Optimisation of antibiotic therapy in cystic fibrosis patients. Pharmacokinetic considerations

Antibiotic therapy plays a central role in the medical management of patients with cystic fibrosis. While totally convincing efficacy data are lacking, antibiotics probably have a pronounced beneficial effect on both morbidity and mortality. Much has been learned in the past 20 years about antibiotic use in this population. At the same time, new antimicrobial agents with the potential to treat this condition have become available for use. The pharmacokinetics of a number of antibiotic classes, including beta-lactams, aminoglycosides and quinolones, are altered in this patient population. Increased total body clearance is a common occurrence but is not always changed enough to warrant altered dosages. Nonetheless, in light of altered pharmacokinetics in the cystic fibrosis population, appropriate dosage and monitoring parameters for a number of antibiotics have been determined.     

Cement versus cementless fixation in total knee arthroplasty

A prospectively studied group of 55 uncemented Press Fit Condylar total knee arthroplasties was compared retrospectively with a matched group of 51 cemented Press Fit Condylar total knee arthroplasties at a mean of 10 years after operation. For the cemented group, the pain and function scores improved from 32 and 45 preoperatively to 95 and 77, respectively. For the uncemented group the scores improved from 33 and 50 preoperatively to 93 and 60, respectively. There were 10 revisions in the uncemented group for femoral or tibial aseptic loosening or osteolysis compared with two revisions in the cemented group. Exclusive of problems related to patellar metal backing, survival to revision for aseptic failure or radiographic loosening was 72% in the uncemented group and 94% in the cemented group at 10 years. A significantly higher revision rate was found in the uncemented compared with cemented total knee arthroplasty of the Press Fit Condylar design.     

A cholera toxin-sensitive guanyl nucleotide binding protein mediates the movement of pituitary luteinizing hormone into a releasable pool: loss of this event is associated with the onset of homologous desensitization to gonadotropin-releasing hormone

Cholera toxin (CTX; 5 micrograms/ml), but not pertussis toxin (100 ng/ml), when preincubated with pituitary cells for 18 h, enhances the percentage of cellular LH released in response to continuous or pulsatile administration of 5 x 10(-9) M GnRH. This effect occurs without increasing total (intracellular plus extracellular) LH, indicating that it is best explained by redistribution of LH from a nonreleasable to a releasable pool. This site of action is consistent with the observation that CTX-pretreated cells are also sensitized to stimulation of LH release by the Ca2+ ionophore A23187. The observations that CTX stimulates the production of cAMP in these cells and that the sensitizing action of CTX is mimicked by (Bu)2cAMP (1 mM) are consistent with the view that a CTX-stimulated guanyl nucleotide binding protein, capable of activating adenylyl cyclase, is mediating this sensitization. We used a perifused cell system to show that the movement of LH into a releasable pool is lost with the onset of homologous desensitization due to high pulse frequency or constant administration of GnRH (5 x 10(-9) M, continuous or a pulse each 15 min). Sensitization to CTX is restored by stimulation with a high concentration of GnRH (10(-6) M) or by resetting the pulse frequency to the rate measured in vivo (a pulse each 90 min). Both of these treatments also circumvent the desensitized state, restoring LH release. These results identify a novel lesion associated with the development of desensitization in the gonadotrope and support the role of a CTX-sensitive guanyl nucleotide binding protein in regulation of pituitary responsiveness to GnRH.     

Effects of fibinolysis on neurite growth from dorsal root ganglia cultured in two- and three-dimensional fibrin gels

The mechanism of neurite penetration of three-dimensional fibrin matrices was investigated by culturing embryonic chick dorsal root ganglia (DRGs) within fibrin gels, upon fibrin gels, and upon laminin. The length of neurites within three-dimensional matrices of fibrin was decreased in a concentration-dependent manner by agents that inhibited plasmin, e.g. aprotinin, or that inhibited plasminogen activation, e.g., epsilon-aminocaproic acid (EACA), or plasminogen antiserum. In contrast, such agents increased the length of neurites growing out from DRGs cultured upon two-dimensional substrates of fibrin and had no effect on the length of neurites growing out from DRGs cultured upon laminin. Visualization of neurites within three-dimensional fibrin matrices demonstrated that the distance between fibrin strands was much smaller than the diameter of neurites. All these data were consistent with the hypothesis that fibrinolysis localized to the region of the neurite tip is an important mechanism for neurite penetration of a physical barrier of fibrin strands arranged in a three-dimensional matrix.