Comparison of bactericidal activity of five antibiotics against Staphylococcus aureus

Ten volunteers were given each of five antibiotics, sequentially, until steady state was reached. Peak and trough sera were then drawn, and bactericidal titers were determined to two different isolates of Staphylococcus aureus, both sensitive in vitro to all antibiotics tested. The antibiotics were cephalexin, trimethoprim/sulfamethoxazole (TMP/SMZ), clindamycin, dicloxacillin, and ciprofloxacin. Mean peak serum bactericidal titers (SBT) were significantly higher for cephalexin than for dicloxacillin, ciprofloxacin, and TMP/SMZ (P less than .05). The difference between cephalexin and clindamycin did not achieve statistical significance. Dicloxacillin, clindamycin, and ciprofloxacin were not statistically different from each other. Mean SBT for TMP/SMZ was less than 1:2, significantly less than that achieved by the other antibiotics. Only clindamycin achieved a trough SBT greater than 1:2. This was statistically significant compared with each of the other antibiotics.

Cephalexin concentrations in human serum, gingiva, and mandibular bone following a single oral administration

1. Cephalexin concentrations in human serum, gingiva, and mandibular bone after a single oral administration of cephalexin (500 mg) were measured by the paper disc method. 2. The peak times of serum, gingiva, and mandibular bone were approximately 90, 120 and 120 min, respectively. 3. The peak concentrations of serum, gingiva, and mandibular bone were 10.58 micrograms/ml, 5.57 micrograms/g and 2.12 micrograms/g, respectively. 4. The concentration ratio of gingiva/serum and mandibular bone/serum peak time of serum were 0.47 and 0.18, respectively. 5. Cephalexin concentrations in gingiva and mandibular bond did not exceed the MIC80s for clinically isolated strains of Staphylococcus aureus spp., alpha-Streptococci and Peptostreptococcus spp.

Significance of "extravascular" protein binding for antimicrobial pharmacodynamics in an in vitro capillary model of infection

The effect of protein binding in an "extravascular" space on antimicrobial pharmacodynamics was studied in an in vitro capillary model of infection. Simulated 500-mg oral doses of dicloxacillin (approximately 96% bound) or cephalexin (less than 5% bound) were administered every 6 h for four doses. A 10-fold-higher dose of dicloxacillin was also studied to determine the effect of drug concentration on the reduction of bacterial killing in the presence of protein. Staphylococcus aureus ATCC 25923 was inoculated into peripheral chambers filled with either Mueller-Hinton broth or Mueller-Hinton broth plus 25% human serum. Serial samples for bacterial counts were collected over 24 h. The presence of serum in the chambers significantly reduced bacterial killing by dicloxacillin but not by cephalexin during the first 6 h (two-way analysis of variance, F = 6.04, P less than 0.05) but not at 24 h. Reduction of dicloxacillin activity in serum-containing chambers persisted with the higher dose. These data suggest that despite attaining higher total drug concentrations in protein-containing extravascular spaces with highly bound drugs, protein binding reduces bactericidal activity during the early stages of treatment in this model.

Microbore liquid chromatographic determination of cadralazine and cephalexin in plasma with large-volume injection

The application of microbore systems (15 cm X 1 mm I.D. columns filled with Nucleosil C18, 5 microns particle size) to the determination of cephalexin and cadralazine in plasma was investigated. Factors such as mobile phase flow-rate, detector flow-cell volume and injection volume were examined with regard to the needs of routine drug analysis. Mobile phase flow-rates of 50-60 microliters/min were used. A flow cell with an optical path length of 6 mm and an intermediary volume (2.4 microliters) was selected for UV detection in order to obtain sufficient sensitivity. Large volumes of non-eluting solvent containing the drug were injected on the column. The addition of an ion-pairing reagent to samples containing cephalexin and cefroxadin prior to the injection was found to improve the chromatographic performance. The blood sample size required for analysis with microbore columns was smaller than that with conventional columns. The analysis time was similar and the limit of quantitation was also similar, provided that large sample volumes were injected on the microbore column.

Pharmacokinetics of cephalexin in dogs and cats after oral, subcutaneous and intramuscular administration

A three-way crossover study was carried out in 10 dogs and nine cats to establish the pharmacokinetic parameters of the semi-synthetic cephalosporin antibiotic, cephalexin sodium, when administered orally, subcutaneously or intramuscularly. Ten dogs received a subcutaneous or intramuscular injection of 10 mg/kg bodyweight cephalexin or an oral dose of three 50 mg cephalexin tablets; the peak serum concentrations achieved were 24.9, 31.9 and 18.6 micrograms/ml, respectively, and the times taken to reach these peak levels were 1.2, 0.9 and 1.8 hours. Nine cats received either a subcutaneous or intramuscular dose of 0.25 ml cephalexin suspension (approximately 20 mg/kg bodyweight) or an oral dose of one 50 mg tablet; the peak serum concentrations achieved were 54.0, 61.8 and 18.7 micrograms/ml for the subcutaneous, intramuscular and oral administrations respectively, with times to peak concentrations of 1.1, 0.7 and 2.6 hours.

High performance liquid chromatographic analysis of cephalexin in serum and urine

A rapid, highly sensitive high performance liquid chromatographic method has been developed for the determination of cephalexin in serum and urine. Serum protein was precipitated with 1% zinc sulphate solution containing cephradine as the internal standard. The drugs were eluted from a 5 micron, C-18 reversed-phase column at ambient temperature with a mobile phase consisting of acetonitrile-methanol-acetate buffer of pH 4.2 (10:10:80%), at a flow rate of 1.4 ml/min with ultraviolet detection at 254 nm. Each analysis lasted 9 min. Quantification was achieved by the measurement of the peak-height ratio and the relative and absolute recoveries varied from 98 to 103%. Detection limits for cephalexin were 1 microgram/ml in serum and 5 micrograms/ml in urine. Within-run coefficient of variation ranged from 0.73 to 5.63% at three different concentrations for the serum and urine assay.

Liquid-chromatographic determination of five orally active cephalosporins--cefixime, cefaclor, cefadroxil, cephalexin, and cephradine--in human serum

We report an isocratic "high-performance" liquid-chromatographic (HPLC) procedure for measurement of five orally administered cephalosporins (cefixime, cefaclor, cefadroxil, cephalexin, and cephradine) in 0.1 mL of human serum. Serum protein is precipitated with acetonitrile, the sample is centrifuged, and the supernate is evaporated under nitrogen. The residue is reconstituted in 0.1 mL of mobile phase, and 50 to 80 microL of this is injected onto a reversed-phase Altex Ultrasphere Octyl (C8) column. The five cephalosporins are resolved by elution with a pH 2.6 mobile phase of methanol/monobasic phosphate buffer (20/80) by vol), flow rate 2 mL/min. The column effluent is monitored at 240 nm. Cefixime serves as the internal standard for the analysis of the four other compounds, cephalexin as the internal standard for cefixime. We used two standard curves for all compounds: a low-range curve for concentrations commonly observed clinically and a higher-range curve for higher concentrations. The former were linear from 1.0 to 10 mg/L for cefaclor, cefadroxil, cephalexin, and cephradine and from 0.1 to 1 mg/L for cefixime. The high-concentration curves were linear from 1 to 10 mg/L for cefixime and from 10 to 100 mg/L for the other compounds. The detection limits were 0.1 mg/L for cefixime, 1 mg/L for the other cephalosporins. Mean within-run and day-to-day CVs were always less than 15% for all compounds studied.

Therapeutic efficacy of cefadroxil and cephalexin for pneumonia in a rat test model

The therapeutic efficacies of cefadroxil and cephalexin were compared in a Streptococcus pyogenes-induced lung infection in rats. Although MICs, rates of in vitro killing in rat serum, and antibiotic serum levels after oral administration were similar for both drugs, cefadroxil was about eight times more effective than cephalexin in reducing the number of viable streptococci at the site of infection. This excellent in vivo bactericidal activity of cefadroxil in lung tissue and bronchial secretions was reflected in the 50% protective dose (PD50) after single or multiple oral treatments. A single treatment given 24 h after infection resulted in a PD50 of 2.8 mg of cefadroxil per kg, compared with 21 mg of cephalexin per kg. When treatment was administered three times, at 24, 27, and 30 h postinfection, the PD50s of cefadroxil and cephalexin were 0.7 and 8.0 mg/kg, respectively. In infected animals, treated 24 h postinfection, the area under the lung tissue concentration versus time curve for cefadroxil was significantly greater than that of cephalexin. This difference in pharmacokinetic behavior may account, at least in part, for the superior therapeutic results obtained with cefadroxil in this experimental pulmonary infection.

A new dosing regimen in renal insufficiency: application to cephalexin

We describe a new method of drug dosage adjustment. The method simultaneously considers glomerular and tubular functions as parameters, because nonparallel decreases in both functions limit the use of the conventional endogenous creatinine clearance (CLCR) method for dosage adjustment. In the new method, CLCR and the 15-minute phenolsulfonphthalein (PSP15') test were used and applied to patients with renal insufficiency with cephalexin (CEX) as a model drug for renal tubular secretion. The results clearly demonstrate good control of plasma CEX concentrations by the CLCR-PSP15' method, whereas there were marked changes in plasma CEX levels with the CLCR method alone. Our method appears to be more useful for patients with renal impairment than the conventional CLCR method for CEX, which is mainly excreted in urine by renal tubular secretion. A nomogram for the CEX dosing interval is proposed for application to clinical practice.

Serum and dialysate concentrations of cephalexin following repeated dosing in CAPD patients

Oral cephalexin, 1 to 2 g daily for 3 days, was given to six stable, noninfected patients receiving maintenance continuous ambulatory peritoneal dialysis (CAPD). The peak serum concentration after a 2 g initial dose was between 73 and 123 mg/L. On the second and third day in five patients who received a 2 g daily oral dose, the serum concentrations were between 35 and 118 mg/L in serum obtained 1 to 1.5 hours after the dosing. Similar serum concentrations were seen in one patient who only received a 1 g oral dose on the second and third day. Cephalexin concentrations in the peritoneal dialysate reached a peak on the first day between 4 to 14 hours after the dose and were between 31 to 78 mg/L. During the second and third day, the highest cephalexin concentration was 118 mg/L and the lowest was 12 mg/L. The data are consistent with the feasibility of oral cephalexin for treatment of CAPD-associated peritonitis with microorganisms that are sensitive to these levels of cephalexin.

A pharmacokinetic comparison of cephalexin and cefadroxil using HPLC assay procedures

The pharmacokinetics of cephalexin and cefadroxil were compared following single 500 mg oral doses to 12 healthy male volunteers. Doses were administered after an overnight fast according to a crossover design. Plasma and urinary levels of both compounds were determined by HPLC procedures. Cephalexin was absorbed rapidly, achieving a mean peak plasma level of 17.5 micrograms ml-1 at 1 h, compared to 16 micrograms ml-1 at 1.8 h for cefadroxil. Elimination half-lives of cephalexin and cefadroxil were 0.7 and 1.1 h, respectively. The area under the cefadroxil plasma curve was significantly larger than that for cephalexin. However, after allowing for differences in elimination rate constants and assuming equal distribution volumes, plasma data indicated the compounds were equally well absorbed. Only 70 per cent of cefadroxil was recovered in urine compared to 87 per cent of cephalexin during the 12 h following drug administration. The therapeutic significance of the different pharmacokinetic characteristics of cephalexin and cefadroxil, if any, may be a function also of their pharmacologic activity and/or the sensitivity of the target organism.

[Study on the transfer of cefroxadine to human tears]

A comparative study to determine the transfer of cefroxadine (CXD), an oral cephem antibiotic, to the human tears was undertaken using cephalexin (CEX) as the control drug. The mean tear levels of 250 mg each of CXD and CEX after oral administration in 6 volunteers were equally peaked at 0.26 micrograms/ml with CXD after 1 to 2 hours and with CEX after 2 hours. The changes of tear levels were also equal for both drugs. The ratios between the tear and the blood levels at 2 hours after oral administration were almost equal with 4.1% for CXD and 3.7% for CEX. From the above evidence it has been confirmed that the both drugs were equivalent with regard to the concentration profiles in human tears after oral medication.

Antibiotic concentration in the serum of dogs and cats following a single oral dose of cephalexin

Six dogs and six cats were given a single oral tableted dose containing approximately 15 mg/kg bodyweight of the semisynthetic cephalosporin antibiotic, cephalexin. Three dogs and four cats were similarly dosed using a liquid preparation of the same antibiotic. At intervals after dosing, blood samples were taken and the level of antibiotic in the serum was determined by bioassay. After fitting the results to a mathematical model the calculated peak serum level of antibiotic was found to be about 15 micrograms/ml and to occur between one and two hours after dosing. Results agree with the performance of the antibiotic in human medicine.

[Assay of blood and urinary levels of 2 different solutions of cephalexin for oral administration]

The characteristic of different cephalosporin derivates have been reviewed with the aim to correlate their pharmacokinetic. On the basis of these date it is possible to confirm that no difference exist between the two compounds.

Comparison of pharmacokinetics of sodium and lysine cephalexin in calves

The pharmacokinetics of sodium and lysine cephalexins were investigated after intravenous and intramuscular administration of a single dose rate of 30 mg.kg-1 body weight in calves. The data for the two salts administered intravenously were pooled, the resulting pharmacokinetic disposition of cephalexin indicating a distribution half-time (t1/2 alpha) and an elimination half-time (t1/2 beta) of 9.78 and 62.0 min, respectively. Following intramuscular administration some pharmacokinetic differences were recorded between the cephalexin preparations: lysine cephalexin was more rapidly eliminated (t1/2kel = 55.2 min) than sodium cephalexin (t1/2kel = 89.8 min), although the peak blood level was higher and attained after a longer time with lysine cephalexin.

Cefazolin and cephalexin kinetics in continuous ambulatory peritoneal dialysis

We studied single-dose cefazolin (CFZ) and cephalexin (CPX) kinetics in continuous ambulatory peritoneal dialysis (CAPD) patients to establish therapeutic guidelines for two cephalosporins commonly used to treat peritonitis in these patients. CFZ, 10 mg/kg, was given intravenously and intraperitoneally, while CPX, 500 mg, was given orally. CFZ led to serum concentrations of 25 microgram/ml at 24 hr, with a half-life (t 1/2) of 33 hr. CAPD accounted for only 20% of total body clearance. When CFZ was given intraperitoneally, 74% of the dose was absorbed and similar serum concentrations had much the same t 1/2. CPX, on the other hand, had a serum t 1/2 of 8.6 hr and resulted in much lower peritoneal concentrations than CFZ. The kinetic principal of superposition provided a model for the prediction of plasma concentrations after repeated intraperitoneal doses of CFZ. The model predicts that a 10-mg/kg intraperitoneal loading dose, followed by 5-mg/kg doses in each exchange the first day and 2.5-mg/kg doses thereafter, will lead to steady-state plasma concentrations of 50 to 65 microgram/ml. The data suggest that CFZ needs be given only intraperitoneally at doses lower than those in current use. CPX probably adds little to the treatment of peritonitis.