Displaying publications 1 - 20 of 24 in total

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  1. Reuter SE, Upton RN, Evans AM, Navaratnam V, Olliaro PL
    J. Antimicrob. Chemother., 2015 Mar;70(3):868-76.
    PMID: 25377567 DOI: 10.1093/jac/dku430
    BACKGROUND: The determination of dosing regimens for the treatment of malaria is largely empirical and thus a better understanding of the pharmacokinetic/pharmacodynamic properties of antimalarial agents is required to assess the adequacy of current treatment regimens and identify sources of suboptimal dosing that could select for drug-resistant parasites. Mefloquine is a widely used antimalarial, commonly given in combination with artesunate.

    PATIENTS AND METHODS: Mefloquine pharmacokinetics was assessed in 24 healthy adults and 43 patients with Plasmodium falciparum malaria administered mefloquine in combination with artesunate. Population pharmacokinetic modelling was conducted using NONMEM.

    RESULTS: A two-compartment model with a single transit compartment and first-order elimination from the central compartment most adequately described mefloquine concentration-time data. The model incorporated population parameter variability for clearance (CL/F), central volume of distribution (VC/F) and absorption rate constant (KA) and identified, in addition to body weight, malaria infection as a covariate for VC/F (but not CL/F). Monte Carlo simulations predict that falciparum malaria infection is associated with a shorter elimination half-life (407 versus 566 h) and T>MIC (766 versus 893 h).

    CONCLUSIONS: This is the first known population pharmacokinetic study to show falciparum malaria to influence mefloquine disposition. Protein binding, anaemia and other factors may contribute to differences between healthy individuals and patients. As VC/F is related to the earlier portion of the concentration-time profiles, which occurs during acute malaria, and CL/F is more related to the terminal phase during convalescence after treatment, this may explain why malaria was found to be a covariate for VC/F but not CL/F.

  2. Kim MJ, Bae IK, Jeong SH, Kim SH, Song JH, Choi JY, et al.
    J. Antimicrob. Chemother., 2013 Dec;68(12):2820-4.
    PMID: 23843299 DOI: 10.1093/jac/dkt269
    To investigate the epidemiological traits of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa (MPPA) clinical isolates collected by the Asian Network for Surveillance of Resistant Pathogens (ANSORP).
  3. Islahudin F, Pleass RJ, Avery SV, Ting KN
    J. Antimicrob. Chemother., 2012 Oct;67(10):2501-5.
    PMID: 22763566 DOI: 10.1093/jac/dks253
    OBJECTIVES: Recent work with the yeast model revealed that the antiprotozoal drug quinine competes with tryptophan for uptake via a common transport protein, causing cellular tryptophan starvation. In the present work, it was hypothesized that similar interactions may occur in malaria patients receiving quinine therapy.

    PATIENTS AND METHODS: A direct observational study was conducted in which plasma levels of drug and amino acids (tryptophan, tyrosine and phenylalanine) were monitored during quinine treatment of malaria patients with Plasmodium falciparum infections.

    RESULTS: Consistent with competition for uptake from plasma into cells, plasma tryptophan and tyrosine levels increased ≥2-fold during quinine therapy. Plasma quinine levels in individual plasma samples were significantly and positively correlated with tryptophan and tyrosine in the same samples. Control studies indicated no effect on phenylalanine. Chloroquine treatment of Plasmodium vivax-infected patients did not affect plasma tryptophan or tyrosine. During quinine treatment, plasma tryptophan was significantly lower (and quinine significantly higher) in patients experiencing adverse drug reactions.

    CONCLUSIONS: Plasma quinine levels during therapy are related to patient tryptophan and tyrosine levels, and these interactions can determine patient responses to quinine. The study also highlights the potential for extrapolating insights directly from the yeast model to human malaria patients.

  4. Mendes RE, Hogan PA, Jones RN, Sader HS, Flamm RK
    J. Antimicrob. Chemother., 2016 Jul;71(7):1860-5.
    PMID: 27013481 DOI: 10.1093/jac/dkw052
    OBJECTIVES: The objective of this study was to report the linezolid in vitro activity observed during the Zyvox(®) Annual Appraisal of Potency and Spectrum (ZAAPS) programme for 2014.

    METHODS: In total, 7541 organisms causing documented infections were consecutively collected in 66 centres in 33 countries, excluding the USA. Susceptibility testing was performed by broth microdilution. Isolates displaying linezolid MIC results of ≥4 mg/L were molecularly characterized.

    RESULTS: Linezolid inhibited all Staphylococcus aureus at ≤2 mg/L, with MIC50 results of 1 mg/L, regardless of methicillin resistance. A similar linezolid MIC50 result (i.e. 0.5 mg/L) was observed against CoNS, with the vast majority of isolates (99.4%) also inhibited at ≤2 mg/L. Six CoNS that exhibited elevated linezolid MIC values were found to contain alterations in the 23S rRNA and/or L3 ribosomal protein. Linezolid exhibited consistent modal MIC and MIC50 results (1 mg/L) against enterococci, regardless of species or vancomycin resistance. Three Enterococcus faecalis from Galway and Dublin (Ireland) and Kelantan (Malaysia) showed MIC results of 4 to 8 mg/L and carried optrA. All Streptococcus pneumoniae, viridans-group streptococci and β-haemolytic streptococci were inhibited by linezolid at ≤2, ≤2 and ≤1 mg/L, respectively, with equivalent MIC90 results (1 mg/L for all groups).

    CONCLUSIONS: These results document the continued long-term and stable in vitro potency of linezolid and reveal a limited number of isolates with decreased susceptibility to linezolid (i.e. MIC ≥4 mg/L). The latter isolates primarily showed mutations in the 23S rRNA gene and/or L3 protein, but cfr was not detected. Moreover, this study shows that isolates carrying the newly described ABC transporter optrA are not restricted to China.

  5. Jiménez-Castellanos JC, Wan Ahmad Kamil WN, Cheung CH, Tobin MS, Brown J, Isaac SG, et al.
    J. Antimicrob. Chemother., 2016 Jul;71(7):1820-5.
    PMID: 27029850 DOI: 10.1093/jac/dkw088
    OBJECTIVES: In Klebsiella pneumoniae, overproduction of RamA and RarA leads to increased MICs of various antibiotics; MarA and SoxS are predicted to perform a similar function. We have compared the relative effects of overproducing these four AraC-type regulators on envelope permeability (a combination of outer membrane permeability and efflux), efflux pump and porin production, and antibiotic susceptibility in K. pneumoniae.

    METHODS: Regulators were overproduced using a pBAD expression vector. Antibiotic susceptibility was measured using disc testing. Envelope permeability was estimated using a fluorescent dye accumulation assay. Porin and efflux pump production was quantified using proteomics and validated using real-time quantitative RT-PCR.

    RESULTS: Envelope permeability and antibiotic disc inhibition zone diameters both reduced during overproduction of RamA and to a lesser extent RarA or SoxS, but did not change following overproduction of MarA. These effects were associated with overproduction of the efflux pumps AcrAB (for RamA and SoxS) and OqxAB (for RamA and RarA) and the outer membrane protein TolC (for all regulators). Effects on porin production were strain specific.

    CONCLUSIONS: RamA is the most potent regulator of antibiotic permeability in K. pneumoniae, followed by RarA then SoxS, with MarA having very little effect. This observed relative potency correlates well with the frequency at which these regulators are reportedly overproduced in clinical isolates.

  6. Mohamed AF, Kristoffersson AN, Karvanen M, Nielsen EI, Cars O, Friberg LE
    J. Antimicrob. Chemother., 2016 May;71(5):1279-90.
    PMID: 26850719 DOI: 10.1093/jac/dkv488
    Combination therapy can be a strategy to ensure effective bacterial killing when treating Pseudomonas aeruginosa, a Gram-negative bacterium with high potential for developing resistance. The aim of this study was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model that describes the in vitro bacterial time-kill curves of colistin and meropenem alone and in combination for one WT and one meropenem-resistant strain of P. aeruginosa.
  7. Kamaruzzaman NF, Firdessa R, Good L
    J. Antimicrob. Chemother., 2016 May;71(5):1252-9.
    PMID: 26825118 DOI: 10.1093/jac/dkv474
    The treatment of skin infections caused by Staphylococcus aureus is limited by acquired antibiotic resistance and poor drug delivery into pathogen and host cells. Here, we investigated the antibacterial activities of six topically used antimicrobials and a cationic polymer, polyhexamethylene biguanide (PHMB), against intracellular MSSA strain RN4420 and MRSA strains EMRSA-15 and USA 300.
  8. Shin J, Baek JY, Kim SH, Song JH, Ko KS
    J. Antimicrob. Chemother., 2011 May;66(5):1001-4.
    PMID: 21393143 DOI: 10.1093/jac/dkr048
    BACKGROUND: After 7-valent pneumococcal conjugate vaccine (PCV7) introduction, non-vaccine serotypes such as 19A are increasing among Streptococcus pneumoniae. However, only limited data on 19A S. pneumoniae are available in Asian countries.
    METHODS: Out of 1637 S. pneumoniae clinical pneumonia isolates collected during 2008 and 2009 from 10 Asian countries (Korea, Malaysia, Taiwan, Thailand, Saudi Arabia, Hong Kong, India, Japan, the Philippines and Vietnam), 91 serotype 19A S. pneumoniae isolates were identified. Capsular swelling reaction identified serotype 19A isolates. Antimicrobial susceptibility testing was performed on the serotype 19A isolates using the broth microdilution method, and the genotypes of the isolates were assessed using multilocus sequence typing.
    RESULTS: Thirty different sequence types (STs) were identified. The most prevalent clone was ST320 (46 isolates, 51.1%). ST320 was found in Hong Kong, India, Korea, Malaysia, Saudi Arabia and Taiwan. ST320 isolates were mostly multidrug resistant (MDR) and showed significantly higher resistance rates than other STs for cefuroxime, clindamycin, and trimethoprim/sulfamethoxazole.
    CONCLUSIONS: Although diverse clones were identified among 19A S. pneumoniae isolates, MDR ST320 was the predominant clone in Asian countries. Its predominance, even in countries with no or low coverage of PCV7, may indicate that its emergence and dissemination was due to more than just vaccine selection pressure in Asian countries. A longitudinal investigation of the change of serotypes and genotypes since the introduction of PCV7 is required to understand the emergence and dissemination mechanisms of a certain clone of 19A S. pneumoniae isolates.
  9. Aarestrup FM, Lertworapreecha M, Evans MC, Bangtrakulnonth A, Chalermchaikit T, Hendriksen RS, et al.
    J. Antimicrob. Chemother., 2003 Oct;52(4):715-8.
    PMID: 12972453
    This study was conducted to investigate the occurrence of antimicrobial resistance among Salmonella Weltevreden isolates from different sources in South-East Asia (Indonesia, Laos, Malaysia, Taiwan, Thailand, Vietnam), Australia, Denmark, New Zealand and the USA.
  10. Song JH, Chang HH, Suh JY, Ko KS, Jung SI, Oh WS, et al.
    J. Antimicrob. Chemother., 2004 Mar;53(3):457-63.
    PMID: 14963068
    To characterize mechanisms of macrolide resistance among Streptococcus pneumoniae from 10 Asian countries during 1998-2001.
  11. Fisher D, Michaels J, Hase R, Zhang J, Kataria S, Sim B, et al.
    J. Antimicrob. Chemother., 2017 04 01;72(4):1221-1226.
    PMID: 28077673 DOI: 10.1093/jac/dkw551
    Objectives: Healthcare facilities internationally have grown outpatient parenteral antibiotic administration services for the last few decades. The literature contains publications from dozens of countries describing systematized processes with specialist oversight and their levels of service provision and outcomes. Such descriptions are absent in the majority of Asian countries. We sought to elucidate the extent and nature of outpatient parenteral antibiotic therapy (OPAT) in Asia and to consider the ramifications and opportunities for improvement.
    Methods: Utilizing colleagues and their personal networks, we surveyed healthcare facilities across 17 countries in Asia to ascertain the current means (if any) of providing OPAT. In that survey we also sought to explore the capacity and interest of these facilities in developing systematized OPAT services.
    Results: Responses were received from 171 different healthcare facilities from 17 countries. Most (97/171, 57%) stated that they administer outpatient parenteral antibiotics, but only 5 of 162 facilities (3%) outside of Singapore described comprehensive services with specialist oversight.
    Conclusions: There is very likely a large unrecognized problem of unchecked outpatient parenteral antibiotic administration in Asia. Developing comprehensive and systematized OPAT in Asia is needed as a priority in an environment in which the infectious diseases community is demanding broad stewardship approaches. There are nonetheless challenges in establishing and sustaining OPAT programmes. Local champions and leverage off identified local incentives and needs are key to regional advancement.
    Study site: unclear (convenient sample from contacts of investigators)
    Note: Questionnaire available here:
    https://academic.oup.com/jac/article/72/4/1221/2888431#supplementary-data
  12. Jeong W, Snell GI, Levvey BJ, Westall GP, Morrissey CO, Ivulich S, et al.
    J. Antimicrob. Chemother., 2017 Jul 01;72(7):2089-2092.
    PMID: 28369489 DOI: 10.1093/jac/dkx085
    Objectives: This study describes the clinical outcomes and therapeutic drug monitoring (TDM) following posaconazole suspension pre-emptive therapy in lung transplant (LTx) recipients.

    Methods: This was a single-centre, retrospective cohort study evaluating posaconazole suspension pre-emptive therapy in LTx recipients between January 2009 and December 2015.

    Results: Forty-two LTx recipients were prescribed posaconazole suspension pre-emptively. Aspergillus fumigatus was the most commonly isolated fungal organism. Of the patients receiving posaconazole suspension as the initial antifungal post-LTx, 93% had eradication of colonization at 6 months after commencing therapy. In contrast, only 61% had eradication of fungal colonization when posaconazole suspension was administered following initial therapy with voriconazole. Posaconazole suspension appeared to be well tolerated, although one case was curtailed following concern about abnormal liver function and another due to nausea/vomiting. TDM was performed in 37 patients. The initial median (IQR) trough plasma concentration ( C min ) following 400 mg twice-daily posaconazole suspension was 0.78 (0.46-1.19) mg/L. Doses beyond 800 mg daily did not appear to result in a higher median C min.

    Conclusions: Early initiation of posaconazole suspension pre-emptive therapy in LTx recipients appears to be well tolerated and may potentially afford favourable clinical outcomes.

  13. Hassandarvish P, Oo A, Jokar A, Zukiwski A, Proniuk S, Abu Bakar S, et al.
    J. Antimicrob. Chemother., 2017 09 01;72(9):2438-2442.
    PMID: 28666323 DOI: 10.1093/jac/dkx191
    Objectives: With no clinically effective antiviral options available, infections and fatalities associated with dengue virus (DENV) have reached an alarming level worldwide. We have designed this study to evaluate the efficacy of the celecoxib derivative AR-12 against the in vitro replication of all four DENV serotypes.

    Methods: Each 24-well plate of Vero cells infected with all four DENV serotypes, singly, was subjected to treatments with various doses of AR-12. Following 48 h of incubation, inhibitory efficacies of AR-12 against the different DENV serotypes were evaluated by conducting a virus yield reduction assay whereby DENV RNA copy numbers present in the collected supernatant were quantified using qRT-PCR. The underlying mechanism(s) possibly involved in the compound's inhibitory activities were then investigated by performing molecular docking on several potential target human and DENV protein domains.

    Results: The qRT-PCR data demonstrated that DENV-3 was most potently inhibited by AR-12, followed by DENV-1, DENV-2 and DENV-4. Our molecular docking findings suggested that AR-12 possibly exerted its inhibitory effects by interfering with the chaperone activities of heat shock proteins.

    Conclusions: These results serve as vital information for the design of future studies involving in vitro mechanistic studies and animal models, aiming to decipher the potential of AR-12 as a potential therapeutic option for DENV infection.

  14. Kengkla K, Kongpakwattana K, Saokaew S, Apisarnthanarak A, Chaiyakunapruk N
    J. Antimicrob. Chemother., 2018 Jan 01;73(1):22-32.
    PMID: 29069421 DOI: 10.1093/jac/dkx368
    Objectives: To comprehensively compare and rank the efficacy and safety of available treatment options for patients with MDR and XDR Acinetobacter baumannii (AB) infection.

    Methods: We searched PubMed, Embase and the Cochrane register of trials systematically for studies that examined treatment options for patients with MDR- and XDR-AB infections until April 2016. Network meta-analysis (NMA) was performed to estimate the risk ratio (RR) and 95% CI from both direct and indirect evidence. Primary outcomes were clinical cure and microbiological cure. Secondary outcomes were all-cause mortality and nephrotoxic and non-nephrotoxic adverse events.

    Results: A total of 29 studies with 2529 patients (median age 60 years; 65% male; median APACHE II score 19.0) were included. Although there were no statistically significant differences between treatment options, triple therapy with colistin, sulbactam and tigecycline had the highest clinical cure rate. Colistin in combination with sulbactam was associated with a significantly higher microbiological cure rate compared with colistin in combination with tigecycline (RR 1.23; 95% CI 1.03-1.47) and colistin monotherapy (RR 1.21; 95% CI 1.06-1.38). No significant differences in all-cause mortality were noted between treatment options. Tigecycline-based therapy also appeared less effective for achieving a microbiological cure and is not appropriate for treating bloodstream MDR- and XDR-AB infections.

    Conclusions: Combination therapy of colistin with sulbactam demonstrates superiority in terms of microbiological cure with a safety profile similar to that of colistin monotherapy. Thus, our findings support the use of this combination as a treatment for MDR- and XDR-AB infections.

  15. Phan MD, Nhu NTK, Achard MES, Forde BM, Hong KW, Chong TM, et al.
    J. Antimicrob. Chemother., 2017 10 01;72(10):2729-2736.
    PMID: 29091192 DOI: 10.1093/jac/dkx204
    Objectives: Polymyxins remain one of the last-resort drugs to treat infections caused by MDR Gram-negative pathogens. Here, we determined the mechanisms by which chromosomally encoded resistance to colistin and polymyxin B can arise in the MDR uropathogenic Escherichia coli ST131 reference strain EC958.

    Methods: Two complementary approaches, saturated transposon mutagenesis and spontaneous mutation induction with high concentrations of colistin and polymyxin B, were employed to select for mutations associated with resistance to polymyxins. Mutants were identified using transposon-directed insertion-site sequencing or Illumina WGS. A resistance phenotype was confirmed by MIC and further investigated using RT-PCR. Competitive growth assays were used to measure fitness cost.

    Results: A transposon insertion at nucleotide 41 of the pmrB gene (EC958pmrB41-Tn5) enhanced its transcript level, resulting in a 64- and 32-fold increased MIC of colistin and polymyxin B, respectively. Three spontaneous mutations, also located within the pmrB gene, conferred resistance to both colistin and polymyxin B with a corresponding increase in transcription of the pmrCAB genes. All three mutations incurred a fitness cost in the absence of colistin and polymyxin B.

    Conclusions: This study identified the pmrB gene as the main chromosomal target for induction of colistin and polymyxin B resistance in E. coli.

  16. Jiménez-Castellanos JC, Wan Nur Ismah WAK, Takebayashi Y, Findlay J, Schneiders T, Heesom KJ, et al.
    J. Antimicrob. Chemother., 2018 Jan 01;73(1):88-94.
    PMID: 29029194 DOI: 10.1093/jac/dkx345
    Objectives: In Klebsiella pneumoniae, overproduction of RamA results in reduced envelope permeability and reduced antimicrobial susceptibility but clinically relevant resistance is rarely observed. Here we have tested whether RamA overproduction can enhance acquired β-lactam resistance mechanisms in K. pneumoniae and have defined the envelope protein abundance changes upon RamA overproduction during growth in low and high osmolarity media.

    Methods: Envelope permeability was estimated using a fluorescent dye accumulation assay. β-Lactam susceptibility was measured using disc testing. Total envelope protein production was quantified using LC-MS/MS proteomics and transcript levels were quantified using real-time RT-PCR.

    Results: RamA overproduction enhanced β-lactamase-mediated β-lactam resistance, in some cases dramatically, without altering β-lactamase production. It increased production of efflux pumps and decreased OmpK35 porin production, though micF overexpression showed that OmpK35 reduction has little impact on envelope permeability. A survey of K. pneumoniae bloodstream isolates revealed ramA hyperexpression in 3 of 4 carbapenemase producers, 1 of 21 CTX-M producers and 2 of 19 strains not carrying CTX-M or carbapenemases.

    Conclusions: Whilst RamA is not a key mediator of antibiotic resistance in K. pneumoniae on its own, it is potentially important for enhancing the spectrum of acquired β-lactamase-mediated β-lactam resistance. LC-MS/MS proteomics analysis has revealed that this enhancement is achieved predominantly through activation of efflux pump production.

  17. Jeong W, Snell GI, Levvey BJ, Westall GP, Morrissey CO, Wolfe R, et al.
    J. Antimicrob. Chemother., 2018 Mar 01;73(3):748-756.
    PMID: 29211913 DOI: 10.1093/jac/dkx440
    Objectives: This study describes therapeutic drug monitoring (TDM) of posaconazole suspension and modified release (MR) tablets in lung transplant (LTx) recipients and evaluates factors that may affect posaconazole trough plasma concentration (Cmin).

    Methods: A single-centre, retrospective study evaluating posaconazole Cmin in LTx recipients receiving posaconazole suspension or MR tablets between January 2014 and December 2016.

    Results: Forty-seven LTx patients received posaconazole suspension, and 78 received the MR tablet formulation; a total of 421 and 617 Cmin measurements were made, respectively. Posaconazole was concurrently administered with proton pump inhibitor in ≥ 90% of patients. The median (IQR) of initial posaconazole Cmin following 300 mg daily of posaconazole tablet was significantly higher than that of 800 mg daily of posaconazole suspension [1.65 (0.97-2.13) mg/L versus 0.81 (0.48-1.15) mg/L, P 

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