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Physicochemical properties of amphoteric beta-lactam antibiotics. II: Solubility and dissolution behavior of aminocephalosporins as a function of pH.

The solubility of aminocephalosporins in aqueous solution at 37 degrees and an ionic strength of 0.5 exhibited U-shaped curves against pH. At their isoelectric pH, cephradine monohydrate was the most soluble, followed by cephalexin monohydrate and cephaloglycin dihydrate, with intrinsic solubilities of 26.0, 17.2, and 14.8 mg/ml, respectively. The dissolution rate constants from the rotating disk were also determined as a function of the pH of the dissolution medium and interpreted reasonably by the simultaneous dissociation equilibrium reaction and the diffusion kinetics model. Energies for the solubility and dissolution were determined for these three aminocephalosporins.

Cephalexin↗

Plasma glutathione peroxidase and its relationship to renal proximal tubule function.

Selenium-dependent extracellular glutathione peroxidase (E-GPx) is found in plasma and other extracellular fluids. Previous studies have indicated that patients with chronic renal failure on dialysis have low plasma GPx activity. In this study, dialysis patients had approximately 40% of control plasma GPx activity, while anephric individuals had lowest plasma GPx activities ranging from 2 to 22% of control. The residual plasma GPx activity in anephric individuals could be completely precipitated by anti-E-GPx antibodies, indicating that all plasma GPx activity can be attributed to E-GPx in both normal and anephric individuals. Plasma GPx activity rises rapidly following kidney transplantation, often reaching normal values within 10 days. The plasma GPx activity in some transplanted patients rises to levels higher than the normal range, followed by a return to the normal range. Since E-GPx in the kidney is primarily synthesized in the proximal tubules, we investigated whether nephrotoxic agents known to disrupt proximal tubule function also affected plasma GPx activity. The beta-lactam antibiotic cephaloglycin rapidly caused a decrease in plasma GPx activity in rabbits. In addition, the chemotherapeutic agent ifosfamide caused a decrease in plasma GPx activity in pediatric osteosarcoma patients. Fanconi syndrome associated with either ifosfamide therapy or valproic acid therapy also caused a decrease in plasma GPx activity. Thus plasma GPx activity is related to kidney function and is decreased in certain situations where nephrotoxic drugs are administered. Monitoring plasma GPx activity may have predictive value in evaluating the function of transplanted kidneys or in predicting those patients particularly at risk of nephrotoxic injury associated with certain medications.

Adult↗

Toxicity of cephalosporins to fatty acid metabolism in rabbit renal cortical mitochondria.

UNLABELLED: Cephaloglycin (Cgl) and cephaloridine (Cld) are acutely toxic to the proximal renal tubule, in part because of their cellular uptake by a contraluminal anionic secretory carrier and in part through their intracellular attack on the mitochondrial transport and oxidation of tricarboxylic acid (TCA) cycle anionic substrates. Preliminary studies with Cgl have provided evidence of a role of fatty acid (FA) metabolism in its nephrotoxicity, and work with Cld has shown it to be a potent inhibitor of renal tubular cell and mitochondrial carnitine (Carn) transport. Studies were therefore done to examine the effects of Cgl and Cld on the mitochondrial metabolism of butyrate, the anion of a short-chain FA that does not require the Carn shuttle to enter the inner matrix, and the effects of Cgl on the metabolism of palmitoylcarnitine (PCarn), the Carn conjugate of a long-chain FA that does enter the mitochondrion by the Carn shuttle. The following was found: (1) Cgl reduced the oxidation and uptake of butyrate after in vitro (2000 micrograms/mL, immediate effect) and after in vivo (300 mg/kg body weight, 1 hr before killing) exposure; (2) Cld caused milder in vitro toxicity, and no significant in vivo toxicity, to mitochondrial butyrate metabolism; (3) like Cld, Cgl reduced PCarn-mediated respiration after in vivo exposure, but, unlike Cld, it did not inhibit respiration with PCarn in vitro; (4) the Carn carrier was stimulated slightly by in vitro Cgl but was unaffected by in vivo Cgl; (5) in vivo Cgl had no effect on mitochondrial free Carn or long-chain acylCarn concentrations in the in situ kidney; (6) Cgl increased the excretion of Carn minimally compared with the effect of Cld; and (7) cephalexin, a nontoxic cephalosporin, caused mild reductions of respiration with butyrate and PCarn during in vitro exposure, but stimulated respiration with both substrates after in vivo exposure. CONCLUSIONS: Cgl has essentially the same patterns of in vitro and in vivo toxicity against mitochondrial butyrate uptake and oxidation that both Cgl and Cld have against TCA-cycle substrates. Cld has little or no in vivo toxicity to mitochondrial butyrate metabolism, whereas in vivo Cgl is as toxic as Cld to respiration with PCarn. The greater overall in vivo toxicity of Cgl to mitochondrial FA metabolism, with lower cortical concentrations and AUCs than those of Cld, supports earlier evidence that Cld is less toxic than Cgl at the molecular level.

Animals↗

Synthesis and antibacterial activities of new (alpha-hydrazinobenzyl)cephalosporins.

Some (alpha-hydrazinobenzyl)cephalosporins, I (R = Me, CH2OAc, Cl) and II (R = Me, CH2OAc), structurally related (formula; see text) to cephalexin, cephaloglycin, and cefaclor have been prepared and evaluated in vitro for their antimicrobial activity. The synthesis involves the condensation of the chloride hydrochloride III (R = H or Me) with the 7-aminocephem derivatives IV. The hydrazino compound I (R = Cl), an analogue of cefaclor, resulted in being the most active compound of the series.

Bacteria↗

Pathogenesis of nephrotoxicity of cephalosporins and aminoglycosides: a review of current concepts.

Third-generation cephalosporins promise to replace combinations containing aminoglycosides as safer, broad-spectrum antibiotic therapy. First, however, the possibility of nephrotoxicity as demonstrated with cephaloridine, must be excluded. For this reason, we must understand more about how cephalosporins and aminoglycosides damage the kidneys. Aminoglycosides accumulate in the renal lysosomes and may interfere with Na+-, K+-dependent adenosine triphosphatase activity. Experiments with cephaloridine and cephaloglycin, two nephrotoxic cephalosporins, indicate that they cause mitochondrial injury that leads to impaired cellular respiration. Results of experiments on the effects of treatments that combine cephalosporin with aminoglycosides or other drugs are confusing because inappropriate experimental models were used. Use of insensitive animals, administration of diuretics without prior induction of tubule damage, and insufficient dosages of drugs all cloud the interpretation of results. The standards for animal studies of cephalosporin nephrotoxicity should be revised to make them more relevant to humans.

Aminoglycosides↗

In vitro activity of five oral cephalosporins against anaerobic pathogenic bacteria.

The in vitro inhibitory activities of cefaclor and and cefatrizine, two new orally absorbed cephalosporin antibiotics, against 44 isolates of anaerobic pathogenic bacteria were measured using the agar dilution procedure of the World Health Organization-International Collaborative Study. Tests also were performed with cephalexin, cephaloglycin, and cephadrine, as well as with the parenteral cephamycin antibiotic cefoxitin. Cefoxitin was the most active antibiotic and inhibited the majority of isolates at a concentration of less than or equal to 4 microgram/ml. None of the oral cephalosporins was clearly superior against all of the anaerobic isolates; only cephadrine and cefatrizine appeared to have any potential clinical value.

Bacteroides↗

Pharmacokinetics of cephalosporins in patients with normal or reduced renal function.

The pharmacokinetic distribution of 10 cephalosporin compounds, cephalothin, cephaloridine, cephaloglycine, cephalexin, cefazolin, cephapirin, cephradine, cephacentrile, cefoxitin, and cefamandole, in patients with various degrees of renal function was reviewed. The mean serum half-life (t1/2) of each cephalosporin compound was calculated from reported data in patients grouped according to their degree of renal function, as determined by the rate of creatinine clearance. Mean t1/2 values in patients with normal renal function were compared with t1/2 values for the same cephalosporin in patients with moderate renal failure and severe renal azotemia. The effect of hemodialysis and peritoneal dialysis on the mean serum t1/2 of each cephalosporin was also determined. The mean serum t1/2 of each cephalosporin progressively increased as the rate of creatinine clearance decreased. Hemodialysis decreases the t1/2 of cephaloridine, cephalexin, cefazolin, and cephacetrile but only minimally influences the t1/2 of cephalothin and cefamandole. Peritoneal dialysis reduces the t1/2 of cephalothin and cephaloridine but only minimally influences the t1/2 of cefazolin and cefamandole.

Cephalexin↗

Prevention of cephalosporin nephrotoxicity by other cephalosporins and by penicillins without significant inhibition of renal cortical uptake.

Prevention of cephalosporin nephrotoxicity in animal models by probenecid or p-aminohippurate requires treatment regimen that produce sustained inhibition of cortical accumulation of the toxic antibiotic. In contrast, cephaloridine nephrotoxicity in the rabbit can be prevented by a limited single dose of cephalothin. In the present report further studies were done in which it was demonstrated that cephaloridine nephrotoxicity can be prevented by doses of other cephalosporins or penicillins that produce little or no reduction of the cortical concentrations of toxic cephalosporin. More limited studies revealed similar protection by benzylpenicillin against cephaloglycin, also without reduction of cortical concentration. Finally, similar limited-dose administration of penicillin eliminated tha additive toxicity of cefazolin and neomycin. This selective protection against the toxic cephalosporins by the less toxic or nontoxic cephalosporins and by the penicillins, without inhibition of overall cortical accumulation of the toxic antibiotic, may provide a subcellular probe for the study of the molecular basis of cephalosporin nephrotoxicity.

Animals↗

Effects of ureteral obstruction on the toxicity of cephalosporins in the rabbit kidney.

The nephrotoxicity of the cephalosporin antibiotics is closely related to their secretory transport into the proximal tubular cell at the antiluminal (blood) site. The present report describes the effects of transient ureteral obstruction, which increases intracellular concentrations of secreted organic anions, on the cortical uptake and the proximal tubular toxicity of several cephalosporins given in mildly toxic doses. Unilateral obstruction for 1-2 hr increased the cytotoxicity of cephaloglycin and cefaclor, both of which are rapidly secreted across the tubular cell, but not of cephaloridine, which undergoes minimal secretion. Bilateral obstruction significantly increased the toxicity of cefaclor, which is rapidly secreted, but not of cefazolin, which is slowly secreted. Finally, there was a further augmentation of the effects of obstruction on the toxicity of cefaclor by a minimally toxic pretreatment regimen of neomycin. Studies of cortical antibiotic concentrations support the conclusion that the effects on toxicity are largely the result of the increased intracellular accumulation that results from obstruction.

Animals↗

Synthesis of beta-lactam antibiotics containing alpha-aminophenylacetyl group in the acyl moiety catalyzed by D-(-)-phenylglycyl-beta-lactamide amidohydrolase.

D-(-)-Phenylglycyl-beta-lactamide amidohydrolase was isolated from Xanthomonas sp., purified, and characterized. A characteristic feature of the enzyme is its high specificity for substrates containing an alpha-aminophenylacetic group in the acyl moiety. Cephalexin and D-C-(-)-phenylglycine methyl ester (MEPG), being nonspecific penicillin acylase (EC 3.5.1.11) substrates, have the highest values of bimolecular constant kcat/Km (2.8 x 10(5) and 2.0 x 10(5) M-1 x s-1, respectively) in the case of amidohydrolase. On the contrary, benzylpenicillin is not hydrolyzed by D-(-)-phenylglycyl-beta-lactamide amidohydrolase. The other peculiarity of the enzyme is its affinity for the charged forms of substrates. Using the amidohydrolase, it was found that the values of delta Go'pH7.0 for hydrolysis of the amide bond in cephalexin and ampicillin are -3.3 and -2.3 kJ mol-1, respectively. They are less by a minimum of 2.7 kJ mol-1 than those for other beta-lactam antibiotics. Detailed thermodynamic and kinetic studies of the synthesis of cephalexin from MEPG and 7-aminodeacetoxycephalosporanic acid (7-ADCA) catalyzed by D-(-)-phenylglycyl-beta-lactamide amidohydrolase were undertaken. A kinetic scheme is proposed which describes well the experimental curves. The value of conversion of "nucleus" was found to be 76% when the synthesis was carried out from a 31.5 mM solution of 7-ADCA and an 88.5 mM solution of MEPG at pH 6.2 (optimum conditions). A 75% conversion of 7-aminocephalosporanic acid (7-ACA) was achieved in the synthesis of cephaloglycine catalyzed by D-(-)-phenylglycyl-beta-lactamide amidohydrolase.

Amidohydrolases↗

Expression of penicillin G acylase gene from Bacillus megaterium ATCC 14945 in Escherichia coli and Bacillus subtilis.

Penicillin G acylase gene from Bacillus megaterium ATCC 14945 has been isolated. Recombinant Escherichia coli clones were screened for clear halo forming activity on the lawn of Staphylococcus aureus ATCC 6538P using the enzymatic acylating reaction of 7-aminodeacetoxycephalosporanic acid (7-ADCA) and D-(alpha)-phenylglycine methylester. The gene was contained within a 2.8 kb DNA fragment and expressed efficiently when transferred from E. coli to Bacillus subtilis. A twenty times greater amount of enzyme was produced in B. subtilis transformant than that in B. megaterium. The purified enzyme from subcloned B. subtilis showed that the native enzyme consisted of two identical subunits, each with a molecular weight of 57,000. The enzyme was able to react on various cephalosporins, i.e., cephalothin, cefamandole, cephaloridine, cephaloglycin, cephalexin and cephradine.

Bacillus megaterium↗

Structural specificity requirements in the binding of beta lactam antibiotics to human serum albumin.

The binding of some cephalosporins of pharmacological interest, to human serum albumin was studied using ultrafiltration method. The identification of the binding sites in albumin was also performed using probes for the so-called sites I, II, bilirubin and fatty acids binding sites. Cephalosporins were classified into three groups according to their affinity for albumin: low affinity (K = 10-10(2) M-1), medium affinity (K = 10(3) M-1) and high affinity (K = 10(4) M-1). Cephalosporin binding to albumin produced a perturbation of several basic amino acids of the protein such as histidine and lysine. It was found that only cefuroxime, ceftazidime and cefoperazone interact slightly with site I on serum albumin, while site II possesses capacity to bind: cephradine, cephalexin, ceftazidime, ceftriaxone, cefoperazone, cefaclor and cefsulodin. The bilirubin binding site showed capacity to interact with a great number of cephalosporins: ceftriaxone, cefazolin, cephaloglycin, cefamandole, cefotaxime, cefoxitin, cefuroxime, cefoperazone and cefadroxil. Ceftriaxone showed capacity to bind to the fatty acid binding site on HSA. No relation was found between the displacement of the marker and the chemical nature of the substituents at R1 and R2. Cephalosporins interact with HSA at the binding region that involves: tyrosyl 411, histidyl 146 and lysyls 195, 199, 225, 240 and 525 residues. The chemical modification of specific amino acids showed that the interaction of these amino acids with beta lactam antibiotics is not carried out to the same extent for all the cephalosporins tested. The results obtained revealed that the binding sites for cephalosporins on albumin are structurally heterogeneous, having different amino acids in the vicinity of the ligand molecule.

Acid-Base Equilibrium↗

Synthesis and biological activity of some broad-spectrum N-acylphenyglycine cephalosporins.

The synthesis and the in vitro and in vivo antibacterial activities of a series of N-acylated phenylglycine cephalosporins are described. These compounds exhibit activity against a broad spectrum of gram-positive and gram-negative bacteria including some strains of Pseudomonas aeruginosa, a bacterial species normally insensitive to the cephalosporin antibiotics. The cephalosporins were prepared by acylation of cephaloglycin or its 3-tetrazolylthiomethyl analogue. In several cases, the acylations produced mixtures of diastereomeric cephalosporins, the components of which, when separated, showed different levels of antibiotic activity. Optimum activity was obtained when the acyl moiety on the phenylglycine nitrogen contained an oxygen atom centrally located between the amide carbonyl and a carboxyl substituent, preferably in a three- or five-membered ring. Replacement of acetoxymethyl by (1-methyl-1H-tetrazol-5-yl)thiomethyl at the 3 position resulted in overall improvement in activity both in vitro and in vivo. Against a group of P. aeruginosa strains, the best compounds of this series showed activity on the order of carbenicillin.

Animals↗

Comparison of oral cephalosporins with penicillin therapy for group A streptococcal pharyngitis.

The purpose of the study was to compare the efficacy of cefaclor with that of penicillin V potassium (penicillin) in patients with Group A streptococcal pharyngitis. One hundred four children with pharyngitis and serologically confirmed Group A streptococci were randomly treated with cefaclor or penicillin using a mean dosage of 20 mg/kg/day for 10 days. The difference in failure rates (14% for 51 cefaclor- and 30% for 53 penicillin V-treated patients) was statistically significant (P = 0.04). In four earlier similar studies I found that cephaloglycin, cephalexin (two studies) and cefatrizine were consistently but not significantly more effective than penicillin therapy. When the data from the five studies are combined the difference between the failure rates (11% for 263 oral cephalosporin- and 23% for 230 penicillin-treated patients) becomes highly significant (P less than 0.001). The 95% confidence interval for the odds for treatment failure are 2.4 times greater for patients receiving penicillin than for those receiving one of the oral cephalosporins. On the basis of these data I conclude that the oral cephalosporins appear to be more effective than penicillin for therapy of Group A streptococcal pharyngitis.

Administration, Oral↗

Substrate inhibition of beta-lactamases, a method for predicting enzymatic stability of cephalosporins.

Selected cephalosporins, including cefamandole, cephaloridine, cephaloglycin, and cefoxitin, were examined for their ability to inhibit the enzymatic activity of and act as substrates for beta-lactamases produced by Enterobacter cloacae and Staphylococcus aureus. Enzyme inhibition was determined by Michaelis-Menten kinetic measurements and by a spot plate assay using a chromogenic substrate (Glaxo compound 87/312). These two methods provide comparable estimates of kinetic parameters. Inhibition of beta-lactamase, as measured by these two methods, was generally found to correlate with resistance to hydrolysis and is proposed as a preliminary method of assessing susceptibility of cephalosporins to beta-lactamase hydrolysis. Four 7-alphaOCH(3), 7-alphaH cephalosporin analogue pairs were also examined. The presence of the 7-alphaOCH(3) substituent invariably resulted in reduced susceptibility to enzymatic hydrolysis, regardless of the other C7 substituent. The 7-alphaOCH(3) compounds were also better inhibitors than were their 7-alphaH analogues, with the exception that 7-alphaOCH(3) compounds having C7 adipic acid substituents were less inhibitory to the S. aureus enzyme than were the corresponding 7-alphaH analogues. Response of these two enzymes to 7-alphaOCH(3) and 7-alphaH cephalosporins suggests that beta-lactamase hydrolysis of these compounds involves attack at the alpha side of the betalactam ring.

Amidohydrolases↗

Iodometric assay method for beta-lactamase with various beta-lactam antibiotics as substrates.

The rapid fixed-time assay for penicillinase was modified for measuring beta-lactamase activity with twelve substrates, i.e., benzylpenicillin, ampicillin, cloxacillin, methicillin, carbenicillin, cefazolin, cephalothin, cephaloglycin, cephalexin, cephalosporin C, 7-aminocephalosporanic acid, and cefoxitin. The method depends upon the reduction of iodine by the hydrolyzed substrate. Determined experimentally, 1 mol of hydrolyzed penicillins consumed 3.4 to 4.0 mol of iodine (I(2)). Iodine consumption of hydrolyzed cephalosporins varied widely from 1.7 for cephalothin to 3.7 for cefazolin. The method is useful for routine assay of beta-lactamase activity with various substrates.

Amidohydrolases↗

In vitro susceptibility of Mycoplasma hyopneumoniae and Mycoplasma hyorhinis to fifty-one antimicrobial agents.

By a tube dilution assay technique, 51 antimicrobial agents were singly tested against 9 strains of Mycoplasma hyopneumoniae and 1 strain of M. hyorhinis for the purpose of obtaining information useful for selecting an agent for testing in vivo against porcine mycoplasmal pneumonia. Based on determining minimal inhibitory concentrations and chemically grouping the agents into nine classes, all M. hyopneumoniae strains were found resistant to penicillins and peptides and susceptible to sulfonamides and tetracyclines, and, in other classes, were either susceptible or resistant depending on the particular agent being tested. Strains were susceptible to the same 33 of the 51 agents. Minimal inhibitory concentrations ranged from 0.06 to 9.20 mug/ml. M. hyorhinis was susceptible to 19 of the 33 agents that M. hyopneumoniae was susceptible to. Minimal inhibitory concentrations ranged from 0.03 to 8.10 mug/ml. All strains of M. hyopneumoniae differed from M. hyorhinis in that they were susceptible to cephaloglycin and nitrofurazone.

Anti-Bacterial Agents↗

Cephalosporinase activity in Bacteroides fragilis.

Cephalosporinase activity was demonstrated in all of 10 strains of Bacteroides fragilis investigated. Low rates of hydrolysis of cephalosporins (0.25 to 3.5 mumol of cephaloridine per h per 10(9) cells) were found, but no activity against penicillin substrates was detected. In two strains the cephalosporinase activity was increased 40-and 80-fold by growing cells in the presence of penicillin. No permeability barrier for these antibiotics was demonstrated. In most cases the substrate profile showed decreasing activity in the following order: cephaloridine > cephalothin > cephaloglycin > cephalexin. The cephalosporinase from these organisms differed from that found in facultative and aerobic gram-negative bacilli in that it was inhibited by both cloxacillin and p-chloromercuribenzoate. Among nine strains of Bacteroides fragilis subspecies fragilis, correlation was found between in vitro resistance to cephaloridine and amount of beta-lactamase activity in sonically disrupted cells.

Amidohydrolases↗