Drug therapy. Serum bactericidal activity as a monitor of antibiotic therapy

In Vitro Susceptibility Tests in the Context of Antifungal Resistance: Beyond Minimum Inhibitory Concentration in Candida spp

Antimicrobial resistance is a matter of rising concern, especially in fungal diseases. Multiple reports all over the world are highlighting a worrisome increase in azole- and echinocandin-resistance among fungal pathogens, especially in Candida species, as reported in the recently published fungal pathogens priority list made by WHO. Despite continuous efforts and advances in infection control, development of new antifungal molecules, and research on molecular mechanisms of antifungal resistance made by the scientific community, trends in invasive fungal diseases and associated antifungal resistance are on the rise, hindering therapeutic options and clinical cures. In this context, in vitro susceptibility testing aimed at evaluating minimum inhibitory concentrations, is still a milestone in the management of fungal diseases. However, such testing is not the only type at a microbiologist's disposal. There are other adjunctive in vitro tests aimed at evaluating fungicidal activity of antifungal molecules and also exploring tolerance to antifungals. This plethora of in vitro tests are still left behind and performed only for research purposes, but their role in the context of invasive fungal diseases associated with antifungal resistance might add resourceful information to the clinical management of patients. The aim of this review was therefore to revise and explore all other in vitro tests that could be potentially implemented in current clinical practice in resistant and difficult-to-treat cases.

Successful Treatment of Aortic Endocarditis by Achromobacter xylosoxidans with Cefiderocol Combination Therapy in a Non-Hodgkin Lymphoma Patient: Case Report and Literature Review

Achromobacter xylosoxidans is a Gram-negative aerobic opportunistic bacterium, belonging to the order of Burkholderiales, that can cause infections of virtually all body districts in patients with underlying diseases. However, A. xylosoxidans has rarely been associated with infective endocarditis. The treatment of A. xylosoxidans infections is complicated by both intrinsic and acquired resistance. Here we report on a case of aortic endocarditis by A. xylosoxidans in a Non-Hodgkin lymphoma patient treated with a combination of cefiderocol and other antibiotics, and summarize the available literature.

Serum bactericidal titres for monitoring antimicrobial therapy: current status and potential role in the management of multidrug-resistant Gram-negative infections

BACKGROUND

Serum bactericidal titres (SBTs) were widely used in the 1970s and 1980s to monitor antimicrobial therapy but are now seldom recommended. It is the only laboratory test that integrates drug pharmacodynamics, host pharmacokinetics and synergistic or antagonistic interactions of antimicrobial combinations into a single index of antimicrobial activity. We hypothesized that SBTs could play a renewed role in monitoring antibiotic treatment of multidrug-resistant Gram-negative infections. However, the last critical appraisal of the test was published over 30 years ago.

OBJECTIVES

This narrative review provides an updated assessment of the SBT test and its methodological limitations. We performed a diagnostic meta-analysis to estimate the value of SBTs for predicting clinical failure or death during antibiotic treatment.

SOURCES

A comprehensive literature search of PubMed including all English publications was performed in December 2019 using the Medical Subject Headings (MeSH search terms "serum", "bactericidal", "inhibitory", "titre", "monitoring", "anti-infective agents" "antimicrobial therapy" and "therapeutic drug monitoring").

CONTENT

Although standardized methods for performing SBTs were approved in 1999, the test remains labour intensive, and results may not be available until 72 hr. However, the use of non-culture-based endpoints (i.e. spectrophotometric or fluorescent) may shorten test time to 24 hr. Despite considerable heterogeneity in published studies, a meta-analysis of 11 evaluable studies published from 1974 to 2007 indicated a critical SBT result (peak SBT ≤1:8 or trough ≤1:2) is associated with a diagnostic odds ratio for clinical failure during antibiotic treatment of 12.27 (95% confidence interval 5.28-28.54) and a 5.32 (95% 1.32-21.42) odds of death.

IMPLICATIONS

SBTs have prognostic value for identifying patients at high risk for antibiotic treatment failure, but the slow turnaround time of the current test limits its clinical utility. Standardization of a more rapid SBT testing method is needed.

Antibiotic Treatment of Chronic Central Venous Hemodialysis Catheter inFection without Catheter Removal

Most catheter or shunt infections in hemodialysis patients require the removal of the access before the infection is eradicated. A hemodialysis patient is reported who had multiple previous vascular accesses which failed and thus who had very limited sites for future access placement. When a recurrent Proteus mirabilis catheter infection occurred, a 6-week course of ampicillin intraluminal and tobramycin systematically, eradicated the infection and thus the central venous catheter was salvaged. Serum bactericidal levels with these two antibiotics were obtained early in the course and supported the continued use of antibiotics alone to treat the infection.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. As resistance continues to emerge among a wide range of clinically relevant bacteria, the complexity of this communication increases. This updated version provides an overview of the important susceptibility concerns for most commonly isolated bacterial pathogens.

Predictive value of the serum bactericidal test for mortality in patients infected with multidrug-resistant Acinetobacter baumannii

OBJECTIVE

Strains of Acinetobacter baumannii resistant to all available antibiotics except polymyxin B have circulated in Taiwan since 1998 and have caused a variety of nosocomial infections. There are no standard tests to measure outcome in patients infected with these strains. Our aim was to determine whether a serum bactericidal test (SBT) could be used for this purpose.

METHODS

This SBT was performed in 57 infected patients.

RESULTS

Among the 35 patients who survived and 22 patients who died, peak SBT titer negatively correlated with mortality rate (correlation coefficient -0.43). The survival rate in patients with a peak SBT titer > or = 1:16, > or = 1:8, and < or = 1:4 was 100%, 87.5%, and 42.4%, respectively (p=0.001). Mortality was found to be closely related to illness severity and the presence of multiple organ failure. In subgroup analysis, the power of SBT to predict mortality was significant for patients without multiple organ failure (p=0.004), and also patients without disease defined as rapidly fatal by McCabe classification (p=0.044).

CONCLUSION

In a region with few therapeutic options for multi-drug resistant Acinetobacter baumannii (MDRAB), such as in Taiwan, SBT could be used as a prognosis indicator and indicator of the need to modify treatment in patients infected with MDRAB.

Antibacterial activity of remifentanil and mixtures of remifentanil and propofol

STUDY OBJECTIVE

To investigate the antibacterial activity of glycine, which is contained in remifentanil, when combined with propofol.

DESIGN

Prospective study.

SETTING

Departments of anesthesiology and microbiology of a university hospital.

MEASUREMENTS

Growth of the microorganisms Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans in propofol 1%; saline dilutions of remifentanil at one-, 10-, and 100-microg/mL concentrations; and 1:1 mixtures of propofol with remifentanil solutions was determined.

MAIN RESULTS

Remifentanil inhibits bacterial growth in a concentration-dependent manner. The antibacterial effects were more pronounced with Staphylococcus aureus and Pseudomonas aeruginosa at cultures obtained at the fifth hour. The inhibition of bacterial growth was less influenced with Escherichia coli and Candida albicans.

CONCLUSIONS

Propofol and remifentanil mixtures decreased bacterial growth, and combinations may reduce the infectious complications from accidentally contaminated propofol.

The Importance of Bactericidal Drugs: Future Directions in Infectious Disease

BACKGROUND

Although a considerable amount of research has gone into the study of the role of bactericidal versus bacteriostatic antimicrobial agents in the treatment of different infectious diseases, there is no accepted standard of practice.

METHODS

A panel of infectious diseases specialists reviewed the available literature to try to define specific recommendations for clinical practice.

RESULTS

In infections of the central nervous system, the rapidity with which the organism is killed may be an important determinant, because of the serious damage that may occur during these clinical situations. The failure of bacteriostatic antibiotics to adequately treat endocarditis is well documented, both in human studies and in animal models.

CONCLUSION

The bulk of the evidence supports the concept that, in treating endocarditis and meningitis, it is important to use antibacterial agents with in vitro bactericidal activity. This conclusion is based on both human and animal data. The data to support bactericidal drugs' superiority to bacteriostatic drugs do not exist for most other clinical situations, and animal models do not support this concept in some situations. Clinicians should be aware that drugs that are bacteriostatic for one organism may in fact be bactericidal for another organism or another strain of the same organism.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. The emergence of resistance in nearly all commonly isolated bacterial organisms has highlighted the need for ongoing dialogue between the laboratory and those who use its services.

Concentrations of moxifloxacin in serum and synovial fluid, and ex vivo bactericidal activity against arthritis-causing pathogens

Three doses of moxifloxacin 400 mg qd were administered orally to 20 candidates for knee arthroscopy (mean age, 71.2 years). The procedure was scheduled at four different points of time after the last dose: 2, 6, 12, and 24 h. Five patients were studied at each point of time. Drug levels were determined by the bioassay method. Bactericidal activity against four bacterial pathogens (two strains of each) was studied on serum and synovial fluid samples obtained during arthroscopy using the NCCLS guidelines. Mean (+/-S.D.) peak serum and synovial fluid concentrations were 3.46 +/- 0.78 mg/L and 3.42 +/- 0.51 mg/L, respectively. Levels above 1.0 mg/L were detected as long as 24 h. The peak bactericidal titers were (in serum and synovial fluid, respectively) 1:18.3 and 1:32 against Staphylococcus aureus, 1:18.3 and 1:22.6 against Streptococcus pyogenes, 1:45.2 and 1:64.0 against Klebsiella pneumoniae, and 1:2.3 and 1:1.7 against Pseudomonas aeruginosa. Bactericidal titers >1:2 were documented against the first three pathogens up to 24 h after dosing. On the basis of its pharmacokinetic and pharmacodynamic characteristics, moxifloxacin seems to be an excellent candidate for the treatment of joint infections, except those caused by P. aeruginosa.

Serum bactericidal activity of trovafloxacin, in combination with cefepime or amikacin, in healthy volunteers

OBJECTIVE

To investigate the phamacokinetics and serum bactericidal activities (SBAs) of trovafloxacin, cefepime and amikacin alone and trovafloxacin in combination with cefepime or amikacin, so that the most favorable combination with trovafloxacin can be determined.

METHODS

In this open, randomized, crossover study, 12 healthy volunteers (six females, six males; mean age +/- SD, 25.1 +/- 2.6 years) received an infusion of either 300 mg of alatrovafloxacin or 2000 mg of cefepime or 6 mg/kg body weight amikacin alone, or 300 mg of alatrovafloxacin plus 2000 mg of cefepime or plus 6 mg/kg body weight amikacin. The SBAs against Pseudomonas aeruginosa, Staphylococcus aureus (11 strains each), Citrobacter freundii and Acinetobacter spp. (10 strains each) 1, 10 and 24 h after drug administration were measured by a standard microdilution method. Concentrations of trovafloxacin, cefepime and amikacin in serum and urine were analyzed before and up to 10 and 12 h, respectively, after drug infusion.

RESULTS

Significant synergistic effects on SBA were observed with the combination of trovafloxacin and cefepime against P. aeruginosa, S. aureus and Acinetobacter spp. 1 h after drug administration, and against Citrobacter freundii 1, 10 and 24 h after drug administration. The combination of trovafloxacin and amikacin showed significant synergistic effects against P. aeruginosa, S. aureus and C. freundii 1 h after drug administration. The combination of trovafloxacin and cefepime was, in general, more active than the combination of trovafloxacin and amikacin. No significant differences in the serum concentrations of trovafloxacin were observed between single and combined administration. However, the maximal concentration of cefepime was significantly lower when it was used in combination with trovafloxacin.

CONCLUSION

Our study suggests a favorable interaction between trovafloxacin and cefepime. This combination showed more synergistic bactericidal activity against most of the test strains compared to the combination of trovafloxacin and amikacin. However, for P. aeruginosa, the bactericidal activity of cepefime alone was higher than that of the combination with trovafloxacin.

Bactericidal activities of methoxyfluoroquinolones gatifloxacin and moxifloxacin against aerobic and anaerobic respiratory pathogens in serum

Gatifloxacin (Bristol-Myers Squibb) and moxifloxacin (Bayer) are new methoxyfluoroquinolones with broad-spectrum activity against aerobic and anaerobic pathogens of the respiratory tract. In this investigation, we analyzed the bactericidal activity in serum over time of these antimicrobials against three aerobic (Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus) and four anaerobic (Peptostreptococcus micros, Peptostreptococcus magnus, Fusobacterium nucleatum, and Prevotella melaninogenica) bacteria associated with respiratory tract infections. Serum samples were obtained from 11 healthy male subjects following a single 400-mg oral dose of gatifloxacin and moxifloxacin. These samples were collected prior to and at 2, 6, 12, and 24 h after the dose of each drug. Gatifloxacin exhibited bactericidal activity for a median of 12 h against Streptococcus pneumoniae (MIC = 0.5 micro g/ml), Peptostreptococcus micros (MIC = 0.25 micro g/ml), and F. nucleatum (MIC = 0.5 micro g/ml) and 24 h against H. influenzae (MIC = 0.03 micro g/ml), Staphylococcus aureus (MIC = 0.125 micro g/ml), Peptostreptococcus magnus (MIC = 0.125 micro g/ml), and Prevotella melaninogenica (MIC = 0.5 micro g/ml). Moxifloxacin exhibited bactericidal activity for a median of 24 h against Streptococcus pneumoniae (MIC = 0.125 micro g/ml), H. influenzae (MIC = 0.015 micro g/ml), Staphylococcus aureus (MIC = 0.06 micro g/ml), F. nucleatum (MIC = 0.5 micro g/ml), Prevotella melaninogenica (MIC =0.5 micro g/ml), Peptostreptococcus magnus (MIC = 0.125 micro g/ml), and Peptostreptococcus micros (MIC = 0.25 micro g/ml). The results from this pharmacodynamic study suggest that these fluoroquinolones would have prolonged killing activity against these organisms in vivo and may have clinical utility in the treatment of mixed aerobic-anaerobic respiratory tract infections.

Rapid imipenem/cilastatin desensitization for multidrug-resistant Acinetobacter pneumonia

OBJECTIVE

To report a successful case of rapid imipenem desensitization in a critically ill patient with multidrug-resistant Acinetobacter baumannii ventilator-associated pnemonia (VAP).

CASE SUMMARY

A 40-year-old white man who had a lengthy stay in the intensive care unit (ICU) following a motorcycle accident developed VAP caused by A. baumannii. treatment with imipenem was necessary due to the bacteria's resistance to all other antibiotics. However, this patient was diagnosed with an allergy to imipenem following exposure earlier in his hospitalization in addition to a positive penicillin skin test. Thus, we attempted rapid desensitization to imipenem using a continuous infusion protocol. The patient was desensitized within 4 hours and was successfully treated for 21 days with a continuous infusion of imipenem combined with daily amikacin. He experienced no adverse reaction during the desensitization process or the remainder of his treatment course.

DISCUSSION

The protocol used in this case was modified from a previously reported case, and differed in the speed of desensitization and total daily dose. We assumed that a more gradual escalation of the dose in our modified protocol would prevent the occurrence of adverse events, thereby resulting in more rapid desensitization. Rapid desensitization was necessary in this patient due to the presence of a life-threatening infection. The lower total daily dose of imipenem was in response to impaired renal function.

CONCLUSIONS

Therapeutic options for multidrug-resistant pneumonia in the ICU are significantly limited in the presence of imipenem allergy. An option of last resort is to desensitize the patient using a rapid administration protocol. Our modified rapid imipenem desensitization protocol was successful and allowed for effective treatment of life-threatening pneumonia.

Serum bactericidal activity of extended-release clarithromycin against macrolide-resistant strains of Streptococcus pneumoniae

STUDY OBJECTIVE

To investigate the serum bactericidal activity (SBA) over time of extended-release clarithromycin against moderately resistant strains of Streptococcus pneumoniae.

DESIGN

Prospective, single-dose pharmacodynamic study.

SETTING

University-affiliated research center.

SUBJECTS

Eleven healthy male volunteers.

INTERVENTION

All volunteers received a single dose of extended-release clarithromycin as two 500-mg tablets, and blood samples were obtained at 0, 2, 6, 12, and 24 hours after administration of the dose.

MEASUREMENTS AND MAIN RESULTS

For each blood sample, a serum bactericidal titer (SBT) was determined against S. pneumoniae strains with minimum inhibitory concentrations (MICs) of 0.5, 1.0, 2.0, 4.0, and 8.0 microg/ml to clarithromycin. The median SBT was determined for each time period. The extended-release formulation of clarithromycin exhibited SBA for 24 hours against pneumococcal strains with MICs of 0.5, 1.0, and 2.0 microg/ml. No SBA was observed against isolates with MICs of 4.0 or 8.0 microg/ml.

CONCLUSION

The extended-release formulation of clarithromycin, taken once/day, will provide SBA for 24 hours against strains of S. pneumoniae with MICs of 2.0 microg/ml or less.

Antibacterials for the prophylaxis and treatment of bacterial endocarditis in children

Although the overall incidence of infective endocarditis in the paediatric population is considered to be low, over the last 20 years a rising trend in infective endocarditis has been observed among children. This could be due to several reasons including the availability of improved diagnostic techniques, use of continuous central venous catheters and cardiac implants increasing the risk of infection, and the survival of a greater number of infants with congenital heart disease as a result of improved medical management. The predominant causative organisms of paediatric endocarditis include staphylococci and streptococci. There is increased concern surrounding the emergence of endocarditis in children caused by methicillin-resistant Staphylococcus aureus and drug resistant strains of Streptococcus pneumoniae. The treatment approach to paediatric endocarditis is similar to that for adult patients with endocarditis because of similarities in disease pathogenesis and aetiology. The therapeutic goal is to achieve sterilisation of the cardiac vegetations. The choice of antibacterial is dependent upon the susceptibility profile of the causative organism. Vancomycin or gentamicin is recommended for enterococcal endocarditis, according to guidelines from the American Heart Association. For staphylococcal endocarditis in patients with no prosthetic valve, oxacillin or nafcillin with or without gentamicin is the treatment of choice. In the case of endocarditis caused by methicillin-resistant S. aureus, vancomycin is commonly used in patients with no prosthetic valve and a combination of vancomycin, gentamicin and rifampicin (rifampin) for patients with prosthetic material. Cefazolin or ceftriaxone is the treatment of choice for penicillin allergic paediatric patients with endocarditis caused by viridans streptococci. While there have been no major changes in endocarditis therapy for the last decade, the current focus is on the recognition of multiple-drug resistant pathogens and the use of newer agents such as quinupristin/dalfopristin in the treatment of resistant bacterial endocarditis. Prophylactic antibacterial therapy is recommended for procedures thought to be associated with the occurrence of bacteraemia involving organisms commonly associated with endocarditis. These include dental extractions and oral, respiratory tract, genitourinary, gastrointestinal or oesophageal procedures. Prophylactic antibacterials recommended by the American Heart Association during genitourinary and gastrointestinal surgical procedures in high risk patients include ampicillin + gentamicin or vancomycin + gentamicin in high risk patients with penicillin allergy. Ampicillin has been recommended for prophylaxis of bacterial endocarditis in children undergoing oral, respiratory tract or oesophageal procedures. In the case of penicillin allergy in these patients, cephalosporins, clindamycin, azithromycin or clarithromycin have been recommended. The general consensus is that antibacterial prophylaxis during dental procedure is unnecessary, and in fact propagates bacterial resistance.

Outpatient parenteral antimicrobial therapy (OPAT) for the treatment of osteomyelitis: evaluation of efficacy, tolerance and cost

OBJECTIVES

To evaluate the feasibility, efficacy, and cost of outpatient parenteral antimicrobial therapy (OPAT) in the treatment of osteomyelitis.

SUBJECTS

39 patients with an osteomyelitis requiring parenterally administered antibiotics for more than 4 weeks, and able to receive antibiotics at home.

METHODS

All patients had a totally implanted catheter. Antibiotics were administered by continuous infusion using a portable elastomeric infusion system, which was changed every day by the patient or by the home-care nurse. Laboratory monitoring and surveillance were performed weekly. Clinical efficacy, adverse effects and quality of life were recorded.

RESULTS

The most commonly used antibiotics were vancomycin (51%) and beta-lactam (44%) antibiotics. Thirty patients were available for follow-up for a minimum of 12 months after completion of therapy. Twenty-eight (93%) were considered cured of their infection with a mean of 24 +/- 4 months after completion of antibiotic therapy. Adverse effects among the study patients were rare. The 39 patients in our OPAT programme resulted in a potential saving of US $1 873 885 relative to conventional therapy.

CONCLUSION

OPAT is practicable and effective and may be the best alternative treatment for patients suffering from osteomyelitis requiring intravenous therapy.

Influence of diminished susceptibility of Streptococcus pneumoniae to ciprofloxacin on the serum bactericidal activity of gemifloxacin and trovafloxacin after a single dose in healthy volunteers

The serum bactericidal activity against 2 Streptococcus pneumoniae strains (ciprofloxacin MIC 1 and 4 mg/l) was measured in 12 volunteers who received oral single doses of gemifloxacin 320 mg and trovafloxacin 200 mg in a crossover fashion. The 4-fold increase in ciprofloxacin MIC from the susceptible to the resistant strain resulted in a 2-fold increase in MIC (from 0.015 to 0.03 mg/l), a 2-fold decrease in C(max)/MIC (104 vs 52) and in AUC(0-24 h)/MIC (532 vs 266), but a 5.6-fold decrease in area under the bactericidal curve (AUBC: 168 vs 30) for gemifloxacin. Trovafloxacin showed a 4-fold higher MIC (0.25 vs 0.06 mg/l), a 4-fold lower C(max)/MIC (8.6 vs 36), a 4-fold lower AUC(0-24 h)/MIC (85 vs 356) and a 11-fold lower AUBCs (2 vs 22) against the resistant isolate compared with the susceptible one. Trovafloxacin serum bactericidal titres against the ciprofloxacin-resistant strain were measurable generally only at 1 h after dosing (median titre=2). Gemifloxacin showed similar ex vivo bactericidal activity against the ciprofloxacin-resistant strain to that of trovafloxacin against the ciprofloxacin-susceptible strain.

Comparative serum bactericidal activity of clarithromycin and azithromycin against macrolide-sensitive and resistant strains of Streptococcus pneumoniae

The serum pharmacodynamics of clarithromycin and azithromycin were studied against isolates of S. pneumoniae, including efflux resistant (M. phenotype) strains, by analyzing their serum bactericidal activity (SBA) over time. Normal healthy subjects were given a single 500 mg oral dose of these macrolides and serum samples were collected over 12 hrs. Paired isolates with MICs ranging from 0.25 ug/ml to 8.0 ug/ml were analyzed. Prolonged (at least 6 hrs) SBA was observed with clarithromycin for strains with MICs < or = 2.0 ug/ml. No SBA was observed in strains with MICs >or = 4.0 ug/ml. Azithromycin exhibited SBA for at least 6 hrs for strains up to a MIC = 0.5 ug/ml. No SBA was observed for isolates with MICs > or = 1.0 ug/ml. In contrast to azithromycin, clarithromycin exhibited SBA for at least one-half of its normal dosing interval against S. pneumoniae strains well above its current susceptibility breakpoint concentration of 0.25 microg/ml. These findings may have relevance to the ongoing debate as to the appropriate susceptibility breakpoints for the newer macrolides.

Monitoring the treatment of sepsis with vancomycin in term newborn infants

A prospective study was conducted to determine if standardized vancomycin doses could produce adequate serum concentrations in 25 term newborn infants with sepsis.

PURPOSE

The therapeutic response of neonatal sepsis by Staphylococcus sp. treated with vancomycin was evaluated through serum concentrations of vancomycin, serum bactericidal titers (SBT), and minimum inhibitory concentration (MIC).

METHOD

Vancomycin serum concentrations were determined by the fluorescence polarization immunoassay technique, SBT by the macro-broth dilution method, and MIC by diffusion test in agar.

RESULTS

Thirteen newborn infants (59.1%) had adequate peak vancomycin serum concentrations (20 - 40 mg/mL) and one had peak concentration with potential ototoxicity risk (>40 microg/mL). Only 48% had adequate trough concentrations (5 - 10 mg/mL), and seven (28%) had a potential nephrotoxicity risk (>10 microg/mL). There was no significant agreement regarding normality for peak and trough vancomycin method (McNemar test : p = 0.7905). Peak serum vancomycin concentrations were compared with the clinical evaluation (good or bad clinical evolution) of the infants, with no significant difference found (U=51.5; p=0.1947). There was also no significant difference between the patients' trough concentrations and good or bad clinical evolution (U = 77.0; p=0.1710). All Staphylococcus isolates were sensitive to vancomycin according to the MIC. Half of the patients with adequate trough SBT (1/8), also had adequate trough vancomycin concentrations and satisfactory clinical evolution.

CONCLUSIONS

Recommended vancomycin schedules for term newborn infants with neonatal sepsis should be based on the weight and postconceptual age only to start antimicrobial therapy. There is no ideal pattern of vancomycin dosing; vancomycin dosages must be individualized. SBT interpretation should be made in conjunction with the patient's clinical presentation and vancomycin serum concentrations. Those laboratory and clinical data favor elucidation of the probable cause of patient's bad evolution, which would facilitate drug adjustment and reduce the risk of toxicity or failing to achieve therapeutic doses.

Levofloxacin pharmacokinetics and serum bactericidal activities against five enterobacterial species

After oral administration of 500 mg of levofloxacin to 12 volunteers, we investigated the pharmacokinetics and serum bactericidal activities (SBAs) against five strains of members of the family Enterobacteriaceae. Pharmacokinetic data were as follows: maximum concentration in serum, 6.36 +/- 0.57 mg/liter; area under the concentration-time curve, 43.6 +/- 6.23 mg. h/liter; elimination half-life 4.23 +/- 0.87 h. SBAs were present for 24 h against Escherichia coli and Citrobacter freundii. The SBAs at 1, 12, and 24 h after administration against E. coli were 1:108, 1:29, and 1:7, respectively, and those against Citrobacter freundii were 1:74, 1:25, and 1:7, respectively. The SBAs were present for 12 h against the other three organisms tested. The SBAs against Serratia marcescens were 1:28 and 1:9 at 1 and 12 h, respectively; the SBAs against Klebsiella pneumoniae were 1:25 and 1:7 at 1 and 12 h, respectively; and the SBAs against Enterobacter cloacae were 1:24 and 1:10 at 1 and 12 h, respectively.

Pharmacodynamic effects of amoxicillin versus cefotaxime against penicillin-susceptible and penicillin-resistant pneumococcal strains: a phase I study

Serum bactericidal activity against a penicillin-susceptible strain and a penicillin-resistant strain of Streptococcus pneumoniae (amoxicillin and cefotaxime MICs, 0.001 and 1 microg/ml, respectively, and MBCs, 0.01 and 2 microg/ml, respectively) was measured in 12 healthy volunteers who each received an oral 875-mg dose of amoxicillin and an intramuscular 1-g dose of cefotaxime in a crossover fashion. The areas under the bactericidal activity-time curves for the two strains were found to be similar for both antibiotics despite the significantly higher (P < 0.002) AUC/MIC and peak level/MIC values for cefotaxime.

Therapeutic Drug Monitoring of Therapy for Infectious Diseases

Optimal use of antimicrobial agents is dependent on a multitude of factors. Empiric therapy should be based on the patient's underlying disease states, the most likely organisms suspected, and susceptibility patterns. Once susceptibilities are known, therapy should be streamlined. A number of factors must be evaluated during therapy. The site of infections must be considered when choosing antimicrobial agents. The minimum inhibitory concentration (MIC) should be evaluated; the antimicrobial agent's MIC should be at or below the breakpoint for the organism to be considered susceptible. Antimicrobial agent selec tion and dosing should take into consideration not only the MIC, but also the post-antibiotic effect, if appli cable. Serum concentrations of antimicrobial agents should be obtained and evaluated to ensure thera peutic levels and to avoid potential toxicities. The choice of an antimicrobial agent is complicated by the emergence of antibiotic resistance. Drug-resistant gram-positive and gram-negative infections are in creasing. We must attempt to control resistance by choosing appropriate antimicrobial agents and maxi mizing dosages. Pharmacists can play a critical role in the management of patients who receive antimi crobial agents.

Serum bactericidal activities and comparative pharmacokinetics of meropenem and imipenem-cilastatin

The pharmacokinetics and serum bactericidal activities (SBAs) of imipenem and meropenem were investigated in a randomized crossover study. Twelve healthy male volunteers received a constant 30-min infusion of either 1 g of imipenem plus 1 g of cilastatin or 1 g of meropenem. The concentrations of the drugs in serum and urine were determined by bioassay and high-pressure liquid chromatography. Pharmacokinetic parameters were based on an open two-compartment model and a noncompartmental technique. At the end of infusion, the mean concentrations of imipenem and meropenem measured in serum were 61.2 +/- 9.8 and 51.6 +/- 6.5 mg/liter, respectively; urinary recoveries were 48.6% +/- 8.2% and 60.0% +/- 6.5% of the dose in 12 h, respectively; and the areas under the concentration-time curve from time zero to infinity were 96.1 +/- 14.4 and 70.5 +/- 10.3 mg.h/liter, respectively (P < or = 0.02). Imipenem had a mean half-life of 66.7 +/- 10.4 min; that of meropenem was 64.4 +/- 6.9 min. The volumes of distribution at steady state of imipenem and meropenem were 15.3 +/- 3.3 and 18.6 +/- 3.0 liters/70 kg, respectively, and the mean renal clearances per 1.73 m2 were 85.6 +/- 17.6 and 144.6 +/- 26.0 ml/min, respectively. Both antibiotics were well tolerated in this single-dose administration study. The SBAs were measured by the microdilution method of Reller and Stratton (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977) against 40 clinically isolated strains. Mean reciprocal bactericidal titers were measured 1 and 6 h after administration. After 1 and 6 h the median SBAs for imipenem and meropenem, were 409 and 34.9 and 97.9 and 5.8, respectively, against Staphylococcus aureus, 19.9 and 4.4 and 19.4 and 4.8, respectively, against Pseudomonas aeruginosa, 34.3 and 2.2 and 232 and 15.5, respectively, against Enterobacter cloacae, and 13.4 and 2.25 and 90.7 and 7.9, respectively, against Proteus mirabilis. Both drugs had rather short biological elimination half-lives and a predominantly renal route of elimination. Both carbapenems revealed high SBAs against clinically important pathogens at 1 h; meropenem had a higher SBA against E. cloacae and P. mirabilis, and the SBA of imipenem against S. aureus was greater than the SBA of meropenem.

Therapeutic Drug Monitoring of Therapy for Infectious Diseases

Optimal use of antimicrobial agents is dependent on a multitude of factors. Empiric therapy should be based on the patient's underlying disease states, the most likely organisms suspected, and susceptibility patterns. Once susceptibilities are known, therapy should be streamlined. A number of factors must be evaluated during therapy. The site of infections must be considered when choosing antimicrobial agents. The minimum inhibitory concentration (MIC) should be evaluated ; the antimicrobial agent's MIC should be at or below the breakpoint for the organism to be considered susceptible. Antimicrobial agent selection and dosing should take into consideration not only the MIC, but also the post-antibiotic effect, if applicable. Serum concentrations of antimicrobial agents should be obtained and evaluated to ensure therapeutic levels and to avoid potential toxicities. The choice of an antimicrobial agent is complicated by the emergence of antibiotic resistance. Drug-resistant gram-positive and gram-negative infections are increasing. We must attempt to control resistance by choosing appropriate antimicrobial agents and maximizing dosages. Pharmacists can play a critical role in the management of patients who receive antimicrobial agents.

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).

Optimal adaptive control of pharmacodynamic effects with aminoglycoside antibiotics: a required approach for the future

Many factors are considered in designing optimal drug regimens, including dose, route of administration, and the frequency and rate of administration. It is evident that the first parameter to be considered in dosage regimen determinations is the pharmacokinetics of the drug in the treated patient, or more extensively in the corresponding specific population of patients characterized by a similar pathophysiological status, e.g. neutropenics, ICU patients, subjects with renal insufficiency, children, geriatrics... Therefore, over the last two decades, pharmacokinetic principles have widely, and almost exclusively influenced the optimal adaptative control of antibiotics with a small therapeutic index. The large number of available new drugs associated with medical progress, specially in considering the increase of surviving patients with severe diseases or precarious physiopathological status (e.g., neutropenia, AIDS, ICU patients ...) have demonstrated the limits of this approach and pointed out the necessity of the determination of suitable parameters reflecting the in vivo efficacy. Thus, the search for pharmacodynamic parameters that can be accurately related to pharmacokinetic profiles in patients becomes a major tool. The progress in measurement of antibiotics and the additional dimension of the antibiotic's efficacy evaluation based on the analysis of the time course of the antibacterial effects, have provided the basis for the coupled evaluation of pharmacokinetics and pharmacodynamics of antibiotics, which has been largely assessed by in vivo animal models. In an attempt to propose a methodology that can provide information directly applicable to patients to be treated, we have developed a human in vivo/ex vivo model of analysis of the pharmacodynamics of antibiotics. This model has been applied to several drugs and particularly to aminoglycosides. It allows one to have a more rational evaluation of the dose-concentration-effect relations for antibiotics in man. The pharmacodynamics of aminoglycosides is characterized by a strong concentration dependent bactericidal activity and a significant post-antibiotic effect against Gram-negative bacilli. Experimental animal studies confirmed by investigations in man have shown that in vivo efficacy is enhanced by increasing the Cmax and the AUC of these antibiotics regardless of the possible below-MIC value of the C min. Moreover, the in vivo efficacy seems to be the same whether the total dose of aminoglycoside is given as a once a day dosing or as several doses while the toxic risk appears to be attenuated by the first dosage schedule. These data also emphasize the need for the development of models and software for optimal adaptive control including the pharmacodynamic parameters of antibiotics.

Comparative serum bactericidal activities of three doses of ciprofloxacin administered intravenously

The pharmacokinetics and serum bactericidal activities of three intravenous doses of ciprofloxacin were studied comparatively in 30 patients. Single 200-, 300-, and 400-mg intravenous doses of ciprofloxacin were given over 30 min to 10 patients each, and serum samples were obtained at 0.5, 1, 2, 3, 4, 8, and 12 h after the start of the infusion. Serum drug concentrations were determined by high-pressure liquid chromatography. Pharmacokinetic parameters were estimated by using noncompartmental analysis methods. Serum bactericidal activity against clinical isolates of Escherichia coli, Enterobacter cloacae, Pseudomonas aeruginosa, Acinetobacter calcoaceticus, and Staphylococcus aureus was determined for samples obtained at 0.5, 4, 8, and 12 h. Excellent activity was demonstrated up to 12 h by all doses against E. coli and E. cloacae. Much poorer titers were observed for the remaining organisms, although the 400-mg dose prompted improved results against P. aeruginosa with a mean bactericidal titer of 1:2.9 at 8 h. In conclusion, while the 200-mg dose appears to be largely adequate for infections caused by members of the family Enterobacteriaceae, it seems that when P. aeruginosa is involved, 400 mg twice a day or even three times a day is more appropriate. Intravenous ciprofloxacin performs poorly against A. calcoaceticus and S. aureus, even at a higher dose.

MIC and serum bactericidal activity of clindamycin against methicillin-resistant and -sensitive staphylococci

Six volunteers were given 600 mg clindamycin intravenously to investigate the serum bactericidal activity (SBA) against 50 methicillin susceptible (MSSA) and 50 methicillin resistant Staphylococcus aureus (MRSA) strains. Minimal inhibitory concentrations (MIC) against MSSA, MRSA and 50 methicillin resistant strains of Staphylococcus epidermidis (MRSE), of which 50% were slime-producing, were determined. SBA of clindamycin against MSSA and MRSA was equally high (mean reciprocal SBA titer against MSSA vs MRSA 1 h after application was 13.0 vs 13.45), although MICs against MRSA were markedly higher than against MSSA (MIC 90 of MRSA vs MSSA: 0.06 vs > 32 mg/l). There was no difference in MICs between slime- and non-slime-producing MRSE.

Serum bactericidal activity after administration of four cephalosporins in healthy volunteers

Serum bactericidal activity (SBA) was determined against ten strains each of Staphylococcus aureus, Klebsiella pneumoniae, Proteus vulgaris and Enterobacter cloacae in six volunteers 1 h and 4 h after intravenous infusion of 1 g and 2 g cefotaxime and cefmenoxime, and 2 g flomoxef, and against ten strains of Pseudomonas aeruginosa after infusion of 1 g and 2 g ceftazidime. Flomoxef showed the highest SBA against methicillin-susceptible Staphylococcus aureus. All cephalosporins had high SBA against gram-negative rods. Cefotaxime had the highest SBA against Klebsiella pneumoniae and Enterobacter cloacae. The SBA against Pseudomonas aeruginosa after 1 g and 2 g doses of ceftazidime was very similar.

Comparative pharmacokinetics and serum bactericidal activities of SCE-2787 and ceftazidime

Ceftazidime and the new SCE-2787 are parenteral cephalosporins with a broad antimicrobial spectrum. Pharmacokinetics, serum bactericidal activities, and side effects were investigated in a randomized crossover study. A total of 12 healthy volunteers received a 20-min infusion of 1.5 g of SCE-2787 or 2.0 g of ceftazidime. Serum and urine concentrations were determined by the bioassay method and by high-pressure liquid chromatography (HPLC). The mean (+/- standard deviation) drug concentrations in serum at the end of infusion of SCE-2787 and ceftazidime were 124.4 +/- 23.8 and 233.1 +/- 54.1 mg/liter, respectively. The urine recovery of SCE-2787 was 87.8% +/- 5.5% of dose in 24 h and for ceftazidime was 85.8% +/- 6.3% of dose in 24 h. Metabolites of SCE-2787 could not be detected by HPLC in serum or urine. Pharmacokinetic parameters were calculated both with a noncompartmental analysis and on the basis of an open two-compartment model (drugs are administered into and eliminated from a central compartment only. However, reversible drug distribution from the central space occurs simultaneously into one peripheral space). The area under the concentration time curve from 0 h to infinity of SCE-2787 was 197.9 +/- 25.4 mg.h/liter, and that of ceftazidime was 334.2 +/- 40.0 mg.h/liter. SCE-2787 had a mean terminal half-life in the elimination phase of 109.0 +/- 15.3 min, while that of ceftazidime was 99.0 +/- 13.4 min. The volume of distribution at steady state of SCE-2787 was 17.1 +/- 1.6 liters/70 kg, and that of ceftazidime was 122.9 +/- 1.3 liters/70 kg. The mean residence time of SCE-2787 was 136.4 +/- 15.4 min, and that of ceftazidime was 122.9 +/- 12.7 min. The renal clearance per. 1.73 m2 of SCE-2787 was 103.1 +/- 12.3 ml/min, and that of ceftazidime was 80.6 +/- 13.2 ml/min. The serum bactericidal activities were measured with the microdilution method of Stratton and Reller (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977) against 40 clinically isolated strains. One hour after administration, we measured mean reciprocal bactericidal titers of SCE-2787 and ceftazidime, respectively, against Escherichia coli of 388 and 243, against Klebsiella pneumoniae of 395 and 138, against Pseudomonas aeruginosa of 13.0 and 12.7, and against Staphylococcus aureus of 32.2 and 4.0. No severe side effects were observed in this single drug administration.

Pharmacodynamics of intravenous ciprofloxacin in seriously ill patients

Seventy-four acutely ill patients were treated with intravenous ciprofloxacin at dosages ranging between 200 mg every 12 h and 400 mg every 8 h. A population pharmacokinetic-pharmacodynamic analysis relating drug exposure (and other factors) to infectious outcome was performed. Plasma samples were obtained and assayed for ciprofloxacin by high-performance liquid chromatography. Samples from patients were frequently cultured so that the day of bacterial eradication could be determined. The pharmacokinetic data were fitted by iterative two-stage analysis, assuming a linear two-compartment model. Logistic regression was used to model ciprofloxacin exposure (and other potential covariates) versus the probabilities of achieving clinical and microbiologic cures. The same variables were also modelled versus the time to bacterial eradication by proportional hazards regression. The independent variables considered were dose, site of infection, infecting organism and the MIC for it, percent time above the MIC, peak, peak/MIC ratio, trough, trough/MIC ratio, 24-h area under the concentration-time curve (AUC), AUC/MIC ratio (AUIC), presence of other active antibacterial agents, and patient characteristics. The most important predictor for all three measures of ciprofloxacin pharmacodynamics was the AUIC. A 24-h AUIC of 125 SIT-1.h (inverse serum inhibitory titer integrated over time) was found to be a significant breakpoint for probabilities of both clinical and microbiologic cures. At an AUIC below 125 (19 patients), the percent probabilities of clinical and microbiologic cures were 42 and 26%, respectively. At an AUIC above 125 (45 patients), the probabilities were 80% (P < 0.005) and 82% (P < 0.001), respectively. There were two significant breakpoints in the time-to-bacterial-eradication data. At an AUIC below 125 (21 patients), the median time to eradication exceeded 32 days; at an AUIC of 125 to 250 (15 patients), time to eradication was 6.6 days: and at AUIC above 250 (28 patients), the median time to eradication was 1.9 days (groups differed; P < 0.005). These findings, when combined with pharmacokinetic data reported in the companion article, provide the rationale and tools needed for targeting the dosage of intravenous ciprofloxacin to individual patients' pharmacokinetics and their bacterial pathogens' susceptibilities. An a priori dosing algorithm (based on MIC, patient creatine clearance and weight, and the clinician-specified AUIC target) was developed. This approach was shown, retrospectively, to be more precise than current guidelines, and it can be used to achieve more rapid bacteriologic and clinical responses to ciprofloxacin, as a consequence of targeting the AUIC.

Pharmacokinetics and bactericidal activities of one 800-milligram dose versus two 400-milligram doses of intravenously administered pefloxacin in healthy volunteers

Pefloxacin pharmacokinetics and serum bactericidal activities (SBA) against Escherichia coli and Staphylococcus aureus were compared after intravenous infusion of either a single 800-mg dose or twice-daily 400-mg doses into 16 healthy volunteers. Plasma pefloxacin concentrations were measured for up to 60 h, and SBAs were determined 1, 12, and 24 h after the start of the infusion. The mean areas under the concentration-versus-time curve for plasma were not different (138 versus 136 h.mg/liter). The mean clearances, volumes of distribution, and half-lives were also comparable. The mean (+/- standard deviation) maximal concentration after the 800-mg infusion was 12.11 +/- 1.35 versus 6.51 +/- 0.73 mg/liter after the first 400-mg infusion and 7.42 +/- 0.76 mg/liter after the second 400-mg infusion. Mean trough concentrations at 24 h were significantly different: 2.77 +/- 0.63 (800 mg) versus 1.93 +/- 0.49 (400 mg twice) mg/liter (P = 0.0007). Mean SBAs against E. coli after 800 mg of pefloxacin were higher than 1/128 (1 h), 1/32 (12 h), and 1/16 (24 h). Mean SBAs against S. aureus under the same conditions were higher than 1/64 (1 h), 1/16 (12 h), and 1/8 (24 h). Mean SBAs at 1 and 12 h were significantly higher after the 800-mg infusion than after the 400-mg infusion but were similar at 24 h for both regimens. Comparison of SBAs according to National Committee for Clinical Laboratory Standards criteria showed a similar adequacy at 24 h for both regimens against both strains. Administration of 800 mg of pefloxacin once a day is bioequivalent to 400 mg twice a day, and bactericidal activity of the 800-mg infusion is not less than that of two 400-mg infusions.

Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance

Bactericidal testing has been used for several decades as a guide for antimicrobial therapy of serious infections. Such testing is most frequently performed when bactericidal antimicrobial agent therapy is considered necessary (such as when treating infectious endocarditis or infection in an immunocompromised host). It has also been used to ensure that the infecting organism is killed by (not tolerant to) usually bactericidal compounds. However, few data are available to support the role of such tests in direct patient care. Several important variables affect the reproducibility of the test results; however, proposed reference methods are now available for performing the MBC test. With minor modifications, these can provide a standardized approach for laboratories that need to perform them. Currently, little evidence is available to support the routine use of such testing for the care of individual patients. However, testing of new (investigational) antimicrobial agents can be beneficial in determining their potential to provide bactericidal antimicrobial activity during clinical use. New methods to assess bactericidal activity are being developed, but as yet none have been rigorously tested in patient care settings; further, for most of these methods, little information is available as to which technical parameters affect their results. In clinical laboratories, all bactericidal tests must be performed with rigorously standardized techniques and adequate controls, bearing in mind the limitations of the currently available test procedures.

Single-dose antibiotic therapy: what has the past taught us?

The proper dosage schedule of antibiotics has generally been determined empirically, due to the difficulty of clinical trials. Initially, the dosage was chosen to allow high sustained levels greater than MIC in the blood. Antibiotics (beta lactams, tetracyclins, macrolides) were given at high doses three to six times daily, whatever their kinetic properties. The data obtained by Eagle3 with beta lactams in animal models of streptococcal and treponemal infections outlined the importance of interval between doses on the in vivo efficacy. They also showed that increasing the dose of penicillin had a positive effect on the bactericidal activity only through the persistence of effective levels (greater than MIC) at the site of infection. Further illustrations were given through experimental and clinical studies with beta lactams or other compounds on different types of infections: LRTIs, UTIs, meningitis, and endocarditis. The importance of both dynamic (i.e., pattern of bactericidal effect) and kinetic (elimination half-life) parameters was thus further identified. Information on toxicity with some compounds with a narrow therapeutic index, such as aminoglycosides, indicated that increasing the dose to enhance efficacy had some limitations. This led to numerous studies on the relations between concentration and toxicity, stating that nephro- or ototoxicity were not directly related to peak level in serum. Experimental studies showed that OD administration of aminoglycosides was both more efficient and less toxic than the multiple-dose regimen of the same daily amount. Economic considerations progressively justified attempts to both reduce the dose and the work load related to multiple administrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Bactericidal titers of loracarbef (LY 163892) in serum and killing rates in volunteers receiving 400 versus 200 milligrams

In a randomized crossover trial, six volunteers received 200- and 400-mg doses of loracarbef (LY 163892), a new oral cephalosporin. Mean +/- standard error of the mean concentrations in serum obtained after 1.5 and 3 h were 13.2 +/- 2.8 and 4.3 +/- 0.7 mg/liter, respectively, after the 400-mg dose and 6.9 +/- 1.0 and 1.7 +/- 0.2 mg/liter, respectively, after the 200-mg dose. Bactericidal reciprocal titers measured against respiratory pathogens in serum suggested that loracarbef would be highly effective against Streptococcus pneumoniae and Streptococcus pyogenes (median titers, 8 to 128 at 1.5 h and less than 2 to 32 at 3 h) and beta-lactamase-negative Haemophilus influenzae (median titers, 4 at 1.5 h and 2 to 4 at 3 h). Other species (Branhamella catarrhalis, Streptococcus anginosus, Staphylococcus aureus) were associated with lower bactericidal titers. Killing curves performed against 12 strains demonstrated that the bioactivity of loracarbef (measured by the reduction in the area under the control growth curve) was significantly correlated with the concentration/MIC ratio, whereas the initial rate of killing was not, once the concentration was greater than the MIC. Our results suggest that administration of 400 mg of loracarbef every 8 h might be associated with more favorable pharmacodynamic parameters against target bacteria.

Therapy of bovine bacterial pneumonia

Practical strategies for developing rational therapeutic regimens based on in vitro sensitivity and pharmacokinetic disposition are presented. Special attention is given to Pasteurella haemolytica, which is regarded as the most frequent cause of bovine bacterial pneumonia. Bacterial-dependent and host-dependent causes of therapeutic failure and potentially valuable novel therapies and drug combinations are considered.

Mathematical examination of dual individualization principles (I): Relationships between AUC above MIC and area under the inhibitory curve for cefmenoxime, ciprofloxacin, and tobramycin

Traditional antibiotic dosage adjustments target predetermined serum concentrations, whereas a host of in vitro studies and recent clinical trials establish that bacteria vary in their susceptibility. Dual individualization, which considers the variance in both antibiotic pharmacokinetics and bacterial susceptibility, has been employed to describe different rates of bacterial eradication in relation to varying serum concentrations. In patients with nosocomial pneumonia, one of the model compounds studied was cefmenoxime, where a target six-hour area under the serum concentration-time curve (AUC) of 140 micrograms.h/mL above minimum inhibitory concentration (MIC) was previously associated with bacterial eradication in an average of four days. The target AUC value of 140 micrograms.h/mL above MIC is unique to cefmenoxime. Ideally, there should be a dual individualized target useful to adjust the dose of any antibiotic. Computer simulations performed to evaluate this hypothesis suggested that each antibiotic had a unique value for target AUC above MIC. These simulations indicated that an optimal AUC above MIC was about 80 percent of the total AUC above the MIC. Predictable rates of bacterial eradication would presumably result from maintaining these relationships across the range of bacterial susceptibility and the range of serum concentration profiles. Each antibiotic has a unique and different 24-hour AUC over MIC value associated with bacterial eradication in 4 days. For cefmenoxime, the target was 540 area units over MIC per 24 hours, tobramycin with 34 area units, and ciprofloxacin with 23 area units per 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacodynamic parameters and toxicity of netilmicin (6 milligrams/kilogram/day) given once daily or in three divided doses to cancer patients with urinary tract infection

The pharmacologic parameters and toxicity of netilmicin (6 mg/kg/day) given once daily (qd) or thrice daily (tid) for the treatment of urinary tract infections were studied in a randomized prospective study of 60 cancer patients. The overall efficacy was 96%. Nephrotoxicity, assessed by the measure of urinary excretion of phospholipids, was lower for the patients receiving the qd regimen than for those receiving the tid regimen. Elevation of serum creatinine (20% over baseline) occurred in one patient receiving the qd regimen and in three receiving the tid regimen. Cochleotoxicity, assessed by pure-tone audiometry (250 to 18,000 Hz) occurred in one patient receiving the qd regimen and none receiving the tid regimen. Concentrations in sera were measured on days 1 and 5. No significant accumulation was observed in either group. Median serum bactericidal titers, expressed as reciprocal values (percentage of the sera with a titer greater than or equal to 8), were measured against 25 test organisms in samples collected 6 h after the administration of netilmicin and were, for the qd group, 16 (82%) against members of the family Enterobacteriaceae and less than 2 (8%) against Pseudomonas aeruginosa, and for the tid group, 4 (57%) against members of the Enterobacteriaceae and less than 2 (0%) against P. aeruginosa. The rate of killing in serum was rapid (2 to 3 log in 2 h against P. aeruginosa; 3 to 5 log in 2 h against members of the Enterobacteriaceae) and correlated with the sampling time and hence the concentration in serum of netilmicin. The duration of the postantibiotic effect in serum depended also on the strain and the sampling time of the serum.

D-lactic acid production as a monitor of the effectiveness of antimicrobial agents

Most bacteria at an infection site obtain energy by the breakdown of glucose via microaerophilic or anaerobic pathways and in the process yield various end products. In this study, production of D-lactic acid by Staphylococcus aureus and Escherichia coli was correlated with glucose utilization by bacteria during exposure to antibiotics at subinhibitory, inhibitory, and suprainhibitory concentrations. D-Lactic acid production was further correlated with production of a tissue-destroying enzyme, hyaluronidase, by S. aureus. For E. coli, all agents tested showed dose-related bacterial killing, with the most noticeable being with ampicillin, piperacillin, and ciprofloxacin. Imipenem, ciprofloxacin, and chloramphenicol had the most dose-related effects on D-lactic acid production. With few exceptions, hyaluronidase production correlated well with D-lactic acid production in S. aureus. Subinhibitory concentrations of erythromycin and clindamycin effectively decreased accumulation of D-lactic acid and hyaluronidase. Determination of D-lactic acid production may perhaps serve as a means of independently monitoring the effects of antimicrobial agents on bacterial metabolic activity, which is an important aspect of antimicrobial action that remains relatively unexplored.