[Analysis of multiple cephalosporins in blood and urine by HPLC]

OBJECTIVE

To establish a new high performance liquid chromatography (HPLC) method for determining the concentration of cefazolin, cefradine, cefoperazone and cefotaxime in blood and urine, as well as to investigate its applicability.

METHODS

Protein in blood and urine was precipitated directly by acetonitrile with acetanilide was used as the internal standard using Agilent Zorbax SB-Aq column (250 mm x 4.6 mm, 5 microm). The mixed solvents of water (triethylamine 0.12%, acetic acid 0.12%) and acetonitrile were used as the mobile phase to separate cephalosporins using gradient elution method at 1 mL/min (flow rate) and 254 nm (detection wavelength).

RESULTS

The working curve of four cephalosporins showed a good correlation (r = 0.9993), with the detection limit up to 0.01 microg/mL. The recovery rate was more than 81.2%.

CONCLUSION

This method is fast, easy and accurate. It is suitable for biological analysis of the 4 cephalosporins of the blood and urine in practical cases.

Subcutaneous pharmacokinetics and dosage regimen of cefotaxime in buffalo calves (Bubalus bubalis)

The pharmacokinetics and dosage regimen of cefotaxime following its single subcutaneous administration (10 mg/kg) were investigated in buffalo calves. Plasma and urine samples were collected over 10 and 24 h post administration, respectively. Cefotaxime in plasma and urine was estimated by microbiological assay technique using E. coli as test organism. The pharmacokinetic profiles fitted one-compartment open model. The peak plasma levels of cefotaxime were 6.48 ± 0.52 µg/ml at 30 min and the drug was detected upto 10 h. The absorption half-life and elimination half-life were 0.173 ± 0.033 h and 1.77 ± 0.02 h, respectively. The apparent volume of distribution and total body clearance were 1.17 ± 0.10 l/kg and 0.45 ± 0.03 l/kg/h, respectively. The urinary excretion of cefotaxime in 24 h, was 5.36 ± 1.19 percent of total administrated dose. A satisfactory subcutaneous dosage regimen for cefotaxime in buffalo calves would be 13 mg/kg repeated at 12 h intervals.

New spectrophotometric procedure for determining cefotaxime based on derivatization with 1,2-naphthoquinone-4-sulphonate into solid-phase extraction cartridges--application to pharmaceutical and urine samples

Cefotaxime was derivatised with 1,2-naphthoquinone-4-sulphonate (NQS), extracted into solid-phase cartridges (C18) and detected using a UV-visible detection system. Optimum conditions for this new procedure were: hydrogencarbonate-carbonate buffer, pH 10.5, 5-min reaction time at 25 degrees C and an NQS concentration of 7.1x10(-3) mol l(-1). The accuracy and the precision of the liquid-solid procedure were tested. The procedure was used to measure cefotaxime in pharmaceutical and urine samples. The results obtained were contrasted with those reported for a HPLC method for urine samples. The generalized H-point standard additions method was used to measure cefotaxime in urine samples.

Pharmacokinetics of cefixime in children with urinary tract infections after a single oral dose

The pharmacokinetics of cefixime, a third-generation broad-spectrum cephalosporin, were determined following administration of a 8 mg/kg single oral dose of cefixime suspension to six children with urinary tract infections, ages from 6 to 13 years and weights from 17 to 60 kg. Blood samples for determination of plasma cefixime concentrations were obtained for up to 12 hr and complete urine collections were obtained for urinary excretion of unchanged parent drug for up to 24 hr after administration. Plasma and urine concentrations of cefixime were determined using a reversed phase HPLC assay and pertinent pharmacokinetic parameters were estimated by model-independent standard methods. Mean peak plasma concentration was 4.04 micrograms/ml and was reached after 3.2 hr. The mean area under the plasma concentration-time curve was 33.07 micrograms.hr/ml and the mean elimination half-life was 3.91 hr. The mean apparent total clearance was 4.74 ml/min./kg and about 15% of the dose administered was recovered unchanged in urine. In conclusion, the estimated pharmacokinetic values of cefixime were comparable to those observed in healthy adult subjects based on equivalent mg/ kg doses. Plasma and urine concentrations of the drug were well above the reported minimal plasma and urinary concentrations for most common urinary tract pathogens for up to 12 and 24 hr after administration, respectively.

NONMEM analysis in determining the tri-exponential disposition of cefotaxime: a method of evaluating serum and urinary phase I data

The time above the minimum inhibitory concentration (MIC) is an important surrogate parameter for the efficacy of cephalosporines. In clinical practice cefotaxime (CTX) is usually administered every 8 h or 12 h. Unfortunately the limit of quantification (LOQ) of the available assay is not low enough to detect CTX concentrations in serum later than 6 h after a 2 g i.v. dose. Consequently the time above MIC has to be estimated by extrapolation of the available serum data. Due to the concentrating properties of the kidney, concentrations in urine following a 2 g dose however remain above the LOQ for up to 16 h. It is therefore possible to follow the pharmacokinetics of CTX in urine within a 12 h dosing interval. Due to the linear pharmacokinetics of CTX, serum concentrations, and accordingly the time above MIC, can be estimated by using the measured urinary excretion and the calculated renal clearance. The pharmacokinetics of cefotaxime were studied in 12 healthy subjects who received a single 2 g i.v. dose administered as a short infusion. Blood and fractional urine were collected up to 24 h after dosing. For the characterization of the true terminal half-life only sparse and unbalanced serum and urinary data was available. In such situations, the population approach is the method of choice for estimating the kinetic parameters. The combined analysis of serum and urinary data using NONMEM shows the superiority of a tri-exponential compared to a bi-exponential pharmacokinetics model. As a result, the predicted serum trough levels of cefotaxime following twice daily dosing are about 30-fold higher than those extrapolated from the bi-exponential model. Consequently, the concentrations of CTX- and its metabolite desacetyl-CTX--are above the MIC of many therapeutically relevant pathogens for a longer period of time than previously assumed. In conclusion, a twice daily dosing regimen for cefotaxime is adequate for a number of clinically relevant pathogens. This is supported by the positive outcome in previous clinical trials following this dosing regimen.

Urinary excretion of adenosine deaminase binding protein in neonates treated with tobramycin

The potential tubulotoxicity of tobramycin and cefotaxim were assessed in neonates by measuring the urinary level of adenosine deaminase binding protein (ABP) and urinary alpha 1-microglobulin and beta 2-microglobulin. In a prospective study, 33 neonates who received tobramycin and cefotaxim for suspected neonatal sepsis were compared with 48 untreated newborns during the first 10 days of life. The urinary concentrations of ABP and its excretion rates, corrected for body weight and body surface area, were significantly increased from the 1st day of treatment. Urinary alpha 1-microglobulin and beta 2-microglobulin were not elevated under tobramycin and cefotaxim during the first 2 days of treatment. We conclude that ABP may be a sensitive marker for the detection of proximal renal tubular injury during tobramycin and cefotaxim treatments of neonates. The increase in urinary ABP which occurs before an elevation of urinary alpha 1-microglobulin and beta 2-microglobulin may reflect earlier structural than functional alterations. However, since none of the treated infants had signs of electrolyte disorders or glomerular dysfunction, the clinical relevance of ABP measurement should be reevaluated.

The relation between type of renal disease and renal drug clearance in children

It is generally assumed that the renal clearance of drugs in patients with renal impairment are affected to a similar extent regardless of the type of renal disease (intact nephron hypothesis). We have studied the effect of underlying renal disease on the pharmacokinetics of cefotaxime and desacetylcefotaxime in two groups of children (ages 7 to 16 y) with varying degrees of renal dysfunction. Patients in group 1 (n = 5) had intrinsic renal disease and those in group 2 (n = 5) had extrinsic renal disease, as identified by the primary renal lesion. After a single intravenous dose of cefotaxime timed blood and urine samples were collected for 24 h; cefotaxime and desacetylcefotaxime were measured by HPLC. There were no significant differences between the groups in age, body surface area, urine output, creatinine clearance, total body clearance, nonrenal clearance, renal clearance, and volume of distribution at steady state of cefotaxime, and renal clearance of desacetylcefotaxime. However, the renal clearance: creatinine clearance (CLR:CLCR) ratios for both cefotaxime [1.34 in group 1 vs. 0.51 in group 2] and desacetylcefotaxime [1.58 in group 1 vs. 0.75 in group 2] were statistically significant between the two groups. Group 1 patients had an average CLR:CLCR ratio greater than 1 for both the parent compound and the metabolite, suggesting that net tubular secretion was still intact, despite a diminished glomerular filtration rate (CLCR = 24 ml.min-1.73 m-2).(ABSTRACT TRUNCATED AT 250 WORDS)

Parameters characterizing the in vitro activity of cefixime, a new oral broad spectrum cephalosporin, against respiratory and urinary pathogens

The wide and potent in vitro activity of cefixime, a new oral broad spectrum cephalosporin, has been confirmed on a collection of respiratory and urinary pathogens recently isolated in Italy. The new cephem emerged as the most bactericidal of all the comparators tested against several fast as well as slowly-growing gram-negative species including Enterobacteria, Haemophilus and Moraxella, irrespective of their ability to synthetize beta-lactamases. Among the gram-positive species Streptococcus pyogenes and S. pneumoniae were effectively covered. Cefixime activity was not adversely influenced by several important variables such as pH (over the range from 5 to 8), inoculum size (from 10(5) to 10(8) CFU per ml) and the presence of 50% human serum or urine. Time-kill tests confirmed a pronounced bactericidal potency of the drug especially towards common respiratory pathogens (H. influenzae, M. catarrhalis, S. pneumoniae and S. pyogenes). Killing of urinary strains was optimal at cefixime concentrations reached in urine since eradication, except for Proteus mirabilis, was enhanced with increasing levels of the drug. The absence of an untoward paradoxic effect on the rate of cefixime bactericidal action was confirmed by employing a dynamic bladder model simulating the pharmacokinetic parameters of the drug after a single 200 mg daily dosage. Interactions of cefixime with several other drugs that may be employed in combination therapy were generally prone to provide indifference and synergism while antagonism was never observed. Favorable interactions were also registered when cefixime acted with other antibiotics on partially resistant species such as Staphylococci and Pseudomonas. The new cephem seems to provide excellent opportunities for expanding oral cephalosporin therapy to a wide range of infections produced by susceptible pathogens in the adult and pediatric populations.

[A clinical study on postantibiotic effect (PAE) and its application to chemotherapy for complicated cystitis with an automatic simulator of urinary drug concentration]

In an in vitro complicated cystitis model, the concentrations of the urinary antimicrobial agents were determined using a computer-controlled automatic urine concentration simulator. The effects on the bacterial count curves showing the presence or absence of PAE in antimicrobial agents were studied by comparing the times required for regrowth to the concentration at the initial inoculation, i.e., effective regrowth time (ERT). The following results were obtained. 1. When beta-lactam antimicrobial agents (such as AMPC and CFIX) with no PAE against the gram-negative rods were tested, the ERT of the gram-negative rods were about two hours shorter than that of the gram-positive coccus. 2. When new quinolone antimicrobial agents (such as OFLX) and aminoglycosides (such as ISP) that possess PAE against both the gram-positive and negative organisms were used there was no difference between ERT of the gram-negative rods and gram-positive coccus. Therefore, it was demonstrated that the presence or absence of PAE is also reflected in the cell number curve in the case of this in vitro model, more closely related to clinical cases, when the antibiotics is simulated in urinary concentration shifting.

Determination of cefixime and its metabolites by high-performance capillary electrophoresis

Cefixime (CX), an oral cephalosporin antibiotic, and its metabolites in human digestive organs were separated by various modes of high-performance capillary electrophoresis. The zone electrophoresis mode in phosphate buffer (pH 6.8) containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate gave the best separation, permitting the complete resolution of CX and all of five metabolites. On the other hand, the plain zone electrophoresis mode in phosphate buffer (pH 6.8) offered a simple procedure for the direct determination of urinary CX concentration using intact urine samples.

Relationship between renal function and disposition of oral cefixime

The pharmacokinetics of cefixime following a single oral dose of 200 mg have been investigated in 6 normal subjects and in 22 patients with various degrees of renal insufficiency. Serum and urine samples were collected between 0 and 72 h and were subjected to two methods of analysis: bioassay and HPLC. There was a linear relationship between the two sets of results from 228 samples. This result suggests that none of the metabolites, which may accumulate in uraemic patients, has antibacterial activity. In normal subjects, the peak serum level (Cmax) was 2.50 micrograms.ml-1 at 2.83 h (tmax); the apparent elimination half-life (t1/2) was 3.73 h; the apparent total body clearance (CL.f-1) was 154 ml.min-1, the mean renal clearance (CLR) was 39.1 ml.min-1 and the apparent fraction of the dose recovered in 24 h urine was 0.22. In uraemic patients, Cmax and tmax were slightly increased and t1/2 was increased to 12-14 h in patients with an endogenous creatinine clearance below 20 ml.min-1. The apparent volume of distribution was decreased. Apparent total and renal clearances were lower in proportion to the degree of renal insufficiency. Linear relationships were found between CL/f, CLR and creatinine clearance (CLCR). The findings suggest that the dose of cefixime needs to be reduced only in patients with severe renal failure.

[Pharmacokinetic studies on oral antibiotics in pediatrics. I. A pharmacokinetic study on cefixime in pediatrics]

A pharmacokinetic study on cefixime (CFIX) 5% granules for pediatric use was performed, and pharmacokinetic parameter were calculated. 1. Six school children were administered orally with CFIX granules at a dose level of 3 mg/kg either at 30 minutes before meal or at 30 minutes after meal on a crossover design, and serum concentrations and urinary excretion rates of CFIX were determined. Tmax, Cmax, T 1/2 and urinary excretion rate (0-12 hours) following the administration before meal were 3.33 +/- 0.42 hours, 1.03 +/- 0.17 micrograms/ml, 2.31 +/- 0.26 hours and 15.3 +/- 2.2%, respectively, Tmax, Cmax, T 1/2 and urinary excretion rate following the the administration after meal were 4.00 +/- 0.52 hours, 0.90 +/- 0.09 micrograms/ml, 3.11 +/- 0.21 hours and 11.3 +/- 1.6%, respectively. Earlier Tmax, higher Cmax and higher urinary excretion rate were observed when the drug was administered before meal than when administered after meal. These differences between the 2 groups were not statistically significant. 2. Five school children were administered orally with CFIX granules at 30 minutes after meal at a dose level of either 3 mg/kg or 6 mg/kg on a crossover design, and serum concentrations and urinary excretion rates of CFIX were determined. Cmax and AUC at a dose level of 3 mg/kg were 1.01 +/- 0.26 mg/ml and 5.86 +/- 1.13 micrograms.hr/ml, respectively, and Cmax and AUC at a dose level of 6 mg/kg were 1.76 +/- 0.29 micrograms/ml, 12.54 +/- 1.77 micrograms.hr/ml, respectively. A dose response relationship was thus observed. Seven infants (3 mg/kg) and 3 infants (6 mg/kg) were administered orally with CFIX granules at 30 minutes after meal. Cmax and AUC at a dose level of 3 mg/kg were 2.45 +/- 0.26 micrograms/ml, 33.50 +/- 7.62 micrograms.hr/ml, respectively, and Cmax and AUC at a dose level of 6 mg/kg were 4.42 +/- 0.98 micrograms/ml, 66.85 +/- 25.19 micrograms.hr/ml, respectively. A dose response was observed. 3. Eleven school children, 5 younger children and 7 infants were administered orally with CFIX granules at a dose level of 3 mg/kg at 30 minutes after meal, and serum concentrations and urinary excretion rates of CFIX were determined. Tmax in school children, younger children and infants were 3.82 +/- 0.33 hours, 5.20 +/- 0.49 hours and 5.43 +/- 0.37 hours, respectively. Earlier Tmax's were observed in school children than in other children. Cmax in school children, younger children and infants were 0.95 +/- 0.12 micrograms/ml, 0.56 +/- 0.06 micrograms/ml and 2.45 +/- 0.26 micrograms/ml, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacokinetics of cefodizime in children

The single-dose pharmacokinetics of cefodizime were studied in ten hospitalized children aged between two and 15 years and weighing 12.5-26.2 kg. Six subjects received the drug (25 mg/kg) im and four received it iv. Cefodizime concentrations in blood and urine (iv dosage only) sampled up to 12h post dose were measured by microbiological assay and pharmacokinetic parameters were derived on the basis of a two-compartment open model. Peak serum concentrations were 131 +/- 22.7 mg/l (15 min post iv dose) and 54.8 +/- 17.8 mg/l (60 min post im dose). Mean T1/2 beta were 1.9 +/- 0.13 h (iv) and 1.88 +/- 0.25 h (im). Mean AUCs were 217.2 +/- 37.9 mg.h/l (iv) and 150.85 +/- 22.98 mg.h/l (im). Mean volumes of distribution were 7.6 +/- 2.5 l (iv) and 7.9 +/- 1.41 (im). Twelve hours after the iv administration the cumulative urinary excretion was 78-87% of the dose. The pharmacokinetic behaviour of cefodizime in children is thus similar to that of other compounds in this class.

Relative bioavailability of three cefixime formulations

Three galenic formulations of cefixime (tablet, syrup and dry suspension) containing 200 mg each were compared with respect to their relative bioavailability in twelve healthy volunteers. All three formulations showed reliable absorption. Mean peak plasma concentrations were reached after 3.3-3.5 h, mean terminal half lives were 2.9-3.1 h. 18-24% of the dose administered were recovered unchanged in the urine. Best bioavailability was obtained with the dry suspension (AUC0-infinity = 25.8 +/- 7.0 micrograms/ml h; Cmax = 3.4 +/- 0.9 microgram/ml), followed by the tablet (AUC0-infinity = 20.9 +/- 8.1 micrograms/ml h; Cmax = 3.0 +/- 1.0 micrograms/ml) and the syrup which is based on triglycerides (AUC0-infinity = 17.8 +/- 5.9 micrograms/ml h; Cmax = 2.4 +/- 0.7 micrograms/ml). The statistical analysis resulted in bioinequivalence between dry suspension and syrup. It is concluded that best bioavailability of cefixime after oral administration is guaranteed when taken in an "aqueous medium" either as dry suspension or as tablet with "plenty of liquid".

[Tonsil diffusion of cefixime in children]

Cefixime is a new oral cephalosporin antibiotic, with broad-spectrum of activity, near than of third generation cephalosporin, especially against betelactamase producers bacteria. Cefixime has been assayed with microbiological method in tonsils of 21 children (mean age 59 months). Tonsillectomy was performed 5 hours after a third dose of 4 mg/kg cefixime. Plasma levels were evaluated 10 hours after the second dose, with mean level of 0.84 micrograms/ml (0 to 1.35). Blood level was evaluated after third dose, during amygdalectomy was 1.24 micrograms/ml (0.1 to 3.9). Tonsils levels were: for right tonsils 0.74 micrograms/g and for left tonsils 0.53 micrograms/g. Cefixime was not detected in both tonsils of 6 children, and in one of the two tonsils in 11 of them. The tonsils penetration of cefixime was about 1 microgram/g in the case where cefixime was detectable. This penetration is not regular as for other betalactam antibiotics in relation with fibrosis of tonsils tissue inhibiting a good diffusion of antibiotic.

Pharmacokinetics of cefixime in the young and elderly

The pharmacokinetics of cefixime were compared in 12 young and 12 elderly subjects receiving 400 mg once-a-day for five days. Mean peak serum concentrations (Cmax) on days one and five in the elderly (4.90 and 5.68 mg/l) were comparable (P greater than 0.05) to those in the young subjects (3.88 and 4.74 mg/l). Serum area under the curve (AUC) values on days one and five in the elderly (41.0 and 49.5 mg.h/l) were higher (P less than 0.05) than those in young subjects (28.6 and 34.9 mg.h/l). In addition, the elimination half-life, mean residence time, average concentration, minimal concentration and renal clearance (Clr) values were significantly higher (P less than 0.05) in the elderly. A significant linear correlation (P less than 0.05) was found between the Clr of cefixime (total and unbound) and creatinine clearance. The urinary recovery (Ae0----24) and protein binding of cefixime on days one and five was similar in the elderly and young. Overall, there is no need for any dosage adjustment of the drug in the elderly.

The pharmacokinetics of cefixime in the fasted and fed state

Twenty healthy adult volunteers received single 400 mg oral doses of cefixime in an open, randomized, crossover study, administered twice in the fasted state and twice with a standard breakfast. The study design allowed both an evaluation of a potential food effect and also an analysis of both intrasubject and intersubject variability in the fasted and fed state. There was a small but significantly longer (approximately 1 h) time to peak concentration when the drug was given with food. Peak serum concentrations, area under the curve, and 24 h urinary recovery values were unchanged in the fed and fasted states. The terminal elimination half-life of the drug given after a meal (3.6 h) was slightly longer than that observed after dosing in the fasting condition (3.5 h). The intrasubject and intersubject variabilities were less than 12% and 33% respectively, for both area under the curve and 24 h urinary recovery, and were virtually the same for the fasted and fed occasions. Therefore, the drug may be administered with or without food.

Determination of cefixime in biological samples by reversed-phase high-performance liquid chromatography

A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method has been developed and validated for the determination of a new cephalosporin in human serum and urine. Human serum samples, calibration standards and quality control samples (250 microliter) were combined with an equal volume of 6% trichloroacetic acid (TCA). Human urine (0.1 ml) was combined with 6% TCA solution containing the internal standard. The compounds were detected by ultraviolet absorbance set to 280 nm for the serum assay and 313 nm for the urine assay. The method for the determination of cefixime in serum was linear from 100 ng/ml to 30.0 micrograms/ml (r = 0.999), and for the urine assay from 5 micrograms/ml to 100 micrograms/ml (r = 0.999). The minimum reportable quantity for the serum assay was 0.05 microgram/ml. The within- and between-day assay variation for both assays were found to be less than 10% in an extensive assay validation scheme. Results of a storage stability study indicated that human serum and urine samples could be safely stored for up to six months at -18 degrees C and three months at -10 degrees C, respectively.

Determination of cefodizime in biological materials by high-performance liquid chromatography

Cefodizime (THR-221) is a new semi-synthetic cephalosporin. A high-performance liquid chromatographic method has been developed for the determination of cefodizime in biological materials. A plasma or serum sample was deproteinized with methanol and the resulting methanol eluate was concentrated to a volume of 0.5 ml. Urine and bile samples were diluted with buffer and each diluted sample was filtered. Faeces samples were homogenized and the supernate obtained after centrifugation was filtered. Visceral tissue samples were homogenized, the centrifuged supernate was deproteinized with methanol, and the methanol eluate was concentrated to a volume of 0.5 ml. Aliquots of each preparation were chromatographed on a reversed-phase column with an ion-pair chromatographic technique on a high-performance liquid chromatograph equipped with an UV detector set at 264 nm. The detection limits for cefodizime were 0.1 microgram/ml in plasma or serum, 0.3 microgram/ml in bile, and 0.5 microgram/ml in urine, 0.5 microgram/g in faeces and visceral tissue. This precise and sensitive assay for the determination of cefodizime is described, and its stability in several media is reported.

Pharmacokinetics of cefmenoxime in patients with impaired renal function and in those undergoing hemodialysis

The pharmacokinetics of cefmenoxime were studied after a single intravenous 1.0-g dose to 24 subjects grouped according to their renal functions. Creatinine clearance was above 85, 50 to 85, 10 to 50, and below 10 ml/min per 1.73 m2 in groups 1, 2, 3, and 4, respectively. Cefmenoxime obeyed two-compartment-model kinetics in all four groups. The volume of distribution based on the area under the serum concentration-time curve was renal function independent, the average value being 0.270 +/- 0.075 liters/kg. The elimination-phase half-life (t1/2 beta) was 0.82 +/- 0.30 h in group 1, 1.38 +/- 0.36 h in group 2, 3.32 +/- 1.82 h in group 3, and 7.60 +/- 1.28 h in group 4. Cumulative 24-h urinary excretion accounted for 65.5 +/- 7.6% of the dose in group 1 and for 7.50 +/- 3.72% in group 4. Recommendations for dosage adjustment in patients with renal insufficiency are proposed based on the data obtained in this study. The effect of hemodialysis on cefmenoxime pharmacokinetics was studied in six patients in group 4; hemodialysis shortened the average t1/2 beta from 7.60 +/- 1.28 to 4.19 +/- 1.66 h. It was estimated that in a hypothetical anephric subject with a body weight of 60 kg, 5-h hemodialysis would remove 28.2% of the drug present in the body at the start of hemodialysis.

Comparative study of serum bactericidal activity of cefotaxime alone or in combination with tobramycin

The objectives of this study were to investigate the bactericidal activity in serum of cefotaxime alone or in combination with tobramycin against clinical strains and to determine the influence of tobramycin on the pharmacokinetics of cefotaxime. The peak bactericidal activity in serum of cefotaxime alone against Klebsiella oxytoca, Enterobacter aerogenes, Serratia marcescens, Pseudomonas cepacia, and Listeria monocytogenes varied between 1:4 and 1:256. Bactericidal activity could still be detected at 6 h against K. oxytoca and L. monocytogenes. The addition of tobramycin increased the bactericidal activity of cefotaxime against E. aerogenes from 1:16 to 1:128 (P less than 0.01). Cefotaxime recovery from urine was significantly decreased when tobramycin was added. Our data are comparable with those of other investigators who have shown a limited increase in the bactericidal activity of cefotaxime when aminoglycosides are added.

Pharmacokinetics of SCE-1141, a stereoisomer of cefmenoxime, in rats

The pharmacokinetic properties of SCE-1141, an anti stereoisomer of cefmenoxime, were compared with those of cefmenoxime. SCE-1141 levels in plasma and tissues peaked at 30 min after the intramuscular administration of 20 mg/kg; the plasma level declined with a half-life of about 18 min. The area under the concentration-time curve in plasma and the half-life after intravenous administration were similar to those after intramuscular administration. SCE-1141 was distributed at high concentrations in the liver and kidney of normal rats, and at lower concentrations in the liver of rats with acute liver impairment. SCE-1141 levels in plasma and tissues, except liver, were lower than those of cefmenoxime. The 24-h biliary and urinary excretions of SCE-1141 were 73% and 26% of the dose, respectively; these were significantly different from those of cefmenoxime: 33% in bile and 55% in urine. In rats with acute liver impairment, the biliary excretion of SCE-1141 was decreased, and the urinary excretion increased.

Pharmacokinetics and quantitative characterization of cefotiam excretion after intravenous administration to patients after cholecystectomy

Six patients, aged 52 to 71 years, with T-tube drainage of the common bile duct and a urinary catheter after cholecystectomy, were studied in order to evaluate the urinary and biliary excretion and pharmacokinetics of cefotiam in the early postoperative period. Each patient received cefotiam 1 g i.v. as a bolus injection. Cefotiam in plasma, urine, and bile were determined by HPLC. A 2-compartment open model with elimination from the central compartment satisfactorily fitted the plasma levels of the drug. The renal clearance of cefotiam (CLR = 133 ml/min) was an order of magnitude greater than its biliary clearance (CLB = 11.8 ml/min). Glomerular filtration was the main mechanism for elimination of cefotiam. The values of CLR and CLB in relation to the total plasma clearance (CL = 138. ml/min) demonstrated the negligible role of metabolism in elimination of cefotiam in these patients.

Cefodizime penetration into skin suction blister fluid following a single intravenous dose

Cefodizime pharmacokinetics was investigated, evaluating drug concentrations in serum, skin suction blister fluid (SBF), saliva and urine in six healthy male subjects who were administered a 1-g dose intravenously. Serum levels in five subjects can be described according to a two-compartment open model; terminal half-life is 181 +/- 14 min. Volume of distribution (Vd beta) amounts to 15.3 +/- 1.61, serum clearance to 59 +/- 6 ml/min, renal clearance to 33 +/- 3 ml/min. Of the administered dose, 54% is renally excreted unchanged within 27 h. Unbound drug fraction in serum is 19.0% and in SBF 38.4%. Thus renal clearance of free cefodizime amounts to 172 ml/min, Vdss to 68.9 l (free drug). Whereas cefodizime has not been detected in saliva samples, SBF concentration 3-9 h post administration parallel serum levels, amounting to 40% of the respective serum concentration. At 9 h, unbound cefodizime concentrations in SBF amount to 1.4 +/- 0.4 micrograms/ml, this value being well above the MIC90% values of many clinically relevant bacteria.

Cefotaxime and desacetylcefotaxime pharmacokinetics in infants and children with meningitis

The pharmacokinetics and cerebrospinal fluid (CSF) penetration of cefotaxime (Ctx) and desacetylcefotaxime (dCtx) were evaluated in 13 infants and children with meningitis after dose 6 of Ctx in a multiple-dose intermittent intravenous infusion regimen (50 mg/kg every 6 h). Model-dependent and noncompartmental pharmacokinetic parameters were determined and were found to be congruous. The disposition of both Ctx and dCtx was described adequately by a one-compartment, open model. Noncompartmental pharmacokinetic parameters are reported. The mean Ctx serum concentration at 0.25 h postinfusion was 121.2 micrograms/ml, and the mean CSF concentration at 1 h postinfusion was 6.2 micrograms/ml. The CSF/serum ratio was variable (0 to 20%), with a mean penetration of 10.1%. The mean Ctx elimination half-life, apparent steady-state volume of distribution, and total body clearance were 0.8 h, 0.361 liter/kg, and 0.289 liter/h per kg, respectively. For Ctx, 61% of the dose was excreted unchanged in the urine during the 6-h postinfusion period, and the estimated renal clearance was 0.174 liter/h per kg. No significant correlations were observed between Ctx pharmacokinetic parameters and demographic parameters. The mean peak concentration of dCtx in serum (21.6 micrograms/ml) occurred at approximately 1.5 h postinfusion, and the mean concentration in CSF at 1 h postinfusion was 5.6 micrograms/ml. The CSF/serum ratio was extremely variable (0 to 103%), and the mean penetration was 28.8%. The mean apparent elimination half-life for dCtx was 2.1 h. In infants and children with normal renal function, a 50-mg/kg dose of Ctx administered every 6 h should provide adequate concentrations in serum and CSF in the majority of patients with meningitis.

Pharmacokinetics of intravenous and intraperitoneal cefotaxime in chronic ambulatory peritoneal dialysis

We investigated the kinetics of cefotaxime in eight subjects undergoing continuous ambulatory peritoneal dialysis (CAPD). A single 1 gm iv dose was injected and a 1 gm dose was given intraperitoneally in the CAPD fluid during a 4-hour dwell time. Cefotaxime and desacetylcefotaxime were assayed by HPLC. After intravenous injection the cefotaxime serum kinetic parameters were as follows: plasma t 1/2, 2.31 +/- 0.20 hours; volume of distribution, 0.35 +/- 0.04 L/kg; total plasma clearance, 118.7 +/- 12.3 ml/min; and peritoneal clearance, 6.7 +/- 1.3 ml/min. Dialysate cefotaxime concentrations rose rapidly, but only 5% of the dose was eliminated by the peritoneal route. After intraperitoneal instillation, cefotaxime appeared in the serum rapidly and the peak serum concentrations ranged from 9 to 20 micrograms/ml between 1 and 3 hours. The absorption of cefotaxime from peritoneal space was 58.7% +/- 5.4%. Data suggest that cefotaxime has bidirectional exchange characteristics through the peritoneal membrane. Instillation of cefotaxime in CAPD fluid may permit rapid absorption to achieve therapeutic serum concentrations.

Cefotaxime and desacetyl cefotaxime kinetics in renal impairment

Cefotaxime and desacetyl cefotaxime kinetics after a single, 1 gm intravenous dose were evaluated in five groups of subjects: group I, normal creatinine clearance (CLCR greater than 90 ml/min); group II, mild renal insufficiency (CLCR 30 to 89 ml/min); group III, moderate renal insufficiency (CLCR 16 to 29 ml/min); group IV, severe renal insufficiency (CLCR 4 to 15 ml/min); and group V, end-stage renal disease requiring maintenance hemodialysis (CLCR less than 6 ml/min). The steady-state volume of distribution (Vss) ranged from 10% to 55% of body weight but was not related to CLCR. The terminal t1/2 values of cefotaxime and desacetyl cefotaxime were 0.79 and 0.70, 1.09 and 3.95, 1.55 and 5.65, 2.54 and 14.23, and 1.63 and 23.15 hours in groups I to V, respectively. There were no significant changes in Vss or t1/2 after multiple dosing, but there were significant correlations between CLCR and cefotaxime total body clearance, cefotaxime and desacetyl cefotaxime renal clearance, and cefotaxime nonrenal clearance. Dosage regimens for the use of cefotaxime in patients with renal impairment are proposed.

Single-dose ceftriaxone kinetics in the newborn

Ceftriaxone kinetics were characterized after a single, 2-minute, intravenous infusion of 50 mg/kg to 20 sick infants 1 to 8 days old who weighed 1.78 to 4.36 kg. Plasma binding parameters could be determined by equilibrium dialysis in 16 of the infants, in whom kinetic parameters for free ceftriaxone in plasma were also determined. Compared with corresponding values in adults, the elimination t1/2 was longer in infants (19 and 8.4 hours) because of reduced total systemic clearance (4.48 and 8.51 ml/min/m2). The apparent steady-state volume of distribution was of the same order in infants and adults (5,130 and 5,350 ml/m2). Both renal and nonrenal clearance of free ceftriaxone were reduced in infants, but these decreases were partially offset by an increased free fraction; plasma binding affinity and capacity constants for infants were about half the adult values. The mean fraction of dose excreted unchanged in urine was estimated at 70% in the neonates and 46% in adults. There were no clinically significant correlations between the kinetic parameters and either age since birth or age since conception. The fraction of free ceftriaxone in plasma inversely correlated with age since conception and was lower in female infants, which decreased the systemic clearance and volume of distribution of total drug in the female infants compared with the male infants. Values for the volume of distribution and clearance parameters were not related to body size (weight or body surface area). From our results, a ceftriaxone dosage of 50 to 100 mg/day is recommended during the first week of life for newborn infants who weigh between 1.8 and 4.4 kg. Impaired renal function may require a reduction in dosage.

Pharmacokinetics of ceftriaxone in subjects with renal insufficiency

The pharmacokinetics of ceftriaxone was studied in 14 men and women volunteers with renal insufficiency. Subjects were grouped by renal function: those with end-stage renal disease (CLcr less than 15 mL/min/1.73 sq m) but not receiving dialysis, those with severe renal insufficiency (CLcr 16-30 mL/min/1.73 sq m), and those with moderate renal insufficiency (CLcr 31-60 mL/min/1.73 sq m). Ceftriaxone 1 g as the sodium salt was administered by i.v. infusion over 30 minutes, and blood and urine samples were collected before and up to 48 hours after drug administration. The pharmacokinetic data were described using a nonlinear least-squares computer program. For volunteers with a creatinine clearance of less than 15 mL/min/1.73 sq m, the mean half-life was 15.6 hours. For subjects with a creatinine clearance of 31-60 mL/min/1.73 sq m, the mean half-life was 11.9 hours. Plasma ceftriaxone concentrations measured at the conclusion of the infusion (mean peak concentration 122 +/- 53.1 micrograms/mL) or 24 hours after the infusion (mean concentration 20.2 +/- 6.14 micrograms/mL) were similar in each study group. A dose of ceftriaxone 1 g every 24 hours in patients with renal insufficiency is probably adequate for inhibiting most susceptible gram-positive and gram-negative microorganisms.

Pharmacokinetics of cefotiam in humans

After intravenous bolus injections of 0.5, 1, and 2 g of cefotiam to three healthy volunteers, the mean (+/- standard deviation) total plasma clearances measured for each dose were, respectively, 26.8 +/- 2.7, 22.8 +/- 0.8, and 17.8 +/- 0.9 liters/h; the terminal elimination half-lives were 54.0 +/- 0.1, 68 +/- 15, and 98 +/- 36 min; and the renal clearances were 16.0 +/- 2.9, 13.3 +/- 1.4, and 11.3 +/- 2.6 liters/h. The 24-h urinary recovery was independent of the dose and averaged 53% of the dose. After intramuscular administration of 1 g of cefotiam to three healthy volunteers, a mean (+/- standard deviation) peak concentration of 16.6 +/- 5.1 micrograms/ml was reached at 0.75 to 1 h post dosing. The concurrent intramuscular administration of lidocaine and cefotiam did not modify the kinetics of cefotiam. During a constant-rate infusion, the steady-state plasma clearance decreased slightly when the infusion rate was increased. There was no trend towards accumulation of cefotiam in plasma during chronic treatment with 1 g intravenously every 12 h for 10 days.

Pharmacokinetic study of cefmenoxime (SCE 1365-CMX) in healthy adults

Cefmenoxime pharmacokinetics were investigated in six healthy volunteers after intravenous and intramuscular administration of 0.5, 1, and 2 g. Blood and urine samples were analyzed by reversed-phase high-pressure liquid chromatography using ultraviolet detection at 275 nm. The assay is precise and linear up to 200 micrograms/ml-1, with 0.02 micrograms/ml-1 as the limit of detection. Linearity of cefmenoxime kinetics was demonstrated because the area under the plasma concentrations is proportional to studied doses. Eight hours after 1 g of cefmenoxime intramuscularly, mean plasma concentrations are, respectively, 0.6 +/- 0.1 and 0.3 +/- 0.1 microgram/ml-1. Intramuscular cefmenoxime is rapidly absorbed (Ka = 7.28 hours-1) with complete bioavailability (F = 0.99); apparent volume of distribution is 0.35 liters/kg-1 and elimination half-life 1.5 hours. The fraction of cefmenoxime excreted unchanged in the urine after intramuscular administration is 0.72, indicating a major contribution of renal clearance in total clearance. Experimental data after intramuscular administration were well fitted with a two-compartment model.

Pharmacokinetics of cefotiam in patients with impaired renal function and in those undergoing hemodialysis

The pharmacokinetics of cefotiam were studied after a single intravenous 1.0-g dose to 18 subjects grouped according to their creatinine clearances (CLCR); CLCR was above 75, 75 to 20, and below 20 ml/min per 1.73 m2 in groups 1, 2, and 3, respectively. Cefotiam obeyed two-compartment model kinetics in all three groups. The volume of distribution based on the area under serum concentration-time curve (Varea) was renal function independent, the average value being 0.350 +/- 0.159 liters/kg. The elimination-phase half-life (t1/2 beta) was 0.916 +/- 0.090 h in group 1, 2.03 +/- 1.62 h in group 2, and 7.09 +/- 3.06 h in group 3. Cumulative 24-h urinary excretion accounted for 65 to 93% of the dose in four subjects with CLCRS above 80 ml/min per 1.73 m2 and 19 to 41% in three subjects with CLCRS below 20 ml/min per 1.73 m2. We give recommendations for dosage adjustment in patients with renal insufficiency. The effect of hemodialysis on cefotiam pharmacokinetics was studied in six patients in end-stage renal failure; hemodialysis shortened the average t1/2 beta from 8.02 +/- 4.04 h to 2.74 +/- 2.15 h. We estimated that in a hypothetical anephric patient with a body weight of 60 kg, 6-h hemodialysis would remove 49.7% of the drug present in the body at the start of dialysis.

Pharmacokinetics of ceftriaxone in neonates and infants with meningitis

The pharmacokinetics of ceftriaxone was studied in the plasma, urine, and cerebrospinal fluid of seven neonates and seven infants with meningitis. In addition, plasma and urine data were obtained in five neonates and one infant receiving ceftriaxone for other serious infections. All neonates younger than 14 days received daily doses of 50 mg/kg ceftriaxone; all other patients but two received 100 mg/kg. The average weight-corrected values for total body clearance (ClT), volume of distribution (Vdss), and biologic half-life (t 1/2) were 0.37 ml/min/kg, 0.45 L/kg, and 16.2 hours in neonates younger than 1 week; 0.77 ml/min/kg, 0.48 L/kg, and 9.2 hours in neonates older than 1 week; and 1.03 ml/min/kg, 0.39 L/kg, and 7.1 hours in older infants, respectively. There was a significant difference in ClT and t 1/2 between the neonates younger and both neonates older than 1 week, and infants. The Vdss was not significantly different among the three age groups. The average renal clearance in neonates younger than 1 week (0.28 ml/min/kg was 70%, in neonates older than 1 week (0.54 ml/min/kg) was 77%, and in older infants (0.49 ml/min/kg) was 47% of ClT, indicating that nonrenal elimination was less developed in neonates. The quantitation of CSF diffusion of ceftriaxone was assessed by comparison of the areas under the CSF and plasma concentration-time curve. The mean ceftriaxone penetration into the CSF in neonates and infants with bacterial meningitis was 17%. On the other hand, penetration in patients with aseptic meningitis amounted to only 4%. Mean ceftriaxone concentrations in the CSF in patients with bacterial meningitis were 2.8 mg/L after 24 hours, exceeding by many times the minimum inhibitory concentration of the common meningitis pathogens at this time.

[Basic studies of cefmenoxime]

Blood levels and urinary excretion of cefmenoxime (CMX) in children of 8 to 13 years old who received 50 mg/kg of CMX by one shot intravenous injection or 1-hour drip infusion were evaluated. One shot intravenous injection (1) Blood levels--The mean blood levels in 2 cases by intravenous injection were 125.0 +/- 24.0, 56.8 +/- 10.0, 17.8 +/- 6.2, 2.2 +/- 0.7 and 0.4 +/- 0.2 micrograms/ml, after 1/2, 1, 2, 4 and 6 hours, respectively. The mean biological half-life was approximately 0.7 hour. (2) Urinary excretion--The average urinary excretion rate in 2 cases were 57.8, 63.9 and 64.1% after 2, 4 and 6 hours, respectively. 1-hour drip infusion (1) Blood levels--The mean blood levels in 2 cases by drip infusion were 115.5 +/- 0.5, 29.05 +/- 0.25, 5.0 +/- 0.8 and 1.15 +/- 0.45 micrograms/ml, immediately after the completion of infusion, after 1, 3 and 5 hours, respectively. The mean biological half-life after drip infusion was approximately 0.8 hour. (2) Urinary excretion--The average urinary excretion rate in 2 cases were 42.2, 55.5 and 56.5% after 2, 4 and 6 hours, respectively. On the basis of these results, it was concluded that CMX was excreted relatively rapidly in a massive dose of 50 mg/kg a time.

Liquid-chromatographic assay of cefmenoxime in serum and urine

This is a simple, precise liquid-chromatographic procedure for determining cefmenoxime in patients' serum and urine. p-Anisic acid is used as the internal standard. Protein is precipitated from 0.5 mL of serum or dilute urine with 100 microL of perchloric acid. The clear supernate is injected directly onto a mu-Bondapak CN reversed-phase column. The mobile phase is acetate buffer, pH 3.8 (25 degrees C). The flow rate is 2.5 mL/min. Column effluent is monitored at 254 nm. Extraction recovery from serum averaged 74.6%. Calibration curves were linear from 0.5 mg/L, the lower limit of quantification, to 100 mg/L. We present cefmenoxime concentrations in serum from a patient being treated for pneumonia. The procedure was evaluated in the clinical setting to determine its applicability to the study of cefmenoxime pharmacokinetics in critically ill patients.

Treatment of complicated urinary tract infections with the long acting cephalosporin, ceftriaxone

Ceftriaxone, a new broad spectrum cephalosporin with a long biological half-life has been used on a single intravenous daily dosage regimen over a five day period to treat complicated urinary tract infection. Bacteriological analysis of urine up to six weeks after such treatment, indicated that ceftriaxone was successful in 13 out of 15 cases treated compared with two out of 15 cases treated with cefuroxime given three times daily over the five day treatment period.

Determination of ceftriaxone, a novel cephalosporin, in plasma, urine and saliva by high-performance liquid chromatography on an NH2 bonded-phase column

A high-performance liquid chromatographic method has been developed for the determination of a new cephalosporin antibiotic in plasma, urine and saliva (mixed saliva) using normal-phase technique and an NH2 bonded-phase column. The eluent mixture was a combination of acetonitrile and an aqueous solution of ammonium carbonate. The rapid method involved precipitation of protein from fluids by means of acetonitrile followed by automatic injection of the supernatant. The detection limit was 0.4 micrograms/ml for plasma, 3 micrograms/ml for urine and 0.03 micrograms/ml for saliva using UV detection.

Determination of cefmenoxime in human body fluids by high-performance liquid chromatography

A rapid and reliable method for the quantitative determination of cefmenoxime in serum and urine by reversed phase high-performance liquid chromatography is described. Serum was deproteinized with acetonitrile. Urine was diluted with dilute acetic acid (17.5 mmol/l). Separations were performed in isocratic mode using a C18 type column and a precolumn packed with Perisorb RP/8. The eluant consisted of a mixture of acetonitrile and 25.0 mmol/l acetic acid in a ratio of 32/69 (vol/vol). In normal subjects cefmenoxime was well separated from endogenous compounds and various added drugs. Its complete separation was confirmed by selective degradation with beta-lactamase from Bacillus cereus and UV spectrophotometry. The detection limit was 0.3 mg/l at a detection wave-length of 254 nm. Peak areas gave linear results up to concentrations of 500 mg/l. Within-batch precision (coefficient of variation) ranged from 1.1 to 6.2%. Recovery rates varied from 99.0 to 103.3%. Results of a standard microbiological assay correlated well with those obtained by the present HPLC method. Eight healthy volunteers who were given a single intravenous dose of 1 g cefmenoxime excreted 86.3 +/- 5.8% of the unchanged drug within 24 h in urine.

[Elimination of desacetyl cefotaxime in geriatric patients with multiple diseases]

Plasma concentrations of cefotaxime and desacetyl cefotaxime were determined by HPLC in geriatric patients with multiple diseases. Comparison with a younger control group of healthy volunteers showed a prolongation of half-life of CTX and dCTX in the older patients. A significant correlation between pharmacokinetic parameters of dCTX and other clinical and chemical parameters was found. Half-life of dCTX was positively correlated with age of the geriatric patients (P less than 0.05). There was also a significant relationship between CHE in serum and plasma peak concentrations of dCTX. Time until reaching plasma peak concentrations correlated closely with total bilirubin (P less than 0.01), CHE (P less than 0.001), cholesterol (P less than 0.01), and urea (P less than 0.01). Accumulation of the pharmacologically active metabolite dCTX could not be excluded in one patient with kidney disease. In accordance with other investigators it is recommended to reduce the dose of cefotaxime in geriatric patients with kidney diseases.

Pharmacokinetics of cefotiam in normal humans

Doses of 0.5, 1.0, and 2.0 g of cefotiam were infused intravenously over a 15-min period in a crossover fashion to eight volunteers. Doses of 1.0 and 2.0 g were infused intravenously over periods of 30 and 60 min in a double crossover fashion to another eight volunteers. Serum concentrations fell rapidly from peak levels between 30 and 170 micrograms/ml at the end of the infusion to less than 1.0 micrograms/ml within 6 h after all regimens. The terminal half-life in plasma varied between 0.6 and 1.1 h. The slopes of the time-concentration curves with the different regimens showed different half-life data. The urinary excretion of cefotiam was mostly completed within 4 h of the beginning of drug administration. The pharmacokinetics of cefotiam were dose dependent. With the 2-g dose, the peak plasma concentrations and the values for the area under the curve were more than twice the values observed with 1 g; decreasing values of plasma clearance were observed with higher doses. Injection of cefotiam caused no immediate discomfort or reaction at the infusion site.

[Kinetic and clinical studies on a new cephalosporin: Cefotiam]

Kinetic and clinical evaluation of cefotiam, a new cephalosporin, is reported. It was found that the drug is rapidly distributed to the tissues. Equilibrium between tissues and plasma is reached in about an hour. Some 90-91% of the dose administered is excreted in the urine, and accumulation does not occur. A clinical cure was obtained in 27 of a series of 35 patients (77.1%). Improvement was observed in 7 cases (20%). The antibiotic proved ineffective in the remaining cases (2.8%). Tolerance was excellent and there were no side-effects worthy of note.

Metabolism of cefotaxime in animals and humans

The metabolism of [14C]cefotaxime was studied in vivo in rats, dogs, and humans and in vitro in cells of rats and rabbits. Excretion of radioactivity was similar in all species, and greater than 80% of the dose was recovered in the urine. Approximately one-third of the dose was eliminated unchanged, and the major metabolite was desacetylcefotaxime. Under normal circumstances these two products, both with antibacterial activity, were the only materials detected in the plasma. Two further metabolites, designated M2 and M3, (formerly known as UP1 and UP2, respectively, were observed in canine and human urine. Although M2 and M3 were not present in the plasma of normal animals, they were found in the plasma and bile of nephrectomized rats. Extensive studies have shown that the metabolic pathway follows the route: cefotaxime leads to desacetylcefotaxime leads to desacetylcefotaxime lactone leads to M metabolites. The rate-limiting step is the formation of desacetylcefotaxime lactone. All of these reactions take place in the liver. It is concluded that species differences in the metabolism of cefotaxime are more likely to be quantitative than qualitative and that both rat and dog are suitable species for toxicity studies.

Elimination kinetics of ceftizoxime in humans with and without renal insufficiency

The pharmacokinetics of a single 500-mg intramuscular dose of ceftizoxime were studied in 11 healthy adult volunteers and in 22 patients with various degrees of renal dysfunction. The mean serum half-life of ceftizoxime was 1.44 h in normal subjects and 30.2 h in hemodialysis patients. A significant correlation (P less than 0.001) between the elimination rate constant of ceftizoxime and creatinine clearance was demonstrated. The mean urinary recovery in normal subjects was 75.6% within 6 h of dosage; recovery decreased progressively with reduced renal function.

Biliary excretion of amoxycillin and ceftriaxone after intravenous administration in man

1 Plasma and biliary concentrations of amoxycillin and ceftriaxone were measured after bolus intravenous administration (500 mg) in four subjects with normal hepato-biliary and renal function. 2 The mean plasma elimination half-life for ceftriaxone (t 1/2 = 330 +/- 30 min) was considerably longer than that for amoxycillin (t 1/2 = 60 +/- 9 min). 3 The biliary concentration of ceftriaxone was above plasma concentration of the drug throughout the study period, whereas amoxycillin concentration in the bile was lower than that in plasma. 4 Both plasma and biliary concentrations of ceftriaxone were substantially higher than previously determined minimum inhibitory concentration (MIC) values for E. coli (and several other common biliary tract pathogens) for over 6 h following drug administration. Amoxycillin concentration in plasma fell below MIC by 2 h, and did not reach inhibitory concentrations in bile.

[Studies on the pharmacokinetics of cefotaxime in neonates]

The pharmacokinetics of cefotaxime was investigated in neonates. The following results were obtained. 1. The peak serum concentration of cefotaxime, seen 15-minutes after a single intravenous of 20 mg/kg, was 51.6 +/- 9.3 mcg/ml by bioassay. After 6 hours the mean serum concentration decreased to 5.6 +/- 3.1 mcg/ml. Concentrations obtained by HPLC paralleled those determined by bioassay. The peak serum concentration of the desacetyl metabolite was attained 30 minutes to 2 hours after injection. The mean serum desacetyl metabolite concentration was about 1/2.5 times higher than the cefotaxime concentration. The half-life was inversely related to the age of the neonates, decreasing to 1.64 hours on day 11 postpartum. 2. Serum concentrations determined by bioassay and HPLC after administering a dose of 10 mg/kg of cefotaxime by 30-minute intravenous drip infusion were comparable. The peak serum concentration at the completion of intravenous drip infusion was 21.0 mcg/ml by bioassay. The half-life of cefotaxime was 2.85 hours. The peak serum concentration of the desacetyl metabolite, seen at the completion of intravenous drip infusion, was about 1/2 times that of the peak cefotaxime concentration. 3. The peak serum concentration at the completion of a 30-minute intravenous drip infusion of 20 mg/kg displayed a mean value of 33.5 +/- 10.3 mcg/ml by bioassay. After 6 hours the mean serum concentration was 4.0 +/- 1.0 mcg/ml. The peak serum concentration of the desacetyl metabolite, seen at the completion of infusion to 2 hours thereafter, was equivalent to about 1/2.2 the peak cefotaxime concentration. 4. Mean urinary excretion rate of cefotaxime in 2-day-old neonates was 23.4% by bioassay 6 hours after a 30-minute intravenous drip infusion of 10 mg/kg. The mean urinary excretion rate of the desacetyl metabolite was 8.7%. Mean 6-hour excretion rates in 2-day-old and 4-day-old neonates administered 20 mg/kg of cefotaxime by 30-minute intravenous drip infusion were 6.2% and mean 37.7%, respectively. The corresponding values for the desacetyl metabolite were 2.4% and 12.4%, respectively.