Physiologically Based Pharmacokinetic Modeling of Renally Cleared Drugs in Pregnant Women

BACKGROUND

Since pregnant women are considerably underrepresented in clinical trials, information on optimal dosing in pregnancy is widely lacking. Physiologically based pharmacokinetic (PBPK) modeling may provide a method for predicting pharmacokinetic changes in pregnancy to guide subsequent in vivo pharmacokinetic trials in pregnant women, minimizing associated risks.

OBJECTIVES

The goal of this study was to build and verify a population PBPK model that predicts the maternal pharmacokinetics of three predominantly renally cleared drugs (namely cefazolin, cefuroxime, and cefradine) at different stages of pregnancy. It was further evaluated whether the fraction unbound (f _u) could be estimated in pregnant women using a proposed scaling approach.

METHODS

Based on a recent literature review on anatomical and physiological changes during pregnancy, a pregnancy population PBPK model was built using the software PK-Sim^®/MoBi^®. This model comprised 27 compartments, including nine pregnancy-specific compartments. The PBPK model was verified by comparing the predicted maternal pharmacokinetics of cefazolin, cefuroxime, and cefradine with observed in vivo data taken from the literature. The proposed scaling approach for estimating the f _u in pregnancy was evaluated by comparing the predicted f _u with experimentally observed f _u values of 32 drugs taken from the literature.

RESULTS

The pregnancy population PBPK model successfully predicted the pharmacokinetics of cefazolin, cefuroxime, and cefradine at all tested stages of pregnancy. All predicted plasma concentrations fell within a 2-fold error range and 85% of the predicted concentrations within a 1.25-fold error range. The f _u in pregnancy could be adequately predicted using the proposed scaling approach, although a slight underestimation was evident in case of drugs bound to α₁-acidic glycoprotein.

CONCLUSION

Pregnancy population PBPK models can provide a valuable tool to predict a priori the pharmacokinetics of predominantly renally cleared drugs in pregnant women. These models can ultimately support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Transport Characteristics of Cephalosporin Antibiotics Across Intestinal Brush-border Membrane in Man, Rat and Rabbit

The uptake of orally active cephalosporins, ceftibuten and cephradine, by intestinal brush-border membrane vesicles isolated from man, rat and rabbit was studied. In the presence of an inward H+ gradient, ceftibuten but not cephradine was taken up into intestinal brush-border membrane vesicles of man and rat against the concentration gradient (overshoot phenomenon). In rabbit jejunal brush-border membrane vesicles, the uptake of both cephalosporins in the presence of an inward H+ gradient exhibited the overshoot phenomenon. In human and rat vesicles, the initial uptake of ceftibuten was strongly inhibited by compound V, an analogue of ceftibuten, but the uptake of cephradine was not affected by any of the cephalosporins tested, whereas in the rabbit brush-border membrane vesicles, initial uptake of both ceftibuten and cephradine were markedly inhibited by all cephalosporins and dipeptides used. These results suggest that the transport characteristics of human and rat intestinal brush-border membrane for cephalosporins are comparable, and that rabbit is an inadequate animal for investigating the transport characteristics of β-lactam antibiotics.

Pharmacokinetic study of cephradine in Pakistani healthy male volunteers

To observe and discuss the difference in the pharmacokinetics of cephradine in Pakistani population with the reported data of other ethnic origins. A Single group pharmacokinetic study was conducted having six healthy male volunteers of 20-24 years of age. Blood samples were collected at appropriate times up to 7 hours. Plasma concentrations of cephradine was determined by HPLC technique and pharmacokinetic parameters were determined by both compartmental and noncompartmental methods using Kinetica ver 4.4.1 and Winnonlin ver 5.01. Peak plasma concentration was 11.49+/-1.73 microg/ ml achieved at 0.76+/-0.12 hr, after the administration of 250 mg cephradine to fasting volunteers. Area under the serum concentration-time curve was found to be 16.4+/-1.71 g.hr/ ml. Absorption, distribution, disposition and elimination half lives were calculated as 0.183 +/- 0.038 hr, 0.248 +/- 0.143 hr, 2.126 +/- 0.341 hr and 0.441+/-0.193 hr respectively where as the volume of central compartment and total body clearance were found to be 9.65+/-3.78 L and 15.4+/-1.89 L/hr. The plasma concentration time curves showed the absorption rate constant was 3.968 +/- 0.05 hr(-1), disposition rate constant was 0.333+/-0.05 hr(-1), distribution rate constant was 3.64+/-2.18 hr(-1) and elimination rate constant was 1.738+/-0.468 hr(-1). The value of micro-constants i.e. K(12) (central to peripheral compartment) and K(21) (peripheral to central compartment) were found to be 1.529+/- 1.499 hr(-1) and 0.704 +/- 0.44 hr(-1) respectively, where as MRT and AUMC were calculated as 2.04+/-0.09 hr and 35.92+/-1.86 hr(2) microg/ ml. The findings showed that the results of Pakistani subjects are slightly different when compared with the reported data of other ethnic origin.

Quantitative prediction of oral absorption of PEPT1 substrates based on in vitro uptake into Caco-2 cells

The method for predicting the fraction absorbed (Fa) of the PEPT1 substrates was established based on the in vitro uptake into Caco-2 cells. Uptake of a drug into Caco-2 cells was measured, and the carrier-mediated initial uptake clearance (DeltaCL uptake) was calculated as the difference between the uptake clearance in the absence of glycyl-sarcosine (Gly-Sar) and that in the presence of 30 mM Gly-Sar. The DeltaCL uptake of each drug was then divided by that of cephradine to obtain DeltaCL*uptake, which was a normalized parameter to correct for inter-day and/or inter-cell variability. Then, cephradine (CED), cefixime (CFIX), and cefotiam (CTM) were selected as marker compounds having excellent, medium and poor absorption, respectively. The DeltaCL*uptake and Fa values for CED, CFIX and CTM were fitted to the equation derived from the complete radial mixing (CRM) model, and the scaling factor (A') was obtained. Using the A' value, Fa was predicted from the DeltaCL*uptake value of each drug. Good correlation was observed between the predicted and reported Fa values, which demonstrated that Fa of PEPT1 substrates can be predicted based on the in vitro uptake in Caco-2 cells.

A specific and rapid HPLC assay for the determination of cefroxadine in human plasma and its application to pharmacokinetic study in Korean

A specific and rapid high performance liquid chromatographic (HPLC) method with UV detection (254 nm) was developed for the determination of cefroxadine in human plasma. The sample extraction was performed by a simple procedure, vortexing and centrifugation of sample following addition of 60% trichloroacetic acid. Cephalexin was used as an internal standard (I.S.). The HPLC analysis was carried out on a Capcell Pak C18 analytical column with a mobile phase of 50 mM ammonium formate buffer/pH 3.5 and acetonitrile (90:10, v/v). No interference was observed near the peaks of cefroxadine and I.S. The calibration curve was linear over the range of 0.5-40 microg/mL and the lower limit of quantification (LLOQ) was 0.5 microg/mL. The method was validated with excellent sensitivity, accuracy, precision and stability. This assay was successfully applied to determine the pharmacokinetic parameters of cefroxadine in Korean healthy volunteers after an oral administration of two 250 mg cefroxadine capsules. As a result, the plasma half-life was 1.00+/-0.26 h and the mean AUC(0-6 h) was 46.25+/-6.41microgh/mL. The maximum plasma concentration (C(max)) of 17.62+/-4.87 microg/mL reached 1.44+/-0.39 h after administration.

Properties and active substance release kinetics from gelatin-alginate matrices

The aim of the study was to evaluate the effect of composition and technological processing on pharmaceutical availability of active substance as well as on the properties of porous gelatin-alginate matrices. The active substance carrier included glycerol or peanut oil apart from gelatin and sodium alginate, and some matrices were additionally modified with calcium lactate. The obtained matrices were characterized by good sorption properties and high resistance to proteolytic enzymes. The release of the model antibiotic followed the pattern of first order kinetics, while half-release time in vitro (in the experimental conditions) was 1.5 to 3 hrs.

Inhibitory effect of zinc on PEPT1-mediated transport of glycylsarcosine and beta-lactam antibiotics in human intestinal cell line Caco-2

PURPOSE

The aim of this study was to examine the effects of zinc on the intestinal peptide transporters (PEPT1 and basolateral peptide transporter) and to elucidate the mechanism of the interactions.

METHODS

Caco-2 cells were pretreated with zinc, and the uptake studies were carried out.

RESULTS

Zinc treatment resulted in the inhibition of [14C]glycylsarcosine (Gly-Sar) uptake via PEPT1 in a concentration-dependent manner, whereas it showed moderate inhibitory effect on the basolateral peptide transporter. Zinc also inhibited the uptake of oral beta-lactam antibiotics such as ceftibuten and cephradine by PEPT1. Kinetic analysis showed that zinc treatment increased Km values without affecting Vmax values of the [14C]Gly-Sar uptake. The inhibition of [14C]Gly-Sar uptake induced by zinc was observed in the presence of an H+ gradient but not in the absence of an H+ gradient.

CONCLUSIONS

These results indicate that zinc is a competitive inhibitor of PEPT1. Zinc inhibited the PEPT1 function, possibly by interacting with histidine residues of PEPT1 that are part of an H+-binding site. These findings would provide important information for clinical, physiologic, and biochemical aspects of peptide transporters.

A recirculatory model with enterohepatic circulation by measuring portal and systemic blood concentration difference

The present study describes a recirculatory model for the evaluation of pharmacokinetic characteristics of drugs possessing enterohepatic circulation (EHC). The advantage of the model is to separately define the extent and rate of absorption for the dosage and EHC after oral administration. Cephradine was used as a model drug and was intravenously or orally administered to rats. Portal and systemic bloods were simultaneously collected in order to estimate various local moments after defining the global moments obtained by non-compartment analysis. For the zero-order moments, bioavailability (BA), the hepatic recovery ratio (Fh), the sum of the local absorption ratio for the dosage and recirculatory local absorption ratio for EHC (F(a)po), and the recirculatory local absorption ratio for EHC (F(a)ehc) after oral administration were estimated to be 95.6, 77.9, 172, and 71.5%, respectively. These data indicate that a complete absorption and substantial EHC contribute high oral exposure of cephradine. For the first-order moments, the sum of the mean local absorption times for the dosage and EHC (t(a)po) and the mean transit time for a single pass of EHC (tc) were 2.50 and 0.117 hr, suggesting a rapid EHC of cephradine compared with the absorption from the dosage. With this model, the absorption rate-time profiles for the dosage and EHC were separately simulated by using a program of nonlinear least squares (MULTI) with fast inverse Laplace transform (FILT). The cumulative biliary excretion ratio (Fbile) calculated by the model was in good agreement with the experimental value obtained in the bile ductcannulated rats. These results suggest that the model proposed in this study would be useful for evaluating the extent and rate of ECH along with absorption from the dosage after oral administration of drugs.

Effect of composition on the physicochemical properties and active substance release from gelatin-alginate sponge

The aim the study was physicochemically characterize and develop ability of the active substance (cefradine) from the implantable porous carriers. The drug delivery systems consisting of the gelatine and alginic acid sodium salt and glycerol (GL) or peanut oil (AO). Gelatin-alginate sponge was prepared by foamed components and next freeze-dried this foam. The composition of the sponges affected on the sorption ability and on the stability to proteolytic enzymes. Owing to porous structure obtained specific profile of active substance release.

Prolonged intestinal absorption of cephradine with chitosan-coated ethylcellulose microparticles in rats

Cephradine-containing ethylcellulose microparticles (MPC) were prepared by the solvent evaporation method. Chitosan-coated MPC (Chi-MPC) were prepared by doping MPC with viscous chitosan solution and subsequently drying. When fluorescein isothiocyanate (FITC)-labeled chitosan-coated ethylcellulose microparticles without drug were administered intraduodenally, they moved slowly in the intestine, that is, most of them were retained at the upper and middle parts of the small intestine for more than 8 h, which is considered due to mucoadhesive properties of coated chitosan. When MPC and Chi-MPC was incubated at 37 degrees C in the JP 14 second fluid, pH 6.8, both released the drug slowly with similar release rates. Cephradine solution and suspension, MPC and Chi-MPC were administered intraduodenally to investigate intestinal drug absorption. Only Chi-MPC suppressed the initial plasma level and maintained the plasma concentration for a long time up to 24 h, suggesting Chi-MPC would be useful for prolonged intestinal absorption of cephradine.

Concentration-dependent preferences of absorptive and excretive transport cause atypical intestinal absorption of cyclic phenylalanylserine: small intestine acts as an interface between the body and ingested compounds

Intestinal absorption of cyclic phenylalanylserine (cyclo(Phe-Ser)), a precursor of gliotoxin, was studied in isolated rat small intestine as a model cyclic dipeptide. Absorption clearance (CLabs) decreased in the presence of glycylsarcosine, cephalexin or cephradine, substrates for H+/oligopeptide cotransporter (PEPT1). CLabs of cyclo(Phe-Ser) also decreased at 4 degrees C. These indicate that cyclo(Phe-Ser) is in part transported by PEPT1. However, Eadie-Hofstee plot of absorption revealed an atypical profile at lower concentrations of cyclo(Phe-Ser) (around 0.1 mM). Moreover, comparative experiments of absorptive and excretive transport showed that excretive transport from the serosal to mucosal side of isolated intestinal tissue at a 0.1 mM cyclo(Phe-Ser) was superior to absorptive transport from the mucosal side to the serosal side, and vise versa at a 1 mM cyclo(Phe-Ser). These results as well as the results of kinetic analysis indicate that intestinal absorption consists of passive transport, carrier-mediated absorptive transport by PEPT1 and carrier-mediated excretive transport, resulting in atypical absorption. Although cyclic dipeptides have potentials for drug, their intestinal absorption may be complex. The results of this study lead us conclude that absorptive and excretive transport by the small intestine acts as an interface between the body and ingested compounds.

Determination of the cephalosporin antibiotic cephradine in human plasma by high-performance liquid chromatography with ultraviolet detection

A simple and sensitive high-performance liquid chromatographic method, for the determination of cephradine in human plasma samples has been developed and validated. Cephradine and cephaloridine (internal standard) were extracted from human plasma by perchloric acid protein precipitation followed by centrifugation. Aliquots of the extracts were analysed by reversed-phase high-performance liquid chromatography (HPLC) utilising a polymeric reversed-phase PLRP-S column, followed by ultraviolet detection at 260 nm. The method has a working dynamic range from 0.2 to 30.0 microg/ml from 200 microl human plasma. The precision of the method at 0.2 microg/ml was 4.9% (intra-assay) and negligible (inter-assay) as calculated by one-way analysis of variance and the accuracy of the method at 0.2 microg/ml was -4.1% in terms of percentage bias. This method has been successfully applied to clinical studies including an oral bioequivalence study comparing the pharmacokinetics of 500 mg tablets of Kefdrin with 500 mg tablets of Velosef in healthy human volunteers.

pH-dependent inhibitory effects of angiotensin-converting enzyme inhibitors on cefroxadine uptake by rabbit small intestinal brush-border membrane vesicles and their relationship with hydrophobicity and the ratio of zwitterionic species

The inhibitory effects of five angiotensin-converting enzyme (ACE) inhibitors on the uptake of an aminocephalosporin antibiotic, cefroxadine, by rabbit small intestinal brush-border membrane vesicles were examined in the presence of an inward H+ gradient. Dixon plot analysis showed that all these ACE inhibitors inhibited the uptake of cefroxadine, which is transported by a H+/oligopeptide transporter in the membrane, in the order of enalapril<quinapril, benazepril<temocapril, trandolapril at extravesicular pH 6.0. These drugs, except for enalapril, which are relatively hydrophobic, exhibited a mix of competitive and noncompetitive inhibition. We also examined the inhibitory effects of quinapril and temocapril at extravesicular pH 5.5, at which the ratio of the zwitterionic species of the drugs increased. The inhibition occurred in a nearly competitive manner at this pH and the inhibitory effects were stronger than at pH 6.0. Regression analysis of the inhibitory effects suggested that the affinity of these ACE inhibitors for the transporter was regulated by the hydrophobicity of these ACE inhibitors and the ratio of the zwitterionic species of the drugs.

Cephradin-plaga microspheres for sustained delivery to cattle

In the field of controlled drug delivery, most of the reported work is aimed at introducing new systems, or at providing basic information on the critical parameters which affect release profiles in vitro and occasionally in vivo. The situation is totally different when one wants to fulfil the specific requirements imposed by the marketing of a sustained release device to be used in humans or in animals eaten by human beings. The control of the release characteristics is then a difficult challenge. In this work, attempts were made to combine cephradin, a hydrophilic beta-lactam antibiotic, and bioresorbable polymeric matrices of a poly(alpha-hydroxy acid) in the form of microspheres with the aim of delivering the antibiotic to cattle at a dose rate of 4-5 mg/kg/day over a 3-4 days period after i.m. injection. PLAGA aliphatic polyesters were selected because they are already FDA approved as matrices. The solvent evaporation technique using PVA as the emulsion stabilizer was selected because it is efficient and can be extended to an industrial scale. Various experimental conditions were used in order to obtain the highest encapsulation yields compatible with the desired specifications. Decreasing the volume of the aqueous phase and adding a water-miscible organic solvent/non-solvent of cephradin failed. In contrast, microspheres containing up to 30% cephradin were prepared after addition of sodium chloride to the aqueous dispersing phase. The amount of entrapped drug was raised to 40% by decreasing the temperature and the pressure. Preliminary investigations using dogs showed that 20% cephradin microspheres prepared under these conditions extended the presence of cephradin in the blood circulation up to 48 h. Increasing the load led to higher blood concentrations but shorter sustained release. The fact that the microspheres were for cattle limited the volume of the injection and thus the amount of microspheres to be administered. The other limiting factors were related to microsphere morphology.

Analysis of intestinal perfusion data for highly permeable drugs using a numerical aqueous resistance--nonlinear regression method

PURPOSE

To develop, validate and apply a method for analyzing the intestinal perfusion data of highly permeable compounds using the Numerical Aqueous Resistance (NAR) theory and nonlinear regression (NAR-NLR) and to compare the results with the well-established Modified Boundary Layer (MBL) Analysis.

METHODS

The NAR-NLR method was validated and the results were compared to the MBL analysis results using previously reported cephradine jejunal perfusion data. Using the Single Pass Intestinal Perfusion (SPIP) method, the concentration dependence of intestinal permeability was investigated for formycin B, proline, and thymidine, three compounds reported to be absorbed by carrier-mediated transport processes. The MBL and NAR-NLR analyses were then applied to the three sets of SPIP data.

RESULTS

The results demonstrate that the intrinsic MBL transport parameters were highly variable and, in one case, the analyses failed to give a statistically significant Michaelis constant. The MBL mean dimensionless wall permeabilities (P*w) were greater than the NAR-NLR P*w and were also highly variable. In all cases, the NAR-NLR variability was significantly lower than the MBL variability. The extreme variability in the MBL-calculated P*w is due to the sensitivity of P*w when the fraction of unabsorbed drug (Cm/Co) is low or, alternatively, when P*w approached the aqueous permeability, P*aq.

CONCLUSIONS

The NAR-NLR method facilitates the analysis of intestinal perfusion data for highly permeable compounds such as those absorbed by carrier-mediated processes at concentrations below their Km. The method also allows for the use of a wider range of flow conditions than the MBL analysis resulting in more reliable and less variable estimates of intestinal transport parameters as well as intestinal wall permeabilities.

In vitro and in vivo studies on microcapsules and tabletted microcapsules of cephradine

Cephradine was microencapsulated by coacervation. Ethyl cellulose was used as the polymer and a core/wall ratio of 1:1 was selected. The repose angle, apparent and tapped density, particle size distribution of cephradine microcapsules (CM) and of cephradine powder were examined. Then flat-surfaced tablets of CM were prepared using Avicel PH 101 and magnesium stearate. In vitro and in vivo properties of CM and tabletted CM (both equivalent to 150 mg cephradine) were compared with commercial capsules (equivalent to 250 mg cephradine). The dissolution studies were carried out by the rotating basket method and the agar diffusion method was applied for quantitative determinations. Among the investigated kinetic models for the release of cephradine from CM and tabletted CM the best fit was found with the Higuchi model. In vivo studies were made in rabbits. Bioavailabilities of CM and their tabletted form were higher than that of the commercial capsules. In vitro/in vivo correlations between mean residence time (MRT) and mean dissolution time (MDT) for CM and tabletted CM were calculated. A good correlation was found between the in vitro and in vivo results.

Characteristics of uptake of cefroxadine by rabbit small intestinal brush border membrane vesicles

Characteristics of transport of an oral aminocephalosporin, cefroxadine, in rabbit small intestinal brush border membrane vesicles were examined. Uptake rate of cefroxadine was saturable in the presence of an inward H+ gradient, and kinetic parameters were similar to those of cephradine. However, the uptake rate was almost linear with the concentration in the absence of an inward H+ gradient up to 5 mM. Overshoot phenomenon was observed in the presence of an inward H+ gradient at 37 degrees C, but it disappeared with decrease of temperature. The Arrhenius plot of uptake rate constant showed a break point at approximately 30 degrees C. Cefroxadine uptake was optimum in the vicinity of pH 5.5 at 37 degrees C, but the dependence on extravesicular pH disappeared at 15 degrees C. The uptake of cefroxadine in the presence of an inward H+ gradient was markedly inhibited by other aminocephalosporins such as cephalexin, but the inhibition was only slight in the absence of an inward H+ gradient. Alkyl alcohols such as n-hexyl alcohol also inhibited H(+)-coupled uptake of cefroxadine at the concentration range at which the alcohols increased the membrane fluidity, and overshoot phenomenon diminished, suggesting that H(+)-coupled transport of cefroxadine is sensitive to the alcohol-induced increase in membrane fluidity. On the other hand, the alcohols rather stimulated its uptake in the absence of an H+ gradient.

Noncompetitive inhibition of cephradine uptake by enalapril in rabbit intestinal brush-border membrane vesicles: an enalapril specific inhibitory binding site on the peptide carrier

ACE inhibitors, as well as aminocephalosporins with peptide-like structures, are transported by the intestinal peptide carrier. We investigated the transport mechanism using intestinal brush-border membrane vesicles from rabbits and observed that enalapril, an angiotensin converting enzyme inhibitor and substrate of the peptide carrier, noncompetitively inhibited the uptake of cephradine, an aminocephalosporin and substrate of the peptide carrier, with an inhibition constant (Ki) of 2.6 mM when it was present on the cis side (outside) of the vesicles. By contrast, enalaprilat, cefadroxil and GlyPro competitively inhibited cephradine transport with Ki values of 5.4, 3.8 and 5.1, respectively. These results suggest the presence of an enalapril-specific inhibitory binding site on the peptide carrier. In addition, enalapril on the trans side (inside) of the vesicles inhibited the uptake of cephradine, suggesting an apparent reduction of carrier availability by a trapping mechanism. On the other hand, cefadroxil stimulated the uptake of cephradine in the trans experiment, consistent with the concept of countertransport. These findings reveal the uniqueness of enalapril regarding its mode of interaction with the peptide carrier(s) which has been of increasing interest regarding its role in the intestinal absorption of peptide-type drugs.

Disposition kinetics of cephradine in normal and Escherichia coli infected goats

The pharmacokinetics of cephradine was studied following single and repeated intramuscular injections in normal and Escherichia coli infected goats. Bioavailability of cephradine was determined in normal goats after a single intramuscular dose. The serum concentrations of cephradine following a single and repeated intramuscular administration of 10 mg/kg b.wt. twice daily for five consecutive days, peaked 2 hours after each intramuscular dose with a lower significant value recorded in E. coli infected goats than in normal goats. The absorption half-lives (t0.5(ab)) following a single intramuscular injection of cephradine was significantly higher in E. coli infected goats (1.18 h) than in normal goats (0.64 h). The elimination half-lives (t0.5(beta)) of cephradine were significantly higher in E. coli infected goats than in normal goats following the administration of fifth and ninth doses. The urine and milk concentrations of cephradine were significantly lower in E. coli infected goats than in normal goats. The mean systemic bioavailability of cephradine following a single intramuscular injection in normal goats was 73.9%.

The intestinal uptake of "enzymatically-stable" peptide drugs in rats as influenced by D-glucose in situ

In previous in situ and in vivo rat perfusion studies, the intestinal absorption of several low molecular weight drugs was increased by the presence of luminal D-glucose. The intent of this study was to determine the potential of this fed-state effect to improve the intestinal uptake of poorly permeable, small peptide and peptide-like drugs. Jejunal wall permeabilities (Pw*) of di-(D-kyotorphin), tri-(cephradine), hexa-(growth hormone releasing peptide, GHRP-6) and octa-(octreotide, a somatostatin analogue) peptides and corresponding net water fluxes were determined in rats using an in situ single-pass perfusion technique. Glucose was shown to enhance the uptake of the smaller (di- and tri-) peptides but not the larger peptides despite the fact that glucose elicited a significant net water absorption with each of the four peptide drugs. It is concluded that glucose enhances jejunal permeabilities of smaller peptides by solvent drag and the enhancement is limited in situ by peptide molecular size. The studies with nonmetabolizable 3-O-methylglucose suggest that the augmentation of the proton gradient across the transmucosal membrane by glucose contributes to the carrier-mediated transport observed with the smaller peptides.

Intestinal brush-border transport of the oral cephalosporin antibiotic, cefdinir, mediated by dipeptide and monocarboxylic acid transport systems in rabbits

Intestinal absorption of the orally active cephalosporin, cefdinir, was investigated using brush-border membrane vesicles prepared from rabbit small intestine. The initial uptake of cefdinir was pH-dependent, with increased uptake at acidic pH, and was not influenced by either sodium gradient or membrane potential difference. Cefdinir uptake was saturable with an apparent Michaelis constant of 8.1 mM. Initial uptake of cefdinir was inhibited by dipeptides (glycyl-L-proline and glycylsarcosine), beta-lactam antibiotics (cephradine, cefixime and penicillin V), and monocarboxylic acids (acetic acid and L-lactic acid), whereas the uptake of cephradine and cefixime was not inhibited by monocarboxylic acids. Cefdinir significantly inhibited the initial uptake of cephradine, cefixime and [3H]acetic acid. From these results, it was suggested that cefdinir was transported across brush-border membranes by both dipeptide and monocarboxylic acid carriers.

In vivo release of water-soluble drugs from stabilized water-in-oil-in-water (W/O/W) type multiple emulsions following intravenous administrations using rats

The in vivo release of four water-soluble drugs, cefadroxil, cephradine, antipyrine and 4-aminoantipyrine, from a stabilizing water-in-oil-in-water (W/O/W) type multiple emulsion was studied using rats. The W/O/W type multiple emulsion used in this study could be stabilized for 30 d after preparation at room temperature and also for 24 h in pH 7.4 isotonic phosphate buffer or in rat plasma at 37 degrees C. The cefadroxil and cephradine concentrations in rat plasma following intravenous administrations of their W/O/W type multiple emulsions containing drugs were considerably prolonged compared with those of respective aqueous solutions. Sustained-releasing properties of cefadroxil and cephradine from W/O/W type multiple emulsions could be explained by the mechanism underlying the long residence time of W/O/W type multiple emulsions and delay-release of drugs from the W/O/W type multiple emulsions circulated with rat blood stream. However, antipyrine and 4-aminoantipyrine decreased rapidly following W/O/W type multiple emulsions and these plasma profiles coincided precisely with those following intravenous administration of the aqueous solutions of drugs. These in vivo releasing data correlated with in vitro drug release observation stated in the previous papers.

Peptide carrier-mediated transport in intestinal brush border membrane vesicles of rats and rabbits: cephradine uptake and inhibition

The uptake kinetics of cephradine, an amino-beta-lactam antibiotic, were studied in rat and rabbit intestinal brush border membrane vesicles preparations using both the Ca2+ and the Mg2+ methods of preparation, in the presence of an inward proton gradient. The Ca2+ method demonstrated greater uptake of cephradine in intestinal brush border vesicles prepared from both rat and rabbit and was used for these studies. The transport was observed to be of Michaelis-Menten carrier-mediated type with a passive transport component. The kinetic parameters obtained were as follows: for rat and rabbit, respectively, Km, 1.6 and 1.9 mM; Jmax', 1.7 and 20.7 nmol/mg/min; Pc' (= Jmax'/Km), 1.1 and 10.9 microL/mg/min; and Pm', 0.4 and 0.8 microL/mg/min. The kinetic parameters for the rat vesicles are consistent with those from our previous perfusion study using a conversion factor of 0.71 cm2/mg protein. The rabbit vesicles exhibited a similar Michaelis constant and a 10-fold larger maximal transport velocity, suggesting a quantitative advantage for the study of carrier-mediated transport in the rabbit compared to rat vesicles from the intestine. Cephradine uptake was inhibited by phenylpropionylproline, a proline derivative, and enalapril, an ACE inhibitor, which do not have an alpha-amino group, as well as dipeptides, tripeptides, and amino-beta-lactam antibiotics in both rat and rabbit vesicles. These results support the suggestion that they share the same peptide carrier pathway for oral absorption and that the vesicles may be a useful tool in developing orally effective peptide-type drugs.

An alternative approach for assessment of rate of absorption in bioequivalence studies

The partial area method was investigated for evaluation of equivalency in the rate of absorption of immediate release formulations. The applicability of the method was demonstrated with four drugs with different pharmacokinetic/pharmacodynamic characteristics. The confidence interval approach currently employed for bioequivalence determinations was applied to the relevant absorption parameters, including Cmax and partial AUCs. The method was found to be more discriminating than Cmax and/or Tmax in the evaluation of the absorption rate of drugs. The cutoff time or point for partial AUC calculation may vary with the type of drug under study, depending on its clinical use and onset of action. The method was shown to be useful in the assessment of rate of absorption in bioequivalence studies.

Comparative pharmacokinetics of cefoperazone and cephradine in untreated streptozotocin diabetic rats

Experimental diabetes mellitus was induced in adult male rats by injecting streptozotocin (STZ; 60 mg/kg iv) for the purpose of surveying changes in the pharmacokinetics of biliary excretion after the intravenous administration of 40 mg/kg of cefoperazone (CPZ) or cephradine (CED). CPZ, CED, and other organic anions share affinity for the organic anion transport system in the bile canalicular membrane. The STZ treatment had a marked influence on the distribution and elimination of both cephalosporins. The blood levels of both cephalosporins at each time point after administration differed significantly between the STZ-treated and control rats. The values of mean residence time (MRT) of CPZ and CED were significantly decreased in the STZ-treated rats. Basal bile flow rates were increased after the administration of CPZ in the control and STZ-treated rats. Biliary clearance (CLbile) of CPZ was more than 60% of the CLtot, whereas CLbile of CED was less than 20% of CLtot in both groups of rats. The mean CLbile value of CPZ in the STZ-treated rats was 1.0 ml/min higher than that of the control rats, whereas the mean CLbile value of CED was almost the same as that of the control rats. The increased CLbile of CPZ suggested that diabetes alters the biliary excretion of CPZ. The changes in MRT of CPZ in the STZ-treated and control rats are mainly caused by an increase in the biliary excretory rate and renal clearance. The changes in MRT of CED in the STZ-treated and control rats are caused by a decrease in the apparent volume of distribution and increased renal clearance.

Is antibiotic penetration compromised in the ischaemic tissues of patients undergoing amputation?

Antibiotic prophylaxis is indicated for patients undergoing amputation for severe ischaemia or gangrene. However, the adequacy of tissue levels of antibiotics in ischaemic tissue is not known. In this study the serum and tissue antibiotic levels were measured after intravenous administration of metronidazole (15 mg/kg body weight) and cephradine (20 mg/kg body weight). In 11 patients, venous samples were taken at time 0 (induction of anaesthesia) 10, 30 and 60 min. Samples of 2 g each of fat and muscle were collected from the amputation site and three distal sites. Metronidazole and cephradine levels were measured and the degree of limb ischaemia estimated preoperatively by an isotope limb blood flow method. Our results indicate that both metronidazole and cephradine penetrate ischaemic tissues to levels equivalent of a Mean Inhibitory Concentration (MIC) 50 for most organisms encountered in vascular surgery, and that the degree of ischaemia does not alter this.

Effect of gastrointestinal maturation on absorption of beta-lactam antibiotics

Gastrointestinal absorption of cefazolin, which is poorly absorbed in adults, and of cephradine, which is well absorbed in adults, was studied in rats during their development. Significantly higher concentrations of cefazolin in plasma after oral administration were observed in 1- and 2-week-old rats compared with 3-week-old and adult rats. A marked difference in the absorption of cefazolin by 2- and 3-week-old rats (at weaning period) was observed. No such marked difference in the absorption of cephradine by rats of various age groups was found. With cefazolin, a similar pattern of developmental change in jejunal uptake was observed. Cortisone, which causes early maturation of the intestinal membrane, was given as a preweaning injection to 2-week-old rats. This treatment decreased concentrations of cefazolin in plasma and jejunal uptake of cefazolin. Thus, the absorption of cefazolin in 1- and 2-week-old rats seems to depend on the permeability of the immature intestinal membrane before weaning. Cephradine absorption from the intestine of 1-week-old rats became saturated and inhibited by carnosine and glycylglycine when studied by the in situ loop method. Cefazolin absorption was proportional to luminally administered doses and was not affected by carnosine and glycylglycine. A nonsaturable process for cefazolin and a saturable process for cephradine were also observed in an in vitro uptake experiment.

Transepithelial transport of oral cephalosporins by monolayers of intestinal epithelial cell line Caco-2: specific transport systems in apical and basolateral membranes

The accumulation and the transepithelial transport of p.o. cephalosporins by monolayers of human intestinal epithelial cell line Caco-2 grown on microporous membrane filters were evaluated. Cephradine was accumulated concentratively in the monolayers from the apical side, and was transported to the basolateral side. The accumulation and the apical-to-basolateral transport of cephradine were temperature-dependent and sensitive to the pH of the apical side, with the optimal pH 6.0 to 6.5. The efflux of cephradine from the monolayers to the basolateral side was also temperature-dependent and was more rapid than its efflux to the apical side. The accumulation and the apical-to-basolateral transport of cephradine, cephalexin and cefixime, all p.o. agents, were significantly higher than those of cefotiam, a parenteral agent. The apparent Km and Vmax values for cephradine accumulation were 8.3 mM and 2.49 nmol/mg of protein per min, respectively. Dipeptides inhibited the accumulation and the apical-to-basolateral transport of cephradine. Both the accumulation and the efflux of cephradine in the monolayers were inhibited significantly by the sulfhydryl reagent p-chloromercuribenzene sulfonate. These findings suggest that p.o. cephalosporins accumulate in the Caco-2 cell monolayers via the H+/dipeptide cotransport system localized in the apical membranes and that a specific transport system is involved in the efflux of these antibiotics across the basolateral membranes.

Peroral absorption of cefroxadine in patients within the first day after severe trauma: comparison to cefroxadine pharmacokinetics in fasted, healthy volunteers

Peroral absorption of cefroxadine given to 7 24-h fasted trauma patients by nasogastric tube within the first day of admission was compared to that obtained in fasted healthy volunteers. The trauma patients exhibited significantly lower Cmax and reduced AUC. Even though rate and extent of bioavailability cannot be determined from these two different population groups since the total clearance must be assumed to be different in patients and healthy subjects, a reduced bioavailability is assumed based on pathophysiologic reflections.

Interaction of ofloxacin with organic cation transport system in rat renal brush-border membranes

Ofloxacin, a pyridonecarboxylic acid derivative, was examined for its effects on the transport of tetraethylammonium (cation), cephalexin and cephradine (zwitterions), p-aminohippurate (anion) and D-glucose in brush-border membrane vesicles isolated from rat renal cortex. The initial uptake of tetraethylammonium in the presence or absence of an outward H+ gradient was inhibited by ofloxacin in a dose-dependent manner, although the equilibrium value of tetraethylammonium uptake was not affected. This inhibition occurred in a competitive manner (Ki = 0.11 mM). Ofloxacin also inhibited the initial uptake of cephalexin and cephradine, which can be transported via the H+/organic cation antiport system in renal brush-border membranes. In contrast, ofloxacin had no effect on p-aminohippurate. These data suggest that ofloxacin interacts with the organic cation transport system in renal brush-border membranes, and this system may play an important role in the tubular secretion of ofloxacin.

Pharmacokinetics of cefroxadine after infusion to healthy volunteers

The pharmacokinetics of cefroxadine in healthy human volunteers was studied in plasma and urine, after an infusion administration of 1 g of this drug for 0.5 h. Blood and urine samples were microbiologically quantified by diffusion on solid gelose using Bacillus Subtilis ATCC 6633 as the test organism. Plasma and urine profiles were fitted to a reduced two-compartment model not having inactivating biotransformation as a route of elimination. The parameters of distribution for this model show a rapid disposition (t1/2 alpha = 0.28 h) and an average volume of the central compartment of 0.15 +/- 0.04 l/kg (range 0.20-0.09). The dominant terminal half-life (beta-phase) was 1.17 +/- 0.26 h (range 0.90-1.67). The total body volume 0.41 +/- 0.09 l/kg (range 0.30-0.52) indicates that there is no diffusion of the antibiotic into intracellular fluids of poorly perfused tissues due to its high elimination rate.

Pharmacokinetics of cephradine administered intravenously and orally to young and elderly subjects

The pharmacokinetics of IV and oral cephradine in healthy young male and female volunteers (ages 19 to 25, n = 10) were compared to those of older individuals (ages 65 to 81, n = 9). Subjects received 1 gram of cephradine by a 5-minute intravenous (IV) infusion followed the next day by a 1-gram oral dose. Serial serum and urine samples collected over a period of 12 hours after the dose were analyzed for cephradine concentration by a microbiologic assay. After IV administration, mean serum cephradine concentrations in the elderly group were significantly higher at both 6 hours (1.52 +/- 0.41 mcg/mL) and 8 hours (0.73 +/- 0.22 mcg/mL) than in the young group at 6 hours (0.43 +/- 0.11 mcg/mL). Total systemic clearance was significantly lower (2.64 +/- 0.34 vs. 4.81 +/- 0.59 ml/min/kg) and the elimination half-life was significantly longer (1.71 +/- 0.20 vs 1.12 +/- 0.13 hours) in the elderly group (P = .0001). Systemic cephradine clearance correlated positively with creatinine clearance (r2 = 0.34, P = .0110) and negatively with age (r2 = 0.79, P = .0052). The mean volume of distribution was not significantly different between the two groups. Mean renal clearance was significantly lower in the elderly group (P = .0001), but more than 80% of the dose was excreted in the urine within 6 hours in both groups. After oral administration, the mean peak concentration and time to peak concentration did not differ between groups. The relative oral bioavailability was approximately 94% in both groups. The mean serum concentrations in the elderly were higher at both 6 and 8 hours than in the young group at 6 hours. There were no differences in pharmacokinetic parameters between male and female subjects. Because of reduced cephradine clearance secondary to an age-related decline in renal function, administration of cephradine every 8 hours, rather than every 6 hours, may be sufficient in elderly patients.

Transport mechanisms of bestatin in rabbit intestinal brush-border membranes: role of H+/dipeptide cotransport system

Bestatin [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-leucine], a potent inhibitor of aminopeptidase B and leucine aminopeptidase, enhances the immune response to activate the defense mechanism of the living organism and suppresses the growth and metastasis of cancer. Bestatin has been effectively used by p.o. administration, but the mechanisms of intestinal absorption remain to be solved. The present study was undertaken to examine whether bestatin, a dipeptide containing an unusual amino acid, is transported via dipeptide carriers in intestinal brush-border membranes, by using cephradine as a probe for the H+/dipeptide cotransport system. The initial uptake of cephradine in the presence or absence of an inward H+ gradient, driving force, was inhibited by bestatin and this inhibition occurred in a competitive manner (Ki = 0.47 mM). The uptake of cephradine was stimulated by the countertransport effect of bestatin, the definitive criterion for ascertaining a common transport system. These findings indicate that bestatin, as well as cephradine and other p.o. cephalosporins, can be transported via dipeptide carriers in intestinal brush-border membranes.

Effect of various chemical modifiers on H+ coupled transport of cephradine via dipeptide carriers in rabbit intestinal brush-border membranes: role of histidine residues

We examined the effect of diethylpyrocarbonate (DEPC), a histidine specific reagent, on H+ coupled transport of cephradine via dipeptide carriers in the intestinal brush-border membranes, in comparison with the effects of other chemical modifiers. Pretreatment of membrane vesicles with DEPC resulted in the inhibition of cephradine transport in the presence or absence of an inward H+ gradient. This inhibition was reversed by subsequent treatment with hydroxylamine, but not with dithiothreitol. The inactivation by DEPC pretreatment was abolished by the presence of cephradine or glycylsarcosine. In the DEPC-pretreated membranes, the V(max) value of cephradine uptake was decreased without any change in the Km value. In contrast, cephradine uptake was not changed by the pretreatment with N-acetylimidazole, a tyrosine specific reagent, or p-chloromercuribenzene sulfonate, a sulfhydryl reagent. These results suggest that histidine residues in the carriers are essential for H+ coupled transport of amiocephalosporins.

Cephradine penetration of mandibular bone

The concentration of cephradine in serum and mandibular bone was assayed in 22 patients undergoing third molar surgery following a single 1-g intramuscular injection. Serum and cortical bone samples taken simultaneously contained mean cephradine concentrations of 12.41 micrograms/mL and 1.25 micrograms/g, respectively. These results, when compared with those reported for other bony sites, including femoral head and knee, show a reduced bone penetration with a bone-to-serum ratio of approximately 0.10:1.

Determination of serum and bone concentrations of cephradine and cefuroxime by HPLC in patients undergoing hip and knee joint replacement surgery

Bone and serum concentrations of cephradine and cefuroxime were measured by HPLC in 21 patients undergoing hip and knee joint replacement surgery. An intravenous dose of 750 mg of each cephalosporin was given to patients at induction of anaesthesia. The serum and bone concentrations of both compounds were similar in individual patients although there was considerable interpatient variation. The mean concentrations in the femoral head bone supernatant in hip replacements were 7.2 mg/kg of cephradine and 8.0 mg/kg of cefuroxime. In knee replacement the femoral condyle bone concentrations were 5.1 mg/kg of cephradine and 4.2 mg/kg of cefuroxime, and for tibial bone 5.6 and 4.6 mg/kg respectively. Both cephradine and cefuroxime diffuse well into bone giving bone concentrations effective against common pathogens such as Staphylococcus aureus and S. epidermidis.

H+ coupled transport of p.o. cephalosporins via dipeptide carriers in rabbit intestinal brush-border membranes: difference of transport characteristics between cefixime and cephradine

We demonstrated previously that aminocephalosporins, such as cephradine, possessing a alpha-amino group and a carboxyl group, are transported via H+/dipeptide carrier system in the intestinal brush-border membranes. The present study examined the transport characteristics of cefixime, a new p.o. cephalosporin with two carboxyl groups, by the rabbit intestinal brush-border membrane vesicles in comparison with those of cephradine. With an intravesicular pH of 7.5, apparent optimum extravesicular pH was 6.0 for cephradine uptake and more acidic (pH 4.5-5.0) for cefixime uptake. An inward H+ gradient [( pH]i = 7.5, [pH]o = 5.0) induced overshoot uptake of cefixime, and this uptake was reduced in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone, a protonophore. Cefixime uptake at pH 5.0 was trans-stimulated (countertransport effect) and cis-inhibited by dipeptides and aminocephalosporins but not at pH 7.5. Cephradine uptake at pH 7.5 was stimulated by the countertransport effect of dipeptide but not by cefixime. Cefixime and cephradine uptake at pH 5.0 was greatly inhibited by 4,4'-diisothiocyano-2,2'-disulfonic stilbene. These findings indicate that cefixime is transported by an inward H+ gradient via dipeptide carrier only in an acidic pH region, whereas cephradine is transported via dipeptide carrier in both neutral and acidic pH regions, suggesting the existence of multiple transport systems for dipeptides; a neutral pH preferring system (Type I) and an acidic pH preferring system (Type II).

Correlation between plasma and tonsillar levels of cefroxadine

Serum and tonsillary tissue levels of cefroxadine, a new broad-spectrum cephalosporin, proving to be effective in several infections, particularly in the ENT ones, were measured in patients scheduled for tonsillectomy. Twenty patients (12 males, 8 females) aged between 11 and 25 years (mean 18.0 years) were given cefroxadine for 2 days (500 mg every 12 h), and on the 3rd day 500 mg of the drug was given before surgical operation. Tonsillar tissues were taken 2 h after dosing and blood samples before, 1, 2, 4 and 6 h after the drug administration in 8 out of 20 enrolled patients. Cefroxadine concentrations were measured according to microbiological methods. Cefroxadine tonsillary levels were 1.13 +/- 1.73 micrograms/g, approaching the MIC for sensitive bacteria. The time course of plasma levels is superimposable to previous studies. These findings suggest a rapid penetration of cefroxadine in tonsillar tissue and seem to confirm the clinical efficacy of the drug in ENT infections.

Saturation of the tubular excretion of beta-lactam antibiotics

1 The saturability of the tubular excretion of cloxacillin, benzylpenicillin and cephradine was investigated. 2 Volunteers received a continuous infusion of one of the antibiotics at increasing infusion rates in order to maintain constant plasma concentrations at three different levels. Blood and urine samples were taken every 30 min. Sufficient urinary flow was ensured by a saline infusion (500 ml h-1). 3 Renal clearance of the antibiotic was calculated for the non-protein bound fraction of the drug. 4 Tubular clearance and tubular excretion rate were estimated by using the renal clearance of the antibiotic minus the glomerular filtration rate; the latter was considered to be equal to creatinine clearance. 5 Data were fitted to a Scatchard transformation and, by nonlinear methods, to a Michaelis-Menten equation. 6 Parameters of saturability, i.e. EC50 and maximal tubular excretion rate, were established. The values found for EC50 were 7.7, 93.0 and 266 mg l-1 for cloxacillin, benzylpenicillin and cephradine, respectively. The values calculated for the maximal tubular excretion rate were 1017, 5535 and 4537 mg h-1, respectively.

The penetration of antibiotics into the normal intervertebral disc

The role of antibiotics in the treatment of disc-space infection is controversial. This study assessed the tissue penetration of flucloxacillin and cephradine into the normal intervertebral disc after intravenous administration of a bolus dose of antibiotic. Twenty-five discs were removed from 12 adolescent patients having anterior spinal surgery to correct scoliosis; antibiotic had been administered between 30 minutes and four hours before operation. Despite high blood levels, no antibiotic could be detected by bioassay or by high-pressure liquid chromatography (h.p.l.c.) in any of the specimens from the nucleus pulposus or the annulus fibrosus.

Clinical pharmacokinetics of five oral cephalosporins in calves

The minimal inhibitory concentrations (MIC) of cephalexin, cephradine, cefaclor, cefatrizine and cefadroxil for Salmonella species, Escherichia coli and Pasteurella multocida isolated previously from young calves were determined. The MIC90 values for cephalexin, cephradine and cefadroxil ranged between 3.12 micrograms ml-1 and 12.5 micrograms ml-1, whereas those of cefatrizine and cefaclor were 3.12 micrograms ml-1 and 0.78 microgram ml-1, respectively. Each drug was administered intravenously and orally to groups of pre-ruminating calves and orally to early ruminating calves. Although the pharmacokinetic characteristics of the drugs after intravenous injection were similar to other beta-lactam antibiotics, significant differences between the cephalosporins examined were found in respect of certain kinetic parameters. The drugs showed rapid absorption into the systemic circulation after oral administration to pre-ruminating calves but the elimination half-life values (t1/2 beta) varied between three hours (cefaclor and cefadroxil) and nine hours (cefatrizine). The bioavailability of the drugs was about 35 per cent of the administered dose. Co-administration of probenecid with each antibiotic caused a twofold or greater increase in peak serum drug concentrations (Cmax) but the effect on t1/2 beta was variable. Cephalexin, cephradine and cefaclor given to the ruminating calves resulted in very low serum or plasma concentrations and their use should be restricted to younger calves. Cefadroxil was found to give the highest serum concentrations in this age group but had significantly lower bioavailability when compared with the unweaned calves. Provisional oral dosage regimens were computed for each cephalosporin on the basis of the MIC data and the kinetic parameters derived from intravenous and oral drug administration.