Disposition of ceftriaxone in rat: application of a pharmacokinetic-protein binding model and comparison with cefotaxime

Evaluation of Galleria mellonella larvae for measuring the efficacy and pharmacokinetics of antibiotic therapies against Pseudomonas aeruginosa infection

The aim of this study was to determine whether Galleria mellonella larvae can be used (i) as an in vivo infection model for Pseudomonas aeruginosa and (ii) for evaluating the pharmacokinetics and efficacy of antipseudomonal antibiotics. Two strains of P. aeruginosa were employed, NCTC 10662 (antibiotic-susceptible) and NCTC 13437 (multidrug-resistant). Larvae were infected with increasing doses of either P. aeruginosa strain to investigate the effect of inoculum size on survival. Subsequently, infected larvae were treated with a range of antibiotics to examine whether these agents were effective against P. aeruginosa infection in vivo and whether the efficacy of these drugs matched the known susceptibilities of each bacterial strain. Larval burden of P. aeruginosa was also determined after infection and treatment with cefotaxime. Pharmacokinetic properties of the antibiotics tested were measured using a well diffusion assay to determine the concentration of antibiotics in larval haemolymph over time. Galleria mellonella larvae were sensitive to P. aeruginosa infection, and increasing inoculum doses of live cells resulted in greater larval mortality. Heat-killed bacteria had no detrimental effect on survival. Antibiotic efficacy against P. aeruginosa-infected G. mellonella correlated with the measured in vitro sensitivities of the two strains tested. The therapeutic benefit arising from administration of cefotaxime correlated with a reduced burden of bacteria present in the haemolymph. There was a clear correlation between measured antibiotic pharmacokinetics and the therapeutic effect. This study strongly supports future application of the G. mellonella infection model to initial studies of novel antipseudomonal treatments.

LB11058, a new cephalosporin with high penicillin-binding protein 2a affinity and activity in experimental endocarditis due to homogeneously methicillin-resistant Staphylococcus aureus

LB11058 is a new synthetic cephalosporin with good affinity for staphylococcal penicillin-binding protein 2a (PBP2a). LB11058 was tested in vitro and in rats with experimental aortic endocarditis against three methicillin-resistant Staphylococcus aureus (MRSA) strains, one penicillinase-negative strain (strain COL), and two penicillinase-producing strains (COL-Bla+ and P8-Hom). The MICs of LB11058 for the organisms were 1 mg/liter. The MICs of vancomycin and ceftriaxone were 1 and >/=64 mg/liter, respectively. In population analysis profiles, none of the MRSA strains grew at >/=2 mg of LB11058/liter. Rats with endocarditis were treated for 5 days. LB11058 was highly bound to serum proteins in rats (>/=98%). However, binding was saturable above a threshold of 250 mg/liter. Therefore, continuous concentrations of 250 mg/liter in serum were infused to ensure a free fraction (>/=5 mg/liter) above the drug's MIC for the entire infusion period. Control treatments included simulation of human serum kinetics produced by intravenous vancomycin (1 g twice daily, free drug concentration above MIC, >/=90% of infusion period) or ceftriaxone (2 g/24 h, free drug concentrations above the MIC, 0% of infusion period). LB11058 successfully treated 10 of 10 (100%) and 13 of 14 (93%) of rats infected with COL-Bla+ and P8-Hom, respectively. This was comparable to vancomycin (sterilization of 8 of 12 [66%] and 6 of 8 [75%] rats, respectively). Ceftriaxone was inactive. Low concentrations of LB11058 (5 and 10 mg/liter, continuously infused) in serum were ineffective, as predicted by the pharmacodynamic parameters. At appropriate doses, LB11058 was highly effective both in vitro and in vivo. This finding supports the development of this beta-lactam with high PBP2a affinity for the treatment of MRSA infections.

Enhanced oral bioavailability of poorly absorbed drugs. I. Screening of absorption carrier for the ceftriaxone complex

In this study, we attempted to improve the oral absorption of ceftriaxone (CTX) by using an absorption carrier and the CTX complex together. After the CTX-Ca-carrageenan gel complex was prepared, several kinds of compounds (Capmul MCM C10, Gelucire 44/14, glycyrrhizin) were screened as potential oral enhancers for our experiment and the intestinal morphologies in rats were examined. Of these compounds, the mono- and diglyceride mixtures, Capmul MCM C10 greatly enhanced the gastrointestinal absorption of CTX when this carrier was coadministered with the complex in rats. Percent bioavailability was attained in rats by the enteral route ranging from 55 to 79% when this complex was administered with various doses of Capmul MCM C10. Furthermore, the surface morphology of the complex has a highly smooth appearance as seen under scanning electron microscopy after preparation. No treatment-related signs of any damage were observed on the administrations intestinal membrane when morphologies were examined in rats after the complex and the absorption carrier were coadministered. The results of the observation suggest that Capmul MCM C10 is a promising carrier, having a good balance between bioavailability enhancing activity and safety, for the oral delivery of CTX when it is coadministered with complex.

Determination of unbound ceftriaxone in rat blood by on-line microdialysis and microbore liquid chromatography

In vivo microdialysis was used to determine unbound ceftriaxone in rat blood. A microdialysis probe was inserted into the jugular vein/right atrium of Sprague-Dawley rats, and dose of 10 mg/kg ceftriaxone was then administered via the femoral vein. Dialysates were automatically collected and injected into a liquid chromatographic system via an on-line injector. Isocratic elution of ceftriaxone within 10 min was achieved using a microbore liquid chromatographic system. The chromatographic mobile phase consisted of methanol-100 mM monosodium phosphoric acid (15:85, v/v, pH 7.0). The wavelength of the UV detector was set at 280 nm. Intra- and inter-assay accuracy and precision of the assay were less than 15%. The detection limit of ceftriaxone was 20 ng/ml. The results suggest that unbound ceftriaxone in rat blood is best fit to a biexponential decay model.

Comparison of plasma and free tissue levels of ceftriaxone in rats by microdialysis

Ceftriaxone has a very high plasma protein binding (up to 98%) that is saturable and decreases with higher concentrations. This high protein binding results in high concentrations in plasma that are frequently related to the anti-infective activity. However, because only the free fraction of the drug is pharmacologically active and most of the infections are located in the tissues, it is more relevant to evaluate unbound concentrations in the interstitial space. Plasma and tissue pharmacokinetics of ceftriaxone in rats after single intravenous administration were investigated at two different concentrations (50 and 100 mg/kg). Both plasma and tissue samples were taken simultaneously from the same animal and analyzed by reversed-phase high-performance liquid chromatography. Free tissue levels in the thigh muscle were measured by microdialysis. The concentration in plasma is much higher than the free concentration in tissue. After determination of nonlinear protein binding by microdialysis and including these parameters in the pharmacokinetic model, it is possible to predict free concentrations in the interstitial space from plasma levels for any given dose.