Metal-carbenicillin framework-based nanoantibiotics with enhanced penetration and highly efficient inhibition of MRSA.

The development of effective therapies to control methicillin-resistant Staphylococcus aureus (MRSA) infections is challenging because antibiotics can be degraded by the production of certain enzymes, for example, ß-lactamases. Additionally, the antibiotics themselves fail to penetrate the full depth of biofilms formed from extracellular polymers. Nanoparticle-based carriers can deliver antibiotics with better biofilm penetration, thus combating bacterial resistance. In this study, we describe a general approach for the construction of ß-lactam antibiotics and ß-lactamase inhibitors co-delivery of nanoantibiotics based on metal-carbenicillin framework-coated mesoporous silica nanoparticles (MSN) to overcome MRSA. Carbenicillin, a ß-lactam antibiotic, was used as an organic ligand that coordinates with Fe3+ to form a metal-carbenicillin framework to block the pores of the MSN. Furthermore, these ß-lactamase inhibitor-loaded nanoantibiotics were stable under physiological conditions and could synchronously release antibiotic molecules and inhibitors at the bacterial infection site to achieve a better elimination of antibiotic resistant bacterial strains and biofilms. We confirmed that these ß-lactamase inhibitor-loaded nanoantibiotics had better penetration depth into biofilms and an obvious effect on the inhibition of MRSA both in vitro and in vivo.

Role of the monocarboxylic acid transport system in the intestinal absorption of an orally active beta-lactam prodrug: carindacillin as a model.

Transport of carbenicillin (CBPC) and its orally active prodrug (carindacillin, CIPC) was studied with rat intestinal brush border membrane vesicles (BBMV). CIPC was transported uphill into BBMV in the presence of a H(+) gradient, indicating that CIPC absorption is carrier-mediated. Indeed, CIPC was predominantly transported by the monocarboxylic acid transport system, although it might be possible that CIPC possesses some affinity to the oligopeptide transporter. In contrast, CBPC exhibited no affinity to either the oligopeptide or the monocarboxylic acid transport system. Apparent uptake clearance of CIPC was approximately 70-fold greater than that of CBPC. It was clarified that the modification of the chemical structure of CBPC (a dicarboxylic acid) to CIPC (a monocarboxylic acid) by ester formation may have resulted in the increased affinity to the monocarboxylic acid transport system, which, in turn, led to improved absorption of the prodrug.

Mechanism of intestinal absorption of an orally active beta-lactam prodrug: uptake and transport of carindacillin in Caco-2 cells.

Absorption characteristics of carindacillin (CIPC) were investigated using Caco-2 cells, and the results were compared with those of its parent drug, carbenicillin (CBPC). Uptake of CBPC was not affected by the metabolic inhibitor or the change in extracellular pH. CBPC appeared to be taken up into Caco-2 cells by passive diffusion. In contrast, the uptake of CIPC was greater at lower extracellular pH and was inhibited in the presence of carbonyl cyanide p-(trifluoromethoxy)phenyl hydrazone, a protonophore. Also, transport of CIPC through Caco-2 cell monolayer was energy and temperature dependent. Moreover, the uptake and transport of CIPC were significantly inhibited in the presence of various monocarboxylic acids, which are the substrates of the monocarboxylic acid transport system(s), whereas the substrates of the oligopeptide transporter had no effect on the uptake or transport of CIPC. These results suggested that the absorption of CIPC may be mediated by the monocarboxylic acid transport system(s), not by the oligopeptide transporter. Furthermore, the uptake and transport of CIPC were approximately 40-fold greater than those of CBPC. Therefore, it is likely that the participation of a carrier-mediated transport in the absorption of CIPC may significantly contribute to the improved absorption of the prodrug over the parent drug.

Stereoselective renal secretion of carbenicillin in rabbits: role of the organic anion transporter at the renal brush border membrane.

Stereoselectivity in the renal secretion of carbenicillin (CBPC) was studied in rabbits. Significant renal secretion of CBPC was observed in vivo, with the secretion of the S-epimer being greater than that of the R-epimer. Stereoselective transport of CBPC was further studied in vitro using basolateral and brush border membrane vesicles prepared from rabbit kidneys. The transport of CBPC by the organic anion transporter into the basolateral membrane vesicles (BLMV) was not stereoselective. In contrast, a distinct stereoselectivity was observed in the transport of CBPC by the organic anion transporter into the brush border membrane vesicles (BBMV), with the transport of the S-epimer being more favorable. Significant epimer-epimer interactions were also observed in the transport into BBMV. The stereoselectivity of the transport of CBPC was calculated from the kinetic parameters with consideration of epimer-epimer interactions and was similar to that observed in vivo. It was concluded that the observed stereoselectivity in the renal secretion of CBPC in vivo reflected that of transport via the organic anion transporter located at the brush border membrane.

Lack of renal secretion of carbenicillin in rats: poor affinity to the organic anion transporter at renal brush border membrane.

The renal secretion of carbenicillin (CBPC) was studied in rats. The results obtained in the in vivo study indicated very poor renal secretion of CBPC in rats, which was entirely different from those observed in humans and rabbits. In humans and rabbits, significant and stereoselective renal secretion of CBPC was observed in vivo. In order to verify the poor renal secretion of CBPC in rats, the transport characteristics of the organic anion transporters were studied in vitro using basolateral and brush border membrane vesicles. Transport of p-aminohippuric acid (PAH) into the basolateral membrane vesicles (BLMVs) was inhibited by CBPC, indicating that the organic anion transporter located at the BLM may have affinity to CBPC. In contrast, the transport of PAH into the brush border membrane vesicles (BBMVs) was not inhibited by CBPC, suggesting that the organic anion transporter located at the BBM may not have affinity to CBPC. Similar results were obtained for sulbenicillin (SBPC). Since CBPC and SBPC exist as di-anions at physiological pH, the organic anion transporter located at the rat renal BBM may not exhibit affinity to water-soluble di-anions, which in turn will result in poor renal secretion of these compounds.

The effect of the renal portal system on pharmacokinetic parameters in the red-eared slider (Trachemys scripta elegans).

The premise that drugs not be injected into the caudal body of reptiles because they will be carried by the renal portal system to the kidneys, where they may be nephrotoxic or rapidly excreted, was tested by comparing the pharmacokinetics of gentamicin (excreted via glomerular filtration in mammals) and carbenicillin (excreted partly via renal tubular secretion in mammals) following injection into the forelimb or hindlimb of red-eared sliders (Trachemys scripta elegans). Ten sliders received intramuscular gentamicin (10 mg/kg) in a forelimb (n = 5) or a hindlimb (n = 5), and plasma levels of the drug were assayed over time. Following drug clearance, the experiment was repeated with the site of injection reversed so that each animal acted as its own control. Another 10 sliders were similarly treated, using intramuscular carbenicillin (200 mg/kg). Injection site of gentamicin had no effect on any pharmacokinetic parameter (time to maximum plasma concentration, maximum plasma concentration, half-life, area under the curve, clearance, and volume of distribution). However, the area under the curve of plasma carbenicillin concentration vs. time was significantly lower following hindlimb injection, in comparison with forelimb injection, at 1, 4, and 8 hr, which may reflect reduced bioavailability of the drug, as would be expected with renal portal perfusion and tubular excretion on first pass through the kidney. This effect on carbenicillin likely is not clinically important because plasma levels remained above recommended minimum inhibitory concentrations. Because blood draining the caudal body of reptiles passes through the kidneys or the liver before reaching the central circulation, the effect on the pharmacokinetics of a drug injected in that region will vary with its renal or hepatic extraction rate. Generally, this effect is unlikely to be significant.

Stereoselective renal tubular secretion of carbenicillin.

The stereoselective disposition of carbenicillin epimers was studied in healthy human volunteers. There was a difference between the two epimers in the extent of plasma protein binding in vitro, with the unbound fraction of the R epimer being greater than that of the S epimer. Renal clearance (CLR) of each epimer was greater than the glomerular filtration rate, suggesting renal tubular secretion of both epimers. Although the CLR was greater for the R epimer, renal tubular secretion was greater for the S epimer. When probenecid was coadministered, the CLR of each epimer was significantly reduced and was approximately equal to the glomerular filtration rate. The difference in CLR between the two epimers was simply due to differences in plasma protein binding. The observations in the present study suggest that both carbenicillin epimers are secreted by an organic anion transport system in the renal proximal tubule in humans and that the two epimers may be distinguished in the secretion process, resulting in the differences in the secretion rates.

The kinetic disposition and dosage regimen for carbenicillin in buffalo calves.

The distribution half-life, elimination half-life, apparent volume of distribution and total body clearance of carbenicillin in healthy buffalo calves following a single intravenous administration (50 mg/kg) were 0.057 +/- 0.005 h, 1.688 +/- 0.11 h, 0.185 +/- 0.021 L kg-1 and 75.97 +/- 6.519 ml kg-1 h-1 respectively. A satisfactory dosage regimen for carbenicillin in buffalo calves was calculated to be 56 mg/kg followed by 52 mg/kg body weight repeated at 6 h intervals.

Drug delivery through soft contact lenses.

Clinical studies were conducted on 466 patients waiting for senile cataract surgery and receiving chloromycetin, gentamicin, or carbenicillin subconjunctivally and through New Sauflon 70 and New Sauflon 85 lenses. The aqueous drug levels were biologically estimated at various time intervals. Soft contact lenses provided significantly higher drug penetration than subconjunctival therapy. Both modes of treatment provided therapeutically effective levels against most of the common ocular pathogens for varying intervals of 2 to 12 hours.

[Antibiotic pharmacokinetics in rats with an infected inflammation]. / Farmakokinetika nekotorykh antibiotikov u krys s infitsirovannym vospaleniem.

Penetration of antibiotics into infected inflammation foci depended on the level of their binding to serum proteins. Low binding ampicillin provided the highest levels of the free antibiotic in both serum and the inflammation foci. At the same time coefficients of antibiotic penetration into purulent infiltrates and infected tissues were close and amounted approximately to 70-80 per cent. Antibiotic elimination from the infection foci was retarded as compared to that from serum.