Quantification of amikacin in bronchial epithelial lining fluid in neonates.

Amikacin efficacy is based on peak concentrations and the possibility of reaching therapeutic levels at the infection site. This study aimed to describe amikacin concentrations in the epithelial lining fluid (ELF) through bronchoalveolar lavage (BAL) in newborns. BAL fluid was collected in ventilated neonates treated with intravenous (i.v.) amikacin. Clinical characteristics, amikacin therapeutic drug monitoring serum concentrations, and the concentrations of urea in plasma were extracted from the individual patient files. Amikacin and urea BAL fluid concentrations were determined using liquid chromatography with pulsed electrochemical detection (LC-PED) and capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D), respectively. ELF amikacin concentrations were converted from BAL fluid concentrations through quantification of dilution (urea in plasma/urea in BAL fluid) during the BAL procedure. Twenty-two observations in 17 neonates (postmenstrual age, 31.9 [range, 25.1 to 41] weeks; postnatal age, 3.5 [range, 2 to 37] days) were collected. Median trough and peak amikacin serum concentrations were 2.1 (range, 1 to 7.1) mg/liter and 39.1 (range, 24.1 to 73.2) mg/liter; the median urea plasma concentration was 30 (8 to 90) mg/dl. The median amikacin concentration in ELF was 6.5 mg/liter, the minimum measured concentration was 1.5 mg/liter, and the maximum (peak) was 23 mg/liter. The highest measured ELF concentration was reached between 6 and 14.5 h after i.v. amikacin administration, and an estimated terminal elimination half-life was 8 to 10 h. The median and highest (peak) ELF amikacin concentrations observed in our study population were, respectively, 6.5 and 23 mg/liter. Despite the frequent use of amikacin in neonatal (pulmonary) infections, this is the first report of amikacin quantification in ELF in newborns.

Synthetic inhibitors of the processing of pretransfer RNA by the ribonuclease P ribozyme: enzyme inhibitors which act by binding to substrate.

2,2'-p-Phenylene bis[6-(4-methyl-1-piperazinyl)]benzimidazole, 2,2'-bis(3,5-dihydroxyphenyl)-6,6'-bis benzimidazole, and 2,2'-bis(4-hydroxyphenyl)-6,6'-bis benzimidazole are shown by UV-visible and fluorescence spectrophotometry to be strong ligands for tRNA, giving simple, hyperbolic binding isotherms with apparent dissociation constants in the micromolar range. Hydroxyl radical footprinting indicates that they may bind in the D and T loops. On the basis of this tRNA recognition as a rationale, they were tested as inhibitors of the processing of precursor tRNAs by the RNA subunit of Escherichia coli RNase P (M1 RNA). Preliminary studies show that inhibition of the processing of Drosophila tRNA precursor molecules by phosphodiester bond cleavage, releasing the extraneous 5'-portion of RNA and the mature tRNA molecule, was dependent on both the structure of the inhibitor and the structure of the particular tRNA precursor substrate for tRNA(Ala), tRNA(Val), and tRNA(His). In more detailed followup using the tRNA(His) precursor as the substrate, experiments to determine the concentration dependence of the reaction showed that inhibition took time to reach its maximum extent. I(50) values (concentrations for 50% inhibition) were between 5.3 and 20.8 microM, making these compounds among the strongest known inhibitors of this ribozyme, and the first inhibitors of it not based on natural products. These compounds effect their inhibition by binding to the substrate of the enzyme reaction, making them examples of an unusual class of enzyme inhibitors. They provide novel, small-molecule, inhibitor frameworks for this endoribonuclease ribozyme.