Continuous infusion of beta-lactam antibiotics

Beta-lactam antibiotics: is continuous infusion the preferred method of administration?

OBJECTIVE

To examine the pharmacodynamic properties of the beta-lactam class of antibiotics and the rationale for their continuous infusion (CI), and to explore reasons that this mode of administration has not replaced intermittent infusion as the standard of practice.

DATA SOURCES

A Medline search of the English-language literature evaluating CI administration of beta-lactam antibiotics was conducted. Bibliographic searches of these articles also were performed.

STUDY SELECTION

Because there were few human trials, all available trials were considered for review. A cross section of clinical trials, animal studies, and in vitro studies examining the impact of the route of antibiotic administration was selected for each pharmacodynamic variable addressed.

DATA SYNTHESIS

The support for CI as the preferred method of beta-lactam administration comes primarily from in vitro and animal data. Most beta-lactam antibiotics do not demonstrate concentration-dependent killing and have an appreciable postantibiotic effect only against gram-positive cocci. Their efficacy appears to be optimized by maintaining suprainhibitory concentrations throughout the dosing interval. Therefore, CI of beta-lactams could potentially enhance the efficacy of treatment or allow less drug to be used on a daily basis. This has yet to be demonstrated convincingly in human clinical trials. Comparative trials need to continue to explore the impact of the method of administration on patient outcomes such as duration and cost of therapy, as well as morbidity and mortality.

CONCLUSIONS

Results of many animal and in vitro studies suggest that CI may be the optimal method of beta-lactam administration. Clinical trials need to further document the impact of the method of beta-lactam administration on the incidence of adverse effects, emergence of bacterial resistance, and patient outcome. Pharmacodynamic studies defining target beta-lactam concentrations, the practicality of CI in patients requiring multiple intravenous fluids and medications, and the pertinence of this issue when beta-lactam antibiotics are used as sole agents or in combination with other antimicrobials require further exploration.

Continuous infusion of ceftazidime in febrile neutropenic patients with acute myeloid leukemia

Twelve febrile patients with severe neutropenia, who had undergone aggressive chemotherapy for acute myeloid leukemia, were treated empirically with a continuous infusion of ceftazidime 100 mg/kg/day after a 500 mg loading dose, in order to study the pharmacokinetics of ceftazidime after continuous infusion and to examine the clinical applicability of continuous infusion in this patient population. Three patients had a slight decrease in renal function. All patients attained a steady-state ceftazidime serum level of > 20 micrograms/ml within 180 to 240 min, which was considered effective against most pathogens in neutropenic patients. The median volume of distribution for the patient group was 29.1 l, the elimination half-life was 2.5 h and the clearance of ceftazidime was 7.7 l/h. A subnormal kidney function influenced half-lives and clearance (but not volume of distribution), as expected. When precautions were taken to avoid known interactions between ceftazidime and other compounds to be infused simultaneously, continuous infusion of ceftazidime was applicable for treatment of neutropenic patients without major side effects.

Postantibiotic effects and postantibiotic sub-MIC effects of roxithromycin, clarithromycin, and azithromycin on respiratory tract pathogens

Pharmacodynamic parameters have become increasingly important for the determination of the optimal dosing schedules of antibiotics. In this study, the postantibiotic effects (PAEs), the postantibiotic sub-MIC effects (PA SMEs), and the sub-MIC effects (SMEs) of roxithromycin, clarithromycin, and azithromycin on reference strains of Streptococcus pyogenes group A, Streptococcus pneumoniae, and Haemophilus influenzae were investigated. The PAE was induced by 2x MICs (S. pneumoniae) or 10x MICs of the different drugs for 2 h, and the antibiotics were eliminated by washing and dilution. The PA SMEs were studied by addition of 0.1, 0.2, and 0.3x MICs during the postantibiotic phase of the bacteria, and the SMEs were studied by exposition of the bacteria to the drugs at the sub-MICs only. Growth curves were followed by viable counts for 24 h. The SMEs were generally very short. A PAE of 2.9 to 8 h was noted for all antibiotics against all strains. Clarithromycin induced a statistically significantly shorter PAE on S. pneumoniae than did roxithromycin and azithromycin and did so also against H. influenzae in comparison with azithromycin. The PA SMEs were long and varied at 0.3x MIC between 6.4 19.6 h. This pronounced suppression of regrowth of bacteria which are first treated with a suprainhibitory concentration of antibiotics and then reexposed to sub-MIC levels indicates that long dosing intervals for macrolides and azalides can be allowed.

Pharmacokinetic contributions to postantibiotic effects. Focus on aminoglycosides

The postantibiotic effect (PAE) refers to a period of time after complete removal of an antimicrobial 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. Various factors influence the presence or duration of the PAE including the type of organism, type of antimicrobial, concentration of antimicrobial, duration of antimicrobial exposure, antimicrobial combinations, and inoculum and medium used. beta-Lactams demonstrate a PAE against Gram-positive cocci, but produce only a short PAE with Gram-negative bacilli. Antimicrobial agents that inhibit RNA or protein synthesis have a PAE against Gram-positive cocci and Gram-negative bacilli. In vivo studies of aminoglycosides suggest that area under the plasma concentration-time curve is the pharmacokinetic parameter that best correlates with clinical efficacy. This is thought to be due to the concentration-dependent killing and PAE possessed by these antimicrobials. Animal and human studies have reported that once-daily administration of aminoglycoside is as effective as, or more effective than, and possibly less toxic than traditional multiple daily administration.

Efficacies of different vancomycin dosing regimens against Staphylococcus aureus determined with a dynamic in vitro model

A dynamic in vitro model was used to assess four different vancomycin dosing regimens against Staphylococcus aureus. These regimens achieved peak drug concentrations of 48 micrograms/ml (single dose) and 30 micrograms/ml (dosed every 12 h) and constant concentrations of 16 and 8 micrograms/ml. Analysis of the area under the bacterial concentration-time curve, area under the first moment of the bacterial concentration-time curve, and bacterial elimination rate constant showed no difference in the rate or extent of bacterial killing. The optimal dosing method may be that which achieves the lowest area under the curve while concentrations are maintained above the MBC.

Pharmacodynamics of piperacillin alone and in combination with tazobactam against piperacillin-resistant and -susceptible organisms in an in vitro model of infection

The pharmacodynamics of dosage regimens of piperacillin alone or in combination with tazobactam against piperacillin-resistant or -susceptible bacteria were studied in an in vitro model of infection. Experiments were conducted by using a fixed daily exposure of 12 g of piperacillin, given as 3 g alone or in combination with tazobactam at 0.375 g every 6 h, or the same total dose of the combination given as 4 g of piperacillin plus 0.5 g of tazobactam every 8 h. The addition of tazobactam to piperacillin, irrespective of the dosing interval, did not alter the killing of piperacillin-susceptible organisms (Escherichia coli J53 and Pseudomonas aeruginosa ATCC 27853). In contrast, experiments with an isogenic TEM-3-containing transconjugant of E. coli J53 (E. coli J53.2-TEM-3) that was resistant to piperacillin (MIC, 128 micrograms/ml) showed that the addition of tazobactam resulted in bacterial killing similar to that observed with the wild-type strain. Although tazobactam concentrations fell to less than 4 mg/liter (the concentration associated with a reduction in the piperacillin MIC from 128 to 2 mg/liter) 2 to 3 h after a dose, a similar degree of bacterial killing was observed when the same total 24-h dose of piperacillin-tazobactam was fractionated into dosing intervals of every 6 or 8 h. Investigations with Staphylococcus aureus 7176 (piperacillin MIC, 128 micrograms/ml) showed that the addition of tazobactam, again irrespective of dosing interval, also resulted in net bacterial killing which was not seen with piperacillin alone. These data support the use of extended dosing intervals (every 8 h) of piperacillin-tazobactam in the treatment of infections caused by piperacillin-resistant bacteria.

Killing of Pseudomonas aeruginosa during continuous and intermittent infusion of ceftazidime in an in vitro pharmacokinetic model

An in vitro pharmacokinetic model mimicking human serum drug concentrations, based on a dialyzer unit, was developed to study the efficacies of continuous infusion and intermittent administration of ceftazidime over a period of 36 h. The daily dose of ceftazidime was 300 mg/liter/24 h given either as a continuous infusion or as three bolus doses. The intermittent dosing regimen yielded peak and trough concentrations after the fourth dose of 92.3 (standard deviation, 8.0) and 1.4 (standard deviation, 0.9) mg/liter, respectively. Continuous administration yielded concentrations of approximately 20 mg/liter. To study efficacy, three Pseudomonas aeruginosa strains, ATCC 27853, CF4, and CF16, were used. The MICs of ceftazidime for these strains were 1, 4, and 16 mg/liter, respectively. Strain CF16 was killed initially during both regimens and then started to regrow. At the end of the fourth dosing interval, i.e., after 32 h, viable counts showed no difference between the regimens. Strains ATCC 27853 and CF4 were killed initially during both dosing schedules, and after the first dosing interval viable counts were similar. However, after the fourth interval, there was a marked difference between bacterial counts during continuous and intermittent infusion, being 2.2 and 2.8 log10, respectively, demonstrating a greater efficacy during continuous infusion. The results indicate that, in the absence of other factors, a sustained level of ceftazidime around or slightly above the MIC is not high enough to maintain efficacy over more than one (8-h) dosing interval. When sustained concentrations higher than four times the MIC are employed, continuous administration in this model is more efficacious than intermittent dosing.

Clinical pharmacokinetics of cefotetan

Cefotetan is a 7-alpha-methoxy beta-lactam. A long serum half-life and resistance to beta-lactamase hydrolysis have made cefotetan an attractive chemotherapeutic agent, and the results of clinical trials worldwide have demonstrated its efficacy in a wide variety of clinical situations. Cefotetan can be administered intravenously (bolus or infusion) or intramuscularly with lidocaine (lignocaine) 0.5%. Mean peak plasma concentrations are almost linearly related to dose. The volume of distribution is between 8 and 13L and is not different from other cephalosporins. No accumulation is seen after repeated doses and no metabolite has been detected in either plasma or urine. Total body clearance is 1.8 to 2.9 L/h. Renal clearance accounts for about 64 to 84% of a dose, and 75% of a dose is excreted in the urine within 24 hours. The plasma elimination half-life is between 3 and 4 hours after intravenous and intramuscular doses. Half-life is considerably prolonged in patients with renal impairment (up to 10 hours). Cefotetan concentrations are likely to be active against susceptible bacteria in most tissues and body fluids. Breast milk and cerebrospinal fluid concentrations are low. The recommended dosage is 1g every 12 hours, increasing to 2g in severe infections and 3g in life-threatening infections. In surgical prophylaxis, a single dose of 2g is given with the induction of anaesthesia; an additional dose of 2g may be administered 12 hours later. In children over 6 months, the recommended dosage is 30 mg/kg given 12-hourly. In patients with a creatinine clearance of 10 to 40 ml/min (0.6 to 2.4 L/h), the dose is halved or the dosage interval is doubled. When creatinine clearance is less than 10 ml/min (0.6 L/h), the dose is quartered or the dosage interval quadrupled.

Post-antibiotic effect of FK-037 and biapenem tested against five bacterial species

The in-vitro post-antibiotic effect (PAE) was determined for two newer beta-lactams, FK-037 (a cephalosporin) and biapenem (a carbapenem). Our PAE results for these drugs were consistent with what has been reported previously for similar beta-lactams, e.g. Gram-positive organisms had measurable effects (0.4-2.2 hours), while Gram-negatives had variable results (0.0 to 1.4 hours). Even though the PAE test conditions generally coincided with achievable clinical levels for most organisms tested (< or = 4 mg/L for biapenem and < or = 8 mg/L for FK-037), the marginal or species dependent, short PAE values support the selection of multiple daily doses (two-to-four) based on conventional pharmacokinetic parameters such as the Cmax, AUC, and serum elimination half-life.

High-level penicillin resistance and penicillin-gentamicin synergy in Enterococcus faecium

Thirty-seven Enterococcus faecium strains with different levels of penicillin susceptibility were studied in time-kill experiments with a fixed concentration (5 micrograms/ml) of gentamicin combined with different penicillin concentrations (6 to 600 micrograms/ml). Synergy was defined as a relative decrease in counts of greater than 2 log10 CFU per milliliter after 24 h of incubation when the combination of the antibiotics was compared with its most active component alone. The minimal synergistic penicillin concentrations found were 6 micrograms/ml for 16 of 16 strains for which penicillin MICs were < or = 25 micrograms/ml, 20 to 100 micrograms/ml for 14 of 17 strains for which penicillin MICs were 50 to 200 micrograms/ml, and 200 to 500 micrograms/ml for 4 of 4 strains for which MICs penicillin were > 200 micrograms/ml. Penicillin-gentamicin synergy was observed even in high-level penicillin-resistant E. faecium strains at penicillin concentrations close to one-half the penicillin MIC. The possibility of treating infections caused by high-level penicillin-resistant E. faecium strains with penicillin-gentamicin combinations in particular cases may depend on the penicillin levels attainable in vivo.

Cefpirome clinical pharmacokinetics

Cefpirome is a new cephalosporin that exhibits similar in vitro potency to ceftazidime against Gram-negative organisms but has significantly greater in vitro potency against Gram-positive organisms. Cefpirome differs from cefotaxime in that a 3'-pyridinium moiety replaces the acetoxy moiety of cefotaxime. This structural change imparts greater beta-lactamase stability, increases the ability to penetrate the outer membrane of Gram-negative bacteria, and enhances activity against Gram-positive organisms. The pharmacokinetic properties of cefpirome are typical of cephalosporins. The drug can be administered by intravenous or intramuscular injection, but is not well absorbed after oral administration. Bioavailability following intramuscular injection exceeds 90%. Cefpirome exhibits low protein binding (approximately 10%) and has a volume of distribution similar to extracellular fluid volume. Cefpirome penetrates the prostate gland, lung, blister fluid, cerebrospinal fluid and peritoneal fluid, reaching concentrations that are similar to those achieved by other later generation cephalosporins. Approximately 80% of an intravenous dose is eliminated unchanged in the urine. No active metabolites of cefpirome have been identified. The elimination half-life of cefpirome is approximately 2 hours. Elimination appears to be primarily by glomerular filtration since the total clearance of cefpirome is approximately equal to creatinine clearance. The time during which drug concentrations exceed the minimum inhibitory concentration (MIC) represents the most clinically important pharmacodynamic parameter for beta-lactam agents. When cefpirome is administered at a dosage of 2g every 12 hours to patients without renal insufficiency [creatinine clearance 70 ml/min (4.2 L/h)], drug concentrations continuously remain above the MIC for pathogens with MIC values of < or = 2 micrograms/ml. With this dosage regimen, drug concentrations will be above the MIC for a pathogen with an MIC of 4 micrograms/ml for 80% of the dosage interval. The time above MIC for pathogens with an MIC of 8 micrograms/ml is only 60% of the dosage interval.

Outpatient parenteral antibiotic therapy. Management of serious infections. Part II: Amenable infections and models for delivery. Osteomyelitis

Osteomyelitis is one of the most common and well-established indications for outpatient parenteral antibiotic therapy. Because patients are usually otherwise healthy and therapy is prolonged (four to six weeks), this infection is especially suited to outpatient management. While most gram-negative infections in adults can be treated with an oral quinolone, others usually require IV therapy.

Outpatient parenteral antibiotic therapy. Management of serious infections. Part I: Medical, socioeconomic, and legal issues. Selecting the antibiotic

Variations in antibiotic pharmacokinetics and pharmacodynamics allow therapy to be readily adapted to the outpatient setting. Factors to be taken into account when designing an outpatient parenteral regimen include minimal inhibitory and bactericidal concentrations, post-antibiotic effect, half-life, protein binding, drug stability, IM versus i.v. administration, and continuous versus intermittent infusion.