Optimal dosing of antibiotics in critically ill patients by using continuous/extended infusions: a systematic review and meta-analysis

Introduction

The aim of this study was to determine whether using pharmacodynamic-based dosing of antimicrobials, such as extended/continuous infusions, in critically ill patients is associated with improved outcomes as compared with traditional dosing methods.

Methods

We searched Medline, HealthStar, EMBASE, Cochrane Clinical Trial Registry, and CINAHL from inception to September 2013 without language restrictions for studies comparing the use of extended/continuous infusions with traditional dosing. Two authors independently selected studies, extracted data on methodology and outcomes, and performed quality assessment. Meta-analyses were performed by using random-effects models.

Results

Of 1,319 citations, 13 randomized controlled trials (RCTs) (n = 782 patients) and 13 cohort studies (n = 2,117 patients) met the inclusion criteria. Compared with traditional non-pharmacodynamic-based dosing, RCTs of continuous/extended infusions significantly reduced clinical failure rates (relative risk (RR) 0.68; 95% confidence interval (CI) 0.49 to 0.94, P = 0.02) and intensive care unit length of stay (mean difference, −1.5; 95% CI, −2.8 to −0.2 days, P = 0.02), but not mortality (RR, 0.87; 95% CI, 0.64 to 1.19; P = 0.38). No significant between-trial heterogeneity was found for these analyses (I² = 0). Reduced mortality rates almost achieved statistical significance when the results of all included studies (RCTs and cohort studies) were pooled (RR, 0.83; 95% CI, 0.69 to 1.00; P = 0.054).

Conclusions

Pooled results from small RCTs suggest reduced clinical failure rates and intensive care unit length-of-stay when using continuous/extended infusions of antibiotics in critically ill patients. Reduced mortality rates almost achieved statistical significance when the results of RCTs were combined with cohort studies. These results support the conduct of adequately powered RCTs to define better the utility of continuous/extended infusions in the era of antibiotic resistance.     

Cell-body rocking is a dominant mechanism for flagellar synchronization in a swimming alga

The unicellular green alga Chlamydomonas swims with two flagella that can synchronize their beat. Synchronized beating is required to swim both fast and straight. A long-standing hypothesis proposes that synchronization of flagella results from hydrodynamic coupling, but the details are not understood. Here, we present realistic hydrodynamic computations and high-speed tracking experiments of swimming cells that show how a perturbation from the synchronized state causes rotational motion of the cell body. This rotation feeds back on the flagellar dynamics via hydrodynamic friction forces and rapidly restores the synchronized state in our theory. We calculate that this “cell-body rocking” provides the dominant contribution to synchronization in swimming cells, whereas direct hydrodynamic interactions between the flagella contribute negligibly. We experimentally confirmed the two-way coupling between flagellar beating and cell-body rocking predicted by our theory.Eukaryotic cilia and flagella are long, slender cell appendages that can bend rhythmically and thus present a prime example of a biological oscillator (1). The flagellar beat is driven by the collective action of dynein molecular motors, which are distributed along the length of the flagellum. The beat of flagella, with typical frequencies ranging from 20–60 Hz, pumps fluids, for example, mucus in mammalian airways (2), and propels unicellular microswimmers such as Paramecia, spermatozoa, and algae (3). The coordinated beating of collections of flagella is important for efficient fluid transport (2, 4, 5) and fast swimming (6). This coordinated beating represents a striking example for the synchronization of oscillators, prompting the question of how flagella couple their beat. Identifying the specific mechanism of synchronization can be difficult because synchronization may occur even for weak coupling (7). Further, the effect of the coupling is difficult to detect once the synchronized state has been reached.Hydrodynamic forces were suggested to play a significant role for flagellar synchronization already in 1951 by Taylor (8). Since then, direct hydrodynamic interactions between flagella were studied theoretically as a possible mechanism for flagellar synchronization (9–12). Another synchronization mechanism that is independent of hydrodynamic interactions was recently described in the context of a minimal model swimmer (13–15). This mechanism crucially relies on the interplay of swimming motion and flagellar beating.Here, we address the hydrodynamic coupling between the two flagella in a model organism for flagellar coordination (16–19), the unicellular green alga Chlamydomonas reinhardtii. Chlamydomonas propels its ellipsoidal cell body, which has typical diameter of 10 μm, using a pair of flagella, whose lengths are about 10 μm (16). The two flagella beat approximately in a common plane, which is collinear with the long axis of the cell body. In that plane, the two beat patterns are nearly mirror-symmetric with respect to this long axis. The beating of the two flagella of Chlamydomonas can synchronize, that is, adopt a common beat frequency and a fixed phase relationship (16–19). In-phase synchronization of the two flagella is required for swimming along a straight path (19). The specific mechanism leading to flagellar synchrony is unclear.Here, we use a combination of realistic hydrodynamic computations and high-speed tracking experiments to reveal the nature of the hydrodynamic coupling between the two flagella of free-swimming Chlamydomonas cells. Previous hydrodynamic computations for Chlamydomonas used either resistive force theory (20, 21), which does not account for hydrodynamic interactions between the two flagella, or computationally intensive finite element methods (22). We employ an alternative approach and represent the geometry of a Chlamydomonas cell by spherical shape primitives, which provides a computationally convenient method that fully accounts for hydrodynamic interactions between different parts of the cell. Our theory characterizes flagellar swimming and synchronization by a minimal set of effective degrees of freedom. The corresponding equation of motion follows naturally from the framework of Lagrangian mechanics, which was used previously to describe synchronization in a minimal model swimmer (13, 15). These equations of motion embody the key assumption that the flagellar beat speeds up or slows down according to the hydrodynamic friction forces acting on the flagellum, that is, if there is more friction and therefore higher hydrodynamic load, then the beat will slow down. This assumption is supported by previous experiments that showed that the flagellar beat frequency decreases when the viscosity of the surrounding fluid is increased (23, 24). The simple force–velocity relationship for the flagellar beat employed by us coarse-grains the behavior of thousands of dynein molecular motors that collectively drive the beat. Similar force–velocity properties have been described for individual molecular motors (25) and reflect a typical behavior of active force generating systems.Our theory predicts that any perturbation of synchronized beating results in a significant yawing motion of the cell, reminiscent of rocking of the cell body. This rotational motion imparts different hydrodynamic forces on the two flagella, causing one of them to beat faster and the other to slow down. This interplay between flagellar beating and cell-body rocking rapidly restores flagellar synchrony after a perturbation. Using the framework provided by our theory, we analyze high-speed tracking experiments of swimming cells, confirming the proposed two-way coupling between flagellar beating and cell-body rocking.Previous experiments restrained Chlamydomonas cells from swimming, holding their cell body in a micropipette (17–19). Remarkably, flagellar synchronization was observed also for these constrained cells. This observation seems to argue against a synchronization mechanism that relies on swimming motion. However, the rate of synchronization observed in these experiments was faster by an order of magnitude than the rate we predict for synchronization by direct hydrodynamic interactions between the two flagella in the absence of any motion. In contrast, we show that rotational motion with a small amplitude of a few degrees only, which may result from either a residual rotational compliance of the clamped cell or an elastic anchorage of the flagellar pair, provides a possible mechanism for rapid synchronization, which is analogous to synchronization by cell-body rocking in free-swimming cells.     

Heme impairs the ball-and-chain inactivation of potassium channels

Fine-tuned regulation of K⁺ channel inactivation enables excitable cells to adjust action potential firing. Fast inactivation present in some K⁺ channels is mediated by the distal N-terminal structure (ball) occluding the ion permeation pathway. Here we show that Kv1.4 K⁺ channels are potently regulated by intracellular free heme; heme binds to the N-terminal inactivation domain and thereby impairs the inactivation process, thus enhancing the K⁺ current with an apparent EC₅₀ value of ∼20 nM. Functional studies on channel mutants and structural investigations on recombinant inactivation ball domain peptides encompassing the first 61 residues of Kv1.4 revealed a heme-responsive binding motif involving Cys13:His16 and a secondary histidine at position 35. Heme binding to the N-terminal inactivation domain induces a conformational constraint that prevents it from reaching its receptor site at the vestibule of the channel pore.A-type K⁺ channels, a family of voltage-gated K⁺ (Kv) channels, play a vital role in the control of neuronal excitability, regulation of presynaptic spike duration, Ca²⁺ entry, and neurotransmitter release (1). One of the prominent features of A-type K⁺ channels is their inactivation, which is mediated by two structurally distinct processes (2, 3). The fast inactivation is initiated by the N-terminal protein structure, thereby termed N-type inactivation, whereas the slow C-type inactivation is related to the pore structure (2, 3). N-type inactivation proceeds according to a “ball-and-chain” mechanism; the positive charges of the N-terminal ball domains bring the structures to the pore domain of the channel and the distal segment of one of the four intrinsically disordered N-terminal ball domains enters the hydrophobic central cavity/vestibule of the inner pore of the channel thus obstructing the flow of K⁺ (2–5).Acute enzymatic or mutational removal of the distal N terminus eliminates N-type inactivation, and in such inactivation-removed channels, intracellular application of peptides corresponding to the N-terminal sequence restores inactivation (4, 6, 7). Structural analysis suggests that the N-terminal inactivation structure needs to be flexible or even intrinsically disordered to reach the receptor in the channel’s cavity (8, 9).“Tuning” of rapid N-type inactivation is an effective way of adapting cells to specific needs. For example, molecular processes affecting the speed and degree of N-type inactivation in Kv1.4 (KCNA4) channels include redox regulation of a cysteine residue in the N-terminal ball structure (C13) (10), protonation of histidine at position 16 (11), interaction with membrane lipids (12), and Ca²⁺-dependent phosphorylation (13). Furthermore, low-molecular-weight compounds affecting N-type inactivation (N-type disinactivators) have been discussed as potential drugs regulating cellular excitability (14).Heme [Fe(II) protoporphyrin-IX] is well known as a protein cofactor, often conferring gas sensitivity as exemplified in hemoglobin, cytochromes, myoglobin, and soluble guanylyl cyclase. In many heme proteins including soluble guanylyl cyclase, heme is bound or coordinated in part by an amino acid sequence typically containing a histidine or cysteine residue, which acts as an axial fifth ligand (in addition to the four bonds provided by the nitrogen atoms of the protoporphyrin-IX ring to the iron center) to the redox-sensitive iron center, and water or a bound gas molecule acts as the sixth ligand (15). However, recent advances revealed a novel role of heme as a nongenomic modulator of ion channel functions, first exemplified for the large-conductance voltage- and Ca²⁺-dependent K⁺ channel (Slo1 BK) (16) and later for the epithelial Na⁺ channel (17). Detailed analysis of the biophysical action of heme [ferrous iron (Fe²⁺)] or hemin [ferric iron (Fe³⁺)] on the Slo1 BK channel demonstrated that hemin is a potent modulator of the allosteric gating mechanism of the channel (18), and mutagenesis studies have indicated the sequence CKACH located in the cytoplasmic C terminus of the channel plays a critical role (16, 19). However, neither for Slo1 BK channels nor for epithelial Na⁺ channels, the interaction of heme with the ion channel protein is structurally resolved. In this study, we found that the fast N-type inactivation of Kv1.4 A-type K⁺ channels is potently modulated by heme/hemin. Furthermore, we provide structural insight into heme interaction with a channel explaining how heme prevents A-type channels from entering an inactivated state.     

Poor Glycemic Control Is Related to Increased Nitric Oxide Activity Within the Renal Circulation of Patients With Type 2 Diabetes

OBJECTIVE

Experimental studies have shown that glucose releases endothelial nitric oxide (NO) and that NO contributes to renal hyperperfusion in models of diabetes. To examine whether this translates into the human condition, we studied the relationship between glycemic control and renal NO activity in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 113 patients with type 2 diabetes and a wide range of HbA_1c concentrations were included. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were determined by constant infusion input clearance. Functional NO activity in the renal circulation was determined as change of RPF to infusion of the NO synthase (NOS) inhibitor N(G)-monomethyl-l-arginine (l-NMMA) (4.25 mg/kg). As additional markers, we measured urinary excretion of NO (UNOx) and l-arginine–to–asymmetrical dimethylarginine (ADMA) ratio in plasma.

RESULTS

Subjects within the highest tertile of HbA_1c concentration had increased RPF (low, medium, and high tertiles 576 ± 17 vs. 585 ± 22 vs. 627 ± 33 mL/min/m², P = 0.05 by one-way ANOVA), while GFR was similar across tertiles. The response of RPF to NOS blockade was augmented in subjects with higher HbA_1c levels (−55 ± 7 vs. −64 ± 8 vs. −86 ± 8 mL/min, P = 0.04 by one-way ANOVA). Further, l-arginine–to–ADMA ratio and UNOx were increased in subjects with higher HbA_1c levels.

CONCLUSIONS

In line with experimental evidence, we could demonstrate in humans that poor glycemic control is related to higher NO activity and hyperperfusion of the kidney. The renal NO system may thus be a novel therapeutic target for improving renal hemodynamics in patients with diabetes.The incidence of end-stage renal disease owing to diabetic nephropathy is increasing in developed countries (1). In order to reduce the burden of end-stage diabetic kidney disease, targeting glomerular hyperfiltration and hyperperfusion, early hemodynamic abnormalities that have been linked with greater risk of developing albuminuria and loss of renal function over time (2,3), may be an attractive therapeutic option.Others and we have shown that nitric oxide (NO) is an important regulator of renal hemodynamics in humans (4–6). Experimental studies have demonstrated that increased production of NO in the kidney contributes to the renal hemodynamic alterations in models of type 1 and type 2 diabetes (7–12). As a pathogenetic factor, hyperglycemia has been shown to stimulate acute release of NO from cultured endothelial cells (13,14), including endothelial cells derived from the glomerulum (15).In human subjects with diabetes, data on the role of NO for renal hemodynamics are very limited. A few studies are available that have assessed NO production with a biochemical approach. Hiragushi et al. showed that in subjects with type 2 diabetes, urinary NO (UNOx) excretion rates were higher in those with increased glomerular filtration rate (GFR) versus those with normal GFR (16). Additional studies suggested that it is the hyperglycemia that drives increased NO production associated with glomerular hyperfiltration (17,18).Using a much more direct way of assessing the functional contribution of NO to renal hemodynamics, Cherney et al. (19) studied the renal response to pharmacological NO synthase (NOS) inhibition in subjects with type 1 diabetes without complications. NOS inhibition led to a significantly greater decline of GFR and renal plasma flow (RPF) in hyperfiltering versus the normofiltering subjects with type 1 diabetes.The role of NO in renal hemodynamics of subjects with type 2 diabetes, a more heterogenous group of subjects with regard to concomitant diseases and vascular risk factors, and the influence of glycemic control have not been studied. To this end, we examined renal hemodynamic responses to pharmacological NOS inhibition across a wide range of HbA_1c levels in a large cohort of subjects with type 2 diabetes.     

Das longitudinale Modul Schmerzmedizin (LoMoS)

Background

Pain medicine as an interdisciplinary, multifaceted field has not yet been assigned the status of a separate medical subject in the curriculum of medical schools in Germany. Pain medicine is often taught by anesthesiologists, neurologists, orthopedic or neurological surgeons either by assignment by the Dean’s office or because of their own enthusiasm. In the near future pain medicine as an interdisciplinary course will be mandatory in undergraduate medical education. The authors were interested to investigate the needs and demands of both students and instructors from theoretical and clinical fields in order to develop a longitudinal pain medicine curriculum.

Methods

Based on Kern’s curriculum development model, the opinions of students and instructors were investigated: quantitative items were analyzed using Student’s t-test for independent variables and heterogenic variance and the content of free text answers was analyzed by forming subsets of similar or identical answers. A concise curriculum was developed.

Results

Students from advanced classes noted a bigger discrepancy between the needs formulated and what was actually offered as compared to younger students. Instructors from different theoretical and clinical specialties were unaware of the topics of colleagues from other departments. The analysis of written answers revealed a different understanding of the term pain medicine.

Conclusion

At the Hannover Medical School, a standardized needs assessment helped to develop LoMoS, the longitudinal pain medicine curriculum, which may also serve as a model for other medical faculties. Students required more practical instruction and teachers were interested in improving networking and discussion among specialists.     

The effect of a subretinal injection of Toxoplasma gondii on the serum antibody titer in a rabbit model of ocular toxoplasmosis

A single subretinal injection of RH toxoplasma initiated an experimental toxoplasmosis of the eyes in big chinchilla rabbits. This animal model was used to study the development of the serum IgG level against toxoplasma. As a rule, the specific antibody level rose between the 9th and the 20th day following injection. At that time, the peak of inflammation had already been exceeded. An influence of cyclophosphamide0 or complete Freund's adjuvant on the humoral immune response of the animals to toxoplasma could not be detected. An attempt is made to interpret the findings deviating from the toxoplasmosis of the human eye.     

Amifostine is a Potent Radioprotector of Salivary Glands in Radioiodine Therapy Structural and Ultrastructural Findings*

Background and Purpose:   

Salivary gland impairment following high-dose radioiodine treatment is well recognized. Since differentiated thyroid cancer has a good prognosis, reduction of long-term side effects is important. This study investigates the radioprotective effects of amifostine in salivary glands of rabbits receiving high-dose radioiodine therapy so as to obtain deeper insight in changes on the cellular and ultrastructural level.     

Bronchial and vascular effects of Paf in the rat isolated lung are completely blocked by WEB 2086, a novel specific Paf antagonist.

1 The effect of the platelet-activating factor (Paf) antagonist, WEB 2086, on Paf-induced increase of pulmonary artery perfusion pressure (Pp), bronchial inflation pressure (Pi) and wet-to-dry lung weight ratios (W/D) was investigated in the rat isolated lung. 2 Lungs were perfused with Krebs-Ringer solution (KRS) as controls or with KRS containing WEB 2086 (0.1, 1.0, 10.0 or 100 micrograms ml-1) and then injected with a bolus of 20 micrograms Paf. 3 A dose-related inhibition of the Paf-induced increase of Pp, Pi and W/D was observed, being almost maximal for the 10.0 micrograms ml-1 and complete for the 100 micrograms ml-1 doses of WEB 2086 when compared to controls. 4 It is concluded that WEB 2086 is a highly effective and specific Paf antagonist in the pulmonary vasculature and bronchial tract.