Antibiotic dosing in the 'at risk' critically ill patient: Linking pathophysiology with pharmacokinetics/pharmacodynamics in sepsis and trauma patients

Background

Critical illness, mediated by trauma or sepsis, can lead to physiological changes that alter the pharmacokinetics of antibiotics and may result in sub-therapeutic concentrations at the sites of infection. The first aim of this project is to identify the clinical characteristics of critically ill patients with significant trauma that have been recently admitted to ICU that may predict the dosing requirements for the antibiotic, cefazolin. The second aim of this is to identify the clinical characteristics of critically ill patients with sepsis that may predict the dosing requirements for the combination antibiotic, piperacillin-tazobactam.

Methods/Design

This is an observational pharmacokinetic study of patients with trauma (cefazolin) or with sepsis (piperacillin-tazobactam). Participants will have samples from blood and urine, collected at different intervals. Patients will also have a microdialysis catheter inserted into subcutaneous tissue to measure interstitial fluid penetration of the antibiotic. Participants will be administered sinistrin, indocyanine green and sodium bromide as well as have cardiac output monitoring performed and tetrapolar bioimpedance to determine physiological changes resulting from pathology. Analysis of samples will be performed using validated liquid chromatography tandem mass-spectrometry. Pharmacokinetic analysis will be performed using non-linear mixed effects modeling to determine individual and population pharmacokinetic parameters of antibiotics.

Discussion

The study will describe cefazolin and piperacillin-tazobactam concentrations in plasma and the interstitial fluid of tissues in trauma and sepsis patients respectively. The results of this study will guide clinicians to effectively dose these antibiotics in order to maximize the concentration of antibiotics in the interstitial fluid of tissues.     

Wheat germ phosphoglycerate mutase: evidence for a metalloenzyme

Wheat germ phosphoglycerate mutase, exposed to 3.4 M guanidinium chloride at 22 degrees C and pH 7.8, slowly undergoes time-dependent inactivation which can be fully reversed by adding excess Co2+ or Mn2+ to a 50-fold dilution of the denaturing medium. Titration of the denatured enzyme with either Co2+ or Mn2+ shows that wheat germ mutase preferentially binds Co2+. Assuming 1:1 complexation between metal atom and protein, the apparent dissociation constants (Kd) for E Co2+ and E Mn2+ at 22 degrees C and pH 8.7 are approximately 1.06 and 1.84, respectively. Other metal atoms (e.g., Cr2+, Cu2+, Fe2+, Fe3+, Mg2+, and Ni2+) have no effect in restoring the apoenzyme's catalytic activity. At low concentrations (0.11-0.23 mM) Zn2+ partially restores activity, but promotes protein precipitation at elevated concentrations. Evidence suggests that all bisphosphoglycerate-independent phosphoglycerate mutases require either an intra- or an extramolecular metal atom in order to function. Attempts to characterize wheat germ mutase as a glycoprotein have yielded negative results.     

Single-amino-acid deletion in the RYR1 gene, associated with malignant hyperthermia susceptibility and unusual contraction phenotype

Malignant hyperthermia (MH) is an anesthetic-drug-induced, life-threatening hypermetabolic syndrome caused by abnormal calcium regulation in skeletal muscle. Often inherited as an autosomal dominant trait, MH has linkage to 30 different mutations in the RYR1 gene, which encodes a calcium-release-channel protein found in the sarcoplasmic reticulum membrane in skeletal muscle. All published RYR1 mutations exclusively represent single-nucleotide changes. The present report documents, in exon 44 of RYR1 in two unrelated, MH-susceptible families, a 3-bp deletion that results in deletion of a conserved glutamic acid at position 2347. This is the first deletion, in RYR1, found to be associated with MH susceptibility. MH susceptibility was confirmed among some family members by in vitro diagnostic pharmacological contracture testing of biopsied skeletal muscle. Although a single-amino-acid deletion appears to be a subtle change in the protein, the deletion of Glu2347 from RYR1 produces an unusually large electrically evoked contraction tension in MH-positive individuals, suggesting that this deletion produces an alteration in skeletal-muscle calcium regulation, even in the absence of pharmacological agents.     

Effect of temperature on seed production in the invasive grass Glyceria maxima (Hartm.) Holmb. (Poaceae) in South Africa

Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in KwaZulu-Natal failed to yield a single seed, only empty panicles. Laboratory experiments showed that vernalisation had no consistent effect on seed production. Field- and laboratory-grown plants produced seeds in the 2010/2011 season, because of having sufficient time at optimum temperatures required for seed production (1 491 and 1 585 hours, respectively), compared to a shorter period (1 352 hours) of suitable temperatures during the 2009/2010 growing season. An inadequate period of optimum temperatures (15–25°C) during seed production resulted in the lack of seeds in the field in the 2009/2010 growing season. This study showed that temperature and duration of exposure thereto during the seed-production period play vital roles in G. maxima sexual reproduction.