Penetration of aztreonam into cerebrospinal fluid of patients with and without inflamed meninges

New Antibiotics for the Treatment of Nosocomial Central Nervous System Infections

Nosocomial central nervous system (CNS) infections with carbapenem- and colistin-resistant Gram-negative and vancomycin-resistant Gram-positive bacteria are an increasing therapeutic challenge. Here, we review pharmacokinetic and pharmacodynamic data and clinical experiences with new antibiotics administered intravenously for the treatment of CNS infections by multi-resistant bacteria. Cefiderocol, a new siderophore extended-spectrum cephalosporin, pharmacokinetically behaves similar to established cephalosporins and at high doses will probably be a valuable addition in our therapeutic armamentarium for CNS infections. The new glycopeptides dalbavancin, telavancin, and oritavancin are highly bound to plasma proteins. Although effective in animal models of meningitis, it is unlikely that they reach effective cerebrospinal fluid (CSF) concentrations after intravenous administration alone. The β-lactam/β-lactamase inhibitor combinations have the principal problem that both compounds must achieve adequate CSF concentrations. In the commercially available combinations, the dose of the β-lactamase inhibitor tends to be too low to achieve adequate CSF concentrations. The oxazolidinone tedizolid has a broader spectrum but a less suitable pharmacokinetic profile than linezolid. The halogenated tetracycline eravacycline does not reach CSF concentrations sufficient to treat colistin-resistant Gram-negative bacteria with usual intravenous dosing. Generally, treatment of CNS infections should be intravenous, whenever possible, to avoid adverse effects of intraventricular therapy (IVT). An additional IVT can overcome the limited penetration of many new antibiotics into CSF. It should be considered for patients in which the CNS infection responds poorly to systemic antimicrobial therapy alone.

The Blood-Brain Barrier and Pharmacokinetic/Pharmacodynamic Optimization of Antibiotics for the Treatment of Central Nervous System Infections in Adults

Bacterial central nervous system (CNS) infections are serious and carry significant morbidity and mortality. They encompass many syndromes, the most common being meningitis, which may occur spontaneously or as a consequence of neurosurgical procedures. Many classes of antimicrobials are in clinical use for therapy of CNS infections, some with established roles and indications, others with experimental reporting based on case studies or small series. This review delves into the specifics of the commonly utilized antibacterial agents, updating their therapeutic use in CNS infections from the pharmacokinetic and pharmacodynamic perspectives, with a focus on the optimization of dosing and route of administration that have been described to achieve good clinical outcomes. We also provide a concise synopsis regarding the most focused, clinically relevant information as pertains to each class and subclass of antimicrobial therapeutics. CNS infection morbidity and mortality remain high, and aggressive management is critical in ensuring favorable patient outcomes while averting toxicity and upholding patient safety.

Central nervous system infections and antimicrobial resistance: an evolving challenge

PURPOSE OF REVIEW

Antimicrobial resistance is an increasing threat to patients also in nosocomial central nervous system (CNS) infections. The present review focusses on optimizing intravenous treatment in order to achieve sufficient concentrations of antibiotics in the different compartments of the CNS when the causative pathogens have reduced sensitivity to antibiotics or/and the impairment of the blood-cerebrospinal fluid (CSF) and blood-brain barrier is mild.

RECENT FINDINGS

Experience has been gathered with treatment protocols for several established antibiotics using increased doses or continuous instead of intermittent intravenous therapy. Continuous infusion in general does not increase the average CSF concentrations (or the area under the concentration-time curve in CSF) compared to equal daily doses administered by short-term infusion. In some cases, it is postulated that it can reduce toxicity caused by high peak plasma concentrations. In case reports, new β-lactam/β-lactamase inhibitor combinations were shown to be effective treatments of CNS infections.

SUMMARY

Several antibiotics with a low to moderate toxicity (in particular, β-lactam antibiotics, fosfomycin, trimethoprim-sulfamethoxazole, rifampicin, vancomycin) can be administered at increased doses compared to traditional dosing with low or tolerable adverse effects. Intrathecal administration of antibiotics is only indicated, when multiresistant pathogens cannot be eliminated by systemic therapy. Intravenous should always accompany intrathecal treatment.

Detectable prednisolone is delayed in pericardial fluid, compared with plasma of patients with tuberculous pericarditis: A pilot study

Background

In patients with tuberculous pericarditis [TBP] adjunctive prednisolone reduces the incidence of constrictive pericarditis. It is unknown whether prednisolone permeates adequately into pericardial fluid. Drug measurements in pericardial fluid require invasive procedures, and thus less invasive methods are needed to perform full pharmacokinetic characterization of prednisolone in large numbers of patients. We sought to evaluate the relationship between prednisolone concentrations in pericardial fluid, plasma, and saliva.

Methods

Plasma, pericardial fluid, and saliva samples were collected at 7 time points from TBP patients randomized to 120 mg prednisolone or placebo. Compartmental pharmacokinetic parameters, peak concentration [C_max], and 0-24 h area under the concentration-time curve [AUC_0-24] were identified in plasma, saliva and pericardial fluid.

Results

There were five patients each in the prednisolone and placebo groups. Prednisolone concentrations were best described using a one compartment model. The absorption half-life into plasma was 1 h, while that into pericardial fluid was 9.4 h, which led to a median time-to-maximum concentration in plasma of 2.0 h versus 5.0 h in pericardial fluid [p = 0.048]. The concentration-time profiles in pericardial fluid versus plasma exhibited system hysteresis. The pericardial fluid-to-plasma C_max peak concentration ratio was 0.28 (p = 0.032), while the AUC_0-24 ratio was 0.793. The concentration-time profiles in saliva had a similar shape to those in plasma, but the saliva-to-plasma C_max was 0.59 [p = 0.032].

Conclusion

The prednisolone AUC_0-24 achieved in pericardial fluid approximates that in plasma, but the C_max is low due to delayed absorption. Saliva can be used as surrogate sampling site for pericardial fluid prednisolone.

A review of the pharmacokinetics and pharmacodynamics of aztreonam

The monobactam aztreonam is currently being re-examined as a therapeutic agent in light of the global spread of carbapenem resistance in aerobic Gram-negative bacilli and aztreonam's stability to Ambler class B metallo-β-lactamases. Of particular interest are the pharmacokinetic and pharmacodynamic properties of aztreonam alone and in combination with β-lactamase inhibitors. The choice of inhibitor may vary depending on the spectrum of β-lactamases produced by Enterobacteriaceae. The monobactam ring is also being used to produce new developmental monobactams. Thus, a greater understanding of aztreonam pharmacokinetics and dynamics is of great relevance in drug development. This review summarizes the pharmacokinetic profile of aztreonam in man and its pharmacodynamics in human and pre-clinical studies when studied alone and with β-lactamase inhibitors.

Successful treatment of Pasteurella multocida meningitis with aztreonam

This is the first reported case of the successful treatment of Pasteurella multocida meningitis with aztreonam in a patient with multiple antibiotic allergies.

Successful treatment of Pasteurella multocida meningitis with aztreonam

This is the first reported case of the successful treatment of Pasteurella multocida meningitis with aztreonam in a patient with multiple antibiotic allergies.

Study of different off-line sample processing procedures and the measurement of antibiotic and antiviral levels in human serum by high-performance liquid chromatography

We attempted to devise a preparation method for clinical samples that could be used for all antibiotics and antivirals. We studied thirteen antibiotics, including five penicillins, four cephalosporins, metronidazole, ofloxacin, and sulfamethoxazole and four protease inhibitors including indinavir, retonavir, nelfinavir, and sequinavir. We compared four sample preparation techniques including solvent precipitation, filtration and resin column. We employ HPLC methods based on a minimal number of columns and mobile phases. We were unable to find one sample preparation method that could be used for all antibiotics and antivirals. But, we did develop an algorithm for determining optimal processing procedures for all drugs.

The penetration of anti-infectives into the central nervous system

The blood-brain barrier, blood-cerebrospinal fluid (CSF) barrier, and meninges are a complex and difficult-to-study system charged with protecting the central nervous system (CNS) from toxins, including drugs. Current estimates of CNS drug exposure are limited to CSF to blood ratios, of which area-under-the curve (AUC) estimates provide the most robust measure of drug exposure. Different classes of drugs and individual drugs within classes have different CNS penetration potential that is dependent upon a variety of biologic and pharmacologic factors. Clinical data (AUC and point ratios) regarding the penetration of several anti-infective agents used for the treatment of CNS infections are provided in this article.

Pharmacokinetics and pharmacodynamics of antibiotics in meningitis

The penetration of antimicrobials into the CSF is dependent on lipid solubility, molecular size, capillary and choroid plexus efflux pumps, protein binding, and the degree of inflammation. Penicillins, certain cephalosporins, carbapenems, fluoroquinolones, vancomycin, and rifampin provide the highest ratios of CSF levels to the MBC for common infecting organisms. For beta-lactam antibiotics, it is the duration of time that CSF concentrations exceed the MBC that determines the rate of bactericidal activity. It appears that levels should exceed the MBC for more than 50% of the dosing interval. The peak/MBC and AUC/MBC ratios are important determinants of efficacy for aminoglycosides and fluoroquinolones. Once-daily dosing of aminoglycosides is as effective as multiple-daily dosing regimens in experimental meningitis, probably because of drug-induced prolonged persistent effects. Fluoroquinolones do not produce as prolonged persistent effects and are slightly less effective when administered once daily. Although steroid use can reduce the penetration and decrease the bactericidal activity of some antimicrobials, such as vancomycin, in experimental meningitis, the clinical impact of steroid use in human meningitis is still unclear.

Carbapenems and monobactams: imipenem, meropenem, and aztreonam

Imipenem and meropenem, members of the carbapenem class of beta-lactam antibiotics, are among the most broadly active antibiotics available for systemic use in humans. They are active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem and meropenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; Stenotrophomonas maltophilia is typically resistant to both imipenem and meropenem. Like the penicillins, the carbapenems have inhibitory activity against enterococci. In general, the in vitro activity of imipenem against aerobic gram-positive cocci is somewhat greater than that of meropenem, whereas the in vitro activity of meropenem against aerobic gram-negative bacilli is somewhat greater than that of imipenem. Daily dosages may range from 0.5 to 1 g every 6 to 8 hours in patients with normal renal function; the daily dose of meropenem, however, can be safely increased to 6 g. Infusion-related nausea and vomiting, as well as seizures, which have been the main toxic effects of imipenem, occur no more frequently during treatment with meropenem than during treatment with other beta-lactam antibiotics. The carbapenems should be considered for treatment of mixed bacterial infections and aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. Indiscriminate use of these drugs will promote resistance to them. Aztreonam, the first marketed monobactam, has activity against most aerobic gram-negative bacilli including P. aeruginosa. The drug is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; the primary route of elimination is urinary excretion. In patients with normal renal function, the recommended dosing interval is every 8 hours. Patients with renal impairment require dosage adjustment. Aztreonam is used primarily as an alternative to aminoglycosides and for the treatment of aerobic gram-negative infections. It is often used in combination therapy for mixed aerobic and anaerobic infections. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism has been determined in patients who are seriously ill or at risk for gram-positive or anaerobic infection.

Aztreonam

Aztreonam is a monocyclic beta-lactam antibiotic that is active exclusively against the aerobic gram-negative bacilli. It is not ototoxic or nephrotoxic and so is used as an alternative to aminoglycosides in a variety of clinical situations. In polymicrobial infections or when used for empiric therapy, aztreonam must be combined with other antimicrobial agents active against gram-positive and anaerobic species. Aztreonam is often effective against resistant strains of gram-negative organisms, which are often involved in nosocomial infections. Overuse of aztreonam should be avoided to prevent the emergence of resistant P. aeruginosa strains. Except in the treatment of P. aeruginosa infections, aztreonam should not be added to beta-lactam regimens for additional gram-negative coverage.

Relationship between structure and convulsant properties of some beta-lactam antibiotics following intracerebroventricular microinjection in rats

The epileptogenic activities of several beta-lactam antibiotics were compared following their intracerebroventricular administration in rats. Different convulsant potencies were observed among the various beta-lactam antibiotics tested, but the epileptogenic patterns were similar. The patterns consisted of an initial phase characterized by wet-dog shakes followed by head tremor, nodding, and clonic convulsions. After the largest doses of beta-lactam antibiotics injected, clonus of all four limbs and/or the trunk, rearing, jumping, falling down, escape response, transient tonic-clonic seizures, and sometimes generalized seizures were observed, followed by a postictal period with a fatal outcome. At a dose of 0.033 mumol per rat, cefazolin was the most powerful epileptogenic compound among the drugs tested. It was approximately three times more potent than benzylpenicillin in generating a response and much more potent than other cephalosporins, such as ceftriaxone, cefoperazone, and cefamandole. No epileptogenic signs were observed with equimolar doses of cefotaxime, cefonicid, cefixime, and ceftizoxime in this model. The more convulsant compounds (i.e., cefazolin and ceftezole) are both characterized by the presence of a tetrazole nucleus at position 7 and show a marked chemical similarity to pentylenetetrazole. Imipenem and meropenem, the two carbapenems tested, also showed epileptogenic properties, but imipenem was more potent than meropenem, with a convulsant potency similar to those of ceftezole and benzylpenicillin. In addition, the monobactam aztreonam possessed convulsant properties more potent than those of cefoperazone and cefamandole. This suggest that the beta-lactam ring is a possible determinant of production of epileptogenic activity, with likely contributory factors in the substitutions at the 7-aminocephalosporanic or 6-aminopenicillanic acid that may increase or reduce the epileptogenic properties of the beta-lactam antibiotics. While the structure-activity relationship was also investigated, there seem to be no convincing correlations among the rank order of lipophilicities and the convulsant potencies of the compounds studied. The lack of marked convulsant properties of cefixime, cefonicid, cefuroxime, and cephradine suggests that these antibiotics may interact with a binding site which is different from that by which the beta-lactam antibiotics exert their convulsant effects or may demonstrate a reduced affinity for the relevant site(s).

The monobactams

The monobactam antibiotics are synthetic compounds, although monocyclic beta-lactam compounds have been found in nature in various soil bacteria. Although additional orally and parenterally administered monobactams are under investigation, the first marketed monobactam was aztreonam. This agent has an antimicrobial spectrum similar to that of gentamicin and tobramycin, aminoglycoside antibiotics. Aztreonam, however, is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; absorption after oral administration is poor. The primary route of elimination is the urine. The serum half-life of the drug in patients with normal renal function is 1.5 to 2.1 hours; the recommended dosing interval in patients with normal renal function is every 8 hours. Dosage adjustment is necessary in patients with renal impairment. The strictly gram-negative aerobic spectrum of aztreonam limits its use as a single empiric agent. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism (or organisms) has been determined in patients who are seriously ill and at risk for gram-positive or anaerobic infections.

Aztreonam activity, pharmacology, and clinical uses

Aztreonam, the first monobactam, has been used extensively in the treatment of a variety of infections caused by gram-negative pathogens. It has been shown to be highly effective against susceptible bacteria without causing serious adverse reactions. Its pharmacologic profile can be attributed to its unique chemical properties and mechanisms of action, which differ substantially from those of the bicyclic beta-lactams, such as the penicillins and cephalosporins. Administered parenterally, aztreonam provides peak serum concentrations for most Enterobacteriaceae and Pseudomonas aeruginosa. It is widely distributed throughout the body. Excretion is largely dependent on renal mechanisms, so dosage can be adjusted in the presence of renal impairment. The clinical uses of aztreonam include treatment of urinary tract, lower respiratory tract, and intraabdominal infections, as well as septicemia, endometritis, pelvic cellulitis, and skin and skin structure infections due to aerobic gram-negative organisms. It is concluded that aztreonam can be used with confidence in the single-drug treatment of susceptible aerobic, gram-negative pathogens. In the treatment of mixed infections, or those of unknown etiology, however, combination therapy is recommended to ensure coverage of gram-positive and anaerobic bacteria.

Aztreonam: the first monobactam

There are several areas in which the use of aztreonam seems logical. Infections caused by organisms sensitive to aztreonam that are known to be multiresistant to other agents can be treated directly with aztreonam in single, directed therapy, thus making the use of more toxic agents unnecessary. In types of infection in which both gram positive and gram negative bacteria are present, aztreonam can replace the usual aminoglycoside component of the therapeutic regimen. In settings of mixed infections suspected of being caused by drug-resistant strains of Enterobacteriaceae and/or P. aeruginosa, aztreonam can be combined with an agent active against gram positive organisms or with one active against anaerobes. Aztreonam has proven to be effective, safe therapy for serious and life-threatening infections caused by multiresistant aerobic gram negative bacteria. It should be used in combination with drugs that inhibit gram positive species if the etiology of the infection is not known, particularly in the immunocompromised, neutropenic patient. Doses of 1 g every 8 to 12 hours will be adequate for treatment of infections caused by most Enterobacteriaceae. Whether 2 g doses every 8 hours would be preferred for treatment of systemic Pseudomonas infections remains to be determined. Urinary infections caused by gram negative bacteria can be treated with 500 mg administered IM once or twice daily. The dosage of aztreonam should be adjusted in patients with renal failure. Clearly, aztreonam is a useful addition to the antimicrobial agents available to the physician.

Clinical pharmacokinetics of aztreonam

Aztreonam (azthreonam) is practically completely absorbed after intramuscular injection. After intravenous injection plasma concentrations follow a 2-compartment open model, with a t1/2 alpha of 0.20 hours. Volume of distribution at steady-state (Vdss) after intravenous or intramuscular injection is about 0.16 L/kg (0.42 L/kg for the free drug). After oral administration less than 1% of the drug is absorbed. Over a large dosage range plasma concentrations increase linearly with dose. No accumulation occurs after multiple dosing. Plasma binding in healthy subjects is about 56% and is not concentration dependent. Diffusion into tissues is generally slow, and the ratio between mean tissue and plasma concentration seems to depend mainly on the composition of the tissue. In inflamed meninges, penetration of aztreonam into CSF is more rapid than with uninflamed meninges. Diffusion through the placenta is poor, as is diffusion into breast milk. The main route of elimination of aztreonam is by the kidney, partly by active tubular excretion, but this can be inhibited by probenecid. Extrarenal clearance is probably due to excretion by the liver. Metabolism occurs to a very limited extent. Total plasma clearance in healthy adults is about 140 ml/min (8.4 L/h) or 2 ml/min/kg (0.12 L/h/kg), and terminal half-life is 1.7 hours. In children clearance is similar to that in adults when expressed as a function of bodyweight, but in neonates, especially in low birthweight infants, it is less [about 1 ml/min/kg (0.06 L/h/kg)]. In various disease states the Vdss of aztreonam is not appreciably different from that found in healthy individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Penetration of aztreonam into cerebrospinal fluid and brain of noninfected rabbits and rabbits with experimental meningitis caused by Pseudomonas aeruginosa

This study examined the penetration of aztreonam into the cerebrospinal fluid (CSF) and brain in noninfected rabbits and rabbits with experimental meningitis caused by Pseudomonas aeruginosa. Animals received either 600 or 1,200 mg of aztreonam administered intravenously over 6 h. Aztreonam did not readily enter the CSF in the absence of meningitis. In noninfected animals, mean concentrations in the CSF ranged from 1.1 to 3.0 micrograms/ml with the 600-mg dose and from 2.3 to 4.7 micrograms/ml with the 1,200-mg dose. In contrast, mean concentrations of aztreonam in the CSF were significantly higher (P less than 0.01) at each sampling time in rabbits with experimental meningitis caused by P. aeruginosa. They ranged from 10.2 to 14.6 micrograms/ml with the 600-mg dose and from 29 to 40 micrograms/ml with the 1,200-mg dose. Although concentrations in the brain measured at 6 h tended to be higher in infected rabbits, this difference was not statistically significant. Aztreonam therapy produced a substantial decline in CSF bacterium counts over 6 h: mean CSF counts decreased 2.4 log10 CFU/ml in the 600-mg dose group and 3.0 log10 CFU/ml in the 1,200-mg dose group. The results of this study suggest that aztreonam may be useful in the therapy of meningitis caused by P. aeruginosa.

Aztreonam concentrations in human tissues obtained during thoracic and gynecologic surgery

The concentrations of aztreonam in human tissues obtained during surgery were measured after a single 2-g intravenous dose. The average concentration in the skeletal muscle, atrial appendage, lung, sternum, pericardial fluid, endometrium, myometrium, fallopian tube, and ovary varied from 3 to 33 micrograms/g (or microgram/ml). These concentrations significantly exceed the MIC for 90% of strains for most members of the family Enterobacteriaceae.

Aztreonam. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Aztreonam (azthreonam; SQ 26,776) is the first member of a new class of beta-lactam antibiotics, the monobactams. Aztreonam is selectively active against Gram-negative aerobic bacteria and inactive against Gram-positive bacteria. Thus, in vitro, aztreonam is inhibitory at low concentrations (MIC90 less than or equal to 1.6 mg/L) against Enterobacteriaceae except Enterobacter species, and is active against Pseudomonas aeruginosa, 90% of pseudomonads being inhibited by 12 to 32 mg/L. Aztreonam is inactive against Gram-positive aerobic bacteria and anaerobes, including Bacteroides fragilis. Therefore, when administered alone, aztreonam has minimal effect on indigenous faecal anaerobes. Aztreonam must be administered intravenously or intramuscularly when used to treat systemic infections, since absolute bioavailability is very low (about 1%) after oral administration. Since elimination half-life is less than 2 hours, 6- or 8-hourly administration is used in the treatment of moderately severe or severe infections, although 12-hourly injection is adequate in less severe systemic and some urinary tract infections. Therapeutic trials have shown aztreonam to be effective in Gram-negative infections including complicated infections of the urinary tract, in lower respiratory tract infections and in gynaecological and obstetric, intra-abdominal, joint and bone, skin and soft tissue infections, uncomplicated gonorrhoea and septicaemia. In comparisons with other antibiotics, aztreonam has been at least as effective or more effective than cefamandole in urinary tract infections and similar in efficacy to tobramycin or gentamicin. Where necessary, aztreonam and the standard drug have both been combined with another antibiotic active against Gram-positive and/or anaerobic bacteria. Aztreonam has been effective in eradicating pseudomonal infections in most patients (except in patients with cystic fibrosis), but the inevitably limited number of pseudomonal infections available for study prevents any conclusions as to the relative efficacy of aztreonam compared with other appropriate regimens against these infections. Thus, with an antibacterial spectrum which differs from that of other antibiotics, aztreonam should be a useful alternative to aminoglycosides or 'third generation' cephalosporins in patients with proven or suspected serious Gram-negative infections.

Penetration of aztreonam into cerebrospinal fluid of patients with bacterial meningitis

The penetration of aztreonam into the cerebrospinal fluid was determined in 16 patients with bacterial meningitis undergoing treatment with other antibiotics. Three aztreonam doses of 30 mg/kg were infused intravenously over 30 to 45 min at 8-h intervals, first between days 2 and 4 and again between days 11 and 20 after onset of the disease. Concentrations of aztreonam in serum and cerebrospinal fluid samples obtained at 60, 90, 120, and 240 min after the third aztreonam dose were measured by high-pressure liquid chromatography. The concentrations of aztreonam in cerebrospinal fluid ranged from 3.5 to 62 micrograms/ml, depending on the sampling time and the time elapsed since the onset of the disease. These concentrations were equal to or higher than the MICs for most of the gram-negative bacilli (including Pseudomonas aeruginosa).