Gemfibrozil enhances the listeriacidal effects of fluoroquinolone antibiotics in J774 macrophages.

J774 macrophage-like cells express organic anion transporters that promote the efflux of fluoroquinolone antibiotics such as norfloxacin (NFX) from these cells. Gemfibrozil (GFZ) blocks organic anion transport in J774 cells, thereby facilitating the intracellular accumulation of NFX (Cao, C., H.C. Neu, and S.C. Silverstein. 1991. J. Cell Biol. 115:467a [Abstr.]). To determine whether GFZ enhances the efficacy of fluoroquinolone antibiotics against intracellular bacterial pathogens, J774 cells were infected with Listeria monocytogenes and incubated in medium containing a fluoroquinolone antibiotic in the presence or absence of GFZ. Intracellular growth of L. monocytogenes was evaluated by lysing J774 cells and assaying for colony-forming units of Listeria. GFZ intensified the bacteriostatic effect of 4 micrograms/ml NFX and rendered 8 micrograms/ml bactericidal for L. monocytogenes. GFZ had a similar potentiating effect when used in combination with 2 micrograms/ml ciprofloxacin (CFX). CFX plus GFZ was bactericidal for intracellular L. monocytogenes. Treatment of J774 cells with NFX plus GFZ markedly reduced the cytotoxic effect of the bacteria on these cells. Over 55% of cells treated with 8 micrograms/ml NFX alone were dead 16 h after infection, whereas only 5% of cells treated with 8 micrograms/ml NFX plus GFZ were dead at 16 h. Similarly, GFZ potentiated the ability of 2 micrograms/ml to protect J774 cells against the cytocidal effect of Listeria. NFX in combination with GFZ limited cell-to-cell spread of L. monocytogenes. In antibiotic-free medium, > 99% of J774 cells contained intracellular L. monocytogenes at 14 h after infection. NFX alone in the medium did not change this outcome. However, 4 micrograms/ml NFX plus GFZ decreased bacterial spread by approximately 40% at 24 h postinfection, and 8 micrograms/ml NFX plus GFZ prevented all spread beyond the initially infected cell population. These results suggest that GFZ could be used clinically to enhance the efficacy of fluoroquinolone and of other anionic antibiotics against bacteria that grow and/or reside within macrophages and/or other cells.

The crisis in antibiotic resistance.

The synthesis of large numbers of antibiotics over the past three decades has caused complacency about the threat of bacterial resistance. Bacteria have become resistant to antimicrobial agents as a result of chromosomal changes or the exchange of the exchange of genetic material via plasmids and transposons. Streptococcus pneumoniae, Streptococcus pyogenes, and staphylococci, organisms that cause respiratory and cutaneous infections, and members of the Enterobacteriaceae and Pseudomonas families, organisms that cause diarrhea, urinary infection, and sepsis, are now resistant to virtually all of the older antibiotics. The extensive use of antibiotics in the community and hospitals has fueled this crisis. Mechanisms such as antibiotic control programs, better hygiene, and synthesis of agents with improved antimicrobial activity need to be adopted in order to limit bacterial resistance.

Digoxin-inactivating bacteria: identification in human gut flora.

Digoxin, the most widely used cardiac glycoside, undergoes significant metabolic conversion in many patients to cardioinactive metabolites in which the lactone ring is reduced. This appears to occur within the gastrointestinal tract. An attempt was made to isolate and identify the organisms capable of reducing digoxin from stool cultures obtained from human volunteers. Of hundreds of isolates studied, only Eubacterium lentum, a common anaerobe of the human colonic flora, converted digoxin to reduced derivatives. Such organisms were also isolated in high concentrations from the stools of individuals who did not excrete these metabolites when given digoxin in vivo. When the growth of E. lentum was stimulated by arginine, inactivation of digoxin was inhibited. Neither the presence of these organisms alone nor their concentration within the gut flora appeared to determine whether digoxin would be inactivated by this pathway in vivo.

Clinical utility of DNA gyrase inhibitors.

Quinolone antibiotics provide potentially important therapy for many infections. These DNA gyrase inhibitors are established as excellent therapy of urinary infections and of diarrheal disease. As reviewed, the compounds have important use in respiratory, skin-structure and bone infections. It is possible that with more extensive use these drugs will show adverse reactions which to date are unknown. A number of other agents in this class with different pharmacological and improved anti-gram-positive and anti-anaerobic activity are in development. These agents will be used increasingly in medicine because of their in vitro activity, pharmacology, and cost-saving by oral therapy.

Clinical efficacy of ceftazidime. Treatment of serious infection due to multiresistant Pseudomonas and other gram-negative bacteria.

Ceftazidime, a beta-lactamase stable cephalosporin, was administered to 57 patients. Substantial underlying disease was present in the majority of patients, and 50% were in critical or poor condition. Ceftazidime inhibited all initial isolates of Enterobacteriaceae at 8 mg/L or less, regardless of resistance to other antibiotics and the majority of Pseudomonas aeruginosa at 12 mg/L or less. The mean serum level after infusion of 1 g during 30 minutes was 62 mg/L. Overall clinical response was 84%, and the bacteriological response was 72% excluding cystic fibrosis patients. No major adverse effects were encountered. Resistance developed in Pseudomonas from patients with cystic fibrosis and in Enterobacter from two other patients. Ceftazidime was an effective, safe therapy for serious infection due to multiply resistant Pseudomonas and other aerobic gram-negative bacilli including aminoglycoside-resistant Serratia and Klebsiella.

Mupirocin treatment of nasal staphylococcal colonization.

The effectiveness and safety of mupirocin calcium ointment applied to the anterior part of the nares for 5 days in the eradication of nasal carriage of Staphylococcus aureus was investigated in a placebo-controlled, double-blind study. Subjects were healthy medical center staff who had two positive cultures of the anterior nares for S aureus. Antimicrobial susceptibility, phage typing, and restriction endonuclease analysis of plasmid DNA were used to monitor the identity of relapsing and persisting strains. Mupirocin eliminated 74% of S aureus at early follow-up and 91% of original strains. At 4 weeks, 78% of the original strains were eradicated, whereas all of the placebo group remained colonized. Recolonization with mupirocin-resistant strains occurred in six patients, but these were of different phage and plasmid types from the original isolates. None of the subjects had serious adverse effects. Applied intranasally for 5 days, a calcium preparation of mupirocin in a paraffin base is effective in eliminating S aureus nasal carriage and is well tolerated.

Clinical evaluation of piperacillin therapy for infection.

Piperacillin sodium, a semisynthetic penicillin that inhibits many Klebsiella and Pseudomonas aeruginosa organisms resistant to carbenicillin, was used to treat 41 episodes of infection in 35 patients. Infectious sites included lungs, urinary tract, and tissue, including peritonitis. Seven patients had bacteremia. Clinical and bacteriological cures were achieved in 85% of infections. Cure was achieved with piperacillin in patients infected with carbenicillin-resistant P aeruginosa and Klebsiella organisms. Adverse effects were minor and included rash in two patients. Serum levels were easily maintained above the inhibitory levels for susceptible organisms. Piperacillin was a safe, well-tolerated, and effective antimicrobial agent.

Acute interstitial nephritis associated with carbenicillin therapy.

Although acute interstitial nephritis has been documented during therapy with many antibiotics of the penicillin class, it has not previously been reported in association with carbenicillin therapy. We report here the case of a patient who developed the characteristic clinical features of this form of injury while receiving prolonged large doses of carbenicillin. Histologic examination confirmed the presence of a striking interstitial nephritis. Carbenicillin should be considered a potential cause of renal damage in patients who develop rash, eosinophilia, and microscopic hematuria in association with deterioration of renal function.

Kinetics of mezlocillin and carbenicillin.

The kinetics of mezlocillin, a semisynthetic acylureido penicillin, more active than carbenicillin against many gram-negative bacteria, were compared with those of carbenicillin. Following an intravenous infusion of 4 gm in 5 min to 8 normal men there was an average serum level of 294 microgram/ml for mezlocillin and 365 microgram/ml for carbenicillin. The t1/2 for mezlocillin was 47 min and that for carbencillin was 70 min. The apparent volume of distribution was 13.4 L for mezlocillin and 14.4 L for carbenicillin. The mean urinary recovery of mezlocillin was 72% and that for carbenicillin was 92%. Constant infusion of 5 mg of mezlocillin over 2 hr gave steady-state levels of 234 microgram/ml. Half-life, apparent volume of distribution, and serum and renal clearance of mezlocillin after constant infusion were in the same range as those after rapid infusion.

Kinetics of netilmicin and gentamicin.

The kinetic parameters of netilmicin were studied in normal human subjects. In the intravenous study a steady-state was obtained in 4 subjects by the constant infusion of 2 mg/kg of netilmicin during the first hour followed by 0.5 mg/kg/hr for each of three successive hours. Creatinine clearance was greater than the simultaneous serum and renal clearance of netilmicin. In the intramuscular study 6 subjects received a single injection of 1 mg/kg of netilmicin followed by the same dose of gentamicin 1 wk later. A mean peak serum levels of 3.9 microgram/ml was found for both antibiotics, but the mean serum half-life of netilmicin was shorter than that of gentamicin. Doubling the intramuscular dose of netilmicin approximately doubled the peak serum level. In both studies 75% to 90% of the netilmicin was recovered in the urine within the first 24 hr. Netilmicin appears to be primarily excreted by glomerular filtration. The apparent volume of distribution was similar to that reported for other related aminoglycosides. Netilmicin and gentamicin have similar kinetic parameters. There were wide individual differences among normal subjects with both drugs.

Intravenous azlocillin kinetics in patients on long-term hemodialysis.

The kinetics of the antipseudomonas penicillin, azlocillin, was studied after intravenous injection in 9 patients with creatinine clearance under 7 ml/min. All were on long-term hemodialysis; 3 were also studied during a dialysis-free period. Kinetic parameters were derived using a 2-compartment open model. The mean serum azlocillin half-life (t 1/2) was 1.93 hr in patients on dialysis and approximately 5 hr off dialysis. Thirty percent of the dose was recovered in the dialysate during a 4-hr period. An approach to the use of azlocillin in patients undergoing dialysis is presented.

Kinetics of intravenous mezlocillin in chronic hemodialysis patients.

The kinetics of intravenous mezlocillin was studied in 8 patients with creatinine clearances under 7 ml/min who were undergoing chronic hemodialysis. Kinetic parameters were determined using a 2-compartment linear model. The mezlocillin serum half-life (t 1/2) in these patients ranged from 2.9 to 7.8 hr (mean, 5.4). The t 1/2 decreased to 1.57 +/- 0.09 hr during dialysis. Approximately 18% of the dose was recovered in the dialysate in 4 hr of dialysis. There was a 30% reduction per hour in serum concentration. The kinetics of mezlocillin, due to removal by nonrenal mechanisms, more closely resemble the kinetics of penicillin G and ampicillin than of carbenicillin and ticarcillin. A dosage schedule for use of intravenous mezlocillin in patients undergoing hemodialysis is presented.

Kinetics of intravenous amoxicillin in patients on long-term dialysis.

The kinetics of intravenous amoxicillin was studied in 8 patients with creatinine clearances of less than 7 ml/min who were on long-term hemodialysis. Kinetic parameters were determined using a 2-compartment linear model. The serum half-life (t1/2) of amoxicillin in these patients ranged from 7.5 to 21 hr. The t1/2 fell to 2.84 +/- 0.45 hr during dialysis. Approximately 30% of the dose was recovered in the dialysate during 4 hr of dialysis and there was a 25% reduction per hour in serum concentration. We present a dosage schedule for intravenous amoxicillin in patients with reduced renal function who are undergoing hemodialysis.

The pharmacokinetic and bactericidal characteristics of oral cefixime.

The pharmacokinetics of cefixime (FK 027), a broad-spectrum cephalosporin, were assessed in 12 normal subjects after single oral doses of 50, 100, 200, and 400 mg. Mean peak serum concentrations were 1.02, 1.46, 2.63, and 3.85 micrograms/ml after the four respective doses. Respective mean serum levels at 12 hours were 0.16, 0.33, 0.72, and 1.13 micrograms/ml. Volumes of distribution averaged 0.1 L/kg body weight, and the elimination t1/2 was 3 hours for all doses. The AUC was 7.01, 11.4, 22.5, and 36.4 micrograms X hr/ml for the four doses, respectively. Serum clearance averaged 0.4 mg/min/kg and mean 24-hour urinary recovery was 21%, 19%, 20%, and 16% for the four respective doses. Serum bactericidal titers at 4 hours exceeded 1:16 for Streptococcus pneumoniae, S. pyogenes, Hemophilus influenzae, and Branhamella catarrhalis. Urine bactericidal titers exceeded 1:8 for Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae resistant to the available oral cephalosporins.

Cefotaxime kinetics after intravenous and intramuscular injection of single and multiple doses.

The kinetics of cefotaxime, a cephalosporin with an unusually broad antibacterial spectrum, were examined in humans after intravenous bolus injection, intravenous infusion every 6 hr for 14 days, and intramuscular injection every 8 hr for 10 days. Mean peak serum level after bolus injection of 500 mg was 37.9 microgram/ml; after 1 gm, 102.4 microgram/ml; and after 2 gm, 214.1 microgram/ml. The half-life (t1/2) was 1 hr for the 3 doses. Total serum clearance was the same for all doses. Overall excretion was 50% to 60%; part of the drug was excreted as the desacetyl derivative. After multiple intravenous infusion the elimination rate constants and t1/2 were the same on days 1 and 15. Assayable levels were present on all days 5 min before injection of a dose. Multiple intramuscular injections of 500 mg produced serum levels of 9.2 to 11.9 microgram/ml. The t1/2 was 0.93 hr. Mean serum levels at 8 hr ranged from 0.08 to 0.55 microgram/ml. Serum levels produced by intravenous infusion or intramuscular injection were inhibitory for most (90%) aerobic gram-positive and gram-negative organisms susceptible to cefotaxime.

Antibiotics in the second half of the 1980s. Areas of future development and the effect of new agents on aminoglycoside use.

Articles in this supplement have examined in detail the role of aminoglycosides in the therapy of infections, addressing problems of resistance, toxicity, and efficacy. This article discusses other agents and their potential utility and effect on aminoglycosides. Penem antibiotics, which have activity against only aerobic gram-negative bacteria, have recently been synthesized. These agents have proved effective in animal experiments; to date, however, results of human clinical trials are not available. Carboxypenicillins and ureidopenicillins will still have to be administered with aminoglycosides in patients with serious life-threatening infections or in those institutions in which organisms such as Klebsiella, Enterobacter, and Pseudomonas exhibit high levels of resistance. What will be the role of aminothiazolyl cephalosporins? In some institutions, these agents might be used as sole therapy, particularly if they become less costly as a result of competition. In other settings, concern over the resistance of organisms, such as Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, and Pseudomonas aeruginosa, will result in the use of aminoglycosides with these relatively beta-lactamase-stable cephalosporins. It will be necessary to monitor the development of resistance to the new antibiotics and to determine whether the use of aminoglycosides plus third-generation cephalosporin combinations results in decreased resistance. Other agents to be considered include the directed therapy monobactams aztreonam and carumonam, the broad-spectrum carbapenem imipenem, and the penems under development. It is unclear whether these compounds might be used with aminoglycosides in critically ill, infected patients. It is also unclear what role oral beta-lactamase-stable cephalosporins will have in the therapy of nosocomial infections, since they probably will not be effective against many of the urinary or cutaneous infections that are treated with aminoglycosides. Quinolone agents can be used successfully against many infections. However, the likelihood of bacterial resistance developing and their potential for toxicity are still unknown. Thus, despite the emergence of many new agents, it appears that the time-tested aminoglycosides will continue to play an important role in antimicrobial therapy for some time to come.

Pharmacokinetics, microbiology, cost: interrelated problems for the 1990s that impact on the use of fluoroquinolone antimicrobial agents.

Correlation of pharmacokinetic and pharmacodynamic properties of antimicrobial agents with in vitro activity is critical to proper use of antibiotics. Knowledge of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) is essential for life-threatening infections and has increased relevance with regard to development of resistance when treating selected urinary tract and wound infections. Factors that decrease absorption of oral agents profoundly affect clinical efficacy. The dose and frequency of dosing programs of the new oral fluoroquinolones should be correlated with the body site of infection, the organism being treated, and the propensity of the organism to become resistant. The long elimination half-life and high urine concentrations of newer fluoroquinolones permit once-daily therapy in many infections.

Urinary tract infections.

The populations at risk for urinary tract infection include the newborn, particularly the premature, prepubertal girls, young boys, sexually active young women, elderly males, and elderly females. Risk factors that contribute to lower tract infection in women include sexual intercourse, diaphragm-spermicide use, and voiding behavior. Host factors, more than bacterial virulence, are probably the most important contributors to infection. The genetic factors that are important contributors are secretor status and P blood group phenotype. Which patients to culture, when to culture, and the number of organisms required to define infection have changed in the past decade. A concentration of 10(2) colony forming units/mL can cause an acute urinary tract infection in the healthy woman. The presence of leukocytes in the urine is of increasing diagnostic importance. Complicated urinary tract infections occur in neonates with such congenital anomalies of the urinary tract as urethral valves or in patients with neurologic disease resulting in urinary stasis. In older men or women, complicated urinary tract infections occur with obstruction, instrumentation, surgery, anatomic abnormalities, or stones. Single-dose therapy of uncomplicated urinary tract infection is useful in only a small subset of patients, specifically in patients less than 45 years of age who have short duration of symptoms. The majority of patients with uncomplicated infections should receive treatment for 3-5 days. Response to therapy and long-term cure rates in complicated urinary tract infection are related both to the type of underlying abnormality and to the species of the infecting organism. Complicated urinary tract infections should be treated for 7-14 days.

Chemical evolution of the fluoroquinolone antimicrobial agents.

In the past decade, significant progress has been made in understanding structure-function relationships of the new quinolones, which have a N-1-substituted, 1,4-dihydro-4-oxo-pyridine-3-carboxylic acid moiety as the basic nucleus. Modification of the groups affixed to positions C-6, C-7, and C-8 has made a major change in the antimicrobial activity, pharmacokinetic, and metabolic properties of the quinolones as have changes in the moieties affixed to the N-1 nitrogen. The new quinolones have a carboxyl group at position 3 and a keto group at C-4. The presence of a fluorine atom at C-6 enhances the deoxyribonucleic acid (DNA) gyrase inhibitory activity as well as the ability of the compounds to inhibit staphylococci. Position C-7 has been one of the most modified sites. Addition of a piperazinyl group markedly increased gram-positive activity, primarily antistaphylococcal activity; lowered the minimal inhibitory concentrations against Enterobacteriaceae, Haemophilus spp., and Neisseria spp.; and added activity against Pseudomonas aeruginosa compared with nalidixic acid. Methyl derivatives of the piperazine group or of the pyrroles have longer half-lives than do unsubstituted moieties. At the N-1 position, a cyclopropyl group appears to be most potent with respect to minimal inhibitory concentrations against Enterobacteriaceae and Pseudomonas. Ofloxacin is unique in that it has an oxygen substituted at C-8 with the substituent part of the ring system formed by fusion to the N-1 position. This has produced excellent in vitro activity against gram-positive species comparable with that of ciprofloxacin, excellent activity against the Enterobacteriaceae, and antipseudomonal activity superior to agents with an ethyl substitution at position N-1. The oxazine ring of ofloxacin provides excellent oral absorption with virtually 95 percent bioavailability; this modification also has prevented metabolism and has provided a long half-life of seven to eight hours.

Penicillin-binding proteins and role of amdinocillin in causing bacterial cell death.

The activity of penicillins against bacteria is in large part related to binding to specific receptor proteins involved in cell wall biosynthesis. These proteins have been designated penicillin-binding proteins. They can be separated into distinct entities through the use of acrylamide gel electrophoresis and binding of radioactive 14C-labeled penicillin G. Six major proteins have been defined in the Enterobacteriaceae, penicillin-binding proteins 1 to 6. Selection of mutants has shown that there are three essential proteins: penicillin-binding protein 1, which is divided into penicillin-binding protein 1Bs, a peptidoglycan transpeptidase, and penicillin-binding protein 1A, which acts as a replacement for penicillin-binding protein 1Bs. Penicillin-binding protein 2 is a murein-elongation initiating enzyme and penicillin-binding protein 3 is a septal murein-synthesizing enzyme. Penicillin-binding proteins 4, 5, and 6 are not essential for bacterial survival. Binding of penicillins to penicillin-binding protein 1Bs produces lysis, binding to penicillin-binding protein 2 produces round cells, and binding to penicillin-binding protein 3 produces long filaments. Amdinocillin is a beta-amidino penicillanic acid derivative that binds specifically to penicillin-binding protein 2. The compound is more beta-lactamase stable than ampicillin and has no major delay in entry into the periplasmic space as do some penicillins. Amdinocillin inhibits most of the Enterobacteriaceae, with the exception of some indole-positive Proteus species, but it does not inhibit gram-positive cocci or Pseudomonas aeruginosa. Amdinocillin produces spherical bacterial cells that eventually lyse. Its activity in vitro is markedly affected by ionic content of media. This agent acts synergistically with many penicillins, such as ampicillin, carbenicillin, and the like, and with cephalosporins, cefazolin, cefamandole, or cefoxitin to inhibit gram-negative bacilli, probably on the basis of binding to different proteins needed for the production of the peptidoglycan of the bacterial cell wall. Amdinocillin possesses a number of the essentials for effective antimicrobial activity and, by virtue of its enhancement of the activity of other beta-lactams, may prove to be a useful agent in the chemotherapy of certain infections.