Comparison of in vitro antibacterial activity of three oral cephalosporins: cefaclor, cephalexin, and cephradine

Frequency of Dosing of Cephalexin for Oral Step-Down Therapy of Pediatric Osteoarticular Infections Caused by Methicillin-Sensitive Staphylococcus Aureus

Osteoarticular infections are one of the more common invasive bacterial infections encountered in children. There exist significant practice variations in both the diagnosis and treatment of such infections. However, the practice of transitioning from parenteral therapy to oral antibiotics has been well validated by several studies. For methicillin-sensitive Staphylococcus aureus (MSSA), cephalexin is often recommended. Prospective, controlled data regarding optimal dosing of cephalexin in pediatric osteomyelitis are not available. We sought to review our retrospective, uncontrolled data on four times daily (QID) versus three times daily (TID) dosing of cephalexin for pediatric osteoarticular infections. Children ≥1 month to <18 years of age admitted to Rady Children's Hospital-San Diego with a diagnosis of osteomyelitis or septic arthritis between January 1, 2002, and November 30, 2007, were identified and previously reported. Only patients with culture-positive MSSA infections are included in this report. Demographic and clinical data were manually extracted from the electronic medical record. Fifty-nine patients were treated with cephalexin and had records available for review through our electronic medical record. Thirty-eight patients (64.4%) were treated QID, and 21 patients (35.6%) were treated TID. Clinical cure was achieved in all patients with only one adverse event occurring in the QID group. In this retrospective chart review of children with osteoarticular infections caused by MSSA treated with cephalexin, similar clinical outcomes were found with QID versus TID dosing.

Pharmacokinetics and pharmacodynamics of oral cephalexin in children with osteoarticular infections

BACKGROUND

Osteoarticular infections lead to significant morbidity in children. Cephalexin has in vitro activity against methicillin-susceptible Staphylococcus aureus, a predominant pathogen in osteoarticular infection. However, cephalexin pharmacokinetics (PK) and pharmacodynamics (PD) are poorly described in children. This study described cephalexin PK in children treated for osteoarticular infection and assessed the proportion of children achieving surrogate PK/PD target for efficacy in methicillin-susceptible S. aureus infection.

METHODS

Children with osteoarticular infection, 1 to 18 years of age, were eligible for this study if they were receiving oral cephalexin per standard of care. PK plasma samples were collected at specified times after multiple doses. PK parameters were estimated using noncompartmental analysis. PK/PD target for efficacy was calculated using the child's PK parameters, minimum inhibitory concentration (MIC) of the isolate when available and previously described MIC of 2 and 4 mg/L.

RESULTS

Twelve children were enrolled and PK profiles were obtained from 11 of them. Median age was 7 years, and median cephalexin dose was 40 mg/kg/dose every 8 hours. Median apparent oral clearance, apparent oral volume of distribution and elimination half-life (T1/2) were 0.29 L/h/kg, 0.44 L/kg and 1.1 h, respectively. Time above MIC (T>MIC) was greater than 40% of the dosing interval in 100%, 90% and 80% of the children when MICs were 0.25, 2 and 4 mg/L, respectively.

CONCLUSIONS

Oral cephalexin achieved optimal plasma exposure and was well tolerated in children with osteoarticular infection. Correlation between osteoarticular infection clinical outcome and PK/PD parameters needs further evaluation.

Oral cephalosporins: current perspectives

Oral cephalosporins had been, for years, a small group of compounds belonging to the first or second-generation cephalosporins, with a limited antimicrobial spectrum. New oral first-generation cephalosporins include cefprozil and loracarbef, similar to cefadroxil and cefaclor, respectively, with activity similar to cefaclor but with pharmacokinetic improvements. Second-generation oral cephalosporins are esters of already available cephalosporins, and third-generation oral cephalosporins include a number of drugs whose activity is similar to available parenteral drugs, showing pharmacokinetic advantages and, some of them, better resistance to hydrolysis mediated by extended wide-spectrum beta-lactamases. They may be a good alternative against mild to moderate ENT infections, UTIs, STDs, lower respiratory tract and skin and soft tissue infections, mainly in the outpatient setting.

Bioequivalency of oral suspension formulations of cefixime

A study was performed in 24 healthy male subjects to establish that two suspension formulations of cefixime were bioequivalent to each other and to a reference oral solution. A single 400 mg oral dose of the drug was given in a randomized three-way crossover design as two suspensions (a research suspension (RS) used during clinical trials and a suspension intended for marketing (MS] and a reference oral solution (SOL). Each dose was separated from the other by a 3-day washout period. Mean peak serum concentrations (Cmax) were 4.67, 4.10, and 4.27 micrograms ml-1 after the MS, RS, and SOL, respectively. Although comparison (ANOVA) of the mean pharmacokinetic parameters for cefixime found significant differences (p less than 0.05) in Cmax, the time to Cmax, and area under the serum concentration time curve (AUC 0----infinity) values among the three formulations, the mean differences were less than 20 per cent. No significant differences (p greater than 0.05) were found in either the elimination half-life or renal clearance of unchanged drug. Overall, with a 98 per cent power to detect a 20 per cent difference in AUC0----infinity or urinary recovery values between the formulations tested, the results show that the MS was bioequivalent to the RS and that both suspensions were bioequivalent to the SOL.

Comparative in vitro activity of the new oral cephalosporin cefixime

Cefixime was 8 to 10 times more active than cefaclor and augmentin against isolates of Escherichia coli, Klebsiella pneumoniae and Salmonella typhi, MIC90 values ranging from 0.06 to 0.25 micrograms/ml. However, none of these three drugs was particularly active against isolates of more resistant gram-negative bacilli such as Enterobacter, Serratia, Citrobacter, Acinetobacter, Providencia and Achromobacter spp. The lowest MIC values for gram-negative bacilli were seen with ciprofloxacin, except for isolates of Acinetobacter, where cotrimoxazole was the most active of the five drugs studied. Augmentin and ciprofloxacin exhibited the lowest MICs for isolates of streptococci and corynebacteria. Although cefixime may be among the most active oral beta-lactam drugs, it does not appear to be useful for treatment of infections caused by more resistant gram-negative bacilli.

In vitro protein binding interaction studies involving cefixime

Cefixime is a new oral cephalosporin currently undergoing clinical trials. Selected agents with the likelihood for coadministration with cefixime in man were examined for their influence on the in vitro binding of cefixime in pooled serum from dog, monkey, and man. Results from these experiments showed no significant change in cerfixime binding in any animal species studied or in man by acetaminophen, heparin, phenytoin, diazepam, ibuprofen or furosemide at their maximum reported therapeutic concentrations. In contrast, both salicylic acid and probenecid resulted in concentration-dependent increases in the free fraction of cefixime (up to 2.5-fold). These findings demonstrate the usefulness of in vitro protein binding screening procedures for studying potential drug interactions that are mediated, at least in part, by changes in the protein binding of a drug.

Variable in vitro activity of cefaclor, cephalothin and cefadroxil against Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis

The in vitro activity of cefaclor, cephalothin and cefadroxil to 50 Escherichia coli, 23 Klebsiella pneumoniae and 20 Proteus mirabilis strains was tested with the disc diffusion and microdilution plate techniques. Cefaclor was more active than cefadroxil, while cephalothin was intermediate. The differences seriously affected the classification into the routine SIR system. For susceptibility testing we question the use of cephalothin as a class representative of oral cephalosporins.

Cefaclor versus amoxicillin in the treatment of bacterial pneumonia: a comparative double-blind study

A randomized double-blind controlled trial was carried out to compare the effectiveness and side-effects of cefaclor with those of amoxicillin in the treatment of 34 patients hospitalized because of acute bacterial pulmonary infection. Cefaclor and amoxicillin were given three times daily before meals in a dosage of 500 and 750 mg respectively for seven days. The cure rate was 94% in the group of patients treated with cefaclor and 89% in the group treated with amoxicillin. According to all the parameters used to assess outcome, no significant difference was found between the two antibiotics tested. In this study, cefaclor and amoxicillin appeared to be of equal value in the treatment of bacterial pneumonia or bronchopneumonia.

Single oral dose of cefaclor for the treatment of infections with penicillinase-producing strains of Neisseria gonorrhoeae

A single oral dose of 3 g cefaclor was effective in the treatment of uncomplicated gonococcal infection in women due to penicillinase-producing strains of Neisseria gonorrhoeae (PPNG). Cefaclor was equally active in vitro against both PPNG (MIC range, 0.01-1.0 microgram/ml) and non-PPNG strains (MIC range, 0.005-2.0 micrograms/ml). As empirical treatment cefaclor was effective in 53 of 57 (93%) patients compared with ampicillin, to which only 37 of 53 (69.8%) patients responded. This difference was attributed to the 40% incidence of PPNG in the patients studied; as expected, such patients responded poorly to ampicillin.

The cephalosporins: activity and clinical use

The cephalosporin antibiotics have been employed with increasing frequency since their introduction into clinical practice in the early 1960s. With the exception of cephaloridine, cephalosporin compounds are not associated with the production of significant untoward effects. The availability of newer cephalosporins, both oral and parenteral, with enhanced antibacterial activity, has expanded the clinical indications for administration of these antibiotics.

[Comparative study of cefaclor versus amoxicillin in urinary tract infections (author's transl)]

In a comparative, prospective, open randomised clinical study, the efficacy and tolerance of cefaclor (3 x 500 mg) and amoxicillin (3 x 750 mg) in the treatment of urinary tract infection (UTI) were investigated and compared. A total of 110 patients (51 males and 59 females) age 10 to 83 years were treated for a period of five to 14 days (average 10 days). Fifty-nine of the patients had complicated, and 51 uncomplicated UTI. In all patients , organisms were cultured from the urine which were sensitive to both antibiotics in vitro. In each group there were three cases of mixed infection and 35 cases of Escherichia coli monoinfection. The distribution of pathogens in the other patients was likewise very similar. Better results, i.e. a reduction in the cell count to < 10(4)/ml immediately after completion of therapy, were obtained in patients treated with cefaclor. This is largely due to a statistically significantly higher rate of elimination in E. coli infections. The long-term results at follow-up examinations 14 to 60 days after completion of therapy in both groups with uncomplicated infections were, however, equally as good in about half the cases. In complicated infections therapy was successful overall in only about a quarter of the cases, better results being obtained in the amoxicillin group. It must be taken into account that among the patients treated, the groups with complicated UTI are difficult to compare, relapses primarily being determined by underlying disease. Both antibiotics were tolerated well.

[In vitro activity of oral cephalosporins (author's transl)]

The in vitro activity of cephradine, cephalexin, and cefaclor was studied in comparison with that of cephalothin. Cefaclor inhibits peptidoglycan synthesis somewhat more than cephalexin and cephradine. There is no marked difference in the stability of the three substances in the presence of beta-lactamases, and the outer membrane of Escherichia coli is no barrier to permeation of any of the three antibiotics.

[The antibacterial efficacy of cefaclor against bacteria resistant to ampicillin, tetracycline and co-trimoxazole (author's transl)]

The antibacterial activity of the new oral cephalosporin cefaclor was investigated using 623 freshly isolated bacterial strains. A high degree of efficacy of cefaclor was noticed against Escherichia coli, Proteus mirabilis and Klebsiella. Nearly all strains which were sensitive to ampicillin, tetracycline and co-trimoxazole were also inhibited by cefaclor. Some of the strains resistant to the three above-mentioned antibiotics were also sensitive to cefaclor as follows: all of ten P. mirabilis strains resistant to co-trimoxazole, 54% of the E. coli strains resistant to ampicillin, tetracycline and co-trimoxazole, and 18% of the Klebsiella strains resistant to tetracycline and co-trimoxazole.

Summary of laboratory studies on the antibacterial activity of cefaclor

Laboratory aspects of cefaclor, a new orally-effective cephalosporin antibiotic, are summarized. On the basis of data from a variety of studies, the useful antibacterial spectrum of cefaclor is shown to include all classes of bacteria that are generally susceptible to cephalothin and cephalexin. Cefaclor has a significant potency advantage over cephalexin against many Enterobacteriaceae, Haemophilus sp. and Streptococcus pneumoniae. Bacteria that are susceptible to cefaclor are killed by concentrations at or near the inhibitory concentration. In vitro enzymatic hydrolysis experiments have shown that cefaclor is a relatively good substrate for several beta-lactamases. Orally administered cefaclor is effective in protection of mice from the lethal effects of intraperitoneal challenges with cefaclor-susceptible bacteria. The chemical instability of cefaclor, test medium composition and inoculum density influence the results of in vitro susceptibility tests with cefaclor. Methods for routine susceptibility testing are described.

[Resistance of gram-negative bacteria against cefaclor and other antibiotics (author's transl)]

Five hundred and eighty-six strains of eight species of Enterobacteriaceae were tested for their resistance against cefaclor, cefamandole, cephalothin, ampicillin, mezocillin, tetracycline and co-trimoxazole. Cefaclor showed a low rate of resistance against Escherichia coli (1.2%), Klebsiella (2%) and Proteus mirabilis (3.1%), but a high rate of resistance against indole-positive Proteus species (60%) and Serratia (80%). Cefamandole was also effective against cefaclor and ampicillin resistant strains. Multiresistant strains were predominant especially amongst Enterobacter, Serratia and indole-positive Proteus species. Of 266 ampicillin resistant strains, 198 strains (74.4%) proved to be sensitive to cefaclor. Among the orally administered antibiotics cefaclor exhibited the best result with 12.1% resistant strains compared to 14.8% strains resistant to co-trimoxazole and 45.4% resistant to ampicillin.

[Experience with cefaclor in the treatment of ear, nose and throat infections. Indications for cefaclor therapy (author's transl)]

The efficacy and tolerance of the new oral cephalosporin cefaclor was tested in 61 patients treated for a variety of moderate to severe ENT infections which were not expected to undergo a spontaneous remission without antibacterial therapy. The most frequently isolated pathogens were streptococci and Staphylococcus aureus. The dosage consisted of 500 mg cefaclor three times daily, and the treatment lasted between 4 and 43 days (average 14 days). In 35 cases, some of whom had already been treated unsuccussfully with another antibiotic, the results were very good. In 22 patients locally applied medicaments or surgery contributed to the good result. In four patients an unequivocal evaluation was not possible or therapy was not successful. The frequently noted rapid response to treatment with cefaclor was impressive. No relapses were recorded. In pharmacokinetic studies a cefaclor concentration of 2.8 mcg/g was obtained in the tonsils 90 minutes after oral administration of 1000 mg. Clinical examinations in 61 patients and a complete range of laboratory tests in 47 patients did not reveal any case of allergic reaction. One patient only complained of nausea and diarrhoea. In two patients temporary low grade thrombopenia and thrombocytosis respectively were observed. In several patients a slight transitory rise in transaminases was seen. Cefaclor thus proved to be an effective and well-tolerated antibiotic. Its indications in the treatment of ENT infections are discussed.

[Influence of cefaclor on experimental pyelonephritis (author's transl)]

A comparative study on the antibiotic activity of cefaclor and cephradine was performed in an infection and therapy model of acute pyelonephritis in the rat. Pathogens were Escherichia coli and Klebsiella pneumoniae. The antibiotics, which were administered orally, both had a pronounced effect in comparison to the untreated control group. Cefaclor was superior to cephradine in infections caused by K. pneumoniae.

[In vitro activity of cefaclor (author's transl)]

A comparative study was conducted on the in vitro activity of cefaclor and other oral cephalosporins against a large number of freshly isolated clinical strains of gram-negative and gram-positive bacteria. The activity of cefaclor against gram-positive pathogens is very similar to that of cephalexin. The action of cefaclor against Streptococcus pneumoniae is superior. Cefaclor is the most active antibiotic against strains of Haemophilus influenzae, and is also more active than cephalexin and cephradine against non-beta-lactamase producing strains of Escherichia coli, Klebsiella species and Proteus mirabilis.

Comparison between agar and broth minimum inhibitory concentrations of cefamandole, Cefoxitin, and cefuroxime

The in vitro susceptibility to cefamandole, cefoxitin, and cefuroxime of clinical isolates of Streptococcus faecalis, Klebsiella, and indole-positive Proteus was assayed using minimum inhibitory concentration (MIC) determinations in broth and on solid media. It could be demonstrated that the agar dilution MICs obtained when S. faecalis was tested against cefuroxime and when indole-positive Proteus strains were tested against cefamandole tended to be considerably lower than those obtained with the broth dilution technique. The Klebsiella strains tested did not show any major differences with regard to MICs in broth or on solid media. Using an animal experimental infection model it could be demonstrated that with indole-positive Proteus the higher broth MIC correlated better to the observed data than the lower agar MIC when a beta-lactamase-producing strain was tested. The data obtained indicated that the beta-lactamase of the indole-positive Proteus strain was inducible. The results of the study gave evidence for a risk of false susceptibility of some bacterial species against cefamandole when agar techniques, e.g. paper disk diffusion, are used. For cefuroxime, the same phenomenon can be expected with S. faecalis and to some extent with indole-positive Proteus. In this study, cefoxitin seemed considerably less affected by the technique used for susceptibility testing.

Concentration relationships of cefaclor in serum, interstitial fluid, bile, and urine of dogs

The concentrations of cefaclor in the serum, urine, bile, and tissue fluids of the abdominal wall, kidney, and liver of dogs were compared over a 4-h period after oral administration of a single dose of this drug. The concentration of cefaclor in the soft-tissue interstitial fluid peaked 2 h after administration, thereby demonstrating a diffusion rate similar to those of other cephalosporins. Both urine and bile concentrations greatly exceeded the serum levels, whereas none of the tissue fluid concentrations were greater than the serum concentrations at the times of measurement.

Pharmacology of cefaclor in normal volunteers and patients with renal failure

After a 500-mg dose of cefaclor, the mean peak plasma level was 12.4 mug/ml and after a 250-mg dose it was 5 mug/ml in normal volunteers. Food intake significantly reduced absorption. Probenecid prolonged plasma levels. Mean plasma half-life in normal volunteers was 0.8 h. Only about 50% of the dose was excreted in the urine within 4 h in normal volunteers. Plasma half-life in patients with renal insufficiency was only about 3 h, which suggests that cefaclor may be eliminated by nonrenal mechanisms in humans. Urinary levels of cefaclor were adequate to inhibit susceptible pathogens even in patients with moderately severe renal failure. Plasma half-life during hemodialysis was 2.1 h and rose to 2.8 h after dialysis.

Susceptibility of Staphylococcus aureus to cefaclor and cephalothin: laboratory and clinical studies

In vitro susceptibility tests of 201 strains of Staphylococcus aureus by agar dilution revealed 90% to be susceptible to 8 mug or less of cefaclor per ml. Strains from hospitalized children and adults were more often resistant than those from patients with bullous impetigo. Cephalothin was more active than cefaclor against all strains tested. Results with disk tests, including those strains examined from the clinical investigation, revealed some discrepancies in identifying strains more resistant to cefaclor. In clinical studies, cefaclor proved quite effective for the treatment of bullous impetigo. Of 73 patients, 90% were cured and 7% improved after completing 5 or more days of treatment. Prompt improvement was noted among most patients seen 3 to 5 days after treatment was begun. One patient experienced mild diarrhea. There were no other adverse or toxic manifestations attributable to therapy.