Pharmacokinetics and tissue fluid distribution of cephalexin in the horse after oral and i.v. administration

Recent advances on quinoxalines as target-oriented chemotherapeutic anticancer agents through apoptosis

The current review outlines all possible recent synthetic platforms to quinoxaline derivatives and the potent stimulated apoptosis mechanisms targeted by anticancer therapies. The currently reported results disclosed that quinoxaline derivatives had promising anticancer potencies against a wide array of cancer cell lines, better than the reference drugs, through target inhibition. This review summarizes some potent quinoxaline derivatives with their synthesis strategies and their potential activities against various molecular targets. Quinoxalines can be considered an important scaffold for apoptosis inducers in cancer cells through inhibiting some molecular targets, so they can be further developed as target-oriented chemotherapeutics.

Prescribed drugs containing nitrogen heterocycles: an overview

Heteroatoms as well as heterocyclic scaffolds are frequently present as the common cores in a plethora of active pharmaceuticals natural products. Statistically, more than 85% of all biologically active compounds are heterocycles or comprise a heterocycle and most frequently, nitrogen heterocycles as a backbone in their complex structures. These facts disclose and emphasize the vital role of heterocycles in modern drug design and drug discovery. In this review, we try to present a comprehensive overview of top prescribed drugs containing nitrogen heterocycles, describing their pharmacological properties, medical applications and their selected synthetic pathways. It is worth mentioning that the reported examples are actually limited to current top selling drugs, being or containing N-heterocycles and their synthetic information has been extracted from both scientific journals and the wider patent literature.

Pharmacokinetics of single doses of maropitant citrate in adult horses

The neurokinin-1 (NK) receptor antagonist, maropitant citrate, mitigates nausea and vomiting in dogs and cats. Nausea is poorly understood and likely under-recognized in horses. Use of NK-1 receptor antagonists in horses has not been reported. The purpose of this study was to determine the pharmacokinetic profile of maropitant in seven adult horses after single intravenous (IV; 1 mg/kg) and intragastric (IG; 2 mg/kg) doses. A randomized, crossover design was performed. Serial blood samples were collected after dosing; maropitant concentrations were measured using LC-MS/MS. Pharmacokinetic parameters were determined using noncompartmental analysis. The mean plasma maropitant concentration 3 min after IV administration was 800 ± 140 ng/ml, elimination half-life was 10.37 ± 2.07 h, and volume of distribution was 6.54 ± 1.84 L/kg. The maximum concentration following IG administration was 80 ± 40 ng/ml, and elimination half-life was 9.64 ± 1.27 hr. Oral bioavailability was variable at 13.3 ± 5.3%. Maropitant concentrations achieved after IG administration were comparable to those in small animals. Concentrations after IV administration were lower than in dogs and cats. Elimination half-life was longer than in dogs and shorter than in cats. This study is the basis for further investigations into using maropitant in horses.

Comparative plasma and interstitial fluid pharmacokinetics and tissue residues of ceftiofur crystalline-free acid in cattle with induced coliform mastitis

Ceftiofur (CEF) is a third-generation cephalosporin that is the most widely used antimicrobial in the dairy industry. Currently, violative meat residues in cull dairy cattle are commonly associated with CEF. One potential cause for violative residues is altered pharmacokinetics of the drug due to disease, which could increase the time needed for the residue to deplete. The objectives of this study were (a) to determine the absolute bioavailability of CEF crystalline-free acid (CFA) in healthy versus diseased cows; (b) to compare the plasma and interstitial fluid pharmacokinetics and plasma protein binding of CEF between healthy dairy cows and those with disease; and (c) to determine the CEF residue profile in tissues of diseased cows. For this trial, disease was induced through intramammary Escherichia coli infusion. Following disease induction and CEF CFA administration, for plasma concentrations, there was not a significant effect of treatment (p = 0.068), but the treatment-by-time interaction (p = 0.005) was significant. There was a significantly greater concentration of CEF in the plasma of the DIS cows at T2 hr (p = 0.002), T8 hr (p < 0.001), T12 hr (p = 0.001), and T16 hr (p = 0.002). For PK parameters in plasma, the slope of the terminal phase of the concentration versus time curve was significantly lower (p = 0.007), terminal half-life was significantly longer (p = 0.014), and apparent volume of distribution during the elimination phase was significantly higher (p = 0.028) diseased group. There was no difference in plasma protein binding of CEF and interstitial fluid pharmacokinetics. None of the cows had kidney CEF residues above the US tolerance level following observation of the drug's withdrawal period, but one cow with a larger apparent volume of distribution and longer terminal half-life had tissue residues slightly below the tolerance. Whereas these findings do not support the hypothesis that severely ill cows need longer withdrawal times, alterations in the terminal half-life suggest that it is theoretically possible.

Pharmacokinetics of ceftazidime after regional limb perfusion in standing horses

OBJECTIVE

To determine the metacarpophalangeal joint fluid concentrations of ceftazidime administered via regional limb perfusion (RLP).

ANIMALS

Eight healthy horses.

METHODS

RLP was performed by injecting 2 g of ceftazidime and 60 mL of perfusate volume in the cephalic vein of standing, sedated horses. Serum and synovial fluid from the metacarpophalangeal joint were collected before perfusion and at 0.5, 2, 6, 12, 24 hours postperfusion. Ceftazidime concentrations were measured via liquid chromatography. Maximal concentration (C_max ), area under the curve (AUC), half-life of the drug (T ½), and the timing of C_max (T_max ) were determined to assess ceftazidime as a candidate drug for RLP. Continuous parameters were compared with the Mann-Whitney U test. P value ≤ .05 was considered statistically significant.

RESULTS

The C_max of ceftazidime in synovial fluid (235 µg/mL) was 15 times higher than the minimal inhibitory concentration (MIC) for most bacteria involved in orthopedic infections, including resistant pathogens such as Pseudomonas aeruginosa (MIC = 16 µg/mL). However, synovial concentrations decreased quickly and remained above the MIC in only 1 horse by 6 hours postperfusion.

CONCLUSION

RLP generated high synovial fluid concentrations of ceftazidime in the distal limb, but these concentrations decreased rapidly below the deliberately high MIC selected.

CLINICAL RELEVANCE

Once daily RLP, as applied in our study, with 2 g ceftazidime in standing horses, cannot be recommended for use in a clinical setting.

Determination of anisomycin in tissues and serum by LC-MS/MS: application to pharmacokinetic and distribution studies in rats

The first study on anisomycin pharmacokinetics in rats using a new preparation method for tissues and serum and LC-MS/MS analysis.

Ultrafiltration of equine digital lamellar tissue

There are no experimentally validated pharmacological means of preventing laminitis; however, locally acting pharmaceutical agents with the potential to prevent laminitis have been identified. Demonstrating therapeutic drug concentrations in lamellar tissue is essential for evaluating the efficacy of these agents. The aim of this study was to develop an experimental technique for repeatedly sampling lamellar interstitial fluid. A technique for placing ultrafiltration probes was developed in vitro using 15 cadaver limbs. Subsequently, lamellar ultrafiltration probes were placed in one forelimb in six living horses. Interstitial fluid was collected continuously from the probes as ultrafiltrate for 4 (n = 4) or 14 days (n = 2). The rate of ultrafiltrate collection was calculated every 12 h. Biochemical analyses were performed on ultrafiltrate collected on night 1 (12-24 h post-implantation) and night 4 (84-96 h post-implantation). Sections surrounding the probe and control tissue from the contralateral limb were harvested, stained with H&E and Masson's trichrome and scored based on the tissue response to the probe. Ultrafiltration probes were placed in the lamellar tissue in all six horses. Ultrafiltrate was collected from these probes at 55 (30-63) μL/h (median [interquartile range]). Fluid production decreased significantly with time from night 3 onwards (P < 0.05). There was no significant change in the constituents of the ultrafiltrate between nights 1 and 4 (P > 0.05). The technique was well tolerated. This study demonstrates that ultrafiltration can be used to sample equine digital lamellar interstitial fluid, and has potential for measuring lamellar drug levels.

Distribution of enrofloxacin and its active metabolite, using an in vivo ultrafiltration sampling technique after the injection of enrofloxacin to pigs

The objective of this study was to determine the pharmacokinetics (PK) of enrofloxacin in pigs and compare to the tissue interstitial fluid (ISF). Six healthy, young pigs were administered 7.5 mg/kg enrofloxacin subcutaneously (SC). Blood and ISF samples were collected from preplaced intravenous catheters and ultrafiltration sampling probes placed in three different tissue sites (intramuscular, subcutaneous, and intrapleural). Enrofloxacin concentrations were measured using high-pressure liquid chromatography with fluorescence detection, PK parameters were analyzed using a one-compartment model, and protein binding was determined using a microcentrifugation system. Concentrations of the active metabolite ciprofloxacin were negligible. The mean ± SD enrofloxacin plasma half-life, volume of distribution, clearance, and peak concentration were 26.6 ± 6.2 h (harmonic mean), 6.4 ± 1.2 L/kg, 0.18 ± 0.08 L/kg/h, and 1.1 ± 0.3 μg/mL, respectively. The half-life of enrofloxacin from the tissues was 23.6 h, and the maximum concentration was 1.26 μg/mL. Tissue penetration, as measured by a ratio of area-under-the-curve (AUC), was 139% (± 69%). Plasma protein binding was 31.1% and 37.13% for high and low concentrations, respectively. This study demonstrated that the concentration of biologically active enrofloxacin in tissues exceeds the concentration predicted by the unbound fraction of enrofloxacin in pig plasma. At a dose of 7.5 mg/kg SC, the high tissue concentrations and long half-life produce an AUC/MIC ratio sufficient for the pathogens that cause respiratory infections in pigs.

Dermal drug levels of antibiotic (cephalexin) determined by electroporation and transcutaneous sampling (ETS) technique

The purpose of this project was to assess the validity of a novel Electroporation and transcutaneous sampling (ETS) technique for sampling cephalexin from the dermal extracellular fluid (ECF). This work also investigated the plausibility of using cephalexin levels in the dermal ECF as a surrogate for the drug levels in the synovial fluid. In vitro and in vivo studies were carried out using hairless rats to assess the workability of ETS. Cephalexin (20 mg/kg) was administered (i.v.) through tail vein and the time course of drug concentration in the plasma was determined. In the same rats, cephalexin concentration in the dermal ECF was determined by ETS and microdialysis techniques. In a separate set of rats, only intraarticular microdialysis was carried out to determine the time course of cephalexin concentration in synovial fluid. The drug concentration in the dermal ECF determined by ETS and microdialysis did not differ significantly from each other and so as were the pharmacokinetic parameters. The results provide validity to the ETS technique. Further, there was a good correlation ( approximately 0.9) between synovial fluid and dermal ECF levels of cephalexin indicating that dermal ECF levels could be used as a potential surrogate for cephalexin concentration in the synovial fluid.

Sorption mechanisms of cephapirin, a veterinary antibiotic, onto quartz and feldspar minerals as detected by Raman spectroscopy

Raman spectroscopy was used to investigate sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO(2)) and feldspar (KAlSi(3)O(8)) at different pH. Sorption occurs by electrostatic attraction, monodentate and bidentate complexation. The zwitterion (CHP(o)) adsorbs to a quartz((+)) surface by electrostatic attraction of the carboxylate anion group (-COO(-)) at low pH, but adsorbs to a quartz((-)) surface through electrostatic attraction of the pyridinium cation, and possibly COO(-) bridge complexes, at higher pH. CHP(-) bonds to quartz((-)) surfaces by bidentate complexation between one oxygen of -COO(-) and oxygen from carbonyl of an acetoxymethyl group. On a feldspar((+/-)) surface, CHP(o) forms monodentate complexes between CO, and possible -COO(-) bridges and/or electrostatic attachments to localized edge (hydr)oxy-Al surfaces. CHP(-) adsorbs to feldspar((-)) through monodentate CO complexation. Similar mechanisms may operate for other cephalosporins. Results demonstrate, for the first time, that Raman techniques can be effective for evaluating sorption mechanisms of antibiotics.

Mucosal permeability of water-soluble drugs in the equine jejunum: a preliminary investigation

Ussing chambers have been used to study the mucosal permeability of drugs in humans, rats and other species. This data can then be used to develop in vitro/in vivo correlations (IVIVC) for drugs based on the Biopharmaceutics Classification System (BCS). Due to the poor oral bioavailability of many drugs in the horse, this method may be useful for screening drugs before development to determine if they warrant further study. Cephalexin (CPX), marbofloxacin (MAR), metronidazole (MTZ) and fluconazole (FCZ) were chosen for this study based on the wide range of physicochemical properties and bioavailability in the horse. Permeability was ranked as follows: MTZ > FCZ > MAR > CPX. This correlated with the bioavailability (R(2) = 0.633447), the Log P (R(2) = 0.648517), as well as the molecular weight (R(2) = 0.851208) of the drugs. Metronidazole induced a decrease in the tissue transepithelial resistance, suggestive of the possibility of tissue toxicity, which may have falsely increased its permeability. The low permeability of cephalexin across the tissue may indicate a lack of active transporters that are found in other species. From this study, we can conclude that the Ussing chamber is a promising method for determining mucosal permeability in the horse.

Development of enzyme-linked immunosorbent assays for the detection of deacetoxycephalosporin C and isopenicillin N synthase activity

Although there are a number of existing assays for monitoring the activity of both isopenicillin N synthase (IPNS) and deacetoxycephalosporin C synthase (DAOCS), none have demonstrated the qualities required for screening a mutant library. Hence, enzyme-linked immunosorbent assays (ELISAs) for IPNS and DAOCS were developed based on the detection of the catalytic turnover products isopenicillin N and cephalexin/phenylacetyl-7-aminodeacetoxycephalosporanic acid (G-7-ADCA), respectively. These assays are relatively fast compared to existing assays, such as the hole-plate bioassay, and are amenable with high-throughput screening. Both the IPNS and DAOCS-ELISAs were optimised for use with crude protein extracts rather than purified protein, thereby eliminating any additional time required for purification. The ELISA developed for the detection of cephalexin had an IC50 value of 154+/-9 ng mL(-1) and LOD of 7.2+/-2.2 ng mL(-1) under conditions required for the assay. Good recoveries and correlation was observed for spiked samples when the concentration of crude protein was kept below 1 mg mL(-1). The DAOCS-ELISA was found to have increased sensitivity compared to the hole-plate bioassay (10.3 microg mL(-1)). The IPNS-ELISA did not significantly increase the sensitivity (approximately 5 microg mL(-1)) compared to that of the hole-plate bioassay (16 microg mL(-1)) for isopenicillin N. The minimum amount of crude protein extract required for producing detectable amounts of product for both assays was below 0.5% of the maximum amount of protein that the assay could contain without any effect on the ELISA. This suggests that when screening a mutant library, mutants producing low amounts of the product could still be detected using these assays.