Determination of cefetamet and its orally active ester, cefetamet pivoxyl, in biological fluids by high-performance liquid chromatography

Whole blood stability in quantitative bioanalysis

Establishing stability at all stages of a sample’s lifespan is a critical part of performing regulated bioanalysis. For plasma assays, this includes the duration between when blood is drawn and when that blood is centrifuged to produce plasma. Here, we provide a discussion of current regulatory expectations around whole blood stability testing for LC–MS plasma assays, as well as the two primary experimental approaches utilized to assess whole blood stability. Next, we interrogated a large dataset of validated methods (1076 methods, the vast majority of which were for measurement of small molecules) to assess the correlation between whole blood and plasma stability profiles, finding them to be highly correlated. Finally, we summarize unique case studies; we have encountered during WB stability testing which offer lessons that may be broadly applicable.

Factors affecting the stability of drugs and drug metabolites in biological matrices

Evaluation of the stability of drugs and drug metabolites in a biological matrix is a critical element to bioanalytical method validation. It is critical to understand the most common factors that affect the stability of such analytes in order to properly develop methods for their detection and measurement. The degradation of drugs and drug metabolites in samples can occur through either reversible or irreversible processes. Common factors that affect this stability include temperature, light, pH, oxidation and enzymatic degradation. Special considerations are also required when dealing with chiral molecules, deuterated internal standards and large biomolecules. Relevant examples of these degradation effects and approaches for dealing with them are presented is this review as taken from the fields of pharmaceutical testing, clinical research and forensic analysis. It is demonstrated through these examples how an understanding of the chemical and physical factors that affect sample stability can be used to avoid stability problems and to create robust and accurate methods for the analysis of drugs and related compounds.

Stabilizing Drug Molecules in Biological Samples

Stability is one of the basic parameters, along with accuracy, precision, selectivity, and sensitivity, for bioanalytic method validation in nonhuman and clinical pharmacology/toxicology, bioavailability (BA), bioequivalence (BE), and other studies related to the drug approval process. In the drug development stage where stability evaluation is obligatory, instability of drug candidates in biologic samples will seriously complicate assay validation. In this article, we review the general strategies and methodologies such as temperature adjustment, pH control, derivatization, and addition of inhibitors and oxidant that are commonly employed to stabilize pharmaceuticals that might be unstable in biologic samples.

The influence of pH, temperature and buffers on the degradation kinetics of cefetamet pivoxil hydrochloride in aqueous solutions

The first-order hydrolysis kinetics of cefetamet pivoxil (CP) were investigated as a function of pH, temperature and buffers. The degradation was followed by HPLC. Buffer catalysis was observed in acetate and phosphate buffers. The pH-rate profiles for hydrolysis of cefetamet pivoxil were obtained at 333, 343, 353 and 363K. The pH-rate expression was k(pH)=kH+aH+ + kH2OkOH-aOH-, where kH+ and kOH- are the second-order rate constants (mol(-1)ls(-1)) for hydrogen ion activity and for hydroxyl ion activity respectively, and kH2O is the pseudo-first-order rate constant (s(-1)) for spontaneous reaction under the influence of water. The pH-rate profile was characteristically U-shaped. Maximum stability was observed in the pH region from 3 to 5.

LC method for the analysis of cefetamet pivoxil hydrochloride in drug substance and powder for oral suspension

A high-performance liquid chromatography isocratic procedure was developed for the assay of cefetamet pivoxil hydrochloride in drug substance and powder for oral suspension. The method validation yielded good results and included the range, linearity, precision intra- inter-day, accuracy, specificity, LOD and LOQ values. The chromatographic system consisted of a C(18) absorbosphere column (150 x 4.6 mm i.d., 5 microm particle size), a mobile phase composed of water-acetonitrile-methanol-phosphate buffer, pH 3.5 (50:35:10:5, v/v), flow rate of 1.5 ml min(-1) and UV detection at 254 nm. The relative standard deviation varied between 0.03 and 1.76%, and accuracy of 100.09% was found. Calibration curve was linear from 30.0-80.0 microg ml(-1); its correlation coefficient was 0.99989.

Analysis of recent antimicrobial agents in human biological fluids by high-performance liquid chromatography

Our previous review on the liquid chromatographic (LC) analysis of anti-bacterial agents was published in 1990 in a special issue of the Journal of Chromatography. Eight years later, some new agents have been registered and numerous other are under clinical experiment. In spite of therapeutic problems encountered with certain bacterial pathogens, the development of novel drug candidates has slowed partially due to the need for identification of new bacterial targets and the cost of the research. The present overview updates the LC methods for the quantitations of recent antimicrobial agents (marketed and in clinical development) in human biological fluids. Consideration has been given to procedures permitting the determination of isomers and metabolites as well as methods regarding tissue extracts or liquid sampled from physiological sanctuaries. LC methods are available for the quantitation of almost all registered or investigated recent anti-infective drugs and some are applicable in routine practice. Nevertheless, few techniques have been validated for the determination in tissue extracts limiting the development of penetration studies.

Determination of third-generation cephalosporins by high-performance liquid chromatography in connection with pharmacokinetic studies

The third-generation cephalosporins are semisynthetic beta-lactam antibiotics, including several oral and parental agents with extended activity against Gram-negative pathogens. They are generally determined either by microbiological techniques or by high-performance liquid chromatography (HPLC). The major drawback or bioassays is the lack of specificity, especially when a biotransformation of the cephalosporin molecule leads to active metabolites, or when the antibacterial therapy is based on association with drugs. Thus, for many years, numerous reversed-phase HPLC procedures have been proposed to overcome these difficulties. This review presents different HPLC methods proposed for the quantification in biological fluids of fourteen third-generation cephalosporins, ranged between parenteral and oral compounds. The sensitivity and specificity of these chromatographic procedures are discussed with regard to the pharmacokinetic properties of the antibiotics studied.

Penetration of cefetamet pivoxil and cefuroxime axetil into the maxillary sinus mucosa at steady state

The penetration of cefetamet and cefuroxime into the maxillary sinus mucosa after the administration of cefetamet pivoxil and cefuroxime axetil was investigated in patients undergoing elective surgery of the maxillary sinus. A total of 27 patients, 13 for cefetamet pivoxil and 14 for cefuroxime axetil, ranging from 15 to 70 years of age participated in this study. Each patient received three oral doses of either one tablet of cefetamet pivoxil (500 mg of GLOBOCEF) or two film tablets of cefuroxime axetil (125 and 250 mg of ZINAT) every 12 h. Sinus mucosa tissue samples were removed during surgery at times ranging from 2 to 4.5 h after the last oral administration. Blood samples were collected before drug administration, 2 h after the first and third doses, and concomitantly with tissue sample collection during surgery. All samples were analyzed by high-performance liquid chromatography. The concentrations of cefetamet and cefuroxime in plasma samples measured concomitantly with those in tissue samples ranged between 0.83 and 4.5 micrograms/ml for cefetamet and 0.59 and 3 micrograms/ml for cefuroxime. The mean tissue-to-plasma ratios calculated with reference to total (bound plus unbound) plasma drug concentrations were 0.60 (range, 0.52 to 0.77) for cefetamet (n = 4) and 0.38 (range, 0.28 to 0.44) for cefuroxime (n = 6). Both drugs seem to penetrate freely and easily into the sinus mucosa. The antibacterial activities of cefetamet pivoxil and cefuroxime axetil in cases of sinusitis therefore depend mainly on their achieved active plasma drug concentrations and their intrinsic activities in inhibiting the causative organism(s).

Influence of maturation and growth on cefetamet pivoxil pharmacokinetics: rational dosing for infants

The pharmacokinetics of intravenous (i.v.) cefetamet and the bioavailability of oral cefetamet pivoxil in infants aged 3.5 to 17.3 months who were hospitalized for urological surgery were characterized. The absorption of cefetamet pivoxil administered in a syrup formulation was 38 +/- 19% (n = 5) for infants, which was comparable to values observed for children and adults. The plasma half-life of i.v. cefetamet was 3.03 +/- 0.96 h (mean +/- standard deviation; n = 20) in the infants. This was not different from the value observed for normal adult subjects but was longer than that reported for children aged 3 to 12 years. Urinary recovery of cefetamet after i.v. administration to infants was 63.4 +/- 17.7% (n = 16), which was less than the 80% recovery found in older children and adults. The steady-state volume of distribution was 399 +/- 116 ml/kg of body weight. It was comparable in size and showed the same dependence on body weight as it did in children and adults. The mean systemic clearance per kilogram of body weight in the infants was lower than that in children and adults, apparently because of immaturity of clearance processes. A model that accounted for maturation and growth with increasing age was developed for the clearance. On the basis of this model, the clearance capacity increased from birth to 5 years by a factor of 4.5 because of maturation. Maturation progressed exponentially, with a half-life of 14 months. This model was used to develop dosing regimen guidelines for pediatric patients aged 3.5 months and older.

Pharmacokinetics of cefetamet in plasma and skin blister fluid

Cefetamet pivoxil is an oral cephalosporin with enhanced affinity for the target penicillin-binding proteins 1 and 3 and an increased stability to beta-lactamases compared with older cephalosporins, such as cefalexin or cefaclor. The pharmacokinetics of cefetamet pivoxil was determined after the seventh and final dose of 500 mg of cefetamet pivoxil in eight healthy volunteers. Concentrations in plasma and cantharidin-induced skin blister fluid were determined by a high-performance liquid chromatography method. In addition, protein binding was assessed. Cmax was 4.8 +/- 1.7 micrograms/ml in skin blister fluid and 5.1 +/- 2.1 micrograms/ml in plasma. Tmax was delayed in skin blister fluid compared with plasma (3.9 +/- 1 versus 2.8 +/- 0.8 h; P < 0.001), and t1/2 was longer in skin blister fluid than in plasma (3.1 +/- 0.5 versus 2.3 +/- 0.3; P < 0.005). The mean percent penetration into cantharide blister fluid was 129% +/- 24% when measured as total drug and 149% +/- 28% when measured as free drug (P < 0.001). These data suggest that cefetamet has an excellent penetration into inflammatory interstitial fluid.

Bioavailability of syrup and tablet formulations of cefetamet pivoxil

Two studies examining the bioavailability of cefetamet pivoxil in healthy male subjects were conducted. In the first, the bioavailabilities of the 250-mg (M250) and M500 tablet formulations of cefetamet pivoxil to be marketed were compared with that of a tablet used in clinical trials. All products were given with food at a dose of 500 mg. In the second study, the bioavailability of the syrup formulation was evaluated under both fasting and nonfasting conditions and compared with that of the M500 tablet formulation given with food. The absolute bioavailabilities of the M500 and M250 tablets (55.0% +/- 8.0% and 55.7% +/- 7.0%, respectively) were not significantly different from that of the clinical-trial formulation (49.8% +/- 8.5%). The newer tablet formulations exhibited faster absorption as evidenced by higher peak concentrations (3.8 [M500] and 3.9 [M250] mg/liter compared with 3.2 mg/liter for the clinical-trial formulation), a shorter time to peak concentration, and a shorter mean absorption time. The syrup formulation was found to have significantly lower absolute bioavailability (37.9% +/- 6.0%) compared with that of the M500 tablet (58.4% +/- 9.0%) when both were given with food. Food had no significant effect on the bioavailability of the syrup, which averaged 34.0% +/- 8.6% under fasting conditions, although absorption was delayed by food (mean absorption time increased from 2.2 to 3.9 h). This contrasts with the results of previous studies documenting significant increases in tablet bioavailability with food. Despite the lower bioavailability of the syrup, unbound-cefetamet concentrations are expected to remain above the MICs for 90% of the strains tested for susceptible organisms for approximately 10 h of the usual 12-h dosing interval with both syrup and tablet formulations of cefetamet pivoxil given with food.

Models for describing absorption rate and estimating extent of bioavailability: application to cefetamet pivoxil

Five absorption rate models have been compared for describing cefetamet data in 34 adults after oral administration of cefetamet pivoxil with food alone or in combination with either an antacid or an H2 antagonist. A sequential zero- then first-order input process provided the most flexible description of the absorption rate of cefetamet. If the first-order rate constant is linked to the zero-order input parameters the model can be interpreted as the consequence of solubility-limited absorption. While a sequential input is theoretically reasonable to assume, the first-order process appeared to be independent of the zero-order input. A population-based approach was applied to estimate the effect of dose and gastric pH increase on absorption and disposition. There appeared to be a dose-associated change in several parameters. The most marked change was an increase in volume of distribution of cefetamet. Treatments expected to increase gastric pH slowed the first-order component of the absorption process. Three models for estimating the extent of bioavailability have been compared using observations from 18 adults and 13 children receiving iv cefetamet and oral cefetamet pivoxil on two separate occasions. The most consistent estimates of the disposition parameters and the extent of bioavailability were achieved with the sequential zero- and first-order model under the assumption that steady state volume of distribution and nonrenal clearance were the same after iv and oral treatment.

Effects of cefetamet (Ro 15-8074) on Treponema pallidum and experimental syphilis

Cefetamet pivoxil (Ro 15-8075) is a newly developed, expanded-spectrum cephalosporin that is orally active. In vitro, the active form, cefetamet (Ro 15-8074), at a concentration of 0.05 micrograms/ml killed and lysed Treponema pallidum. Rabbit serum did not diminish its effectiveness. The antibiotic rapidly entered the circulation following intramuscular injection into rabbits, attaining its highest levels of 24 to 37 micrograms/ml within 10 to 30 min. Animals were infected intradermally with T. pallidum and then treated with different doses of cefetamet. Accelerated healing was detected following treatment with 15 and 30 mg/kg of body weight. The antibiotic was also effective in killing organisms that had disseminated to distant tissues. In three separate sets of experiments, rabbits were infected with treponemes and then treated with cefetamet intramuscularly at 1, 15, or 30 mg/kg as follows: (i) after lesions had just become clinically apparent, (ii) after lesions were enlarged and well developed, or (iii) prior to the appearance of clinical lesions. Antibiotic effectiveness was determined by sacrificing the animals 1 week after antibiotic treatment and examining splenic tissue for residual, disseminated treponemes. Cefetamet was treponemicidal in all three situations. Maximum effects occurred when the antibiotic was injected before lesions had become clinically apparent (incubation period). These results suggest that cefetamet pivoxil might be useful for treating syphilitic infections.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in children

The pharmacokinetics of cefetamet were determined after intravenous (i.v.) administration of cefetamet and oral administration of cefetamet pivoxil syrup to patients between the ages of 3 and 12 years. The patients were hospitalized for reconstructive urological surgery; to prevent infection, prophylactic i.v. cefetamet was administered on the day of surgery and oral cefetamet pivoxil was administered 2 days later. After i.v. administration, the mean (+/- standard deviation) half-life of cefetamet was 1.97 +/- 0.60 h (n = 18), which was different from the 2.46 +/- 0.33 h reported for nine adults (22 to 68 years old) in a previous study. The average values for the mean residence times were 2.35 +/- 0.94 and 2.83 +/- 0.34 h and the average values for the fraction of the dose eliminated unchanged in the urine were 79.9% +/- 8.99% and 80% +/- 11% in children and adults, respectively. Plots of mean systemic clearance and steady-state volume of distribution versus body weight for the children and comparative adults were linear on log-log coordinates, and the slopes of the plots were 0.661 and 0.880, respectively. These slope values suggested that mean systemic clearance values per unit of body surface area were similar in children and adults and that maintenance doses for children should be the adult maintenance dose multiplied by the child's surface area divided by 1.73 m2. The mean (+/- standard deviation) oral bioavailabilities of cefetamet pivoxil were 49.3% +/- 15.7% in 3- to 7-year-old children who received a 500-mg dose and 37.9% +/- 10.0% in 8- to 12-year-old children who received a 1,000-mg dose. These values were not different from that observed in the adult group after two 500-mg tablets. Likewise, the peak concentration of cefetamet in plasma and its time of occurrence in children were in line with the values which have been observed for adults.

High-performance liquid chromatography of antibiotics

High-performance liquid chromatographic (HPLC) monitoring of antimicrobial agents has recently become more widely used, and represents an interesting alternative to other methods. The methodology is characterized by good specificity and accuracy, and it is applicable to almost all antibiotics. This review first describes the successive steps to investigate for the development of an HPLC method for a new antibiotic, and how to make use of it. Particular emphasis is put on the problems related to the standardization of sample preparation and to the development of mobile phases for use with different molecules belonging to the same class. The second part of the review describes one or more HPLC techniques for a representative antibiotic of each major class.

Influence of antacid and ranitidine on the pharmacokinetics of oral cefetamet pivoxil

The purpose of this investigation was to assess the influence that treatment with antacid and ranitidine had on the pharmacokinetics of oral cefetamet pivoxil in 18 healthy male volunteers. Each subject received, in an open-labeled, randomized, three-way crossover design, a single oral dose of 1,000 mg (two tablets) of cefetamet pivoxil 10 min after a standard breakfast during each of the following treatments: treatment A, control period; treatment B, antacid (80 ml of suspension; Maalox 70) administered on the evening before cefetamet pivoxil dosing (-12.5 h) and again 2 h before and 2 h after a standard breakfast; treatment C, ranitidine (150 mg) administered twice a day for 4 days and again 1 h and 10 min prior to cefetamet pivoxil dosing. Plasma and urine samples were collected over a 24-h period following cefetamet pivoxil administration. Cefetamet was analyzed by high-performance liquid chromatography. Oral bioavailability parameters (area under the concentration-time curve from 0 to 12 h, area under the concentration-time curve from 0 h to infinity, time to maximum concentration of drug in plasma, and maximum concentration of drug in plasma) were obtained by noncompartmental techniques. The results showed that none of these bioavailability parameters was significantly (P greater than 0.05) affected by antacid or rantidine coadministration. A compartmental analysis showed no significant differences. In addition, the terminal elimination half-life and the fraction of cefetamet excreted unchanged in the urine was also not significantly (P greater than 0.05) affected by antacid or ranitidine exposure. Relatively wide intrasubject variability was observed for time to maximum concentration of drug in plasma and terminal elimination half-life in several of the 18 subjects studied. Although these irregularities did not appear to be strongly associated with a particular treatment, they increased in subjects in both the antacid and H2-receptor antagonist treatment groups compared with those in subjects in the control treatment group. We conclude that antacid and ranitidine treatment likely does not alter the bioavailability of oral cefetamet pivoxil.

Effects of timing of food and fluid volume on cefetamet pivoxil absorption in healthy normal volunteers

Cefetamet pivoxil (1,000 mg orally) absorption was evaluated in 16 male subjects (age, 23.4 +/- 1.7 years; weight, 73.9 +/- 7.0 kg) 1 h before (BE), with (WI), and 1 h after (AF) a standard breakfast. The time to peak concentration of cefetamet in plasma (Tmax) was increased from 3.25 +/- 1.44 h in the BE group to 4.31 +/- 1.54 and 4.13 +/- 1.54 h in the WI and AF groups, respectively (P less than 0.05). The maximum cefetamet concentration in plasma (Cmax) and the area under the plasma cefetamet concentration-time profiles (AUC) in the BE, WI, and AF groups were 5.50 +/- 1.06, 5.47 +/- 1.4, and 6.57 +/- 0.93 micrograms/ml and 38.2 +/- 10.1, 35.7 +/- 11.9, and 42.8 +/- 6.8 micrograms.h/ml, respectively. The Cmax and AUC values were not different between the BE and WI groups (P greater than 0.05). However, differences in these values were found between the WI and AF groups (P less than 0.05). The effect of fluid volume intake on cefetamet pivoxil (1,000 mg orally) absorption was evaluated in 12 male subjects (age, 23.8 +/- 2.3 years; weight, 74.9 +/- 9.0 kg) under fasted and WI conditions. Increasing fluid volume intake from 250 to 450 ml under the fasted condition had no effect on the absorption of the prodrug (Tmax, 2.50 +/- 0.52 versus 2.83 +/- 0.94 h; Cmax, 4.89 +/- 1.04 versus 4.84 +/- 0.89 micrograms/ml; AUC, 29.6 +/- 5.1 versus 30.7 +/- 7.1 micrograms.h/ml; P greater than 0.05. Thus, independent of fluid volume intake, cefetamet pivoxil absorption is enhanced when it is given within 1 h of a meal, and it is recommended that the prodrug should be taken during this period of increased bioavailability.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in patients with hepatic cirrhosis

The pharmacokinetics of orally administered cefetamet pivoxil and intravenously administered cefetamet were studied in 12 healthy subjects and 12 patients with hepatic cirrhosis without ascites. Cirrhosis had no detectable effect on the pharmacokinetics of cefetamet and on the bioavailability of cefetamet pivoxil. After intravenous cefetamet in control versus cirrhotic subjects, respectively, the following mean +/- standard deviation values were observed: total body clearance, 128 +/- 10.2 versus 123 +/- 28.8 ml/min; steady-state volume of distribution, 23.2 +/- 2.2 versus 22.7 +/- 4.6 liters; half-life, 2.42 +/- 0.21 versus 2.35 +/- 0.41 h. Renal and nonrenal clearances of cefetamet were similar in both groups, as were the mean residence times and areas under the plasma concentration-time curve. For oral cefetamet pivoxil, no differences were detected in the mean values of the percentage of dose absorbed: 44.6 +/- 9.1 versus 50.1 +/- 12.9. The rate of appearance of cefetamet in the plasma also was not affected by cirrhosis: similar mean values were found for the mean residence time and the maximum concentration in plasma and its time of occurrence.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in patients with renal insufficiency

The pharmacokinetics of cefetamet after a short intravenous infusion of cefetamet (515 mg) and oral administration of 1,000 mg of cefetamet pivoxil were studied in 9 healthy subjects and in 38 patients with various degrees of renal impairment. The results showed that cefetamet elimination was dependent on renal function. After intravenous dosing, total body (CLS), renal (CLR), and nonrenal (CLNR) clearances were linearly related to creatinine clearance (CLCR; r = 0.95, 0.92, and 0.59, respectively). Elimination half-life (t1/2 beta) was prolonged from 2.46 +/- 0.33 h in normal subjects to 29.1 +/- 13.9 h in patients with CLCR of less than 10 ml/min per 1.73 m2. Correspondingly, CLS and CLR decreased from 1.77 +/- 0.27 and 1.42 +/- 0.25 ml/min per kg to 0.14 +/- 0.04 and 0.04 +/- 0.03 ml/min per kg, respectively. The volume of distribution at steady state (0.298 +/- 0.049 liter/kg) for cefetamet was not altered by renal insufficiency (P greater than 0.05). After oral administration, the elimination parameters, t1/2 beta and CLR, were insignificantly different from the intravenous data (P greater than 0.05). Furthermore, the bioavailability (F) of cefetamet pivoxil (45 +/- 13%) was not altered by renal failure (P greater than 0.05). However, maximum concentration in plasma and the time to achieve this value were significantly increased (5.86 +/- 0.74 versus 14.8 +/- 6.14 micrograms/ml and 3.9 +/- 1.1 versus 8.4 +/- 1.7 h, respectively; P less than 0.05). Based on these observations, it is recommended that patients with CLcr of <10 ml/min per 1.73 m2 and between 10 and 39 ml/min per 1.73 m2 be given one-quarter of the normal daily dose either once or twice daily. Patients with CLcr between 40 and 80 ml/min per 1.73 m2 should receive one-half of the normal dose twice daily. For patients with CLcr of <10 ml/min per 1.73 m2, it would be recommended that they receive a normal standard dose as a loading dose on day 1 of treatment.

Pharmacokinetics of cefetamet pivoxil (Ro 15-8075) with ascending oral doses in normal healthy volunteers

The pharmacokinetics of cefetamet pivoxil during administration of ascending oral doses were studied in 16 male normal healthy volunteers (age, 24.5 +/- 2.1 years; weight, 73.5 +/- 8.5 kg). The subjects were randomly assigned to four oral treatments of 500, 1,000, 1,500, and 2,000 mg of cefetamet pivoxil according to a four-by-four Latin square design. After an overnight fast, the drug was administered 10 min after a standard breakfast. It was found that both the rate and extent of prodrug absorption, measured as cefetamet adsorption, were reduced with increasing doses. The time to maximum concentration of cefetamet in serum was delayed from 4.00 +/- 0.81 to 4.88 +/- 0.96 h (P less than 0.05) when the dose of cefetamet pivoxil was increased from 500 to 2,000 mg. The dose-normalized values of area under the curve from 0 h to infinity for cefetamet and fraction of dose excreted as cefetamet were reduced by averages of 10.3 and 12.5%, respectively, over the dose range studied (P less than 0.05). The changes in rate and extent of prodrug absorption are thought to be the main factors contributing to the nonlinear relationship between maximum concentration in serum and dose. The change in absorption characteristics of cefetamet pivoxil with dose is, however, expected to have few clinical consequences because the magnitudes of these changes are comparable with their respective intragroup variations.

Pharmacokinetics of intravenous cefetamet (Ro 15-8074) and oral cefetamet pivoxil (Ro 15-8075) in young and elderly subjects

The purpose of this investigation was to evaluate the effect of advanced age on the pharmacokinetics of cefetamet and its prodrug, cefetamet pivoxil. A secondary objective of this study was to assess the effect of food on the absorption of cefetamet pivoxil in the elderly. Twenty-four healthy subjects (twelve young and twelve elderly) received (in a Latin square design) a single-dose, 515-mg infusion of cefetamet, a single 1,000-mg oral dose of cefetamet pivoxil during fasted conditions, and a single 1,000-mg oral dose of cefetamet pivoxil 10 min after a standardized low-fat breakfast. Serial blood and urine samples were collected over a 36-h period and analyzed by high-performance liquid chromatography. Intravenous and oral pharmacokinetic parameters were obtained by using model-independent techniques. The systemic clearance and renal clearance of cefetamet were significantly lower (P less than 0.05) in elderly subjects compared with in young controls after intravenous administration. No significant difference was observed in the apparent volumes of distribution at steady state between the two groups. Consequently, half-life and mean residence time were prolonged. A trend toward a lower renal clearance/creatinine clearance ratio was observed in our elderly population. Oral clearance of cefetamet was only slightly reduced in our elderly subjects, consistent with an increase in plasma half-life. Otherwise, oral pharmacokinetic parameters were comparable between elderly and young subjects. Additionally, the same effects of food were observed on the absorption characteristics of cefetamet (no change in maximum concentration of drug in plasma and an increase in both time to maximum concentration of drug in plasma and bioavailability) in our elderly subjects as in our young volunteers. Age did not appear to alter the deesterification and bioavailability of cefetamet pivoxil. We conclude that the small reduction in the elimination of cefetamet in the elderly would not require dose adjustment for this population.