Concentrations of ticarcillin and clavulanic acid in human bone after prophylactic administration of 5.2 g of timentin

Bone penetration of amoxicillin and clavulanic acid evaluated by population pharmacokinetics and Monte Carlo simulation

Amoxicillin (amoxicilline)-clavulanic acid has promising activity against pathogens that cause bone infections. We present the first evaluation of the bone penetration of a beta-lactam by population pharmacokinetics and pharmacodynamic profiling via Monte Carlo simulations. Twenty uninfected patients undergoing total hip replacement received a single intravenous infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid before surgery. Blood and bone specimens were collected. Bone samples were pulverized under liquid nitrogen with a cryogenic mill, including an internal standard. The drug concentrations in serum and total bone were analyzed by liquid chromatography-tandem mass spectrometry. We used NONMEM and S-ADAPT for population pharmacokinetic analysis and a target time of the non-protein-bound drug concentration above the MIC for > or = 50% of the dosing interval for near-maximal bactericidal activity in serum. The median of the ratio of the area under the curve (AUC) for bone/AUC for serum was 20% (10th to 90th percentile for between-subject variability [variability], 16 to 25%) in cortical bone and 18% (variability, 11 to 29%) in cancellous bone for amoxicillin and 15% (variability, 11 to 21%) in cortical bone and 10% (variability, 5.1 to 21%) in cancellous bone for clavulanic acid. Analysis in S-ADAPT yielded similar results. The equilibration half-lives between serum and bone were 12 min for amoxicillin and 14 min for clavulanic acid. For a 30-min infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid every 4 h, amoxicillin achieved robust (> or = 90%) probabilities of target attainment (PTAs) for MICs of < or = 12 mg/liter in serum and 2 to 3 mg/liter in bone and population PTAs above 95% against methicillin-susceptible Staphylococcus aureus in bone and serum. The AUC of amoxicillin-clavulanic acid was 5 to 10 times lower in bone than in serum, and amoxicillin-clavulanic acid achieved a rapid equilibrium and favorable population PTAs against pathogens commonly encountered in bone infections.

A practical look at the clinical usefulness of the beta-lactam/beta-lactamase inhibitor combinations

OBJECTIVE

To aid clinicians in developing an approach to the use of intravenous beta-lactam/beta-lactamase inhibitors on a patient-specific basis. To achieve this, the pharmacology, in vitro activity, and clinical use of the intravenous beta-lactam/beta-lactamase inhibitor combinations in the treatment of selected infections seen in hospitalized patients are discussed.

DATA IDENTIFICATION

An English-language literature search using MEDLINE (1987-1995); Index Medicus (1987-1995); program and abstracts of the 32nd (1992), 33rd (1993), 34th (1994), and 35th (1995) Interscience Conference on Antimicrobial Agents and Chemotherapy; bibliographic reviews of review articles; and package inserts.

STUDY SELECTION

In vitro and in vivo studies on the pharmacokinetics, microbiology, pharmacology, and clinical effectiveness of ampicillin/sulbactam, ticarcillin/clavulanate, and piperacillin/tazobactam were evaluated.

DATA SYNTHESIS

Many properties of the beta-lactam/beta-lactamase inhibitor combinations are similar. Differences in dosing, susceptibilities, and clinical applications are important considerations for clinicians. Potential roles for these agents in the clinical setting include pneumonia, intraabdominal infections, and soft tissue infections. A short discussion on susceptibility data interpretation is also presented.

CONCLUSIONS

There are important differences among the available beta-lactam/beta-lactamase inhibitor combinations, such as spectra of activity, which need to be considered in choosing an agent for a patient-specific case. These products can be useful alternatives to conventional two- to three-drug regimens in mixed infections such as foot infections in patients with diabetes and hospital-acquired intraabdominal infections.

Penetration of piperacillin-tazobactam into cancellous and cortical bone tissues

The penetration characteristics of piperacillin-tazobactam into cortical and cancellous bone tissues were investigated in 10 patients undergoing total hip replacement. The concentration ratios of piperacillin/tazobactam were 9.4 +/- 1.8 in cancellous bone tissue and 8.0 +/- 2.2 in cortical bone tissue, which were close to the 8:1 ratio of drugs administered. The mean ratios of drug concentrations in bone and plasma for cancellous and cortical tissue were 23 and 18%, respectively, for piperacillin and 26 and 22%, respectively, for tazobactam. The concentrations of tazobactam achieved are sufficient to exert anti-beta-lactamase activity and supportive of clinical trials involving bone and joint infections, including those caused by beta-lactamase-producing pathogens.

Penicillin concentration in the compact bone of the mandible

During surgical removal of impacted third molars, the concentration of Penicillin G was determined in the compact bone of the mandible. Fifteen patients received 5 million IU and 15 received 10 million IU of Penicillin G intravenously as a single dose before surgery began. In both groups concentrations of penicillin with a bactericidal effect on most pathogenically relevant oral bacteria were detected during osteotomy. Taking into account the considerable interindividual variation, the one-shot application of 10 million IU of Penicillin G was more effective in certain cases than the 5 million IU dose. The factors influencing the decision on the high single-dose application include expected length of operation, body weight, kidney function, and infusion period. Assuming that in intraoral osteotomies the bone becomes contaminated with bacteria that are highly sensitive to penicillins, the results indicate that preoperative infusion of Penicillin G could be an effective method of preventing wound infection.

Simulation of human serum pharmacokinetics of ticarcillin-clavulanic acid and ceftazidime in rabbits, and efficacy against experimental Klebsiella pneumoniae meningitis

The penetration into cerebrospinal fluid (CSF) and efficacy of ticarcillin-clavulanic acid, ticarcillin alone, and ceftazidime were compared in rabbits with experimentally induced Klebsiella pneumoniae meningitis. The compounds were administered to simulate in rabbit plasma the concentration-versus-time curves observed in humans after 30-min infusions of Timentin (3 g of ticarcillin plus 100 mg of clavulanic acid), ticarcillin (3 g), and ceftazidime (2 g). Single- and multiple-dosing schedules were used. The penetrations of clavulanic acid into CSF (expressed as [area under the concentration-time curve for CSF/area under the curve for plasma] x 100) after the two dosing schedules were 28 and 24.5%, similar to that for ceftazidime (21%; multiple-dosing only) and greater than those for ticarcillin (8.4 and 9.3%). Ticarcillin was ineffective in reducing viable counts in CSF but, in the presence of clavulanic acid, reduced bacterial numbers by approximately 99% at 4 h after a single dose and by 99.99% at 12 h after three doses given at 4-h intervals. Two doses of ceftazidime given 8 h apart were more effective than the three doses of ticarcillin-clavulanic acid, in keeping with the in vitro activities of these compounds against the infecting organism. These results illustrate the ability of clavulanic acid to penetrate the blood-CSF barrier such that concentrations of the inhibitor in CSF potentiate the activity of ticarcillin against the ticarcillin-resistant, beta-lactamase-producing strain of K. pneumoniae.

Pharmacokinetic disposition of quinolones in human body fluids and tissues

The unique pharmacokinetic properties as well as the body fluid and tissue penetration of quinolones are discussed. Quinolones are well absorbed from the gastrointestinal tract and are eliminated with considerable differences in their terminal half-lives. The major elimination pathways of quinolones are renal excretion and hepatic metabolism. Renally, these drugs undergo the potential excretion mechanisms (glomerular filtration, tubular secretion, reabsorption). In the liver, they are metabolised primarily by oxidation as well as by conjugative pathways. However, the metabolic pattern and extent of metabolism differ significantly between individual agents. Alterations in the pharmacokinetic disposition of these agents in liver and renal failure as well as in elderly patients are observed as predicted from their excretion pattern. In addition, quinolones can interact with a number of other compounds at hepatic (e.g. with xanthine derivatives), renal (with probenecid) and gastrointestinal (with antacids) sites. The volume of distribution of quinolones is considerably higher than body volume, which suggests intracellular penetration. Studies on tissue penetration show that concentrations exceeding plasma levels are obtained in most tissues. The highest tissue/plasma concentration ratios are achieved in lung and kidney, whereas concentrations in fat are considerably lower than in plasma. Body fluid penetration is introduced as a new approach to evaluate distribution kinetics of quinolones. With the exception of those in nasal secretions and ejaculate, body fluid levels of these drugs rarely reach plasma levels. The body fluid penetration model allows for differentiation among individual agents. There is no apparent relationship between differences in body fluid penetration of quinolones and differences in volume of distribution. For the clinical use of these drugs it is important that the concentrations achieved in body fluids and tissues are sufficient to kill most pathogens. A discussion on the relationship between plasma and tissue levels and the MICs of quinolones is, however, beyond the scope of this article.

Clinical pharmacokinetics of enzyme inhibitors in antimicrobial chemotherapy

The effectiveness of some antimicrobial agents can be enhanced by using them in combination; such combinations are termed synergistic. Where one compound potentiates the effect of a second drug they may be coformulated. Inhibition of the bacterial degradation of an active antimicrobial is the basis of clavulanate and sulbactam-potentiated penicillin combinations, and inhibition of degradative pathways in the host is the rationale behind imipenem/cilastatin therapy. Trimethoprim/sulphonamide combinations depend on the maintenance of an effective ratio for synergistic action. In order to achieve potentiation the coformulated drugs should have similar pharmacokinetics. Trimethoprim was originally matched with sulphamethoxazole, since these two drugs have similar elimination half-lives, but the significantly poorer penetration of sulphonamides, their greater non-renal clearance, the emergence of resistance, and the adverse reactions attributable to them argue against the rationale that underlies their coformulation. Time-dependent inhibition of bacterial beta-lactamases by clavulanic acid and sulbactam has extended the use of penicillins which are highly susceptible to beta-lactamase inactivation. The beta-lactamase inhibitors must penetrate to the same extent as the penicillin used with them, and be present long enough to effect inhibition; thus, rapid penetration, similar or slower elimination and equivalent volume of distribution are necessary. These requirements are met for amoxycillin/clavulanic acid, ticarcillin/clavulanic acid and ampicillin/sulbactam combinations. Clavulanic acid is absorbed orally and is given with amoxycillin. However, since sulbactam is labile by this route, the combination of sulbactam with ampicillin to form the prodrug sultamicillin has been necessary to enable an oral form to be developed. Imipenem is metabolised by renal brush-border dehydropeptidases, and may cause proximal tubular necrosis. Cilastatin was designed to inhibit this metabolism, which it effectively does, thereby both potentiating the effect of imipenem and avoiding toxicity. Appropriate matching of the kinetics of coformulated drugs is intended to maximise potentiation and minimise the risk of emergent resistance. The kinetics of the above combinations are discussed in the light of these requirements and the effects of age and disease.