Development and validation of an UPLC-MS/MS assay for the simultaneous quantification of seven commonly used antibiotics in human plasma and its application in therapeutic drug monitoring.

OBJECTIVE: To develop and validate an UPLC-MS/MS assay for simultaneous determination of the total concentration of ceftazidime, ciprofloxacin, flucloxacillin, piperacillin, tazobactam, sulfamethoxazole, N-acetyl sulfamethoxazole and trimethoprim, and the protein-unbound concentration of flucloxacillin, in human plasma to be used for research and clinical practice. METHODS: Sample pretreatment included protein precipitation with methanol. For the measurement of protein-unbound flucloxacillin, ultrafiltration was performed at physiological temperature. For all compounds, a stable isotopically labelled internal standard was used. Reliability of the results was assessed by participation in an international quality control programme. RESULTS: The assay was successfully validated according to the EMA guidelines over a concentration range of 0.5-100 mg/L for ceftazidime, 0.05-10 mg/L for ciprofloxacin, 0.4-125 mg/L for flucloxacillin, 0.2-60 mg/L for piperacillin, 0.15-30 mg/L for tazobactam, 1-200 mg/L for sulfamethoxazole and N-acetyl sulfamethoxazole, 0.05-10 mg/L for trimethoprim and 0.10-50 mg/L for unbound flucloxacillin. For measurement of total concentrations, the within- and between-day accuracy ranged from 90.0% to 109%, and 93.4% to 108%, respectively. Within- and between-day precision (variation coefficients, CVs) ranged from 1.70% to 11.2%, and 0.290% to 5.30%, respectively. For unbound flucloxacillin, within-day accuracy ranged from 103% to 106% and between-day accuracy from 102% to 105%. The within- and between-day CVs ranged from 1.92% to 7.11%. Results of the international quality control programme showed that the assay is reliable. CONCLUSIONS: The method provided reliable, precise and accurate measurement of seven commonly prescribed antibiotics, including the unbound concentration of flucloxacillin. This method is now routinely applied in research and clinical practice.

[Flucloxacillin-induced hypokalemia]. / Door flucloxacilline geïnduceerde hypokaliëmie.

Flucloxacillin-induced hypokalaemia can be progressive and life-threatening, despite of potassium supplementation. In this case description, a high dose of intravenous flucloxacillin was started after a 68-year-old patient presented with an infected knee replacement. After two days, hypokalaemia was noted with an inadequate response to potassium supplementation. It was decided to change antibiotics and increase potassium supplementation, with good results. It is advisable to include monitoring of potassium levels in local treatment protocols when flucloxacillin is prescribed.

Oral antimicrobial therapy for cellulitis versus outpatient parenteral antimicrobial therapy: a single-centre audit of cellulitis outcomes.

BACKGROUND: Cellulitis is a common acute skin and soft tissue infection that causes substantial morbidity and healthcare costs. AIMS: To audit the impact on cellulitis management, regimen tolerability and outcomes of switching from outpatient parenteral antimicrobial therapy (OPAT) using intravenous (i.v.) cefazolin once daily plus probenecid to oral beta-lactam therapy (OBLT) using oral flucloxacillin plus probenecid. METHODS: We undertook a retrospective audit on cellulitis management, regimen tolerability and outcomes at the Dunedin Public Hospital Emergency Department (ED) before and after a change of the local outpatient cellulitis treatment pathway from OPAT using i.v. cefazolin once daily plus probenecid to OBLT using oral flucloxacillin plus probenecid. RESULTS: OPAT was used in 97/123 (78.9%) patients with cellulitis before compared to 1/70 (1.4%) after the pathway change (odds ratio (OR), 0.04, P < 0.01). OBLT was used in 26/123 (21.1%) patients with cellulitis before and 69/70 (98.6%) after (OR, 218.8, P < 0.01). Antimicrobial change due to intolerance occurred in 4/123 (3.2%) patients with cellulitis before and 4/70 (5.7%) after (OR, 1.8, P, not significant (NS)) the pathway change. Inpatient admission within 28 days occurred in 15/123 (12.2%) cellulitis patients before and 9/70 (12.9%) after (OR, 1.1, P, NS) the pathway change. CONCLUSIONS: Implementation of a change in outpatient cellulitis treatment pathway resulted in a significant change in prescribing practice. Our findings suggest that OBLT was both tolerable and had similar outcomes to OPAT.

Flucloxacillin worsens while imipenem-cilastatin protects against vancomycin-induced kidney injury in a translational rat model.

BACKGROUND AND PURPOSE: Vancomycin is one of the most common clinical antibiotics, yet acute kidney injury is a major limiting factor. Common combinations of antibiotics with vancomycin have been reported to worsen and improve vancomycin-induced kidney injury. We aimed to study the impact of flucloxacillin and imipenem-cilastatin on kidney injury when combined with vancomycin in our translational rat model. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats received allometrically scaled (1) vancomycin, (2) flucloxacillin, (3) vancomycin + flucloxacillin, (4) vancomycin + imipenem-cilastatin or (5) saline for 4 days. Kidney injury was evaluated via drug accumulation and urinary biomarkers including urinary output, kidney injury molecule-1 (KIM-1), clusterin and osteopontin. Relationships between vancomycin accumulation in the kidney and urinary kidney injury biomarkers were explored. KEY RESULTS: Urinary output increased every study day for vancomycin + flucloxacillin, but after the first dose only in the vancomycin group. In the vancomycin + flucloxacillin group, urinary KIM-1 increased on all days compared with vancomycin. In the vancomycin + imipenem-cilastatin group, urinary KIM-1 was decreased on Days 1 and 2 compared with vancomycin. Similar trends were observed for clusterin. More vancomycin accumulated in the kidney with vancomycin + flucloxacillin compared with vancomycin and vancomycin + imipenem-cilastatin. The accumulation of vancomycin in the kidney tissue correlated with increasing urinary KIM-1. CONCLUSIONS AND IMPLICATIONS: Vancomycin + flucloxacillin caused more kidney injury compared with vancomycin alone and vancomycin + imipenem-cilastatin in a translational rat model. The combination of vancomycin + imipenem-cilastatin was nephroprotective.

Single-cell patterning and characterisation of antibiotic persistent bacteria using bio-sCAPA.

In microbiology, accessing single-cell information within large populations is pivotal. Here we introduce bio-sCAPA, a technique for patterning bacterial cells in defined geometric arrangements and monitoring their growth in various nutrient environments. We demonstrate bio-sCAPA with a study of subpopulations of antibiotic-tolerant bacteria, known as persister cells, which can survive exposure to high doses of antibiotics despite lacking any genetic resistance to the drug. Persister cells are associated with chronic and relapsing infections, yet are difficult to study due in part to a lack of scalable, single-cell characterisation methods. As >105 cells can be patterned on each template, and multiple templates can be patterned in parallel, bio-sCAPA allows for very rare population phenotypes to be monitored with single-cell precision across various environmental conditions. Using bio-sCAPA, we analysed the phenotypic characteristics of single Staphylococcus aureus cells tolerant to flucloxacillin and rifampicin killing. We find that antibiotic-tolerant S. aureus cells do not display significant heterogeneity in growth rate and are instead characterised by prolonged lag-time phenotypes alone.

Incidence and predisposing factors for flucloxacillin-related hepatotoxicity in children.

BACKGROUND: Flucloxacillin-induced hepatotoxicity is well established in adults. However, there are few paediatric studies of flucloxacillin-induced hepatotoxicity despite this drug being among the most commonly prescribed in children. We aimed to determine the incidence of flucloxacillin-induced hepatotoxicity in children receiving IV therapy as well as identify risk factors for this adverse drug reaction. METHODS: We undertook a 2 year retrospective audit of children aged 0-18 years admitted to the Royal Children's Hospital (March 2019 to March 2021) who had liver function tests determined before and after receiving IV flucloxacillin for at least 24 hours duration. Causality was assessed using the Roussel Uclaf Causality Assessment Method and Naranjo criteria. RESULTS: Overall, the incidence of hepatotoxicity was 66/393 (17%). The median age of children with hepatotoxicity was 1.1 years (IQR 0.3-11.9), 43 (65%) received two or more concomitant hepatotoxic medications and 23 (35%) were receiving total parenteral nutrition. The median timing of onset of hepatotoxicity after commencement of flucloxacillin was 4 days (range 2-7). Severe hepatotoxicity (Common Terminology Criteria for Adverse Events grade 3 or above) occurred in 9/66 (14%) for bilirubin, 13/66 (20%) for ALT and 10/66 (15%) for GGT. Predisposing factors for hepatotoxicity were increasing age (OR 1.06 per additional year, 95% CI 1.01-1.10, P = 0.02), with adolescents aged 12-18 years having the highest risk (OR 5.10, 95% CI 2.02-12.85, P = 0.001), and two or more concomitant hepatotoxic medications (OR 2.51, 95% CI 1.02-6.18, P = 0.05). The median time to resolution of hepatotoxicity after cessation of flucloxacillin was 5 days (range 2-10). CONCLUSIONS: In children, older patients and those receiving two or more concomitant hepatotoxic medications are at greater risk of flucloxacillin-induced hepatotoxicity.

Reduced bacterial resistance antibiotics with improved microbiota tolerance in human intestinal: Molecular design and mechanism analysis.

Antibiotic selectivity and bacterial resistance are critical global public health issues. We constructed a multi-class machine learning model to study antibiotic effects on human intestinal microbiota abundance and identified key features. Binding energies of ß-lactam antibiotics with Escherichia coli PBP3 mutant protein were calculated, and a 2D-QSAR model for bacterial resistance was established. Sensitivity analysis identified key features affecting bacterial resistance. By coupling key features from the machine learning model and 2D-QSAR model, we designed ten flucloxacillin (FLU) substitutes that improved intestinal microbiota tolerance and reduced antibiotic bacterial resistance. Concurrently, the substitutes exhibited superior degradability in soil, aquatic environments, and under photolytic conditions, coupled with a reduced environmental toxicity compared to the FLU. Evaluations under combined medication revealed significant improvements in functionality and bacterial resistance for 80% of FLU substitutes, with 50% showing more than a twofold increase. Mechanistic analysis demonstrated enhanced binding to target proteins and increased biodegradability for FLU substitutes due to more concentrated surface charges. Reduced solvent hindrance and increased cell membrane permeability of FLU substitutes, mainly due to enhanced interactions with phospholipid bilayers, contributed to their functional selectivity. This study aims to address poor antibiotic selectivity and strong bacterial resistance, providing guidance for designing antibiotic substitutes.

The Neonatal and Paediatric Pharmacokinetics of Antimicrobials study (NAPPA): investigating amoxicillin, benzylpenicillin, flucloxacillin and piperacillin pharmacokinetics from birth to adolescence.

BACKGROUND: Pharmacokinetic (PK) data underlying paediatric penicillin dosing remain limited, especially in critical care. OBJECTIVES: The primary objective of the Neonatal and Paediatric Pharmacokinetics of Antimicrobials study (NAPPA) was to characterize PK profiles of commonly used penicillins using data obtained during routine care, to further understanding of PK variability and inform future evidence-based dosing. METHODS: NAPPA was a multicentre study of amoxicillin, co-amoxiclav, benzylpenicillin, flucloxacillin and piperacillin/tazobactam. Patients were recruited with informed consent. Antibiotic dosing followed standard of care. PK samples were obtained opportunistically or at optimal times, frozen and analysed using UPLC with tandem MS. Pharmacometric analysis was undertaken using NONMEM software (v7.3). Model-based simulations (n = 10 000) tested PTA with British National Formulary for Children (BNFC) and WHO dosing. The study had ethical approval. RESULTS: For the combined IV PK model, 963 PK samples from 370 participants were analysed simultaneously incorporating amoxicillin, benzylpenicillin, flucloxacillin and piperacillin data. BNFC high-dose regimen simulations gave these PTA results (median fT>MIC at breakpoints of specified pathogens): amoxicillin 100% (Streptococcus pneumoniae); benzylpenicillin 100% (Group B Streptococcus); flucloxacillin 48% (MSSA); and piperacillin 100% (Pseudomonas aeruginosa). Oral population PK models for flucloxacillin and amoxicillin enabled estimation of first-order absorption rate constants (1.16 h-1 and 1.3 h-1) and bioavailability terms (62.7% and 58.7%, respectively). CONCLUSIONS: NAPPA represents, to our knowledge, the largest prospective combined paediatric penicillin PK study undertaken to date, and the first paediatric flucloxacillin oral PK model. The PTA results provide evidence supportive of BNFC high-dose IV regimens for amoxicillin, benzylpenicillin and piperacillin.

Oral antimicrobial agents in patients with short bowel syndrome: worth a try!

BACKGROUND: The use of oral antimicrobial agents in patients with short bowel syndrome (SBS) is challenging due to the changes in gastrointestinal anatomy that may result in diminished absorption and altered drug bioavailability. Prospective studies evaluating bioavailability of antimicrobial agents after oral administration in SBS patients are lacking. OBJECTIVES: To determine the bioavailability of orally administered antimicrobial agents commonly used for treatment in SBS patients to guide clinical decision making when faced with infections. METHODS: We performed an explorative, clinical study investigating the pharmacokinetics (PK) of clindamycin, ciprofloxacin, flucloxacillin and fluconazole in SBS patients with intestinal failure. Participants received a combination of two antimicrobial agents simultaneously. To determine the oral bioavailability, participants received a single oral and IV dose of both agents on two occasions, after which they underwent intensive PK sampling on six predefined time points up to 12 hours after administration. Primary outcome was the oral bioavailability of these antimicrobial agents. Secondary outcomes were intravenous PK characteristics following non-compartmental analysis. RESULTS: Eighteen SBS patients were included: the mean (SD) age was 59 (17) years and 61% of participants were female. The median observed (IQR) bioavailability of ciprofloxacin, clindamycin, flucloxacillin and fluconazole were 36% (24-50), 93% (56-106), 50% (32-76) and 98% (61-107), respectively. CONCLUSION: The bioavailability of selected antimicrobial agents in certain patients with SBS appeared to be better than expected, providing a feasible treatment option. Due to the large observed differences between patients, therapeutic drug monitoring should be part of the treatment to safeguard adequate exposure in all patients. TRIAL REGISTRATION: Registered in the Dutch Trial Register (NL7796) and EudraCT number 2019-002587-28.

It cuts both ways: A single-center retrospective review describing a three-way interaction between flucloxacillin, voriconazole and tacrolimus.

AIM: Tacrolimus is a CYP3A4 substrate with a narrow therapeutic index that requires dose adjustment when used with voriconazole, a recognized CYP3A4 inhibitor. Interactions involving flucloxacillin and tacrolimus or voriconazole individually have been shown to result in decreased concentrations of the latter two drugs. Tacrolimus concentrations have been reported to be unaffected by flucloxacillin when voriconazole is administered; however, this has not been extensively investigated. METHODS: Retrospective review of voriconazole and tacrolimus concentrations and subsequent dose adjustment following flucloxacillin administration. RESULTS: Eight transplant recipients (five lung, two re-do lung, one heart) received concurrent flucloxacillin, voriconazole and tacrolimus. Voriconazole trough concentrations were measured before flucloxacillin initiation in three of eight patients and all trough concentrations were therapeutic. Following flucloxacillin initiation, all eight patients exhibited subtherapeutic concentrations of voriconazole (median concentration 0.15 mg/L [interquartile range (IQR) 0.10-0.28]). In five patients, voriconazole concentrations remained subtherapeutic despite dose increases, and treatment for two patients was changed to alternative antifungal agents. All eight patients required tacrolimus dose increases to maintain therapeutic concentrations after flucloxacillin initiation. Median total daily dose prior to flucloxacillin treatment was 3.5 mg [IQR 2.0-4.3] and this increased to 13.5 mg [IQR 9.5-20] (P=0.0026) during flucloxacillin treatment. When flucloxacillin was ceased, the median tacrolimus total daily dose reduced to 2.2 mg [IQR 1.9-4.7]. Supra-therapeutic tacrolimus concentrations were observed in seven patients after flucloxacillin discontinuation (median concentration 19.7 µg/L [IQR 17.9-28.0]). CONCLUSION: A significant three-way interaction was shown between flucloxacillin, voriconazole and tacrolimus, resulting in subtherapeutic voriconazole concentrations, and requiring substantial tacrolimus dose increases. Administration of flucloxacillin to patients receiving voriconazole should be avoided. Tacrolimus concentrations should be closely monitored, and dosing adjusted during and after flucloxacillin administration.

Are insect bites responsible for the rise in summer flucloxacillin prescribing in United Kingdom general practices?

BACKGROUND: Insect bite inflammation may mimic cellulitis and promote unnecessary antibiotic usage, contributing to antimicrobial resistance in primary care. We wondered how general practice clinicians assess and manage insect bites, diagnose cellulitis, and prescribe antibiotics. METHOD: This is a Quality Improvement study in which 10 general practices in England and Wales investigated patients attending for the first time with insect bites between April and September 2021 to their practices. Mode of consultation, presentation, management plan, and reattendance or referral were noted. Total practice flucloxacillin prescribing was compared to that for insect bites. RESULTS: A combined list size of 161,346 yielded 355 insect bite consultations. Nearly two-thirds were female, ages 3-89 years old, with July as the peak month and a mean weekly incidence of 8 per 100,000. GPs still undertook most consultations; most were phone consultations, with photo support for over half. Over 40% presented between days 1 and 3 and common symptoms were redness, itchness, pain, and heat. Vital sign recording was not common, and only 22% of patients were already taking an antihistamine despite 45% complaining of itch. Antibiotics were prescribed to nearly three-quarters of the patients, mainly orally and mostly as flucloxacillin. Reattendance occurred for 12% and referral to hospital for 2%. Flucloxacillin for insect bites contributed a mean of 5.1% of total practice flucloxacillin prescriptions, with a peak of 10.7% in July. CONCLUSIONS: Antibiotics are likely to be overused in our insect bite practice and patients could make more use of antihistamines for itch before consulting.

It can be difficult to know if redness, heat, swelling, and pain from insect bites are due to inflammation or infection. Prescribing unnecessary antibiotics may result in germs becoming resistant to antibiotics when needed. Ten general practices in England and Wales investigated their management of insect bites in the 6 months of April to September 2021 inclusive. There were 355 bites; women presented more often than men, and ages were from 3 to 89 years old, half of them were 30­69 years old. People mainly consulted their GP by phone with photos of their bites. Key symptoms were redness, itchness, heat, and pain. More people had itch than were taking antihistamines or using steroid cream. Most people (nearly 7 out of 10) were prescribed an oral antibiotic, usually flucloxacillin, which accounted for about 5% of total flucloxacillin prescribed in the practices. Only 2 in 100 people needed further hospital care. It is likely that general practice clinicians are over-using antibiotics for insect bites and that home management before seeking medical help with painkillers, antihistamines, and steroid creams could be used more. Now that we have baseline data, there is a need to set up studies to prove that these reduce antibiotic usage.

Flucloxacillin Is a Weak Inducer of CYP3A4 in Healthy Adults and 3D Spheroid of Primary Human Hepatocytes.

Flucloxacillin is a widely used antibiotic. It is an agonist to the nuclear receptor PXR that regulates the expression of cytochrome P450 (CYP) enzymes. Treatment with flucloxacillin reduces warfarin efficacy and plasma concentrations of tacrolimus, voriconazole, and repaglinide. We conducted a translational study to investigate if flucloxacillin induces CYP enzymes. We also investigated if flucloxacillin induces its own metabolism as an autoinducer. We performed a randomized, unblinded, two-period, cross-over, clinical pharmacokinetic cocktail study. Twelve healthy adults completed the study. They ingested 1 g flucloxacillin 3 times daily for 31 days, and we assessed the full pharmacokinetics of the Basel cocktail drugs on days 0, 10, and 28, and plasma concentrations of flucloxacillin on days 0, 9, and 27. The 3D spheroid of primary human hepatocytes (PHHs) were exposed to flucloxacillin (concentration range: 0.15-250 µM) for 96 hours. Induction of mRNA expression, protein abundance, and enzyme activity of CYP enzymes were assessed. Flucloxacillin treatment reduced the metabolic ratio of midazolam (CYP3A4), (geometric mean ratio (GMR) 10 days (95% confidence interval (CI)): 0.75 (0.64-0.89)) and (GMR 28 days (95% CI): 0.72 (0.62-0.85)). Plasma concentrations of flucloxacillin did not change during 27 days of treatment. Flucloxacillin caused concentration-dependent induction of CYP3A4 and CYP2B6 (mRNA, protein, and activity), CYP2C9 (mRNA and protein), CYP2C19 (mRNA and activity), and CYP2D6 (activity) in 3D spheroid PHH. In conclusion, flucloxacillin is a weak inducer of CYP3A4, which may lead to clinically relevant drug-drug interactions for some narrow therapeutic range drugs that are substrates of CYP3A4.

Stability of 10 Beta-Lactam Antibiotics in Human Plasma at Different Storage Conditions.

BACKGROUND: Recently, several studies have assessed the effects of therapeutic drug monitoring of frequently prescribed beta-lactam antibiotics, for which they were quantified in human plasma samples. Beta-lactams are considered unstable, leading to extra challenges in quantification. Therefore, to ensure sample stability and minimize sample degradation before analysis, stability studies are crucial. This study investigated the stability of 10 frequently used beta-lactam antibiotics in human plasma at relevant storage conditions for clinical use. METHODS: Amoxicillin, benzylpenicillin, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, flucloxacillin, imipenem, meropenem, and piperacillin were analyzed using ultraperformance convergence chromatography tandem mass spectrometry and liquid chromatography tandem mass spectrometry. Their short-term and long-term stabilities were investigated by measuring quality control samples at low and high concentrations against freshly prepared calibration standards. Measured concentrations at each time point were compared with the concentrations at T = 0. Antibiotics were considered stable if recovery results were between 85% and 115%. RESULTS: Short-term stability results indicated ceftriaxone, cefuroxime, and meropenem to be stable up to 24 hours at room temperature. All evaluated antibiotics, except imipenem, were stable on ice in a cool box for 24 hours. Amoxicillin, benzylpenicillin, and piperacillin were stable for 24 hours at 4-6°C. Cefotaxime, ceftazidime, cefuroxime, and meropenem were stable at 4-6°C up to 72 hours. Ceftriaxone and flucloxacillin were stable for 1 week at 4-6°C. Long-term stability results showed that all antibiotics were stable up to 1 year at -80°C, except imipenem and piperacillin, which were stable for 6 months at -80°C. CONCLUSIONS: Plasma samples for amoxicillin, benzylpenicillin, cefotaxime, ceftazidime, flucloxacillin, and piperacillin may be stored for a maximum of 24 hours in a cool box. Refrigeration is suitable for plasma samples of amoxicillin, benzylpenicillin, meropenem, and piperacillin for up to 24 hours and cefotaxime, ceftriaxone, ceftazidime and cefuroxime for 72 hours. Plasma samples for imipenem should be frozen directly at -80°C. For long-term storage, plasma samples can be stored at -80°C for a maximum of 6 months for imipenem and piperacillin and 12 months for all other evaluated antibiotics.

Effect of Microdoses of Incisional Antibiotics on the Rate of Surgical Site Infections in Skin Cancer Surgery: A Randomized Clinical Trial.

Importance: Surgical site infections (SSIs) represent a costly and preventable complication of cutaneous surgery. However, there is a paucity of randomized clinical trials investigating antibiotic prophylaxis for reducing SSIs in skin cancer surgery, and evidence-based guidelines are lacking. Incisional antibiotics have been shown to reduce the rate of SSIs before Mohs micrographic surgery, but this represents a small subset of skin cancer surgery. Objective: To determine whether microdosed incisional antibiotics reduce the rate of SSIs before skin cancer surgery. Design, Setting, and Participants: In this double-blind, controlled, parallel-design randomized clinical trial, adult patients presenting to a high-volume skin cancer treatment center in Auckland, New Zealand, for any form of skin cancer surgery over 6 months from February to July 2019 were included. Patient presentations were randomized to one of 3 treatment arms. Data were analyzed from October 2021 to February 2022. Interventions: Patients received an incision site injection of buffered local anesthetic alone (control), buffered local anesthetic with microdosed flucloxacillin (500 µg/mL), or buffered local anesthetic with microdosed clindamycin (500 µg/mL). Main Outcomes and Measures: The primary end point was the rate of postoperative SSI (calculated as number of lesions with SSI per total number of lesions in the group), defined as a standardized postoperative wound infection score of 5 or more. Results: A total of 681 patients (721 total presentations; 1133 total lesions) returned for postoperative assessments and were analyzed. Of these, 413 (60.6%) were male, and the mean (SD) age was 70.4 (14.8) years. Based on treatment received, the proportion of lesions exhibiting a postoperative wound infection score of 5 or greater was 5.7% (22 of 388) in the control arm, 5.3% (17 of 323) in the flucloxacillin arm, and 2.1% (9 of 422) in the clindamycin arm (P = .01 for clindamycin vs control). Findings were similar after adjusting for baseline differences among arms. Compared with lesions in the control arm (31 of 388 [8.0%]), significantly fewer lesions in the clindamycin arm (9 of 422 [2.1%]; P < .001) and flucloxacillin (13 of 323 [4.0%]; P = .03) arms required postoperative systemic antibiotics. Conclusions and Relevance: This study evaluated the use of incisional antibiotics for SSI prophylaxis in general skin cancer surgery and compared the efficacy of flucloxacillin vs clindamycin relative to control in cutaneous surgery. The significant reduction in SSI with locally applied microdosed incisional clindamycin provides robust evidence to inform treatment guidelines in this area, which are currently lacking. Trial Registration: anzctr.org.au Identifier: ACTRN12616000364471.

Dicloxacillin-warfarin drug-drug interaction-A register-based study and in vitro investigations in 3D spheroid primary human hepatocytes.

AIMS: Dicloxacillin is used to treat staphylococcal infections and we have previously shown that dicloxacillin is an inducer of cytochrome P450 enzymes (CYPs). Here, we employed a translational approach to investigate the effect of a treatment with dicloxacillin on warfarin efficacy in Danish registries. Furthermore, we assessed dicloxacillin as an inducer of CYPs in vitro. METHODS: We conducted a register-based study and analysed international normalized ratio (INR) levels in chronic warfarin users before and after short- and long-term use of dicloxacillin (n = 1023) and flucloxacillin (n = 123). Induction of CYPs were investigated in a novel liver model of 3D spheroid primary human hepatocytes at the level of mRNA, and protein and enzyme activity. RESULTS: Short- and long-term dicloxacillin treatments decreased INR levels by -0.65 (95% confidence interval [CI]: -0.57 to -0.74) and -0.76 (95% CI: -0.50 to -1.02), respectively. More than 90% of individuals experienced subtherapeutic INR levels (below 2) after long-term dicloxacillin treatment. Flucloxacillin decreased INR levels by -0.37 (95% CI: -0.14 to -0.60). In 3D spheroid primary human hepatocytes, the maximal induction of CYP3A4 mRNA, protein and enzyme activity by dicloxacillin were 4.9-, 2.9- and 2.4-fold, respectively. Dicloxacillin also induced CYP2C9 mRNA by 1.7-fold. CONCLUSION: Dicloxacillin induces CYPs and reduces the clinical efficacy of warfarin in patients. This effect is substantially exacerbated during long-term treatment with dicloxacillin. The in vitro results corroborated this drug-drug interaction and correlated to the clinical findings. Caution is warranted for warfarin patients that initiate dicloxacillin or flucloxacillin, especially for a long-term treatment of endocarditis.

Drug-drug interaction: decreased posaconazole trough concentrations during concomitant flucloxacillin treatment.

BACKGROUND AND OBJECTIVES: Posaconazole is used as prophylaxis of invasive fungal disease in immune-compromised haematological patients with prolonged neutropenia after intensive chemotherapy. During routine therapeutic drug monitoring of posaconazole, we repeatedly observed low posaconazole serum concentrations in patients that were concomitantly treated with flucloxacillin. A possible interaction between flucloxacillin and posaconazole was explored in this case series. PATIENTS AND METHODS: Posaconazole trough serum concentrations during and before/after flucloxacillin treatment were collected from 10 patients. RESULTS: With a median concentration of 0.5 mg/L (IQR 0.3-0.6), the posaconazole trough serum concentration decreased by 47% during flucloxacillin treatment compared with the concentration before/after flucloxacillin treatment (0.9 mg/L, IQR 0.6-1.3). As a result, the posaconazole target trough concentration of ≥0.7 mg/L was only achieved in five out of nine patients during flucloxacillin treatment. CONCLUSIONS: Careful monitoring of posaconazole serum trough concentrations is recommended when concomitant use of flucloxacillin cannot be avoided.

Development of mouse models with restricted HLA-B∗57:01 presentation for the study of flucloxacillin-driven T-cell activation and tolerance in liver injury.

BACKGROUND: Flucloxacillin (FLX)-induced liver injury is immune-mediated and highly associated to HLA-B∗57:01 expression. Host factors leading to drug-induced liver injury are not yet well understood. OBJECTIVE: Characterize in vivo immune mechanisms determining the development of CD8+ T cells reactive to FLX in animals expressing the risk human leukocyte antigen (HLA) allotype. METHODS: HLA-B∗57:01 transgenic mice (Tg) or Tg strains with H2-KbDb knockout (Tg/KO) or H2-KbDb/PD-1 double knockout (Tg/DKO) were treated with drug and/or anti-CD4 antibody. Drug-induced liver injury was evaluated on the basis of liver enzyme and histologic changes at day 10 of treatment. FLX-reactive CD8+ T cells were characterized in vitro by release of effector molecules on drug restimulation, gene expression, and flow cytometry analysis, and functionality tested for hepatic cytotoxicity. RESULTS: CD8+ T-cell responses to FLX in Tg were dependent on both HLA and mouse major histocompatibility complex I presentation and in vivo priming. Eliminating H2-KbDb in Tg/KO to allow exclusive presentation of FLX by HLA resulted in a less robust drug-specific CD8+T-cell response unless CD4+ cells, including regulatory T cells, were depleted. Treatment of Tg/KO with anti-CD4 antibody and FLX led to subclinical liver inflammation associated with an increase in PD1+CD8+ T cells in the lymphoid organs and liver. Impaired PD-1 expression in Tg/DKO led to liver histopathologic and transcriptional alterations but without hepatic enzyme elevations. Moreover, effector lymphocytes accumulated in the liver and showed FLX-dependent hepatic cytotoxicity in vitro when tolerogenic liver cells were depleted. CONCLUSIONS: In our in vivo models, FLX primes CD8+ T cells to recognize drug presented by HLA-B∗57:01 and murine major histocompatibility complex I. HLA-B∗57:01-dependent CD8+ T-cell reaction to FLX is limited by the presence of CD4+ cells, presumably regulatory T cells, and PD-1 expression. Tolerogenic hepatic cells limit clinical disease through PD-L1 or additional unexplored mechanisms.

Optimization of ß-Lactam Dosing Regimens in Neonatal Infections: Continuous and Extended Administration versus Intermittent Administration.

BACKGROUND AND OBJECTIVE: In neonates, ß-Lactam antibiotics are almost exclusively administered by intermittent infusion. However, continuous or prolonged infusion may be more beneficial because of the time-dependent antibacterial activity. In this pharmacokinetic/pharmacodynamic simulation study, we aimed to compare treatment with continuous, extended and intermittent infusion of ß-lactam antibiotics for neonates with infectious diseases. METHODS: We selected population pharmacokinetic models of penicillin G, amoxicillin, flucloxacillin, cefotaxime, ceftazidime and meropenem, and performed a Monte Carlo simulation with 30,000 neonates. Four different dosing regimens were simulated: intermittent infusion in 30 min, prolonged infusion in 4 h, continuous infusion, and continuous infusion with a loading dose. The primary endpoint was 90% probability of target attainment (PTA) for 100% ƒT>MIC during the first 48 h of treatment. RESULTS: For all antibiotics except cefotaxime, continuous infusion with a loading dose resulted in a higher PTA compared with other dosing regimens. Sufficient exposure (PTA >90%) using continuous infusion with a loading dose was reached for amoxicillin (90.3%), penicillin G (PTA 98.4%), flucloxacillin (PTA 94.3%), cefotaxime (PTA 100%), and ceftazidime (PTA 100%). Independent of dosing regimen, higher meropenem (PTA for continuous infusion with a loading dose of 85.5%) doses might be needed to treat severe infections in neonates. Ceftazidime and cefotaxime dose might be unnecessarily high, as even with dose reductions, a PTA > 90% was retained. CONCLUSIONS: Continuous infusion after a loading dose leads to a higher PTA compared with continuous, intermittent or prolonged infusion, and therefore has the potential to improve treatment with ß-lactam antibiotics in neonates.

Comparative effectiveness of ß-lactams for empirical treatment of methicillin-susceptible Staphylococcus aureus bacteraemia: a prospective cohort study.

OBJECTIVES: Standard once-daily dosing of ceftriaxone may not lead to adequate antibiotic exposure in all cases of Staphylococcus aureus bacteraemia (SAB). Therefore, we compared clinical effectiveness of empirical antibiotic treatment with flucloxacillin, cefuroxime and ceftriaxone in adult patients with MSSA bacteraemia. METHODS: We analysed data from the Improved Diagnostic Strategies in Staphylococcus aureus bacteraemia (IDISA) study, a multicentre prospective cohort study of adult patients with MSSA bacteraemia. Duration of bacteraemia and 30 day SAB-related mortality were compared between the three groups using multivariable mixed-effects Cox regression analyses. RESULTS: In total, 268 patients with MSSA bacteraemia were included in the analyses. Median duration of empirical antibiotic therapy was 3 (IQR 2-3) days in the total study population. Median duration of bacteraemia was 1.0 (IQR 1.0-3.0) day in the flucloxacillin, cefuroxime and ceftriaxone groups. In multivariable analyses, neither ceftriaxone nor cefuroxime was associated with increased duration of bacteraemia compared with flucloxacillin (HR 1.08, 95% CI 0.73-1.60 and HR 1.22, 95% CI 0.88-1.71). In multivariable analysis, neither cefuroxime nor ceftriaxone was associated with higher 30 day SAB-related mortality compared with flucloxacillin [subdistribution HR (sHR) 1.37, 95% CI 0.42-4.52 and sHR 1.93, 95% CI 0.67-5.60]. CONCLUSIONS: In this study, we could not demonstrate a difference in duration of bacteraemia and 30 day SAB-related mortality between patients with SAB empirically treated with flucloxacillin, cefuroxime or ceftriaxone. Since sample size was limited, it is possible the study was underpowered to find a clinically relevant effect.