Evaluation of intravenous ciprofloxacin in patients with nosocomial lower respiratory tract infections. Impact of plasma concentrations, organism, minimum inhibitory concentration, and clinical condition on bacterial eradication.

Fifty patients with gram-negative lower respiratory tract infections were treated with intravenous ciprofloxacin to evaluate efficacy and safety. Relationships between individual pharmacokinetics and clinical and bacteriologic outcome were studied. Ciprofloxacin concentrations in plasma were determined by high-performance liquid chromatography. Respiratory secretion cultures were obtained daily to determine the eradication day of the infecting organism. Susceptibility (minimum inhibitory concentration) to ciprofloxacin and other antimicrobials was determined using standard microdilution techniques. The mean age of the patients was 70 years. They had multiple underlying diseases, and two thirds of them were ventilator dependent at entry. Approximately 50% of the patients had failed previous treatment for the same infections. Patients infected with Enterobacteriaceae or Haemophilus influenzae with minimum inhibitory concentrations of less than 0.25 mg/L responded well to intravenous ciprofloxacin therapy (200 mg every 12 hours). The organisms were eradicated from sputum cultures usually within 1 day after ciprofloxacin therapy was started. Most clinical failures occurred in patients who were infected with Pseudomonas aeruginosa and had multiple underlying diseases. Pseudomonas aeruginosa was isolated from 10 patients with pneumonia, 2 patients with lung abscess, and 1 patient with bronchiectasis. The Pseudomonas isolate acquired resistance during ciprofloxacin treatment in 7 patients with pneumonia and in all of the remaining 3 patients. We conclude that ciprofloxacin is safe and effective at a dosage of 200 mg administered intravenously every 12 hours for nosocomial lower respiratory tract infections caused by Enterobacteriaceae or Haemophilus species. Many patients who had failed previous antibiotic treatment for Enterobacteriaceae infections had good clinical response to ciprofloxacin therapy. Studies using either higher dosages of ciprofloxacin or combination therapy should be conducted to determine if acquired resistance can be avoided in Pseudomonas infections.

Effect of protein binding on cefmenoxime steady-state kinetics in critical patients.

The effect of protein binding on cefmenoxime steady-state kinetics was studied in 20 critical patients with gram-negative pneumonia. Sixteen patients were given 1 gm cefmenoxime every 6 hr, two received 2 gm every 6 hr, and two received 2 gm every 8 hr. Serum protein binding was measured by equilibrium dialysis. Assays were by HPLC. Serum cefmenoxime concentration-time data were characterized by a model-independent method based on statistical moment theory. Despite varying renal function in patients, mean cefmenoxime serum concentration-time curves for all three dosing regimens were closely aligned, reflecting successful empiric dosage adjustment. Terminal phase t 1/2 ranged from 0.8 to 2.9 hr and was significantly related to creatinine clearance. Cefmenoxime total clearance was significantly related to both lambda z (2.303 times the slope of the terminal portion of the log-concentration-time curve) and creatinine clearance (CCr). Plasma clearance of free cefmenoxime was more strongly correlated with CCr than the clearance of total cefmenoxime. Drug recovery from 24-hr urine collections at steady state was 76.9 +/- 19.8% of the daily dose (mean +/- SD, n = 13). Cefmenoxime protein binding in patients differed markedly from normal values. A regression equation derived from data on 11 cephalosporins appeared to predict total volume of distribution in the steady state (Vdss-Total) from the fraction of unbound drug accurately. Since cefmenoxime has a high therapeutic index, no clinical consequences are expected to result from variation in protein binding. Observed differences in protein binding between patients and normal subjects could have clinical consequences for highly bound acidic drugs that, unlike cefmenoxime, have narrow therapeutic indices.

Cefmenoxime efficacy, safety, and pharmacokinetics in critical care patients with nosocomial pneumonia.

Nephrotoxicity frequently complicates the use of aminoglycosides in severely compromised acute care patients. Therefore, an open clinical trial was initiated to determine if cefmenoxime alone is useful in serious nosocomial pneumonias. Thirty consecutive patients were entered in the trial, and 28 patients with an average age of 66 years were evaluable. Most were malnourished at entry, with serum albumin averaging 2.8 g/dl and prognostic nutritional index values over 70 percent (normal less than 40 percent). One-half the patients had severe chronic obstructive pulmonary disease and 68 percent required ventilators. Fifty-seven percent had concomitant cardiac disease, and 79 percent had previously been treated with antibiotics. Pneumonia was proven to be present by new infiltrate on chest x-ray, new fever, elevated white blood cell count, and gram-negative rods on gram stain and in cultures of tracheal aspirates or sputum. Patients were given cefmenoxime 1 to 2 g every six hours an average of 12 days. Cefmenoxime peak (one hour) and trough concentrations were measured by high pressure liquid chromatography and averaged 58 and 7 micrograms ml, respectively. Pharmacokinetic data in 18 patients were determined from serum profiles. Gram-positive organisms, Escherichia coli, Klebsiella, and Hemophilus influenzae were usually eradicated. Persistence was noted for some Enterobacter, Pseudomonas, Serratia, and Acinetobacter. Persistence in patients with good clinical response was considered colonization rather than superinfection. Overall, a satisfactory clinical response rate was noted in 78.6 percent of evaluable patients, whereas four patients responded satisfactorily with recurrence and two treatments had an unsatisfactory response. No serious adverse effects were observed. Cefmenoxime is a promising agent in the treatment of susceptible pneumonias in critical care patients.

Oral ciprofloxacin in the treatment of serious soft tissue and bone infections. Efficacy, safety, and pharmacokinetics.

Forty-eight patients were enrolled in a clinical study of oral ciprofloxacin for the treatment of soft tissue or bone infections. Patients received 500 to 750 mg of ciprofloxacin every 12 hours. In the predominantly older population studied, there were 13 patients with osteomyelitis, 24 diabetic patients with soft tissue infection and probable osteomyelitis, and 11 patients with other soft tissue infections. Infecting pathogens included Pseudomonas aeruginosa in 25 patients, Serratia species in nine patients, Staphylococcus aureus in 13 patients, and other aerobic gram-negative rods in 21 patients. Clinical response (defined as resolution or improvement) was noted in 84 percent of patients with non-diabetic osteomyelitis, in 79 percent of patients with diabetic infections, and in 91 percent of patients with soft tissue infections. Microbiologic outcome was very favorable in 75 percent of cases, and Pseudomonas responded as well as any other pathogen. Pharmacokinetic properties of ciprofloxacin were evaluated in 12 patients, and the data were analyzed using both compartmental and non-compartmental analyses. Mean values for compartmental rate constants (hours-1) were as follows: absorption rate constant = 1.15; intercompartmental rate constants, k12 = 0.48, and k21 = 0.58; elimination rate constant = 0.46; distribution rate constant = 1.31; and terminal elimination rate constant = 0.19. The apparent volume of distribution at steady state/bioavailability was 196 liters and total body clearance/bioavailability was 45.9 liters/hour. The mean time to peak concentration was 1.3 hours. The mean peak concentration as determined by compartmental fitting (2.4 micrograms/ml) underestimated the observed peak (3.2 micrograms/ml) by 24.8 percent. Clearance of ciprofloxacin was similar regardless of the method used to fit the data, whereas the volume of distribution was significantly different when the two analysis techniques were compared. Ciprofloxacin was well tolerated, with the most frequent adverse reactions being rash, gastrointestinal intolerance, and increased levels of liver enzymes, each of which occurred in five patients.

Dual individualization of intravenous ciprofloxacin in patients with nosocomial lower respiratory tract infections.

Dual individualization is the integration of patient-specific pharmacokinetic parameters with the pharmacodynamics (concentration versus response) of the infecting pathogen. This technique allows description of the time of in vivo bacterial eradication, and allows estimation of optimal dosages using small numbers of seriously ill patients. In an ongoing study, 11 patients with nosocomial lower respiratory tract infections were given 200 mg of intravenous ciprofloxacin every 12 hours. Ten blood samples were taken after the first dose, with additional peaks and troughs measured on Day 4 and at the end of treatment. Bacterial isolates had minimal inhibitory concentrations (MICs) determined by standard microdilution techniques. In the 11 patients, there were 14 bacterial isolates, of which seven were Pseudomonas aeruginosa and the remainder were other pathogens. Ciprofloxacin MICs ranged from 0.008 to 1.0 microgram/ml. The pharmacokinetics of ciprofloxacin in these patients varied with renal function, and average peak serum concentrations ranged from 1.7 to 4.9 micrograms/ml. Eradication of bacteria from tracheal aspirates occurred between Days 1 and 7, except in four patients in whom the organism persisted. Correlations were observed between the day of eradication and the length of time ciprofloxacin concentrations remained above the minimal inhibitory concentration (MIC). Essentially all bacteria with MICs of less than 0.25 were eradicated. Of the non-eradicated bacteria, most had either MICs of more than 0.25, or less than 100 percent time above the MIC. The clinical response was satisfactory. It is concluded that 200 mg of intravenous ciprofloxacin every 12 hours is highly effective for bacteria with MICs less than 0.25 microgram/ml, but higher dosages may be required to eradicate organisms with higher MICs.

Clinical and economic evaluation of oral ciprofloxacin after an abbreviated course of intravenous antibiotics.

PURPOSE: Oral ciprofloxacin has the requisite pharmacokinetic and antibacterial properties to rival the potency of intravenous antibiotics. This study was designed to determine whether oral ciprofloxacin could abbreviate the course of intravenous antibiotics in the treatment of serious infections. PATIENTS AND METHODS: Hospitalized adult patients were eligible for enrollment if they had a serious infection that was expected to require 8 or more days of intravenous antibiotic treatment. After conventional intravenous antibiotics were administered for 3 days, informed consent was obtained and patients were randomly assigned to either continue parenteral antibiotics (n = 53) or switch to oral ciprofloxacin 750 mg taken twice daily (n = 52). Ninety-nine of the 105 patients were evaluable for the assessment of efficacy. Clinical and bacteriologic efficacy, adverse events, and costs of the two treatments were compared. RESULTS: The two treatment groups were comparable for demographic characteristics, types of infections, bacteria isolated, initial intravenous antibiotic regimens, and duration of antibiotic treatment. The most common infections were of the skin and skin structure; bacteremia and infections of the lower respiratory tract, urinary tract, and bone and joint were also represented. The most commonly isolated pathogens were Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The most frequently prescribed intravenous antibiotics before randomization included aminoglycosides, cephalosporins, vancomycin, and nafcillin; 52 evaluable patients were treated with combination therapy while 47 received monotherapy. The clinical and bacteriologic outcomes and adverse reaction frequency with oral ciprofloxacin were comparable to those of the continued intravenous antibiotic regimens. Ciprofloxacin was associated with an average cost savings of $293 per patient. CONCLUSION: When used after 3 days of intravenous antibiotics, oral ciprofloxacin was as safe and effective as full courses of intravenous antibiotics and provided substantial cost savings.

Changing the infection control paradigm from off-line to real time: the experience at Millard Fillmore Health System.

In 1993, several departments at Millard Fillmore Health System joined efforts to initiate a new approach to infection control. The main emphasis of this program is to move infection control to a real-time mode to manage patient outcomes daily. The principal objective was to decrease the number of nosocomial infections by 10%, with a particular emphasis on surgical-site infections. Besides real-time surveillance, we are critically evaluating several aspects of the management of nosocomial infections. High-level computer support has been the frame-work upon which this program was built. We have microcomputers that are linked directly to microbiology, pharmacy, billing, and admissions, downloading data several times daily. An expert software system merges all of the data, and from this we can target patients for real-time interventions. The computer system allows all inpatients to be screened for either infection control or antibiotic management interventions on a daily basis, with minimal time being spent on data collection and maximal efforts devoted to interventions at the bedside. Additionally, the infection management program will assist in maintaining the extraordinarily low expenditures on antimicrobial agents. During 1993, the Millard Fillmore Health System spent $924,884 on antibiotics, an amount approximately 50% that of comparably sized hospitals.

Changes in antimicrobial agent usage resulting from interactions among clinical pharmacy, the infectious disease division, and the microbiology laboratory.

Rapid reporting of culture and susceptibility data is the first of several important steps in the successful management of infected patients. As has been said many times, rapidly reported data are of little value unless the patient directly benefits. Benefit requires better overall communication and an action plan linked to timely use of these results. In 1989 the Millard Fillmore Hospital Antibiotic Review Committee developed and implemented a prototype approach to hospital wide antimicrobial management. The formulary was revised and the drug use evaluation process modified to enhance effectiveness and to lower the cost of therapy and inventory. Clinical pharmacy antimicrobial agent management specialists were then recruited to individualize patient treatments to the isolated pathogens in conjunction with the Division of Infectious Diseases. To provide the clinical pharmacy specialists with rapid and clinically useful information, a real-time computer link was created between the pharmacy (antibiotic orders) and the microbiology laboratory (culture results). Customized software was implemented to screen all patients automatically for mismatches between pathogens and drugs, or to screen for doses inappropriate to minimum inhibitory concentration or renal function. Special attention was paid to identification of opportunities to target a more appropriate narrow-spectrum regimen after culture results became available. Changes in antimicrobial regimen or dosage were made by contacting the prescribing physician. Over 90% of the recommended changes were made, and virtually all changed regimens had satisfactory clinical outcome. Real dollar expenditures for antimicrobial agents declined by > $200,000 per year. Prior to the institution of this computerized clinical management strategy, antimicrobial purchases were rising yearly at the rate of 12%-15%. The combined efforts of clinical pharmacy, microbiology, and infectious disease personnel successfully optimized antimicrobial therapy on a hospital wide basis. Antimicrobial agent optimization improved patient outcome, and the cost savings more than covered the costs of the program personnel and software.

Prolonged use of a diaphragm and toxic shock syndrome.

PIP: A case report is presented that involves the extended use of a contraceptive diaphragm and illustrates the problems in promptly establishing a clinical diagnosis of staphylococcal toxin syndrome. A 27-year old woman, 2 months postpartum, was admitted to the hospital after 24 hours of fever, shaking, chills, sweats, nausea and vomiting, and diminished urine output. She had been unable to remove a new coil spring diaphragm, used for the 1st time since parturition, for 3-1/2 days before admission. On the day of admission the diaphragm was removed with some difficulty. A purulent, foul-smelling vaginal discharge at the time the diaphragm was extracted was noted. She was lactating and had had no menses since conception. Her past medical history was unremarkable except for mitral valve prolapse. Evaluation at the time of admission was remarkable for a pulse rate of 120 beats/minute and orthostatic lightheadness. The blood pressure was 110/70 mm Hg when the patient was supine and fell less than 15 mm Hg systolic when she was seated. The white blood cell count was 17,000 with 63% segmented and 33% juvenile polymorphonuclear leukocytes. The sedimentation rate was 45 mm/hour. Multiple cultures of vagina, throat, urine, and blood were obtained. Vigorous intravenous fluid and electrolyte therapy was administered, and the patient was initially begun on ampicillin and tobramycin. Shortly after the appearance of the rash, staphylococcal toxic shock syndrome (TSS) was suspected, and the ampicillin was changed to oxacillin. The rash and strawberry tongue faded within 24 hours, and she became normotensive and afebrile by the 2nd hospital day. She was changed to oral dicloxacillin as the only antibiotic on the 4th hospital day, after the culture results were confirmed. At the time of discharge on the 6th hospital day, desquamation of the skin on the palms and soles had started and continued for another 7-10 days. A 10 day course of dicloxacillin was completed. Follow-up vaginal, cervical, and pharyngeal cultures 3 and 5 months later contained no S. aureus. The patient had resumed menstruation but was not using tampons or a diaphragm. Increased vigilance for the potential dangers of using vaginal occulusive devices when the lower genital tract is colonized by S. aureus is necessary.^ieng

Kinetics and dynamics of tobramycin action in patients with bacteriuria given single doses.

We studied the effect of a single intravenous dose of tobramycin on the rate of bacterial eradication from urine in 10 patients with bladder catheters. The catheter was replaced 4 to 6 h after the tobramycin dose. Pseudomonas aeruginosa was found in 7 of the 10 patients, while members of the family Enterobacteriaceae accounted for the remaining pathogens. The MIC for each bacterium was determined in both broth and urine. Tobramycin eradicated the bacteria from eight patients. Bacteriuria resolved in 21.8 +/- 18.0 h, and urine bactericidal activity persisted for 43.4 +/- 20.3 h after the dose of tobramycin. Most patients were recolonized by another bacterial species if use of Foley catheters was resumed on a continuous basis. Two patients required additional doses of tobramycin to eradicate the original pathogen. There were significant temporal relationships between the pharmacokinetics of tobramycin and the change in colony count of bacteria in urine.

Cefmenoxime in the treatment of nosocomial pneumonias in critical care patients.

Nephrotoxicity frequently complicates the use of aminoglycosides in severely compromised acute care patients. Therefore, we initiated an open clinical trial to determine if cefmenoxime alone is useful for serious Gram-negative pneumonias in this population. Thirty consecutive patients were studied. Average age was 66 years. Most were malnourished at entry, with serum albumin averaging 2.8 g/dl and prognostic nutritional index values over 70% (normal less than 40%). One-half of the patients had severe COPD and 67.9% were on ventilators. Fifty-seven per cent suffered concomitant cardiac disease, and 78.6% had been previously treated with antibiotics. Pneumonia was proven by new infiltrates on chest X-ray, new fever, elevated WBC count and Gram-negative rods on Gram's stain and in cultures of tracheal aspirate or sputum. Patients were given cefmenoxime 1-2 g every 6 h for an average of 12 days. Cefmenoxime peak (1 h) and trough concentrations were measured by HPLC and averaged 58 and 7 mg/l respectively. Gram-positive organisms, Escherichia coli, Klebsiella spp. and Haemophilus influenzae were usually eradicated. Persistence was noted for Enterobacter, Pseudomonas and Acinetobacter spp. Persistence in patients with good clinical response was considered colonization rather than superinfection. Overall, satisfactory clinical response rate was noted in 78.6%, while four patients responded satisfactorily with recurrence, and two treatments were unsatisfactory. No serious adverse effects were observed. Cefmenoxime is a promising agent for treatment of susceptible pneumonias in critical care patients.

Mathematical examination of dual individualization principles. (III): Development of a scoring system for pneumonia staging and quantitation of response to antibiotics: results in cefmenoxime-treated patients.

OBJECTIVE: In order to quantitatively express the important, time-related aspects of response to antimicrobial therapy in patients with pneumonia, we required validated measures of the time course of events during the infection. To quantitate the changes in clinical status in relation to changes in cultures, we developed a scoring system to be used for patient assessment during therapy. DESIGN: Retrospective data collection, prospective analysis of factors. SETTING: Intensive care unit, Millard Fillmore Hospital. PATIENTS: Twenty-eight patients with nosocomial pneumonia. MAIN OUTCOME MEASURES: Clinical parameters were assessed daily for the duration of antimicrobial therapy. Using linear regression, the rate of clinical change in each patient treated was quantified. Eradication of the pathogen was determined by serial cultures of the infection site. RESULTS: Seventeen of the patients demonstrated eradication of the organism, and 11 demonstrated persistence of the pathogen (7 were considered colonization). The system described the patients at baseline in that the mean baseline scores were similar in both groups of patients (p = 0.79). Patients in whom the pathogen was eradicated showed a rate of clinical improvement significantly different from those who had persistence of the organism (p = 0.04). In patients demonstrating eradication, the time to eradication inversely correlated with the rate of clinical improvement (p < 0.05). Of the ten parameters descriptive of the disease, those most sensitive to change after eradication of bacteria were body temperature, bacterial Gram stain, white blood cell Gram stain, and volume of sputum. CONCLUSIONS: In this set of pneumonia patients, the scoring system effectively quantified both baseline and time-related changes in clinical status. The system distinguished between the clinical course of the patient with organism eradication versus organism persistence. A shorter time to eradication was associated with a better clinical response. Prospective study of the system will determine its sensitivity.

Accumulation pharmacokinetics of tobramycin.

Tobramycin pharmacokinetics is usually described by a one-compartment model, but this model fails to account for both the incomplete urinary recovery and prolonged post-treatment persistence noted with this drug. We examined the multiple-dose behavior of tobramycin in 35 treated patients with stable renal function, using peak and trough serum concentrations, urine recovery, and postmortem tissue analysis. Serum concentrations rose slowly throughout treatment and declined in two phases after the drug was stopped. The first-phase half-life correlated well with renal function, but the second averaged 146 h and was poorly related to creatinine clearance. A two-compartment model was used to describe the biphasic decline in serum concentrations and to calculate the amount of drug in the tissue compartment at all times during and after treatment. Predicted tissue amounts rose continually throughout treatment in all study patients. In 5 patients, the total amount of tobramycin in the body after the final dose was recovered in the urine, but urine had to be collected for 10 to 20 days to achieve complete recovery of the drug. In four patients, the predicted tissue amount was recovered from postmortem tissues. Regardless of the dose, tobramycin accumulated in the tissues of all patients receiving this antibiotic. The two-compartment pharmacokinetic model explains both the rising peak and trough concentrations during treatment and the detection of the drug in serum and urine long after the last dose.

Gentamicin tissue accumulation and nephrotoxic reactions.

In 64 adults treated with gentamicin sulfate, peak and trough serum concentrations rose gradually and declined in two phases after the final dose. Seventeen patients experienced renal damage. The 17 patients had greater amounts of gentamicin in tissues even after the first dose and before any renal effects were noted. This pharmacokinetics analysis provided evidence that patients who experience gentamicin-related nephrotoxic effects while receiving recommended doses of gentamicin could be distinguished from patients with no toxic effects because they experienced abnormal tissue accumulation before detectable changes in renal function occurred.

Predicted tissue accumulation of netilmicin in patients.

The two-compartment pharmacokinetics of netilmicin were investigated in 11 patients with stable renal function who were being treated for gram-negative infections. The initial dosage of netilmicin ranged from 2.5 to 5.0 mg/kg per day, with subsequent changes made on the basis of serum concentrations. Venous blood samples were obtained every 2 to 4 days during therapy and daily for an average of 10 days after the final dose. Serum concentrations were measured by both microbiological assay and radioimmunoassay. Peak and trough netilmicin concentrations were significantly greater (P less than 0.01) at the end of therapy than at the first dose, even though renal function was stable throughout treatment in all patients. After the final dose, serum concentrations declined in a biphasic manner, with a first-phase half-life of 5.4 h and a terminal half-life of 198 h. The total body clearance averaged 31 ml/min. An average of 99 mg of netilmicin (approximately 5% of the total dose) was predicted to be in the tissue compartment at the end of therapy. A comparison of these pharmacokinetic parameters with those obtained in a previously reported but similar study with gentamicin showed no significant differences between the two aminoglycosides with respect to peak and trough concentrations (initially or at the end of therapy), volumes of distribution, total body clearance, or amount of drug in the tissue compartment at the end of therapy. The terminal half-life of netilmicin was significantly greater than that of gentamicin, whereas the rate constant of netilmicin for tissue influx (k12) was significantly less.

The development of a bedside algorithm capable of targeting anti-endotoxins to the responder subpopulations.

The published selection criteria for use of anti-endotoxin antibodies are modeled on the criteria used in protocol enrollment of patients. These criteria are not suitable for therapeutic decision-making, because the trials themselves prove that the enrollment criteria have both low sensitivity and low specificity. In order to develop a selection method with greater sensitivity and specificity, we examined the charts and records of 23 patients that we enrolled in the multicenter trials of E5 and HA-1A. We retrospectively determined that seven of our 23 enrolled patients were optimal candidates, based on a pattern of rapid clinical deterioration followed by improvement in 24-96 h. We then explored a variety of different modes of bedside patient selection, in search of a method to select as many of the seven optimal candidates as possible while at the same time rejecting the greatest number of the 16 who showed no benefit when treated. None of the resulting selection methods has perfect performance, but nearly all were better than the original protocol enrollment criteria. In our patients, bacteremia had 57% sensitivity and 56% specificity, which was quite similar to the findings in the HA-1A multicenter trial. Shock had 100% sensitivity and 44% specificity, while a baseline organ dysfunction score of > or = 5 had 100% sensitivity and 69% specificity. A new algorithm that we developed based on a patient's need for vasopressors and baseline organ dysfunction had 100% sensitivity and 81% specificity. This algorithm could identify all seven of the optimal candidates, plus three more.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue persistence of gentamicin in man.

A two-compartment pharmcokinetic model was used to caracterize serum concentrations and to predict tissue accumulation of gentamicin in 47 treated patients. Postmortem tissues were obtained in six cases; in each instance, tissues yielded the predicted amount of drug. Slow release of tissue-bound gentamicin accounts for its prolonged retention in the body. The two-compartment model adequately predicts gentamicin accumulation from serum concentrations and explains why this antibiotic persists in serum and urine.

Genesis of methicillin-resistant Staphylococcus aureus (MRSA), how treatment of MRSA infections has selected for vancomycin-resistant Enterococcus faecium, and the importance of antibiotic management and infection control.

We extensively studied the epidemiology and time course of endemic methicillin-resistant Staphylococcus aureus (MRSA) in the Millard Fillmore Hospital, a 600-bed teaching hospital in Buffalo. The changeover from methicillin-susceptible S. aureus to MRSA begins on the first hospital day, when patients are given cefazolin as presurgical prophylaxis. Under selective antibiotic pressure, colonizing flora change within 24 to 48 hours. For patients remaining hospitalized, subsequent courses of third-generation cephalosporins further select and amplify the colonizing MRSA population. Therefore, managing antibiotic selective pressure might be essential. Other strategies include attention to dosing, so that serum concentrations of drug exceed the minimum inhibitory concentration, and antibiotic cycling. Although there are some promising new antibiotics on the horizon, it is necessary to deal with many resistance patterns by using the combined strategies of infection control and antibiotic management.

Mathematical examination of dual individualization principles (II): The rate of bacterial eradication at the same area under the inhibitory curve is more rapid for ciprofloxacin than for cefmenoxime.

OBJECTIVE: To compare two antibiotics at equal ranges of area under the inhibitory curve (AUIC) exposure to determine if the rate of bacterial eradication differed between these antibiotics. DESIGN: Retrospective comparison of two previously collected studies of similar patients with nosocomial pneumonia. SETTING: Hospitalized patients, most intubated in critical care units with nosocomial pneumonia. PARTICIPANTS: Patients treated with either i.v. ciprofloxacin (n = 74) or the i.v. third-generation cephalosporin cefmenoxime (n = 43) were compared for their length of treatment required to eradicate bacterial pathogens from their respective infection sites, using serial cultures from the site of infection. All patients were also assessed for clinical outcomes. Serum samples were obtained to evaluate individual patient antibiotic pharmacokinetics, which were used to model pharmacodynamics of response. The HPLC assay used for each antibiotic had interday coefficients of variation < 10 percent. Serum concentration versus time profiles were fit using the computer program ADAPT II to determine pharmacokinetic parameters for each patient. The primary drug exposure measure that related to response was the AUIC, calculated as steady-state AUC0-24/minimum inhibitory concentration. RESULTS: AUIC values in the patients ranged from 6.0 to more than 7000, yet the AUIC value was highly predictive of time to bacterial eradication (p < 0.001). Although more than 75 percent of patients eventually achieved eradication of pathogens from tracheal aspirate cultures, ciprofloxacin and cefmenoxime differed significantly in the time required to sterilize these cultures. At appropriate AUIC values (> 250) for ciprofloxacin, the median time to eradication was two days, while cefmenoxime (also at AUIC values > 250) required six days to achieve the same result. CONCLUSIONS: We conclude that the more rapid in vitro bacterial killing, which is characteristic of ciprofloxacin at optimal AUIC values, can manifest in vivo as more rapid clearance of bacteria from the respiratory tract of patients, even when both agents are controlled for initial antibacterial exposure (i.e., same AUIC).

In nosocomial pneumonia, optimizing antibiotics other than aminoglycosides is a more important determinant of successful clinical outcome, and a better means of avoiding resistance.

In in vitro and animal models, antibiotics show good relationships between concentration and response, when response is quantified as the rate of bacterial eradication. The strength of these in vitro relationships promises their utility for dosage regimen design and predictable cure of infections such as nosocomial pneumonia. In spite of their intuitive logic, close relationships between dosage and bacterial eradication have not been easy to show in clinical studies of nosocomial pneumonia. Presumably, a variety of patient, disease, bacterial, and pharmacokinetic variables cloud these relationships in patients, and delay their elucidation in patient trials. Patients with serious infections like nosocomial pneumonia require bactericidal antimicrobial activity. Studies in our laboratory show that the minimum effective antimicrobial action is an area under the inhibitory titer (AUIC) of 125, in which AUIC is calculated as the 24 hour serum area under the curve (AUC) divided by the minimum inhibitory concentration (MIC) of the pathogen. This target AUIC may be achieved with either a single antibiotic or it can be the sum of AUIC values of two or more antibiotics. There is considerable variability in the actual AUIC value for patients when antibiotics are administered in their usual recommended dosages. Examples of this variance will be provided using aminoglycosides, fluoroquinolones, and beta-lactams. The achievement of minimally effective antibiotic action, consisting of an AUIC of at least 125, is associated with bacterial eradication in about 7 days for beta-lactams and quinolones. Adding an aminoglycoside to beta-lactams may produce a slight increase in their rate of bacterial killing in vivo, but because of their narrow therapeutic window, and the associated low doses in relation to MIC, there are situations in which the aminoglycosides may be unable to add sufficient additional AUIC. Antibiotic activity indices allow clinicians to evaluate individualized patient regimens. Furthermore, antibiotic activity is a predictable clinical endpoint with predictable clinical outcome. This value also is highly predictive of the development of bacterial resistance. Antimicrobial regimens that do not achieve an AUIC of at least 125 cannot prevent the selective pressure that leads to overgrowth of resistant bacterial subpopulations. The methods based on the determination of AUIC have clinical applicability in routine practice, through software developed for this purpose. These indices can assist with patient management strategies in a prospective manner because they can identify patients at high risk of therapeutic failure or acquired resistance early in therapy before therapy fails. Our studies show that calculations of AUIC can be used to prospectively target regimens to improve the chances of cure with nosocomial pneumonia and other serious infections. A clinical intervention team has been organized to optimize antimicrobial regimens as early in therapy as possible, to lower the high cost events such as failure and acquired bacterial resistance.