Variable pharmacokinetics of extended interval tobramycin or gentamicin among critically ill patients undergoing continuous venovenous hemofiltration.

BACKGROUND/AIMS: Aminoglycosides are a major weapon against serious Gram-negative rod infections, yet aminoglycoside usage is limited by the risk of nephrotoxicity. The risk of toxicity is reduced by extended-interval dosing of aminoglycosides, defined as 5 - 7 mg/kg given intravenously in intervals of 24 hours or greater based on serum drug concentrations. In critically ill patients undergoing continuous venovenous hemofiltration, there are few published reports of the pharmacokinetics of extended-interval dosing of aminoglycosides. METHODS: We evaluated the pharmacokinetics of extended-interval dosing of gentamicin and tobramycin in 9 critically ill patients on continuous venovenous hemofiltration at Dartmouth-Hitchcock Medical Center between April 2007 and September 2011. RESULTS: Aminoglycoside elimination half-life values were highly variable (median 7 hours, range 3 - 26 hours) and did not correlate with total body weight or estimated creatinine clearance derived from the dose of continuous venovenous hemofiltration. Five of 9 patients cleared infection, but only 4 patients survived to hospital discharge, 2 of whom were dialysis-dependent. CONCLUSION: Extended interval aminoglycoside dosing during continuous venovenous hemofiltration yields unpredictable half-lives and drug levels among high-risk critically ill patients. Close monitoring of serum aminoglycoside levels is required.

Global analysis of IL-2 target genes: identification of chromosomal clusters of expressed genes.

T lymphocytes play a central role in controlling adaptive immune responses. IL-2 critically regulates both T cell growth and death and is involved in maintaining peripheral tolerance, but the molecules involved in these and other IL-2 actions are only partially known. We now provide a comprehensive compendium of the genes expressed in T cells and of those regulated by IL-2 based on a combination of DNA microarrays and serial analysis of gene expression (SAGE). The newly identified IL-2 target genes include many genes previously linked to apoptosis in other cellular systems that may contribute to IL-2-dependent survival functions. We also studied the mRNA expression of known regulators of signaling pathways for their induction in response to IL-2 in order to identify potential novel positive and/or negative feedback regulators of IL-2 signaling. We show that IL-2 regulates only a limited number of these genes. These include suppressors of cytokine signaling (SOCS) 1, SOCS2, dual-specificity phosphatase (DUSP) 5, DUSP6 and non-receptor type phosphatase-7 (PTPN7). Additionally, we provide evidence that many genes expressed in T cells locate in chromosomal clusters, and that select IL-2-regulated genes are located in at least two clusters, one at 5q31, a known cytokine gene cluster, and the other at 6p21.3, a region that contains genes encoding the tumor necrosis factor (TNF) superfamily members TNF, LT-alpha and LT-beta.

Analysis of gamma c-family cytokine target genes. Identification of dual-specificity phosphatase 5 (DUSP5) as a regulator of mitogen-activated protein kinase activity in interleukin-2 signaling.

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on their sharing the common cytokine receptor gamma chain, gamma(c), which is mutated in X-linked severe combined immunodeficiency (SCID). As a step toward further elucidating the mechanism of action of these cytokines in T-cell biology, we compared the gene expression profiles of IL-2, IL-4, IL-7, and IL-15 in T cells using cDNA microarrays. IL-2, IL-7, and IL-15 each induced a highly similar set of genes, whereas IL-4 induced distinct genes correlating with differential STAT protein activation by this cytokine. One gene induced by IL-2, IL-7, and IL-15 but not IL-4 was dual-specificity phosphatase 5 (DUSP5). In IL-2-dependent CTLL-2 cells, we show that IL-2-induced ERK-1/2 activity was inhibited by wild type DUSP5 but markedly increased by an inactive form of DUSP5, suggesting a negative feedback role for DUSP5 in IL-2 signaling. Our findings provide insights into the shared versus distinctive actions by different members of the gamma(c) family of cytokines. Moreover, we have identified a DUSP5-dependent negative regulatory pathway for MAPK activity in T cells.