Population pharmacokinetics of free flucloxacillin in patients treated with oral flucloxacillin plus probenecid.

Oral flucloxacillin may be coadministered with probenecid to reduce flucloxacillin clearance and increase attainment of pharmacokinetic-pharmacodynamic (PK/PD) targets. The aims of this study were to develop a population PK model of free flucloxacillin when administered orally with probenecid, and to identify optimal dosing regimens for this combination. METHODS: We performed a prospective observational study of adults (45 participants) treated with oral flucloxacillin 1000 mg and probenecid 500 mg 8-hourly for proven or probable staphylococcal infections. Steady-state mid-dose-interval flucloxacillin measurements (45 concentrations) were combined with existing data from a crossover study of healthy participants receiving flucloxacillin with and without probenecid (11 participants, 363 concentrations). We developed a population pharmacokinetic model of free flucloxacillin concentrations within Monolix, and used Monte Carlo simulation to explore optimal dosing regimens to attain PK/PD targets proposed in the literature (free drug time above minimum inhibitory concentration). RESULTS: Flucloxacillin disposition was best described by a 1-compartment model with a lag time and first-order absorption. Free flucloxacillin clearance depended on probenecid, allometrically-scaled fat free mass (FFM) and estimated glomerular filtration rate (eGFR). Predicted PK/PD target attainment was suboptimal with standard dosing regimens with flucloxacillin alone, but substantially improved in the presence of probenecid. CONCLUSION: The simulation results reported can be used to identify dose regimens that optimise flucloxacillin exposure according to eGFR and FFM. Patients with higher FFM and eGFR may require the addition of probenecid and 6-hourly dosing to achieve PK/PD targets. The regimen was well-tolerated, suggesting a potential for further evaluation in controlled clinical trials to establish efficacy.

Antimicrobial susceptibility of bacterial isolates from clinical specimens in four Pacific Island countries, 2017-2021.

Background: There are limited antimicrobial resistance (AMR) surveillance data from low- and middle-income countries, especially from the Pacific Islands region. AMR surveillance data is essential to inform strategies for AMR pathogen control. Methods: We performed a retrospective analysis of antimicrobial susceptibility results from the national microbiology laboratories of four Pacific Island countries - the Cook Islands, Kiribati, Samoa and Tonga - between 2017 and 2021. We focused on four bacteria that have been identified as 'Priority Pathogens' by the World Health Organization: Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Findings: Following deduplication, a total of 20,902 bacterial isolates was included in the analysis. The most common organism was E. coli (n = 8455) followed by S. aureus (n = 7830), K. pneumoniae (n = 2689) and P. aeruginosa (n = 1928). The prevalence of methicillin resistance among S. aureus isolates varied between countries, ranging from 8% to 26% in the Cook Islands and Kiribati, to 43% in both Samoa and Tonga. Ceftriaxone susceptibility remained high to moderate among E. coli (87%-94%) and K. pneumoniae (72%-90%), whereas amoxicillin + clavulanate susceptibility was low against these two organisms (50%-54% and 43%-61%, respectively). High susceptibility was observed for all anti-pseudomonal agents (83%-99%). Interpretation: Despite challenges, these Pacific Island laboratories were able to conduct AMR surveillance. These data provide valuable contemporary estimates of AMR prevalence, which will inform local antibiotic formularies, treatment guidelines, and national priorities for AMR policy. Funding: Supported by the National Health and Medical Research Council.

Liquid-Immersion Reprocessing Effects on Filtration Efficiency of 'Single-Use' Commercial Medical Face Masks.

PURPOSE: Medical masks have inferior filtration efficiency and fit to filtering facepiece respirators (FFRs) but are widely used in healthcare and the community. These masks are intended for disposal after use but in the event of mask shortage re-use after reprocessing may be an option. We investigated eight reprocessing methods that each involved washing or soaking in liquid, are likely to eliminate respiratory viruses, and are safe and available in most community and healthcare settings. METHODS: Three brands of EN 14683 standards-compliant commercial medical mask were each reprocessed 10 times by one of eight methods. We measured filtration efficiency for poly-dispersed sodium chloride particles and pressure differential. RESULTS: Compared with new medical masks, reprocessed masks had significantly reduced filtration efficiency. The reduction was mild-moderate (6.5-25.8%) after warm water wash, hot water soak or boiling water soak; and moderate-large (24.1-51.5%) after detergent, soap or laundry machine wash, or bleach soak. There were mixed and minor changes in pressure differential. Most reprocessed standards-compliant masks had better filtration efficiency than new non-standard commercial masks and then cotton and cotton-polyester mix fabric samples, even triple-layered fabrics. CONCLUSIONS: High-quality commercial medical masks reprocessed 10 times by water immersion methods had better filtration efficiency than new non-standard masks and washable fabrics. These findings have particular relevance for community and low-resource healthcare settings.

Probenecid effects on cephalexin pharmacokinetics and pharmacodynamics in healthy volunteers.

OBJECTIVES: We evaluated the effects of probenecid on the Pharmaco Kinetics (PK) and pharmacodynamics (PD) of oral cephalexin in healthy volunteers. METHODS: Cephalexin 1000 mg was administered orally to 11 healthy volunteers following a standardized meal, with and without probenecid 500 mg orally, on two separate days one week apart. Total plasma concentrations of cephalexin and probenecid over a 12 h period were measured by liquid chromatography tandem mass spectrometry. Standard pharmacokinetic measures and contemporary PK/PD targets were compared. RESULTS: Probenecid increased the mean (95% CI) cephalexin area under the concentration-time curve (AUC0-∞) 1.73-fold (1.61-1.85, p < 0.0001), peak concentration 1.37-fold (1.16-1.58, p < 0.01), time to peak concentration 1.45-fold (1.1-1.8, p < 0.01), and half-life 1.33-fold (1.03-1.62, p < 0.05). The effects resulted in clinically meaningful increases in the probability of PK/PD target attainment (PTA). As an example, the PTA of total concentrations above the minimum inhibitory concentration required to inhibit methicillin-susceptible Staphylococcus aureus isolates (MIC ≤ 8 mg/L) for 70% of a 6 h dose interval approached 100% for cephalexin + probenecid while for cephalexin alone it was <15%. CONCLUSIONS: Probenecid prolonged and flattened the plasma concentration-time curve, enhancing the probability of attaining PK/PD targets. Co-administration of probenecid may expand the clinical benefits of oral cephalexin.

Probenecid and food effects on flucloxacillin pharmacokinetics and pharmacodynamics in healthy volunteers.

OBJECTIVES: To measure the effect of probenecid, fasting and fed, on flucloxacillin pharmacokinetic and pharmacodynamic endpoints. METHODS: Flucloxacillin 1000 mg orally was given to 11 volunteers alone while fasting ('flucloxacillin alone'), and with probenecid 500 mg orally while fasting ('probenecid fasting') and with food ('probenecid fed'). Flucloxacillin pharmacokinetic and pharmacodynamic endpoints were compared. RESULTS: Probenecid, fasting and fed, increased free plasma flucloxacillin area under the concentration-time curve (zero to infinity) ∼1.65-fold (p < 0.01) versus flucloxacillin alone. Probenecid fed prolonged time to peak flucloxacillin concentrations ∼2-fold versus the other two regimens (p < 0.01). Probenecid fasting or fed increased free flucloxacillin concentrations exceeding 30%, 50% and 70% of the first 6, 8 and 12 h post-dose by 1.58- to 5.48-fold compared with flucloxacillin alone. As an example of this pharmacodynamic improvement, the probability of target attainment of free concentrations above the minimum inhibitory concentration for Staphylococcus aureus (0.5 mg/L) for 50% of a 6-hour dose interval was > 80% for flucloxacillin plus probenecid (fasting or fed) and < 20% for flucloxacillin alone. CONCLUSIONS: Probenecid increased flucloxacillin exposure, with predicted pharmacodynamic effects greater than pharmacokinetic effects because of the altered shape of the concentration-time curve. Probenecid may improve the applicability of oral flucloxacillin regimens.

The burden of Legionnaires' disease in New Zealand (LegiNZ): a national surveillance study.

BACKGROUND: Legionnaires' disease is under-diagnosed because of inconsistent use of diagnostic tests and uncertainty about whom to test. We assessed the increase in case detection following large-scale introduction of routine PCR testing of respiratory specimens in New Zealand. METHODS: LegiNZ was a national surveillance study done over 1-year in which active case-finding was used to maximise the identification of cases of Legionnaires' disease in hospitals. Respiratory specimens from patients of any age with pneumonia, who could provide an eligible lower respiratory specimen, admitted to one of 20 participating hospitals, covering a catchment area of 96% of New Zealand's population, were routinely tested for legionella by PCR. Additional cases of Legionnaires' disease in hospital were identified through mandatory notification. FINDINGS: Between May 21, 2015, and May 20, 2016, 5622 eligible specimens from 4862 patients were tested by PCR. From these, 197 cases of Legionnaires' disease were detected. An additional 41 cases were identified from notification data, giving 238 cases requiring hospitalisation. The overall incidence of Legionnaires' disease cases in hospital in the study area was 5·4 per 100 000 people per year, and Legionella longbeachae was the predominant cause, found in 150 (63%) of 238 cases. INTERPRETATION: The rate of notified disease during the study period was three-times the average over the preceding 3 years. Active case-finding through systematic PCR testing better clarified the regional epidemiology of Legionnaires' disease and uncovered an otherwise hidden burden of disease. These data inform local Legionnaires' disease testing strategies, allow targeted antibiotic therapy, and help identify outbreaks and effective prevention strategies. The same approach might have similar benefits if applied elsewhere in the world. FUNDING: Health Research Council of New Zealand.

In healthy volunteers, taking flucloxacillin with food does not compromise effective plasma concentrations in most circumstances.

It is usually recommended that flucloxacillin is given on an empty stomach. The aim of this study was to compare total and free flucloxacillin concentrations after oral flucloxacillin, given with and without food, based on contemporary pharmacokinetic and pharmacodynamic targets. Flucloxacillin 1000 mg orally was given to 12 volunteers, after a standardised breakfast and while fasting, on two separate occasions. Flucloxacillin concentrations over 12 hours were measured by liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters, and pharmacodynamic endpoints related to target concentration achievement, were compared in the fed and fasting states. For free flucloxacillin, the fed/fasting area under the concentration-time curve from zero to infinity (AUC0-∞) ratio was 0.80 (p<0.01, 90% CI 0.70-0.92), the peak concentraton (Cmax) ratio 0.51 (p<0.001, 0.42-0.62) and the time to peak concentration (Tmax) ratio 2.2 (p<0.001, 1.87-2.55). The ratios for total flucloxacillin concentrations were similar. The mean (90% CI) fed/fasting ratios of free concentrations exceeded for 30%, 50% and 70% of the first 6 hours post-dose were 0.74 (0.63-0.87, fed inferior p<0.01), 0.95 (0.81-1.11, bioequivalent) and 1.15 (0.97-1.36, fed non-inferior), respectively. Results for 8 hours post-dose and those predicted for steady state were similar. Comparison of probability of target attainments for fed versus fasting across a range of minimum inhibitory concentrations (MICs) were in line with these results. Overall, this study shows that food reduced the AUC0-∞ and Cmax, and prolonged the Tmax of both free and total flucloxacillin concentrations compared with the fasting state, but achievement of free concentration targets associated with efficacy was in most circumstances equivalent. These results suggest that taking flucloxacillin with food is unlikely to compromise efficacy in most circumstances.

Acute pulmonary edema caused by quinine.

A 57-year-old man who had been intermittently taking one 300-mg tablet of quinine sulfate orally for leg cramps experienced transient acute pulmonary edema and hypotension 30-40 minutes after ingestion on two consecutive occasions. He was not taking any concomitant drugs, and there was no alternative explanation for either event. Serial troponin T tests and electrocardiograms, obtained on admission to the hospital, followed by an outpatient echocardiogram and a coronary angiogram, were essentially normal. We compared this case with one previously published and nine previously unpublished reports of quinine-associated pulmonary edema and conclude that some cases of pulmonary edema or adult respiratory distress syndrome in patients with malaria may be caused by an adverse reaction to quinine. Although infrequent, clinicians should be aware of this potentially serious and costly adverse reaction.

Successful antimicrobial therapy and implant retention for streptococcal infection of prosthetic joints.

BACKGROUND: Streptococci cause up to 20% of prosthetic joint infections but this has received little attention in the published literature. METHODS: We reviewed retrospectively our experience with treatment of streptococcal prosthetic joint infections. Patients were followed up for up to 15 years after discontinuation of antimicrobial therapy and up to 8.5 years while on continuous antimicrobial therapy. RESULTS: Eighteen cases were diagnosed between 1984 and 1995. These included one group A, seven group B, one group D, seven group G and one viridans-group streptococcal infection as well as one group B and D streptococcal co-infection. All were late-onset infections and most (11 of 18, 61%) were acute. Hip and knee joints were equally affected. Six of seven group G streptococcal infections were associated with skin or soft tissue infections. Sixteen patients were treated primarily with antimicrobial agents including 5 days to 6 weeks given intravenously and 2 weeks to 8.5 years given orally. At latest follow up, 10 patients had been off antimicrobial therapy for at least 18 months without relapse, one patient had been off antimicrobial therapy for 7 months without relapse and four infections were successfully controlled with long-term suppressive antimicrobial therapy. One infection was unable to be controlled with antimicrobial therapy. CONCLUSIONS: Our results, and those of others, show that prosthetic joint infections caused by streptococci have a relatively good outcome with primary antimicrobial therapy and, when necessary, drainage, lavage or debridement. Provided the prosthesis is stable and the patient can tolerate long-term antimicrobial therapy, this may be an effective alternative to excision arthroplasty.

The utility of routine conjunctival swabs in management of conjunctivitis.

AIM: To determine the accuracy of preliminary results of conjunctival swab culture and to evaluate the utility of preliminary and final conjunctival swab culture results in the routine management of conjunctivitis. METHODS: We prospectively identified 164 conjunctival swabs from adults and children over 3 weeks of age and compared preliminary (next day) with final culture results. We modelled the would-be effect on treatment and clinical outcome of three strategies (indiscriminant, delayed and targeted) for management of acute conjunctivitis. RESULTS: In total, 54 of 164 (33%) samples yielded significant bacterial growth. Compared to final culture, preliminary culture had a sensitivity of 86%, positive predictive value of 98% and specificity of 99%. Modelling showed that an indiscriminant approach to management (all patients given topical antibacterial treatment, no swabs taken) was the most effective at reducing symptoms but led to substantial unnecessary use of topical antibacterial treatment. Modelling showed that a delayed treatment strategy (patients start topical antibacterial treatment only if not improving satisfactorily after 2 days, no swabs taken) was the least effective at reducing symptoms and lead to moderate unnecessary use of topical antibacterial treatment. The targeted treatment strategy (topical antibacterial treatment given to those with clinical predictors of bacterial infection on day 0, positive preliminary culture results on day 1 and positive final culture results on day 2) was highly effective at reducing symptoms and potentially the least wasteful of topical antibacterial treatment. CONCLUSION: Preliminary (next day) conjunctival swab culture results are highly predictive of the final result and could be used by practitioners to guide prescription of topical antibacterial treatment.

Acute infective conjunctivitis: evidence review and management advice for New Zealand practitioners.

In this review we present and discuss recent data and provide recommendations for New Zealand practitioners regarding the diagnosis and management of acute infective conjunctivitis. In particular, we discuss clinical predictors of bacterial versus viral conjunctivitis, a potential role for routine conjunctival culture, the benefits of topical antibiotic therapy for bacterial infections, delayed treatment algorithms, choice of topical antibiotic and the restriction of selected patients from work, school or early childhood care.

Short-course therapy for bloodstream infections in immunocompetent adults.

Short courses of antibiotic therapy have many advantages. However, determining which patients may safely receive abbreviated therapy can be challenging. In this review we present data for bloodstream infections caused by various organisms, linking outcomes to factors such as the duration of symptoms and bacteraemia before and after initiation of treatment, community vs. hospital acquisition of infection, evidence of foci of tissue infection, presence of foreign material, immune status and response to antibiotics. These data support the following recommendations for the minimum duration of antibiotic treatment for carefully selected low-risk patients with bloodstream infections: Staphylococcus aureus, 14 days; coagulase-negative staphylococci, 3-5 days; enterococci, 7 days; viridans-group streptococci, 3-5 days and Candida spp., 7 days. Patients with bloodstream infections treated with short-course therapy must be followed carefully for occult complications, and should ideally be under the care of an infectious diseases physician.