Linezolid brain penetration in neurointensive care patients.

BACKGROUND: Linezolid exposure in critically ill patients is associated with high inter-individual variability, potentially resulting in subtherapeutic antibiotic exposure. Linezolid exhibits good penetration into the CSF, but its penetration into cerebral interstitial fluid (ISF) is unknown. OBJECTIVES: To determine linezolid penetration into CSF and cerebral ISF of neurointensive care patients. PATIENTS AND METHODS: Five neurocritical care patients received 600 mg of linezolid IV twice daily for treatment of extracerebral infections. At steady state, blood and CSF samples were collected from arterial and ventricular catheters, and microdialysate was obtained from a cerebral intraparenchymal probe. RESULTS: The median fAUC0-24 was 57.6 (24.9-365) mg·h/L in plasma, 64.1 (43.5-306.1) mg·h/L in CSF, and 27.0 (10.7-217.6) mg·h/L in cerebral ISF. The median penetration ratio (fAUCbrain_or_CSF/fAUCplasma) was 0.5 (0.25-0.81) for cerebral ISF and 0.92 (0.79-1) for CSF. Cerebral ISF concentrations correlated well with plasma (R = 0.93, P < 0.001) and CSF levels (R = 0.93, P < 0.001).The median fAUC0-24/MIC ratio was ≥100 in plasma and CSF for MICs of ≤0.5 mg/L, and in cerebral ISF for MICs of ≤0.25 mg/L. The median fT>MIC was ≥80% of the dosing interval in CSF for MICs of ≤0.5 mg/L, and in plasma and cerebral ISF for MICs of ≤0.25 mg/L. CONCLUSIONS: Linezolid demonstrates a high degree of cerebral penetration, and brain concentrations correlate well with plasma and CSF levels. However, substantial variability in plasma levels, and thus cerebral concentrations, may result in subtherapeutic tissue concentrations in critically ill patients with standard dosing, necessitating therapeutic drug monitoring.

Perioperative administration of cefazolin and metronidazole in obese and non-obese patients: a pharmacokinetic study in plasma and interstitial fluid.

OBJECTIVES: To assess plasma and tissue pharmacokinetics of cefazolin and metronidazole in obese patients undergoing bariatric surgery and non-obese patients undergoing intra-abdominal surgery. PATIENTS AND METHODS: Fifteen obese and 15 non-obese patients received an IV short infusion of 2 g cefazolin and 0.5 g metronidazole for perioperative prophylaxis. Plasma and microdialysate from subcutaneous tissue were sampled until 8 h after dosing. Drug concentrations were determined by HPLC-UV. Pharmacokinetic parameters were calculated non-compartmentally. RESULTS: In obese patients (BMI 39.5-69.3 kg/m2) compared with non-obese patients (BMI 18.7-29.8 kg/m2), mean Cmax of total cefazolin in plasma was lower (115 versus 174 mg/L) and Vss was higher (19.4 versus 14.2 L). The mean differences in t½ (2.7 versus 2.4 h), CL (5.14 versus 4.63 L/h) and AUC∞ (402 versus 450 mg·h/L) were not significant. The influence of obesity on the pharmacokinetics of metronidazole was similar (Cmax 8.99 versus 14.7 mg/L, Vss 73.9 versus 51.8 L, t½ 11.9 versus 9.1 h, CL 4.62 versus 4.13 L/h, AUC∞ 116 versus 127 mg·h/L). Regarding interstitial fluid (ISF), mean concentrations of cefazolin remained >4 mg/L until 6 h in both groups, and those of metronidazole up to 8 h in the non-obese group. In obese patients, the mean ISF concentrations of metronidazole were between 3 and 3.5 mg/L throughout the measuring interval. CONCLUSIONS: During the time of surgery, cefazolin concentrations in plasma and ISF of subcutaneous tissue were lower in obese patients, but not clinically relevant. Regarding metronidazole, the respective differences were higher, and may influence dosing of metronidazole for perioperative prophylaxis in obese patients.

Measurement of Free Plasma Concentrations of Beta-Lactam Antibiotics: An Applicability Study in Intensive Care Unit Patients.

BACKGROUND: The antibacterial effect of antibiotics is linked to the free drug concentration. This study investigated the applicability of an ultrafiltration method to determine free plasma concentrations of beta-lactam antibiotics in ICU patients. METHODS: Eligible patients included adult ICU patients treated with ceftazidime (CAZ), meropenem (MEM), piperacillin (PIP)/tazobactam (TAZ), or flucloxacillin (FXN) by continuous infusion. Up to 2 arterial blood samples were drawn at steady state. Patients could be included more than once if they received another antibiotic. Free drug concentrations were determined by high-performance liquid chromatography with ultraviolet detection after ultrafiltration, using a method that maintained physiological conditions (pH 7.4/37°C). Total drug concentrations were determined to calculate the unbound fraction. In a post-hoc analysis, free concentrations were compared with the target value of 4× the epidemiological cut-off value (ECOFF) for Pseudomonas aeruginosa as a worst-case scenario for empirical therapy with CAZ, MEM or PIP/tazobactam and against methicillin-sensitive Staphylococcus aureus for targeted therapy with FXN. RESULTS: Fifty different antibiotic treatment periods in 38 patients were evaluated. The concentrations of the antibiotics showed a wide range because of the fixed dosing regimen in a mixed population with variable kidney function. The mean unbound fractions (fu) of CAZ, MEM, and PIP were 102.5%, 98.4%, and 95.7%, with interpatient variability of <6%. The mean fu of FXN was 11.6%, with interpatient variability of 39%. It was observed that 2 of 12 free concentrations of CAZ, 1 of 40 concentrations of MEM, and 11 of 23 concentrations of PIP were below the applied target concentration of 4 × ECOFF for P. aeruginosa. All concentrations of FXN (9 samples from 6 patients) were >8 × ECOFF for methicillin-sensitive Staphylococcus aureus. CONCLUSIONS: For therapeutic drug monitoring purposes, measuring total or free concentrations of CAZ, MEM, or PIP is seemingly adequate. For highly protein-bound beta-lactams such as FXN, free concentrations should be favored in ICU patients with prevalent hypoalbuminemia.

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.

Plasma and tissue pharmacokinetics of fosfomycin in morbidly obese and non-obese surgical patients: a controlled clinical trial.

OBJECTIVES: To assess the pharmacokinetics and tissue penetration of fosfomycin in obese and non-obese surgical patients. METHODS: Fifteen obese patients undergoing bariatric surgery and 15 non-obese patients undergoing major intra-abdominal surgery received an intravenous single short infusion of 8 g of fosfomycin. Fosfomycin concentrations were determined by LC-MS/MS in plasma and microdialysate from subcutaneous tissue up to 8 h after dosing. The pharmacokinetic analysis was performed in plasma and interstitial fluid (ISF) by non-compartmental methods. RESULTS: Thirteen obese patients (BMI 38-50 kg/m2) and 14 non-obese patients (BMI 0-29 kg/m2) were evaluable. The pharmacokinetics of fosfomycin in obese versus non-obese patients were characterized by lower peak plasma concentrations (468 ±âŸ139 versus 594 ±âŸ149 mg/L, P = 0.040) and higher V (24.4 ±âŸ6.4 versus 19.0 ±âŸ3.1 L, P = 0.010). The differences in AUC∞ were not significant (1275 ±âŸ477 versus 1515 ±âŸ352 mg·h/L, P = 0.16). The peak concentrations in subcutaneous tissue were reached rapidly and declined in parallel with the plasma concentrations. The drug exposure in tissue was nearly halved in obese compared with non-obese patients (AUC∞ 1052 ±âŸ394 versus 1929 ±âŸ725 mg·h/L, P = 0.0010). The tissue/plasma ratio (AUCISF/AUCplasma) was 0.86 ±âŸ0.32 versus 1.27 ±âŸ0.34 (P = 0.0047). CONCLUSIONS: Whereas the pharmacokinetics of fosfomycin in plasma of surgical patients were only marginally different between obese and non-obese patients, the drug exposure in subcutaneous tissue was significantly lower in the obese patients.

Can systemically administered antibiotics be detected in wound tissues and surfaces under negative pressure wound therapy?

In this study, we evaluated a new aspect of negative pressure wound therapy (NPWT) as an analytical tool for pharmacokinetic studies. Twenty-one patients with soft tissue defects scheduled to receive NPWT were included in this study. Concomitant to NPWT, all patients received intravenous moxifloxacin (MX). At different time intervals, blood plasma levels of MX were sampled and compared with synchronous concentrations of MX in the exudate obtained from the NPWT drainage system. Serial measurements were performed upon initiation of the therapy as well as in the steady state (after 5 days). At steady state, wound tissue was obtained intraoperatively. High-performance liquid-chromatography (HPLC) was used for analysis. At 1 hour post-administration, the exudate/plasma levels (mg/L) were 1.92/3.07; at 12 hours, 0.80/1.14; at 24 hours, 0.26/0.43; and at 120 hours (steady state), 0.42/0.47. There was a correlation between exudate and plasma levels reaching approximately 0.75. Until now, methods for pharmacokinetic studies concerning interstitial fluid are difficult to apply in the clinical context. The presented method showed limitations, but we believe that, after methodological improvements, measurements of substances in the interstitial fluid by means of NPWT are feasible.

Variable Linezolid Exposure in Intensive Care Unit Patients-Possible Role of Drug-Drug Interactions.

BACKGROUND: Standard doses of linezolid may not be suitable for all patient groups. Intensive care unit (ICU) patients in particular may be at risk of inadequate concentrations. This study investigated variability of drug exposure and its potential sources in this population. METHODS: Plasma concentrations of linezolid were determined by high-performance liquid chromatography in a convenience sample of 20 ICU patients treated with intravenous linezolid 600 mg twice daily. Ultrafiltration applying physiological conditions (pH 7.4/37°C) was used to determine the unbound fraction. Individual pharmacokinetic (PK) parameters were estimated by population PK modeling. As measures of exposure to linezolid, area under the concentration-time curve (AUC) and trough concentrations (Cmin) were calculated and compared with published therapeutic ranges (AUC 200-400 mg*h/L, Cmin 2-10 mg/L). Coadministered inhibitors or inducers of cytochrome P450 and/or P-glycoprotein were noted. RESULTS: Data from 18 patients were included into the PK evaluation. Drug exposure was highly variable (median, range: AUC 185, 48-618 mg*h/L, calculated Cmin 2.92, 0.0062-18.9 mg/L), and only a minority of patients had values within the target ranges (6 and 7, respectively). AUC and Cmin were linearly correlated (R = 0.98), and classification of patients (underexposed/within therapeutic range/overexposed) according to AUC or Cmin was concordant in 15 cases. Coadministration of inhibitors was associated with a trend to higher drug exposure, whereas 3 patients treated with levothyroxine showed exceedingly low drug exposure (AUC ∼60 mg*h/L, Cmin <0.4 mg/L). The median unbound fraction in all 20 patients was 90.9%. CONCLUSIONS: Drug exposure after standard doses of linezolid is highly variable and difficult to predict in ICU patients, and therapeutic drug monitoring seems advisable. PK drug-drug interactions might partly be responsible and should be further investigated; protein binding appears to be stable and irrelevant.

Anti-inflammatory effects of cell-based therapy with tyrosine hydroxylase-positive catecholaminergic cells in experimental arthritis.

OBJECTIVES: Studies in rheumatoid arthritis (RA), osteoarthritis (OA) and mice with arthritis demonstrated tyrosine hydroxylase-positive (TH(+)) cells in arthritic synovium and parallel loss of sympathetic nerve fibres. The exact function of TH(+) cells and mode of TH induction are not known. METHODS: Synovial cells of RA/OA were isolated and cultured under normoxic/hypoxic conditions with/without stimulating enzyme cofactors of TH and inhibitors of TH. We studied TH expression and release of cytokines/catecholamines. In vivo function was tested by cell therapy with TH(+) neuronal precursor cells (TH(+) neuronal cells) in DBA/1 mice with collagen type II-induced arthritis (CIA). RESULTS: Compared with normoxic conditions, hypoxia increased TH protein expression and catecholamine synthesis and decreased release of tumour necrosis factor (TNF) in OA/RA synovial cells. This inhibitory effect on TNF was reversed by TH inhibition with α-methyl-para-tyrosine (αMPT), which was particularly evident under hypoxic conditions. Incubation with specific TH cofactors (tetrahydrobiopterin and Fe(2+)) increased hypoxia-induced inhibition of TNF, which was also reversed by αMPT. To address a possible clinical role of TH(+) cells, murine TH(+) neuronal cells were generated from mesenchymal stem cells. TH(+) neuronal cells exhibited a typical catecholaminergic phenotype. Adoptive transfer of TH(+) neuronal cells markedly reduced CIA in mice, and 6-hydroxydopamine, which depletes TH(+) cells, reversed this effect. CONCLUSIONS: The anti-inflammatory effect of TH(+) neuronal cells on experimental arthritis has been presented for the first time. In RA/OA, TH(+) synovial cells have TH-dependent anti-inflammatory capacities, which are augmented under hypoxia. Using generated TH(+) neuronal cells might open new avenues for cell-based therapy.

Protein binding characteristics and pharmacokinetics of ceftriaxone in intensive care unit patients.

AIMS: The aim of the present study was to assess the pharmacokinetics of total and unbound ceftriaxone in intensive care unit (ICU) patients and its protein binding characteristics. METHODS: Twenty patients (m/f 15/5, age 25-86 years, body weight 60-121 kg, APACHE II 7-40, estimated glomerular filtration rate 19-157 ml min(-1) , albumin 11.7-30.1 g l(-1) , total bilirubin <0.1-36.1 mg dl(-1) ) treated with intravenous ceftriaxone were recruited from two ICUs. Timed plasma samples were obtained using an opportunistic study protocol. Ceftriaxone concentrations were determined by high-performance liquid chromatography; unbound concentrations were determined after ultrafiltration using a new method which maintains physiological pH and temperature. The pharmacokinetics was described by a one-compartment model, the protein-binding characteristics by Michaelis-Menten kinetics. RESULTS: For total drug, the volume of distribution was 20.2 l (median; interquartile range 15.6-24.5 l), the half-life 14.5 h (10.0-25.5 h) and the clearance 0.96 l h(-1) (0.55-1.28 l h(-1) ). The clearance of unbound drug was 1.91 l h(-1) (1.46-6.20 l h(-1) ) and linearly correlated with estimated glomerular filtration rate (slope 0.85, y-intercept 0.24 l h(-1) , r(2) = 0.70). The unbound fraction was higher in ICU patients (33.0%; 20.2-44.5%) than reported in healthy volunteers, particularly when renal impairment or severe hyperbilirubinaemia was present. In all patients, unbound concentrations during treatment with ceftriaxone 2 g once daily remained above the EUCAST susceptibility breakpoint (≤1 mg l(-1) ) throughout the whole dosing interval. CONCLUSIONS: Protein binding of ceftriaxone is reduced and variable in ICU patients due to hypoalbuminaemia, but also to altered binding characteristics. Despite these changes, the pharmacokinetics of unbound ceftriaxone is governed by renal function. For patients with normal or reduced renal function, standard doses are sufficient.

Function of cGMP-dependent protein kinase II in volume load-induced diuresis.

Atrial natriuretic peptide (ANP)/cGMPs cause diuresis and natriuresis. Their downstream effectors beyond cGMP remain unclear. To elucidate a probable function of cGMP-dependent protein kinase II (cGKII), we investigated renal parameters in different conditions (basal, salt diets, starving, water load) using a genetically modified mouse model (cGKII-KO), but did not detect any striking differences between WT and cGKII-KO. Thus, cGKII is proposed to play only a marginal role in the adjustment of renal concentration ability to varying salt loads without water restriction or starving conditions. When WT mice were subjected to a volume load (performed by application of a 10-mM glucose solution (3% of BW) via feeding needle), they exhibited a potent diuresis. In contrast, urine volume was decreased significantly in cGKII-KO. We showed that AQP2 plasma membrane (PM) abundance was reduced for about 50% in WT upon volume load, therefore, this might be a main cause for the enhanced diuresis. In contrast, cGKII-KO mice almost completely failed to decrease AQP2-PM distribution. This significant difference between both genotypes is not induced by an altered p-Ser256-AQP2 phosphorylation, as phosphorylation at this site decreases similarly in WT and KO. Furthermore, sodium excretion was lowered in cGKII-KO mice during volume load. In summary, cGKII is only involved to a minor extent in the regulation of basal renal concentration ability. By contrast, cGKII-KO mice are not able to handle an acute volume load. Our results suggest that membrane insertion of AQP2 is inhibited by cGMP/cGKII.

Unbound fraction of ertapenem in intensive care unit patients.

OBJECTIVES: To determine unbound ertapenem concentrations in plasma and to describe the pharmacokinetics of unbound ertapenem in intensive care unit (ICU) patients. PATIENTS AND METHODS: For assessing the influence of experimental conditions and for development of the ultrafiltration protocol, plasma from healthy volunteers was used. Concentrations of total and unbound ertapenem were determined by HPLC in 29 plasma samples from six ICU patients treated with 1 g of ertapenem once daily. The concentration-time courses were described by a one-compartment model. Ertapenem binding to albumin was assessed by Michaelis-Menten kinetics in solutions of human serum albumin, in plasma from healthy volunteers and in plasma from ICU patients. RESULTS: The unbound fraction (fu) of ertapenem was highly susceptible to pH and temperature during ultrafiltration and was ∼20% in plasma from healthy volunteers at clinically relevant concentrations. In ICU patients, fu was substantially higher (range 30.9%-53.6%). The unbound concentrations of ertapenem exceeded 2 mg/L for 72% (median; range 39%-100%) of the 24 h dosing interval and 0.25 mg/L for 100% (range 79%-100%). The number of binding sites per albumin molecule was 1.22 (95% CI 1.07-1.38) in plasma from healthy volunteers and 0.404 (95% CI 0.158-0.650) in samples from ICU patients. CONCLUSIONS: Determination of unbound ertapenem by ultrafiltration is susceptible to experimental conditions. When determined at physiological pH and temperature, fu of ertapenem is 2- to 4-fold higher than previously reported and even higher in ICU patients. Binding studies indicate that hypoalbuminaemia alone does not explain these differences. This issue should be further investigated for its clinical relevance.

The cyclic GMP-dependent protein kinase Iα suppresses kidney fibrosis.

Cyclic guanosine monophosphate (cGMP) is synthesized by nitric oxide or natriuretic peptide-stimulated guanylyl cyclases and exhibits pleiotropic regulatory functions in the kidney. Hence, integration of cGMP signaling by cGMP-dependent protein kinases (cGKs) might play a critical role in renal physiology; however, detailed renal localization of cGKs is still lacking. Here, we performed an immunohistochemical analysis of cGKIα and cGKIß isozymes in the mouse kidney and found both in arterioles, the mesangium, and within the cortical interstitium. In contrast to cGKIα, the ß-isoform was not detected in the juxtaglomerular apparatus or medullary fibroblasts. Since interstitial fibroblasts play a prominent role in interstitial fibrosis, we focused our study on cGKI function in the interstitium, emphasizing a functional differentiation of both isoforms, and determined whether cGKIs influence renal fibrosis induced by unilateral ureter obstruction. Treatment with the guanylyl cyclase activators YC1 or isosorbide dinitrate showed stronger antifibrotic effects in wild-type than in cGKI-knockout or in smooth muscle-cGKIα-rescue mice, which are cGKI deficient in the kidney except in the renal vasculature. Moreover, fibrosis influenced the mRNA and protein expression levels of cGKIα more strongly than cGKIß. Thus, our results indicate that cGMP, acting primarily through cGKIα, is an important suppressor of kidney fibrosis.

Population pharmacokinetics and pharmacodynamic evaluation of intravenous and enteral moxifloxacin in surgical intensive care unit patients.

OBJECTIVES: To describe the plasma concentration-time profile of moxifloxacin after intravenous and enteral administration in intensive care unit (ICU) patients and to provide a pharmacodynamic (PD) evaluation with regard to pneumonia. PATIENTS AND METHODS: Twenty-five adult patients from a cardiothoracic/mixed surgical ICU were enrolled. Moxifloxacin was given as a standard dose (400 mg once daily). Therapy was successfully switched to enteral administration on day 5 in 16 patients. A rich data sampling schedule was performed after intravenous (day 4) and enteral (day 8) administration. Moxifloxacin concentrations were analysed by HPLC. A population pharmacokinetic (PK) model was developed using NONMEM VII. Simulated concentration-time profiles were evaluated for their probability of attaining PK/PD target values relevant for community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP). RESULTS: A linear-elimination two-compartment model described the data adequately. Parameter estimates (coefficient of variation of inter-individual variability) were: absorption rate constant, 1.09/h (135%); enteral bioavailability, 76% (20.0%); central volume of distribution, 55.6 L; peripheral volume of distribution, 59.6 L (15.3%); inter-compartmental clearance, 47.7 L/h; and clearance, 11.3 L/h (23.7%). Both intravenously and enterally administered standard-dose moxifloxacin reliably attained the PK/PD target values for pathogens with MICs ≤ 0.25 mg/L for CAP and ≤ 0.125 mg/L for HAP. CONCLUSIONS: Drug exposure to moxifloxacin in ICU patients was more variable than in healthy volunteers. The standard dosing provides sufficient drug exposure for treatment of CAP but for HAP it does so only when a highly susceptible pathogen is present. Intravenous/enteral sequential therapy may be considered for cautiously selected cases in ICU patients.

Catechol conjugates are in vivo metabolites of Salicis cortex.

After oral administration of 100 mg/kg b. w. (235.8 µmol/kg) salicortin to Wistar rats, peak serum concentrations of 1.43 mg/L (13.0 µM) catechol were detected after 0.5 h in addition to salicylic acid by HPLC-DAD after serum processing with ß-glucuronidase and sulphatase. Both metabolites could also be detected in the serum of healthy volunteers following oral administration of a willow bark extract (Salicis cortex, Salix spec., Salicaceae) corresponding to 240 mg of salicin after processing with both enzymes. In humans, the cmax (1.46 mg/L, 13.3 µM) of catechol was reached after 1.2 h. The predominant phase-II metabolite in humans and rats was catechol sulphate, determined by HPLC analysis of serum samples processed with only one kind of enzyme. Without serum processing with glucuronidase and sulphatase, no unconjugated catechol could be detected in human and animal serum samples. As catechol is described as an anti-inflammatory compound, these results may contribute to the elucidation of the mechanism of the action of willow bark extract.

Tigecycline Soft Tissue Penetration in Obese and Non-obese Surgical Patients Determined by Using In Vivo Microdialysis.

BACKGROUND AND OBJECTIVE: Tigecycline, a broad-spectrum glycylcycline antibiotic, is approved for use at a fixed dose irrespective of body weight. However, its pharmacokinetics may be altered in obesity, which would impact on the antibiotic's effectiveness. The objective of this study was to investigate the plasma and subcutaneous tissue concentrations of tigecycline in obese patients compared with those in a non-obese control group. METHODS: Fifteen obese patients (one class II and 14 class III) undergoing bariatric surgery and 15 non-obese patients undergoing intra-abdominal surgery (mainly tumour resection) received a single dose of 50 or 100 mg tigecycline as an intravenous short infusion. Tigecycline concentrations were measured up to 8 h after dosing in plasma (total concentration), in ultrafiltrate of plasma (free concentration), and in microdialysate from subcutaneous tissue, respectively. RESULTS: In obese patients, total peak plasma concentration (1.31 ± 0.50 vs 2.27 ± 1.40 mg/L) and the area under the concentration-time curve from 0 to 8 h (AUC8h,plasma: 2.15 ± 0.42 vs 2.74 ± 0.73 h⋅mg/L), as normalized to a 100 mg dose, were significantly lower compared with those of non-obese patients. No significant differences were observed regarding the free plasma concentration, as determined by ultrafiltration, or the corresponding AUC8h (fAUC8h,plasma). Concentrations in interstitial fluid (ISF) of subcutaneous tissue were lower than the free plasma concentrations in both groups, and they were lower in obese compared to non-obese patients: the AUC8h in ISF (AUC8h,ISF) was 0.51 ± 0.22 h⋅mg/L in obese and 0.79 ± 0.23 h⋅mg/L in non-obese patients, resulting in a relative tissue drug exposure (AUC8h,ISF/fAUC8h,plasma) of 0.38 ± 0.19 and 0.63 ± 0.24, respectively. CONCLUSION: Following a single dose of tigecycline, concentrations in the ISF of subcutaneous adipose tissue are decreased in heavily obese subjects, calling for an increased loading dose. EU CLINICAL TRIALS REGISTRATION NUMBER: EudraCT No. 2012-004383-22.

Pharmacokinetics of moxifloxacin in plasma and tissue of morbidly obese patients.

OBJECTIVES: To assess the pharmacokinetics of moxifloxacin in morbidly obese patients. METHODS: Twelve morbidly obese patients (2 male/10 female, age 25-61 years, weight 98-166 kg, body mass index 43.0-58.2 kg/m(2)) scheduled for gastric bypass surgery were treated with 400 mg of moxifloxacin orally once daily for 3 days and with 400 mg of moxifloxacin intravenously on day 4 (day of surgery). Pharmacokinetic analysis was performed on day 1 and day 4. Specimens of small intestine, greater omentum and subcutaneous adipose tissue were collected intraoperatively 1.8-3.7 h after moxifloxacin infusion. Moxifloxacin concentrations were determined by HPLC. RESULTS: The plasma pharmacokinetics (mean ±â€ŠSD) was comparable to historical data in normal-weight subjects. Oral bioavailability was 79.6% ±â€Š11.5%. After intravenous administration, plasma clearance was 9.6 ±â€Š2.0 L/h, volume of distribution was 165 ±â€Š30 L and area under the curve was 43.7 ±â€Š11.8 mg·h/L. Linear regression analysis showed the volume of distribution to be better correlated with ideal body weight, lean body weight, fat-free mass or height (R(2) = 0.60-0.67, P = 0.001-0.003) than with total body weight (R(2) = 0.46, P = 0.015). Whereas mean tissue concentrations in small intestine (6.99 ±â€Š2.34 mg/kg) were twice the concomitant plasma concentrations, the concentrations in greater omentum (0.801 ±â€Š0.168 mg/kg) or subcutaneous fat (0.638 ±â€Š0.180 mg/kg) were only one-quarter of those. CONCLUSIONS: The pharmacokinetics of moxifloxacin is not significantly affected by morbid obesity. No dose adjustment seems to be necessary in this particular population.

Cytidylyl and uridylyl cyclase activity of bacillus anthracis edema factor and Bordetella pertussis CyaA.

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are second messengers for numerous mammalian cell functions. The natural occurrence and synthesis of a third cyclic nucleotide (cNMP), cyclic cytidine 3',5'-monophosphate (cCMP), is a matter of controversy, and almost nothing is known about cyclic uridine 3',5'-monophosphate (cUMP). Bacillus anthracis and Bordetella pertussis secrete the adenylyl cyclase (AC) toxins edema factor (EF) and CyaA, respectively, weakening immune responses and facilitating bacterial proliferation. A cell-permeable cCMP analogue inhibits human neutrophil superoxide production. Here, we report that EF and CyaA also possess cytidylyl cyclase (CC) and uridylyl cyclase (UC) activity. CC and UC activity was determined by a radiometric assay, using [alpha-(32)P]CTP and [alpha-(32)P]UTP as substrates, respectively, and by a high-performance liquid chromatography method. The identity of cNMPs was confirmed by mass spectrometry. On the basis of available crystal structures, we developed a model illustrating conversion of CTP to cCMP by bacterial toxins. In conclusion, we have shown both EF and CyaA have a rather broad substrate specificity and exhibit cytidylyl and uridylyl cyclase activity. Both cCMP and cUMP may contribute to toxin actions.

Meropenem Plasma and Interstitial Soft Tissue Concentrations in Obese and Nonobese Patients-A Controlled Clinical Trial.

BACKGROUND: This controlled clinical study aimed to investigate the impact of obesity on plasma and tissue pharmacokinetics of meropenem. METHODS: Obese (body mass index (BMI) ≥ 35 kg/m2) and age-/sex-matched nonobese (18.5 kg/m2 ≥ BMI ≤ 30 kg/m2) surgical patients received a short-term infusion of 1000-mg meropenem. Concentrations were determined via high performance liquid chromatography-ultraviolet (HPLC-UV) in the plasma and microdialysate from the interstitial fluid (ISF) of subcutaneous tissue up to eight h after dosing. An analysis was performed in the plasma and ISF by noncompartmental methods. RESULTS: The maximum plasma concentrations in 15 obese (BMI 49 ± 11 kg/m2) and 15 nonobese (BMI 24 ± 2 kg/m2) patients were 54.0 vs. 63.9 mg/L (95% CI for difference: -18.3 to -3.5). The volume of distribution was 22.4 vs. 17.6 L, (2.6-9.1), but the clearance was comparable (12.5 vs. 11.1 L/h, -1.4 to 3.1), leading to a longer half-life (1.52 vs. 1.31 h, 0.05-0.37) and fairly similar area under the curve (AUC)8h (78.7 vs. 89.2 mg*h/L, -21.4 to 8.6). In the ISF, the maximum concentrations differed significantly (12.6 vs. 18.6 L, -16.8 to -0.8) but not the AUC8h (28.5 vs. 42.0 mg*h/L, -33.9 to 5.4). Time above the MIC (T > MIC) in the plasma and ISF did not differ significantly for MICs of 0.25-8 mg/L. CONCLUSIONS: In morbidly obese patients, meropenem has lower maximum concentrations and higher volumes of distribution. However, due to the slightly longer half-life, obesity has no influence on the T > MIC, so dose adjustments for obesity seem unnecessary.