Pharmacokinetics of oral cefetamet pivoxil (Ro 15-8075) and intravenous cefetamet (Ro 15-8074) in humans: a review

Design, synthesis, and evaluation of prodrugs of ertapenem

Carbapenems are intravenous lifesaving hospital antibiotics. Once patients leave the hospital, they are sent home with antibiotics other than carbapenems since they cannot be administered orally due to lack of oral absorption primarily because of very highly polarity. A prodrug approach is a bona fide strategy to improve oral absorption of compounds. Design and synthesis, in vitro and in vivo evaluation of diversified prodrugs of ertapenem, one of the only once daily dosed carbapenems is described. Many of the prodrugs prepared for evaluation are rapidly hydrolyzed in rat plasma. Only bis-(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (medoxomil) ester prodrug was rapidly hydrolyzed in most of the plasmas including rat, human, dog, and monkey. Although the rate of conversion of ertapenem diethyl ester prodrug (6) was slow in in vitro plasma hydrolysis, it showed the best in vivo pharmacokinetic profile in dog by an intraduodenal dosing giving >31% total oral absorption.

Intestinal absorption mechanism of tebipenem pivoxil, a novel oral carbapenem: involvement of human OATP family in apical membrane transport

Tebipenem pivoxil (TBPM-PI) is an oral carbapenem antibiotic for treating otolaryngologic and respiratory infections in pediatric patients. This agent is a prodrug to improve intestinal absorption of TBPM, an active form, and an absorption rate of TBPM-PI is higher than those of other prodrug-type β-lactam antibiotics. In the present study, we hypothesized that a certain mechanism other than simple diffusion is involved in the process of improved intestinal absorption of TBPM-PI and examined the mechanism. TBPM-PI uptake by Caco-2 cells was decreased by ATP-depletion and lowering the temperature to 4 °C, suggesting the contribution of carrier-mediated transport mechanisms. This uptake was partially decreased by ACE inhibitors, and the reduction of the absorption by captopril was observed by in vivo study and in situ single-pass intestinal perfusion study in rat, supporting the contribution of influx transporters. Since some ACE inhibitors and β-lactam antibiotics are reported to be substrates of PEPT and OATP families, we measured transporting activity of TBPM-PI by intestinally expressed transporters, PEPT1, OATP1A2, and OATP2B1. As a result, significant transport activities were observed by both OATP1A2 and OATP2B1 but not by PEPT1. Interestingly, pH dependence of TBPM-PI transports was different between OATP1A2 and OATP2B1, showing highest activity by OATP1A2 at pH 6.5, while OATP2B1-mediated uptake was higher at neutral and weak alkaline pH. OATP1A2 exhibited higher affinity for TBPM-PI (K(m) = 41.1 μM) than OATP2B1 (K(m) > 1 mM) for this agent. These results suggested that TBPM-PI has high intestinal apical membrane permeability due to plural intestinal transport routes, including the uptake transporters such as OATP1A2 and OATP2B1 as well as simple diffusion.

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.

A dose ranging study of the pharmacokinetics, safety, and preliminary efficacy of lamivudine in children and adolescents with chronic hepatitis B

Fifty-three patients with chronic hepatitis B and active viral replication were studied for 4 weeks while on treatment and for 12 weeks after treatment with the oral nucleoside analogue lamivudine. Children aged 2 to 12 years were randomized to receive twice-daily doses of 0.35, 1.5, or 4 mg of lamivudine solution per kg of body weight or once-daily doses of 3 mg of lamivudine solution per kg. Adolescents aged 13 to 17 years received lamivudine at 100 mg (as tablets). Blood samples for pharmacokinetic assay were taken on days 1 and 28. Lamivudine was rapidly absorbed following oral administration, with the maximum concentration in serum being reached 0.5 to 1 h postdosing. Apparent oral clearance (CL/F) was higher in younger children and decreased with age, with CL/F values for adolescents reaching those seen for adults by the age of 12. All doses produced a dramatic fall in serum hepatitis B virus (HBV) DNA levels, with a median reduction of >/=99.5% after 4 weeks of treatment and with the levels returning to the baseline levels posttreatment. The correlation of dose, area under the concentration-time curve (AUC), and changes in HBV DNA levels, as measured by the Chiron Quantiplex assay, showed maximal antiviral effects (99.9% inhibition and a reduction of the amount of HBV DNA of approximately 3 log(10)) at 3 mg/kg/day, with no discernible increase in effect seen whether the drug was given at 4 mg/kg twice daily or whether it was given once daily or twice daily. The limit of detection of the assay (2.5 pg/ml) was reached for some but not all patients across the dose ranges, with the smallest number (n = 2) of those having values negative by the Chiron Quantiplex assay being in the lowest-dose group. The 13- to 17-year-olds showed a similar overall response in terms of the HBV DNA level reduction compared to that for patients younger than age 13. Analysis of the same samples by PCR, which has a lower limit of sensitivity than the Chiron Quantiplex assay, also showed average drops in HBV DNA levels of about 3 log(10) at 4 weeks for patients for which the AUC was >/=4,000 ng. h/ml, confirming the conclusions given above. Lamivudine treatment was well tolerated at all doses, with no significant adverse events or laboratory data changes. On the basis of pharmacokinetic and pharmacodynamic data, a 3-mg/kg/day dose in children (ages 2 to 12 years) with chronic hepatitis B provides levels of exposure and trough concentrations similar to those seen in adults following the receipt of doses of 100 mg. The 100-mg dose is being evaluated in a large phase III study with HBV-infected pediatric patients.

The use of esters as prodrugs for oral delivery of beta-lactam antibiotics

It is apparent that the sequence of events that has been followed in the approach to the discovery and development of a new beta-lactam prodrug has been similar in many of the case histories we have studied and indeed similar to the approach we have followed. Initially, we select a suitable series of prodrug moieties, which either comprises totally novel structures or is deduced from the data bases available (bearing in mind reports of potential toxicity) or both. The successful preparation of these prodrugs and the studies undertaken to ensure they are of known purity and stability is not easy and, as would be expected, is the initial go/no-go decision. Usually, the next stage has involved the assessment of whether or not bioavailability of the parent molecule is increased after administration of the prodrug ester by gavage to laboratory animal species. The selection of which species to use has very often been made according to which has the most information available in those particular laboratories and in the literature. It is this process that can be dishearteningly misleading as was demonstrated in Table IV and Fig. 1. Increasing the range of animal species does not lead to a better ability to predict bioavailability in humans. Hydrolysis studies are important to ensure that any novel prodrug will hydrolyze in human tissues, and also in the clarification of why a particular prodrug is not performing as expected in animals. After selection, it is essential to determine where and how rapidly hydrolysis takes place in the animal species to be used for safety evaluation prior to the first bioavailability studies in humans. The assessment of absolute oral bioavailability has not always been undertaken. This would seem critical for studies in not only the selected animal species but also in humans. In the absence of these data it is difficult to judge whether oral uptake can be increased further by modifying the ester moieties and at the development stage to determine whether or not modifications in formulation could increase bioavailability. When the prodrug is being developed for an injectable beta-lactam already available for humans, there would be no problem, but it would be an important consideration during the development of an entirely novel beta-lactam antibiotic for which no parenteral data are available in humans. Animal data are not totally predictive. The development of prodrugs is not easy, as a consequence of species differences in the properties of the prodrug superimposed on those of the parent compound during the evaluation. However, technical advances have enabled us to assay concentrations more precisely, determine basic physicochemical properties more efficiently, understand absorption processes by the use of in vitro systems, and analyze data far more comprehensively by the use of ever-evolving computer software. The prodrug approach to increasing the oral bioavailability of beta-lactam antibiotics has provided clinically valuable agents and continues. Despite the inherent difficulties, knowledge gained over the years, of the relationships between physicochemical and biological properties of the parent compound and the intact prodrug ester, has contributed to the design of novel prodrugs and a number of novel auxiliaries have been developed.

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.

Pharmacokinetics of loracarbef and interaction with acetylcysteine

A study was conducted to evaluate the pharmacokinetics of loracarbef, a new synthetic oral carbacephem antibiotic, following administration of 400 mg in normal male volunteers. The influence of food and possible interaction with acetylcysteine, a commonly used mucolytic agent, was also studied. Twelve healthy volunteers participated in the study and randomly received an oral dose of 400 mg loracarbef in the fasting state, 400 mg loracarbef following a standard breakfast or 400 mg loracarbef together with 200 mg acetylcysteine in granular form. Serum and urine concentrations were determined over 24 h by means of a bioassay. Loracarbef was well tolerated. Four volunteers complained of mild, transient headache. The substance was well absorbed with a mean peak level of 19.21 +/- 3.94 mg/l in the fasting state; it was primarily excreted in active form via the kidneys (urine recovery/24 h: 86-92%). The elimination half-life ranged from 70.3 to 102.0 min. Acetylcysteine had no effect on the absorption of loracarbef. The intake together with food delayed the absorption time, but had no influence on the bioavailability.

Future directions in antimicrobial chemotherapy

New developments in the treatment of bacterial infections are discussed. The most important developments include oral broad-spectrum cephalosporin derivatives and extended-spectrum injectable cephalosporins with improved activity against Gram-positive bacteria. Meropenem is a new carbapenem agent with markedly improved activity against Gram-negative bacteria. Many fluoroquinolones are in various phases of development. The most interesting new compound is sparfloxacin. Azithromycin is a new macrolide which, because of its very long half-life, attains very high levels in most tissues. Potential uses of the newer agents are discussed.

Pharmacokinetics of newer drugs in patients with renal impairment (Part I)

Many drugs are eliminated via the renal route and the usual dose must be modified in patients with severe renal impairment. This review is an attempt to supply physicians with the more recent data on pharmacokinetic studies of new drugs administered in uraemic patients. The review is in 2 parts: the first indicates the results of studies on the pharmacokinetics of antibiotic agents, antifungal, antiviral and antiulcer drugs, and nonsteroidal anti-inflammatory drugs. Special mention is made of epoetin (recombinant human erythropoietin). It was not possible to give all the information collected from the recent literature: since mild renal failure has little effect on the fate of a drug, pharmacokinetic data obtained in patients with a creatinine clearance (CLCR) of more than 50 ml/min has been omitted. Both the text and tables give recommendations for treating patients with moderate renal insufficiency (CLCR of about 50 ml/min), more severe renal impairment (CLCR between 10 and 50 ml/min) and end-stage renal failure with a very low creatinine clearance (below 10 ml/min). It was not possible to give uniform recommendations (i.e. reducing the dose while maintaining the same interval, or giving the same dose and prolonging the interval). This article follows the recommendations of the authors, which may vary for drugs in similar classes.

Cefetamet in the treatment of acute sinusitis in adult patients

Cefetamet, an oral third-generation cephalosporin, was investigated in a prospective, randomized, open, comparative trial in 41 outpatients with acute sinusitis. The efficacy of 500 mg cefetamet given orally twice daily for 7 days to 22 patients was compared with that of 500 mg cefaclor given orally three times daily for 7 days to 19 patients. Sinus punctures were performed before antimicrobial therapy in 10 patients from each treatment group. A successful bacteriological response was obtained in all the 21 assessable patients treated with cefetamet and in the cefaclor-treated group 18 assessable patients were cured and two were improved, but one failed to respond to therapy. The tolerability of both drugs was good and no withdrawals from treatment were necessary.

[Pharmacokinetics of cefixime in volunteers and a literature comparison with the new ester prodrug cephalosporins]

The pharmacokinetic parameters of cefixime were determined in healthy volunteers following oral administration of 200 mg cefixime as tablet, syrup and dry suspension, respectively. All three galenic formulations showed reliable absorption. Mean peak plasma concentrations amounted to 2.4-3.4 mg/l and were reached after 3.3-3.5 h. Mean terminal half-lives were 2.9-3.1 h. The mean areas under the plasma concentration-time curves ranged between 18 and 26 mg/l.h; 18-24% of the dose administered were recovered unchanged in the urine. The best bioavailability was obtained with the dry suspension followed by the tablet and the syrup. With respect to the ester pro-drug cephalosporins, cefuroxime axetil, cefetamet pivoxyl and cefotiam hexetil, cefixime exhibits higher plasma half-life and area under the curve as well as, comparable absolute bioavailability but consistently lower urinary recovery which indicates higher non-renal clearance.

Clinical experience with 1000 patients treated with cefetamet pivoxil

Clinical studies have been carried out world-wide on cefetamet pivoxil, a new orally active cephalosporin. This paper reports on the first 1000 patients treated with the antibiotic; another 505 patients received standard antibiotics, mainly cefadroxil and cefaclor, for comparison. The results show that single doses of 1500 and 1200 mg cefetamet pivoxil were fully effective in gonorrhoea. Comparative trials in uncomplicated urinary tract infection indicate a significant superiority of a single dose of 2 g cefetamet pivoxil (n = 158; 90.0% cure) versus 2 g cefadrox (n = 162; 77.0% cure). In complicated urinary tract infections, a comparable outcome was achieved with a single daily dose of 2 g cefetamet pivoxil for 10 days (n = 99; 90% cure) and 1 g cefadroxil twice daily for 10 days (n = 98; 76.5% cure). The clinical response rate in acute exacerbation of chronic bronchitis was 89.4% in the group receiving cefetamet pivoxil (136 patients) and 83% in the cefaclor-treated group (n = 122). Treatment with 1000 or 2000 mg cefetamet pivoxil achieved a (bacteriological) success rate of 96% compared to 95% with cefaclor in acute ear, nose and throat-infections (n = 91). Overall, based on 894 isolated pathogens prior to therapy, the bacteriological response rate was 90% and it would appear that in vivo the spectrum of this cephalosporin covers a wide range of Gram-negative and Gram-positive pathogens, including urinary pathogens, but excluding Enterococci and Pseudomonas. Cefetamet pivoxil proved to be well tolerated. Mild to moderate adverse events were reported in 7.1% of patients but only 2 of the 1000 patients treated with cefetamet pivoxil were withdrawn because of diarrhoea, which subsided rapidly. There were no clinically relevant deviations in laboratory parameters.