Pulse dosing versus continuous infusion of antibiotics. Pharmacokinetic-pharmacodynamic considerations

Continuous-infusion penicillin home-based therapy for serious infections due to penicillin-susceptible pathogens

To evaluate the feasibility of continuous-infusion (CI) penicillin in the treatment of serious bacterial infections, consecutive adult patients with deep-seated infections due to penicillin-susceptible pathogens were treated with CI aqueous penicillin G in a home-based programme, and their treatment outcomes were reviewed. Thirty-one patients with microbiologically proven infections completed the planned course of treatment. Twenty of 31 (65%) were followed for at least 2 months thereafter, and all remained free of relapse. One patient had fever attributable to penicillin hypersensitivity, two patients developed catheter-site infections and one patient developed catheter-related bacteraemia. Thus, CI penicillin is feasible for the home-based treatment of a variety of deep-seated infections with minimal toxicity.

Comparative target site pharmacokinetics of immediate- and modified-release formulations of cefaclor in humans

Optimal dosing of beta-lactam antibiotics aims at maximizing the time at which drug levels in the interstitial space fluid (ISF)--the fluid that surrounds the causative microorganisms at the target site--exceed the minimal inhibitory concentration (MIC). One potentially attractive strategy to achieve this goal is to administer antibiotics as oral sustained-release formulations. The present study was designed to test the hypothesis that sustained-release formulations could lead to a more suitable pharmacokinetic profile in the ISF at the relevant target site. For this purpose, time versus cefaclor concentration profiles attained in the ISF were measured following administration of two formulations, an immediate- (500 mg IR) and a modified-release formulation in two different doses (500 mg MR and 750 mgMR) in a three-way crossover study of healthy male volunteers (n = 12). For the measurement of unbound cefaclor concentrations in the ISF of human skeletal muscle, the in vivo microdialysis technique was employed. For all three formulations, unbound cefaclor concentration in the ISF closely followed individual plasma concentration profiles in a dose-dependent pattern, with ISF to unbound plasma ratios ranging from 0.67 to 0.73. The mean residence time was found to be significantly longer for the MR formulations versus the IR formulation. The data of the present study indicate that time above MIC values at the target site can be substantially prolonged if an antibiotic is administered as a sustained-release product.

Determination of cefepime and cefpirome in human serum by high-performance liquid chromatography using an ultrafiltration for antibiotics serum extraction

The aim of this study was to describe a high-performance liquid chromatography (HPLC) assay for the determination of cefepime and cefpirome in human serum without changing chromatographic conditions. The assay consisted to measure cefepime and cefpirome which were unbound to proteins having a molecular mass of 10,000 or more by ultrafiltration followed by HPLC with a Supelcosil ABZ+ column and UV detection at a wavelength of 263 nm. The assay was been found to be linear and has been validated over the concentration range 200 to 0.50 microg/ml for both cefepime and cefpirome, from 200 microl serum, extracted. In future, the assay will support therapeutic drug monitoring for cefepime and cefpirome in neutropenic patients in correlation with microbiological parameters such as MIC90 (minimal inhibitory concentration of antibiotic which kills 90% of the initial bacterial inoculum) and clinical efficacy.

The clinical efficacy of continuous-infusion flucloxacillin in serious staphylococcal sepsis

Since the efficacy of beta-lactams against pathogens such as methicillin-susceptible Staphylococcus aureus (MSSA) is related to the time for which serum drug concentrations exceed the MIC for the pathogen, administration of anti-staphylococcal beta-lactams by continuous infusion may provide a more suitable means of drug delivery than intermittent dosing. To assess the clinical efficacy of continuous-infusion therapy, we reviewed the outcomes for 20 consecutive patients with proven serious MSSA sepsis (three with endocarditis, ten osteomyelitis, one endocarditis plus osteomyelitis and six deep abscess) treated with continuous-infusion flucloxacillin (8-12 g/day). Patients initially receiving routine intermittent-dose flucloxacillin therapy were changed to continuous-infusion flucloxacillin (mean duration 29 days; range 4-60 days) for completion of their treatment course. In the majority of cases this was given at home. Serum flucloxacillin concentrations during continuous-infusion flucloxacillin 12 g/day were 11.5->40 mg/L (ten patients) and those during continuous-infusion flucloxacillin 8 g/day were 8->40 mg/L (five patients), these concentrations being well above the expected MIC of flucloxacillin for MSSA. Continuous-infusion flucloxacillin was well tolerated by most patients, and 14/17 patients (82%) who completed their course of continuous-infusion flucloxacillin were judged clinically and microbiologically cured at long-term follow-up (mean 67 weeks; range 4-152 weeks). These preliminary data suggest that, following initial intermittent-dose flucloxacillin therapy, continuous-infusion flucloxacillin is an effective treatment option for serious MSSA sepsis, and forms a feasible and possibly preferable alternative to glycopeptides when considering home-based parenteral therapy for these infections. Further studies are needed to identify whether continuous-infusion flucloxacillin can entirely replace intermittent-dose therapy for such infections.

Continuous antibiotic treatment for experimental abdominal sepsis: effects on organ inflammatory cytokine expression and neutrophil sequestration

BACKGROUND

Tumour necrosis factor (TNF) alpha and interleukin (IL) 1 beta are produced in the lung after peritonitis and may contribute to neutrophil-mediated organ injury. It was hypothesized that, during experimental peritonitis, continuous rather than intermittent antibiotic therapy would reduce lung expression of TNF-alpha and IL-1 beta messenger RNA (mRNA) and neutrophil sequestration.

METHODS

After caecal ligation and puncture, mice received either intermittent or continuous cefoxitin, or continuous metronidazole or aztreonam. Cytokine mRNAs were determined by reverse transcription differential polymerase chain reaction and lung neutrophil content by myeloperoxidase (MPO) assay.

RESULTS

Continuous cefoxitin reduced median (interquartile range (i.q.r.)) lung IL-1 beta mRNA expression ((ratio to beta-actin): continuous 0.18 (0.14-0.34), intermittent 0.46 (0.44-0.49), saline 0.43 (0.38-0.53), P < 0.05) and median (i.q.r.) lung MPO content (continuous 22.5 (9.7-40), intermittent 65 (57.5-76), saline 47 (41-64), P < 0.05) compared with intermittent therapy and saline controls. Continuous infusion was also associated with reduced bacteraemia (P < 0.05) but not serum TNF-alpha or endotoxin levels. Both continuous metronidazole and aztreonam reduced lung MPO concentration (P < 0.05) and TNF-alpha and IL-1 beta mRNA expression (P < 0.05) compared with those in saline controls. These effects were dependent on a reduction in the number of susceptible bacteria rather than serum TNF-alpha or endotoxin levels.

CONCLUSION

The stimulus for organ inflammatory cytokine production and neutrophil sequestration during peritonitis is the level of bacteraemia present, which is more effectively controlled with continuous antibiotic therapy.

Pharmacokinetics in vivo and pharmacodynamics ex vivo/in vitro of meropenem and cefpirome in the Yucatan micropig model: continuous infusion versus intermittent injection

OBJECTIVE: To investigate the pharmacodynamic disposition of two recently developed beta-lactam antibiotics, meropenem and cefpirome, in the Yucatan micropig model, and to compare the bactericidal activity of these drugs against bacteria in this in vitro/ex vivo micropig model after administration by both intermittent injection and continuous infusion. METHODS: Cefpirome (1 g) was given to the micropig over a 12-h period by direct intravenous injection and 6-h continuous infusion (500 mg). Meropenem (250 mg) was administered either by 30-min intravenous and 8-h continuous infusion. The two drugs were assayed by HPLC. The pharmacodynamics of these drugs were evaluated by means of (1) serum killing curve against Klebsiella pneumoniae producing extended-spectrum beta-lactamase, stably derepressed Enterobacter cloacae and methicillin-susceptible penicillinase-producing Staphylococcus aureus, and (2) calculations of index of surviving bacteria (ISB). RESULTS: The bactericidal activity of meropenem against K. pneumoniae and E. cloacae in this in vitro/ex vivo model was excellent, with a 4 log decrease at peak concentrations. Meropenem produced a mixed concentration- and time-dependent, killing effect against E. cloacae and K. pneumoniae. The ISB value ranged from 25% to 30% for E. cloacae. With concentrations above MIC for S. aureus (1 mg/L), cefpirome has a time-dependent bactericidal activity, as shown by the ISB ranging from 20% to 80% after 4 h and between 20% and 40% after an 8-h drug exposure. For both antibiotics, the higher concentrations obtained just after intermittent injection had a rapid and strong killing effect against the strains tested, but the trough levels had no bactericidal activity. The continuous infusions produce consistent concentrations of antibiotic that can be maintained above the MIC, and the bactericidal activity of which ranges from 2 to 4 log10 decrease of inoculum. CONCLUSIONS: In the present study the micropig has been shown to be an adequate model for the pharmacodynamic investigation of cefpirome and meropenem. In general, continuous infusion appears to optimize the pharmacodynamic profile of the two tested beta-lactam antibiotics. However, against Gram-negative bacilli, the administration of a loading dose prior to continuous infusion of beta-lactams would eliminate the only potential pharmacokinetic disadvantage of continuous infusion and ensure the rapid onset of antimicrobial activity.

The treatment of staphylococcal infections with special reference to pharmacokinetic, pharmacodynamic and pharmacoeconomic considerations

The choice of antibiotics for the treatment of staphylococcal infections depends to a high degree on the susceptibility patterns in the hospital in question. These may be highly variable and considerable differences between countries and hospitals exist. The insight into the pharmacodynamic aspects of antimicrobial agents has increased considerably in the last 5 years, resulting in new treatments, such as once daily administration of aminoglycosides and continuous infusion of betalactam antibiotics. The antibiotic policy in Dutch hospitals for the treatment of staphylococcal infections is discussed. In most Western countries with a relatively low incidence of MRSA, penicillin-derivatives, such as flucloxacillin (or cloxacillin, methicillin and nafcillin) will be the drug of choice, because of their good in-vitro activity, low toxicity, good clinical efficacy and relatively low cost. If the incidence of MRSA increases, drugs such as the glycopeptides will be of more importance. This will of course have a clear economic impact, as both vancomycin and teicoplanin are considerably more expensive than agents such as flucloxacillin and oral treatment is not possible. Pharmacoeconomic aspects also play a role. As a rule, intravenous antimicrobial agents are considerably more expensive than the oral formulations. Before oral administration can be recommended, a reliable oral absorption, also in seriously ill patients, must have been demonstrated. Other aspects that influence the cost of therapy are hospital stay and the possibility of outpatient treatment.

Using therapeutic drug monitoring to dose the antimycobacterial drugs

The available data suggest that selected patients with tuberculosis and MAC fail to respond to therapy because they malabsorb their medications. In particular, patients with AIDS and known gastrointestinal diseases have problems absorbing these drugs. In addition, because MDR-TB and MAC are so difficult to treat, TDM with the antimycobacterial drugs offers the clinician a chance to ensure that the patient achieves serum concentrations above the MIC of the pathogen. TDM has become the standard of practice at the National Jewish Center for Immunology and Respiratory Medicine. By combining specific and sensitive assays, carefully collected samples, and clinical expertise, we are able to control and optimize antimycobacterial drug therapy. We continue to refine our approach with ongoing pharmacokinetic and pharmacodynamic research, including the development of population pharmacokinetic models. We hope that these efforts will provide insight into the nature of current therapeutic problems. We also hope they will help us improve the clinical outcomes of our patients.

Kill kinetics and regrowth patterns of Pseudomonas aeruginosa exposed to concentration-time profiles of tobramycin simulating in vivo infusion and bolus dosing

Pseudomonas aeruginosa ATCC 27853 was exposed to tobramycin concentration-time profiles modelling in vivo bolus and infusion dosing. Dependence of bactericidal and bacteriostatic activity on the initial profile of peak concentration (bolus effect > infusion) and area under the antibiotic concentration-time curve was observed at peak concentration/MIC ratios of 10 or below.

Preclinical and clinical evaluation of once-daily aminoglycoside chemotherapy

The rationale for and effectiveness of extended dosage intervals for aminoglycosides are reviewed. Aminoglycoside antibiotics have a prolonged postantibiotic effect against a variety of common Gram-negative and Gram-positive organisms: higher serum aminoglycoside levels are associated with a longer postantibiotic effect and increased bactericidal activity. Moreover once daily aminoglycoside administration may reduce the potential for adaptive postexposure resistance by allowing less contact time between bacteria and antibiotic. A longer dosage interval may decrease the risk of nephro- and ototoxicity. At least 33 published clinical trials suggest that once-daily administration of aminoglycosides and conventional regimens involving shorter dosage intervals are equally effective in patients with normal renal function and Gram-negative infections: besides, once-daily administration may reduce the frequency of aminoglycoside toxicity or delay it.

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.

Infection caused by Mycobacterium tuberculosis

OBJECTIVE

To update readers on the clinical management of infections caused by Mycobacterium tuberculosis, to provide a general description of the organism, culture and susceptibility testing, and clinical manifestations of the disease, and to provide several aspects of the treatment of the disease, including historical perspective, current approaches, and research opportunities for the future.

DATA SOURCES

The current medical literature, including abstracts presented at recent international meetings, is reviewed. References were identified through MEDLINE, MEDLARS II, Current Contents, and published meeting abstracts.

STUDY SELECTION

Data regarding the epidemiology, clinical manifestations, culture and susceptibility testing, and treatment of tuberculosis are cited. Specific attention has been focused on the clinical management of patients with noncontagious infection and potentially contagious active disease (TB) caused by M. tuberculosis.

DATA EXTRACTION

Information contributing to the discussion of the topics selected by the authors is reviewed. Data supporting and disputing specific conclusions are presented.

DATA SYNTHESIS

The incidence of TB is increasing in the US, despite the fact that available technologies are capable of controlling the vast majority of existing cases. Fueling the fire is the problem of coinfection with HIV and M. tuberculosis. Very few drugs are available for the treatment of TB, and few of these approach the potency of isoniazid and rifampin. Preventive therapy of patients exposed to multiple-drug-resistant M. tuberculosis (MDR-TB) is controversial and of unknown efficacy. Treatment of active disease caused by MDR-TB requires up to four times longer, is associated with increased toxicity, and is far less successful than the treatment of drug-susceptible TB. Strategies for the management of such cases are presented. The rising incidence of TB in the US reflects a breakdown in the healthcare systems responsible for controlling the disease, which reflects the past budgetary reductions. Although TB control is one of the most cost-effective public health strategies, funding has been cut repeatedly despite the fact that TB was never eliminated. This has helped to produce the current crisis, including the spread of MDR-TB in many urban areas. The elimination of TB will now take decades longer, cost hundreds of millions of dollars more, and result in vastly higher morbidity and mortality rates than would have occurred with timely, adequate measures.

CONCLUSIONS

Tremendous effort and far more funding will be required to eliminate TB in the US. The selection of drug therapy must be based on the susceptibility data for each isolate. Multiple-drug therapy must be continued for 6 to > or = 24 months, and patient adherence to prescribed regimens must be verified in all cases of TB. Significant antimycobacterial drug malabsorption has been documented in AIDS patients with TB, and may result in treatment failure. New agents are needed to improve the clinical outcome in patients with MDR-TB.

Pharmacology of the antimycobacterial drugs

The management of MDR-TB requires that the clinician become familiar with the "second-line" antimycobacterial agents. These drugs are generally less potent and frequently more toxic than isoniazid and rifampin. Because they are less active, innovative dosing schedules may allow us to take advantage of the few strengths that they possess. This approach will require further research into the dose-response relationships for each agent. Based on our current knowledge of these drugs, practical guidelines for their use have been described. These guidelines include the gradual escalation of the oral doses of PAS, cycloserine, and ethionamide over several days, and the intravenous administration of streptomycin and capreomycin. Both ciprofloxacin and ofloxacin may be used for the treatment of MDR-TB, but data from clinical trials are currently lacking. Finally, because patients with AIDS appear to develop antimycobacterial drug malabsorption over the course of their HIV infection, therapeutic drug monitoring can be used to verify drug absorption in the individual patient. This approach may improve therapy for that patient and prevent the selection of additional drug resistance.

Is treatment of acute otitis media with once-a-day amoxicillin feasible? Results of a pilot study

We report a study of the feasibility of once-a-day amoxicillin to treat acute otitis media (AOM). Seventy-seven children between ages 7 months and 12 years with AOM participated in a double-blind, placebo-controlled trial. Subjects received amoxicillin 40 mg/kg/day for 10 days. They were similar in age, sex, history of ear infections, and presenting symptoms. Group I received one total dose of amoxicillin and two doses of placebo daily. Group II received three divided doses of amoxicillin daily. Parents kept a daily diary of symptoms related to the child's illness and possible medication side effects. Ten children were lost to follow-up. In the remaining 67, pneumatic otoscopy and tympanometry after 10 to 14 days revealed that AOM had resolved in 82% of group I and 68% of group II. Groups showed no significant differences in persistence of middle ear effusion; 39% in group I and 24% in group II still had fluid. Diaries showed no significant differences between groups in medication side effects. Thus, reduced-frequency dosing for AOM seems feasible and more realistic than current regimens.

Controversies in the management of Mycobacterium avium complex infection in AIDS patients

OBJECTIVE

To update readers on the clinical management of infections secondary to Mycobacterium avium complex (MAC) in patients with AIDS. A general description of the organism, culture and susceptibility testing, and clinical manifestations of the disease is provided. Several aspects of the treatment of the disease, including an historical perspective, current approaches, and future research opportunities, are described.

DATA SOURCES

Current medical literature, including abstracts presented at international meetings, is reviewed. References were identified through MEDLINE, Current Contents, and published meeting abstracts.

STUDY SELECTION

Data regarding the epidemiology, clinical manifestations, culture and susceptibility testing, and treatment of MAC are cited. Specific attention is given to the management of patients with MAC infection.

DATA EXTRACTION

Information contributing to the discussion of the topics selected by the author is reviewed. Data supporting and disputing specific conclusions are presented.

DATA SYNTHESIS

Disseminated MAC infection is diagnosed antemortem in approximately 30 percent of patients with AIDS; postmortem rates of isolation exceed 50 percent. The incidence of MAC may increase as attempts at isolating the organism become more aggressive. The traditional approach to the isolation, susceptibility testing, and treatment of MAC has been derived from the management of Mycobacterium tuberculosis, with disappointing results. Newer radiometric in vitro methods of susceptibility testing appear to show more promise. Current mouse models of MAC are not true AIDS models; new CD4-deficient mouse models are being developed. Clinical mycobacteriologic and pharmacokinetic laboratory support have been underused, with treatment generally proceeding empirically. New agents that may contribute to the management of disseminated MAC infection include the macrolide derivatives clarithromycin and azithromycin. Research also continues with new rifamycins (including rifabutin) and fluoroquinolones (ciprofloxacin, sparfloxacin). Preliminary results suggest a central role for macrolides in the treatment of disseminated MAC; effective companion drugs are needed to prevent the rapid emergence of macrolide-resistant MAC.

CONCLUSIONS

Treatment results for disseminated MAC infection remain poor. Therapy may be improved by selecting drugs on the basis of susceptibility data for each isolate, rather than by using empiric regimens based on susceptibility trends. Significant antimycobacterial drug malabsorption has been documented, and may contribute to poor outcomes. More-potent agents are needed to improve the clinical outcome in AIDS patients with MAC.

Kill kinetics and regrowth patterns of Escherichia coli exposed to gentamicin concentration-time profiles simulating in vivo bolus and infusion dosing

The relative influence of peak concentration (Cmax) versus the area under the antibiotic concentration-time curve (AUC) on the bactericidal effect of gentamicin against Escherichia coli NCTC 10418 was studied. Bacteria in the lag phase were exposed to an in vitro gentamicin concentration series which mirrored the concentrations determined in patients after 80-mg intravenous bolus (1 min) and 80-mg intravenous infusion (30 min) doses. Bacterial viable cell counts and gentamicin concentrations were measured before and during antibiotic exposure. Both the Cmax and AUC were shown to be factors determining antibacterial activity; however, the Cmax was an independent determinant of effect. These findings indicate that bolus intravenous dosing with gentamicin could maximize bactericidal activity. Increased efficacy could result at any given daily antibiotic dose if delivered via bolus with long intervals (12 to 24 h) between doses if appropriate precautions to avoid toxicity are taken.

Compatibility of ceftazidime and aminophylline admixtures for different methods of intravenous infusion

OBJECTIVE

Aminophylline and ceftazidime are sometimes used concurrently in patients with respiratory disorders. Parenteral aminophylline usually is administered as a constant infusion, and ceftazidime is given intermittently or less commonly as a constant infusion. We evaluated the stability and compatibility of the two drugs when aminophylline is given as a constant intravenous infusion and ceftazidime is administered simultaneously either through a y-site (piggyback method) or as a continuous infusion (constant infusion method).

DESIGN

The chemical stability of intravenous aminophylline and ceftazidime in dextrose 5% and NaCl 0.9% for both methods was studied. Three different formulations of ceftazidime from the same manufacturer were studied (minibag using reconstituted ceftazidime, premixed minibag, and ceftazidime arginine). For the piggyback and constant infusion methods, samples were collected at 0, 1, and 2 hours; and 0, 6, and 24 hours, respectively. All experiments were conducted in triplicate. Samples were analyzed in duplicate by a stability-indicating HPLC assay method.

OUTCOME MEASURE

Ceftazidime and aminophylline were considered stable if concentrations remained above 90 percent of the original concentrations over the time periods studied.

RESULTS

Ceftazidime was determined to be compatible with aminophylline in the piggyback method. In contrast, when aminophylline and ceftazidime were admixed in the same intravenous container (constant infusion method), the two drugs were not stable.

CONCLUSIONS

These data indicate that aminophylline and ceftazidime admixtures are incompatible when prepared in the same intravenous container, which may occur if both are given as a constant infusion. The two drugs are compatible when the ceftazidime is piggybacked into a primary intravenous set in which aminophylline is administered as a constant infusion.

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)

Identification of factors affecting in vivo aminoglycoside activity in an experimental model of gram-negative endocarditis

Aminoglycoside bactericidal activity during the first 24 h of treatment probably is a determining parameter in the prognosis of severe gram-negative infections in immunocompromised patients. To identify the predictive factors involved in the definition of the best therapeutic regimen for Enterobacter cloacae and Serratia marcescens infections, we studied different gentamicin, tobramycin, and amikacin regimens by using an experimental model of rabbit endocarditis. Two factors appear to play an important role in predicting in vivo efficacy: (i) the level of in vivo bactericidal activity, which can differ widely from one aminoglycoside to another for the same bacterial strain and from one strain to another of the same species, and (ii) the critical serum drug concentration (CSC, in milligrams per liter), defined as the lowest serum antibiotic concentration capable of producing a significant CFU reduction (P less than 0.05) in endocarditis vegetations 24 h after the beginning of a continuous infusion. Stepwise regression analysis showed that for gentamicin and S. marcescens, the area under the concentration-time curve above the CSC and then the time above the CSC are the determining parameters for efficacy (R = 0.69; F = 13.5; P = 0.001), whereas for amikacin and S. marcescens, the time above the CSC and then the area under the concentration-time curve above the CSC predict efficacy (R = 0.74; F = 24.0; P = 0.0001). The lowest CSC is that of amikacin (about 8 mg/liter); those of gentamicin and tobramycin are about 15 mg/liter. In severe S. marcescens infections, intermittent amikacin dosing offers excellent bactericidal activity within the first 24 h.

Penetration of netilmicin in the lower respiratory tract after once-daily dosing

A major criticism of the use of aminoglycosides for the treatment of pneumonia is the poor penetration in infected airways. Once-daily dosing of aminoglycosides results in higher peak plasma concentrations without increasing toxic reactions and with optimization of pharmacodynamic properties. To predict intrapulmonary antimicrobial activity after once-daily dosing of aminoglycosides, it is necessary to determine the respective bronchial and alveolar disposition. We prospectively conducted a pharmacokinetic study of netilmicin following the first intravenous administration of a once-daily dosing schedule in 20 ventilated patients with pneumonia. A bronchoscopic sampling of bronchial secretions and a subsegmental bronchoalveolar lavage (BAL) were performed 60, 90, 120, and 180 min (five patients at each time point) on the first treatment day after intravenous administration over 30 min of 450 mg of netilmicin. The netilmicin concentrations in the alveolar lining fluid (ALF) were calculated using urea as an endogenous marker of dilution. In bronchial secretions, a peak concentration of 2.00 (SEM: 0.26) mg/L or 6 percent of the 30-min plasma concentration was reached at 120 min. In ALF, much higher levels were found. At 120 min, a peak ALF concentration of 14.7 (SEM: 2.22) mg/L or 41 percent of the 30-min plasma concentration was reached. Spearman's rank correlation testing failed to show a correlation between bronchial and ALF concentrations. Higher plasma concentrations of netilmicin after once-daily dosing give rise to ALF concentrations exceeding the minimum inhibitory concentration of susceptible respiratory pathogens involved in nosocomial pneumonia, while bronchial concentrations remain low. Aminoglycoside concentrations in bronchial secretions cannot be used to predict alveolar concentrations. Low diffusibility can no longer be considered as a disadvantage of aminoglycosides for treating pneumonias.

Pharmacodynamics and pharmacokinetics of antibiotics with special reference to the fluoroquinolones

The pharmacodynamic and pharmacokinetic properties of antibiotics have received increased attention in recent years, leading to optimization of dosage regimens. In view of these characteristics, certain fluoroquinolones may prove advantageous compared with other antimicrobials for treatment of selected infections. Several new fluoroquinolone antimicrobial agents have potency equal to or greater than that of beta-lactam antibiotics against gram-negative aerobic bacilli, including Pseudomonas aeruginosa. In vitro bactericidal activity of these compounds is more rapid than that of the beta-lactams, often resembling that for the aminoglycosides. Like the aminoglycosides, but in contrast to the beta-lactams, fluoroquinolones exert a significant in vitro postantibiotic effect against some strains of P. aeruginosa and Enterobacteriaceae. However, unlike many beta-lactam and aminoglycoside antimicrobial agents that have similar in vitro activity, fluoroquinolones are often effective both after oral and parenteral administration. Important pharmacokinetic properties of fluoroquinolones include differences in the extent and variability in oral absorption and clearance, which determine the extent of in vivo exposure to drug. Drugs and dosage regimens that result in a high degree of exposure, particularly high peak levels of drug, may be preferable because of a greater extent of bacterial killing and less selection of drug-resistant bacteria.

Pharmacokinetics of tobramycin in pregnant women. Safety and efficacy of a once-daily dose regimen

The pharmacokinetics of tobramycin, an aminoglycoside antibiotic, was investigated after a short intravenous infusion and once-daily dose regimen in two groups of nine pregnant women during the second (Group 1) and the third (Group 2) trimester of pregnancy. During these periods, the risk of infectious diseases is increased. Plasma concentrations of tobramycin were measured by fluorescence polarization immunoassay. The decrease in clearance (21%), at 28 weeks and more of gestation leads to an increase in half-life and the mean residence time (MRT) in the second group (33 and 29% respectively). The volume of distribution was unchanged in the two groups. No accumulation of the drug was observed in pregnant women. Pharmacokinetic disorders are correlated with the term and moreover with the weight deviation of women, i.e. the growth of the fetus. These findings suggest accumulation of the aminoglycoside antibiotic in the fetus. Moreover, the efficacy and the safety of this therapeutic regimen were excellent. To limit the potential nephrotoxicity and ototoxicity of tobramycin for the mother and the fetus, a once-daily dose regimen seems to be acceptable for the treatment of non-neutropenic pregnant women.

The postantibiotic effect: a review of in vitro and in vivo data

The term postantibiotic effect (PAE) refers to a period of time after complete removal of an antibiotic during which there is no growth of the target organism. The PAE appears to be a feature of most antimicrobial agents and has been documented with a variety of common bacterial pathogens. Several factors influence the presence or duration of the PAE including the type of organism, type of antimicrobial, concentration of antimicrobial, duration of antimicrobial exposure, and antimicrobial combinations. In vitro, beta-lactam antimicrobials demonstrate a PAE against gram-positive cocci but fail to produce a PAE with gram-negative bacilli. Antimicrobials that inhibit RNA or protein synthesis produce an in vitro PAE against gram positive cocci and also produce a PAE against gram-negative bacilli. In vitro methods used to determine the PAE include colony counts, optical density, and measurement of adenosine triphosphate in bacteria. The exact mechanisms by which antimicrobials induce the PAE have not been clearly delineated. Animal studies reveal in vivo PAEs in accordance with PAEs obtained in vitro for most organism/antimicrobial combinations. The clinical relevance of the PAE is probably most important when designing dosage regimens. The presence of a long PAE allows aminoglycosides to be dosed infrequently; the lack of an in vivo PAE suggests that beta-lactam antimicrobials require frequent or continuous dosing. Important questions remain to be answered concerning the PAE.

Impact of dosage schedule on the efficacy of gentamicin, tobramycin, or amikacin in an experimental model of Serratia marcescens endocarditis: in vitro-in vivo correlation

Aminoglycosides are usually considered to be concentration-dependent antibiotics and to have similar pharmacodynamic and pharmacokinetic properties. To verify the equivalent activity of the aminoglycosides on a susceptible strain, we tested the killing rate of three aminoglycosides (gentamicin, tobramycin, and amikacin) on one strain of Serratia marcescens both in vitro and in vivo by using a rabbit model of left-ventricle endocarditis. Despite, similar MICs, the time-kill curve of gentamicin was consistently better than those of amikacin and tobramycin, whatever the concentration of each antibiotic used (1, 2, 4, 8, 16, or 32 mg/liter), after a 5-h incubation. The in vivo bacterial reduction in the vegetations was measured 24 h after administration of an intravenous 48-mg/kg bolus of each antibiotic or at the end of a 24-h continuous intravenous infusion of the same dose. Gentamicin was significantly more effective when administered as a bolus than when administered as a continuous infusion (2.8 +/- 0.2 versus 6.4 +/- 1.5 log10 CFU/g of vegetation, respectively; P less than 0.01), whereas amikacin was more effective as a continuous infusion than as a bolus injection (3.6 +/- 2.0 versus 7.5 +/- 1.3 log10 CFU/g of vegetation, respectively; P less than 0.01). Tobramycin was not very effective, whatever the dosage tested (approximately 6.5 to 7 log10 CFU/g). These results suggest that concentration-dependent bactericidal activities, both in vitro and in vivo, may vary greatly among aminoglycosides despite similar MICs.

Pharmacokinetics of ceftazidime in serum and suction blister fluid during continuous and intermittent infusions in healthy volunteers

The pharmacokinetics of ceftazidime were investigated during intermittent (II) and continuous (CI) infusion in eight healthy male volunteers in a crossover fashion. The total daily dose was 75 mg/kg of body weight per 24 h in both regimens, given in three doses of 25 mg/kg/8 h (II) or 60 mg/kg/24 h with 15 mg/kg as a loading dose (CI). After the third dose (II) and during CI, serum and blister fluid samples were taken. Seven new blisters were raised for each timed sample by a suction blister technique. Blisters took 90 min to form. Samples were then taken from four blisters (A samples) and 1 h later were taken from the remaining three (B samples). The concentration of ceftazidime was determined using a high-performance liquid chromatography method. After II, the concentrations in serum immediately after infusion (t = 30 min) and 8 h after the start of the infusion were 137.9 (standard deviation [SD], 27.5) and 4.0 (SD, 0.7) micrograms/ml, respectively. The half-life at alpha phase (t1/2 alpha) was 9.6 min (SD, 4.6), t1/2 beta was 94.8 min (SD, 5.4), area under the concentration-time curve (AUC) was 285.4 micrograms.h/ml (SD, 22.7), total body clearance was 0.115 liter/h.kg (SD, 0.022), and volume of distribution at steady state was 0.178 liter/kg (SD, 0.023). The blister fluid (A) samples showed a decline in concentration parallel to that of the concentrations in serum during the elimination phase with a ratio of 1:1. The t1/2 of the A samples was 96.4 min (SD, 3.2). The concentration of ceftazidime in the B blister fluid samples was significantly higher (27%) than in the A samples over time. This shows that blisters may behave as a separate compartment and establishes the need to raise new blisters for each timed sample. The mean AUC/h during continuous infusion was 21.3 micrograms . h/ml (SD, 3.0). The total body clearance was 0.113 liter/h . kg (SD, 0.018), the urinary clearance was 0.105 liter/h . kg (SD, 0.012), and the ceftazidime/creatinine clearance ratio was 0.885. The mean AUC of blister fluid per hour was 84.5% (18.0 micrograms . h/liter; SD, 3.6) compared with that of serum. The A samples did not differ significantly from the B samples. The implications of continuous infusion of beta-lactams for treatment of serious infections are discussed.

Assessment of cefazolin and cefuroxime tissue penetration by using a continuous intravenous infusion

A continuous intravenous infusion was used to assess the tissue penetration of cefazolin (14 subjects) and cefuroxime (15 subjects) in orthopedic surgery patients. Subjects were randomly assigned to receive a continuous intravenous infusion of cefazolin (mean, 178.6 mg/h) or cefuroxime (mean, 330.0 mg/h) at a rate estimated to achieve a target steady-state total concentration of 50 micrograms/ml in serum. The infusion was initiated 12 to 14 h before surgery, and blood and muscle tissue samples were collected intraoperatively at the times of incision and wound closure. Although there was a significant difference between the free concentrations of cefazolin (at incision, 9.3 micrograms/ml; at closure, 9.2 micrograms/ml) and cefuroxime in serum (at incision, 26.9 micrograms/ml; at closure, 31.8 micrograms/ml), there was no difference in the total concentrations in muscle at either surgical incision (cefazolin, 6.1 micrograms/g; cefuroxime, 5.6 micrograms/g) or wound closure (cefazolin, 7.7 micrograms/g; cefuroxime, 7.4 micrograms/g). There was a significant correlation between the pooled free serum and total muscle concentrations for cefazolin (P = 0.001); however, there was no correlation between these variables with the pooled cefuroxime data (P = 0.403). These findings indicate that the free drug concentration in serum alone is not consistently predictive of the total concentration of cephalosporin in muscle.

Penetration of ampicillin and sulbactam in the lower airways during respiratory infections

We studied the penetration of ampicillin-sulbactam in the alveolar lining fluid (ALF) of eight patients after intravenous administration of 2,000 mg of ampicillin and 1,000 mg of sulbactam three times daily over 30 min. Bronchoalveolar lavage was performed on day 3, 30 min after the end of the morning drug administration. The mean penetration ratios (i.e., the ratios of the concentrations in ALF versus those in serum) were 53% (standard error, 12%) and 61% (standard error 31%) for ampicillin and sulbactam, respectively. The concentration ratio of ampicillin versus sulbactam in serum was not significantly different from that in ALF. From a pharmacokinetic point of view, ampicillin-sulbactam is a good choice for treatment of infectious exacerbation of chronic obstructive pulmonary disease and community-acquired bacterial pneumonia, since the concentrations of both drugs in ALF exceed the MICs for the respiratory pathogens responsible.

High-Technology Home Pharmacotherapy, I: An Overview of Antiinfective and Antineoplastic Therapies

Home care has evolved into a highly technical support system caring for the more acutely ill patient who requires specialized medical attention. Almost every drug is a candidate for home-care administration if adequate patient selection and monitoring criteria are met. Home parenteral antimicrobial therapy has progressed beyond simple intravenous (IV) drip administration. New routes and techniques, and unusual doses and intervals are commonly encountered. Newer infusion devices have enabled antibiotic and other therapies to be accomplished more easily. Parenteral chemotherapy at home has been given by some unusual routes and administered continuously. Management of the potentially severe side effects of antineoplastic therapy has also been successfully accomplished in the home. This article addresses the considerations for initiating home parenteral therapy and provides an overview of the management of antimicrobial and antineoplastic therapies at home.

Alternative dosing strategy for aminoglycosides: impact on efficacy, nephrotoxicity, and ototoxicity

Accumulating evidence suggests that the therapeutic margin of aminoglycoside therapy may be improved by manipulation of dosing strategy. Recent understanding of concentration-dependent bactericidal activity and postantibiotic effect argues that the aminoglycosides may be administered in larger doses and at longer dosing intervals than currently recommended without compromising efficacy. Preliminary clinical experience suggests that once-daily regimens are as efficacious as conventional intermittent injections in the treatment of gram-negative infectious including urinary tract infections, cystic fibrosis, and bacteremia in nonneutropenic patients. The transient, high peak serum concentrations achieved in once-daily dosing have not been associated with excessive nephrotoxicity or ototoxicity thus far. Decreased accumulation in renal cortex as a result of saturable renal uptake after the single daily dose may even reduce the incidence or severity of renal damage. Further studies on more patients are required to substantiate these preliminary findings.