An in vitro biofilm model of Staphylococcus aureus infection of bone.

Chronic osteomyelitis is difficult to treat, with biofilm growth and the diffusion barrier to antibiotics presented by bone contributory factors. The aim of this study was to develop and evaluate an in vitro model of osteomyelitis. A bioluminescent strain of Staphylococcus aureus was grown in bone blocks made from bovine femur. Light output was insufficient for detection of bacterial cells within bone by 24 h and viable counting of crushed bone blocks was used to determine bacterial survival. Challenge of 72 h biofilms with gentamicin and daptomycin for 24 h demonstrated that only concentrations of 10 times the clinical peak serum target levels (100 mg l-1 gentamicin and 1000 mg l-1 daptomycin) resulted in significant reductions in cell viability compared to controls. Once daily dosing over 7 days resulted in ≥3 log reductions in cell numbers by 48 h. Thereafter no significant reduction was achieved, although emergence of resistance was suppressed. Determination of antibiotic concentration in bone blocks over 7 days indicated that neither agent was able to consistently reach levels in bone of >10% of the original dose. The model was, therefore, able to demonstrate the challenges posed by biofilm growth on and within bone. SIGNIFICANCE AND IMPACT OF THE STUDY: The majority of studies of antibiotic efficacy in the treatment of chronic osteomyelitis are carried out in animals. We developed an in vitro model of Staphylococcus aureus infection of bone to evaluate the ability of antibiotics to eradicate mature biofilms on surfaces analogous to necrotic bone. The results demonstrated the difficulties which occur in osteomyelitis treatment, with only very high concentrations of antibiotic able to penetrate the bone sufficiently to reduce bacterial survival whilst still failing to eradicate biofilms. This model could be of use in initial screening of novel compounds intended for use in the treatment of osteomyelitis.

In vitro discrimination of wound-associated bacteria by volatile compound profiling using selected ion flow tube-mass spectrometry.

AIMS: To determine if bacterial species responsible for clinically relevant wound infection produce specific volatile profiles that would allow their speciation. METHODS AND RESULTS: Selected ion flow tube-mass spectrometry (SIFT-MS) in full mass scan mode was used to analyse headspace gases produced by wound-associated bacteria grown in vitro, so as to enable identification of bacterial volatile product ion profiles in the resulting mass spectra. Applying multivariate statistical analysis (hierarchical clustering and principal component analysis) to the resultant mass spectra enabled clear speciation. Moreover, bacterial volatile product ions could be detected from artificially contaminated wound dressing material, although the pattern of product ions detected was influenced by culture conditions. CONCLUSIONS: Using selected product ions from the SIFT-MS mass spectra it is possible to discriminate wound-associated bacterial species grown under specific in vitro culture conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study have shown that wound-associated bacteria can be discriminated using volatile analysis in vitro and that bacterial volatiles can be detected from wound dressing material. This indicates that volatile analysis of wounds or dressing material to identify infecting microbes has potential and warrants further study.

Bone penetration of intravenous flucloxacillin and gentamicin as antibiotic prophylaxis during total hip and knee arthroplasty.

AIMS: To investigate the bone penetration of intravenous antibiotic prophylaxis with flucloxacillin and gentamicin during hip and knee arthroplasty, and their efficacy against Staphylococcus (S.) aureus and S. epidermidis. PATIENTS AND METHODS: Bone samples from the femoral head, neck and acetabulum were collected from 18 patients undergoing total hip arthroplasty (THA) and from the femur and tibia in 21 patients during total knee arthroplasty (TKA). The concentration of both antibiotics in the samples was analysed using high performance liquid chromatography. Penetration was expressed as a percentage of venous blood concentration. The efficacy against common infecting organisms was measured against both the minimum inhibitory concentration 50, and the more stringent epidemiological cutoff value for resistance (ECOFF). RESULTS: The bone penetration of gentamicin was higher than flucloxacillin. Relative to ECOFF, flucloxacillin concentrations were effective against S. aureus and S. epidermidis in all THAs and 20 (95%) TKAs. Gentamicin concentrations were effective against S. epidermidis in all bone samples. Gentamicin was effective against S. aureus in 11 (61.1%) femoral neck samples in THA. Effective concentrations of gentamicin against S. aureus were only achieved in four (19%) femoral and six (29%) tibial samples in TKA. CONCLUSION: Flucloxacillin and gentamicin were found to penetrate bone during THA and TKA. Gentamicin was effective against S. epidermidis in both THA and TKA, while levels were subtherapeutic against S. aureus in most TKAs. Bone penetration of both antibiotics was less in TKA than THA, and may relate to the use of a tourniquet. Using this antibiotic combination, effective cover against the two common infective organisms was achieved in all THAs and all but one TKA. Cite this article: Bone Joint J 2017;99-B:358-64.

Analyses of teicoplanin concentrations from 1994 to 2006 from a UK assay service.

Objectives An analysis of the trough serum concentrations sent to the UK Antimicrobial Reference Laboratory for teicoplanin therapeutic drug monitoring (TDM). Methods All trough concentrations over a 13 year period were analysed and the percentages were calculated for the following: <10 mg/L (a sub-optimal concentration for all); ≥10-<20 mg/L (the target used for ordinary Gram-positive infections); ≥20-<60 mg/L (the target for all severe staphylococcal infections including endocarditis); and ≥60 mg/L (the concentration associated with toxicity). Results The percentage of patients with concentrations of <10 mg/L decreased each year to 13% in 2006. Almost 40% of the samples each year were in the ≥10-<20 mg/L range. In 1996, the percentage of samples in the ≥20-<60 mg/L range reached a study high of ∼70%. That percentage then fell to 30% and increased slowly to 50% at the end of the study. Fewer than 5% of the samples were ≥60 mg/L. Conclusions Our study shows that there is a need to increase the initial dose or extend the number of days that the loading dose is used in a significant number of patients. With such a wide optimal range and a low potential for toxicity, it is unclear why optimal therapy is not achieved in a higher percentage of patients.

[Pharmacokinetic evaluation of linezolid in patients with major thermal injuries]. / Pharmacocinétique du linézolide chez des patients souffrant de brûlures sévères.

The aims of this multicentre open-label study was to evaluate the pharmacokinetics of linezolid in patients with burn injury above 20 % BSA and to compare them with healthy volunteers, matched in age, sex and weight. After a single 600 mg IV dose of linezolid, multiple blood and urine samples were taken from subjects, in order to determine linezolid concentrations, using a HPLC assay. C(max) and volume of distribution at steady state were not different between the two groups. Values describing clearance were altered in burns, leading to a reduction by half in AUC in these patients (42.5 versus 98.1 mghL(-1)). The enhancement of clearance was due to which of non renal clearance (323+/-191 versus 80.4+/-27.5 mLmin(-1)). We conclude that pharmacokinetics of linezolid are altered in burn patients, in a magnitude sufficient that linezolid concentration may be subtherapeutic in some patients and we suggest that the dosage interval may need to be decreased in this patient population.

Development and evaluation of vancomycin dosage guidelines designed to achieve new target concentrations.

OBJECTIVES: The aims of this study were to develop a population pharmacokinetic model of vancomycin in adult patients, to use this model to develop dosage guidelines targeting vancomycin trough concentrations of 10-15 mg/L and to evaluate the performance of these new guidelines. METHODS: All data analyses were performed using NONMEM. A population pharmacokinetic model was first developed from vancomycin dosage and concentration data collected during routine therapeutic drug monitoring in 398 patients, then new vancomycin dosage guidelines were devised by using the model to predict vancomycin trough concentrations in a simulated dataset. Individual estimates of CL and V1 were then obtained in an independent group of 100 patients using the population model and the POSTHOC option. These individual estimates were used to predict vancomycin trough concentrations and steady-state AUC(24)/MIC ratios using the current and new dosage guidelines. RESULTS: The population analysis found that the vancomycin data were best described using a bi-exponential elimination model with a typical CL of 3.0 L/h that changed by 15.4% for every 10 mL/min difference from a CL(CR) of 66 mL/min. V(ss) was 1.4 L/kg. The proposed dosage guidelines were predicted to achieve 55% of vancomycin troughs within 10-15 mg/L and 71% within 10-20 mg/L, which is significantly higher than current guidelines (19% and 22%, respectively). The proportion of AUC(24)/MIC ratios above 400 was also higher, 87% compared with 58%. CONCLUSIONS: New vancomycin dosage guidelines have been developed that achieve trough concentrations of 10-15 mg/L earlier and more consistently than current guidelines.

Pharmacokinetic evaluation of linezolid in patients with major thermal injuries.

AIMS: To evaluate the pharmacokinetics of linezolid following its administration in patients with major thermal injuries and in a group of healthy volunteers. METHODS: In an open-label, multicentre design with two parallel groups, a group of patients with major thermal injuries (>20% body area) and a group of age-, sex- and weight-matched healthy volunteers, subjects received a single 600 mg intravenous dose of linezolid. Serial blood and urine collections were made and the concentrations of linezolid in these samples were determined by HPLC. Non-compartmental analyses were used to describe the pharmacokinetic disposition of linezolid. RESULTS: C(max) concentrations and the volume of distribution at steady state (V(ss)) were not statistically different (P > 0.05) between the two groups of subjects. In contrast, values describing clearance [elimination rate constant (k(el)), t(1/2) and mean residence time (MRT)] were significantly different (P < 0.05) in patients with thermal injuries compared with volunteers, which lead to an approximate reduction by half in AUC(0-infinity) from 98.1 mg.h/L (volunteers) to 42.5 mg.h/L (patients). Although renal clearance was similar in the two groups (24.7 +/- 23 versus 30.6 +/- 14.3 mL/min; P = 0.156), non-renal clearance was substantially increased (323 +/- 191 versus 80.4 +/- 27.5 mL/min) in the patients with thermal injuries, though this difference did not achieve statistical significance (P = 0.063). CONCLUSIONS: The pharmacokinetics of linezolid are altered in patients with major thermal injuries, mainly as a result of increased non-renal clearance. These changes are of sufficient magnitude that linezolid concentrations may be sub-therapeutic in some patients and we suggest that the dosage interval may need to be decreased in this patient population.

Measurements of in vivo intra-articular gentamicin levels from antibiotic loaded articulating spacers in revision total knee replacement.

Previous in vitro studies have found high levels of antibiotic release in the days immediately following implantation of antibiotic loaded articulating spacers. However there are relatively few data describing the elution profile beyond this immediate period. This study was designed to measure if gentamicin levels continue to be clinically therapeutic after an extended period following in vivo implantation. Twelve patients received a gentamicin loaded articulating spacer between a 1st and 2nd stage revision total knee arthroplasty. At the 2nd stage procedure synovial fluid and blood samples were collected and assayed for the presence of gentamicin. The second stage revision occurred at a median of 99 days following spacer insertion. The median intra-articular gentamicin levels were 0.46 mg/L (0.24 to 2.36 mg/L) which would be considered therapeutic. There were no cases of reinfection. In this study, preformed articulating spacers containing gentamicin provided therapeutic concentrations in the synovial fluid surrounding the joint throughout the period of implantation. These data confirm the observations from in vitro studies, where a prolonged elution profile was observed for such spacers.

Development, evaluation and application of an isocratic high-performance liquid chromatography (HPLC) assay for the simultaneous determination of aciclovir and its metabolite 9-carboxymethoxymethylguanine in human serum and cerebrospinal fluid.

9-Carboxymethoxymethylguanine (CMMG), the main metabolite of aciclovir (ACV), is a putative neurotoxin. Measurement of CMMG in body fluids may aid patient management. We describe the development, validation and application of a high-performance liquid chromatography (HPLC) method for the simultaneous determination of ACV and CMMG in human serum and cerebrospinal fluid (CSF). Recovery was between 94% and 100% at all concentrations both from serum (range 0-20 mg/L) and CSF (0-5 mg/L). The intra-assay precision (coefficient of variation (CV)) was <2% and the inter-assay precision (CV) was <5%. The limits of detection and quantification were 0.1 and 0.25 mg/L, respectively, in both body fluids. Significant interference from endogenous material or from drugs in clinical samples was not seen. CMMG was detected in most of the 55 clinical samples containing ACV, but little correlation was found between the levels of the drug and its metabolite.

Variability in the content of Indian generic ciprofloxacin eye drops.

BACKGROUND/AIMS: Under-potent generic antibiotics sold in developing world countries may be contributing to positive selection of resistance organisms and to unpredictability in clinical outcome, leading to a loss of confidence among physicians locally. The objective of this study was to determine whether reports of unpredictable outcome for generic ciprofloxacin antibiotic eye drops in India could be the result of inadequate concentration of preparations sold by pharmacies. METHODS: 130 ciprofloxacin eye drop samples sold by pharmacies were collected from seven locations in north, central, and south India; 30 were randomly selected for testing. All samples were assayed using validated methods of reverse phase chromatography and fluorescence detection at a international antibiotic reference laboratory in the United Kingdom. Results were compared with advertised concentrations within the context of internationally accepted variability ranges. RESULTS: In total, six out of the 30 samples tested had ciprofloxacin concentrations lower than the standard advisory ranges of plus or minus 5% of stated content for 3 mg/ml pharmaceutical preparations. The ciprofloxacin content of these eye drops ranged from -36.4% to -16.1% of the stated content (median -21.73%). 24 out of 30 samples were found to be over the standard advisory ranges of plus or minus 5%, at a median of +19.42% (interquartile range (IQR) +14.28 to +25.13). Intra-batch variability of two selected samples was wide at -22.83% to +33.93% (n=11) and -17.07% to +31.20% (n=12). CONCLUSIONS: Approximately 20% of generic ciprofloxacin eye drops, purchased without prescription in India were under-potent. In a number of preparations the antibiotic content was sufficiently low as to have a potential impact on clinical outcome and possibly lead to the selection of resistant isolates in individual patients. More widespread studies are justified to identify the extent of under-potency of widely used generic antibiotic medications in developing countries.

Residual antibiotics in allograft heart valve tissue samples following antibiotic disinfection.

Antibiotics are routinely used for the decontamination of allograft heart valves. To monitor the efficacy of this process, samples of tissue are sent for microbiological analysis. This investigation was undertaken to determine residual antibiotic concentrations in decontaminated tissue and to assess the likely inhibitory effect on microbiological cultures. After a typical decontamination protocol, both gentamicin and vancomycin were present in all tissue samples and the majority of enrichment broths at concentrations sufficient to inhibit most bacteria. The data presented indicate that protocols used by heart valve banks and associated microbiology laboratories should be reviewed, and support the use of predecontamination cultures to identify particularly virulent micro-organisms.

Penetration of linezolid into bone, fat, muscle and haematoma of patients undergoing routine hip replacement.

Twelve patients undergoing total hip replacement were given 600 mg of linezolid as a 20 min iv infusion along with conventional prophylaxis of 1 g of cefamandole immediately before surgery. Routine total hip arthroplasty was carried out, and at timed intervals during surgery samples of bone, fat, muscle and blood were collected for assay by high-performance liquid chromatography analysis. Samples of the haematoma fluid that formed around the operation site and further blood samples for assay were also collected at timed intervals following the operation. The penetration of linezolid into bone was rapid, with mean concentrations of 9.1 mg/L (95% CI 7.7-10.6 mg/L) achieved at 10 min after the infusion, decreasing to 6.3 mg/L (95% CI 3.9-8.6 mg/L) at 30 min. Correction for the simultaneous blood concentrations gave mean values for bone penetration of 51% at 10 min, 60% at 20 min and 47% at 30 min. Although the penetration of linezolid into fat was also rapid, mean concentrations and degree of penetration were c. 60% of those in bone; at 10 min they were 4.5 mg/L (95% CI 3.0-6.1 mg/L; penetration 27%); at 20 min they were 5.2 mg/L (95% CI 4.0-6.4 mg/L; penetration 37%); and at 30 min, 4.1 mg/L (95% CI 3.3-4.8 mg/L; penetration 31%). For muscle the corresponding values were 10.4 mg/L (95% CI 8.1-12.7 mg/L; penetration 58%) at 10 min, 13.4 mg/L (95% CI 10.2-16.5 mg/L; penetration 94%) at 20 min and 12.0 mg/L (95% CI 9.2-14.8 mg/L; penetration 93%) at 30 min. Mean concentrations of linezolid in the haematoma fluid drained from around the operation site were 8.2 mg/L at 6-8 h and 5.6 mg/L at 10-12 h after the infusion, and 7.0 mg/L at 2-4 h following a second 600 mg infusion given 12 h post-operatively. We conclude that linezolid exhibits rapid penetration into bone, fat and muscle of patients undergoing hip arthroplasty, to achieve levels in excess of its MIC for susceptible organisms (< or=4 mg/L); therapeutic concentrations were maintained in the haematoma fluid that surrounds the operation site for >16 h.

The penetration of ceftriaxone and cefamandole into bone, fat and haematoma and relevance of serum protein binding to their penetration into bone.

Thirteen patients undergoing total hip replacement were given ceftriaxone 1 g and cefamandole 1 g simultaneously, either immediately or 8 h before surgery. For both agents the concentrations seen in the bone and fat during the operation, and for haematoma fluid

Epidemiology and resource utilization for patients hospitalized for lower respiratory tract infection.

OBJECTIVES: To determine referral rates, patient characteristics, and resource utilization for patients admitted to hospital with community-acquired lower respiratory tract infections (LRTI). METHODS: Six hundred and thirteen patients, accounting for 704 LRTI episodes, were included in the study, if the referral diagnosis was LRTI and if both signs and symptoms on admission and patient management were consistent with this diagnosis. Patient records were abstracted to collect information on co-morbidities, patient demographics, resource utilization, episode outcome, pharmacy prescribing and diagnostic service utilization. RESULTS: Annual hospital admissions for LRTI ranged from 15 per 10 000 population in the age range 16-40 years to over 300 per 10 000 in the population aged >79 years, with a population average of 62.3 per 10 000. Less than 37% of admissions were for community-acquired pneumonia and the majority of episodes were in patients with pre-existing respiratory disease (41.2%). Marital status, gender, diabetic status, type of infection and number of days in hospital within the past year were all significantly associated with changes in mean length of stay. CONCLUSIONS: Hospital episodes of LRTI are seen predominantly in the over-60 age group, which account for almost 90% of bed day utilization, yet represent only 27% of the adult population. Referral of patients to hospital with LRTI represents a major resource implication for secondary health-care provision.