Pharmacokinetic and experimental data on beta-lactam antibiotics in the treatment of patients

Meropenem-Tobramycin Combination Regimens Combat Carbapenem-Resistant Pseudomonas aeruginosa in the Hollow-Fiber Infection Model Simulating Augmented Renal Clearance in Critically Ill Patients

Augmented renal clearance (ARC) is common in critically ill patients and is associated with subtherapeutic concentrations of renally eliminated antibiotics. We investigated the impact of ARC on bacterial killing and resistance amplification for meropenem and tobramycin regimens in monotherapy and combination. Two carbapenem-resistant Pseudomonas aeruginosa isolates were studied in static-concentration time-kill studies. One isolate was examined comprehensively in a 7-day hollow-fiber infection model (HFIM). Pharmacokinetic profiles representing substantial ARC (creatinine clearance of 250 ml/min) were generated in the HFIM for meropenem (1 g or 2 g administered every 8 h as 30-min infusion and 3 g/day or 6 g/day as continuous infusion [CI]) and tobramycin (7 mg/kg of body weight every 24 h as 30-min infusion) regimens. The time courses of total and less-susceptible bacterial populations and MICs were determined for the monotherapies and all four combination regimens. Mechanism-based mathematical modeling (MBM) was performed. In the HFIM, maximum bacterial killing with any meropenem monotherapy was ∼3 log₁₀ CFU/ml at 7 h, followed by rapid regrowth with increases in resistant populations by 24 h (meropenem MIC of up to 128 mg/liter). Tobramycin monotherapy produced extensive initial killing (∼7 log₁₀ at 4 h) with rapid regrowth by 24 h, including substantial increases in resistant populations (tobramycin MIC of 32 mg/liter). Combination regimens containing meropenem administered intermittently or as a 3-g/day CI suppressed regrowth for ∼1 to 3 days, with rapid regrowth of resistant bacteria. Only a 6-g/day CI of meropenem combined with tobramycin suppressed regrowth and resistance over 7 days. MBM described bacterial killing and regrowth for all regimens well. The mode of meropenem administration was critical for the combination to be maximally effective against carbapenem-resistant P. aeruginosa.

Optimizing Antibiotic Administration for Pneumonia

Pneumonia, including community-acquired bacterial pneumonia, hospital-acquired bacterial pneumonia, and ventilator-acquired bacterial pneumonia, carries unacceptably high morbidity and mortality. Despite advances in antimicrobial therapy, emergence of multidrug resistance and high rates of treatment failure have made optimization of antibiotic efficacy a priority. This review focuses on pharmacokinetic and pharmacodynamic approaches to antibacterial optimization within the lung environment and in the setting of critical illness. Strategies for including these approaches in drug development programs as well as clinical practice are described and reviewed.

Optimization of a Meropenem-Tobramycin Combination Dosage Regimen against Hypermutable and Nonhypermutable Pseudomonas aeruginosa via Mechanism-Based Modeling and the Hollow-Fiber Infection Model

Hypermutable Pseudomonas aeruginosa strains are prevalent in patients with cystic fibrosis and rapidly become resistant to antibiotic monotherapies. Combination dosage regimens have not been optimized against such strains using mechanism-based modeling (MBM) and the hollow-fiber infection model (HFIM). The PAO1 wild-type strain and its isogenic hypermutable PAOΔmutS strain (MIC_meropenem of 1.0 mg/liter and MIC_tobramycin of 0.5 mg/liter for both) were assessed using 96-h static-concentration time-kill studies (SCTK) and 10-day HFIM studies (inoculum, ∼10^8.4 CFU/ml). MBM of SCTK data were performed to predict expected HFIM outcomes. Regimens studied in the HFIM were meropenem at 1 g every 8 h (0.5-h infusion), meropenem at 3 g/day with continuous infusion, tobramycin at 10 mg/kg of body weight every 24 h (1-h infusion), and both combinations. Meropenem regimens delivered the same total daily dose. Time courses of total and less susceptible populations and MICs were determined. For the PAOΔmutS strain in the HFIM, all monotherapies resulted in rapid regrowth to >10^8.7 CFU/ml with near-complete replacement by less susceptible bacteria by day 3. Meropenem every 8 h with tobramycin caused >7-log₁₀ bacterial killing followed by regrowth to >6 log₁₀ CFU/ml by day 5 and high-level resistance (MIC_meropenem, 32 mg/liter; MIC_tobramycin, 8 mg/liter). Continuous infusion of meropenem with tobramycin achieved >8-log₁₀ bacterial killing without regrowth. For PAO1, meropenem monotherapies suppressed bacterial growth to <4 log₁₀ over 7 to 9 days, with both combination regimens achieving near eradication. An MBM-optimized meropenem plus tobramycin regimen achieved synergistic killing and resistance suppression against a difficult-to-treat hypermutable P. aeruginosa strain. For the combination to be maximally effective, it was critical to achieve the optimal shape of the concentration-time profile for meropenem.

Considerable variation of trough β-lactam concentrations in older adults hospitalized with infection-a prospective observational study

In older adults, few studies confirm that adequate concentrations of antibiotics are achieved using current dosage regimens of intravenous β-lactam antibiotics. Our objective was to investigate trough concentrations of cefotaxime, meropenem, and piperacillin in older adults hospitalized with infection. We included 102 patients above 70 years of age. Total trough antibiotic concentrations were measured and related to suggested target intervals. Information on antibiotic dose, patient characteristics, and 28-day outcomes were collected from medical records and regression models were fitted. Trough concentrations for all three antibiotics exhibited considerable variation. Mean total trough concentrations for cefotaxime, meropenem, and piperacillin were 6.5 mg/L (range 0-44), 3.4 mg/L (range 0-11), and 30.2 mg/L (range 1.2-131), respectively. When a target range of non-species-related breakpoint - 5× non-species-related breakpoint was applied, only 36% of patients had both values within the target range. Regression models revealed that severe sepsis was associated with varying concentration levels and increasing age and diminishing kidney function with high concentration levels. The study was not powered to demonstrate consequences in clinical outcomes. Conclusively, in older adults treated with cefotaxime, meropenem, or piperacillin-tazobactam, trough antibiotic concentrations varied considerably. Better predictors to guide dosing regimens of β-lactam antibiotics or increased use of therapeutic drug monitoring are potential ways to address such variations.

Substantial Impact of Altered Pharmacokinetics in Critically Ill Patients on the Antibacterial Effects of Meropenem Evaluated via the Dynamic Hollow-Fiber Infection Model

Critically ill patients frequently have substantially altered pharmacokinetics compared to non-critically ill patients. We investigated the impact of pharmacokinetic alterations on bacterial killing and resistance for commonly used meropenem dosing regimens. A Pseudomonas aeruginosa isolate (MIC_meropenem 0.25 mg/liter) was studied in the hollow-fiber infection model (inoculum ∼10^7.5 CFU/ml; 10 days). Pharmacokinetic profiles representing critically ill patients with augmented renal clearance (ARC), normal, or impaired renal function (creatinine clearances of 285, 120, or ∼10 ml/min, respectively) were generated for three meropenem regimens (2, 1, and 0.5 g administered as 8-hourly 30-min infusions), plus 1 g given 12 hourly with impaired renal function. The time course of total and less-susceptible populations and MICs were determined. Mechanism-based modeling (MBM) was performed using S-ADAPT. All dosing regimens across all renal functions produced similar initial bacterial killing (≤∼2.5 log₁₀). For all regimens subjected to ARC, regrowth occurred after 7 h. For normal and impaired renal function, bacterial killing continued until 23 to 47 h; regrowth then occurred with 0.5- and 1-g regimens with normal renal function (fT_>5×MIC = 56 and 69%, fC_min/MIC < 2); the emergence of less-susceptible populations (≥32-fold increases in MIC) accompanied all regrowth. Bacterial counts remained suppressed across 10 days with normal (2-g 8-hourly regimen) and impaired (all regimens) renal function (fT_>5×MIC ≥ 82%, fC_min/MIC ≥ 2). The MBM successfully described bacterial killing and regrowth for all renal functions and regimens simultaneously. Optimized dosing regimens, including extended infusions and/or combinations, supported by MBM and Monte Carlo simulations, should be evaluated in the context of ARC to maximize bacterial killing and suppress resistance emergence.

β-Lactam therapeutic drug monitoring in the critically ill: optimising drug exposure in patients with fluctuating renal function and hypoalbuminaemia

β-Lactams are routinely prescribed in the treatment of serious infections. Empirical dosing schedules are typically derived from studies in healthy volunteers and largely fail to consider the significant changes in antibacterial pharmacokinetics often encountered in the critically ill. These changes are primarily driven by the underlying pathophysiology and the interventions provided, leading to altered protein binding, poor tissue penetration, and fluctuations in the volume of distribution and drug clearance. Each separately, and in combination, is likely to complicate successful β-lactam administration in this setting. Although antibacterial therapeutic drug monitoring (TDM) has traditionally been employed to minimise drug toxicity, the challenges to achieving 'optimal' drug concentrations in the critically ill suggest β-lactam TDM as an attractive means to optimise drug exposure. Whilst there is currently little evidence to support routine widespread application of such a service, β-lactam TDM may still have a role in select patients where difficulty in establishing therapeutic concentrations can be illustrated. This series utilises three representative cases from a β-lactam TDM service that highlight the utility of this intervention in optimising antibacterial dosing. These preliminary data support an expanding role for β-lactam TDM in select critically ill patients and provide insight into the subpopulations most at risk of suboptimal drug exposure. Future studies investigating the clinical outcome benefits of β-lactam TDM in these patient groups are now warranted.

Role of the blood-cerebrospinal fluid barrier transporter as a cerebral clearance system for prostaglandin E₂ produced in the brain

An increasing level of prostaglandin (PG) E(2) is involved in the progression of neuroinflammation induced by ischemia and bacterial infection. Although an imbalance in the rates of production and clearance of PGE(2) under these pathological conditions appears to affect the concentration of PGE(2) in the cerebrospinal fluid (CSF), the regulatory system remains incompletely understood. The purpose of this study was to investigate the cellular system of PGE(2) production via microsomal PGE synthetase-1 (mPGES-1), the inducible PGE(2) -generating enzyme, and PGE(2) elimination from the CSF via the blood-CSF barrier (BCSFB). Immunohistochemical analysis revealed that mPGES-1 was expressed in the soma and perivascular sheets of astrocytes, pia mater, and brain blood vessel endothelial cells, suggesting that these cells are local production sites of PGE(2) in the CSF. The in vivo PGE(2) elimination clearance from the CSF was eightfold greater than that of d-mannitol, which is considered to reflect CSF bulk flow. This process was inhibited by the simultaneous injection of unlabeled PGE(2) and β-lactam antibiotics, such as benzylpenicillin, cefazolin, and ceftriaxone, which are substrates and/or inhibitors of organic anion transporter 3 (OAT3). The characteristics of PGE(2) uptake by the isolated choroid plexus were at least partially consistent with those of OAT3. OAT3 was able to mediate PGE(2) transport with a Michaelis-Menten constant of 4.24 μM. These findings indicate that a system regulating the PGE(2) level in the CSF involves OAT3-mediated PGE(2) uptake by choroid plexus epithelial cells, acting as a cerebral clearance pathway via the BCSFB of locally produced PGE(2) .

Therapeutic drug monitoring of antimicrobials

Optimizing the prescription of antimicrobials is required to improve clinical outcome from infections and to reduce the development of antimicrobial resistance. One such method to improve antimicrobial dosing in individual patients is through application of therapeutic drug monitoring (TDM). The aim of this manuscript is to review the place of TDM in the dosing of antimicrobial agents, specifically the importance of pharmacokinetics (PK) and pharmacodynamics (PD) to define the antimicrobial exposures necessary for maximizing killing or inhibition of bacterial growth. In this context, there are robust data for some antimicrobials, including the ratio of a PK parameter (e.g. peak concentration) to the minimal inhibitory concentration of the bacteria associated with maximal antimicrobial effect. Blood sampling of an individual patient can then further define the relevant PK parameter value in that patient and, if necessary, antimicrobial dosing can be adjusted to enable achievement of the target PK/PD ratio. To date, the clinical outcome benefits of a systematic TDM programme for antimicrobials have only been demonstrated for aminoglycosides, although the decreasing susceptibility of bacteria to available antimicrobials and the increasing costs of pharmaceuticals, as well as emerging data on pharmacokinetic variability, suggest that benefits are likely.

Management of ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) management depends on the interaction between the infective agent, the host response, and the antimicrobial drug used. After the pathogen reaches the lungs, two outcomes are possible: either the microorganisms are eliminated by the host immune system, or they overcome the immune system and cause pulmonary infection. When a patient is thought to have VAP, two steps are strongly recommended: etiologic diagnostic testing and the immediate initiation of antibiotics. The daily management of VAP remains a challenge for physicians in the ICU. In recent years, a more dynamic approach has evolved, updating local epidemiology, evaluating VAP and diagnostic tools every day, and assessing host response using clinical and biochemical parameters.

Dynamics of success and failure in phage and antibiotic therapy in experimental infections

BACKGROUND

In 1982 Smith and Huggins showed that bacteriophages could be at least as effective as antibiotics in preventing mortality from experimental infections with a capsulated E. coli (K1) in mice. Phages that required the K1 capsule for infection were more effective than phages that did not require this capsule, but the efficacies of phages and antibiotics in preventing mortality both declined with time between infection and treatment, becoming virtually ineffective within 16 hours.

RESULTS

We develop quantitative microbiological procedures that (1) explore the in vivo processes responsible for the efficacy of phage and antibiotic treatment protocols in experimental infections (the Resistance Competition Assay, or RCA), and (2) survey the therapeutic potential of phages in vitro (the Phage Replication Assay or PRA). We illustrate the application and utility of these methods in a repetition of Smith and Huggins' experiments, using the E. coli K1 mouse thigh infection model, and applying treatments of phages or streptomycin.

CONCLUSIONS

1) The Smith and Huggins phage and antibiotic therapy results are quantitatively and qualitatively robust. (2) Our RCA values reflect the microbiological efficacies of the different phages and of streptomycin in preventing mortality, and reflect the decline in their efficacy with a delay in treatment. These results show specifically that bacteria become refractory to treatment over the term of infection. (3) The K1-specific and non-specific phages had similar replication rates on bacteria grown in broth (based on the PRA), but the K1-specific phage had markedly greater replication rates in mouse serum.

Pharmacological principles of antibiotic prescription in the critically ill

The goal of antimicrobial prescription is to achieve effective drug concentrations. Standard antimicrobial dosing regimens are based on research performed often decades ago and for the most part with patients who were not critically ill. More recent insights into antibiotic activity (e.g. the importance of high peak/MIC ratios for aminoglycosides and time above MIC for beta-lactam antibiotics), drug pharmacokinetics (e.g. increased volume of distribution and altered clearances) and the pathogenesis of sepsis (e.g. third space losses and altered creatinine clearances) have made re-evaluation of dosing regimens necessary for the critically ill. The inflammatory response associated with sepsis results in a rapid decrease in serum albumin levels, large fluid shifts and third space losses, initially with a high cardiac output. In turn these changes result in increased creatinine clearance and increased renal drug clearance. Unless these effects are offset by ensuing renal and/or hepatic impairment, with subsequent drug accumulation, antibiotic levels may be too low for optimal efficacy. The institution of continuous renal replacement therapy separately affects antibiotic clearances, and therefore dosing, even further. This article reviews relevant literature and offers principles for more effective and appropriate antibiotic dosing in the critically ill, based on the pharmacokinetic and pharmacodynamic principles of the main antibiotic groups (aminoglyosides, glycopeptides, beta-lactams, carbapenems and quinolones) and knowledge of the pathophysiology of the inflammatory response syndrome. Finally it also provides some guidance on the basic principles of drug prescription for patients receiving continuous renal replacement therapy.

Antibacterial properties of Pseudomonas aeruginosa immunotype 1 lipopolysaccharide-specific monoclonal antibody (MAb) in a murine thigh infection model: combined effects of MAb and ceftazidime

A murine monoclonal antibody (MAb) specific for the Pseudomonas aeruginosa immunotype 1 (It-1) lipopolysaccharide (LPS) O-side chain was evaluated in terms of its in vitro bactericidal opsonophagocytic activity and in vivo bacterial killing in a mouse thigh infection model. An immunoglobulin (Ig) G2a MAb Ld3-2F2, specific for It-1 LPS, mediated in vitro complement-dependent opsonophagocytic killing at a concentration of 10 microg/ml. MAb-mediated, complement-dependent killing also occurred in the absence of neutrophils at serum concentrations in excess of 20%. A remarkable synergy was observed in opsonophagocytic assays between MAb Ld3-2F2 (0.5 microg/ml) and ceftazidime (1/4 MIC). The administration of MAb Ld3-2F2 at a level of 1 microg resulted in a significant decrease in the number of bacteria in the thigh muscles of normal mice, while 100 microg of the same MAb was required for one log of reduction in the number of bacteria at the same site in neutropenic mice. The combined therapy with MAb Ld3-2F2 and ceftazidime provided a significant reduction in the density of bacteria in the thigh muscle at 9 hr post-infection in normal and neutropenic mice as compared with those after treatment alone or with no treatment (P< 0.01). These favorable in vitro and in vivo interactions of an LPS-specific IgG MAb and ceftazidime strongly support their potential for use in therapy, combined with an LPS-reactive MAb and parenteral antipseudomonas beta-lactam antibiotics in the therapy of systemic Pseudomonas infections in normal and neutropenic hosts.

Postantibiotic effect of ceftriaxone and gentamicin alone and in combination on Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus viridans

A persistent suppression of bacterial growth following limited exposure to an antimicrobial agent, the postantibiotic effect (PAE), has been described for a variety of antibiotics and microorganisms. In this study the PAE of ceftriaxone and gentamicin was determined in vitro on three strains each of Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus viridans. The strains were exposed to the substances for 2 h at varying concentrations. Ceftriaxone was used at the minimal inhibitory concentration (MIC) and 1/2 MIC and gentamicin at 1/2 MIC, 1/4 MIC, and 1/8 MIC, each alone and in combination. Antibiotic concentrations were reduced by 1,000-fold dilution, bacterial regrowth was consequently monitored by viable count. The PAE of ceftriaxone alone reached up to 145 min (MIC) and 50 min (1/2 MIC), that of gentamicin alone up to 170 min (1/2 MIC), 135 min (1/4 MIC) and 70 min (1/8 MIC), depending on the bacterial species. Combinations of the antibiotics produced longer PAEs than one substance alone; the longest PAE was produced by the combination of ceftriaxone (MIC) and gentamicin (1/2 MIC) lasting up to 320 min (S. viridans). It may be important to take the PAE into account when evaluating dosing intervals.

Piperacillin-tazobactam plus amikacin versus ceftazidime plus amikacin as empiric therapy for fever in granulocytopenic patients with cancer. The International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer

Gram-positive bacteria have become the predominant infecting organisms in granulocytopenic cancer patients. Empiric antibiotic regimens used in febrile neutropenic patients often include an extended-spectrum cephalosporin, but the response to therapy in gram-positive coccal bacteremia has been unsatisfactory. Thus, new antibiotics with better activity against gram-positive bacteria should be tested. The objective of this prospective randomized controlled study was to evaluate and compare the efficacy and tolerance of piperacillintazobactam plus amikacin with that of ceftazidime plus amikacin, the standard regimen of the International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer, in the empiric treatment of febrile granulocytopenic cancer patients. A total of 858 episodes were eligible for this study, and 706 episodes were assessable for efficacy. The antibiotic treatment was successful in 210 (61%) of 342 episodes in the piperacillin-tazobactam-amikacin group compared with 196 (54%) of 364 episodes treated with ceftazidime plus amikacin (P = 0.05). The time to defervescence was significantly shorter (P = 0.01) and the time to failure was significantly longer (P = 0.02) in the piperacillin-tazobactam-amikacin group. A significant difference in response to bacteremic infections between the two patient groups was found: piperacillin-tazobactam plus amikacin was successful in 40 of 80 episodes (50%), and ceftazidime plus amikacin was successful in 35 of 101 episodes (35%) (P = 0.05). A multivariate analysis showed that the probability of failure was significantly greater with ceftazidime plus amikacin than with piperacillin-tazobactam plus amikacin (P = 0.02). This trial suggests that piperacillin-tazobactam plus amikacin is more effective than ceftazidime plus amikacin for the empiric treatment of fever and bacteremia in granulocytopenic cancer patients. Although cutaneous reaction was more frequently associated with piperacillin-tazobactam plus amikacin than with ceftazidime-amikacin, this unwanted effect was relatively mild and its incidence was comparable to that of other penicillin compounds.

In-vitro postantibiotic effects of miocamycin and erythromycin on gram-positive cocci

The capability of miocamycin to induce a postantibiotic effect (PAE) on a Group A Streptococcus beta-haemolyticus clinical isolate and on Staphylococcus aureus ATCC 29213 has been studied. Erythromycin was chosen as a reference molecule. The exposure time to antibiotics was 90 min. The removal technique of the antibiotic agents consisted of a 1:200 dilution in cultural broth. Miocamycin displayed a PAE of 2 h 30 min in relation to the minimum inhibitory concentration (MIC) of Streptococcus and a PAE of 2 h 30 min in relation to the MIC of Staphylococcus. The PAE value lasting longer than the others was of 5 h 40 min towards Streptococcus and of 4 h 18 min towards Staphylococcus at a concentration eightfold the MIC. Erythromycin showed a PAE of 1 h 36 min in relation to the MIC of Streptococcus and a PAE of 1 h 30 min in relation to the MIC of Staphylococcus. The PAE value lasting longer than the others was of 3 h 15 min against Streptococcus and of 2 h 30 min against Staphylococcus at a concentration eightfold the MIC. In some cases a PAE was observed in relation to subinhibitory concentrations (1/2 MIC). Miocamycin therefore proved to possess a more evident capability to induce a PAE against the clinical isolate of Group A Streptococcus beta-haemolyticus and on Staphylococcus aureus ATCC 29213 than did erythromycin.

Impact of dosage schedule of antibiotics on the treatment of serious infections

Experimental studies suggest that the importance of the antibiotic dosage schedule for therapeutic efficacy in severe infection and when host defences are impaired is related to the class of antibiotic. The efficacy of beta-lactams is mainly dependent on the maintenance of adequate antibiotic concentrations in plasma during the entire treatment interval, and not on high peak concentrations. The efficacy of aminoglycosides is related to the total dose administered, i.e., the area under the concentration-time curve, irrespective of the frequency of administration. This difference in efficacy between beta-lactams and aminoglycosides in relation to the dosage schedule correlate well with differences between both classes of antibiotics in kinetics of antibacterial activity in vitro and in vivo. Another factor relevant in this respect is the post-antibiotic effect (PAE) which means the suppression of bacterial regrowth at the end of the period of exposure to antibiotic.

Postantibiotic effects of imipenem, norfloxacin, and amikacin in vitro and in vivo

The postantibiotic effects (PAEs) of imipenem and norfloxacin were tested against Staphylococcus aureus, Streptococcus (Enterococcus) faecalis, Escherichia coli, and Pseudomonas aeruginosa. Amikacin was tested against the same bacteria except Streptococcus faecalis. For in vitro tests, a viable count-washing method was used, and for in vivo tests, the thread technique in normal mice was used. All three drugs produced PAEs of 1.1 to 3.8 h in vitro and 1.4 to 4.3 h in vivo against the pathogens tested. In vitro and in vivo results correlated well. The PAE had a significantly (P less than 0.01 to 0.001) longer duration in vivo than in vitro, but the PAE of imipenem on Staphylococcus aureus was longer in vitro. The PAE was not due to residual antibiotics at the site of infection, and no PAE was obtained if at any time the antibiotic concentration at the infection site reached the MIC for the pathogen tested. The results indicate that the presence of a PAE may enable antibiotics to be given more intermittently without a loss of efficacy and that the PAE can only be induced if the level of the antibiotic exceeds the MIC for the pathogen in question for at least several minutes.

Post-antibiotic effect of ciprofloxacin on Pseudomonas aeruginosa

The post-antibiotic effect of ciprofloxacin on five strains of Pseudomonas aeruginosa was examined. Ciprofloxacin demonstrated rapid bactericidal action at concentrations achievable in serum. After removal of the drug persistent suppression of bacterial growth followed by regrowth was observed for all strains after exposure of the organisms to various concentrations of ciprofloxacin for limited periods of time (0.25-3 h). The duration of this post-antibiotic effect increased with the concentration of the drug and duration of exposure up to a point of maximal response. This point was reached after approximately 2.2 h using a ciprofloxacin concentration 5-10 times the MIC and 1-2 h of treatment.

Pharmacokinetics of intravenous antibiotics in acutely ill elderly patients

In a study of 20 acutely ill elderly patients treated with cefotaxime (1 g, 2 X daily) the pharmacokinetics in serum and tissue fluid were examined. Patients with impaired renal function showed increased values for the area under the curve and half-life in both serum and tissue fluid. Patients with pathological peripheral circulation manifested delayed peak concentrations in tissue fluid. Although the passage of cefotaxime into tissue fluid was slow in the elderly, its concentration was higher than the minimal inhibitory concentration for most bacterial species of clinical importance and lasted for 5.5-7h in tissue fluid and for more than 10h in serum. Thus, this study clearly illustrates that the twice-daily dosage regimen used was quite adequate in elderly patients.

Pharmacokinetics of the third-generation cephalosporins

The pharmacokinetics of 10 of the newer, third-generation cephalosporins are reviewed. Important features are tabulated. Generalizations are made about structure-activity relationships, relationships between kinetic features, minimal inhibitory concentrations, dosage regimens, and tissue penetration. Tissue levels of ceftazidime are given as examples. These newer chemotherapeutic agents do not possess unique pharmacokinetic properties, but a combination of high antimicrobial activity, safety, and straightforward kinetics facilitates their use in a number of different clinical settings.