Single-dose pharmacokinetics of meropenem in porcine cancellous bone determined by microdialysis: An animal study

Concentrations of Co-Administered Meropenem and Vancomycin in Spinal Tissues Relevant for the Treatment of Pyogenic Spondylodiscitis-An Experimental Microdialysis Study

Co-administration of meropenem and vancomycin has been suggested as a systemic empirical antibiotic treatment of pyogenic spondylodiscitis. The aim of this study was, in an experimental porcine model, to evaluate the percentage of an 8-h dosing interval of co-administered meropenem and vancomycin concentrations above the relevant minimal inhibitory concentrations (MICs) (%T>MIC) in spinal tissues using microdialysis. Eight female pigs (Danish Landrace breed, weight 78-82 kg) received a single-dose bolus infusion of 1000 mg of meropenem and 1000 mg vancomycin simultaneously before microdialysis sampling. Microdialysis catheters were applied in the third cervical (C3) vertebral cancellous bone, the C3-C4 intervertebral disc, paravertebral muscle, and adjacent subcutaneous tissue. Plasma samples were obtained for reference. The main finding was that for both drugs, the %T>MICs were highly reliant on the applied MIC target, but were heterogeneous across all targeted tissues, ranging from 25-90% for meropenem, and 10-100% for vancomycin. For both MIC targets, the highest %T>MIC was demonstrated in plasma, and the lowest %T>MIC was demonstrated in the vertebral cancellous bone for meropenem, and in the intervertebral disc for vancomycin. When indicated, our findings may suggest a more aggressive dosing approach of both meropenem and vancomycin to increase the spinal tissue concentrations to treat the full spectrum of potentially encountered bacteria in a spondylodiscitis treatment setting.

Comparison of Intravenous Microdialysis and Standard Plasma Sampling for Monitoring of Vancomycin and Meropenem Plasma Concentrations-An Experimental Porcine Study

Microdialysis is a catheter-based method suitable for dynamic sampling of unbound antibiotic concentrations. Intravenous antibiotic concentration sampling by microdialysis has several advantages and may be a superior alternative to standard plasma sampling. We aimed to compare concentrations obtained by continuous intravenous microdialysis sampling and by standard plasma sampling of both vancomycin and meropenem in a porcine model. Eight female pigs received 1 g of both vancomycin and meropenem, simultaneously over 100 and 10 min, respectively. Prior to drug infusion, an intravenous microdialysis catheter was placed in the subclavian vein. Microdialysates were collected for 8 h. From a central venous catheter, plasma samples were collected in the middle of every dialysate sampling interval. A higher area under the concentration/time curve and peak drug concentration were found in standard plasma samples compared to intravenous microdialysis samples, for both vancomycin and meropenem. Both vancomycin and meropenem concentrations obtained with intravenous microdialysis were generally lower than from standard plasma sampling. The differences in key pharmacokinetic parameters between the two sampling techniques underline the importance of further investigations to find the most suitable and reliable method for continuous intravenous antibiotic concentration sampling.

Concentrations of co-administered vancomycin and meropenem in the internal dead space of a cannulated screw and in cancellous bone adjacent to the screw - Evaluated by microdialysis in a porcine model

BACKGROUND

Cannulated screws are often used in the management of open lower extremity fractures. These fractures exhibit broad contamination profiles, necessitating empirical Gram-positive and Gram-negative antibiotic coverage. To ensure full antibiotic protection of the cannulated screw and the bone tissue, it is generally accepted that target tissue antibiotic concentrations, as a minimum, reach and remain above relevant epidemiological cut-off minimal inhibitory concentrations (T>MIC) for a sufficient amount of time.

METHODS

8 female pigs were included. Microdialysis catheters were placed in the internal dead space of a cannulated screw placed in tibial cancellous bone, in tibial cancellous bone adjacent to the screw (mean distance to the screw: 3 mm), and in cancellous bone on the contralateral tibia. Following single-dose simultaneous intravenous administrations of vancomycin (1000 mg) and meropenem (1000 mg), microdialysates and plasma were dynamically sampled over 8 h. The applied MIC targets ranged from 1 to 4 µg/mL for vancomycin and 0.125-2 µg/mL for meropenem RESULTS: For both drugs, and for all MIC targets investigated (except for the high vancomycin target: 4 µg/mL), the internal dead space of the cannulated screw had the shortest T>MIC. At the low MIC targets T>MIC ranged between 88 and 449 min across sampling sites for vancomycin (1 µg/mL), and 148-406 min for meropenem (0.125 µg/mL). For the high MIC targets, T>MIC ranged between 3 and 446 min for vancomycin (4 μg/mL) and 17-181 min for meropenem (2 μg/mL). Vancomycin displayed longer T>MIC (2 and 4 μg/mL), higher area under the concentration time curve (AUC_0-last) and peak drug concentration in the proximal tibial cancellous bone without a screw nearby. For meropenem, only the cancellous bone AUC_0-last was significantly higher on the side with no screw.

CONCLUSION

We found short T>MIC, particularly for the high MIC targets for vancomycin and meropenem, both inside the cannulated screw and in cancellous bone adjacent to the screw. The presence of a cannulated screw impaired the penetration of especially vancomycin into cancellous bone adjacent to the screw. More aggressive or different vancomycin and meropenem approaches may be considered to encompass contaminating differences and to ensure a theoretically more sufficient antibiotic protection of cannulated screws when used in the management of open lower extremity fractures.

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.

Tibial bone and soft-tissue concentrations following combination therapy with vancomycin and meropenem - evaluated by microdialysis in a porcine model : should patients with open fractures have higher doses of antibiotics?

Aims

Prompt and sufficient broad-spectrum empirical antibiotic treatment is key to preventing infection following open tibial fractures. Succeeding co-administration, we dynamically assessed the time for which vancomycin and meropenem concentrations were above relevant epidemiological cut-off (ECOFF) minimal inhibitory concentrations (T > MIC) in tibial compartments for the bacteria most frequently encountered in open fractures. Low and high MIC targets were applied: 1 and 4 µg/ml for vancomycin, and 0.125 and 2 µg/ml for meropenem.

Methods

Eight pigs received a single dose of 1,000 mg vancomycin and 1,000 mg meropenem simultaneously over 100 minutes and 10 minutes, respectively. Microdialysis catheters were placed for sampling over eight hours in tibial cancellous bone, cortical bone, and adjacent subcutaneous adipose tissue. Venous blood samples were collected as references.

Results

Across the targeted ECOFF values, vancomycin displayed longer T > MIC in all the investigated compartments in comparison to meropenem. For both drugs, cortical bone exhibited the shortest T > MIC. For the low MIC targets and across compartments, mean T > MIC ranged between 208 and 449 minutes (46% to 100%) for vancomycin and between 189 and 406 minutes (42% to 90%) for meropenem. For the high MIC targets, mean T > MIC ranged between 30 and 446 minutes (7% to 99%) for vancomycin and between 45 and 181 minutes (10% to 40%) for meropenem.

Conclusion

The differences in the T > MIC between the low and high targets illustrate how the interpretation of these results is highly susceptible to the defined MIC target. To encompass any trauma, contamination, or individual tissue differences, a more aggressive dosing approach may be considered to achieve longer T > MIC in all the exposed tissues, and thereby lower the risk of acquiring an infection after open tibial fractures.

Cite this article: Bone Joint Res 2022;11(2):112–120.

Systemic versus free antibiotic delivery in preventing acute exogenous implant related infection in a rat model

We studied systemic ceftriaxone, and free/local tobramycin and doxycycline in a controlled rat model representing a generic acute exogenous joint infection. We hypothesized that evidence of infection (quantitative colony forming units [CFU], qualitative scanning electron microscopy [SEM], histopathology) (1a) would be reduced with local versus systemic antibiotic, (1b) any antibiotic would be superior to control, (2) there would be a difference among antibiotics, and (3) antibiotic would not be detectable in serum at 4-week euthanasia. Study groups included infected and noninfected (1) control (no treatment), (2) systemic ceftriaxone (daily), (3) local tobramycin, and (4) local doxycycline (10 rats/group; power = 0.8). With IACUC approval, a reliable acute exogenous joint infection was created by slowly injecting 50-μl, 10⁴ CFU Staphylococcus aureus, into the distal femoral medullary canal. The antibiotic formulation was introduced locally to the femoral canal and joint space. After 4 weeks, serum, pin, bone, and synovium were obtained. CFU/ml of bone and synovium were quantified using macrotiter method. SEM imaged biofilm on the surface of the pin, histopathology identified tissue response, liquid chromatography/mass spectrometry quantified plasma antibiotic. (1) Groups receiving any antibiotic reported lower CFU/ml in synovium compared with no treatment. (2) In the synovium, free/local tobramycin reduced CFU/ml to a greater extent than free/local doxycycline (p < 0.05). (3) Antibiotic in plasma after the local application was nondetectable in all groups after 4 weeks. SEM revealed no difference in biofilm on pin among all groups.

Effects of tourniquet inflation on peri- and postoperative cefuroxime concentrations in bone and tissue

Background and purpose - Tourniquet is widely used in orthopedic surgery to reduce intraoperative bleeding and improve visualization. We evaluated the effect of tourniquet application on peri- and postoperative cefuroxime concentrations in subcutaneous tissue, skeletal muscle, calcaneal cancellous bone, and plasma. The primary endpoint was the time for which the free cefuroxime concentration was maintained above the clinical breakpoint minimal inhibitory concentration (T > MIC) for Staphylococcus aureus (4 µg/mL).Patients and methods - 10 patients scheduled for hallux valgus or hallux rigidus surgery were included. Microdialysis catheters were placed for sampling of cefuroxime concentrations bilaterally in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone. A tourniquet was applied on the thigh of the leg scheduled for surgery (tourniquet duration time [range]: 65 minutes [58-77]). Cefuroxime (1.5 g) was administered intravenously 15 minutes prior to tourniquet inflation, followed by a second dose 6 hours later. Dialysates and venous blood samples were collected for 12 hours.Results - A cefuroxime concentration of 4 µg/mL was reached within 23 minutes in all compartments and patients. For cefuroxime the T > MIC (4 µg/mL) ranged between 4.8 and 5.4 hours across compartments, with similar results for the tourniquet and non-tourniquet leg. Comparable T > MIC and penetration ratios were found for the first and second dosing intervals.Interpretation - Administration of cefuroxime (1.5 g) 15 minutes prior to tourniquet inflation is safe in order to achieve tissue concentrations above 4 µg/mL throughout surgery. A tourniquet application time of approximately 1 hour did not affect the cefuroxime tissue penetration in the following dosing interval.

Double-dose cefuroxime concentrations in bone, synovial fluid of the knee joint and subcutaneous adipose tissue-A randomised porcine microdialysis study

This study evaluated target tissue concentrations of double dose cefuroxime administered intravenously as either one 15 min infusion of 3000 mg (Group 1) or two single 15 min infusions of 1500 mg administered 4 h apart (Group 2). Sixteen pigs were randomised into two groups of eight. Cortical and cancellous bone, synovial fluid of the knee joint and subcutaneous adipose tissue concentrations were measured based on sampling via microdialysis. Plasma samples were collected as a reference. Comparison of the groups was based on time with concentrations above relevant minimal inhibitory concentrations (fT>MIC) of 4 μg/mL. The mean time fT>MIC (4 μg/mL) across compartments was longer for Group 2 (280-394 min) than for Group 1 (207-253 min) (p<0.01). Cortical bone showed a tendency towards longer fT>MIC (4 μg/mL) in Group 2 (280 min) than in Group 1 (207 min) (p = 0.053). Within 50 min after administration, the mean concentration of 4 μg/mL was reached in all compartments for both groups. The mean concentrations decreased below 4 μg/mL after approximately 4 h (Group 1) and 3 h (Group 2) from initiation of administration (time zero). During an 8 h interval, double-dose cefuroxime administered as 2 × 1500 mg with a 4 h interval provides longer time above MIC breakpoint for Staphylococcus aureus (4 μg/mL) than a single bolus of 3000 mg cefuroxime. To maintain sufficient tissue concentrations during longer surgeries, re-administration of cefuroxime (1500 mg) should be considered 3 h after the first administration.

Development of a large animal rabbit model for chronic periprosthetic joint infection

Aims

Periprosthetic joint infections (PJIs) and osteomyelitis are clinical challenges that are difficult to eradicate. Well-characterized large animal models necessary for testing and validating new treatment strategies for these conditions are lacking. The purpose of this study was to develop a rabbit model of chronic PJI in the distal femur.

Methods

Fresh suspensions of Staphylococcus aureus (ATCC 25923) were prepared in phosphate-buffered saline (PBS) (1 × 10⁹ colony-forming units (CFUs)/ml). Periprosthetic osteomyelitis in female New Zealand white rabbits was induced by intraosseous injection of planktonic bacterial suspension into a predrilled bone tunnel prior to implant screw placement, examined at five and 28 days (n = 5/group) after surgery, and compared to a control aseptic screw group. Radiographs were obtained weekly, and blood was collected to measure ESR, CRP, and white blood cell (WBC) counts. Bone samples and implanted screws were harvested on day 28, and processed for histological analysis and viability assay of bacteria, respectively.

Results

Intraosseous periprosthetic introduction of planktonic bacteria induced an acute rise in ESR and CRP that subsided by day 14, and resulted in radiologically evident periprosthetic osteolysis by day 28 accompanied by elevated WBC counts and histological evidence of bacteria in the bone tunnels after screw removal. The aseptic screw group induced no increase in ESR, and no lysis developed around the implants. Bacterial viability was confirmed by implant sonication fluid culture.

Conclusion

Intraosseous periprosthetic introduction of planktonic bacteria reliably induces survivable chronic PJI in rabbits.

Cite this article: Bone Joint Res 2021;10(3):156–165.

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.

Timing of Antimicrobial Prophylaxis and Tourniquet Inflation: A Randomized Controlled Microdialysis Study

BACKGROUND

Tourniquets are widely used during extremity surgery. In order to prevent surgical site infection, correct timing of antimicrobial prophylaxis and tourniquet inflation is important. We aimed to evaluate the time for which the free drug concentration of cefuroxime is maintained above the minimum inhibitory concentration (t > MIC) in porcine subcutaneous adipose tissue and calcaneal cancellous bone during 3 clinically relevant tourniquet application scenarios.

METHODS

Twenty-four female Danish Landrace pigs were included. Microdialysis catheters were placed bilaterally for sampling of cefuroxime concentrations in calcaneal cancellous bone and subcutaneous adipose tissue, and a tourniquet was applied to a randomly picked leg of each pig. Subsequently, the pigs were randomized into 3 groups to receive 1.5 g of cefuroxime by intravenous injection 15 minutes prior to tourniquet inflation (Group A), 45 minutes prior to tourniquet inflation (Group B), and at the time of tourniquet release (Group C). The tourniquet duration was 90 minutes in all groups. Dialysates and venous blood samples were collected for 8 hours after cefuroxime administration. Cefuroxime and various ischemic marker concentrations were quantified.

RESULTS

Cefuroxime concentrations were maintained above the clinical breakpoint MIC for Staphylococcus aureus (4 µg/mL) in calcaneal cancellous bone and subcutaneous adipose tissue throughout the 90-minute tourniquet duration in Groups A and B. Cefuroxime administration at the time of tourniquet release (Group C) resulted in concentrations of >4 µg/mL for approximately of 3.5 hours in the tissues on the tourniquet side. Furthermore, tourniquet application induced ischemia (increased lactate:pyruvate ratio) and cell damage (increased glycerol) in subcutaneous adipose tissue and calcaneal cancellous bone. Tissue ischemia was sustained for 2.5 hours after tourniquet release in calcaneal cancellous bone.

CONCLUSIONS

Administration of cefuroxime (1.5 g) in the 15 to 45-minute window prior to tourniquet inflation resulted in sufficient concentrations in calcaneal cancellous bone and subcutaneous adipose tissue throughout the 90-minute tourniquet application. Furthermore, tourniquet-induced tissue ischemia fully resolved 2.5 hours after tourniquet release.

CLINICAL RELEVANCE

Cefuroxime administration 15 to 45 minutes prior to tourniquet inflation seems to be a safe window. If the goal is to maintain postoperative cefuroxime concentrations above relevant MIC values, our results suggest that a second dose of cefuroxime should be administered at the time of tourniquet release.

Pharmacokinetics of double-dose cefuroxime in porcine intervertebral disc and vertebral cancellous bone-a randomized microdialysis study

BACKGROUND CONTEXT

Postoperative pyogenic spondylodiscitis is associated with prolonged antimicrobial therapy and high relapse rates. Cefuroxime is a time-dependent antimicrobial widely used for intravenous perioperative prophylaxis in spine surgery. A previous study has indicated that a single dose of cefuroxime (1.5 g) provides insufficient spine tissue concentrations for spine procedures lasting more than 2 to 3 hours.

PURPOSE

To evaluate the time with concentrations above relevant minimal inhibitory concentrations (T>MIC) in plasma, subcutaneous adipose tissue, vertebral cancellous bone, and intervertebral disc after a twofold increase of the standard dosage of 1.5 g cefuroxime given as one double dose (1×3 g) or two single doses (2×1.5 g) with a four-hour interval.

METHODS

Sixteen pigs were randomized into two groups: Group 1 received one double dose of cefuroxime (1×3 g) as an intravenous bolus and Group 2 received two single doses of cefuroxime (2×1.5 g) as an intravenous bolus with a four-hour interval. Cefuroxime measurements were obtained from plasma, subcutaneous adipose tissue, vertebral cancellous bone, and intervertebral disc for eight hours thereafter. Microdialysis was applied for sampling in solid tissues. The cefuroxime concentrations were determined using ultra-high performance liquid chromatography. This work was supported by grants from the Health Research Foundation of Central Denmark Region (Level E). The funding source did not play any role in the investigation.

RESULTS

The time with concentrations above the Staphylococcus aureus clinical breakpoint minimal inhibitory concentration of 4 μg/mL was higher in all compartments for Group 2 compared to Group 1. The mean T>MIC (4 μg/mL) in all compartments ranged between 47% and 67% for Group 1 and 72% and 92% for Group 2. Furthermore, a delayed tissue penetration into all tissues for both groups was demonstrated.

CONCLUSIONS

This study suggests that cefuroxime should be given at least 45 minutes prior to spine procedures and as two single doses at a maximum interval of four hours for extended spine procedures. Clinical studies verifying these results are warranted.

CLINICAL SIGNIFICANCE

Administering cefuroxime as two single doses (2×1.5 g) with a four-hour interval compared to one double dose (1×3 g) resulted in higher T>MIC. Furthermore, we found delayed and incomplete cefuroxime tissue penetration.

Inflammatory proteins in infected bone tissue - An explorative porcine study

Objective

To explore the in situ inflammatory proteins in the local extracellular fluid of infected bone tissue.

Material and methods

Seven pigs went through a two-step surgery performing a traumatically implant-associated Staphylococcus aureus osteomyelitis in the proximal tibia. Five days later, microdialysis catheters (membrane cut off: 20 kDa) were placed in the implant cavity, infected and healthy cancellous bone, and infected and healthy subcutaneous tissue. Plasma samples were collected simultaneously. We employed an antibody-based proximity extension assay (Olink Inflammatory panel) for the measurement of inflammatory molecules within plasma and extracellular fluid of the investigated tissue compartments.

Results

A higher normalized protein expression in the infected bone tissue in comparison to healthy bone tissue was identified for proteins associated with angiogenesis and bone remodeling: OPG, TGFα, MCP-1, VEGFA, and uPA. Moreover, a parallel detectability of the systemic range of cytokines and chemokines as from the investigated local tissue compartments was demonstrated, indicating the same occurrence of proteins in the local environment as within plasma.

Conclusion

An angiogenic and osteogenic inflammatory protein composition within the extracellular fluid of infected bone tissue was described. The findings support the current histopathological knowledge and, therefore, microdialysis may represent a valid method for sampling of material for protein investigation of the in vivo inflammatory composition within the extracellular environment in infected bone tissue.