Interaction of purulent material with antibiotics used to treat Pseudomonas infections

Fecal microbiota in patients with a stoma decreases anaerobic bacteria and alters taxonomic and functional diversities

Colorectal cancer (CRC) is one of the most common malignant diseases. Generally, stoma construction is performed following surgery for the resection of the primary tumor in patients with CRC. The association of CRC with the gut microbiota has been widely reported, and the gut microbiota is known to play an important role in the carcinogenesis, progression, and treatment of CRC. In this study, we compared the microbiota of patients with CRC between with and without a stoma using fecal metagenomic sequencing data from SCRUM-Japan MONSTAR-SCREEN, a joint industry-academia cancer research project in Japan. We found that the composition of anaerobes was reduced in patients with a stoma. In particular, the abundance of Alistipes, Akkermansia, Intestinimonas, and methane-producing archaea decreased. We also compared gene function (e.g., KEGG Orthology and KEGG pathway) and found that gene function for methane and short-chain fatty acids (SCFAs) production was underrepresented in patients with a stoma. Furthermore, a stoma decreased Shannon diversity based on taxonomic composition but increased that of the KEGG pathway. These results suggest that the feces of patients with a stoma have a reduced abundance of favorable microbes for cancer immunotherapy. In conclusion, we showed that a stoma alters the taxonomic and functional profiles in feces and may be a confounding factor in fecal microbiota analysis.

Pseudomonas aeruginosa susceptibility, antibiogram and clinical interpretation, and antimicrobial prescribing behaviors for dogs with otitis in the Midwestern United States

Pseudomonas aeruginosa (P. aeruginosa) can cause otitis in dogs that is nonresponsive to empirical therapy. This study evaluated P. aeruginosa isolates (N = 216) from canine ear swabs submitted to the Kansas State Veterinary Diagnostic Laboratory from 2018-2020 to create an antibiogram and minimum inhibitory concentration distributions using Clinical Laboratory Standards Institutes breakpoints. Multidrug resistance was defined as non-susceptibility to ≥1 drug from ≥3 antimicrobial classes. Submitting veterinarians (N = 83) were invited to complete a survey about antimicrobial use and otitis management. Susceptibility was higher for aminoglycosides [gentamicin (82%, 177/216) and amikacin (81%, 175/216)] than fluoroquinolones [marbofloxacin (67%, 145/216), enrofloxacin (32%, 70/216), and orbifloxacin (18%, 39/216)]. Most responding veterinarians (54%, 15/28) prescribe topical aminoglycosides as first-line therapy for canine otitis, but 71% (15/21) prescribe fluoroquinolones if rods are seen cytologically. Ceftazidime, imipenem, and piperacillin-tazobactam showed high susceptibility and are used rarely. Multidrug resistance was present in 13% (28/216) of isolates. Based on in vitro susceptibility, topical aminoglycosides might be more effective than fluoroquinolones for P. aeruginosa otitis, but efficacy studies are required. Susceptibility testing is encouraged for cases not responding to empirical therapy but has limitations because topical preparations have high concentrations and otic breakpoints are not available.

Antimicrobial use in critically ill horses

OBJECTIVE

To discuss controversies surrounding antimicrobial use in critically ill horses.

DATA SOURCES

PubMed searches from 1970-present for terms including, but not limited to: "horse," "foal," "antimicrobial," "prophylaxis," "infection," "surgery," "sepsis," and "antimicrobial resistance."

HUMAN DATA SYNTHESIS

Increasing bacterial antimicrobial resistance has changed first-line antimicrobial choices and prompted shortening of the duration of prophylactic and therapeutic treatment. The need to decrease bacterial resistance development to critically important antimicrobials has been highlighted.

VETERINARY DATA SYNTHESIS

Veterinary medicine has followed a similar trend but often without a high-level evidence. Common dilemmas include diseases in which the theoretically most effective drug is a reserved antimicrobial, the inability to differentiate infectious from noninfectious disease, the duration and necessity of prophylactic antimicrobials and use of antimicrobials in primary gastrointestinal disease. These problems are illustrated using examples of purulent infections, neonatal sepsis, colic surgery, and treatment of colitis. Although enrofloxacin, cephalosporins, and doxycycline, in contrast to gentamicin, reach therapeutic concentrations within the lungs of healthy horses, the first two should not be used as first line treatment due to their reserved status. Due to the high risk of bacterial sepsis, antimicrobial treatment remains indispensable in compromised neonatal foals but shortening the length of antimicrobial treatment might be prudent. One prospective randomized study demonstrated no difference between 3 and 5 days of perioperative antimicrobial treatment in colic surgery but shorter durations were not evaluated. High-level evidence to recommend antimicrobial treatment of adult horses with undifferentiated diarrhea does not exist.

CONCLUSIONS

Few evidence-based recommendations can be made. Commonly used antimicrobial combinations remain the mainstay for treating purulent infections. Antimicrobial treatment for compromised foals should not extend beyond recovery. Continuation of prophylactic antimicrobials >3 days is likely unnecessary after colic surgery; shorter durations might be equally effective. Antimicrobial prophylaxis in adult horses with diarrhea is unlikely to be beneficial.

The effect of postbreeding uterine lavage on pregnancy rate in mares

One stallion and 54 mares were used in an experiment to evaluate the effect of postbreeding uterine lavage on pregnancy rate in mares. All mares were inseminated with 250 x 10(6) progressively motile sperm every other day during estrus until detection of ovulation. Mares (n = 18) were randomly assigned to one of three treatment groups: 1) no postbreeding uterine lavage (control); 2) uterine lavage at 0.5 h postbreeding; or 3) uterine lavage at 2 h postbreeding. A dilute solution of povidone-iodine (PIS; 0.05%) previously determined to render spermatozoa immotile in vitro was used to lavage the mare uteri. One liter PIS, prewarmed to 40 degrees C, was used for each lavage. Pregnancy status of mares was determined at 21 d and 36 d post ovulation, using transrectal ultrasonography. The pregnancy rate of Group 1 (66.7%) was higher than that of Group 2 (22.2%; P<0.05) or Group 3 (33.3%); P<0.10). The pregnancy rates of Groups 2 and 3 were similar (P>0.70). Evaluation of endometrial biopsies obtained from a separate set of mares (n = 3) on Day 6 post ovulation, both before and after uterine lavage, revealed no difference in the accumulation of inflammatory cells, suggesting adverse effects of lavage on fertility may have been due to excessive removal of spermatozoa from the uterus during the lavage process or damage to oviductal spermatozoa.

Dry powder versus intravenous and nebulized gentamicin in cystic fibrosis and bronchiectasis. A pilot study

Aminoglycosides are a mainstay of therapy for patients with cystic fibrosis (CF) or non-CF bronchiectasis who are infected with Pseudomonas aeruginosa (Psa). Traditionally, aerosolized antibiotics are delivered by liquid nebulization. The objective of this study was to determine whether a gentamicin dry powder inhaler (DPI) is as microbiologically active and potentially safe as gentamicin inhaled via a small-volume nebulizer (SVN) or given intravenously. The study was done according to a randomized, single-dose, and triple crossover protocol. Ten patients with CF or non-CF bronchiectasis and chronically infected with Psa were recruited. Patients received a single dose of either gentamicin 160 mg via DPI or SVN, or gentamicin at 5 mg/kg by intravenous infusion. In seven of the 10 patients, the minimum inhibitory concentration (MIC) was achieved in sputum after DPI and SVN, with mean (95% confidence interval) gentamicin concentrations at 2 h after administration of 13.1 microgram/g sputum (range: 2.2 to 23.9 microgram/g) and 97.2 microgram/g sputum (range: 0.3 to 194.2 microgram/g), respectively, whereas gentamicin levels in the sputum after intravenous administration failed to reach the MIC. Gentamicin given by DPI and SVN significantly decreased the sputum Psa density (p < 0.05), by almost one order of magnitude. No significant decline in bacterial counts was observed after intravenous gentamicin. When gentamicin was inhaled, blood concentrations were minimal, and were below concentrations known to cause systemic toxicity. For treatment of Psa infections susceptible to gentamicin, gentamicin administration by DPI appeared to be as efficient as by SVN, despite the delivery of a 7-fold lower dose to the airways.

Eradication of mucoid Pseudomonas aeruginosa with fluid liposome-encapsulated tobramycin in an animal model of chronic pulmonary infection

Despite controversies associated with forms and value of antibiotic therapy for cystic fibrosis patients, antibiotherapy remains a cornerstone in the management of those patients. Locally administered liposome-encapsulated antibiotics may offer advantages over free antibiotics, including sustained concentration of the antibiotic, minimal systemic absorption, reduced toxicity, and increased efficacy. We evaluated the efficacy of free and encapsulated tobramycin in fluid and rigid liposomal formulations administered to rats chronically infected with Pseudomonas aeruginosa. Chronic infection in lungs was established by intratracheal administration of 10(5) CFU of a mucoid variant of P. aeruginosa PA 508 prepared in agar beads. Antibiotic treatments were given intratracheally at time intervals of 16 h. After the last treatment, lung bacterial counts were determined and tobramycin levels in the lungs and kidneys were evaluated by high-performance liquid chromatographic analysis and microbiological assay. Two independent experiments showed that animals treated with encapsulated tobramycin in fluid liposomes had a number of CFU less than the minimal CFU number required to be statistically acceptable compared with > or = 10(6) CFU per pair of lungs for animals treated with encapsulated tobramycin in rigid liposomes, free antibiotic, or liposomes without tobramycin. Tobramycin measured in the lungs at 16 h after the last treatment following the administration of encapsulated antibiotic was still active, and its concentration was > or = 27 micrograms/mg of tissue. Low levels of tobramycin were detected in the kidneys (0.59 to 0.87 micrograms/mg of tissue) after the administration of encapsulated antibiotic, while 5.31 micrograms/mg of tissue was detected in the kidneys following the administration of free antibiotic. These results suggest that the local administration of fluid liposomes with encapsulated tobramycin could greatly improve the management of chronic pulmonary infection in cystic fibrosis patients.

Burkholderia (Pseudomonas) cepacia as a cause of brain abscesses secondary to chronic suppurative otitis media

A patient with a cholesteatoma secondary to chronic suppurative otitis media developed infective complications including cerebellar and cerebello-pontine abscesses. Burkholderia cepacia was isolated from ear swabs, infected tissue and surgical pus on five occasions over a six-month period. Despite exhibiting three different antibiotic susceptibility profiles, all five isolates were confirmed as clonally indistinguishable by pulsed-field gel electrophoresis. To the best of the authors' knowledge there are no previous reports of Burkholderia cepacia causing infection of the adult central nervous system.

Influence of pulmonary surfactant on in vitro bactericidal activities of amoxicillin, ceftazidime, and tobramycin

The influence of a natural pulmonary surfactant on antibiotic activity was investigated to assess the possible use of exogenous surfactant as a vehicle for antibiotic delivery to the lung. The influence of surfactant on the bactericidal activity of amoxicillin was tested against Staphylococcus aureus and Streptococcus pneumoniae, and the influence of surfactant on the activities of ceftazidime and tobramycin was tested against Klebsiella pneumoniae, Pseudomonas aeruginosa, S. aureus, and S. pneumoniae. In vitro antibiotic activity was determined by killing curve studies in media with and without surfactant. Amoxicillin and ceftazidime activities were not changed in the presence of surfactant, except for a decreased killing rate of S. pneumoniae by ceftazidime in medium with additional rabbit serum. In contrast, killing curves with low concentrations of tobramycin (0.25x and 1x the MIC) showed a decreased level of activity of tobramycin against all pathogens tested in the presence of surfactant. With higher tobramycin concentrations (4x the MIC) killing rates were decreased less or were unchanged in the presence of surfactant. Concluding from the results of the study, both amoxicillin and ceftazidime can be combined with surfactant without the loss of activity. For mixing surfactant with tobramycin, dosages should be adjusted to overcome the partial inactivation of tobramycin by surfactant.

Macromolecular mechanisms of sputum inhibition of tobramycin activity

Tobramycin, an aminoglycoside antibiotic, is used in the treatment of Pseudomonas aeruginosa infections in cystic fibrosis patients. Tobramycin bioactivity, however, is antagonized by sputum. Glycoproteins (mucins) and high-molecular-weight DNA make up 2 to 3% (P. L. Masson and J. F. Heremans, p. 412-475, In M. J. Dulfano, ed., Sputum: Fundamentals and Clinical Pathology, 1973) and 3 to 10% (W. S. Chernick and G. J. Barbero, Pediatrics 24:739-745, 1959, and R. Picot, I. Das, and L. Reid, Thorax 33:235-242, 1978) of the dry weight of sputum, respectively. tobramycin binds to both mucins and DNA obtained from sputum (R. Ramphal, M. Lhermitte, M. Filliat, and P. Roussel, J. Antimicrob. Chemother. 22:483-490, 1988). In vitro, recombinant human DNase (rhDNase) hydrolyzes high-molecular-weight DNA of > 50 kb within sputum to fragments of 2 to 4 kb. Studying dialyzable tobramycin, we examined drug binding to whole sputum and to "mock sputum," which consisted of porcine gastric mucin and calf thymus DNA. We also studied the effects of rhDNase treatments of sputum, mock sputum, and calf thymus DNA on tobramycin binding. We found that treatments of sputum, mock sputum, and calf thymus DNA with rhDNase did not significantly increase the tobramycin bioactivity within the dialysates; surprisingly, sputum binding of tobramycin was increased by rhDNase. We conclude that rhDNase does not increase the bioactivity of tobramycin in sputum.

[Amikacin concentrations in lung and serum after single intratracheal administration in men]

This study was designed to assess the diffusion into lung tissue and systemic circulation of amikacin administered endotracheally. Eleven consecutive patients, suffering from lung carcinoma and scheduled for elective pneumonectomy or lobectomy, were included in the study. After induction of anaesthesia and before tracheal intubation, a single 500 mg amikacin dose was administered endotracheally through a catheter whose tip was located 5 cm below the vocal cords. Blood was then collected every 15 min for serum assays, until pulmonary resection had been carried out. Pulmonary concentrations were assessed in a healthy area. Measurements were carried out in duplicate using fluorescence polarizing immunoassay and microbiological methods. Serum peak concentrations were found 105 min after administration (7.97 +/- 5.62 micrograms.ml-1). Six and 12 h after administration, serum concentrations were 3.19 +/- 1.87 and 1.20 +/- 0.67 micrograms.ml-1 respectively. Mean lung concentrations were 1.85 +/- 2.12 micrograms.g-1, with a corresponding serum level of 7.22 +/- 4.36 micrograms.ml-1. However, endotracheal instillation of amikacin provided serum concentrations which, were not high enough for treatment of gram negative pneumonia. Lung concentrations are lower than both serum levels and MIC90 for gram negative bacilli. Moreover, there was a major heterogeneity in serum and lung levels, which seemed to be unpredictable. This was probably due to heterogenous tracheal, bronchial and alveolar absorption. The results obtained in this study with a single dose administration should be reassessed in the light of data obtained with long-term amikacin administration.

Significance of tissue levels for prediction of antibiotic efficacy and determination of dosage

Determination of tissue levels is widely thought to provide useful information in the investigation of a new antibiotic, however this assumption is not fully justified. In this paper the following questions are covered. Firstly, the methodological problems encountered in the measurement of antibiotic levels in solid tissues and extravascular fluids are described. Secondly, the difficulties encountered in interpreting tissue concentrations are discussed, given the heterogeneity of distribution of drugs, potential intracellular penetration, binding to tissue proteins and local factors reducing antibacterial activity. Thirdly, the respective importance of animal and human data on tissue levels for prediction of efficacy is analysed. In some animal models it is possible to study the conditions affecting antibacterial activity and to obtain data relevant to the clinical situation. However, the inoculum effect, the metabolism of bacteria, the mechanism of the bactericidal action of drugs and the type of infected tissue are important factors to be taken into account. In humans, data obtained from infected tissue is sparse and contributes little to knowledge. Knowledge of tissue levels may be important for establishing whether data obtained in animals can be applied to humans or not. Fourthly, the importance of tissue levels in determining antibiotic dosages is evaluated. In humans, tissue levels are of limited value in the determination of unitary dose and dosage intervals in relation to the clinical response. Trough serum levels of free drug, half-life at the beta-phase and rate of in vitro killing are the most important parameters to be considered. Their relative importance depends mainly on the mode of action of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal pharmacokinetic changes of gentamicin during enterococcal pyelonephritis

In the present study, the renal pharmacokinetics of gentamicin was investigated in pyelonephritic rats infected with Streptococcus (Enterococcus) faecalis. Four days after the induction of infection, animals were given either a single dose of gentamicin or two daily injections for 7 days. The treated animals were evaluated from 1 h to 6 months posttreatment. After a single injection, limited pharmacokinetic variations were observed, whereas after 14 injections infected kidneys demonstrated significantly higher concentrations and a more extended renal elimination phase of the antibiotic. Analysis of the area under the curve of the concentration in kidney versus time showed more marked renal accumulation by the infected and long-term treated animals than by normal animals or those receiving only one injection of aminoglycoside. Renal function remained normal in both the infected and normal animals treated with this aminoglycoside. These results demonstrate that S. faecalis pyelonephritis disturbs the renal handling of gentamicin and may increase the susceptibility of the kidney to aminoglycosides.

Penetration of aminoglycosides in uninfected pleural exudates and in pleural empyemas

The concentrations of gentamicin, netilmicin, and amikacin were determined after one single intravenous injection in uninfected pleural fluid after thoracotomy and in purulent pleural empyemas. The mean peak concentrations in the pleural fluid after the injection of gentamicin (1.5 mg/kg), netilmicin (2.0 mg/kg), and amikacin (7.5 mg/kg) were 2.9 +/- 0.3 mg/L, 3.7 +/- 0.8 mg/L, and 11.0 +/- 3.1 mg/L, respectively. The pleural penetration of the drugs was very high (from 80.0 to 99.1 percent). By contrast, gentamicin and netilmicin were not detectable in empyema pus; in this exudate the mean peak level of amikacin was 5.7 +/- 2.2 mg/L, with the penetration of this drug being 31.0 percent. The concentrations of parenterally administered aminoglycosides are substantially lower in empyema pus than in sterile pleural fluid. The possibility of poor pleural penetration of some aminoglycosides, as well as the presence of local conditions in pleural empyema unfavorable to the bioactivity of these drugs, must be kept in mind when treating pleural infections.

Pharmacokinetics and therapeutic efficacy of gentamicin in an experimental pleural empyema rabbit model

The pharmacokinetics and therapeutic efficacy of gentamicin were investigated in an experimental pleural empyema rabbit model. Pleural effusion was induced by the intrapleural administration of turpentine, and empyema was induced by direct inoculation of the effusion with Klebsiella pneumoniae. Pleural empyema compared with effusion was characterized by lower pH, oxygen tension (PaO2), and glucose levels and higher leukocyte count, lactic acid concentration, and PaCO2. After a single administration, gentamicin was first detectable in the pleural fluid at 60 min, whereas peak levels in empyema were observed at 180 min. Gentamicin persisted in the empyema longer than in blood. Animals treated with gentamicin only had 60% bacterial cure on day 7; those treated with gentamicin in an oxygen chamber had 100% cure on day 5 (P = 0.004). Low oxygen tension diminished the antibacterial efficacy of gentamicin in this model. An increase in oxygen tension improved the therapeutic results without alteration of the pharmacokinetics of gentamicin.

Benefit from high intrarenal levels of gentamicin in the treatment of E. coli pyelonephritis

The importance of high intrarenal levels of gentamicin on the outcome of experimental pyelonephritis was studied in rats receiving either a short course (three days) of gentamicin (G) alone or combined with a longer course (14 days) of ampicillin (A), cephalothin (C), or trimethoprim (T), or two weeks of therapy with ampicillin, cephalothin, trimethoprim and gentamicin given alone. While ampicillin, cephalothin and trimethoprim were undetectable in the medulla within six hours of cessation of therapy, gentamicin was still detectable in levels six folds above the MIC up to six months after treatment had ceased. Six months after the end of treatment, the percentage of sterile left kidneys in animals treated with ampicillin (50%), cephalothin (15%), trimethoprim (20%) was lower than the percentage of animals receiving 14 days of gentamicin (100%), or the combinations AG:89%, CG:67% and TG:60%, P less than 0.01. Following three days of gentamicin, 50% of the left kidneys were sterilized. When compared to ampicillin, cephalothin or trimethoprim alone, combined therapies significantly reduced the number of CFU in the kidneys P less than 0.01. These combinations were almost as effective as two weeks of therapy with gentamicin. Short-term therapy (three days) with an aminoglycoside which concentrates in the renal parenchyma, combined with an antibiotic which will accumulate in other parts of the nephron, may result in "pharmacological synergy". This new approach to therapy of pyelonephritis may be promising.

Influence of inflammation on the efficacy of antibiotic treatment of experimental pyelonephritis

An acute exudative Escherichia coli pyelonephritis rat model was used to study the influence of progressive pyelonephritis on the efficacy of antibiotic treatment. In this model, transient ureteral obstruction after E. coli bladder inoculation induces early bacterial multiplication in the kidney parenchyma, and the bacterial counts peak by 48 h. The inflammatory response (assessed by the increase in kidney weight) is somewhat delayed, starting 36 h after inoculation and peaking by 72 h. Groups of rats received 4 doses over 48 h of saline, ceftriaxone (100 mg/kg), or ceftriaxone (100 mg/kg) plus gentamicin (4 mg/kg). These treatments were initiated 24, 36, 48, or 72 h after bladder inoculation. Antibiotic treatment started at 24 h was significantly more effective in reducing bacterial counts in the kidney parenchyma than at any later therapy onset. Only when started 24 h after inoculation was the synergistic combination of ceftriaxone plus gentamicin more effective in reducing bacterial counts than ceftriaxone alone. Ceftriaxone and ceftriaxone plus gentamicin regimens started at 24 h reduced significantly (by 42 and 55%, respectively) the incidence of acute exudative pyelonephritis when compared with the incidence in saline-treated controls. Early therapy onset (24 h) strikingly reduced the development of the inflammatory response. This reduction was less marked when antibiotic therapy was started at 36 h and no longer apparent when therapy onset was delayed up to 48 or 72 h. In conclusion, the efficacy of antibiotics in eradicating bacteria from the kidney parenchyma and in preventing acute exudative pyelonephritis was markedly hampered by the development of pyelonephritis.

Relevance of serum protein binding of cefoxitin and cefazolin to their activities against Klebsiella pneumoniae pneumonia in rats

An experimental Klebsiella pneumoniae pneumonia in rats was used to study the effect of protein binding of cefoxitin and cefazolin on their therapeutic activity. Both cephalosporins were similar with respect to their antimicrobial activity against the K. pneumoniae in vitro, but they differed in their degree of protein binding, being 34% for cefoxitin and 89 to 93% for cefazolin in uninfected rats and 24 and 71 to 83%, respectively, in infected rats. Various doses of these agents were administered by continuous infusion, which started 5 h after bacterial inoculation and continued for 65 h. Antimicrobial response was evaluated with respect to the numbers of bacteria recovered from lung and blood at the end of treatment. An inhibitory effect of protein binding on the in vivo antimicrobial activity was demonstrated. Cefoxitin was therapeutically effective at a constant plasma level that reached the MIC. To obtain a similar effect with cefazolin the plasma level of that drug had to be increased to a concentration more than three times the MIC.

A preliminary study on the use of carbenicillin in snakes

The results of a 10 year survey on the in vitro antibiotic resistance patterns of Pseudomonas spp. isolated from clinically ill reptiles, showed a high degree of sensitivity to carbenicillin. On the basis of sensitivity testing, carbenicillin was used to treat nine snakes of four different species, with confirmed Pseudomonas infections. Plasma carbenicillin levels were assayed, by a microbiological agar diffusion technique, at intervals of time after a single intramuscular injection at a dose rate of 400 mg/kg. Peak plasma levels of 177 and 270 micrograms/ml were reached 1 h after the initial injection and therapeutic levels persisted for at least 12 h. This initial study indicated that a suggested dose regime in snakes, derived by extrapolation from mammalian dosages, of 100-125 mg/kg daily was insufficient to produce plasma levels of sufficient magnitude and duration to effectively treat Pseudomonas infections in snakes.

Amikacin concentrations in uninfected postthoracotomy pleural fluid and in serum after intravenous and intrapleural injection

The pharmacokinetics of amikacin after intravenous (IV) and intrapleural injection was compared in 25 patients with pleural drainage after lung resection. In ten patients 7.5 mg/kg of the drug was injected IV; the mean peak concentrations were 31.2 +/- 2.3 micrograms/ml in the serum and 13.3 +/- 3.8 micrograms/ml in the pleural fluid. The penetration of amikacin in the pleural space was 80 percent. After the intrapleural injection of the same dose of amikacin in 15 patients, the pleural fluid concentrations of the drug were extremely high and well sustained during eight hours; however, serum concentrations reached maximal values of 14.1 +/- 4.7 micrograms/ml, indicating a substantial diffusion of amikacin from the pleural space to the blood. In the case of treatment of pleural infections by local injection of aminoglycosides, the serum concentrations must be kept in mind to avoid systemic intoxication from these drugs.

Pseudomonas cepacia infection in cystic fibrosis: an emerging problem

The prevalence of Pseudomonas cepacia infection increased from 10% in 1971 to 18% by 1981 in a population of approximately 500 patients with cystic fibrosis. Carriage of P. aeruginosa has remained unchanged at 70% to 80% over the same period. Patients infected with P. cepacia have greater impairment of pulmonary function than those with P. aeruginosa. A syndrome characterized by high fever, severe progressive respiratory failure, leukocytosis, and elevated erythrocyte sedimentation rate has occurred in eight patients over the past 3 years, with a 62% fatality rate. Because P. cepacia strains are uniformly resistant to ticarcillin, piperacillin, and aminoglycosides, and because ceftazidime is ineffective despite in vitro activity, treatment of these infections is very difficult. Prevention of acquisition and effective treatment of P. cepacia in patients with cystic fibrosis are now major clinical problems in our clinic.

Host factors influencing the response to antimicrobial agents

When the desired clinical response to an antibiotic therapeutic regimen is not achieved, despite appropriate antibiotic selection and organism sensitivity, the clinician must be aware that several host factors exist that may influence the outcome. Examples of the influence of host-related factors on drug disposition have been briefly reviewed in this article. It should be noted, however, that further investigation is needed to determine whether these factors truly exert a significant influence on the outcome of antibiotic utilization.

The pharmacokinetics and tissue levels of polymyxin B, colistin and gentamicin in calves

Following a single intravenous injection of polymyxin B, colistin (5 mg/kg, each) and gentamicin (3 mg/kg) to calves, the decline in serum antibiotic concentration generally suggested a three-compartment (open system) pharmacokinetic model. Tissue binding is a dominant factor in the distribution and elimination kinetics of the drugs. Less than 65% of the dose of polymyxin B and colistin was recovered in the urine during 48 h after treatment. Concentrations of nonbound polymyxin B and colistin in the kidney, liver, lung, heart, and skeletal muscles were similar to total (free and bound) serum drug levels, but considerably higher concentrations were found, in bound form, in chloroform-ethanol extracts of these organs. At 24 h after treatment, more than 50% of the doses of polymyxin B and colistin were present bound to the tissues; the largest amount was in the skeletal muscles. Gentamicin was concentrated in the kidney, predominantly in the free form. At 48 h after treatment the amount of gentamicin in the kidney was 6.3% of the administered dose, being more than five times greater than the corresponding amounts of polymyxin B and colistin. The extent of tissue uptake of polymyxin B and colistin limits the usefulness of kinetic values, which are derived from the analysis of serum drug levels, for the purpose of designing dosage schedules. The strong affinity of the polymyxins to the muscle tissue, and gentamicin to the kidney, can result in drug residues persisting in the body for several weeks.

Studies on some variables influencing aminoglycoside efficacy in vivo and in vitro

The penetration of various aminoglycosides into uninfected and infected fluids of steel net cages, implanted subcutaneously into rabbits, was studied. The pharmacokinetics of the antibiotics tested in these fluids were characterized by a peak concentration which was delayed in relation to that in serum after both intramuscular and intravenous administration, and by a slower elimination from cage fluids than from serum. Comparing amikacin, gentamicin, netilmicin and tobramycin, the latter seemed to have a somewhat lower penetrability into uninfected cage fluids. Infection of the cage fluids with gram-negative aerobic bacteria resulted in a reduction of the measurable concentrations of amikacin, gentamicin or netilmicin in the cage fluids when compared to those obtained in uninfected fluids in the same rabbits. Elimination of the aminoglycosides from the infected cage fluids was slower than from the uninfected ones. The lower concentrations of the aminoglycosides in infected cage fluids were considered to be primarily due to a penetration barrier created by the infection. The viable counts in infected cage fluids were only marginally affected in cages where the aminoglycoside concentrations were above the minimum inhibitory concentrations (MIC's) of the aminoglycosides against the bacterial strains used for infection when tested in vitro according to standard techniques. In infected cage fluids the pO2 and pH were low, while the pCO2 was high. The number of viable bacteria was high. These factors, which in vitro increased the MIC's of the agents, and the low concentrations achieved in infected cage fluids could explain the inefficacy of aminoglycoside treatment in this experimental model.

Interstitial fluid concentrations of cefsulodin, azlocillin and carbenicillin

Cefsulodin, azlocillin and carbenicillin were administered by intramuscular injection to rats in a dose of 100 mg/kg. THe serum concentration in frequent samples after administration was determined and compared with the interstitial fluid (IF) concentration, measured with implanted paper discs enveloped in a dialysis tube. The IF concentration of cefsulodin was significantly higher than that of the other two antibiotics. The AUC in the IF was also larger for cefsulodin.

A double-blind controlled trial of anti-Pseudomonas chemotherapy of acute respiratory exacerbations in patients with cystic fibrosis

A double-blind controlled trail of anti-Pseudomonas chemotherapy was carried out in 24 exacerbations of pulmonary disease in patients with cystic fibrosis. Fifteen exacerbations were treated with oxacillin plus sisomicin and carbenicillin (treatment group); nine were treated with oxacillin alone (control group). The planned length of treatment was 14 days. The difference between the failure rate in the treatment group (3/15) and the control group (7/9) was statistically significant (P less than 0.015). The difference in improvement of forced expiratory volume in 1 second was also significant (P less than 0.025). At the end of the study, Pseudomonas aeruginosa was still present in the sputum of all nine patients in the control group, but was not isolated from six of the 15 patients in the treatment group. The data suggest a beneficial role for anti-Pseudomonas chemotherapy in the treatment of acute pulmonary exacerbations in patients with cystic fibrosis.

The role of bacterial surface structures in pathogenesis

Modern research has revealed that the true surfaces of animal cells consist of polysaccharide chains that are linked to proteins hydrophobically anchored in the membrane and protrude to form a dense glycocalyx. It has become increasingly clear that most pathogenic bacteria must position themselves at the surface of their "target" cell in order to exert their toxic or otherwise deleterious effects. The true surface of most pathogenic bacteria has also been recently shown to consist of a protruding mass of polysaccharide chains--the bacterial glycocalyx--that is composed of teichoic acids in many gram-positive species and of acid polysaccharides in many gram-negative organisms. Through this bacterial glycocalyx certain cell surface proteins and organized protein structures (e.g., pili) are known to project, so that the bacterial surface is a mosaic of polysaccharides and proteins; both of these types of molecules have been implicated in instances of specific pathogenic adhesion. Besides their role in specific adhesion to target cells, these surface components interpose a highly charged, and often very extensive, barrier that can prevent the penetration of antibodies and antibiotics to their target sites in the bacterial cell. They may also frustrate mucociliary clearance, phagocytosis, and other clearance mechanisms of the host. We will discuss the chemical and physical nature of these bacterial surface components that mediate pathogenic adhesion and counteract host defense mechanisms sufficiently to allow infections to become established.

Optimal antibiotic therapy in bronchopulmonary infections

Therapy of bronchopulmonary infections has evolved in the past 30 years. Only in the therapy of pneumococcal infections have, precise dosage programs been developed. Therapy of pneumococcal infection is optimal with penicillin G in low dosage. None of the newer agents has altered morbidity or mortality. The best agent for the treatment of pneumonia due to Staphylococcus aureus or members of the Enterobacteriaceae has not been established. Use of combination therapy consisting of an anti-Pseudomonas penicillin and an aminoglycoside has been shown to offer the greatest success in the treatment of Pseudomonas pulmonary infections. The optimal antibiotic and dosage program for the treatment of acute bacterial exacerbations of chronic bronchitis has yet to be defined. Further comparative studies of the chemotherapy of pulmonary infections are necessary.

Gentamicin antibacterial activity in the presence of human polymorphonuclear leukocytes

Complete protection of Staphylococcus aureus Wood 46 from gentamicin bactericidal activity was documented for microorganisms located within polymorphonuclear leukocytes. The highest, still ineffective gentamicin concentration tested in the phagocytic assay was 80 times higher than the minimal concentration required to kill uningested organisms. Extracellular gentamicin activity was unaffected by the phagocytic process as demonstrated by microbiological and enzymatic assays, and liberation of intracellular S. aureus by lysis of neutrophils showed the bacteria to be fully susceptible to the antibiotic. These results were corroborated by studies performed with [14C]gentamicin; binding of the labeled antibiotic by resting neutrophils, or by neutrophils ingesting live, killed S. aureus or endotoxin-coated paraffin particles, showed no statistical differences and never exceeded 20% of the extracellular concentration. These results show that intraleukocytic S. aureus are protected from the bactericidal action of gentamicin and suggest that this protection can be explained by poor intracellular penetration of the antibiotic.

Endotracheally administered antibiotics for gram-negative bronchopneumonia

Sisomicin or a placebo was administered endotracheally to two groups of 18 and 20 unconscious patients, respectively, who had tracheostomies or endotracheal tubes in place and developed a severe gram-negative broncho-pneumonia. In addition, the patients received systemically a combination of sisomicin and carbenicillin. A favorable clinical response was obtained in 14 (77 percent) of the 18 patients who were treated with sisomicin and in nine (45 percent) of the 20 patients who received the placebo (P less than 0.05). Endotracheal therapy with sisomicin was well tolerated and resulted in high levels of sisomicin and in elevated bactericidal activity within the bronchial secretions. Endotracheally administered amino-glycosides might be an important adjunct to systemically administered antibiotics in the management of severe gram-negative bronchopneumonia.

Clinical and bacteriological evaluation of netilmicin in gram-negative infections

A preliminary study was conducted with netilmicin, a new aminoglycoside antibiotic. Its effectiveness was evaluated in vitro against 546 strains of Enterobacteriaceae and Pseudomonas aeruginosa isolated from clinical material. Its effectiveness against gentamicin-susceptible strains was roughly similar to that of gentamicin and other newer aminoglycoside antibiotics. Cross-resistance to netilmicin was found in 9 of 44 gentamicin-resistant strains. A favorable clinical response was observed in 70% of the patients treated with a dose of netilmicin ranging from 4.5 to 7.5 mg/kg. However, the appearance of granular casts was seen in 7 of 10 patients receiving the higher dosage of netilmicin (7.5 mg/kg) and a rise in blood urea nitrogen or serum creatinine levels was observed in 5 of these patients.

Comparing radioactive and trephine-disk bioassays of dicloxacillin and gentamicin in ocular tissues in vitro

Trephined disks of tissue (6 mm diameter) from fresh rabbit eyes were immersed overnight in solutions of radioactive carbon (14C)-dicloxacillin or gentamicin, then assayed by one of two methods: agar-diffusion bioassay, using filter-paper disks immersed in known concentrations of antibiotic as standards, or radioactive assay. The bioassay underestimated the concentrations of antibiotic in sclera and iris by 38 to 72%, and slightly overestimated those in the cornea. A corrected bioassay was calculated, based on the differences in fluid mass between tissue specimens and filter-paper disks; this value was within 20% of the radioactive assay in 18 of 24 experiments with dicloxacillin, and in 14 of 24 with gentamicin. There was evidence of pronounced binding of gentamicin to ocular tissues (iris greater than sclera greater than cornea); this appeared to be a saturable and reversible phenomenon. Less marked binding of dicloxacillin to iris and sclera was noted. The results indicated that, depending on the degree of accuracy required, the corrected trephine-disk agar-diffusion bioassay provides a reasonable estimate of the antibiotic content of ocular tissues.

Synergistic activity of carbenicillin and gentamicin in experimental Pseudomonas bacteremia in neutropenic rats

Rats made neutropenic with cyclophosphamide were infected intraperitoneally with Pseudomonas aeruginosa. The challenge organism was killed synergistically in vitro by the combination of gentamicin and carbenicillin. Untreated neutropenic rats infected with 3 x 10(6)Pseudomonas died between days 2 and 7, and the overall mortality was 70%. Groups of infected neutropenic rats were treated intramuscularly with 1.5 or 6 mg of gentamicin per kg per dose, 100 or 400 mg of carbenicillin per kg per dose, or 1.5 mg of gentamicin and 100 mg of carbenicillin per kg per dose. Treatment was begun at 2 h postinfection and was continued every 8 h for about 72 h. Cultures of blood and peritoneal washings were performed in control and treated rats at 1, 4, 24, 48, and 72 h postinfection. Gentamicin at either dose level was ineffective in preventing death, but mortality was significantly reduced by high-dose carbenicillin and low-dose combination therapy. In addition, the latter regimens sterilized the peritoneal fluid and blood. Carbenicillin and gentamicin showed in vivo synergy in the treatment of neutropenic Pseudomonas-infected rats.

Inhibition of antibiotic activity in vitro by synthetic melanin

Synthetic melanin (100 to 1,000 mug/ml) markedly inhibited the in vitro activity of aminoglycosides and tetracyclines but did not affect the activity of betalactam antibiotics, erythromycin, or clindamycin.

Treatment of murine coccidioidomycosis with polymyxin B

An agar dilution method was employed to test the susceptibility of 12 strains of Coccidioides immitis to polymyxin B (PB). After 3 days of incubation, eight strains were markedly inhibited by 5.0 mug of PB per ml and four strains did not grow. PB at 10 mug/ml inhibited the growth of all strains through 20 days of incubation. To determine whether PB has anticoccidioidal activity in vivo, mice in groups of 30 were infected intraperitoneally with a mean lethal dose (LD(50)) or 20 LD(50) of arthrospores of C. immitis ATCC 28868 (Silveira). Treatment by intraperitoneal injection of PB (2.5 mg/kg) was begun 2 or 5 days after challenge. By 40 days after infection, 47 and 7% of the untreated mice challenged with an LD(50), respectively, were alive. Of mice infected with an LD(50) or 20 LD(50) and treated with PB beginning 2 days after the challenge, 90% of each group were alive by day 40. Initiation of PB therapy 5 days after infection permitted survival of 84% of the mice infected with an LD(50); however, only 27% of the mice infected with 20 LD(50) survived by day 40. In this latter group there was evidence that PB prolonged life since 56% of the treated mice were alive by day 15 as compared with 30% of the controls. PB in vivo was fungistatic since the majority of treated mice had C. immitis in the liver, lungs, and spleen.