Staphylococcus aureus surface attachment selectively influences tolerance against charged antibiotics

The threat of infection during implant placement surgery remains a considerable burden for millions of patients worldwide. To combat this threat, clinicians employ a range of anti-infective strategies and practices. One of the most common interventions is the use of prophylactic antibiotic treatment during implant placement surgery. However, these practices can be detrimental by promoting the resilience of biofilm-forming bacteria and enabling them to persist throughout treatment and re-emerge later, causing a life-threatening infection. Thus, it is of the utmost importance to elucidate the events occurring during the initial stages of bacterial surface attachment and determine whether any biological processes may be targeted to improve surgical outcomes. Using gene expression analysis, we identified a cellular mechanism of S. aureus which modifies its cell surface charge following attachment to a medical grade titanium surface. We determined the upregulation of two systems involved in the d-alanylation of teichoic acids and the lysylation of phosphatidylglycerol. We supported these molecular findings by utilizing synchrotron-sourced attenuated total reflection Fourier-transform infrared microspectroscopy to analyze the biomolecular properties of the S. aureus cell surface following attachment. As a direct consequence, S. aureus quickly becomes substantially more tolerant to the positively charged vancomycin, but not the negatively charged cefazolin. The present study can assist clinicians in rationally selecting the most potent antibiotic in prophylaxis treatments. Furthermore, it highlights a cellular process that could potentially be targeted by novel technologies and strategies to improve the outcome of antibiotic prophylaxis during implant placement surgery. STATEMENT OF SIGNIFICANCE: The antibiotic tolerance of bacteria in biofilm is a well-established phenomenon. However, the physiological adaptations employed by Staphylococcus aureus to increase its antibiotic tolerance during the early stages of surface attachment are poorly understood. Using multiple techniques, including gene expression analysis and synchrotron-sourced Fourier-transform infrared microspectroscopy, we generated insights into the physiological response of S. aureus following attachment to a medical grade titanium surface. We showed that this phenotypic transition enables S. aureus to better tolerate the positively charged vancomycin, but not the negatively charged cefazolin. These findings shed light on the antibiotic tolerance mechanisms employed by S. aureus to survive prophylactically administered antibiotics and can help clinicians to protect patients from infections.

Prevalence of Efflux Pump and Porin-Related Antimicrobial Resistance in Clinical Klebsiella pneumoniae in Baghdad, Iraq

Klebsiella pneumoniae is an opportunistic bacterium that causes many infections, including septicemia, pneumonia, urinary tract infection, and liver abscesses. There are many mechanisms for antibiotic resistance and K. pneumonia is considered a multidrug-resistant pathogen. This study aimed to find the correlation between the susceptibility of K. pneumonia to certain antibiotics with the porin-related resistance and pumps mechanisms. In total, two genes that are responsible for porin formation were considered in the current study OmpK-35gene and OmpK-36 gene, in addition to other four genes (CfiaS, CfiaL, MFS, and MdtK genes) related to an efflux pump mechanism of antibiotic resistance. The bacterial resistance was investigated towards five cephalosporins (Cefazolin, Cefoxitin, Ceftazidime, Ceftriaxone, and Cefepime) and two carbapenems (imipenem and ertapenem). Clinical samples, including blood, swabs, and urine, consisting of 20 specimens for each group, were collected from patients who attended three hospitals in Baghdad. The VITEK-2 system and genetic tests (polymerase chain reaction and sequencing) of bacterial isolates were applied to confirm the diagnosis of K. pneumoniae and detect the antibiotic sensitivity profile. The results showed that 51 (85%) and 15 (25%) of the total 60 isolates had positive results for OmpK-35 and Omp-K36 genes, respectively. The MFS and MdtK genes were observed (70-88.3%) in cephalosporin-resistant isolates of K. pneumoniae. There were no significant variations of bacterial resistance genes of antibiotics within the specimen groups. It was concluded that the bacterial resistance of the selected antibiotics was elevated markedly with the loss of the OmpK-36 gene with a high expression of MFS and MdtK genes and a slight minimal occurrence in the new generation of carbapenems. The best antimicrobial agent was ertapenem with a percentage of 0% of resistance in all bacterial isolates.

Quantification of cefazolin in serum and adipose tissue by ultra high performance liquid chromatography-Tandem mass spectrometry (UHPLC-MS/MS): application to a pilot study of obese women undergoing cesarean delivery

Higher doses of cefazolin are required in obese patients for preoperative antibiotic prophylaxis, owing to its low lipophilicity. An ultra high performance liquid chromatography-tandem mass spectrometry method was developed to quantify cefazolin in serum and adipose tissue from 6 obese patients undergoing cesarean delivery, and using stable-isotope labeled cefazolin as an internal standard. The method has a 2μg/g lower limit of quantitation. The concentration in adipose tissue was 3.4±1.6μg/mL, which is less than half of the reported minimum inhibitory concentration of 8μg/mL for cefazolin. Serum cefazolin concentrations were more than 30-fold higher than in adipose tissue.

Kinetic behavior of the major multidrug efflux pump AcrB of Escherichia coli

Multidrug efflux transporters, especially those that belong to the resistance-nodulation-division (RND) family, often show very broad substrate specificity and play a major role both in the intrinsic antibiotic resistance and, with increased levels of expression, in the elevated resistance of Gram-negative bacteria. However, it has not been possible to determine the kinetic behavior of these important pumps so far. This is partly because these pumps form a tripartite complex traversing both the cytoplasmic and outer membranes, with an outer membrane channel and a periplasmic adaptor protein, and it is uncertain if the behavior of an isolated component protein reflects that of the protein in this multiprotein complex. Here we use intact cells of Escherichia coli containing the intact multiprotein complex AcrB-AcrA-TolC, and measure the kinetic constants for various cephalosporins, by assessing the periplasmic concentration of the drug from their rate of hydrolysis by periplasmic beta-lactamase and the rate of efflux as the difference between the influx rate and the hydrolysis rate. Nitrocefin efflux showed a K(m) of about 5 microM with little sign of cooperativity. For other compounds (cephalothin, cefamandole, and cephaloridine) that showed lower affinity to the pump, however, kinetics showed strong positive cooperativity, which is consistent with the rotating catalysis model of this trimeric pump. For the very hydrophilic cefazolin there was little sign of efflux.

Cefoselis, a ?-lactam antibiotic, easily penetrates the blood-brain barrier and causes seizure independently by glutamate release

Cefoselis is a widely used beta-lactam antibiotic, but occasionally induces seizures and convulsion in elder and renal failure patients. However, beta-lactams are known not to pass through the blood-brain barrier (BBB). In this study, we examined the BBB penetration of cefoselis in normal and renal failure rats by means of brain microdialysis. Cefoselis was dose-dependently appeared in brain extracellular fluid in proportion to its blood level. The elimination constant from brain extracellular fluid (apparent) was slightly lower than that from blood. These results indicated that cefoselis might penetrate the BBB or be discharged by a certain transport system. In contrast to the result of cefoselis, cefazolin, a leading drug of cephalosporins, could not be detected in the brain extracellular fluid after an intravenous injection. In renal dysfunction rats, the elimination half-lives of cefoselis from both blood and brain were extensively prolonged. This would be one of responsible factors inducing seizures seen in patients. However, the additional factor, such as decrease in brain function related to aging, would be involved in seizures in patient received cefoselis, because an extremely high dose was required to induce seizures even in renal failure rats. A local administration of cefoselis into the hippocampus through the microdialysis probe caused a striking elevation of extracellular glutamate, with a minimum increase in gamma-aminobutyric acid (GABA). However, a systematic cefoselis administration via the tail vein did not elevate extracellular glutamate and GABA concentrations in the hippocampus of renal failure rats that exhibited marked seizures. These results suggested that not the stimulation of glutamate release, but the blockade of GABA receptors might be responsible for the seizure induced by cefoselis.

Expression Levels of Renal Organic Anion Transporters (OATs) and Their Correlation with Anionic Drug Excretion in Patients with Renal Diseases

PURPOSE

Because the urinary excretion of drugs is often decreased in renal diseases, dosage regimens are adjusted to avoid adverse drug reactions. The aim of present study was to clarify the alteration in the levels of renal drug transporters and their correlation with the urinary drug excretion in renal diseases patients.

METHODS

We quantified the mRNA levels of human organic anion transporters (hOATs) by real-time polymerase chain reaction and examined the excretion of the anionic drug, cefazolin, in renal disease patients. Moreover, transport of cefazolin by hOAT1 and hOAT3 were examined using HEK293 transfectants.

RESULTS

Among four hOATs, the level of hOAT1 mRNA was significantly lower in the kidney of patients with renal diseases than in the normal controls. The elimination constant of cefazolin showed a significant correlation with the values of phenolsulfonphthalein test and mRNA levels of hOAT3. The uptake study using HEK293 transfectants revealed that cefazolin and phenolsulfonphthalein were transported by hOAT3.

CONCLUSIONS

These results suggest that hOAT3 plays an important role for anionic drug secretion in patients with renal diseases and that the expression levels of drug transporters may be related to the alteration of renal drug secretion.

A pilot study to determine the feasibility of continuous cefazolin infusion

BACKGROUND

Animal studies have shown that continuous infusion of beta-lactam antibiotics is more effective than intermittent dosing. We studied several dosing regimens of cefazolin in humans to determine safety and whether or not adequate serum and tissue antibiotic concentrations could be achieved in patients undergoing cardiac bypass.

METHODS

A prospective, randomized pilot study was conducted at a university-affiliated teaching hospital over a 2-year period in patients undergoing first-time coronary artery bypass grafting. One hundred and thirty-seven patients were randomized to one of three groups. Group 1 (n = 64) received 1 g of cefazolin intravenously before operation and 1 g intravenously at the end of cardiopulmonary bypass. Group 2 (n = 35) received 2 g of cefazolin intravenously before operation, followed by a continuous intravenous infusion of cefazolin at 20 mg/min throughout surgery. Group 3 (n = 38) received 3 g of cefazolin intravenously before operation, followed by a continuous intravenous infusion of cefazolin at 15 mg/min throughout surgery. Venous blood and subcutaneous fat samples were obtained from the sternal wound in a subset of 34 patients at incision, 0.25 h, 0.5 h, and 1 h; at the end of cardiopulmonary bypass; and at wound closure. Venous blood was sampled in the recovery room and on postoperative day 1. Cefazolin concentrations in the samples were determined by reverse-phase high-performance liquid chromatography using a C18 column.

RESULTS

Serum cefazolin concentrations were higher for group 3 when compared with group 1 at all six intraoperative intervals (p < 0.02) and for group 2 when compared with group 1 at four of six intraoperative intervals (p < 0.04). When compared with group 1, tissue cefazolin concentrations were higher for group 3 at all intraoperative intervals (p < 0.02). No related toxicity or adverse events were observed.

CONCLUSION

Cefazolin administered as a large preoperative bolus with continuous intraoperative infusion resulted in higher serum and tissue concentrations when compared with conventional intermittent dosing. Pharmacodynamically, continuous infusion of beta-lactam antibiotics may be superior to intermittent dosing when used for perioperative prophylaxis against wound infection, especially for cases in which the antibiotic is not redosed intraoperatively.

Cefazolin administration and 2-methyl-1,3,4-thiadiazole-5-thiol in human tissue: possible relationship to hypoprothrombinemia

Cephalosporin antibiotics with structures that include the heterocyclic leaving group 1-methyltetrazole-5-thiol (MTT) can cause hypoprothrombinemia and hemorrhage as a result of MTT-dependent inhibition of the gamma-carboxylation of glutamate. The structure of cefazolin also includes a heterocyclic thiol, 2-methyl-1,3,4-thiadiazole-5-thiol (MTD), and this compound can also inhibit the gamma-carboxylation of glutamate. However, unlike MTT, which is known to be present in vivo after the administration of drugs that include this structure, there have been no reports that MTD is present in vivo after cefazolin administration. We set out to determine whether MTD might be present in the tissues of patients treated with cefazolin prior to surgery. To do that, we took advantage of the fact that heterocyclic thiols can undergo S-methylation catalyzed by the genetically polymorphic drug-metabolizing enzyme thiopurine S-methyltransferase (TPMT). Initially, we tested recombinant human TPMT as a "reagent" to S-methylate MTD. MTD was a substrate for TPMT-catalyzed S-methylation, with an apparent K(m) value of 63 micro M. Recombinant TPMT, with [(14)C-methyl]S-adenosyl-L-methionine as a cosubstrate, was then used to radioactively label a methyl acceptor substrate present in liver and kidney cytosol preparations from patients who had been treated preoperatively with cefazolin. Pooled renal cytosol from 10 of those patients was used to purify and isolate the methylated product by reverse-phase high-performance liquid chromatography. That methylated compound coeluted with S-methyl MTD. When the methylated product was subjected to tandem mass spectrometry, it was identified as S-methyl MTD. Therefore, MTD is present in the tissues of patients treated with cefazolin. These observations also raise the possibility that the TPMT genetic polymorphism may represent a risk factor for cefazolin-induced hypoprothrombinemia since subjects who genetically lack TPMT would be unable to catalyze this MTD biotransformation pathway.

[Diversity within a population of Shigella sonnei according to markers of medicinal preparations]

As revealed in this study, S. sonnei population is represented by two clusters with respect to the sensitivity to different antibiotics. A higher degree of diversity was observed with respect to the action of streptomycin, kefzol, ampicillin, chloramphenicol and kanamycin in comparison with the action of gentamicin, nevigramon, rafampicin, tetracycline and polymyxin. The level of diversity of S. sonnei with respect to the sensitivity to antibiotics under study underwent essential changes during the calendar year. The distributions obtained study quite closely corresponded to changes in Sonne dysentery morbidity observed within the year period: the first cluster corresponded to the period of morbidity between the seasons and the second one, to the seasonal period of morbidity. The minimal coefficient of diversity fell on May while the maximum--on September. The minimal level of S. sonnei diversity, as a rule, corresponds to the minimum biosystems stability.

Therapy with hyperbaric oxygen and cefazolin for experimental osteomyelitis due to Staphylococcus aureus in rats

Hyperbaric oxygen (HBO2) is used as adjunctive therapy for chronic osteomyelitis, yet its efficacy remains controversial. A recently developed rat model for osteomyelitis due to Staphylococcus aureus was used to compare the results of treatment with HBO2, cefazolin, a combination of both, or no treatment. For the induction of tibial osteomyelitis, S. aureus was inoculated into the medullary cavity. Arachidonic acid was used as the sclerosing agent. With that procedure, an infection rate of 96% was attained. For long-term antibiotic treatment, a port system was developed and implanted. Hyperbaric treatment alone reduced the colony-forming units (CFU) from 2.9 x 10(6) to 6.2 x 10(5) x g(-1) of tibial bone. The effect on the infection was more pronounced with antibiotic therapy alone, 10.5 x 10(4) CFU per g of tibial bone were measured. However, changes were most marked using a 4-wk combination therapy consisting of HBO2 and an antibiotic agent. The colony count was 2.7 x 10(3) CFU. Each of the treatment modalities resulted in a significant therapeutic effect. The results not only demonstrated the effectiveness of HBO2 in the treatment of osteomyelitis, but revealed a potential additive effect with the combination of HBO2 and an antibiotic.

Association of borderline oxacillin-susceptible strains of Staphylococcus aureus with surgical wound infections

Staphylococcus aureus isolates which produce type A staphylococcal beta-lactamase have been associated with wound infections complicating the use of cefazolin prophylaxis in surgery. To further evaluate this finding, 215 wound isolates from 14 cities in the United States were characterized by antimicrobial susceptibility and beta-lactamase type and correlated with the preoperative prophylactic regimen. Borderline-susceptible S. aureus isolates of phage group 5 (BSSA-5), which produce large amounts of type A beta-lactamase and exhibit borderline susceptibility to oxacillin, comprised a greater percentage of the 120 wound isolates associated with cefazolin prophylaxis than they did of the 95 isolates associated with other prophylactic regimens (25% versus 12.6%, respectively; P < 0.05). In contrast, methicillin-resistant S. aureus isolates were distributed evenly between the two groups (8.3% versus 11.6%, respectively). In vitro assays demonstrated that cefazolin was hydrolyzed faster by BSSA-5 strains than by other beta-lactamase-producing, methicillin-susceptible strains (1.54 versus 0.50 microg/min/10(8) CFU, respectively; P < 0.0001). These data demonstrate that BSSA-5 strains are a distinct subpopulation of methicillin-susceptible S. aureus which frequently cause deep surgical wound infections. Cefazolin use in prophylaxis is a risk factor for BSSA-5 infection.

[Effects of plasma albumin on theophylline concentration in lung tissue]

To study the relationship between plasma and lung tissue theophylline concentrations, we changed the number of binding sites for theophylline on serum albumin. Cefazoline, which competes with theophylline for those binding sites, was given to rats, and free theophylline was separated by ultrafiltration. The dose of cefazoline was directly related to the percentage of free theophylline and was inversely related to the plasma total theophylline concentration. The plasma free theophylline concentration, however, was unchanged at the lower doses of cefazoline and was low only at the highest dose. The concentration of theophylline in lung tissue was inversely related to the dose of cefazoline. The concentration of 1, 3-dimethyluric acid, a major metabolite of theophylline, was also inversely related to the dose of cefazoline, which suggests that the metabolic rate of theophylline did not increase. Excretion of theophylline via the urine might be accelerated by its diuretic action. We conclude that when the binding of theophylline to plasma proteins is altered in rats, the concentration of free theophylline in plasma does not reflect the concentration of theophylline in lung tissue. Instead, the total theophylline concentration in plasma can be used as an index of the concentration in lung tissue.

Specificity of p-aminohippurate transport system in the OK kidney epithelial cell line

Substrate specificity of the p-aminohippurate (PAH) transport system was investigated in the OK kidney epithelial cells. PAH uptake by OK cells from the basal side was inhibited by beta-lactam antibiotics such as benzylpenicillin (PCG) and cefazolin. The inhibition of PAH uptake by PCG was competitive and the Ki value was calculated as 108.8 microM. Transcellular transport of PCG across OK cell monolayers occurred unidirectionally from the basal to apical side, and transcellular transport and basolateral uptake were inhibited by PAH, probenecid and beta-lactam antibiotics. The basolateral uptake of cefazolin and cefotiam was also inhibited by PAH and probenecid. The basolateral uptake of PAH and PCG were not affected by aliphatic dicarboxylates with 3 or 4 carbon atoms, but were strongly inhibited by those with 5 or 6 carbon atoms. The inhibitory effect became weaker for a longer dicarboxylate with 7 carbon atoms, then increased again with increasing number of carbon atoms. Such a pattern of inhibition by dicarboxylates is essentially the same with that observed in rat renal proximal tubules in situ. These findings suggest that the PAH transport system in OK cells has a substrate specificity similar to that in rat renal proximal tubules, which is involved in the active secretion of various organic anions including drugs.

Inducible beta-lactamases in clinical isolates of non-aeruginosa Pseudomonas

The incidence of antimicrobial resistance and expression of imipenem-inducible beta-lactamase were examined in 22 strains of non-aeruginosa Pseudomonas isolated from clinical specimens. The percentage of strains resistant to form one to eight antibiotics was 45. The most active antibiotics against all strains were norfloxacin, ciprofloxacin and imipenem. Eighteen out of the 22 strains were positive for beta-lactamase in a spectrophotometric assay using nitrocefin as substrate. A low inducible beta-lactamase specific activity (0.001-0.999 nmoles nitrocefin hydrolyzed/min/mg protein) was found in twelve strains whereas six strains had a relatively high specific activity (3.5-159.8 nmoles nitrocefin hydrolyzed/min/mg protein). Five strains representing different Pseudomonas spp. and showing high beta-lactamase activity were studied further. Crude enzymes from two species (Pseudomonas mendocina, Pseudomonas acidovorans) hydrolyzed cefazolin at a higher rate than penicillin and ampicillin. All enzymes from the five species were inhibited by cloxacillin and p-chloromercuribenzoate (1 mM), but were insensitive to inhibition by clavulanic acid, ethylenediamine acetic acid (EDTA) at the same concentration. The isoelectric point and molecular weight of the main beta-lactamase band from the 5 species were 6.5-6.8 and 47,000 respectively.

In vitro and in vivo evaluation of antibiotic diffusion from antibiotic-impregnated polymethylmethacrylate beads

The elution of antibiotics from antibiotic-impregnated polymethylmethacrylate (PMMA) beads was measured in mongrel dogs. The antibiotics, used in mixture with Simplex cement, included cefazolin (Ancef; 4.5 g/40 g cement powder), ciprofloxacin (Cipro; 6 g/40 g powder), clindamycin (Cleocin; 6 g/40 g powder), ticarcillin (Ticar; 12 g/40 g powder), tobramycin (Nebcin; 9.8 g/40 g powder), and vancomycin (Vancocin; 4 g/40 g powder). After a pneumatic drill was used to dredge a trough in the tibia, five beads were implanted. During the next 28 days, seroma samples and serum samples were taken for antibiotic measurements. On Day 28, the dogs were killed, beads removed, and the seroma, serum, bone, and granulation tissue sampled. The results of the study showed that clindamycin, vancomycin, and tobramycin exhibited good elution characteristics and had consistently high levels in bone and granulation tissue.

[Effect of serum albumin concentration on percentage of free theophylline fraction]

The authors experienced three cases in which serum free theophylline concentrations (F) rose with unchanged or decreased serum total theophylline concentrations (T). To clarify the causes of changes in F or T within a short time, we studied the relationship between F and serum albumin concentration or T in patients, and the relationship between T and F using aminophylline alone or aminophylline and cefazoline (CEZ) in rabbits. In patients, the fraction of free theophylline (F/T) showed a reverse relation to the serum albumin concentration, and a positive relation to T. In rabbits, when aminophylline was injected with CEZ, F/T increased in proportion to the dose of CEZ and T decreased when aminophylline alone was injected. The data suggested that F/T increased accompanied with decreasing serum albumin concentration or increasing T, since the albumin binding-site of theophylline is limited. The present study also suggested that the protein-bound theophylline decreased in competition with CEZ, therefore F/T increased when aminophylline was injected with CEZ. It is likely that decreased T is a result of augmented movement of theophylline to the tissue due to decreased serum albumin concentration. To evaluate the clinical conditions of the patients taking theophylline, it is necessary to directly monitor F, or to measure serum albumin concentration if direct measurement of F is not possible.

Influences of cephem antibiotics on the immune response in mice

The effects of six cephem antibiotics, including ceftezole, cefmetazole, cefoxitin, cefotiam, cefoperazone, and cefotaxime, on murine humoral immunity were examined. In female BDF1 mice each cephem antibiotic was administered at a dose of 800 mg/kg/day i.v. for 7 consecutive days. Among the antibiotics tested, only ceftezole and cefoperazone induced a significant increase in serum total IgM, but not in serum total IgG. Especially in case of ceftezole, the mice developed splenomegaly due to the proliferation of IgM-producing cells in the germinal centers. The proliferation of splenic IgM-producing cells was also observed in female thymus-deficient Balb/c-nu/nu mice receiving intravenous ceftezole. Thus, the drug was indicated to enhance the polyclonal IgM production in mice by acting as a B cell mitogen. This is consistent with the in vitro finding that ceftezole exhibited a mitogenic effect on whole spleen cells from BDF1 mice, but not on B cell depleted spleen cells.

Relevance of protein binding to cephalosporin antimicrobial activity in vivo

Protein binding, serum kinetics and minimum inhibitory concentrations (MICs) for Staphylococcus aureus were determined for cefoxitin, cefazolin, ceftazidime and ceftriaxone in the rabbit. MICs of cefazolin and cefoxitin were also measured for Escherichia coli. Varying concentrations of the bacteria were administered intradermally to create areas of cellulitis, which were quantified as mean erythematous areas (EAs). Despite large differences in protein binding of the antibiotics (range 12-88%) and antibiotic dosing to allow serum concentrations to drop below the respective MICs, there was no statistical difference in the mean EAs of the animals after bacterial challenge. Antibiotic protein binding did not alter the course of cellulitis nor correlate with bacterial MIC in this model.

Effect of protein binding on the disposition of cephalexin and cefazolin in a simultaneous perfusion system of rat liver and kidney

The effect of protein binding on the disposition of cephalexin (CEX) and cofazolin (CEZ) was investigated in a simultaneous perfusion system of rat liver and kidney. In the present study, we used bovine serum albumin (BSA) or human serum albumin (HSA) as plasma protein to control the degree of perfusate protein binding of drugs. Total clearance (CLt) of CEX perfused with BSA (0.70 +/- 0.27 ml/min) was slightly smaller than that with HSA (0.89 +/- 0.08 ml/min), corresponding to the unbound fraction of the drug in the perfusate plasma. On the other hand, CLt of CEZ perfused with BSA (0.90 +/- 0.20 ml/min) was significantly larger than that with HSA (0.32 +/- 0.10 ml/min). The unbound fraction of CEZ to BSA (0.703 +/- 0.052) was much larger than that to HSA (0.253 +/- 0.017) and the clearance of the unbound drug did not differ significantly between two kinds of albumin perfusate (1.30 +/- 0.40 ml/min for BSA and 1.26 +/- 0.40 ml/min for HSA). These results suggest that plasma protein binding is an important factor determining the biliary clearance as well as the urinary clearance of drugs.

Efficacy of prophylactic antibiotics in vascular surgery: an arterial wall microbiologic and pharmacokinetic perspective

This prospective study examined microbiologic features of arterial tissue and pharmacokinetics and bioactivity of cefamandole and cefazolin in patients undergoing elective primary prosthetic aortoiliofemoral/infrainguinal reconstruction. Double-blind, randomized, perioperative prophylaxis (1 gm intravenously every 6 hours for nine doses) with cefamandole or cefazolin was administered to 47 patients. Specimens of blood serum, subcutaneous fat, thrombus, atheroma, and arterial wall were obtained for culture and minimal inhibitory concentration and drug level analysis by high-pressure liquid chromatography. The serum half-life (hr +/- SEM) was 1.43 +/- 0.36 for cefamandole and 2.22 +/- 0.40 for cefazolin. Over the first 2 hours of surgery and for all time intervals combined, the serum concentration of cefazolin was significantly higher (p less than 0.025) than cefamandole. Irrespective of sampling time, the tissue concentration of cefazolin was significantly greater (p less than 0.005) than cefamandole. Positive arterial tissue cultures were obtained in 12 of 29 patients (41.4%) from 23 of 116 (19.8%) arterial tissue specimens. Coagulase-negative Staphylococcus was the predominant isolate, 64 of 93 (68.8%). Twenty-five of the 51 coagulase-negative staphylocci tested (49%) were slime-producers. During surgery, the arterial tissue concentration of cefamandole fell below the geometric mean minimal inhibitory concentration against all organisms combined, and against S. aureus (with the highest minimal inhibitory concentration of the prevalent isolates), significantly more often than the concentration of cefazolin. The data show that a significant number of primary elective aortoiliofemoral/infrainguinal reconstructions are associated with positive arterial tissue cultures, which represent a potential source of graft infection.(ABSTRACT TRUNCATED AT 250 WORDS)

[Drug-protein binding in elderly subjects]

It is important to know the magnitude of serum-protein binding of drug dynamics in vivo. The authors investigated the effects of a variety of serum free fatty acids in elderly subjects. Serum albumin levels and ceftezole (CTZ)-protein binding in elderly subjects were lower than in younger subjects. No significant difference was noted between the two groups in regard to total free fatty acid (T-FFA) level. However, compared with younger subjects, palmitolic and oleic acid were higher and myristic and linoleic acid were lower in elderly subjects, suggesting that free fatty acid (FFA) undergoes qualitative changes due to ageing. In elderly subjects CTZ-binding correlated negatively with T-FFA, oleic acid and linoleic acid, but positively with stearic acid. Oleic acid decreased CTZ-protein binding. This decrease was higher than that due to decreased albumin levels in elderly subjects with albumin levels less than 4.0 g/dl. These findings indicated that reduced protein binding in elderly subjects is due to decreased serum albumin and changes in FFA constitution with ageing. Therefore it was suggested that drug-albumin binding may change due to the competitive action of albumin sites, and albumin-drug binding capacity. Since drug-protein binding capacity seriously affect metabolism, excretion, efficacy and side effects due to the presence of free drugs, these aspects require further investigation in elderly subjects.

Penetration of antibiotics into the surgical wound in a canine model

The dose and timing of antimicrobial agents given for surgical wound prophylaxis should be based on the concentration-time profile of the drug in tissue at the site of contamination. However, concentrations of antimicrobial agents in surgical wounds are difficult to determine accurately. Since a surgical wound is a unique extravascular compartment with increased vascular permeability and a high surface area/volume ratio, antibiotic concentrations in sera and surgical wounds should be similar. To test this hypothesis, the pharmacokinetics of single intravenous doses of cefazolin (40 mg/kg) and gentamicin (4 mg/kg) in sera and surgical wounds in a clinically relevant surgical model using dogs were compared. Drug concentrations were determined in interstitial fluid in muscle biopsies taken randomly from wound surfaces and serial wound fluid samples collected after the incisions were closed. Protein binding of cefazolin and gentamicin in sera and wound fluids was low (less than or equal to 29 +/- 9%) in this canine model. Cefazolin and gentamicin equilibrated rapidly (less than or equal to 30 min) between serum and the surgical wound, and concentrations in the two sites declined in parallel. Values for the area under the concentration-time curve, mean residence time, and terminal half-life in serum and the surgical site for each drug were similar. Cefazolin concentrations in serum underestimated the time during which concentrations in surgical wounds exceeded the susceptibility breakpoint MIC for important pathogens by an average of 58 min (range, 26 to 109 min; P = 0.036); for gentamicin, the underestimation averaged 30 min (range, 10 to 60 min; P = 0.036). These data support the concept that the concentration-time profiles of antimicrobial agents in serum may prove valuable clinically as guides to determining the and timing of antibiotic administration necessary for effective antimicrobial prophylaxis in surgery. Further studies are needed to determine the surgical wound pharmacokinetics of highly protein-bound antibodies.

Cefazolin serum protein binding and its inhibition by bilirubin, fatty acids and other drugs

This paper describes the protein binding of cefazolin to human serum and to human serum albumin (HSA) using equilibrium dialysis. The drug is exclusively bound to HSA with a moderate affinity, Ka = 16,600 +/- 1600 M-1, and one saturable binding site, n = 0.73 +/- 0.02. Moreover cefazolin shows a dose-dependent binding leading a possible increase of the free fraction (when its total concentration increases). This antibiotic is displaced by free fatty acids (FFA) and bilirubin. Cefazolin binding to human serum and human serum albumin (HSA) was studied in presence of acidic drugs. At low concentrations clofibric acid and phenylbutazone both exhibiting high affinity for HSA displace strongly cefazolin. Valproic and salicylic acids, sulfamethoxazole, cefoperazone which have approximately the same affinity as cefazolin, must be used at higher concentrations to displace this antibiotic. A particular phenomenon was observed with cefazolin on HSA when associated with furosemide. A low concentration (5-25 microM) of this drug induces a positive cooperativity of binding between cefazolin and HSA. But at a molar ratio of furosemide to albumin greater than one, such cooperative interaction disappears and a competitive inhibition of cefazolin binding occurs. For all drugs studied, a competitive inhibition was found except for tryptophan. Finally, it is concluded that cefazolin shares the warfarin binding site on HSA.

Animal model for evaluating the convulsive liability of beta-lactam antibiotics

The beta-lactam antibiotics imipenem-cilastatin, BMY-26225, and cefazolin significantly lowered the convulsive threshold of pentylenetetrazole in mice. In addition, imipenem-cilastatin and cefazolin were found to inhibit 3H-labeled gamma-aminobutyric acid binding to synaptic membranes from rat brains. Our results suggest that the pentylenetetrazole convulsive model may be useful in evaluating the proconvulsive liabilities of new carbapenems and other beta-lactam antibiotics and that the mechanism of imipenem-cilastatin and cefazolin toxicity may involve interaction with gamma-aminobutyric acid receptors.

In vitro activity of cefotaxime against clinically significant pathogens

The present in vitro antibacterial activities of cefotaxime and 8 other cephalosporins (cefoperazone, cefmenoxime, cefpiramide, latamoxef, cefamandole, cefmetazole, cefotiam and cephazolin) were evaluated simultaneously in 384 strains of Gram-positive cocci, 595 strains of Enterobacteriaceae, 240 strains of non-fermenters and 143 strains of anaerobes and miscellaneous organisms. The results were expressed as minimum inhibitory concentration (MIC) range, MIC50 and MIC90. Of the beta-lactams, cefotaxime and latamoxef exhibited the highest activity against a wide variety of Gram-positive and Gram-negative bacteria. MIC90 of cefotaxime, however, for species of Pseudomonas aeruginosa, Xanthomonas maltophilia, enterococci, Bacteroides sp. and Clostridium difficile were more than 100 mg/L. Cefpiramide and cefoperazone were generally less active than these 2 agents. All strains were tested for beta-lactamase production by the cefinase disc method and the relationship of susceptibility to beta-lactams was evaluated in each species. The need was demonstrated for periodic susceptibility testing to be performed to better guide empirical antimicrobial therapy.

Single-dose antibiotic prophylaxis for biliary surgery. Cefazolin vs moxalactam

Cefazolin was compared with moxalactam for single-dose prophylaxis against infection in a double-blind, prospective, randomized trial of 90 patients undergoing cholecystectomy. Risk factors for infection were present in 65 (72%) of the 90 patients and were evenly distributed. Antibiotic levels in plasma, bile, and tissue measured when the cystic duct was divided were similar for both drugs. Age greater than 65 years but not recent cholecystitis or type of antibiotic was predictive of recovery of bacteria from bile cultures. Wound infections occurred in two patients receiving cefazolin and one patient receiving moxalactam for an overall infection rate of 3%. No toxic reactions to antibiotics, including bleeding disorders, were observed. In conclusion, no significant difference in prophylactic efficacy was detected in this comparison of a first-generation with a third-generation cephalosporin. Because of its lower cost and narrower antimicrobial spectrum, however, cefazolin should remain the agent of choice.

Treatment of established prosthetic vascular graft infection with antibiotics preferentially concentrated in leukocytes

The efficacy of treating established vascular graft infections with rifampin and clindamycin (preferentially concentrated in leukocytes) and cefazolin (not concentrated in leukocytes) was studied in a canine model. Infrarenal aortic, 6 mm by 6 cm knitted Dacron double velour grafts were implanted and infected with 10(8) colony-forming units (CFU) of coagulase-positive Staphyloccus aureus organisms injected intravenously immediately after graft placement. Antibiotic therapy was instituted at 3 months postimplantation. Three groups were studied: (I) untreated controls (n = 3); (II) therapy with intravenous cefazolin 15 mg/kg/8 hr for 28 days (n = 7); and (III) combined therapy with intravenous rifampin 13 mg/kg/24 hr and intravenous clindamycin 13 mg/kg/8 hr for 28 days (n = 7). Grafts were removed for quantitative bacteriologic studies after the 28-day course of therapy. Two group I control grafts remained patent with 6.4 X 10(6) and 8.1 X 10(3) CFU S. aureus/gm of graft. The third control graft was thrombosed. Two group II animals demonstrated 1.6 X 10(7) and 2.3 X 10(5) CFU S. aureus organisms/gram of graft, respectively; the remaining five group II grafts were free of organisms. All group III grafts were sterile--a significant difference (p less than 0.05) from group I grafts. In this experimental model, established prosthetic graft infections were eradicated by intensive treatment with antibiotics preferentially concentrated in leukocytes.

Alteration of gentamicin and cefazolin kinetics with control of the hypothyroid state in humans

We studied the effect of the control of the hypothyroid state in humans on the pharmacokinetic parameters of cefazolin and gentamicin after a single intravenous injection. These two antibiotics were chosen because of their different patterns of binding to serum albumin (0% for gentamicin and 82% for cefazolin). In hypothyroidism, the behavior of cefazolin only was altered, with a decrease in the total body clearance, possibly due to reduced urinary excretion, and a decrease in the volume of distribution without a significant alteration of cefazolin binding to serum protein.

Effect of hemorrhagic shock on cefazolin and gentamicin pharmacokinetics in dogs

The physiologic response to traumatic injury may alter the disposition of drugs and thereby affect their therapeutic or toxic potential. A study was conducted in 10 mongrel dogs to determine the effect of experimental hemorrhagic shock with resuscitation on the pharmacokinetics of gentamicin and cefazolin. Single simultaneous intravenous doses of gentamicin (3 mg/kg) and cefazolin (25 mg/kg) were administered to each animal on an initial study day, after which serial blood and urine collections were performed. After 1 week, a standard hemorrhagic shock model was applied to each animal. Shock was continued for 1 h, after which the animal was resuscitated with either whole blood or saline. After stabilization for 20 min, a second dose of gentamicin and cefazolin was administered, and blood and urine were again collected. Drug clearance was not significantly altered, except for that of cefazolin after saline resuscitation, for which there was a significant increase in drug clearance. After both methods of resuscitation an increase in the volume of distribution was noted for cefazolin and gentamicin. Drug half-life was noted to be increased after shock for cefazolin by both resuscitation methods and for gentamicin after shock by saline resuscitation. Although alterations of pharmacokinetic parameters were noted, mean concentrations of gentamicin and cefazolin in serum were similar for pre- and postshock phases.

Comparison of the pharmacokinetics of cephradine and cefazolin in pregnant and non-pregnant women

The pharmacokinetics of cephradine, a cephalosporin with a low degree of protein binding, was studied in 12 women after oral and intravenous administration of the drug during and after pregnancy. Six of the 12 women also received a cephalosporin with a high degree of protein binding, cefazolin, intravenously during and after pregnancy. For both drugs most pharmacokinetic parameters were altered in pregnancy. The area under the plasma concentration-time curve (AUC) following intravenous administration was smaller for both drugs during as compared to after pregnancy (mean change 39% for cephradine and 31% for cefazolin). Half-lives of both drugs were significantly shorter during compared with after pregnancy (mean change 26% for cephradine and 35% for cefazolin). Consequently, total body clearance was increased during pregnancy. A significant negative correlation between length of gestation and total clearance per kg bodyweight was seen for cephradine. The bioavailability of oral cephradine did not differ significantly during compared with after pregnancy. It is concluded that the dosage of both cefazolin and cephradine should be increased when treating infections in pregnant women in order to obtain the same antibacterial effect as when treating non-pregnant women.

Pharmacokinetic studies on ceftezole

The adult volunteers were given 1 g of ceftezole as a single intramuscular dose to investigate the pharmacokinetic profile of this new cephalosporin. The peak average serum concentration, reached 2 h after injection, was 22.5 micrograms/ml, and the t1/2 beta was 1.5 h; urinary recovery was over 80% within 24 h, the majority of injected ceftezole being excreted within 3 hours.

A comparative trial between cefotetan and cephazolin for wound sepsis prophylaxis during elective upper gastrointestinal surgery with an investigation of cefotetan penetration into the obstructed biliary tree

Cefotetan is a cephamycin antibiotic theoretically suited to prophylaxis of wound infection during upper elective gastrointestinal surgery. In a prophylaxis trial 100 patients undergoing this type of surgery were randomly allocated to receive 1g cefotetan or cephazolin iv at induction of anaesthesia. Cefotetan-treated patients had significantly fewer postoperative infections overall (P less than 0.05) and there were no wound infections recorded in this group. In a separate pharmacokinetic study the penetration of cefotetan into common bile duct bile and gallbladder wall was measured in a further six patients, all of whom had been jaundiced preoperatively. At the time of maximum risk concentrations of cefotetan in bile and biliary tissue as well as blood and wound fat were in excess of the minimum inhibitory concentration for the majority of relevant pathogens. Cefotetan appears to be equally or more effective than cephazolin and is a suitable alternative prophylactic agent in elective upper gastrointestinal surgery.

Pharmacokinetic studies on the concomitant administration of piperacillin and cefazolin, and piperacillin and cefoperazone in rabbits

The pharmacokinetics of each drug on the concomitant administration of piperacillin (PIPC) and cefazolin (CEZ) or cefoperazone (CPZ) were studied in rabbits. When rabbits received the consecutive drip infusion administration of CEZ (0.71 mg/kg/minute) and PIPC (1.38 mg/kg/minute) and likewise of CPZ (0.72 mg/kg/minute) and PIPC (1.54 mg/kg/minute) for 1 hour, respectively, the serum half-lives of CEZ and CPZ were respectively prolonged about 1.8 and 1.6 times during drip infusion of PIPC than administered alone. However, when the sequence of administration were reversed, the serum levels of PIPC were not affected by the consecutive drip infusion administration of CEZ and CPZ. To study these findings in detail, the single intravenous dose of 20 mg/kg of CEZ and CPZ were administered under drip infusion of PIPC (2.65-2.93 mg/kg/minute). The serum half-lives of CEZ and CPZ were also prolonged about 5.4 and 1.9 times, respectively, whereas urinary excretion of CEZ, and urinary and biliary excretion of CPZ were reduced by PIPC. Moreover, when the single intravenous dose of 20 mg/kg of PIPC were administered under drip infusion administration of CEZ (0.96-2.60 2.60 mg/kg/minute), the pharmacokinetics of PIPC was not affected by the presence of CEZ. However, under drip infusion administration of CPZ (2.60-2.70 mg/kg/minute), the PIPC serum half-life was prolonged about 1.4 times, and biliary excretion of PIPC was reduced but urinary excretion was not. From the results of renal clearance experiments, tubular secretion appeared to be the predominant mechanism of renal elimination for these three drugs. These results indicate that PIPC influences the pharmacokinetics of both drugs by the competitively inhibiting tubular secretion in CEZ, and tubular secretion and hepatic transport system in CPZ. Therefore, in this respect PIPC seems to have probenecid-like action.

The cephalosporin antibiotics in pediatric therapy

The cephalosporins have been available for clinical use for nearly 20 years and a large number is presently marketed, including drugs with a wide range of different pharmacokinetic and microbiologic properties. While some of these agents have certain specific uses in which they excel, the cephalosporins have not replaced older antibiotics but do provide the physician with a broader range of choices for the treatment of many infections, allowing greater individualization of therapy.

Pharmacokinetics and protein binding of cefazolin and cephalothin in patients with cirrhosis

The effects of liver disease on the pharmacokinetics and protein binding of cefazolin and cephalothin were studied in patients with cirrhosis, chronic active hepatitis or normal liver function. The T1/2 and mean residence time of cefazolin were significantly shorter in cirrhosis. Cephalothin clearance was decreased by cirrhosis. Plasma protein binding of cefazolin, but not cephalothin was significantly reduced in cirrhosis. It is suggested that no dose reduction is necessary for either drug in severe hepatic impairment.

Reduction of cephamycin concentrations at the infection site in mice with experimental peritoneal infection caused by cephalosporinase-producing bacteria

In an experimental model of peritoneal infection by cephalosporinase- (Ia and Ic) producing bacteria in mice, the reduction of cefoxitin, cefmetazole, and cefazolin concentrations in peritoneal fluid was observed in the mice infected with the Ia enzyme producer, whereas cefbuperazone concentrations were not reduced.

Impaired antibiotic entry into lung tissue following acid injury

The purpose of this study was to compare the lung tissue burden of intravenous (i.v.) and intrabronchial (i.b.) cefazolin, using a standardized hydrochloric acid injury to the lungs. Ten mongrel dogs were anesthetized with pentobarbital and artificially ventilated. Following administration of cefazolin i.v. (N = 5) or i.b. (N = 5), lung biopsies were obtained at 6 hourly intervals. Simultaneous serum levels were also determined. The effective time (Teff) was defined as the period during which all serum and lung specimens demonstrated antibiotic activity exceeding 8 mcg/gm. These levels should provide comprehensive coverage of common lung and wound pathogens that are sensitive to cefazolin. Teff for the i.v. group was 1 hour, while aerosolized cefazolin never produced lung levels exceeding 8 mcg/gm. Thus, these findings suggest an explanation for cefazolin failure in gram negative pneumonia.

Uptake of benzylpenicillin, cefpiramide and cefazolin by freshly prepared rat hepatocytes. Evidence for a carrier-mediated transport system

The kinetics and mechanism of the hepatic uptake of beta-lactam antibiotics were studied by using freshly prepared rat hepatocytes. The initial uptake rates of benzylpenicillin and cefpiramide represented both saturable and nonsaturable transport processes, whereas that of cefazolin showed an apparently nonsaturable uptake process within the concentration range below 4 mM. The apparent nonsaturable uptake rate constants for benzylpenicillin, cefpiramide and cefazolin were 0.580, 0.047 and 0.289 nmoles/min/mg protein/mM respectively. The apparent values of Kt and Vmax describing the saturable transport were 0.473 +/- 0.158 mM and 2.02 +/- 0.48 nmoles/min/mg protein for benzylpenicillin and 0.847 +/- 0.254 mM and 0.70 +/- 0.18 nmoles/min/mg protein for cefpiramide respectively. The Arrhenius plot of benzylpenicillin uptake of 200 microM presented a single straight line in the range of 22 degrees-37 degrees with an activation energy of 16.8 kcal/mole. An energy requirement was also demonstrated for benzylpenicillin uptake as metabolic inhibitors (antimycin A, NaCN, rotenone and 2,4-dinitrophenol) significantly reduced the initial uptake rate of benzylpenicillin (P less than 0.05). Uptake of benzylpenicillin (200 microM) was not inhibited by ouabain (1 mM). Benzylpenicillin uptake was inhibited competitively by phenoxymethylpenicillin, cefpiramide and cefazolin with the inhibition constants, Ki, of 0.680, 0.583 and 11.7 mM respectively. Benzylpenicillin also inhibited competitively the uptake of cefpiramide with a Ki of 0.655 mM. From these results it was considered that a carrier-mediated uptake system participates in the hepatic uptake of at least four of the beta-lactam antibiotics examined in this study.

Age-related change of cefazolin binding to rat serum proteins and its relation to the molar ratio of free fatty acid to serum albumin

The binding of cefazolin to rat sera has been studied as a function of age. A significant difference was observed in the cefazolin binding to serum protein among 1-, 2-, 3-, 5-, 7-, 50- and 100-week-old rats. There was a good correlation between the dissociation constants of cefazolin binding and the molar ratio of free fatty acid to albumin concentration in sera. This suggests that both changes of concentration of albumin and free fatty acid, which could be a major endogenous inhibitor of cefazolin binding, play an important role in the age-related changes of the serum protein binding. Removal of free fatty acid in 1- and 2-week-old rat sera showed marked increases of the cefazolin binding. On the contrary, addition of oleic acid to 7-week-old rat serum produced significant reduction of cefazolin binding to rat serum protein. Accordingly, free fatty acid could effectively inhibit the cefazolin binding in the physiological concentration range with increasing age, and the age-related changes of cefazolin binding to rat serum protein appear to be due to the fluctuation of the molar ratios of free fatty acid to albumin concentration in sera.

Pharmacokinetics of probenecid and the effect of oral probenecid administration on the pharmacokinetics of cefazolin in mares

The pharmacokinetics and bioavailability of probenecid given IV and orally at the dosage level of 10 mg/kg of body weight to mares were investigated. Probenecid given IV was characterized by a rapid disposition phase with a mean half-life of 14.0 minutes and a subsequent slower elimination phase with a mean half-life of 87.8 minutes in 5 of 6 mares. In the remaining mare, a rapid disposition phase was not observed, and the half-life of the elimination phase was slower (172 minutes). The mean residence time of probenecid averaged 116 minutes for all 6 mares and 89.2 minutes for the 5 mares with biphasic disposition. The total plasma clearance of probenecid averaged 1.18 +/- 0.49 ml/min/kg, whereas renal clearance accounted for 42.6 +/- 9.3% of the total clearance. The steady-state volume of distribution of probenecid averaged 116 +/- 28.2 ml/kg. Plasma protein binding of probenecid was extensive, with 99.9% of the drug bound at plasma probenecid concentrations of 10 micrograms/ml. The maximum plasma probenecid concentration after 10 mg/kg orally averaged nearly 30 micrograms/ml. The half-life of probenecid after oral administration was approximately 120 minutes. Oral bioavailability was good with greater than 90% of the dose absorbed. The effect of probenecid on tubular secretion of organic anions was evaluated by determining the pharmacokinetics of IV cefazolin (11 mg/kg) administered alone and 15 minutes after probenecid (10 mg/kg orally). Treatment with probenecid did not affect pharmacokinetic values of cefazolin. This failure of probenecid to alter the pharmacokinetics of cefazolin may be caused by insufficient plasma probenecid concentrations after the oral dose.

Physiologically based pharmacokinetic model for cefazolin in rabbits and its preliminary extrapolation to man

In the present study, the physiologically based pharmacokinetic model, which succeeded previously in predicting the pharmacokinetics of beta-lactam antibiotics in rats [A. Tsuji, T. Yoshikawa, K. Nishide, H. Minami, M. Kimura, E. Nakashima, T. Terasaki, E. Miyamoto, C.H. Nightingale, and T. Yamana: Physiologically based pharmacokinetic model for beta-lactam antibiotics. I: tissue distribution and elimination in rats. J. Pharm. Sci. 72, 1239-1252 (1983)], was applied to cefazolin pharmacokinetics in rabbits and man. After iv bolus dosing in normal rabbits, the time courses of cefazolin concentration in plasma and various tissues (lung, heart, muscle, skin, bone, gut, liver, and kidney) were found to be very similar to those in rats. The values of physiological parameters (tissue plasma flows, tissue volumes, tissue/plasma albumin ratio) and biochemical parameters determined in this study (for nonlinear plasma protein binding, intrinsic renal clearance of active secretion and reabsorption) were incorporated into mass balance equations derived from the model. There was reasonable agreement between the model predictions and the observed data for cefazolin and inulin in rabbits. The model was also successful in the prediction of cefazolin disposition in rabbits with renal failure. Using available information reported for cefazolin in man, a preliminary extrapolation from the present model was attempted, and the overall predicted results after iv administration of 1 g cefazolin in man were compared with the serum and bone tissue data. The length of the effective antibacterial period for the drug is also discussed in terms of its predicted concentration unbound with proteins in various tissue interstitial fluids in man.

Human vitreous levels of selected antistaphylococcal antibiotics

Staphylococcus epidermidis and S. aureus are the most common causes of bacterial endophthalmitis. A study of the penetration of selected antistaphylococcal antibiotics into human vitreous was undertaken in 58 patients. After 2-g intravenous doses of cephalothin, cefazolin, methicillin, oxacillin, or nafcillin were given to patients about to undergo vitreous surgery, mean vitreous levels for each antibiotic were as follows: cephalothin, 0.97 microgram/ml in diabetics and 0.69 microgram/ml in nondiabetics; cefazolin, 0.84 microgram/ml in diabetics and 1.6 microgram/ml in nondiabetics; methicillin, 2.56 micrograms/ml in diabetics and 2.64 micrograms/ml in nondiabetics; oxacillin, 0.62 microgram/ml in diabetics and 0.34 microgram/ml in nondiabetics; and nafcillin, 0.73 microgram/ml in diabetics and 0.75 microgram/ml in nondiabetics. Only cefazolin produced vitreous concentrations consistently above its minimum inhibitory concentration for 90% of S. epidermidis isolates. Staphylococcus aureus isolates were not similarly covered. There was a trend toward higher vitreous antibiotic concentrations in patients with proliferative vitreoretinopathy and rubeosis.

Intraoperative serum and tissue activity of cefazolin and cefoxitin

We determined the intraoperative serum and wound-muscle concentrations of cefazolin and cefoxitin in 40 patients who were undergoing cholecystectomies. The study employed an open-label design in which all of the patients randomly received cefazolin sodium (20 mg/kg) or cefoxitin sodium (30 mg/kg) intravenously while the patient was in the ward ("on call") or with the induction of anesthesia. Multiple blood and wound-muscle samples were collected intraoperatively and assayed for their cephalosporin concentrations. Considerable differences in intraoperative serum and tissue concentrations between antibiotics were apparent; there were usually higher levels of cefazolin. In all of the patients who received cefazolin sodium, the antimicrobial was detectable in wound tissue at wound closure, while it was detectable in 86% and 38% of patients who received cefoxitin sodium with anesthesia and on call, respectively. Because cefoxitin has a much shorter elimination half-life than cefazolin it seems prudent to administer the agent as close to the start of the operation as possible, and readminister the agent every two to three hours until the wound is closed. For cefazolin, on-call administration appears to be acceptable, with readministration not required for at least four hours.

Effects of general and local anesthesia on the pharmacokinetics of cefazolin in patients undergoing orthopedic surgery

The pharmacokinetics of cefazolin in patients undergoing orthopedic surgery with either general (enflurane) or local (lidocaine or marcaine) anesthesia were studied. No differences in either mean serum levels at 30, 60, or 120 min after the intravenous injection of cefazolin or serum half-lives were seen between the two groups of patients.

Effect of extracellular water volume on the distribution kinetics of beta-lactam antibiotics as a function of age

The distribution kinetics of cefazolin in rats has been examined at four different ages (1, 7, 50 and 100 weeks). The steady state distribution volume of cefazolin, estimated from the plasma time course after i.v. injection of 20 mg/kg, varied between 136 ml/kg (50-week-old rats) and 297 ml/kg (1-week-old rats). The extracellular fluid volume, obtained from the steady state distribution volume of inulin, varied between 126 ml/kg (50-week-old rats) and 370 ml/kg (1-week-old rats). There was a good correlation between the steady state distribution volume of cefazolin and extracellular fluid volume (r = 0.977). The influence of changes on the value of the plasma unbound fraction and extracellular fluid volume on the tissue-to-plasma partition coefficient of beta-lactam antibiotics was simulated by using a physiological pharmacokinetic model. The results of the simulation showed that extracellular fluid volume is an important factor affecting the distribution volume of beta-lactam antibiotics and that plasma binding plays a minor role on it. The experimental and simulation results suggested that the change in the interstitial fluid volume is a determinant factor in the age-related changes in the distribution volume of beta-lactam antibiotics.