Pharmacokinetics and pharmacodynamics of outpatient intravenous antimicrobial therapy

Calculated initial parenteral treatment of bacterial infections: Pharmacokinetics and pharmacodynamics

This is the third chapter of the guideline "Calculated initial parenteral treatment of bacterial infections in adults - update 2018" in the 2nd updated version. The German guideline by the Paul-Ehrlich-Gesellschaft für Chemotherapie e.V. (PEG) has been translated to address an international audience. The chapter features the pharmacokinetic and pharmacodynamics properties of the most frequently used antiinfective agents.

Amplification of Antimicrobial Resistance in Gut Flora of Patients Treated with Ceftriaxone

Although antibacterial therapy has an impact on human intestinal flora and the emergence of resistant bacteria, its role in the amplification of antimicrobial resistance and the quantitative exposure-effect relationship is not clear. An observational prospective study was conducted to determine whether and how ceftriaxone exposure is related to amplification of resistance in non-intensive care unit (non-ICU) patients. Serial stool samples from 122 extended-spectrum β-lactamase-positive (ESBL⁺) hospitalized patients were analyzed by quantitative real-time PCR to quantify the resistant gene bla_CTX-M Drug exposure was calculated for each patient by using a population pharmacokinetic model. Multi- and univariate regression and classification regression tree (CART) analyses were used to explore relationships between measures of exposure and amplification of bla_CTX-M genes. Amplification of bla_CTX-M was observed in 0% (0/11) of patients with no treatment and 33% (20/61) of patients treated with ceftriaxone. Stepwise regression analysis showed a significant association between amplification of bla_CTX-M and the plasma area under the concentration-time curve from 0 to 24 h for the unbound fraction of the drug (fAUC_0-24), the maximum concentration of drug in serum for the unbound fraction of the drug (fC_max), and the duration of ceftriaxone therapy. Using CART analysis, amplification of bla_CTX-M was observed in 11/16 (69%) patients treated for >14 days and in 9/40 (23%) patients treated for ≤14 days (P = 0.0019). In the latter group, amplification was observed in 5/7 (71%) patients with an fAUC_0-24 of ≥222 mg · h/liter and in 4/33 (12%) patients with lower drug exposures (P = 0.0033). A similar association was found for an fC_max of ≥30 mg/liter (63% versus 13%, P = 0.0079). A significant association was found between the amplification of bla_CTX-M resistance genes and exposure to ceftriaxone. Both duration of treatment and degree of ceftriaxone exposure have a significant impact on the amplification of resistance genes. (The project described in this paper has been registered at ClinicalTrials.gov under identifier NCT01208519.).

In Vivo Pharmacodynamic Target Investigation of Two Bacterial Topoisomerase Inhibitors, ACT-387042 and ACT-292706, in the Neutropenic Murine Thigh Model against Streptococcus pneumoniae and Staphylococcus aureus

ACT-387042 and ACT-292706 are two novel bacterial topoisomerase inhibitors with broad-spectrum activity against Gram-positive and -negative bacteria, including methicillin-resistant Staphylococcus aureus and penicillin- and fluoroquinolone-resistant Streptococcus pneumoniae We used the neutropenic murine thigh infection model to characterize the pharmacokinetics (PK)/pharmacodynamics (PD) of these investigational compounds against a group of 10 S. aureus and S. pneumoniae isolates with phenotypic resistance to beta-lactams and fluoroquinolones. The in vitro activities of the two compounds were very similar (MIC range, 0.03 to 0.125 mg/liter). Plasma pharmacokinetics were determined for each compound by using four escalating doses administered by the subcutaneous route. In treatment studies, mice had 10(7.4) to 10(8) CFU/thigh at the start of therapy with ACT-387042 and 10(6.7) to 10(8.3) CFU/thigh at the start of therapy with ACT-292706. A dose-response relationship was observed with all isolates over the dose range. Maximal kill approached 3 to 4 log10 CFU/thigh compared to the burden at the start of therapy for the highest doses examined. There was a strong relationship between the PK/PD index AUC/MIC ratio (area under the concentration-time curve over 24 h in the steady state divided by the MIC) and therapeutic efficacy in the model (R(2), 0.63 to 0.82). The 24-h free-drug AUC/MIC ratios associated with net stasis for ACT-387042 against S. aureus and S. pneumoniae were 43 and 10, respectively. The 24-h free-drug AUC/MIC ratios associated with net stasis for ACT-292706 against S. aureus and S. pneumoniae were 69 and 25, respectively. The stasis PD targets were significantly lower for S. pneumoniae (P < 0.05) for both compounds. The 1-log-kill AUC/MIC ratio targets were ∼2- to 4-fold higher than stasis targets. Methicillin, penicillin, or ciprofloxacin resistance did not alter the magnitude of the AUC/MIC ratio required for efficacy. These results should be helpful in the design of clinical trials for topoisomerase inhibitors.

Influence of pharmacokinetics/pharmacodynamics of antibacterials in their dosing regimen selection

The choice of antimicrobial dosing in clinical practice in the past was based upon a 'penicillin mentality', that is, on the assumption that the in vivo antimicrobial efficacy is dependent on the duration of drug levels above the minimum inhibitory concentration of target microorganisms. Really, a rational antimicrobial therapy is strongly related to a basic understanding of the influence the patient has on the antibiotic (pharmacokinetics [PKs]) and the patient's response to the specific drug effects (pharmacodynamics [PDs]). PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. This review will analyze the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach with the most commonly utilized antimicrobial agent classes.

High β-lactamase levels change the pharmacodynamics of β-lactam antibiotics in Pseudomonas aeruginosa biofilms

Resistance to β-lactam antibiotics is a frequent problem in Pseudomonas aeruginosa lung infection of cystic fibrosis (CF) patients. This resistance is mainly due to the hyperproduction of chromosomally encoded β-lactamase and biofilm formation. The purpose of this study was to investigate the role of β-lactamase in the pharmacokinetics (PK) and pharmacodynamics (PD) of ceftazidime and imipenem on P. aeruginosa biofilms. P. aeruginosa PAO1 and its corresponding β-lactamase-overproducing mutant, PAΔDDh2Dh3, were used in this study. Biofilms of these two strains in flow chambers, microtiter plates, and on alginate beads were treated with different concentrations of ceftazidime and imipenem. The kinetics of antibiotics on the biofilms was investigated in vitro by time-kill methods. Time-dependent killing of ceftazidime was observed in PAO1 biofilms, but concentration-dependent killing activity of ceftazidime was observed for β-lactamase-overproducing biofilms of P. aeruginosa in all three models. Ceftazidime showed time-dependent killing on planktonic PAO1 and PAΔDDh2Dh3. This difference is probably due to the special distribution and accumulation in the biofilm matrix of β-lactamase, which can hydrolyze the β-lactam antibiotics. The PK/PD indices of the AUC/MBIC and C(max)/MBIC (AUC is the area under concentration-time curve, MBIC is the minimal biofilm-inhibitory concentration, and C(max) is the maximum concentration of drug in serum) are probably the best parameters to describe the effect of ceftazidime in β-lactamase-overproducing P. aeruginosa biofilms. Meanwhile, imipenem showed time-dependent killing on both PAO1 and PAΔDDh2Dh3 biofilms. An inoculum effect of β-lactams was found for both planktonic and biofilm P. aeruginosa cells. The inoculum effect of ceftazidime for the β-lactamase-overproducing mutant PAΔDDh2Dh3 biofilms was more obvious than for PAO1 biofilms, with a requirement of higher antibiotic concentration and a longer period of treatment.

Staphylococcus aureus biofilms: properties, regulation, and roles in human disease

Increasing attention has been focused on understanding bacterial biofilms and this growth modality's relation to human disease. In this review we explore the genetic regulation and molecular components involved in biofilm formation and maturation in the context of the Gram-positive cocci, Staphylococcus aureus. In addition, we discuss diseases and host immune responses, along with current therapies associated with S. aureus biofilm infections and prevention strategies.

Treating osteomyelitis: antibiotics and surgery

BACKGROUND

Osteomyelitis is an inflammatory disorder of bone caused by infection leading to necrosis and destruction. It can affect all ages and involve any bone. Osteomyelitis may become chronic and cause persistent morbidity. Despite new imaging techniques, diagnosis can be difficult and often delayed. Because infection can recur years after apparent "cure," "remission" is a more appropriate term.

METHODS

The study is a nonsystematic review of literature.

RESULTS

Osteomyelitis usually requires some antibiotic treatment, usually administered systemically but sometimes supplemented by antibiotic-containing beads or cement. Acute hematogenous osteomyelitis can be treated with antibiotics alone. Chronic osteomyelitis, often accompanied by necrotic bone, usually requires surgical therapy. Unfortunately, evidence for optimal treatment regimens or therapy durations largely based upon expert opinion, case series, and animal models. Antimicrobial therapy is now complicated by the increasing prevalence of antibiotic-resistant organisms, especially methicillin-resistant Staphylococcus aureus. Without surgical resection of infected bone, antibiotic treatment must be prolonged (≥4 to 6 weeks). Advances in surgical technique have increased the potential for bone (and often limb) salvage and infection remission.

CONCLUSIONS

Osteomyelitis is best managed by a multidisciplinary team. It requires accurate diagnosis and optimization of host defenses, appropriate anti-infective therapy, and often bone débridement and reconstructive surgery. The antibiotic regimen must target the likely (or optimally proven) causative pathogen, with few adverse effects and reasonable costs. The authors offer practical guidance to the medical and surgical aspects of treating osteomyelitis.

The pharmacokinetics and pharmacodynamics of the carbapanemes: focus on doripenem

Carbapenems are the most potent group of beta-lactam agents, having a broad spectrum of bactericidal activity against both Gram-negative and Gram-positive bacteria including anaerobes. Doripenem is a new carbapenem endowed with excellent bactericidal activity, a wide spectrum of antibacterial activity against difficult nosocomial pathogens, including extended-spectrum beta-lactamase producers. Its high stability in solution render it extremely flexible for dosing and infusion time. It is the only carbapenem which has been registered officially for administration as an extended infusion of more than 4 hours, which can thus enhance its potential clinical efficacy against difficult bacterial pathogens with MICs of 4-8 mg/L.

Outpatient parenteral antibiotic therapy with daptomycin: insights from a patient registry

AIM

To compare and contrast the characteristics and clinical outcomes of patients who have received daptomycin as outpatients and inpatients.

METHODS

The Cubicin Outcomes Registry and Experience (CORE) is a retrospective chart review of patients who have received daptomycin in participating institutions. Patients treated in 2005 were included in this analysis. Demographic characteristics and clinical outcomes (success = cured + improved) were compared among patients who received outpatient parenteral antibiotic therapy (OPAT) and patients who had received inpatient parenteral antibiotic therapy (IPAT).

RESULTS

Of 1172 patients reported by 52 CORE 2005 participating institutions/investigators, 949 (81.0%) patients were evaluable: 539 (56.8%) received OPAT (OPAT patients), and 410 (43.2%) received only IPAT (IPAT patients). Of the 539 OPAT patients, 273 (50.6%) also received some IPAT, usually preceding OPAT therapy. Successful outcomes [no. of successes/(no. of successes + no. of failures)] for OPAT patients vs. IPAT patients were 94.6% and 86.3% respectively (chi-square test, p < 0.001). OPAT patients were younger, had fewer underlying diseases, were clinically stable, and had fewer adverse events than IPAT patients.

CONCLUSIONS

Outpatient parenteral antibiotic therapy use was common (539/949 or 56.8%) among patients in CORE 2005. Clinical outcomes among OPAT patients appeared at least as good as or better than IPAT patients. Better outcomes among OPAT patients were most likely because of patient selection for OPAT. Additional studies should focus on clinical characteristics of patients who would be ideal candidates for daptomycin OPAT.

Safety and efficacy of home intravenous antimicrobial infusion therapy in older patients: a comparative study with younger patients

BACKGROUND

Home intravenous antimicrobial infusion therapy has proved its safety and efficacy in a great number of infections. Despite this there are few published studies about this way of managing in the elderly patient.

OBJECTIVE

To study the safety and efficacy of home intravenous antimicrobial infusion therapy in elderly patients.

STUDY DESIGN

A prospective and comparative study of an elderly group of patients > or =70 years old vs. a cohort of younger adult patients as a control group. All patients were followed until 3 months after discharge.

SETTING

Hospital at Home Programme (HHP) as part of the Internal Medicine Department at Valle de Hebrón Hospital, Barcelona, Spain.

PATIENTS

All patients admitted to HHP diagnosed of infections requiring intravenous antibiotic therapy between March 2006 and March 2007.

RESULTS

We included 145 patients, 90 of whom were 70 years or older. Diabetes mellitus, heart failure and respiratory tract infection were more frequent in these elderly patients. In this group 14 (12%) developed some type of adverse event during treatment, phlebitis being the most common. The majority of those in the elderly patients group were discharged because of satisfactory clinical evolution and only 7 (7%) were re-admitted to hospital. Another 13 (14%) were re-admitted to hospital 3 months after discharge from HHP, mostly for chronic diseases. There were no significant differences between these results and those obtained from the control group.

CONCLUSION

Home intravenous antimicrobial infusion therapy in elderly patients is safe and effective.

Pharmacokinetics/pharmacodynamics of antibacterials in the Intensive Care Unit: setting appropriate dosing regimens

Patients admitted to Intensive Care Units (ICUs) are at very high risk of developing severe nosocomial infections. Consequently, antimicrobials are among the most important and commonly prescribed drugs in the management of these patients. Critically ill patients in ICUs include representatives of all age groups with a range of organ dysfunction related to severe acute illness that may complicate long-term illness. The range of organ dysfunction, together with drug interactions and other therapeutic interventions (e.g. haemodynamically active drugs and continuous renal replacement therapies), may strongly impact on antimicrobial pharmacokinetics in critically ill patients. In the last decade, it has become apparent that the intrinsic pharmacokinetic (PK) and pharmacodynamic (PD) properties are the major determinants of in vivo efficacy of antimicrobial agents. PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. In this review, we analyse the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach of the antimicrobial agent classes commonly utilised in the ICU setting.

Early hospital discharge versus continued hospitalization in febrile pediatric cancer patients with prolonged neutropenia: A randomized, prospective study

BACKGROUND

Hospitalization with single or multi-agent antibiotic therapy has been the standard of care for treatment of febrile neutropenia in cancer patients. We hypothesized that an empiric antibiotic regimen that is effective and that can be administered once-daily will allow for improved hospital utilization by early transition to outpatient care.

PROCEDURE

Febrile pediatric cancer patients with anticipated prolonged neutropenia were randomized between a regimen of once-daily ceftriaxone plus amikacin (C + A) and imipenem monotherapy (control). Afebrile patients on C + A satisfying "Early Discharge Criteria" at 72 hr continued treatment as outpatients. We compared the outcome, adverse events, duration of hospitalization, and cost between both groups.

RESULTS

A prospective randomized controlled clinical trial was conducted on 129 febrile episodes in pediatric cancer patients with prolonged neutropenia. No adverse events were seen in 32 children (84% of study arm) treated on an outpatient basis. We found a statistically significant difference between the duration of hospitalization of the C + A group [median 5 days] and control [median 9 days](P < 0.001), per episode antibiotic cost (P < 0.001) and total episode cost (P < 0.001). There was no statistically significant difference in the response to treatment at 72 hr or after necessary antimicrobial modifications.

CONCLUSIONS

We conclude that pediatric febrile cancer patients initially considered at risk for sepsis due to prolonged neutropenia can be re-evaluated at 72 hr for outpatient therapy. The convenience, low incidence of adverse effects, and cost benefit of the once-daily regimen of C + A may be particularly useful to reduce the overall treatment costs and duration of hospitalization.

Continuous versus intermittent intravenous administration of antibiotics: a meta-analysis of randomised controlled trials

Intermittent intravenous administration of antibiotics is the first-line approach in the management of severe infections worldwide. However, the potential benefits of alternate modes of administration of antibiotics, including continuous intravenous infusion, deserve further evaluation. We did a meta-analysis of randomised controlled trials comparing continuous intravenous infusion with intermittent intravenous administration of the same antibiotic regimen. Nine randomised controlled trials studying beta-lactams, aminoglycosides, and vancomycin were included. Clinical failure was lower, although without statistical significance, in patients receiving continuous infusion of antibiotics (pooled OR 0.73, 95% CI 0.53-1.01); the difference was statistically significant in a subset of randomised controlled trials that used the same total daily antibiotic dose for both intervention arms (0.70, 0.50-0.98, fixed and random effects models). Regarding mortality and nephrotoxicity, no differences were found (mortality 0.89, 0.48-1.64; nephrotoxicity 0.91, 0.56-1.47). In conclusion, the data suggest that the administration of the same total antibiotic dose by continuous intravenous infusion may be more efficient, with regard to clinical effectiveness, compared with the intermittent mode. In an era of gradually increasing resistance among most pathogens, the potential advantages of continuous intravenous administration of antibiotics on several clinical outcomes should be further investigated.

Ertapenem pharmacokinetics and impact on intestinal microflora, in comparison to those of ceftriaxone, after multiple dosing in male and female volunteers

The pharmacokinetics of ertapenem and ceftriaxone were investigated in an open, randomized, two-period crossover study after single- and multiple-dose administration in 10 healthy volunteers (five women and five men). Both antibiotics were administered intravenously once daily for 7 days at dosages of 1 g (ertapenem) and 2 g (ceftriaxone). The concentrations of the antibiotics in serum and urine were quantified by the agar well diffusion method bioassay and, in addition, for ertapenem only, by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). For ertapenem the maximum concentration of the drug in plasma (C(max)) was 256 mg/liter, the half-life was 20.7 h, and the area under the plasma concentration-time curve (AUC) was 830 mg. h/liter. The concentrations in fecal samples were (mean value) 37.2 and 32.7 mg/kg on day 4 and day 8, respectively. Ceftriaxone exhibited a mean C(max) of 315 mg/liter, a half-life of 7.6 h, and an AUC of 1,556 mg. h/liter. The mean concentrations in fecal samples were 153 and 258 mg/kg on day 4 and day 8, respectively. No accumulation of ertapenem or ceftriaxone was detected at steady state. A slightly but significantly decreased AUC for ertapenem was detected for the female volunteers. No serious adverse event was observed. Both antibiotics induced a marked decrease in the anaerobic microflora (4-log-unit decreases in lactobacilli, bifidobacteria, clostridia, and bacteroides) and Escherichia coli, whereas the number of enterococci increased (4 log units). A slight overgrowth of yeasts was observed with both regimens. In all cases the microflora returned to normal levels on days 21 to 35.

Once-Daily Cefazolin and Probenecid for Skin and Soft Tissue Infections

OBJECTIVE

To review the pharmacokinetic and clinical evidence for the use of once-daily cefazolin and probenecid in the treatment of skin and soft tissue infections (SSTI).

DATA SOURCES

MEDLINE (1966–July 2003), EMBASE (1980–July 2003), and PubMed (1966–July 2003) databases for English language, human reports were searched. Search terms included cefazolin, probenecid, cellulitis, and soft tissue infections.

STUDY SELECTION AND DATA EXTRACTION

Studies that described pharmacokinetic and clinical outcomes that evaluated the use of cefazolin in conjunction with probenecid for SSTI were included. All studies were evaluated independently by both authors. For pharmacokinetic studies, the effect of probenecid on the pharmacokinetics of cefazolin was evaluated. For clinical trials, efficacy and safety endpoints were evaluated. For efficacy endpoints, definition of cure was used as defined by each trial.

DATA SYNTHESIS

In all 3 pharmacokinetic studies identified, the addition of probenecid to cefazolin therapy prolonged the half-life and increased serum concentrations of cefazolin. This process allowed serum concentrations to be above the minimal inhibitory concentrations (MIC) for the most likely skin pathogens ( Staphylococcus aureus, β-hemolytic streptococci) at the end of the dosing interval. In the first of 2 clinical trials, 7 (7%) of 96 patients receiving intravenous ceftriaxone 2 g and oral probenecid 1 g daily were reported to fail therapy compared with 8 (8%) of 98 patients receiving intravenous cefazolin 2 g and oral probenecid 1 g daily. In the second clinical trial, clinical success was reported in 51 (86%) of 59 patients receiving the same doses of cefazolin and probenecid as above compared with 55 (96%) of 57 patients receiving intravenous ceftriaxone 1 g and oral placebo daily.

CONCLUSIONS

Limited pharmacokinetic and clinical data suggest that intravenous cefazolin 2 g and oral probenecid 1 g daily is an effective regimen in the treatment of SSTI.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.

Outpatient and home parenteral antibiotic therapy (OHPAT) in low-risk febrile neutropenia: consensus statement of a Belgian panel

Febrile neutropenia requires adequate antibiotic treatment. A subgroup of patients are only at low risk for complications and could be treated at home/as outpatients (OHPAT) after a short initial admission for work up. This position paper by a Belgian panel of experts presents criteria defining low-risk in febrile neutropenia, gives an overview of the existing experience and examines the present obstacles to a more widespread use of OHPAT in this country.

Once-daily intravenous cefazolin plus oral probenecid is equivalent to once-daily intravenous ceftriaxone plus oral placebo for the treatment of moderate-to-severe cellulitis in adults

A once-daily regimen of cefazolin (2 g intravenously [iv]) plus probenecid (1 g by mouth) was compared with a once-daily regimen of ceftriaxone (1 g iv) plus oral placebo in a randomized, double-blind equivalence trial of home-based therapy for moderate-to-severe cellulitis in adults. For the assessable recipients of cefazolin-probenecid (n=59) and ceftriaxone-placebo (n=57), clinical cure occurred at the end of treatment in 86% and 96% (P=.11), respectively, and was maintained at 1 month of follow-up in 96% and 91% (P=.55), respectively. The mean number of treatment doses (+/-standard deviation) given was similar in the 2 treatment arms (6.97+/-2.6 for cefazolin-probenecid and 6.12+/-2.1 for ceftriaxone-placebo; P=.06). The median antibiotic trough concentrations were 2.35 microgram/mL for cefazolin and 15.45 microgram/mL for ceftriaxone. Patients in the 2 treatment arms were similar with regard to overall rates of adverse reaction (P=.15), but nausea was more common among those in the cefazolin-probenecid arm (P=.048). The once-daily regimen of cefazolin-probenecid is a cheap, practical, and effective treatment option for moderate-to-severe cellulitis, and it avoids the need to use third-generation cephalosporins in most patients.

Can PK/PD be used in everyday clinical practice

Over the last decade much insight has been gained in the relationships between dosing regimens of antimicrobials and bacterial eradication and clinical efficacy. These pharmacokinetic-pharmacodynamic (PK/PD) relationships have become available as tools in individualising antimicrobial therapy. To be able to do this, the PK parameters of the antimicrobial in the individual patient have to be known or estimated, and the MIC of the micro-organism causing the infection, known. In our hospital, we have started a programme using this approach. Preliminary results suggest that dose optimisation leads to increased efficacy and lower costs.

Antifungal susceptibility testing: practical aspects and current challenges

Development of standardized antifungal susceptibility testing methods has been the focus of intensive research for the last 15 years. Reference methods for yeasts (NCCLS M27-A) and molds (M38-P) are now available. The development of these methods provides researchers not only with standardized methods for testing but also with an understanding of the variables that affect interlaboratory reproducibility. With this knowledge, we have now moved into the phase of (i) demonstrating the clinical value (or lack thereof) of standardized methods, (ii) developing modifications to these reference methods that address specific problems, and (iii) developing reliable commercial test kits. Clinically relevant testing is now available for selected fungi and drugs: Candida spp. against fluconazole, itraconazole, flucytosine, and (perhaps) amphotericin B; Cryptococcus neoformans against (perhaps) fluconazole and amphotericin B; and Aspergillus spp. against (perhaps) itraconazole. Expanding the range of useful testing procedures is the current focus of research in this area.

Influence of human serum on antifungal pharmacodynamics with Candida albicans

Antifungal susceptibilities (NCCLS, approved standard M27-A, 1997) were determined for the reference strain ATCC 90028 and 21 clinical isolates of Candida albicans with varying levels of fluconazole susceptibility using RPMI 1640 (RPMI) and 80% fresh human serum-20% RPMI (serum). Sixty-four percent (14 of 22) of the isolates tested demonstrated significant decreases (> or = 4-fold) in fluconazole MICs in the presence of serum, and the remaining eight isolates exhibited no change. Itraconazole and ketoconazole, two highly protein-bound antifungal agents, had MICs in serum that were increased or unchanged for 46% (10 of 22) and 41% (9 of 22) of the isolates, respectively. All 10 isolates tested against an investigational antifungal agent, LY303366, demonstrated significant increases in the MIC required in serum, while differences in amphotericin B MICs in the two media were not observed. Four of 10 isolates tested demonstrated fourfold higher flucytosine MICs in serum than in RPMI. Postantifungal effects (PAFEs) and 24-h kill curves were determined by standard methods for selected isolates. At the MIC, fluconazole, itraconazole, ketoconazole, flucytosine, and LY303366 kill curves and PAFEs in RPMI were similar to those in serum. Isolates of fluconazole-resistant C. albicans required lower MICs in serum than in RPMI, without relative increases in fungal killing or PAFEs. Isolates tested against amphotericin B demonstrated significantly reduced killing and shorter PAFEs in serum than in RPMI without observable changes in MIC. In conclusion, antifungal pharmacodynamics in RPMI did not consistently predict antifungal activity in serum for azoles and amphotericin B. Generally speaking, antifungal agents with high protein binding exhibited some form of reduced activity (MIC, killing, or PAFE) in the presence of serum compared to those with low protein binding.

Ambulatory use of parenteral antibacterials: contemporary perspectives

Outpatient parenteral antimicrobial therapy (OPAT) offers increased patient comfort and convenience in appropriately selected patients who require parenteral antibacterial therapy, as well as opportunity for cost savings. Home-based programmes, with drugs being administered by the patient or the caregiver, have become the norm in the USA. Choice of drugs for OPAT is based on antimicrobial spectrum, dosage regimen, drug stability, toxicity profile, and cost. Over the past decade, availability of sophisticated programmable pumps has allowed a wider range of antimicrobial agents to be used in the ambulatory setting. The most popular antibacterial agents in OPAT programmes in the USA are vancomycin and beta-lactams.