Arnold L. Smith

Effect of aerosolized recombinant human DNase on exacerbations of respiratory symptoms and on pulmonary function in patients with cystic fibrosis

BACKGROUND Respiratory disease in patients with cystic fibrosis is characterized by airway obstruction caused by the accumulation of thick, purulent secretions, which results in recurrent, symptomatic exacerbations. The viscoelasticity of the secretions can be reduced in vitro by recombinant human deoxyribonuclease I (rhDNase), a bioengineered copy of the human enzyme. METHODS We performed a randomized, double-blind, placebo-controlled study to determine the effects of once-daily and twice-daily administration of rhDNase on exacerbations of respiratory symptoms requiring parenteral antibiotics and on pulmonary function. A total of 968 adults and children with cystic fibrosis were treated for 24 weeks as outpatients. RESULTS One or more exacerbations occurred in 27 percent of the patients given placebo, 22 percent of those treated with rhDNase once daily, and 19 percent of those treated with rhDNase twice daily. As compared with placebo, the administration of rhDNase once daily and twice daily reduced the age-adjusted risk of respiratory exacerbations by 28 percent (P = 0.04) and 37 percent (P < 0.01), respectively. The administration of rhDNase once daily and twice daily improved forced expiratory volume in one second during the study by a mean (+/- SD) of 5.8 +/- 0.7 and 5.6 +/- 0.7 percent, respectively. None of the patients had anaphylaxis. Voice alteration and laryngitis were more frequent in the rhDNase-treated patients than in those receiving placebo but were rarely severe and resolved within 21 days of onset. CONCLUSIONS In patients with cystic fibrosis, the administration of rhDNase reduced but did not eliminate exacerbations of respiratory symptoms, resulted in slight improvement in pulmonary function, and was well tolerated.

Longitudinal Assessment of Pseudomonas aeruginosa in Young Children with Cystic Fibrosis

Pseudomonas aeruginosa lung infection is an important cause of morbidity and mortality in cystic fibrosis (CF). Longitudinal assessment of the phenotypic changes in P. aeruginosa isolated from young children with CF is lacking. This study investigated genotypic and phenotypic changes in P. aeruginosa from oropharynx (OP) and bronchoalveolar lavage fluid (BALF) in a cohort of 40 CF patients during the first 3 years of life; antibody response was also examined. A high degree of genotypic variability was identified, and each patient had unique genotypes. Early isolates had a phenotype distinct from those of usual CF isolates: generally nonmucoid and antibiotic susceptible. Genotype and phenotype correlated between OP and BALF isolates. As determined by culture, 72.5% of patients demonstrated P. aeruginosa during their first 3 years. On the basis of combined culture and serologic results, 97.5% of patients had evidence of infection by age 3 years, which suggests that P. aeruginosa infection occurs early in CF and may be intermittent or undetectable by culture.

Effect of Chronic Intermittent Administration of Inhaled Tobramycin on Respiratory Microbial Flora in Patients with Cystic Fibrosis

Pseudomonas aeruginosa endobronchial infection causes significant morbidity and mortality among cystic fibrosis patients. Microbiology results from two multicenter, double-blind, placebo-controlled trials of inhaled tobramycin in cystic fibrosis were monitored for longitudinal changes in sputum microbial flora, antibiotic susceptibility, and selection of P. aeruginosa isolates with decreased tobramycin susceptibility. Clinical response was examined to determine whether current susceptibility standards are applicable to aerosolized administration. Treatment with inhaled tobramycin did not increase isolation of Burkholderia cepacia, Stenotrophomonas maltophilia, or Alcaligenes xylosoxidans; however, isolation of Candida albicans and Aspergillus species did increase. Although P. aeruginosa tobramycin susceptibility decreased in the tobramycin group compared with that in the placebo group, there was no evidence of selection for the most resistant isolates to become most prevalent. The definition of resistance for parenteral administration does not apply to inhaled tobramycin: too few patients had P. aeruginosa with a tobramycin MIC >/=16 microgram/mL to define a new break point on the basis of clinical response.

Characterization of non-beta-lactamase-mediated ampicillin resistance in Haemophilus influenzae.

Ampicillin resistance in Haemophilus influenzae is most often due to the plasmid-mediated production of TEM beta-lactamase. We studied four strains with high-level ampicillin resistance (MIC of 32 micrograms/ml with an inoculum of 10(5) CFU on solid media) which did not produce detectable beta-lactamase activity with two different detection methods. Two of the four strains contained extrachromosomal DNA by agarose gel electrophoresis. Conjugation failed to transfer ampicillin resistance; in contrast, transformation yielded ampicillin-resistant transformants in three of the four strains. These transformants did not contain detectable extrachromosomal DNA. In addition, mobilization of the resistance determinant by transformation to, or conjugation with, recombination-deficient strains was unsuccessful. DNA-DNA hybridization experiments revealed no homology of the DNA of these strains with two R plasmids (one coding for ampicillin resistance, the other for chloramphenicol and tetracycline resistance). We conclude that the genetic basis of the non-beta-lactamase ampicillin resistance in these strains appears to be chromosomally mediated. We investigated the mechanism of resistance in these strains. Enzymatic modification of penicillin was not detected by autoradiography of a thin-layer chromatogram of cell sonic extracts of three ampicillin-resistant transformant strains incubated with [14C]penicillin. To assess changes in permeability of the cell envelope, a plasmid coding for beta-lactamase was conjugated into these strains, and the hydrolysis of penicillin by intact cells and cell sonic extracts was compared. Only one of three transformant strains had significantly diminished permeability. Outer membrane proteins of these strains analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed apparent differences in comparison with the isogenic ampicillin-susceptible recipient strain. Autofluorography of a sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Sarkosyl-solubilized crude membrane (the putative inner membranes) from these ampicillin-resistant transformant strains incubated with [3H]penicillin compared with the isogenic ampicillin-susceptible recipient strain revealed reduced binding to PBP 3 and 6, 3 and 4, or 4. In addition, affinity binding studies revealed decreased affinity of PBP 4 for ampicillin of all four transformants tested. We conclude that the major mechanism of resistance in these strains is altered penicillin-binding proteins; however, other mechanisms, including permeability, may also play a role. Images

In vitro antibacterial activity of fluorinated analogs of chloramphenicol and thiamphenicol.

We evaluated the in vitro antimicrobial activity of Sch 24893, Sch 25298, and Sch 25393, three novel analogs of chloramphenicol and thiamphenicol. All of the analogs had minimal inhibitory concentrations of less than or equal to 10 micrograms/ml for 18 chloramphenicol-thiamphenicol-resistant strains of Shigella dysenteriae and 21 strains of resistant Salmonella typhi. The analogs were also more active than were chloramphenicol and thiamphenicol against chloramphenicol-resistant enteric bacteria, including six strains of Escherichia coli, seven strains of Klebsiella pneumoniae, and two strains of Enterobacter cloacae. Fifty-three strains of ampicillin-resistant Haemophilus influenzae were uniformly susceptible to chloramphenicol, thiamphenicol, and the three analogs. Sch 25298 was the most active compound tested (minimal inhibitory concentration, 0.5 microgram/ml for all strains). Four of seven chloramphenicol-thiamphenicol-resistant Haemophilus strains were susceptible to the fluorinated analogs. Of the three Haemophilus strains which were resistant to chloramphenicol, thiamphenicol, and the analogs, two contained less than 10% of the chloramphenicol acetyltransferase activity of the strains which were resistant to only chloramphenicol and thiamphenicol. We conclude that fluorinated analogs of chloramphenicol and thiamphenicol have considerable in vitro activity against a broad spectrum of chloramphenicol-thiamphenicol-resistant, gram-negative bacteria.

Pharmacokinetics of ciprofloxacin in cystic fibrosis.

We studied the pharmacokinetics of ciprofloxacin in 12 adult males with and 12 adult males without cystic fibrosis (CF). In a randomized crossover sequence, the subjects received 200 mg intravenously or 750 mg orally. With intravenous dosing, subjects also received 651 mg of iothalamate, a marker of glomerular filtration, and 700 mg of antipyrine, an indicator of hepatic oxidative drug metabolism. Pharmacokinetic parameters were determined by model independent methods. In the CF subjects, the ciprofloxacin concentration in serum during the first hour after intravenous administration was higher, and the oral absorption rate was slower. Other parameters did not differ between the groups. Mean concentrations in serum 5 min postinfusion were 3.08 and 2.14 micrograms/ml, and mean peak concentrations after oral dosing were 3.24 and 3.34 micrograms/ml in subjects with and without CF, respectively. Mean values for elimination half-life in all subjects were 4.8 and 5.0 h after intravenous and oral administration, respectively. The mean renal clearances in all subjects after intravenous and oral administration were 19.4 and 14.5 liters/h and accounted for 64 and 47% of the total clearance, respectively. These values were significantly greater than renal iothalamate clearance, indicating that tubular secretion contributed to the renal clearance of ciprofloxacin. A total of 69 and 35.4% of the administered ciprofloxacin was recovered from the urine within 48 h after intravenous and oral administration, respectively. The mean bioavailability was 71.2% and did not differ between the groups. We conclude that similar dosing regimens can be used to treat patients with CF and their normal counterparts.

Pathogenesis of Haemophilus influenzae meningitis.

The hypoxia induced by decreased cerebrocortical blood flow contributes to the neurologic deficits found in many survivors of Hib meningitis. Because reduced blood flow is measurable within 48 hours of acquisition of bacteria, the inability of antibiotic therapy to prevent sequelae is more easily understood insofar as damage has already occurred by the time treatment is initiated. Hydrocephalus is probably due to severe choroid plexus necrosis with aqueductal occlusion. These deficiencies, along with the neuronopathy, contribute to permanent cerebrocortical deficits, including impaired learning ability.

Pharmacokinetics of three oral formulations of ciprofloxacin.

We compared the absorption of three formulations of ciprofloxacin after oral administration in 18 normal adult male volunteers. Each subject received 500 mg of ciprofloxacin as two 250-mg tablets, one 500-mg tablet, or a solution in a randomized crossover sequence. Pharmacokinetic parameters were determined by model independent methods. Because a solution is considered to be the ideal oral dosage form, the results determined for the tablets were compared to those for the solution. Mean values for the maximum concentration of drug in serum, the time to maximum concentration of drug in serum, and the elimination half-life were 3.23 micrograms/ml, 1.00 h, and 5.04 h, respectively, for the solution. The mean renal clearance of ciprofloxacin was 372 ml/min and accounted for at least 50% of the total clearance. We recovered 44.4, 48.6, and 55.8% of the administered ciprofloxacin from the urine as unchanged drug within 24 h after dosing with the 250-mg tablets, 500-mg tablets, or solution, respectively. The 500-mg tablets were found to be bioequivalent to the solution with regard to all pharmacokinetic parameters. The 250-mg tablet was not bioequivalent to either of the other formulations; the relative bioavailability values were 78.7 and 74.1%, respectively, for the 500-mg tablet and the solution. The clinical significance of this difference in bioavailability is yet to be determined.

Molecular basis of increased serum resistance among pulmonary isolates of non-typeable Haemophilus influenzae.

Non-typeable Haemophilus influenzae (NTHi), a common commensal of the human pharynx, is also an opportunistic pathogen if it becomes established in the lower respiratory tract (LRT). In comparison to colonizing isolates from the upper airway, LRT isolates, especially those associated with exacerbations of chronic obstructive pulmonary disease, have increased resistance to the complement- and antibody-dependent, bactericidal effect of serum. To define the molecular basis of this resistance, mutants constructed in a serum resistant strain using the mariner transposon were screened for loss of survival in normal human serum. The loci required for serum resistance contribute to the structure of the exposed surface of the bacterial outer membrane. These included loci involved in biosynthesis of the oligosaccharide component of lipooligosaccharide (LOS), and vacJ, which functions with an ABC transporter encoded by yrb genes in retrograde trafficking of phospholipids from the outer to inner leaflet of the cell envelope. Mutations in vacJ and yrb genes reduced the stability of the outer membrane and were associated with increased cell surface hyrophobicity and phospholipid content. Loss of serum resistance in vacJ and yrb mutants correlated with increased binding of natural immunoglobulin M in serum as well as anti-oligosaccharide mAbs. Expression of vacJ and the yrb genes was positively correlated with serum resistance among clinical isolates. Our findings suggest that NTHi adapts to inflammation encountered during infection of the LRT by modulation of its outer leaflet through increased expression of vacJ and yrb genes to minimize recognition by bactericidal anti-oligosaccharide antibodies.

Complications of occult pneumococcal bacteremia in children.

Children with occult pneumococcal bacteremia have not been considered to be at significant risk of developing complications. However, three of seven children, without an apparent source of pneumococcal bactermia, developed meningitis after a period of well-being, and two others developed an identifiable respiratory focus of infection. Meningitis occurred in spite of oral or low-dose intravenous penicillin therapy. We conclude that the identification of occult pneumococcal bacteremia places the child at significant risk to develop serious sequelae and that initiation of high-dose parenteral penicillin therapy, as in the treatment of pneumococcal meningitis, is indicated.