Competitive inhibition of the luminal efflux by multidrug and toxin extrusions, but not basolateral uptake by organic cation transporter 2, is the likely mechanism underlying the pharmacokinetic drug-drug interactions caused by cimetidine in the kidney.

Cimetidine, an H2 receptor antagonist, has been used to investigate the tubular secretion of organic cations in human kidney. We report a systematic comprehensive analysis of the inhibition potency of cimetidine for the influx and efflux transporters of organic cations [human organic cation transporter 1 (hOCT1) and hOCT2 and human multidrug and toxin extrusion 1 (hMATE1) and hMATE2-K, respectively]. Inhibition constants (K(i)) of cimetidine were determined by using five substrates [tetraethylammonium (TEA), metformin, 1-methyl-4-phenylpyridinium, 4-(4-(dimethylamino)styryl)-N-methylpyridinium, and m-iodobenzylguanidine]. They were 95 to 146 µM for hOCT2, providing at most 10% inhibition based on its clinically reported plasma unbound concentrations (3.6-7.8 µM). In contrast, cimetidine is a potent inhibitor of MATE1 and MATE2-K with K(i) values (µM) of 1.1 to 3.8 and 2.1 to 6.9, respectively. The same tendency was observed for mouse Oct1 (mOct1), mOct2, and mouse Mate1. Cimetidine showed a negligible effect on the uptake of metformin by mouse kidney slices at 20 µM. Cimetidine was administered to mice by a constant infusion to achieve a plasma unbound concentration of 21.6 µM to examine its effect on the renal disposition of Mate1 probes (metformin, TEA, and cephalexin) in vivo. The kidney- and liver-to-plasma ratios of metformin both were increased 2.4-fold by cimetidine, whereas the renal clearance was not changed. Cimetidine also increased the kidney-to-plasma ratio of TEA and cephalexin 8.0- and 3.3-fold compared with a control and decreased the renal clearance from 49 to 23 and 11 to 6.6 ml/min/kg, respectively. These results suggest that the inhibition of MATEs, but not OCT2, is a likely mechanism underlying the drug-drug interactions with cimetidine in renal elimination.

Modulation in concentrative nucleoside transporters-mediated intestinal absorption of mizoribine, an immunosuppressive agent, in lipopolysaccharide-treated rats.

The characteristics of intestinal absorption of mizoribine and cephalexin, that are mediated by concentrative nucleoside transporters (CNTs) and PEPT1, respectively, was examined in lipopolysaccharide (LPS)-treated rats. LPS treatment is known to modify the expression of some transporters and induce cholestasis. At 24 h after the LPS treatment, averaged concentrations of IL-6 and total bile acids in plasma were 15-fold and 2-fold that in untreated control rats, respectively, and bile flow rate decreased by 40% of control, indicating the induction of inflammatory and cholestatic states. The oral bioavailability, estimated by urinary excretion percentage of unchanged form, of mizoribine in LPS-treated rats was 1.5-fold higher than that in control rats, whereas the bioavailability of cephalexin remained unchanged. When mizoribine and cephalexin were administered into in-situ jejunum loops, there were no differences in the absorption rates between control and LPS-treated rats. These results indicated that the functional expression of CNT1, CNT2, and PEPT1 were not modulated by LPS treatment. When mizoribine (a CNT1/CNT2 substrate) and gemcitabin (a CNT1 substrate) were administered as a solution dissolved in bile into the intestinal loop, their absorption rates decreased significantly. In contrast, the absorption rate of ribavirin (a CNT2 substrate) remained unchanged. In conclusion, LPS treatment exerted no significant effect on the expression of CNT1 and CNT2 in the intestine. Bile was found to suppress the CNT1-mediated intestinal absorption of mizoribine and gemcitabin. The increased oral bioavailability of mizoribine in LPS-treated rats could be ascribed to the less amount of bile or bile acids in the intestine under cholestatic state of rats.

Reduced renal clearance of a zwitterionic substrate cephalexin in MATE1-deficient mice.

Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1) mediates the transport of not only organic cations but also zwitterions such as cephalexin. However, the contribution of MATE1 to tubular secretion of cephalexin in vivo has not been elucidated. In the present study, we carried out transport experiments of cephalexin via MATE1 and performed pharmacokinetic analyses of cephalexin in Mate1 knockout [Mate1(-/-)] mice. Cephalexin uptake by human MATE1-expressing human embryonic kidney 293 cells exhibited saturable kinetics (K(m) = 5.9 +/- 0.5 mM) and a bell-shaped pH profile with a maximum at pH 7.0. We confirmed that mouse MATE1 also transported cephalexin. After a single intravenous administration of cephalexin (5 mg/kg), Mate1(-/-) mice showed higher plasma concentrations of cephalexin than wild-type [Mate1(+/+)] mice. The urinary excretion of cephalexin for 60 min was significantly reduced, and the renal concentration was markedly increased in Mate1(-/-) mice compared with Mate1(+/+) mice. The renal clearance of cephalexin in Mate1(-/-) mice was approximately 60% of that in Mate1(+/+) mice and seemed to be near the creatinine clearance. In contrast, there were no significant differences between both mice in the pharmacokinetics of anionic cefazolin, which is not a substrate for MATE1. In this study, we demonstrated that MATE1 is responsible for renal tubular secretion of a zwitterionic substrate cephalexin in vivo.

Determination of cephalexin residual level using ultra-high-performance liquid chromatography-tandem mass spectrometry: Residue depletion study in swine.

An ultra-high-performance liquid chromatography-tandem mass spectrometry method was developed to analyze cephalexin in swine tissues, urine, and feces. Samples were extracted with 1% sulfuric acid, followed by purification using MCX cartridges. Mean recoveries were 95.4%-100.7% with inter-day relative standard deviations of <8.6%. The quantitation limit was 5 µg/kg for fat and urine, and 10 µg/kg for muscle, liver, kidney, and feces. Cephalexin residue depletion was determined using 32 healthy pigs, randomly divided into eight (seven treated and one control) groups. Treated groups were intramuscularly administered 10 mg/kg b.w. five times at 24-h intervals and euthanized 6 h and 1, 2, 3, 5, 7, and 10 days after the last injection. Cephalexin was eliminated rapidly in swine muscle, liver, fat, and feces. The highest concentrations among edible organs were detected in the kidney. Moreover, the longest elimination period of cephalexin in swine was determined in urine. These results indicated that kidney and urine were likely target matrices for cephalexin residue detection in swine.

Selective solid-phase extraction of amoxicillin and cephalexin from urine samples using a molecularly imprinted polymer.

In this paper we describe, for the first time, a molecularly imprinted polymer (MIP) for the antibiotic amoxicillin (AMX), synthesised by a noncovalent molecular imprinting approach and used to extract AMX selectively from urine samples. The MIP was applied as a molecularly selective sorbent in molecularly imprinted SPE (MISPE) in an off-line mode, where it showed useful cross-selectivity for a structurally related antibiotic, cephalexin (CPX). By using a MISPE protocol, the MIP was able to selectively extract both AMX and CFX from 5 mL of water spiked with 10 mg/L with recoveries of 75 and 78% for AMX and CFX, respectively. When applied to real samples (urine) at clinically relevant concentrations, recoveries from 2 mL of human urine spiked with 20 mg/L decreased slightly to 65 and 63% for AMX and CFX, respectively. To demonstrate further the selectivity of the MIP obtained, a comparison with commercially available SPE cartridges was performed. Improvements in the retention of both AMX and CFX on the MIP were obtained relative to the commercially available cartridges, and the MISPE extracts were considerably cleaner, due to molecularly selective analyte binding by the MIP.

Clinical pharmacology of cephalexin administered by intravenous injection.

Cephalexin IG was given by intravenous injection to eight normal volunteers, five patients with chronic renal failure, and three patients during a period of haemodialysis. In normal subjects there was a rapid fall in serum concentration and 80% of the administered dose was excreted in the urine within two hours. The mean serum half life was 1.1 hours (range 0.6-1.8 hours). Prior treatment with probenecid in two subjects led to a twofold increase in serum concentration two hours after injection. In the patients with chronic renal failure antimicrobial activity persisted for 24 hours and the half life ranged from 6.1 to 18.1 hours. Haemodialysis led to partial removal of cephalexin from the blood, but antimicrobial activity remained eight hours after injection at the end of the dialysis period. The serum half life in these patients was 5.1, 5.6, and 5.7 hours.

Direct quantitative determination of optically active absorbing drugs in human urine by circular dichroism. Simultaneous direct determination of beta-lactam antibiotics and proteins.

Over 200 urine samples from 61 subjects were analyzed by circular dichroism spectroscopy. The results proved that this technique can be applied to the direct determination of optically active absorbing drugs in urine of subjects under multiple drug administration, independently of the presence of proteins, which can simultaneously be determined. A list of noninterfering drugs is included. The validity of the present method was confirmed by analysis of variance, the beta-lactam antibiotics ampicillin, cefoxitin, and cephalexin being chosen as model drugs and human albumin as the analytical standard for protein determination. The results demonstrated that the proposed method is accurate and precise, the correlation coefficients being higher than 0.9996. A circular dichroism and HPLC data comparison was successfully performed. The principal advantages of this method are simplicity, quickness, and economy, no derivatization or chromatographic separation steps being needed.

Effects of ethanol on the pharmacokinetics of cephalexin and cefadroxil in the rat.

Data are presented on the effect of ethanol on the intestinal absorption and excretion in rats of two beta-lactam antibiotics, cephalexin (CFX) and cefadroxil (CFD). A recirculating perfusion technique within an antibiotic concentration range of 0.5 to 50 mM was used. Ethanol was administered either in an acute form into the intestine or in a chronic form as a 15% drinking solution for 2 months. The results are normalized in relation to the metabolic body weight, intestinal length, and osmotic conditions. Acute ethanol treatment decreases the antibiotic absorption; biliary excretion of CFD is increased, while urinary excretion of CFX is lowered. Chronic treatment shows slight negative effects on the absorption of CFX and CFD. Results are interpreted on the basis of the effect of ethanol on biological membranes. Enhanced urinary excretion after acute ethanol treatment, as well as differences between transport mechanisms, are invoked to explain these effects.

The determination of cephradine and cephalexin by reverse phase high-performance liquid chromatography.

The application of reverse phase high-performance liquid chromatography to the separation and analysis of cephradine and cephalexin is demonstrated. The procedure has been applied to chemicals, pharmaceutical formulations and reaction solutions. The preparation of samples is simple and rapid. Chromatographic conditions are described for both pellicular and small particle columns. The feasibility of determing cephradine and cephalexin in physiological fluids has also been demonstrated.

Evaluation of the effect of cephalexin and enrofloxacin on clinical laboratory measurements of urine glucose in dogs.

OBJECTIVE: To determine the effects of cephalexin and enrofloxacin on results of 4 commercially available urine glucose tests in dogs. ANIMALS: 6 healthy adult female dogs. PROCEDURE: In a crossover design, cephalexin (22 and 44 mg/kg [10 and 20 mg/lb], p.o., q 8 h) or enrofloxacin (5 and 10 mg/kg [2.3 and 4.5 mg/lb], p.o., q 12 h) was administered to dogs for 1 day. Urine samples were tested for glucose at 0, 6, and 24 hours after drug administration. In vitro, dextrose was added to pooled glucose-negative canine urine samples containing either no antimicrobial or known concentrations of either antimicrobial; urine samples were then tested for glucose. RESULTS: In vivo, false-positive results were obtained by use of a tablet test in the presence of both antimicrobials and by use of a strip test in the presence of cephalexin. In vitro, false-positive results were obtained with the tablet test at the highest urine concentration of cephalexin (2,400 microg/mL) and with a strip test at the highest concentration of enrofloxacin (600 microg/mL). Enrofloxacin in urine samples containing dextrose caused the urine glucose tests to underestimate urine glucose concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Cephalexin and enrofloxacin at dosages used in clinical practice may result in false-positive or false-negative urine glucose results, and care should be taken when using urine as a basis for identifying or monitoring diabetic animals.

[Microbiological assay method of cefadroxil in biological specimens (author's transl)].

A microbiological method for quantitative determination of cefadroxil in biological specimens is described. This method is essentially a cylinder-plate or a paper-disc method using Micrococcus luteus ATCC 9341 as the test organism grown in the tryptosoya broth added with 1.5% agar. Cefadroxil standard calibration curves are prepared in pooled human serum, moni-trol I or consera for the determination of serum level of human, and 0.1 M phosphate buffer (pH 6.0) to determine urine level. Cefadroxil in human serum and urine specimens can be measured by cylinder-plate method as low as 0.16 approximately 0.31 micrograms/ml and 0.08 approximately 0.16 micrograms/ml, respectively. Further, any active metabolites of cefadroxil were not detected on human and rat urine specimens by bioautography.

[Pharmacokinetics of cefadroxil in rats: comparison of fasting and non-fasting (author's transl)].

A single dose 50 mg/kg of cefadroxil was administered orally to rats in fasting and non-fasting. In both fasting and non-fasting, the serum levels of cefadroxil were higher than those of cephalexin. In fasting, the biological half-life (T 1/2) of cefadroxil was longer than that of cephalexin. This indicates its prolonged durable action. Ingestion of cefadroxil with food affected the serum level less than that of cephalexin with food, and the serum levels of cefadroxil in non-fasting were same as those of cephalexin in fasting.

[Clinical results of cefadroxil in children and pharmacokinetics of the drug (author's transl)].

Cefadroxil was administered orally at a daily dose of 30-40 mg/kg to 8 cases of the infection of upper respiratory tract mainly due to beta-hemolytic Streptococcus, and efficacy was obtained in 7 cases, this rate being considered to be satisfactory, though the cases were too few to reach a conclusion. As to pathogens of bacterial infection of upper respiratory tract, beta-hemolytic Streptococcus and Staphylococcus aureus were encountered especially frequently, and in view of antibacterial activity against these 2 bacteria, our results could be approved. Further investigations should be performed carefully, however, to determine if cefadroxil may be a drug of first choice in the treatment of severe bacterial pneumonia and pyothorax. No side effects were observed throughout our treatment, though digestive tract disorders, especially diarrhea, are most frequent in literatures. As to pharmacokinetical characteristic of cefadroxil, almost the same results were obtained to other reports, though our data are insufficient as our experience was limited in only 1 case. Serum levels were determined after 35.7 mg/kg of cefadroxil were administered once orally, and a peak of about 38 mcg/ml appeared 2 hours later, and a high level of about 30 mcg/ml was maintained at 5 hours, though an oral dose was high. Efficacy for large area of bacterial infections may be expected from these serum levels. From urine collected simultaneously, about 74% of cefadroxil was recovered within more than 4 hours. This showed that cefadroxil was well absorbed from digestive tract, and a major part was excreted rapidly through kidney. From the results of our experiment, characteristics of cefadroxil may be summarized as follows. Cefadroxil is absorbed well after oral administration, antibacterial action is fully expected from serum level, a major part is excreted through kidney, and clearance is good. Cefadroxil will be recommended especially for bacterial infections of upper respiratory tract due to beta-hemolytic Streptococcus and Staphylococcus aureus.

[Study of S-6437 in pediatrics regarding clinical efficacy, blood levels and urinary excretion (author's transl)].

S-6437 was orally given to 29 patients of 3 months to 12 years and 6 months of age who had respiratory or urinary tract infections. The daily dose used was 25 to 60 mg/kg divided in two doses. The following is the results of this study: 1. With 25 approximately 60 mg/kg/day, satisfactory results were obtained for upper respiratory tract infections. In lower respiratory tract infections, however, the effectiveness seemed not to be so good as that in upper respiratory tract infections. 2. Side effects such as diarrhea, loose stool, abdominal pain and eruption were observed but they were temporary. Therefore, the administration of S-6437 was not discontinued due to such side effects. 3. S-6437 was acceptable to elder children but some of children of 2 approximately 4 years of age disliked this preparation because it was not smooth in their mouths. Therefore, the preparation of S-6437 should be further improved. 4. Since it has been recognized that blood levels of cephalexin following the administration of S-6437 last for a longer period of time than regular cephalexin, S-6437 is considered to be a useful preparation. 5. B.I.D. and T.I.D. regimens of S-6437 will give clinical satisfaction to children over 6 years and ones under 6 years, respectively.

Effects of sodium bicarbonate and ammonium chloride pre-treatments on PEPT2 (SLC15A2) mediated renal clearance of cephalexin in healthy subjects.

PEPT2 mediates the H(+) gradient-driving reabsorption of di- and tri-peptides, and various peptidomimetic compounds in the kidney. This study examines the influence of urinary pH modification through sodium bicarbonate and ammonium chloride pre-treatments on the function of PEPT2 in healthy subjects, using cephalexin as the probe drug. Sixteen male subjects received a single oral dose of 1000 mg cephalexin under ammonium chloride and sodium bicarbonate treatment, respectively, with a wash-out period of one week. The study subjects were genotyped for PEPT2 polymorphic variants. Cephalexin concentrations in plasma and urine were determined by high performance liquid chromatography. The mean renal clearance of cephalexin was significantly higher under ammonium chloride treatment than that under sodium bicarbonate treatment (P < 0.01). This difference was significant for PEPT2*2/*2 (P = 0.017) but not for PEPT2*1/*1 (P = 0.128). No differences were observed for other pharmacokinetic parameters. The findings of this study suggest that urinary pH changes may alter the pharmacokinetics of PEPT2's substrates. This effect was more obvious for the PEPT2*2/*2.