Oral Flucloxacillin for Treating Osteomyelitis: A Narrative Review of Clinical Practice

Assessment and management of diabetes-related foot infection according to the new International Working Group on the Diabetic Foot guidelines 2023-Multidisciplinary grand rounds

Diabetes-related foot disease is a serious and common complication for people with diabetes mellitus. The gold standard care for a person with diabetes-related foot disease is the involvement of a multidisciplinary foot team engaged in evidence-based care. To date, there are seven International Working Group on the Diabetic Foot (IWGDF) guidelines published to assist healthcare providers in managing diabetes-related foot disease around the world. This review discusses the acute management of diabetes-related foot infection with insights from experts of various specialities (internal medicine, infectious disease, vascular surgery, radiology) with a discussion on the implementation of IWGDF guidelines in real life practice and the challenges that healthcare providers may face.

Initial antibiotic therapy for postoperative moderate or severe diabetic foot infections: Broad versus narrow spectrum, empirical versus targeted

AIM

To retrospectively evaluate clinical and microbiological outcomes after combined surgical and medical therapy for diabetic foot infections (DFIs), stratifying between the empirical versus the targeted nature, and between an empirical broad versus a narrow-spectrum, antibiotic therapy.

METHODS

We retrospectively assessed the rate of ultimate therapeutic failures for each of three types of initial postoperative antibiotic therapy: adequate empirical therapy; culture-guided therapy; and empirical inadequate therapy with a switch to targeted treatment based on available microbiological results.

RESULTS

We included data from 332 patients who underwent 716 DFI episodes of surgical debridement, including partial amputations. Clinical failure occurred in 40 of 194 (20.6%) episodes where adequate empirical therapy was given, in 77 of 291 (26.5%) episodes using culture-guided (and correct) therapy from the start, and in 73 of 231 (31.6%) episodes with switching from empirical inadequate therapy to culture-targeted therapy. Equally, a broad-spectrum antibiotic choice could not alter this failure risk. Group comparisons, Kaplan-Meier curves and Cox regression analyses failed to show either statistical superiority or inferiority of any of the initial antibiotic strategies.

CONCLUSIONS

In this study, the microbiological adequacy of the initial antibiotic regimen after (surgical) debridement for DFI did not alter therapeutic outcomes. We recommend that clinicians follow the stewardship approach of avoiding antibiotic de-escalation and start with a narrow-spectrum regimen based on the local epidemiology.

Not recommended fixed-dose antibiotic combinations in low- and middle-income countries - the example of Tanzania

BACKGROUND

Fixed-dose combinations (FDC) are medicine formulations that combine two or more ingredients in fixed ratios in a single dose form. Although advantageous in tuberculosis and malaria (efficacy, adherence, protection against resistance), only a few antibiotic FDC (FDC-AB) have been developed along full microbiological, pharmacological and clinical validation and safety studies. The World Health Organization (WHO) database of Access, Watch and Reserve (AWaRe) antibiotics contains, since 2021, a list of "Not Recommended" FDC-AB (n = 103) which are rejected for use in clinical practice. BODY: The share of non-recommended FDC-AB in global antimicrobial use (2000-2015) was < 3% but substantially higher in middle income countries. The share increases over time, but recent data particular concerning sub-Saharan Africa are rare. Along three non-recommended FDC-AB listed in the Tanzanian National Essential Medicine List (ampicillin-cloxacillin, flucloxacillin-amoxicillin and ceftriaxone-sulbactam) we discuss the concerns and reasons behind use of these products. Non-recommended FDC-AB have poor rationale (ratios of both ingredients), lack evidence of efficacy (pharmacological, microbiological and clinical), have difficulties in dosing (underdosing of the single ingredients, absence of pediatric dosing) and risks of safety (additive toxicity). They are expected to fuel antimicrobial resistance (unnecessary broad spectrum coverage) and are incompatible with antimicrobial stewardship. The specific context of low- and middle-income countries contributes to their increased use: at the side of prescriber and supplier are the lack of diagnostics, poor training in antibiotic prescribing, patients' preferences, role-model of senior prescribers and pharmaceutical promotion. International market mechanisms include economic motivation for development, branding and promotion, poor access to the single antibiotic forms and weak national regulatory capacity.

CONCLUSION AND IMPLICATIONS

There is an urgent need for monitoring consumption of non-recommended FDC-AB in low- and middle-income countries, particular in Sub-Saharan Africa. A multinational and multisectoral antimicrobial stewardship strategy is needed in order to abolish the use of non-recommended FDC-AB.

Steady-state concentrations of flucloxacillin in porcine vertebral cancellous bone and intervertebral disc following oral and intravenous administration assessed by microdialysis

AIMS

Flucloxacillin is a frequently used antibiotic in the treatment of spondylodiscitis. We assessed steady-state concentrations and time above minimal inhibitory concentration (fT > MIC) of flucloxacillin in the intervertebral disc, vertebral cancellous bone, subcutaneous tissue and plasma, after intravenous and oral administration.

METHODS

Sixteen pigs were randomized into two groups; Group Peroral (Group PO) and Group Intravenous (Group IV) received 1 g flucloxacillin every 6 h for 24 h orally or intravenously. Microdialysis was used for sampling in the compartments of interest. A flucloxacillin target of 50% fT > MIC was applied for three MIC targets: 0.125, 0.5 and 2.0 μg/mL.

RESULTS

Intravenous administration resulted in significantly longer fT > MIC for all targets. Target attainment was only reached for the low target of 0.125 μg/mL in Group IV in vertebral cancellous bone, subcutaneous tissue, and plasma (intervertebral disc 47%). In Group IV, mean fT > MIC values in the investigated compartments were in the range of 47-67% of the dosing interval for 0.125 μg/mL, 20-35% for 0.5 μg/mL, and 0-15% for 2.0 μg/mL. In Group PO, mean fT > MIC values for 0.125 μg/mL were in the range of 1-33%. No pigs reached a concentration of 0.5 μg/mL in any of the investigated compartments in Group PO.

CONCLUSION

Administration of 1 g flucloxacillin every 6 h resulted in surprisingly low steady-state fT > MIC after intravenous and oral administration. However, intravenous administration resulted in significantly higher concentrations across compartments compared to oral administration. Sufficient target tissue concentrations for treatment of spondylodiscitis may require a dose increase or alternative dosing regimens.

Population Pharmacokinetics of Flucloxacillin In Bone and Soft Tissue- Standard Dosing is Not Sufficient to Achieve Therapeutic Concentrations

PURPOSE

Flucloxacillin is a β-lactam penicillin commonly used in the treatment of bone and soft tissue infections. In a recent porcine study, we found surprisingly low time for which the free concentration was maintained above the minimal inhibitory concentration (fT>MIC) in bone and soft tissue, following flucloxacillin oral (PO) and intravenous (IV) administration at 1g every 6h (q6h). In addition to plasma, sampling was obtained from subcutaneous tissue, knee joint, cancellous bone and cortical bone, using microdialysis. To identify flucloxacillin dosing regimens that result in theoretically therapeutic concentrations, we developed a population pharmacokinetic (PK) model for the porcine data, and combined it with a human flucloxacillin population PK model for simulations.

METHODS

A four-compartment model was developed, and various dosing regimens and modes of administration were simulated. Predicted concentrations were compared to %fT>MIC (0.5 mg/L and 2 mg/L).

RESULTS

Continuous infusion (CI) resulted in higher %fT>MIC compared to intermittent administration. For intermittent IV dosing (4, 8 and 12g/24h), fT>MIC (0.5 mg/L) was ≥70% in plasma, and ranged between 42-96% in the sampled tissue in a typical individual. By applying CI, 4g/day was sufficient to achieve ≥98% fT>MIC (0.5 mg/L) in all sampled tissues. For MIC 2 mg/L, ≥50% fT>MIC was only achieved in plasma at CI 8 and 12g/24h and IV 3g q6h.

CONCLUSIONS

To reach efficacious flucloxacillin bone and tissue concentrations, dose increment or continuous infusion needs to be considered.

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.

Flucloxacillin bone and soft tissue concentrations assessed by microdialysis in pigs after intravenous and oral administration

Aims

Flucloxacillin is commonly administered intravenously for perioperative antimicrobial prophylaxis, while oral administration is typical for prophylaxis following smaller traumatic wounds. We assessed the time, for which the free flucloxacillin concentration was maintained above the minimum inhibitory concentration (fT > MIC) for methicillin-susceptible Staphylococcus aureus in soft and bone tissue, after intravenous and oral administration, using microdialysis in a porcine model.

Methods

A total of 16 pigs were randomly allocated to either intravenous (Group IV) or oral (Group PO) flucloxacillin 1 g every six hours during a 24-hour period. Microdialysis was used for sampling in cancellous and cortical bone, subcutaneous tissue, and the knee joint. In addition, plasma was sampled. The flucloxacillin fT > MIC was evaluated using a low MIC target (0.5 μg/ml) and a high MIC target (2.0 μg/ml).

Results

Intravenous administration resulted in longer fT > MIC (0.5 μg/ml) compared to oral administration, except for cortical bone. In Group IV, all pigs reached a concentration of 0.5 μg/ml in all compartments. The mean fT > MIC (0.5 μg/ml) was 149 minutes (95% confidence interval (CI) 119 to 179; range 68 to 323) in subcutaneous tissue and 61 minutes (95% CI 29 to 94; range 0 to 121) to 106 minutes (95% CI 76 to 136; range 71 to 154) in bone tissue. In Group PO, 0/8 pigs reached a concentration of 0.5 μg/ml in all compartments. For the high MIC target (2.0 μg/ml), fT > MIC was close to zero minutes in both groups across compartments.

Conclusion

Although intravenous administration of flucloxacillin 1 g provided higher fT > MIC for the low MIC target compared to oral administration, concentrations were surprisingly low, particularly for bone tissue. Achievement of sufficient bone and soft tissue flucloxacillin concentrations may require a dose increase or continuous administration.

Cite this article: Bone Joint Res 2021;10(1):60–67.

Three versus six weeks of antibiotic therapy for diabetic foot osteomyelitis: A prospective, randomized, non-inferiority pilot trial

BACKGROUND

In patients with diabetic foot osteomyelitis (DFO) who underwent surgical debridement, we investigated whether a short (3 weeks), compared with a long (6 weeks) duration of systemic antibiotic treatment is associated with non-inferior results for clinical remission and adverse events (AE).

METHODS

In this prospective, randomized, non-inferiority, pilot trial, we randomized (allocation 1:1), patients with DFO after surgical debridement to either a 3-week or a 6-week course of antibiotic therapy. The minimal duration of follow-up after end of therapy was two months. We compared outcomes using Cox regression and non-inferiority analyses (25% margin, power 80%).

RESULTS

Among 93 enrolled patients (18% females; median age 65 years), 44 were randomized to the 3-week arm and 49 to the 6-week arm. The median number of surgical debridement was 1 (range, 0-2 interventions). In the intention-to-treat (ITT) population, remission occurred in 37 (84%) of the patients in the 3-week arm compared to 36 (73%) in the 6-week arm (p=0.21). The number of AE was similar in the two study arms (17/44 vs. 16/49; p=0.51), as were the remission incidences in the per-protocol (PP) population (33/39 vs. 32/43; p=0.26). In multivariate analysis, treatment with the shorter antibiotic course was not significantly associated with remission (for the ITT population, hazard ratio 1.1, 95%CI 0.6-1.7; for the PP population hazard ratio 0.8, 95%CI 0.5-1.4).

CONCLUSIONS

In this randomized, controlled pilot trial, a post-debridement systemic antibiotic therapy course for DFO of 3-weeks gave similar (and statistically non-inferior) incidences of remission and AE to a course of 6 weeks.

Oral Flucloxacillin for Staphylococcal Osteomyelitis: Obsolete or Underused?

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