Science, medicine, and the future: Microdialysis

A Journey from the Drops of Mercury to the Mysterious Shores of the Brain: The 100-Year Adventure of Voltammetry

Voltammetry, which is at the core of electroanalytical chemistry, is an analytical method that investigates and evaluates the current-potential relationship obtained at a given working electrode. If it is used dropping mercury as working electrode, the method is called as polarography. The current year 2022 marks the 100th anniversary of the discovery of polarography by Czech Jaroslav Heyrovský. He received the Nobel Prize in Chemistry in 1959 for this discovery and his contribution to the scientific world. A hundred years, within the endless existence of the universe is maybe nothing. A hundred years, in the history of mankind is a line, maybe a short paragraph. But, in science, a hundred years can lead to very significant advances in a field and often to the birth and establishment of an entirely new scientific discipline. Indeed, in the last hundred years, the design and use of new electrochemical devices, depending on the progress in microelectronics and computer technologies, has almost revolutionized voltammetry. Besides these developments, due to the fact that the redox (oxidation/reduction) process is very basic for living organisms; the voltammetry, especially with the beginning of the 21st century, has started to be used as a very powerful tool in neuroscience to solve the mystery of the brain (the basic problems of biomolecules with physiological and genetic importance in brain tissue). This review article is an overview of the 100-year history and fascinating development of voltammetry from Heyrovský to the present.

Effect of acidosis on adipose-derived stem cell impairment and gene expression

Based on disappointing results of stem cell-based application in clinical trials for patients with critical limb ischemia, we hypothesized that the acidic environment might be the key factor limiting cell survival and function. In the present study, we used microdialysis to determine presence of acidosis and metabolic imbalance in critical ischemia. Moreover, we explored the effect of extracellular acidosis on adipose-derived stem cells (ADSCs) at molecular and transcriptional level. Our data demonstrate that low pH negatively regulates cell proliferation and survival, also, it results in cell cycle arrest, mitochondrial dynamics disorder, DNA damage as well as the impairment of proangiogenic function in a pH-dependent manner. Further transcriptome profiling identified the pivotal signaling pathways and hub genes in response to acidosis. Collectively, these findings provide strong evidences for a critical role of acidosis in ADSCs impairment with ischemic condition and suggest treatments focus on tissue pH balance and acidosis-mediated hub genes may have therapeutic potential in stem cell-based application.

Intravenous Cefazolin Achieves Sustained High Interstitial Concentrations in Open Lower Extremity Fractures

BACKGROUND

Infection remains a serious clinical concern in patients with open fractures, despite timely antibiotic administration and surgical debridement. Soft tissue and periosteal stripping may alter local tissue homeostasis and antibiotic pharmacokinetics in the injured limb. The tissue (interstitial) concentration of intravenously administered antibiotics at an open fracture site has not been characterized using direct sampling techniques.

QUESTION/PURPOSE

We performed this study to evaluate the concentration and pharmacokinetics of intravenously delivered cefazolin at an open fracture site after surgical debridement.

METHODS

Twelve patients with an open fracture distal to the knee who presented at a regional Level I trauma center were approached for enrollment in this nonrandomized, observational study. Of the 12 patients, eight adults (one female, seven male) with a median age of 32 years (range 23 to 51 years) were enrolled and underwent successful sample collection for analysis. Three patients had incomplete datasets because of equipment malfunction and one elected not to participate. Seven patients had open tibia fractures, and one patient had an open fibula fracture associated with a closed tibia fracture. There were six Gustilo-Anderson Type II injuries and two Type IIIA injuries. Empiric antibiotics were administered in the prehospital setting or in the emergency department according to institutional protocol. When patients were taken to the operating room, a 2-g intravenous dose of cefazolin was administered. After surgical debridement, fracture stabilization, and wound closure, a microdialysis catheter was placed transdermally into the injury zone (within 5 cm of the fracture site) and a second catheter was placed in the contralateral uninjured (control) limb. Additional doses of cefazolin were administered every 8 hours postoperatively. Baseline and periodic interstitial fluid and whole blood (plasma) samples were collected in the operating room and at prespecified times for 24 hours postoperatively. Free cefazolin in the interstitial fluid and plasma samples were analyzed by ultra-high-performance liquid chromatography using C 18 column separation with quadrupole time-of-flight mass spectrometry detection. Data from the second postoperative dose of cefazolin were used to characterize pharmacokinetic parameters through a noncompartmental analysis using time-concentration curves of free cefazolin and assuming first-order elimination. For pharmacodynamic analyses, the modal cefazolin minimum inhibitory concentration (MIC) of Staphylococcus aureus (1 µg/mL) was used.

RESULTS

With the samples available, no difference was observed in the median free cefazolin exposure over 24 hours ( f area under the curve [AUC] 0→24hrs ) between injured limbs (352 μg∙hr/mL [IQR 284 to 594 μg∙hr/mL]) and uninjured limbs (341 μg∙hr/mL [IQR 263 to 438 μg∙hr/mL]; p = 0.64). The median time to achieve the maximum concentration of free cefazolin ( f T max ) for injured limbs was delayed (2.7 hours [IQR 2.2 to 3.1 hours]) compared with control limbs (1.7 hours [IQR 1.2 to 2.0 hours]; p = 0.046). The time to the maximum concentration for plasma was not different from that of control limbs (p = 0.08). The time the cefazolin concentration was above the modal S. aureus MIC (T > MIC) in the injured and control limbs over 24 hours was 100% (IQR 100% to 100%) and 100% (IQR 97% to 100%), respectively.

CONCLUSION

These preliminary findings suggest that current prophylactic cefazolin dosing regimens result in successful antibiotic delivery to the traumatized limb in moderately severe open fractures. Although cefazolin delivery to open-fracture wound beds was delayed compared with healthy tissues, the cefazolin concentration was sustained above the European Union Committee Antimicrobial Susceptibility Testing modal MIC for S. aureus , demonstrating a high likelihood of a prophylactic antimicrobial environment at an open fracture site with this empiric antimicrobial regimen. Importantly, patients in this analysis had Gustilo-Anderson Types II and IIIA injuries. Further research with a larger patient cohort is needed to determine whether antibiotic delivery to traumatized soft tissues in patients with higher-grade open fractures (Gustilo-Anderson Types IIIB and IIIC) demonstrates similar pharmacokinetic characteristics.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Effect of albumin substitution on pharmacokinetics of piperacillin/tazobactam in patients with severe burn injury admitted to the ICU

BACKGROUND

Pathophysiological changes in severely burned patients alter the pharmacokinetics (PK) of anti-infective agents, potentially leading to subtherapeutic concentrations at the target site. Albumin supplementation, to support fluid resuscitation, may affect pharmacokinetic properties by binding drugs. This study aimed to investigate the PK of piperacillin/tazobactam in burn patients admitted to the ICU before and after albumin substitution as total and unbound concentrations in plasma.

PATIENTS AND METHODS

Patients admitted to the ICU and scheduled for 4.5 g piperacillin/tazobactam administration and 200 mL of 20% albumin substitution as part of clinical routine were included. Patients underwent IV microdialysis, and simultaneous arterial plasma sampling, at baseline and multiple timepoints after drug administration. PK analysis of total and unbound drug concentrations under steady-state conditions was performed before and after albumin supplementation.

RESULTS

A total of seven patients with second- to third-degree burns involving 20%-60% of the total body surface were enrolled. Mean (SD) AUC0-8 (h·mg/L) of total piperacillin/tazobactam before and after albumin substitution were 402.1 (242)/53.2 (27) and 521.8 (363)/59.7 (32), respectively. Unbound mean AUC0-8 before and after albumin supplementation were 398.9 (204)/54.5 (25) and 456.4 (439)/64.5 (82), respectively.

CONCLUSIONS

Albumin supplementation had little impact on the PK of piperacillin/tazobactam. After albumin supplementation, there was a numerical increase in mean AUC0-8 of total and unbound piperacillin/tazobactam, whereas similar Cmax values were observed. Future studies may investigate the effect of albumin supplementation on drugs with a higher plasma protein binding.

Surface microdialysis measures local tissue metabolism after Ivor Lewis esophagectomy; an attempt to predict anastomotic defect

Anastomotic defect (AD) after esophagectomy can lead to severe complications with need for surgical or endoscopic intervention. Early detection enables early treatment and can limit the consequences of the AD. As of today, there are limited methods to predict AD. In this study, we have used microdialysis (MD) to measure local metabolism at the intrathoracic anastomosis. Feasibility and possible diagnostic use were investigated. Sixty patients planned for Ivor Lewis esophagectomy were enrolled. After construction of the anastomosis, surface MD (S-MD) probes were attached to the outer surface of the esophageal remnant and the gastric conduit in close vicinity of the anastomosis and left in place for 7 postoperative days (PODs). Continuous sampling of local tissue concentrations of metabolic substances (glucose, lactate, and pyruvate) was performed postoperatively. Outcome, defined as AD or not according to Esophagectomy Complications Consensus Group definitions, was recorded at discharge or at first postoperative follow up. Difference in concentrations of metabolic substances was analyzed retrospectively between the two groups by means of artificial neural network technique. S-MD probes can be attached and removed from the gastric tube reconstruction without any adverse events. Deviating metabolite concentrations on POD 1 were associated with later development of AD. In subjects who developed AD, no difference in metabolic concentrations between the esophageal and the gastric probe was recorded. The technical failure rate of the MD probes/procedure was high. S-MD can be used in a clinical setting after Ivor Lewis esophagectomy. Deviation in local tissue metabolism on POD 1 seems to be associated with development of AD. Further development of MD probes and procedure is required to reduce technical failure.

Evaluation of cefuroxime concentration in the intrathecal and extrathecal compartments of the lumbar spine-an experimental study in pigs

BACKGROUND AND PURPOSE

Optimal antibiotic prophylaxis is crucial to prevent postoperative infection in spinal surgery. Sufficient time above the minimal inhibitory concentration (fT > MIC) for relevant bacteria in target tissues is required for cefuroxime. We assessed cefuroxime concentrations and fT > MIC of 4 μg·ml-1 for Staphylococcus aureus in the intrathecal (spinal cord and cerebrospinal fluid, CSF) and extrathecal (epidural space) compartments of the lumbar spine.

EXPERIMENTAL APPROACH

Eight female pigs were anaesthetized and laminectomized at L3-L4. Microdialysis catheters were placed for sampling in the spinal cord, CSF, and epidural space. A single dose of 1500 mg cefuroxime was administered intravenously over 10 min. Microdialysates and plasma were obtained continuously during 8 h. Cefuroxime concentrations were determined by ultra-high-performance liquid chromatography.

KEY RESULTS

Mean fT > MIC (4 μg·ml-1 ) was 58 min in the spinal cord, 0 min in the CSF, 115 min in the epidural space, and 123 min in plasma. Tissue penetration was 32% in the spinal cord, 7% in the CSF, and 63% in the epidural space.

CONCLUSION AND IMPLICATIONS

fT > MIC (4 μg·ml-1 ) and tissue penetration for cefuroxime were lower in the intrathecal compartments (spinal cord and CSF) than in the extrathecal compartment (epidural space) and plasma, suggesting a significant effect of the blood-brain barrier. In terms of fT > MIC, a single dose of 1500 mg cefuroxime seems inadequate to prevent intrathecal infections related to spinal surgery for bacteria presenting with a MIC target of 4 μg· ml-1 or above.

Pilot Pharmacokinetic Study in Healthy Adults Using Intravascular Microdialysis Catheters Modified for Use in Paediatric Patients to Assess Vancomycin Blood Levels

BACKGROUND AND OBJECTIVE

Exhaustive pharmacokinetic (PK) studies in paediatric patients are unavailable for most antibiotics and feasibility of PK studies is limited by challenges, such as low blood volume and venipuncture-related pain. Microdialysis (MD) represents a promising method to overcome these obstacles. The aim of this proof-of-concept study was to develop and validate modified MD catheters that can be used to obtain concentration-time profiles of antibiotics in paediatric patients.

METHODS

Following extensive in vitro MD experiments, a prospective open-labelled study in ten healthy adult volunteers (HVs) was conducted. Subjects received a single intravenous dose of 1000 mg vancomycin, then plasma and intravascular microdialysate were sampled over 24 h. In vivo MD probe calibration was conducted using the retrodialysis technique. Plasma protein binding was measured using ultrafiltration. Confirmation of the measurements was performed using a Bland-Altman plot, relevant PK parameters were calculated, and a pharmacometric model was established.

RESULTS

No safety issues were encountered. The concentration-time curves of microdialysate and plasma measurements showed good alignment. The Bland-Altman plot yielded a mean bias of 0.19 mg/L and 95% limits of agreement of - 9.34 to 9.71 mg/L. A two-compartment model best described plasma PK, model-based estimates for recovery of the MD probes being in high agreement with the observed values. Quantified estimates of fraction unbound were comparable between plasma and microdialysate (p = 0.56).

CONCLUSIONS

An innovative MD catheter that can be inserted into small intravenous lines was successfully developed and applied in HV. This proof-of-concept study is encouraging and opens the way to further experiments leading towards future use of MD in paediatric patients.

Accelerator mass spectrometry for quantification of micro- and therapeutic dose diclofenac in microdialysis samples

Background: Microdialysis sampling after drug microdosing may provide tissue pharmacokinetic data early in clinical drug development. However, low administered doses and small sample volumes pose an analytical challenge, particularly for highly protein-bound drugs. Materials & methods: Carbon-14 [¹⁴C]diclofenac was used as a model drug to assess the technical and analytical feasibility of in vivo microdialysis after microdose administration in an in vitro setup. Results: [¹⁴C]diclofenac dialysate concentrations were accurately quantified with accelerator MS. [¹⁴C]diclofenac dialysate recoveries were similar in the presence and absence of therapeutic diclofenac concentrations but were considerably decreased when albumin was added to the immersion solution, suggesting high protein binding. Conclusion: These results demonstrate the feasibility of combining microdosing and microdialysis to assess tissue pharmacokinetics.

Microdosing as a Potential Tool to Enhance Clinical Development of Novel Antibiotics: A Tissue and Plasma PK Feasibility Study with Ciprofloxacin

Background and Objective

In microdose studies, drug pharmacokinetics is measured in humans after administration of subtherapeutic doses. While previous microdose studies focused primarily on plasma pharmacokinetics, we set out to evaluate the feasibility of microdosing for a pharmacokinetic assessment in subcutaneous tissue and epithelial lining fluid.

Methods

Healthy subjects received a single intravenous bolus injection of a microdose of [¹⁴C]ciprofloxacin (1.1 µg, 7 kBq) with (cohort A, n = 9) or without (cohort B, n = 9) a prior intravenous infusion of a therapeutic dose of unlabeled ciprofloxacin (400 mg). Microdialysis and bronchoalveolar lavage were applied for determination of subcutaneous and intrapulmonary drug concentrations. Microdose [¹⁴C]ciprofloxacin was quantified by accelerator mass spectrometry and therapeutic-dose ciprofloxacin by liquid chromatography–tandem mass spectrometry.

Results

The pharmacokinetics of therapeutic-dose ciprofloxacin (cohort A) in plasma, subcutaneous tissue, and epithelial lining fluid was in accordance with previous data. In plasma and subcutaneous tissue, the dose-adjusted area under the concentration–time curve of microdose ciprofloxacin was similar in cohorts A and B and within an 0.8-fold to 1.1-fold range of the area under the concentration–time curve of therapeutic-dose ciprofloxacin. Penetration of microdose ciprofloxacin into subcutaneous tissue was similar in cohorts A and B and comparable to that of therapeutic-dose ciprofloxacin with subcutaneous tissue-to-plasma area under the concentration–time curve ratios of 0.44, 0.44, and 0.38, respectively. Penetration of microdose ciprofloxacin into epithelial lining fluid was highly variable and failed to predict the epithelial lining fluid penetration of therapeutic-dose ciprofloxacin.

Conclusions

Our study confirms the feasibility of microdosing for pharmacokinetic measurements in plasma and subcutaneous tissue. Microdosing combined with microdialysis is a potentially useful tool in clinical antimicrobial drug development, but its applicability for the assessment of pulmonary pharmacokinetics with bronchoalveolar lavage requires further studies.

Clinical Trial Registration

ClinicalTrials.gov NCT03177720 (registered 6 June, 2017).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01091-1.

Protein binding of clindamycin in vivo by means of intravascular microdialysis in healthy volunteers

OBJECTIVES

The efficacy of an anti-infective drug is influenced by its protein binding (PB), since only the free fraction is active. We hypothesized that PB may vary in vitro and in vivo, and used clindamycin, a drug with high and concentration-dependent PB to investigate this hypothesis.

METHODS

Six healthy volunteers received a single intravenous infusion of clindamycin 900 mg. Antibiotic plasma concentrations were obtained by blood sampling and unbound drug concentrations were determined by means of in vivo intravascular microdialysis (MD) or in vitro ultrafiltration (UF) for up to 8 h post dosing. Clindamycin was assayed in plasma and MD fluid using a validated HPLC-UV (ultraviolet) method. Non-linear mixed effects modelling in NONMEM® was used to quantify the PB in vivo and in vitro.

RESULTS

C max was 14.95, 3.39 and 2.32 mg/L and AUC0-8h was 41.78, 5.80 and 6.14 mg·h/L for plasma, ultrafiltrate and microdialysate, respectively. Calculated ratio of AUCunbound/AUCtotal showed values of 13.9%±1.8% and 14.7%±3.1% for UF and microdialysate, respectively. Modelling confirmed non-linear, saturable PB for clindamycin with slightly different median (95% CI) dissociation constants (Kd) for the alpha-1 acid glycoprotein (AAG)-clindamycin complex of 1.16 mg/L (0.91-1.37) in vitro versus 0.85 mg/L (0.58-1.01) in vivo. Moreover, the estimated number of binding sites per AAG molecule was 2.07 (1.79-2.25) in vitro versus 1.66 in vivo (1.41-1.79).

CONCLUSIONS

Concentration-dependent PB was observed for both investigated methods with slightly lower levels of unbound drug fractions in vitro as compared with in vivo.

Local Vancomycin Concentrations after Intra-articular Injection into the Knee Joint: An Experimental Porcine Study

Intra-articular injection of vancomycin may be an important antimicrobial prophylactic supplement to systemic administration in the prevention of prosthetic joint infections. In eight female pigs, 500 mg of diluted vancomycin was given by intra-articular injection into the knee joint. Microdialysis was used for dense sampling of vancomycin concentrations over 12 hours in the synovial fluid of the knee joint, and in the adjacent femoral and tibial cancellous bone and subcutaneous tissue. Venous blood samples were obtained as reference. The mean (standard deviation [SD]) peak drug concentration of vancomycin in the synovial fluid of the knee joint was 5,277 (5,668) μg/mL. Only one pig failed to reach a peak drug concentration above 1,000 μg/mL. The concentration remained high throughout the sampling interval with a mean (SD) concentration of 337 (259) μg/mL after 690 minutes. For all extraarticular compartments, the pharmacokinetic parameters (area under the concentration time-curve, peak drug concentration, and time to peak drug concentration) were comparable. The highest extraarticular mean (SD) peak drug concentration of 4.4 (2.3) μg/mL was found in subcutaneous tissue. An intra-articular injection of 500 mg diluted vancomycin was found to provide significant prophylactic mean concentrations for at least 12 hours in the synovial fluid of the knee joint. Correspondingly, the adjacent tissue and plasma concentrations were low but remained stable, signifying low risk of systemic toxic side effects and a slow release or uptake from the synovium to the systemic circulation.

Single-dose pharmacokinetics of temocillin in plasma and soft tissues of healthy volunteers after intravenous and subcutaneous administration: a randomized crossover microdialysis trial

BACKGROUND

The antibiotic temocillin has recently been rediscovered as a promising therapeutic option against MDR Gram-negative bacteria. However, some aspects of the pharmacokinetic (PK) profile of the drug are still to be elucidated: subcutaneous administration of temocillin might be of interest as an alternative to the intravenous route in selected patients. Similarly, information on the penetration of temocillin into human soft tissues is lacking.

OBJECTIVES

To investigate the feasibility and plasma PK of subcutaneous dosing as well as soft tissue PK of temocillin after intravenous administration to healthy volunteers.

METHODS

Eight healthy volunteers received 2 g of temocillin both as intravenous and subcutaneous infusion in a randomized two-period crossover study. Concentration-time profiles of total temocillin in plasma (after both routes) and of unbound temocillin in plasma, muscle and subcutis (only after intravenous dosing) were determined up to 12 h post-dose.

RESULTS

Subcutaneous dosing caused some infusion site discomfort but resulted in sustained drug concentrations over time with only slightly decreased overall exposure compared with intravenous dosing. Plasma protein binding of temocillin showed concentration-dependent behaviour and was higher than previously reported. Still, unbound drug concentrations in muscle and subcutis determined by microdialysis markedly exceeded those in plasma, suggesting good tissue penetration of temocillin.

CONCLUSIONS

The subcutaneous administration of temocillin is a valid and feasible alternative to intravenous dosing. With the description of plasma protein binding and soft tissue PK of temocillin in healthy volunteers, this study provides important information that adds to the ongoing characterization of the PK profile of temocillin and might serve as input for PK/PD considerations.

Evaluation of Benzylpenicillin as an Internal Standard for Measurement of Piperacillin Bone Concentrations Via Microdialysis

Microdialysis is a pharmacokinetic tool that can be advantageous when obtaining tissues' pharmacokinetic information. Since absolute extracellular tissue concentrations are needed in pharmacokinetic studies, calibrating the microdialysis system is necessary. The internal standard method is superior when compared to other calibration methods. However, thorough evaluation of the internal standard is required before it can be used. In vitro experiments and an in vivo study on pigs (n = 8) were conducted to assess the relative recoveries by gain and by loss for piperacillin, both with and without a benzylpenicillin concentration of 5 µg/mL. Furthermore, the in vivo setup allowed for an evaluation of piperacillin cancellous bone and subcutaneous tissue concentrations in a single 8 h dosing interval. Ultra-high performance liquid chromatography (UHPLC) was used to determine piperacillin and benzylpenicillin concentrations. Relative recovery by loss for benzylpenicillin and relative recovery by gain for piperacillin were similar in in vitro and in vivo. Presence of benzylpenicillin did not affect the relative recovery for piperacillin. Relative recovery, pharmacokinetic parameters and fT>MIC were similar when comparing the retrodialysis by drug and the internal standard calibration methods (p > 0.31). Mean fT>MIC (16 µg/mL) for plasma, cancellous bone and subcutaneous tissue were 232 min, 255 min and 295 min, respectively. Our findings suggest that benzylpenicillin is suitable as an internal standard for piperacillin in microdialysis studies. Mean fT>MIC (16 µg/mL) for plasma, cancellous bone, and subcutaneous tissue reached a target of 50% fT>MIC under the investigated conditions (mean range: 52%-66%); however, the target was not obtained in all pigs in all compartments. Moreover, 100% fT>MIC was not obtained in any case, suggesting that different strategies must be taken into consideration if higher targets are employed.

Plasma and soft tissue pharmacokinetics of ceftolozane/tazobactam in healthy volunteers after single and multiple intravenous infusion: a microdialysis study

OBJECTIVES

To investigate ceftolozane/tazobactam pharmacokinetics (PK) in plasma and interstitial space fluid (ISF) of muscle and subcutaneous tissue and establish a population PK model.

METHODS

Eight healthy volunteers received four IV doses of 1000/500 mg ceftolozane/tazobactam q8h in a prospective, open-labelled PK study. ISF concentration-time profiles were determined via in vivo microdialysis up to 8 h post-dose and efficacy of unbound ceftolozane and tazobactam was estimated using the time above MIC (%ƒT>MIC) and time above threshold concentration (%T>CT), respectively. A population PK model was established by merging derived plasma and soft tissue PK data.

RESULTS

Ceftolozane reached %ƒT>MIC values of 100% in plasma, muscle and subcutaneous ISF for Enterobacteriaceae and 87%, 89% and 87%, respectively, for Pseudomonas aeruginosa. Tazobactam %T>CT was 21%, 22% and 21% in plasma, muscle and subcutaneous ISF, respectively. Plasma protein binding was 6.3% for ceftolozane and 8.0% for tazobactam. Multiple-dose ceftolozane AUC0-8 ISF/plasma ratios were 0.92 ± 0.17 in muscle and 0.88 ± 0.18 in subcutis, and tazobactam ratios were 0.89 ± 0.25 in muscle and 0.87 ± 0.21 in subcutis, suggesting substantial soft tissue penetration.

CONCLUSIONS

Tazobactam %T>CT values were distinctly below proposed target values, indicating that tazobactam might be underdosed in the investigated drug combination. However, ISF/unbound plasma ratios of ceftolozane and tazobactam support their use in soft tissue infections. A plasma and soft tissue PK model adds important information on the PK profile of ceftolozane/tazobactam. Further investigations in patients suffering from wound infections are needed to confirm these findings.

Protein unbound pharmacokinetics of ambroxol in the blood and brains of rats and the interaction of ambroxol with Polygala tenuifolia by multiple microdialysis

ETHNOPHARMACOLOGICAL RELEVANCE

Ambroxol elevates glucocerebrosidase (GCase) activity and reduces nigrostriatal alpha-synuclein burden to better ameliorate motor function in Parkinson's disease (PD). Polygala tenuifolia is a potential alternative botanical medicine for the treatment of many nonmotor symptoms of PD commonly used in Taiwanese patients. Co-administration of these two medicines pose potential herb-drug interaction.

AIM OF THE STUDY

Our hypothesis is that ambroxol and P. tenuifolia may potentially possess herbal drug synergetic effects in the blood and brain.

MATERIALS AND METHODS

To investigate this hypothesis, a multiple microdialysis system coupled with validated ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for rat blood and brain samples. Experimental rats were divided into three groups: low-dose and high-dose ambroxol alone (10 mg/kg, i.v. and 30 mg/kg, i.v., respectively) and ambroxol (10 mg/kg, i.v.) pretreated with P. tenuifolia extract (1 g/kg, p.o. for 5 consecutive days).

RESULTS

Ambroxol easily penetrated into the brain and reached a maximum concentration in the striatum at approximately 60 min after low- and high-dose treatment. The area under the concentration curve (AUC) ratio increased proportionally at the doses of 10 and 30 mg/kg, which suggested a linear pharmacokinetic manner of ambroxol. The brain penetration of ambroxol was approximately 30-34%, which was defined as the ambroxol AUC blood-to-brain distribution ratio (AUCbrain/AUCblood). The P. tenuifolia extract did not significantly alter the pharmacokinetics of ambroxol in the blood and brain of rats.

CONCLUSION

The present study suggests that it is safety without pharmacokinetic interactions for this dosing regimen to use P. tenuifolia extract and ambroxol together.

Vancomycin bone and tissue concentrations following tibial intraosseous administration - evaluated in a porcine model

Introduction. Systemic perioperative vancomycin may not provide sufficient prophylactic target-site concentrations in the prevention of prosthetic joint infections. Intraosseous vancomycin potentially provides high target-site concentrations. The objective of the present study was to evaluate the local bone and tissue concentrations following tibial intraosseous vancomycin administration in a porcine model. Methods. Eight pigs received 500 mg diluted vancomycin (50 mg/mL) through an intraosseous cannula into the proximal tibial cancellous bone. No tourniquet was applied. Microdialysis was applied for sampling of vancomycin concentrations in adjacent tibial cancellous bone, in cortical bone, in the intramedullary canal of the diaphysis, in the synovial fluid of the knee joint, and in the subcutaneous tissue. Plasma samples were obtained as a systemic reference. Samples were collected for 12 h. Results. High vancomycin concentrations were found in the tibial cancellous bone with a mean peak drug concentration of 1236 (range 28-5295)  µ g / mL , which remained high throughout the sampling period. The mean (standard deviation) peak drug concentration in plasma was 19 (2)  µ g / mL , which was obtained immediately after administration. Peak drug concentration, time to peak drug concentration, and area under the concentration-time curve were within the same range in the intramedullary canal, the synovial fluid of the knee, and the subcutaneous tissue. Conclusion. Tibial intraosseous administration of vancomycin provided high concentrations in tibial cancellous bone throughout a 12 h period but with an unpredictable and wide range of peak concentration. The systemic absorption was high and immediate, thus mirroring an intravenous administration. Low mean concentrations were found in all the remaining compartments.

Microdialysis for the Assessment of Intervertebral Disc and Vertebral Cancellous Bone Metabolism in a Large Porcine Model

BACKGROUND/AIM

It remains challenging to evaluate the in vivo pathophysiological biochemical characteristics in spine tissue, due to lack of an applicable model and feasible methods. The aim of this study was to apply microdialysis for the assessment of basic metabolites from the C3-C4 intervertebral disc, C3 vertebral cancellous bone and subcutaneous adipose tissue in a large porcine model.

MATERIALS AND METHODS

In 7 pigs, glucose, pyruvate, lactate and glycerol concentrations were evaluated in an 8-hour sampling period.

RESULTS

The mean lactate/pyruvate (L/P) ratios for the intervertebral disc and vertebral cancellous bone were comparable and exceeded the ischemic cut-off value of 25 for the entire sampling interval. For subcutaneous adipose tissue, the L/P ratio was below the ischemic cut-off.

CONCLUSION

This exploratory study confirms previous findings of ischemia in bone and the intervertebral disc. This encourages new microdialysis study designs in spine tissue employing large porcine models to create new knowledge and a greater understanding of the metabolism and pathogenesis in spine tissue.

Local concentrations of gentamicin obtained by microdialysis after a controlled application of a GentaColl sponge in a porcine model

Local treatment with gentamicin may be an important tool in the prevention and treatment of surgical site infections in high-risk procedures and patients. The aim of this study was to evaluate the pharmacokinetic profile of gentamicin in bone and surrounding tissue, released from a controlled application of a GentaColl sponge in a porcine model. In eight female pigs, a GentaColl sponge of 10 × 10 cm (1.3 mg gentamicin/cm² ) was placed in a cancellous bone cavity in the proximal tibia. Microdialysis was used for sampling of gentamicin concentrations over 48 hours from the cavity with the implanted GentaColl sponge, cancellous bone parallel to the cavity over and under the epiphyseal plate, cortical bone, the intramedullary canal, subcutaneous tissue, and the joint cavity of the knee. Venous blood samples were obtained as reference. The main finding was a mean peak drug concentration (95% CI) of gentamicin in the cancellous bone cavity containing the implanted GentaColl sponge of 11 315 (9049-13 581) μg/mL, persisting above 1000 μg/mL until approximately 40 hours after application. Moreover, the concentrations were low (<1 μg/mL) in the surrounding tissues as well as in plasma. The mean peak gentamicin concentration from the cancellous bone cavity after a controlled application of a GentaColl sponge was high and may be adequate for the prevention of biofilm formation. However, high MIC strains and uncontrolled application of the GentaColl sponge may jeopardize this conclusion.

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.

Evaluation of Intrahepatic Lactate/Pyruvate Ratio As a Marker for Ischemic Complications Early After Liver Transplantation-A Clinical Study

Background.

Lactate/pyruvate ratio has been introduced as a sensitive marker for ischemia in the transplanted liver. In the present study, we aimed to evaluate lactate/pyruvate ratio measured in the liver by microdialysis as a marker for ischemic complications early after liver transplantation.

Methods.

Forty-five patients undergoing liver transplantation were included in the study. A microdialysis catheter was placed in the liver graft directly following liver transplantation and the metabolites lactate and pyruvate measured for up to 6 days and the lactate/pyruvate ratio calculated. The association between increased intrahepatic lactate/pyruvate ratio and ischemic complications was studied.

Results.

One of 45 patients developed hepatic arterial thrombosis. Forty-four events with increased lactate/pyruvate ratio were identified in 24 patients. In none of the 24 patients that had a raised lactate/pyruvate ratio could we detect occurrence of any ischemic complication. In the patient that did have hepatic arterial thrombosis, the lactate/pyruvate ratio did not show a significant prolonged rise.

Conclusions.

An increase in the intrahepatic lactate/pyruvate ratio is not necessarily indicative of ischemic complications and is thus not a reliable marker for monitoring of clinically significant ischemia in the liver early after transplantation.

Population pharmacokinetics of piperacillin in plasma and subcutaneous tissue in patients on continuous renal replacement therapy

OBJECTIVES

Piperacillin is a β-lactam antimicrobial frequently used in critically ill patients with acute kidney injury treated with continuous renal replacement therapy (CRRT). However, data regarding piperacillin tissue concentrations in this patient population are limited. A prospective observational study was conducted of free piperacillin concentrations during a single 8-h dosing interval in plasma (8 samples) and subcutaneous tissue (SCT) (13 samples), in 10 patients treated with CRRT following piperacillin 4 g given every 8 h as intermittent administration over 3 min.

METHODS

A population pharmacokinetic model was developed using NONMEM 7.4.3, to simulate alternative administration modes and dosing regimens. SCT concentrations were obtained using microdialysis. Piperacillin concentrations were compared to the clinical breakpoint minimum inhibitory concentration (MIC) for Pseudomonas aeruginosa (16 mg/l), with evaluation of the following pharmacokinetic/pharmacodynamics targets: 50% fT > 1 × MIC, 100% fT > 1 × MIC, and 100% fT > 4 × MIC.

RESULTS

SCT concentrations were generally lower than plasma concentrations. For the target of 50% free time (fT) > 1 × MIC and 100% fT > 1 × MIC, piperacillin 4 g every 8 h resulted in probability of target attainment (PTA) >90% in both plasma and SCT. PTA > 90% for the target of 100% fT > 4 × MIC was only achieved for continuous infusion.

CONCLUSIONS

Piperacillin 4 g every 8 h is likely to provide sufficient exposure in both plasma and SCT to treat P.aeruginosa infections in critically ill patients on CRRT, given that targets of 50% fT > 1 × MIC or 100% fT > 1 × MIC are adequate. However, if a more aggressive target of 100% fT > 4 × MIC is adopted, continuous infusion is needed.

Simultaneous Retrodialysis by Drug for Cefuroxime Using Meropenem as an Internal Standard-A Microdialysis Validation Study

Microdialysis is a valuable pharmacokinetic tool for obtaining samples of drug concentrations from tissues of interest. When an absolute tissue concentration is needed, a calibration of the microdialysis catheter is required. The use of an internal standard offers a number of advantages compared to standard calibration methods. However, meticulous validation both in vitro and in vivo is needed, as this method requires an internal standard with physiochemical similarities to the analyte of interest with no interference. A series of in vitro and in vivo setups were conducted to determine the relative recovery by gain and by loss for cefuroxime, with and without a constant meropenem concentration. The cefuroxime and meropenem concentrations were determined using ultra-HPLC. The main finding was that cefuroxime and meropenem relative recovery behaved similarly both in vitro and in vivo, signifying that meropenem is a representative internal standard for cefuroxime. Furthermore, cefuroxime relative recovery in vitro was not affected by either the cefuroxime concentration or the presence of meropenem, and the in vivo meropenem relative recovery was constant over 6 h.

Lack of dermal penetration of topically applied gentamicin as pharmacokinetic evidence indicating insufficient efficacy

Background

Treatment of skin and superficial soft tissue infections with topically applied antibiotics is a controversial topic, because only few clinical studies exist and target site concentrations after topical treatment are widely unknown.

Objectives

This study aimed to investigate the target site concentration of topically applied gentamicin as a potential cause of therapeutic failure and to explore if microporation by laser might be used to improve penetration of gentamicin through the skin barrier.

Methods

Six healthy volunteers were included in this cross-over Phase 1 study. On two study days, separated by a washout period, microdialysate and plasma sampling was performed for 6 h after administration of 500 mg of gentamicin cream on a predefined area. On one of the study days the skin was microporated before drug application using the P.L.E.A.S.E. Professional laser system.

Results

In intact skin, Cmax and AUC values were 3.3 ± 5.64 ng/mL and 5.4 ± 10.4 ng·h/mL, respectively; thereby far under the threshold needed to treat common pathogens. With a Cmax of 474.2 ± 555.3 ng/mL laser application showed a significant increase in tissue penetration and decrease in pharmacokinetic variability; however, even after microporation no therapeutically active concentrations were achieved as indicated by Cmax/epidemiological cut-off ratios of 0.237 and 0.059 for Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Solely after administration on microporated skin, plasma concentrations of gentamicin were quantifiable (lower limit of quantification 10 pg/mL).

Conclusions

This study confirmed that after topical administration gentamicin penetration through the dermal barrier is insufficient, providing pharmacokinetic evidence that topical gentamicin in its current form might be inappropriate to treat skin infections.

Repeated determination of moxifloxacin concentrations in interstitial space fluid of muscle and subcutis in septic patients

BACKGROUND

For an effective antimicrobial treatment, it is crucial that antibiotics reach sufficient concentrations in plasma and tissue. Currently no data exist regarding moxifloxacin plasma concentrations and exposure levels in tissue under septic conditions.

OBJECTIVES

To determine the pharmacokinetics of moxifloxacin in plasma and interstitial space fluid over a prolonged period.

PATIENTS AND METHODS

Ten septic patients were treated with 400 mg of moxifloxacin once a day; on days 1, 3 and 5 of treatment plasma sampling and microdialysis in the subcutis and muscle of the upper thigh were performed to determine concentrations of moxifloxacin in different compartments. This trial was registered in the German Clinical Trials Register (DRKS, register number DRKS00012985).

RESULTS

Mean unbound fraction of moxifloxacin in plasma was 85.5±3.4%. On day 1, Cmax in subcutis and muscle was 2.8±1.8 and 2.5±1.3 mg/L, respectively, AUC was 24.8±15.1 and 21.3±10.5 mg·h/L, respectively, and fAUC0-24/MIC was 100.9±62.9 and 86.5±38.3 h, respectively. Cmax for unbound moxifloxacin in plasma was 3.5±0.9 mg/L, AUC was 23.5±7.5 mg·h/L and fAUC0-24/MIC was 91.6±24.8 h. Key pharmacokinetic parameters on days 3 and 5 showed no significant differences. Clearance was higher than in healthy adults, but tissue concentrations were comparable, most likely due to a lower protein binding.

CONCLUSIONS

Surprisingly, the first dose already achieved exposure comparable to steady-state conditions. The approved daily dose of 400 mg was adequate in our patient population. Thus, it seems that in septic patients a loading dose on the first day of treatment with moxifloxacin is not required.

Microdialysis-Assessed Adipose Tissue Metabolism, Circulating Cytokines and Outcome in Critical Illness

Microdialysis (MD) can provide continuous information about tissue composition. To assess in critically ill patients adipose tissue metabolic patterns, the relationships between metabolic patterns and blood cytokine concentration associations of adipose tissue energy metabolism and clinical outcome we studied 203 mechanically ventilated general intensive care unit (ICU) patients. Upon ICU admission an MD catheter was inserted into the subcutaneous adipose tissue of the upper thigh to measure lactate (L), glucose, pyruvate (P), and glycerol. Serum concentrations of IL-10, IL-6, IL-8, and TNF-α were determined within 48 h from ICU admission. Mitochondrial dysfunction was defined as L/P ratio >30 and pyruvate ≥70 μmol/L, ischemia as L/P ratio >30 and pyruvate <70 μmol/L and no ischemia/no mitochondrial dysfunction (i.e., aerobic metabolism) was as L/P ratio ≤30. Metabolism was aerobic in 74% of patients. In 13% of patients there was biochemical evidence of ischemia and in 13% of patients of mitochondrial dysfunction. Mitochondrial dysfunction was associated with poor outcome. In conclusion, MD showed that about two thirds of critically ill patients have normal aerobic adipose tissue metabolism. Mitochondrial dysfunction was not common but was associated with poor outcome. Identifying subgroups of critically ill patients is crucial as different treatment strategies may improve survival.

Target site pharmacokinetics of doxycycline for rosacea in healthy volunteers is independent of the food effect

Aims

Doxycycline (DFD‐09) oral capsules 40 mg are approved for the treatment of inflammatory lesions of rosacea. Unlike the food‐induced lowering of doxycycline's peak plasma concentration (C_max), its exposure under fed conditions in the skin, the drug's target site for rosacea, is unknown. The present study explored the effect of food on the dermal pharmacokinetics of doxycycline.

Methods

The pharmacokinetics of doxycycline in the dermal interstitial fluid (d‐ISF) and plasma of healthy volunteers were assessed in parallel groups under fed (n = 6) and fasting (n = 6) conditions during a 14‐day once‐daily treatment course with doxycycline oral capsules 40 mg (DFD‐09). Sampling of d‐ISF and plasma was performed on days 1, 10 (fasting group d‐ISF only) and 14.

Results

Twelve subjects were randomized, and 11 analysed. No causally drug‐related adverse events occurred. Dermal doxycycline exposures (C_max and area under the curve) under the fed state were about 30% lower than under the fasting state at day 1 but were similar at steady state. In analogy to skin, plasma exposure showed no between‐group difference at steady state. Accumulation ratios were higher in the skin than in plasma. Correcting for plasma protein binding (~90%), dermal doxycycline exposure was approximately threefold higher than unbound plasma exposure.

Conclusions

At steady state, doxycycline concentrations in the skin of fed and fasting healthy volunteers were comparable. Doxycycline's efficacy in rosacea is possibly due to considerable dermal accumulation of unbound doxycycline and is independent of the effect of food.

Vancomycin concentrations in the cervical spine after intravenous administration: results from an experimental pig study

Background and purpose - Vancomycin may be an important drug for intravenous perioperative antimicrobial prophylaxis in spine surgery. We assessed single-dose vancomycin intervertebral disc, vertebral cancellous bone, and subcutaneous adipose tissue concentrations using microdialysis in a pig model. Material and methods - 8 female pigs received 1,000 mg of vancomycin intravenously as a single dose over 100 minutes. Microdialysis probes were placed in the C3-C4 intervertebral disc, C3 vertebral cancellous bone, and subcutaneous adipose tissue, and vancomycin concentrations were obtained over 8 hours. Venous blood samples were obtained as reference. Results - Ranging from 0.24 to 0.60, vancomycin tissue penetration, expressed as the ratio of tissue to plasma area under the concentration-time curve from 0 to the last measured value, was incomplete for all compartments. The lowest penetration was found in the intervertebral disc. The time to a mean clinically relevant minimal inhibitory concentration (MIC) of 4 µg/mL was 3, 17, 25, and 156 min for plasma, subcutaneous adipose tissue, vertebral cancellous bone, and the intervertebral disc, respectively. In contrast to the other compartments, a mean MIC of 8 µg/mL was not reached in the intervertebral disc. An approximately 3-times longer elimination rate was observed in the intervertebral disc in comparison with all the other compartments (p < 0.001), and the time to peak drug concentration was higher for all tissues compared with plasma Interpretation - Preoperative administration of 1,000 mg of vancomycin may provide adequate vancomycin tissue concentrations with a considerable delay, though tissue penetration was incomplete. However, in order also to achieve adequate intervertebral disc concentrations in all individuals and accommodating a potentially higher MIC target, supplemental application of vancomycin may be necessary.

Recovery rates of combination antibiotic therapy using in vitro microdialysis simulating in vivo conditions

Microdialysis is a technique used to measure the unbound antibiotic concentration in the interstitial spaces, the target site of action. In vitro recovery studies are essential to calibrating the microdialysis system for in vivo studies. The effect of a combination of antibiotics on recovery into microdialysate requires investigation. In vitro microdialysis recovery studies were conducted on a combination of vancomycin and tobramycin, in a simulated in vivo model. Comparison was made between recoveries for three different concentrations and three different perfusate flow rates. The overall relative recovery for vancomycin was lower than that of tobramycin. For tobramycin, a concentration of 20μg/mL and flow rate of 1.0μL/min had the best recovery. A concentration of 5.0μg/mL and flow rate of 1.0μL/min yielded maximal recovery for vancomycin. Large molecular size and higher protein binding resulted in lower relative recoveries for vancomycin. Perfusate flow rates and drug concentrations affected the relative recovery when a combination of vancomycin and tobramycin was tested. Low perfusate flow rates were associated with higher recovery rates. For combination antibiotic measurement which includes agents that are highly protein bound, in vitro studies performed prior to in vivo studies may ensure the reliable measurement of unbound concentrations.

Population Pharmacokinetics of Meropenem in Plasma and Subcutis from Patients on Extracorporeal Membrane Oxygenation Treatment

The objectives of this study were to describe meropenem pharmacokinetics (PK) in plasma and/or subcutaneous adipose tissue (SCT) in critically ill patients receiving extracorporeal membrane oxygenation (ECMO) treatment and to develop a population PK model to simulate alternative dosing regimens and modes of administration. We conducted a prospective observational study. Ten patients on ECMO treatment received meropenem (1 or 2 g) intravenously over 5 min every 8 h. Serial SCT concentrations were determined using microdialysis and compared with plasma concentrations. A population PK model of SCT and plasma data was developed using NONMEM. Time above clinical breakpoint MIC for Pseudomonas aeruginosa (8 mg/liter) was predicted for each patient. The following targets were evaluated: time for which the free (unbound) concentration is maintained above the MIC of at least 40% (40% fT>MIC), 100% fT>MIC, and 100% fT>4×MIC. For all dosing regimens simulated in both plasma and SCT, 40% fT>MIC was attained. However, prolonged meropenem infusion would be needed for 100% fT>MIC and 100% fT>4×MIC to be obtained. Meropenem plasma and SCT concentrations were associated with estimated creatinine clearance (eCL_Cr). Simulations showed that in patients with increased eCL_Cr, dose increment or continuous infusion may be needed to obtain therapeutic meropenem concentrations. In conclusion, our results show that using traditional targets of 40% fT>MIC for standard meropenem dosing of 1 g intravenously every 8 h is likely to provide sufficient meropenem concentration to treat the problematic pathogen P. aeruginosa for patients receiving ECMO treatment. However, for patients with an increased eCL_Cr, or if more aggressive targets, like 100% fT>MIC or 100% fT>4×MIC, are adopted, incremental dosing or continuous infusion may be needed.

Single-dose bone pharmacokinetics of vancomycin in a porcine implant-associated osteomyelitis model

The increasing incidence of orthopaedic methicillin-resistant Staphylococcus aureus (MRSA) infections represents a significant therapeutic challenge. Being effective against MRSA, the role of vancomycin may become more important in the orthopaedic setting in the years to come. Nonetheless, vancomycin bone and soft tissue penetration during infection remains unclear. In eight pigs, implant-associated osteomyelitis was induced on day 0, using a Staphylococcus aureus strain. Following administration of 1,000 mg of vancomycin on day 5, vancomycin concentrations were obtained with microdialysis for 8 h in the implant bone cavity, in cancellous bone adjacent to the implant cavity, in subcutaneous adipose tissue (SCT) adjacent to the implant cavity, and in healthy cancellous bone and healthy SCT in the contralateral leg. Venous blood samples were also obtained. The extent of infection and inflammation was evaluated by post-mortem computed tomography scans, C-reactive protein serum levels and cultures of blood and swabs. In relation to all the implant cavities, bone destruction was found. Ranging from 0.20 to 0.74, tissue penetration, expressed as the ratio of the area under the concentration-time curve from 0 to the last measured value, was incomplete for all compartments except for healthy SCT. The lowest penetration was found in the implant cavity. In conclusion, Staphylococcus aureus implant-associated osteomyelitis was found to reduce vancomycin bone penetration, especially in the implant cavity. These findings suggest that it may be unsafe to rely solely on vancomycin therapy when treating acute osteomyelitis. Particularly when metaphyseal cavities are present, surgical debridement seems necessary. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1093-1098, 2018.

Interstitial Glucose and Lactate Levels Are Inversely Correlated With the Body Mass Index: Need for In Vivo Calibration of Glucose Sensor Results With Blood Values in Obese Patients

BACKGROUND

Continuously measured glucose and lactate levels in interstitial fluid (ISF) may markedly differ from their respective blood levels.

METHODS

Combining microdialysis with a bioanalytical microsystem, the interstitial glucose and lactate concentrations of eight male volunteers with different body mass index (BMI) were monitored during a 2-fold glucose tolerance test over the period of three hours.

RESULTS

Significant correlations were found between abdominally measured sensor results and reference measurements ( R2 = .967 for glucose and R2 = .936 for lactate, P < .05). The physiological delay of the abdominally observed glucose appearance in the ISF correlated positively with the BMI ( R2 = .787, P < .05). The relative in vivo recovery of glucose and lactate was inversely proportional to the BMI of the volunteers ( R2 = .540 for glucose, R2 = .609 for lactate, P < .05). One subject with a BMI of > 34 kg/m2 showed abdominally as well as the antebrachially significantly reduced tissue glucose values compared to blood glucose values ( P < .001).

CONCLUSIONS

A very good correlation between abdominally measured sensor results and the results of the reference method verified the reliability of the BioMEMS. The abdominally measured glucose level in ISF decreased significantly with increasing BMI. Therefore, an in vivo calibration of glucose levels in ISF with blood levels seems to be necessary especially in markedly obese subjects.

Bone and subcutaneous adipose tissue pharmacokinetics of vancomycin in total knee replacement patients

Background and purpose - The incidence of orthopedic methicillin-resistant Staphylococcus aureus (MRSA) infections is increasing. Vancomycin may therefore play an increasingly important role in orthopedic perioperative antimicrobial prophylaxis. Studies investigating perioperative bone and soft tissue concentrations of vancomycin are sparse and challenged by a lack of appropriate methods. We assessed single-dose plasma, subcutaneous adipose tissue (SCT) and bone concentrations of vancomycin using microdialysis in male patients undergoing total knee replacement. Methods - 1,000 mg of vancomycin was administered postoperatively intravenously over 100 minutes to 10 male patients undergoing primary total knee replacement. Vancomycin concentrations in plasma, SCT, cancellous, and cortical bone were measured over the following 8 hours. Microdialysis was applied for sampling in solid tissues. Results - For all solid tissues, tissue penetration of vancomycin was significantly impaired. The time to a mean clinically relevant minimal inhibitory concentration (MIC) of 2 mg/L was 3, 36, 27, and 110 min for plasma, SCT, cancellous, and cortical bone, respectively. As opposed to the other compartments, a mean MIC of 4 mg/L could not be reached in cortical bone. The area under the concentration-time curve from 0 to the last measured value and peak drug concentrations (C_max) for SCT, cancellous, and cortical bone was lower than that of free plasma. The time to C_max was higher for all tissues compared with free plasma. Interpretation - Postoperative penetration of vancomycin to bone and SCT was impaired and delayed in male patients undergoing total knee replacement surgery. Adequate perioperative vancomycin concentrations may not be reached using standard prophylactic dosage.

Microdialysis as a tool to determine the local tissue concentration of dicloxacillin in man

AIMS

The most common pathogen to cause postoperative infections in Denmark is Staphylococcus aureus. Despite using prophylactic antibiotics, infections are still seen. Whether the tissue concentration is above the minimal inhibitory concentration (MIC) for the pathogen is unknown. Thus, the concentration of dicloxacillin in muscle and adipose tissue was measured after intravenous administration, in healthy men.

METHODS

MIC for dicloxacillin against S. aureus was determined using the broth macrodilution method. A microdialysis (MD) catheter was placed in the subcutaneous tissue of the abdomen and in the lateral vastus muscle of the thigh of six healthy male volunteers. They were given 2 g dicloxacillin intravenously. Samples from blood and MD fluid were collected. The unbound dicloxacillin was isolated from plasma. Samples were analysed with high performance liquid chromatography (HPLC).

RESULTS

The maximum concentration was reached in muscle tissue after 0.5 h and in adipose tissue after 0.8 h. AUC_0-6h for the dicloxacillin concentration in adipose tissue was significantly lower when compared to the unbound dicloxacillin concentration in plasma. The dicloxacillin concentration was above the MIC for sensitive S. aureus for a minimum of 2.3 h and a median of 4.1 h in muscle tissue and a minimum of 1.8 h and a median of 3.2 h in adipose tissue.

CONCLUSIONS

The unbound dicloxacillin concentration in adipose and muscle tissue remained above the MIC for sensitive S. aureus, for a period sufficient for many orthopaedic procedures. Whether this is true in patients with compromised circulation remains to be investigated.

Pharmacokinetics of Cefuroxime in Synovial Fluid

Cefuroxime is frequently used as preoperative antibiotic prophylaxis and may be used for the treatment of septic arthritis. A prerequisite for successful treatment of septic arthritis is the ability of an antibiotic agent to penetrate into the target site. Therefore, the concentration of cefuroxime in synovial fluid was evaluated. Ten patients who underwent elective knee arthroscopy were included in this study. Patients were treated with a single dose of 1,500 mg cefuroxime intravenously, and subsequently, the concentrations in plasma, the interstitial fluid of muscle tissue, and synovial fluid were measured by using microdialysis. Pharmacokinetic/pharmacodynamic calculations to predict bacterial killing were performed using the epidemiologically defined MIC₉₀ for clinical isolates and CLSI breakpoints. Cefuroxime penetrated excellently into muscle tissue (ratio of the area under the concentration-time curve [AUC] for muscle tissue/AUC for free plasma, 1.79) and synovial fluid (ratio of the AUC for synovial fluid/AUC for free plasma, 1.94). The cefuroxime concentration was greater than the MIC₉₀ for Staphylococcus aureus and S. epidermidis strains (≤2 mg/liter) over the complete dosing interval (the percentage of the dosing interval during which the free cefuroxime concentration exceeded the MIC for the pathogen [fT_MIC]). CLSI defines staphylococci with MICs of ≤8 mg/liter to be susceptible to cefuroxime. For staphylococci with MICs of ≤8 mg/liter, the fT_MIC in plasma was 52.5%, while the fT_MIC in muscle tissue and synovial fluid was 93.6% and 96.3%, respectively. Cefuroxime may be used to treat septic arthritis caused by susceptible bacterial strains (MIC ≤ 8 mg/liter). The activity of cefuroxime in septic arthritis might be underestimated when relying exclusively on plasma concentrations.

Tissue and plasma concentrations of cephuroxime during cardiac surgery in cardiopulmonary bypass — a microdialysis study

Aim: Wound and mediastinal infections are still very serious complications of open-heart surgery, in spite of the use of prophylactic antibiotics. The use of cardiopulmonary bypass (CPB) is associated with profound physiological changes affecting the pharmacokinetic behaviour of antibiotics.

The aim of this pilot study was to monitor the tissue concentrations of cephuroxime (prophylactic antibiotic) in skeletal muscle during cardiac surgery using CPB by interstitial microdialysis. These concentrations were compared with plasma concentrations of cephuroxime.

Material and methods: Nine adult patients operated on using CPB were enrolled in this study. Cephuroxime was used as a prophylactic antibiotic (1st dose — 3 g of cefuroxime i.v. with anesthesia induction, 2nd dose — 1.5 g i.v. after CPB with protamine sulphate, 3rd dose — 1.5 g i.v. 8 hours after the surgery).

Interstitial microdialysis was performed by probe CMA 60 (CMA Microdialysis AB, Sweden) inserted into the patient's deltoid muscle. Concentrations of cephuroxime in dialysates and in plasma were determined by the modified fluid chromatography method. The unbound cephuroxime fraction in plasma was obtained by using an ultrafiltration method. Samples of dialysates were collected at the following intervals: before CPB, each 30 minutes of CPB, at the end of CPB. Samples of blood were collected at these intervals: incision, start of CPB, each 30 minutes of CPB, at the end of CPB, at the end of surgery. Concentrations of cephuroxime in tissue were corrected by in vivo recoveries of the microdialysis probes.

Results: Plasma concentrations of cephuroxime were 163.5 ± 40.1, 79.3 ± 17.4, 73.7 ± 16.8, 66.1 ± 18.3, 57.0 ± 10.9, 120.7 ± 29.9 (mg . L—1) and concentrations of free plasma fraction of cephuroxime were 119.5 ± 35.2, 67.8 ± 15.5, 66.0 ± 12.5, 54.8 ± 12.2, 49.6 ± 9.8, 102.6 ± 26.0 (mg . L—1).

The concentrations of cephuroxime in dialysates were 44.3 ± 15.7, 36.1 ± 11.6, 31.9 ± 9.3, 34.6 ± 12.3, 27.6 ± 12.9, 56.7 ± 17.6 (mg . L—1).

The mean in vivo recovery of cephuroxime in this study was 30%.

Corrected concentrations (calculated by in vivo recovery) of cephuroxime in skeletal muscle were 148, 120, 106, 115, 92, 189 (mg . L—1).

Conclusion: Our preliminary results show that CPB can modify the time course of cephuroxime plasma and tissue concentrations. A decrease in plasma drug concentrations occurred at the start of CPB and lasted until CPB ended. An increase in plasma concentrations corresponds to the second drug dose after CPB. The concentrations of cephuroxime in skeletal muscle (corrected by recovery) during CPB are higher than plasma concentrations. It is influenced by important changes during CPB; closely associated with hemodilution, a shift of intravascular volume, solutes and albumin to the extravascular space and inconstant protein binding of cephuroxime during operation. Perfusion (2007) 22, 129—136.

Single- and Repeated-Dose Pharmacokinetics of Ceftaroline in Plasma and Soft Tissues of Healthy Volunteers for Two Different Dosing Regimens of Ceftaroline Fosamil

Ceftaroline fosamil (CPT-F) is currently approved for use for the treatment of complicated skin and soft tissue infections and community-acquired pneumonia at 600 mg twice daily (q12h), but other dosing regimens are under evaluation. To date, very limited data on the soft tissue pharmacokinetics (PK) of the active compound, ceftaroline (CPT), are available. CPT concentrations in the plasma, muscle, and subcutis of 12 male healthy volunteers were measured by microdialysis after single and repeated intravenous administration of 600 mg CPT-F q12h or three times daily (q8h) in two groups of 6 subjects each. Relevant PK and PK/pharmacodynamic (PD) parameters were calculated and compared between groups. In plasma, the area under the concentration-time curve (AUC) from 0 to 24 h for total CPT and the cumulative percentage of the dosing interval during which the free drug concentrations exceeded the MIC (fTMIC) for unbound CPT for the currently established threshold of 1 mg/liter were significantly higher in the group receiving CPT-F q8h. Exposure to free drug in soft tissues was higher in the group receiving CPT-F q8h, but high interindividual variability in relevant PK parameters was observed. The mean ratios of the AUC from time zero to the end of the dosing interval (AUC0-τ) for free CPT in soft tissues and the AUC0-τ for the calculated free fraction in plasma at steady state ranged from 0.66 to 0.75. Administration of CPT-F q8h led to higher levels of drug exposure in all investigated compartments. When MIC values above 1 mg/liter were assumed, the calculated fTMIC after dosing q12h was markedly lower than that after dosing q8h. The clinical implications of these differences are discussed in light of recently completed clinical phase III and PK/PD studies.

Microdialysis Assessment of Cerebral Perfusion during Cardiac Arrest, Extracorporeal Life Support and Cardiopulmonary Resuscitation in Rats - A Pilot Trial

Cerebral metabolic alterations during cardiac arrest, cardiopulmonary resuscitation (CPR) and extracorporeal cardiopulmonary life support (ECLS) are poorly explored. Markers are needed for a more personalized resuscitation and post-resuscitation care. Aim of this study was to investigate early metabolic changes in the hippocampal CA1 region during ventricular fibrillation cardiac arrest (VF-CA) and ECLS versus conventional CPR. Male Sprague-Dawley rats (350g) underwent 8min untreated VF-CA followed by ECLS (n = 8; bloodflow 100ml/kg), mechanical CPR (n = 18; 200/min) until return of spontaneous circulation (ROSC). Shams (n = 2) were included. Glucose, glutamate and lactate/pyruvate ratio were compared between treatment groups and animals with and without ROSC. Ten animals (39%) achieved ROSC (ECLS 5/8 vs. CPR 5/18; OR 4,3;CI:0.7-25;p = 0.189). During VF-CA central nervous glucose decreased (0.32±0.1mmol/l to 0.04±0.01mmol/l; p<0.001) and showed a significant rise (0.53±0.1;p<0.001) after resuscitation. Lactate/pyruvate (L/P) ratio showed a 5fold increase (31 to 164; p<0.001; maximum 8min post ROSC). Glutamate showed a 3.5-fold increase to (2.06±1.5 to 7.12±5.1μmol/L; p<0.001) after CA. All parameters normalized after ROSC with no significant differences between ECLS and CPR. Metabolic changes during ischemia and resuscitation can be displayed by cerebral microdialysis in our VF-CA CPR and ECLS rat model. We found similar microdialysate concentrations and patterns of normalization in both resuscitation methods used. Institutional Protocol Number: GZ0064.11/3b/2011.

An Exploratory Microdialysis Study to Assess the Ocular Pharmacokinetics of Ciprofloxacin Eye Drops in Rabbits

PURPOSE

Despite the high frequency of use, data regarding the ocular in vivo pharmacokinetics (PK) of topically applied antibiotics are sparse. This study seeks to investigate the PK of the widely used fluoroquinolone ciprofloxacin by means of in vivo microdialysis.

METHODS

Twelve New Zealand white rabbits were included in the experiments. Under general anesthesia, microdialysis probes were implanted in the anterior chamber and the posterior segment of the same eye. After a period of 90 min after implantation, one drop of ciprofloxacin was administered onto the ocular surface. Microdialysis samples of the anterior chamber and the vitreous were collected every 30 min for 6 h. Relative recovery was assessed by retrodialysis to calculate absolute concentration values. Samples were analyzed using HPLC.

RESULTS

In the anterior chamber, the maximum total drug concentration (Cmax) amounted to 0.373 ± 0.281 μg/mL and was reached (Tmax) after 116 ± 36 min. Calculated area under the concentration-time curve AUC(0-n) for ciprofloxacin in the anterior chamber was 78.8 ± 47.1 μg min/mL. For the vitreous, Cmax was 0.02 ± 0.03 μg/mL and maximum drug concentration was reached 107 ± 60 min after topical administration. AUC(0-n) for ciprofloxacin in the vitreous was 0.269 ± 0.370 μg min/mL.

CONCLUSION

Microdialysis is a suitable method to assess in vivo pharmacokinetic profiles in the anterior chamber and in the vitreous. In the anterior chamber, maximum drug concentration was reached ∼2 h after single drug administration. Although the drug concentration in the vitreous was considerably lower, time course of drug concentration was comparable.

Simultaneous assessment of the pharmacokinetics of a pleuromutilin, lefamulin, in plasma, soft tissues and pulmonary epithelial lining fluid

BACKGROUND

Lefamulin is a pleuromutilin antibiotic under evaluation for the treatment of bacterial infections, including respiratory tract infections. Currently, there are no high-quality pharmacokinetic data on drug tissue concentrations of lefamulin available.

METHODS

A single dose of intravenous lefamulin (150 mg) was given to 12 healthy men. The registered EudraCT number for this study was 2010-021938-54. Lefamulin concentrations were simultaneously measured in plasma, skeletal muscle tissue, subcutaneous adipose tissue and epithelial lining fluid (ELF) over 24 h, and corresponding pharmacokinetic parameters were calculated. Microdialysis was used to measure unbound lefamulin concentrations in skeletal muscle tissue and subcutaneous adipose tissue, which were similar to unbound lefamulin concentrations in plasma. Bronchoalveolar lavage was performed 1, 2, 4 and 8 h post-dose to determine lefamulin concentrations in ELF.

RESULTS

Unbound lefamulin levels showed a 5.7-fold higher exposure in ELF compared with that in plasma, demonstrating good penetration to the target site.

CONCLUSIONS

Lefamulin may be an addition to the therapeutic armamentarium for the treatment of infections. Simultaneous measurements of unbound drug concentration can guide target attainment for future therapeutic trials.

Pharmacokinetics of single-dose cefuroxime in porcine intervertebral disc and vertebral cancellous bone determined by microdialysis

BACKGROUND

Pyogenic spondylodiscitis is associated with prolonged antimicrobial therapy and high relapse rates. Nevertheless, tissue pharmacokinetic studies of relevant antimicrobials in both prophylactic and therapeutic situations are still sparse. Previous approaches based on bone biopsy and discectomy exhibit important methodological limitations.

PURPOSE

The objective of this study was to assess the C3-C4 intervertebral disc (IVD), C3 vertebral body cancellous bone, and subcutaneous adipose tissue (SCT) pharmacokinetics of cefuroxime by use of microdialysis in a large animal model.

STUDY DESIGN

This was a single-dose, dense sampling large animal study of cefuroxime spine penetration.

METHODS

Ten female pigs were assigned to receive 1,500 mg of cefuroxime intravenously over 15 minutes. Measurements of cefuroxime were obtained from plasma, SCT, vertebral cancellous bone, and IVD for 8 hours thereafter. Microdialysis was applied for sampling in solid tissues.

RESULTS

For both IVD and vertebral cancellous bone, the area under the concentration curve from zero to the last measured value (AUC(0-last)) was significantly lower than that of free plasma. As estimated by the ratio of tissue AUC(0-last) to plasma AUC(0-last), tissue penetration (95% confidence interval) of cefuroxime was significantly incomplete for the IVD 0.78 (0.57; 0.99), whereas for vertebral cancellous bone 0.78 (0.51; 1.04) and SCT 0.94 (0.73; 1.15) it was not. The penetration of cefuroxime from plasma to the IVD was delayed, and the maximal concentration and the elimination of cefuroxime were also reduced compared with both SCT and vertebral cancellous bone. Because of this delay in elimination of cefuroxime, the time with concentrations above the minimal inhibitory concentration (T(>MIC)) was significantly longer in the IVD compared with the remaining compartments up to MICs of 6 µg/mL.

CONCLUSIONS

Microdialysis was successfully applied for serial assessment of the concentration of cefuroxime in the IVD and the vertebral cancellous bone. Penetration of cefuroxime from plasma to IVD was found to be incomplete and delayed, but because of a prolonged elimination, superior T(>MIC) was found in the IVD up to MICs of 6 µg/mL.

In Vivo Microdialysis To Determine Subcutaneous Interstitial Fluid Penetration and Pharmacokinetics of Fluconazole in Intensive Care Unit Patients with Sepsis

The objective of the study was to describe the subcutaneous interstitial fluid (ISF) pharmacokinetics of fluconazole in critically ill patients with sepsis. This prospective observational study was conducted at two tertiary intensive care units in Australia. Serial fluconazole concentrations were measured over 24 h in plasma and subcutaneous ISF using microdialysis. The concentrations in plasma and microdialysate were measured using a validated high-performance liquid chromatography system with electrospray mass spectrometer detector method. Noncompartmental pharmacokinetic analysis was performed. Twelve critically ill patients with sepsis were enrolled. The mean in vivo fluconazole recovery rates ± standard deviation (SD) for microdialysis were 51.4% ± 16.1% with a mean (±SD) fluconazole ISF penetration ratio of 0.52 ± 0.30 (coefficient of variation, 58%). The median free plasma area under the concentration-time curve from 0 to 24 h (AUC0-24) was significantly higher than the median ISF AUC0-24 (340.4 versus 141.1 mg · h/liter; P = 0.004). There was no statistical difference in median fluconazole ISF penetration between patients receiving and not receiving vasopressors (median, 0.28 versus 0.78; P = 0.106). Both minimum and the maximum concentrations of drug in serum (Cmax and Cmin) showed a significant correlation with the fluconazole plasma exposure (Cmax, R(2) = 0.86, P < 0.0001; Cmin, R(2) = 0.75, P < 0.001). Our data suggest that fluconazole was distributed variably, but incompletely, from plasma into subcutaneous interstitial fluid in this cohort of critically ill patients with sepsis. Given the variability of fluconazole interstitial fluid exposures and lack of clinically identifiable factors by which to recognize patients with reduced distribution/exposure, we suggest higher than standard doses to ensure that drug exposure is adequate at the site of infection.

Antibiotic Tissue Penetration in Diabetic Foot Infections A Review of the Microdialysis Literature and Needs for Future Research

Although many antimicrobial agents display good in vitro activity against the pathogens frequently implicated in diabetic foot infections, effective treatment can be complicated by reduced tissue penetration in this population secondary to peripheral arterial disease and emerging antimicrobial resistance, which can result in clinical failure. Improved characterization of antibiotic tissue pharmacokinetics and penetration ratios in diabetic foot infections is needed. Microdialysis offers advantages over the skin blister and tissue homogenate studies historically used to define antibiotic penetration in skin and soft-tissue infections by defining antibiotic penetration into the interstitial fluid over the entire concentration versus time profile. However, only a select number of agents currently recommended for treating diabetic foot infections have been evaluated using these methods, which are described herein. Better characterization of the tissue penetration of antibiotic agents is needed for the development of methods for maximizing the pharmacodynamic profile of these agents to ultimately improve treatment outcomes for patients with diabetic foot infections.