AUBC), were correlated with time over MIC (T>MIC) and area under the antibiotic concentration curve divided by the MIC (AUC/MIC).Results A bactericidal effect at varying static drug concentrations was achieved for all isolates. All isolates showed similar kill curve profiles. In the kinetic model, the effect of nitrofurantoin on E. coli displayed a 4 log reduction in cfu/mL within 6 h at 8 × MIC. The outcome parameters Δcfu0–24 and AUBC had a good correlation with T>MIC (R ≈ 0.83 and R ≈ 0.67, respectively), whereas log(AUC/MIC) was significantly poorer (R ≈ 0.39 andR ≈ 0.53, respectively).Conclusions Nitrofurantoin was highly effective against E. coli and S. saprophyticus isolates; the killing effect against E. faecium was not as rapid, but still significant. Against E. coli, nitrofurantoin was mainly associated with a concentration-dependent action; this was confirmed in the kinetic model, in which T>MIC displayed the best correlation.
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