Binding of amino beta-lactam antibiotics to soluble protein from rat intestinal mucosa--I. Purification of drug-binding protein

Increased therapeutic failure for cephalexin versus comparator antibiotics in the treatment of uncomplicated outpatient cellulitis

We reviewed records of outpatients to determine the therapeutic failure rate of cephalexin in treating uncomplicated cellulitis. Therapeutic failure was defined as an increase in antibiotic dosage, prescription renewal, or addition or substitution of another antibiotic. Demographics, physical characteristics, risk factors, intervention, and outcome data were collected. Twenty-seven percent of patients failed therapy with an oral antibiotic. The failure rate for cephalexin was 40% versus 20% for comparator antibiotics (p=0.02, odds ratio [OR] 2.62, 95% confidence interval [CI] 1.18-5.75). We identified no statistically significant variables related to cephalexin failure. Concomitant acid suppressive therapy was administered with cephalexin in 42% of failures and 20% of nonfailures (p=0.11, OR 2.78, 95% CI 0.77-9.87). These data suggest that cephalexin's efficacy was less than that of other antimicrobials in treating cellulitis, possibly related to concurrent acid suppression.

Restricted intestinal absorption of some beta-lactam antibiotics by an energy-dependent efflux system in rat intestine

PURPOSE

The purpose of this study was to examine factors limiting the intestinal absorption of orally inactive beta-lactam antibiotics.

METHODS

Permeation behaviors of various beta-lactam antibiotics across rat intestinal segments were evaluated in vitro using diffusion cells.

RESULTS

Poorly absorbed beta-lactam antibiotics, like cephaloridine and cefoperazone, commonly exhibit greater serosal-to-mucosal permeation than mucosal-to-serosal permeation, while cephalexin permeation was greater in the mucosal-to-serosal direction. In the absence of D-glucose, secretory-oriented permeation of cephaloridine and cefoperazone disappeared. Addition of sodium azide into an experimental buffer including D-glucose significantly and selectively enhanced mucosal-to-serosal permeation of cephaloridine and cefoperazone. Although benzylpenicillin, ampicillin, and amoxicillin all showed secretory-oriented permeation, the tendency to permeation was greatest with benzylpenicillin and least with amoxicillin. Probenecid stimulated mucosal-to-serosal permeation of cephaloridine, but verapamil and p-aminohippuric acid had no significant effect on it.

CONCLUSIONS

It has been suggested that mechanisms which induce secretory-oriented permeation of orally inactive beta-lactam antibiotics are factors limiting intestinal absorption of such antibiotics. This energy-demanding efflux system was distinct from P-glycoprotein-mediated transport. A free alpha-amino group in the molecule is an important factor for reducing an affinity with the efflux system.

The transport mechanisms of organic cations and their zwitterionic derivatives across rat intestinal brush-border membrane. 1. Binding characteristics to the bio- and lipid-membranes

The uptake mechanisms of organic cations such as tryptamine, tyramine, 5-benzyloxytryptamine (BOTA) and their zwitterionic derivatives (tyrosine, tryptophan, 5-benzyloxytryptophan (BOTP)) by rat intestinal brush-border membrane vesicles and liposome containing phosphatidylserine were studied and compared. As compared to their zwitterionic derivatives, uptake rates by rat intestinal brush-border membrane of these three cations were far superior. The binding of cationic compounds to the brush-border membrane was also higher than those of their zwitterionic derivatives. Furthermore, the binding behaviour of BOTA and tryptamine to phospholipid liposome clearly amplified with increasing amounts of phosphatidylserine. In contrast, the contents of phosphatidylserine, a negatively charged phospholipid, exhibited no effects on the binding of zwitterionic derivatives (tryptophan and BOTP). The double-reciprocal plot of tryptamine binding with BOTA to liposome showed competitive inhibition. These results suggest that the binding of organic cations to the membrane lipid has a relatively high specificity despite the absence of membrane protein such as a transport-carrier in the liposome, and that the binding of cationic compounds play an important role in the uptake to the cell membrane systems.

Uptake characteristics of polyamines into rat intestinal brush-border membrane

The uptake characteristics of polyamines, such as spermine, spermidine and putrescine, have been investigated using brush-border membrane vesicles isolated from the small intestine of rats. The uptake of these polyamines into the membrane vesicles was high and the order of uptake was spermine greater than spermidine greater than putrescine at medium pH 7.5, respectively. The medium pH considerably affected the uptake of these polyamines and the amount of uptake increased remarkably with an increase of the medium pH (pH 7.5 or 8.0 greater than pH 5.5). An inward Na+ gradient did not stimulate the uptake rate of any of these polyamines. We have also examined the binding behaviour to the membrane lipid, phospholipids and total lipid, and there was a good correlation in the binding properties, pH-dependency and uptake activity, between the liposomes and brush-border membrane vesicles. These results suggest that the uptake of the polyamine into the vesicles consisted of rapid binding to the outside intestinal surface and slower binding to the inside membrane after permeation. Furthermore, findings from experiments concerning the mutual inhibition among these polyamines and concerning the effect of other polycations, having 2-5 amines in number, on the uptake of spermine, suggest that the number of amino groups in the polyamine molecules plays an important role in the uptake process into the brush-border membrane vesicles.

Contribution of passive transport mechanisms to the intestinal absorption of beta-lactam antibiotics

The transport characteristics of aminopenicillins (ampicillin and amoxicillin), aminocephalosporins (cephalexin, cephradine and cefadroxil) and cefazolin have been compared with those of an actively transported substance (D-glucose) and a passively transported substance (L-glucose). Although the initial uptake of the aminocephalosporins was stimulated in the presence of an inward H+ gradient, there was no overshoot in the uptake of any of the drugs tested, even in the presence of an H+ gradient. Also, the time course and the degree of uptake of these drugs were similar to those of L-glucose, especially in the absence of an H+ gradient. These results suggest that the beta-lactam antibiotics tested, like L-glucose, pass through the rat intestinal brush border membrane mainly by passive diffusion. However, the differences in absorption between these drugs, like the differences in their disappearance from a proximal loop of rat intestine, cannot be explained by a simple permeation process alone.

Comparison of transport characteristics of amino beta-lactam antibiotics and dipeptides across rat intestinal brush border membrane

The transport characteristics of amino beta-lactam antibiotics, ampicillin and cephradine, have been examined and compared with that of glycylglycine using brush border membrane vesicles isolated from rat small intestine. The initial rate of glycylglycine uptake was markedly stimulated in the presence of an inward H+ gradient compared with the uptake rates in the absence of an H+ gradient. With the same H+ gradient the stimulation of cephradine uptake was lower and ampicillin uptake was not altered. Cephradine uptake, however, was greater than that of glycylglycine in both vesicular conditions ((pH)i greater than (pH)o and (pH)i = (pH)o). Inhibitory effects of dipeptides, ampicillin and cephradine on the initial uptake of glycylglycine were also examined. Glycylglycine uptake was significantly decreased in the presence of L-phenylalanylglycine or carnosine. Ampicillin and cephradine did not alter the uptake of glycylglycine. These results suggest that the contribution of the inward H+ gradient to the permeation of ampicillin, cephradine and glycylglycine across the rat small intestinal brush border membranes is different for each of the substances examined.

Effect of chlorpromazine on the permeability of beta-lactam antibiotics across rat intestinal brush border membrane vesicles

The effect of chlorpromazine on the membrane permeability of beta-lactam antibiotics (benzylpenicillin, ampicillin, cephradine and cephalexin) and actively transported substances (glycylglycine and D-glucose) has been studied using rat intestinal brush border membrane vesicles. Except for cephalexin, the initial uptakes at 25 degrees C of these antibiotics were significantly enhanced in the presence of chlorpromazine. In contrast, the transport of glycylglycine and D-glucose was significantly inhibited. These results suggest that the two groups, drugs and actively transported substances, have a different permeation process. The effect of chlorpromazine concentration on membrane lipid fluidity, as assessed by the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-anilino-8-naphthalene sulphonate (ANS), was also examined. The fluorescence polarization of ANS decreased with increasing concentration of chlorpromazine, while that of DPH increased suggesting an increase of membrane surface fluidity might affect the permeation of beta-lactam antibiotics and actively transported substances in a different manner.