Comparative pharmacokinetics of SCE-2787 and related antibiotics in experimental animals

Protein Binding in Translational Antimicrobial Development-Focus on Interspecies Differences

Background/Introduction: Plasma protein binding (PPB) continues to be a key aspect of antibiotic development and clinical use. PPB is essential to understand several properties of drug candidates, including antimicrobial activity, drug-drug interaction, drug clearance, volume of distribution, and therapeutic index. Focus areas of the review: In this review, we discuss the basics of PPB, including the main drug binding proteins i.e., Albumin and α-1-acid glycoprotein (AAG). Furthermore, we present the effects of PPB on the antimicrobial activity of antibiotics and the current role of PPB in in vitro pharmacodynamic (PD) models of antibiotics. Moreover, the effect of PPB on the PK/PD of antibiotics has been discussed in this review. A key aspect of this paper is a concise evaluation of PPB between animal species (dog, rat, mouse, rabbit and monkey) and humans. Our statistical analysis of the data available in the literature suggests a significant difference between antibiotic binding in humans and that of dogs or mice, with the majority of measurements from the pre-clinical species falling within five-fold of the human plasma value. Conversely, no significant difference in binding was found between humans and rats, rabbits, or monkeys. This information may be helpful for drug researchers to select the most relevant animal species in which the metabolism of a compound can be studied for extrapolating the results to humans. Furthermore, state-of-the-art methods for determining PPB such as equilibrium dialysis, ultracentrifugation, microdialysis, gel filtration, chromatographic methods and fluorescence spectroscopy are highlighted with their advantages and disadvantages.

Ceftazidime pharmacokinetics in dogs after intravenous injection and delivered with the RxActuator Mini-Infuser infusion pump

OBJECTIVE

To test the feasibility of an SC mini-infusion pump to deliver ceftazidime in dogs and produce plasma concentrations sufficient to reach a therapeutic target for 48 hours.

SETTING

University research laboratory.

ANIMALS

Six healthy Beagle dogs.

INTERVENTIONS

Ceftazidime was administered by 2 routes to 6 healthy Beagle dogs. The first route was an IV bolus injection into a cephalic vein at a dose of 25 mg/kg. Blood samples were collected for 8 hours following injection. The second route was a SC infusion for 48 hours using the RxActuator Mini-Infuser wearable SC constant rate infusion pump. Blood samples were collected for 58 hours following application of the pump. All plasma samples were analyzed by high-pressure liquid chromatography and subject to pharmacokinetic analysis.

MAIN RESULTS

After the IV bolus injection, there was rapid distribution and elimination. The elimination half-life was 0.95 hours, and the clearance was rapid at 0.176 ml/h/kg. After the 48-hour SC infusion, the half-life was slightly shorter, and the clearance was higher. The percent bioavailability from the SC infusion was approximately 72%. The SC infusion maintained plasma concentration near our target of 8 μg/ml for most of the dose interval but slightly lower after 24 hours. The concentrations below the target were attributed to slight drug loss, less than 100% bioavailability, and faster clearance from SC administration.

CONCLUSIONS

This study demonstrated the successful application of the RxActuator Mini-Infuser wearable SC constant rate infusion pump for delivering an antimicrobial needed for serious, and sometimes resistant, infections in dogs.

Pharmacokinetics of ceftazidime in Northern leopard frogs (Lithobates pipiens) at two different doses and administration routes

OBJECTIVE

To determine an optimal ceftazidime dosing strategy in Northern leopard frogs (Lithobates pipiens) by evaluation of 2 different doses administered SC and 1 dose administered transcutaneously.

ANIMALS

44 Northern leopard frogs (including 10 that were replaced).

PROCEDURES

Ceftazidime was administered to frogs SC in a forelimb at 20 mg/kg (n = 10; SC20 group) and 40 mg/kg (10; SC40 group) or transcutaneously on the cranial dorsum at 20 mg/kg (10; TC20 group). Two frogs in each ceftazidime group were euthanized 12, 24, 48, 72, and 96 hours after drug administration. Plasma, renal, and skin concentrations of ceftazidime were measured by means of reversed-phase high-performance liquid chromatography. Four control frogs were used for assay validation.

RESULTS

Mean plasma half-life of ceftazidime in the SC20, SC40, and TC20 groups was 9.01 hours, 14.49 hours, and too low to determine, respectively. Mean maximum plasma ceftazidime concentration was 92.9, 96.0, and 1.3 μg/mL, respectively. For 24 hours after drug administration in the SC20 and SC40 groups, plasma ceftazidime concentration exceeded 8 μg/mL. Renal and skin concentrations were detectable at both doses and routes of administration; however, skin concentrations were significantly lower than renal and plasma concentrations.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings indicated that ceftazidime administration to Northern leopard frogs at 20 mg/kg, SC, every 24 hours would achieve a plasma concentration exceeding the value considered effective against common amphibian pathogens. Transcutaneous administration of the injectable ceftazidime formulation at 20 mg/kg warrants further investigation but is not currently recommended because of a potential lack of efficacy.

Modelling concentrations of antimicrobial drugs: comparative pharmacokinetics of cephalosporin antimicrobials and accuracy of allometric scaling in food-producing and companion animals

Background

To optimize antimicrobial dosing in different animal species, pharmacokinetic information is necessary. Due to the plethora of cephalosporin antimicrobials and animal species in which they are used, assessment of pharmacokinetics in all species is unfeasible. In this study we aimed to describe pharmacokinetic data of cephalosporins by reviewing the available literature for food producing and companion animal species. We assessed the accuracy of interspecies extrapolation using allometric scaling techniques to determine pharmacokinetic characteristics of cephalosporins in animal species for which literature data is unavailable. We assessed the accuracy of allometric scaling by comparing the predicted and the published pharmacokinetic value in an animal species/humans not included in the allometric modelling.

Results

In general, excretion of cephalosporins takes place mainly through renal mechanisms in the unchanged form and volume of distribution is limited in all animal species. Differences in plasma protein binding capacity and elimination half-life are observed but available information was limited. Using allometric scaling, correlations between body weight (BW) and volume of distribution (Vd) and clearance (Cl) were R² > 0.97 and R² > 0.95 respectively for ceftazidime, ceftiofur, cefquinome and cefepime but not ceftriaxone. The allometric exponent ranged from 0.80 to 1.31 for Vd and 0.83 to 1.24 for Cl. Correlations on half-life ranged from R² 0.07–0.655 (literature) and R² 0.102–0.876 (calculated).

Conclusions

Allometric scaling can be applied for interspecies extrapolation of cephalosporin pharmacokinetic parameters Vd and Cl, but not elimination half-life. We hypothesize that the accuracy could be improved by using more refined scaling techniques.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0817-2) contains supplementary material, which is available to authorized users.

Interspecies scaling of excretory amounts using allometry - retrospective analysis with rifapentine, aztreonam, carumonam, pefloxacin, miloxacin, trovafloxacin, doripenem, imipenem, cefozopran, ceftazidime, linezolid for urinary excretion and rifapentine, cabotegravir, and dolutegravir for fecal excretion

1. Interspecies allometry scaling for prediction of human excretory amounts in urine or feces was performed for numerous antibacterials. Antibacterials used for urinary scaling were: rifapentine, pefloxacin, trovafloxacin (Gr1/low; <10%); miloxacin, linezolid, PNU-142300 (Gr2/medium; 10-40%); aztreonam, carumonam, cefozopran, doripenem, imipenem, and ceftazidime (Gr3/high; >50%). Rifapentine, cabotegravir, and dolutegravir was used for fecal scaling (high; >50%). 2. The employment of allometry equation: Y = aW(b) enabled scaling of urine/fecal amounts from animal species. Corresponding predicted amounts were converted into % recovery by considering the respective human dose. Comparison of predicted/observed values enabled fold difference and error calculations (mean absolute error [MAE] and root mean square error [RMSE]). Comparisons were made for urinary/fecal data; and qualitative assessment was made amongst Gr1/Gr2/Gr3 for urine. 3. Average correlation coefficient for the allometry scaling was >0.995. Excretory amount predictions were largely within 0.75- to 1.5-fold differences. Average MAE and RMSE were within ±22% and 23%, respectively. Although robust predictions were achieved for higher urinary/fecal excretion (>50%), interspecies scaling was applicable for low/medium excretory drugs. 4. Based on the data, interspecies scaling of urine or fecal excretory amounts may be potentially used as a tool to understand the significance of either urinary or fecal routes of elimination in humans in early development.

Pharmacokinetics and penetration of ceftazidime and avibactam into epithelial lining fluid in thigh- and lung-infected mice

Ceftazidime and the β-lactamase inhibitor avibactam constitute a new, potentially highly active combination in the battle against extended-spectrum-β-lactamase (ESBL)-producing bacteria. To determine possible clinical use, it is important to know the pharmacokinetic profiles of the compounds related to each other in plasma and the different compartments of infection in experimentally infected animals and in humans. We used a neutropenic murine thigh infection model and lung infection model to study pharmacokinetics in plasma and epithelial lining fluid (ELF). Mice were infected with ca. 10(6) CFU of Pseudomonas aeruginosa intramuscularly into the thigh or intranasally to cause pneumonia and were given 8 different (single) subcutaneous doses of ceftazidime and avibactam in various combined concentrations, ranging from 1 to 128 mg/kg of body weight in 2-fold increases. Concomitant samples of serum and bronchoalveolar lavage fluid were taken at up to 12 time points until 6 h after administration. Pharmacokinetics of both compounds were linear and dose proportional in plasma and ELF and were independent of the infection type, with estimated half-lives (standard deviations [SD]) in plasma of ceftazidime of 0.28 (0.02) h and of avibactam of 0.24 (0.04) h and volumes of distribution of 0.80 (0.14) and 1.18 (0.34) liters/kg. The ELF-plasma (area under the concentration-time curve [AUC]) ratios (standard errors [SE]) were 0.24 (0.03) for total ceftazidime and 0.27 (0.03) for unbound ceftazidime; for avibactam, the ratios were 0.20 (0.02) and 0.22 (0.02), respectively. No pharmacokinetic interaction between ceftazidime and avibactam was observed. Ceftazidime and avibactam showed linear plasma pharmacokinetics that were independent of the dose combinations used or the infection site in mice. Assuming pharmacokinetic similarity in humans, this indicates that similar dose ratios of ceftazidime and avibactam could be used for different types and sites of infection.

Broad-spectrum β-lactam antibiotics for treating experimental peritonitis in mice due to Klebsiella pneumoniae producing the carbapenemase OXA-48

A lethal peritonitis model was induced in mice with a Klebsiella pneumoniae isolate producing the carbapenemase OXA-48. Administration of a single dose (up to 100 mg/kg) of the antibiotic piperacillin-tazobactam, imipenem-cilastatin, ertapenem, or cefotaxime had little or no impact on lethality. Ceftazidime had the highest efficacy in vivo, which mirrored its in vitro activity; this was not the case for carbapenems. Therefore, ceftazidime may be recommended for the treatment of infections due to OXA-48 producers if they do not coproduce an extended-spectrum β-lactamase or a plasmid-mediated AmpC cephalosporinase.

Influence of experimentally induced fever on the disposition of cefpirome in buffalo calves

The influence of Escherichia coli endotoxin-induced fever on the disposition of cefpirome was investigated in five male buffalo calves following a single intravenous dose of 10mgkg(-1). Blood samples were collected from 1min to 24h of drug administration. The drug concentration in plasma was estimated by microbiological assay using E. coli as a test organism. The disposition of cefpirome followed two-compartment open model and the drug was detected above the minimum inhibitory concentration in plasma up to 12h. The Vd(area) and AUC were 0.75±0.01Lkg(-1) and 35.1±0.46μgml(-1)h, respectively. The elimination half-life of 1.81±0.009h and Cl(B) of 0.29±0.004Lkg(-1)h(-1) reflected rapid elimination and body clearance of cefpirome in febrile buffalo calves. Based on the results, a satisfactory dosage regimen of cefpirome in febrile buffalo calves was calculated to be 6mgkg(-1) to be repeated at 8h intervals.

Pharmacokinetics of ceftazidime after intravenous and intramuscular administration to domestic cats

The pharmacokinetic properties of ceftazidime, a third generation cephalosporin, were investigated in five cats after single intravenous (IV) and intramuscular (IM) administration at a dose rate of 30 mg/kg. Minimum inhibitory concentrations (MICs) of ceftazidime for some Gram-negative (Escherichia coli, n=11) and Gram-positive (Staphylococcus spp., n=10) strains isolated from clinical cases were determined. An efficacy predictor, measured as the time over which the active drug exceeds the bacteria minimum inhibitory concentration (T>MIC), was calculated. Serum ceftazidime disposition was best fitted by a bi-compartmental and a mono-compartmental open model with first-order elimination after IV and IM dosing, respectively. After IV administration, distribution was rapid (t(1/2(d)) 0.04+/-0.03 h), with an area under the ceftazidime serum concentration:time curve (AUC((0-infinity))) of 173.14+/-48.69 microg h/mL and a volume of distribution (V((d(ss)))) of 0.18+/-0.04 L/kg. Furthermore, elimination was rapid with a plasma clearance of 0.19+/-0.08 L/hkg and a t(1/2) of 0.77+/-0.06 h. Peak serum concentration (C(max)), T(max), AUC((0-infinity)) and bioavailability for the IM administration were 89.42+/-12.15 microg/mL, 0.48+/-0.49 h, 192.68+/-65.28 microg h/mL and 82.47+/-14.37%, respectively. Ceftazidime MIC for E. coli ranged from 0.0625 to 32 microg/mL and for Staphylococcus spp. from 1 to 64 microg/mL. T>MIC was in the range 35-52% (IV) and 48-72% (IM) of the recommended dosing interval (8-12h) for bacteria with a MIC(90)4 microg/mL.

Disposition kinetics and urinary excretion of cefpirome after intravenous injection in buffalo calves

We investigated the disposition kinetics and urinary excretion of cefpirome in buffalo calves after a single intravenous administration of 10 mg/kg. Also, an appropriate dosage regimen was calculated. At 1 min after injection, the concentration of cefpirome in the plasma was 57.4 +/- 0.72 microg/ml, which declined to 0.22 +/- 0.01 microg/ml at 24 h. The cefpirome was rapidly distributed from the blood to the tissue compartment as shown by the high distribution coefficient values (8.67 +/- 0.46/h), and by the drug's rate of transfer constant from the central to the peripheral compartment, K(12) (4.94 +/- 0.31/h). The elimination halflife and the volume of distribution were 2.14 +/- 0.02 h and 0.42 +/- 0.005 l/kg, respectively. Once the distribution equilibrium was reached between the tissues and plasma, the total body clearance (Cl(B)) and the ratio of the drug present in the peripheral to the central compartment (T/P ratio) were 0.14 +/- 0.002 l/kg/h and 1.73 +/- 0.06, respectively. Based on the pharmacokinetic parameters we obtained, an appropriate intravenous cefpirome dosage regimen for treating cefpiromesensitive bacteria in buffalo calves would be 8.0 mg/kg repeated at 12 h intervals for 5 days, or until persistence of the bacterial infection occurred.

A delayed nonlinear PBPK model for genistein dosimetry in rats

Genistein is an endocrine-active compound (EAC) found in soy products. It has been linked to beneficial effects such as mammary tumor growth suppression and adverse endocrine-related effects such as reduced birth weight in rats and humans. In its conjugated form, genistein is excreted in the bile, which is a significant factor in its pharmacokinetics. Experimental data suggest that genistein induces a concentration-dependent suppression of biliary excretion. In this article, we describe a physiologically based pharmacokinetic (PBPK) model that focuses on biliary excretion with the goal of accurately simulating the observed suppression. The mathematical model is a system of nonlinear differential equations with state-dependent delay to describe biliary excretion. The model was analyzed to examine local existence and uniqueness of a solution to the equations. Furthermore, unknown parameters were estimated, and the mathematical model was compared against published experimental data.

Species-specific uncertainty factors for compounds eliminated principally by renal excretion in humans

An uncertainty factor of 100 is used to derive health-based guidance values for human intakes of chemicals based on data from studies in animals. The 100-fold factor comprises 10-fold factors for species differences and for interindividual differences in response. Each 10-fold factor can be subdivided into toxicokinetic and toxicodynamic aspects with a 4.0-fold factor to allow for kinetic differences between test species and humans. The current work determined the extent of interspecies differences in the internal dose (toxicokinetics) of compounds which are eliminated primarily by renal excretion in humans. An analysis of the published data showed that renal excretion was also the main route of elimination in the test species for most of the identified probe substrates. Interspecies differences were apparent for both the mechanism of renal excretion (glomerular filtration, tubular secretion and/or reabsorption) and the extent of plasma protein binding, both of which may affect renal clearance and therefore the magnitude of species differences in the internal dose. For compounds which are eliminated unchanged by both humans and the test species, the average differences in the internal doses between humans and animals were 1.6 for dogs, 3.3 for rabbits, 5.2 for rats and 13 for mice. This suggests that for renal excretion, the differences between humans and the rat and especially the mouse may exceed the 4.0-fold default factor for toxicokinetics.

In vitro and in vivo antifungal activities of TAK-456, a novel oral triazole with a broad antifungal spectrum

TAK-456 is a novel oral triazole compound with potent and broad-spectrum in vitro antifungal activity and strong in vivo efficacy against Candida albicans and Aspergillus fumigatus. TAK-456 inhibited sterol synthesis of C. albicans and A. fumigatus by 50% at 3 to 11 ng/ml. TAK-456 showed strong in vitro activity against clinical isolates of Candida spp., Aspergillus spp., and Cryptococcus neoformans, except for Candida glabrata. The MICs at which 90% of the isolates tested were inhibited byTAK-456, fluconazole, itraconazole, voriconazole, and amphotericin B were 0.25, 4, 0.5, 0.13, and 0.5 microg/ml, respectively, for clinical isolates of C. albicans and 1, >64, 0.5, 0.5, and 0.5 microg/ml, respectively, for clinical isolates of A. fumigatus. Therapeutic activities of TAK-456 and reference triazoles against systemic lethal infections caused by C. albicans and A. fumigatus in mice were investigated by orally administering drugs once daily for 5 days, and efficacies of the compounds were evaluated by the prolongation of survival. In normal mice, TAK-456 and fluconazole were effective against infection caused by fluconazole-susceptible C. albicans at a dose of 1 mg/kg. In transiently neutropenic mice, therapeutic activity of TAK-456 at 1 mg/kg of body weight against infection with the same strain was stronger than those at 1 mg/kg of fluconazole. TAK-456 was effective against infections with two strains of fluconazole-resistant C. albicans at a dose of 10 mg/kg. TAK-456 also expressed activities similar to or higher than those of itraconazole against the infections caused by two strains of A. fumigatus in neutropenic mice at a dose of 10 mg/kg. These results suggest that TAK-456 is a promising candidate for development for the treatment of candidiasis and aspergillosis in humans.

Pharmacokinetics of ceftazidime in dogs following subcutaneous administration and continuous infusion and the association with in vitro susceptibility of Pseudomonas aeruginosa

OBJECTIVE

To determine the pharmacokinetics of ceftazidime following subcutaneous administration and continuous IV infusion to healthy dogs and to determine the minimum inhibitory concentration (MIC) of ceftazidime for clinical isolates of Pseudomonas aeruginosa.

ANIMALS

10 healthy adult dogs.

PROCEDURE

MIC of ceftazidime for 101 clinical isolates of P aeruginosa was determined in vitro. Serum concentrations of ceftazidime were determined following subcutaneous administration of ceftazidime (30 mg/kg of body weight) to 5 dogs and continuous IV infusion of ceftazidime (loading dose, 4.4 mg/kg; infusion rate, 4.1 mg/kg/h) for 36 hours to 5 dogs.

RESULTS

The MIC of ceftazidime for P aeruginosa was < or = 8 microg/ml; all isolates were considered susceptible. Following SC administration of ceftazidime, mean beta disappearance half-life was 0.8 hours, and mean serum ceftazidime concentration exceeded the MIC for P aeruginosa for only 4.3 hours. Two dogs had gastrointestinal tract effects. Mean serum ceftazidime concentration exceeded 16 microg/ml during continuous IV infusion. None of the dogs developed adverse effects.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of ceftazidime subcutaneously (30 mg/kg, q 4 h) or as a constant IV infusion (loading dose, 4.4 mg/kg; rate, 4.1 mg/kg/h) would maintain serum ceftazidime concentrations above the MIC determined for 101 clinical isolates of P aeruginosa. Use of these dosages may be appropriate for treatment of dogs with infections caused by P aeruginosa.

Enterococcus faecalis aggravates pyelonephritis caused by Pseudomonas aeruginosa in experimental ascending mixed urinary tract infection in mice

Mixed urinary tract infection was caused by simultaneous inoculation of 10(4) CFU each of Enterococcus faecalis TN2005 and Pseudomonas aeruginosa P9 into the bladders of CBA/J mice. Both organisms proliferated in the kidneys, and viable cell counts of E. faecalis TN2005 reached a peak level of 4.1 x 10(5) CFU per pair of kidneys within the first 24 h, while P. aeruginosa P9 counts increased more slowly. The number of P. aeruginosa P9 cells peaked at 8.3 x 10(6) CFU per pair of kidneys 5 days after infection. Five days after mixed infection, infiltration of neutrophils into the renal pelvis and renal medulla was observed. Immunohistochemical staining revealed the presence of E. faecalis antigen in the renal medulla. P. aeruginosa antigen was detected mainly in the renal pelvis 5 days after infection and in the renal medulla as well as the renal pelvis 14 days after infection. Mixed infection induced pyelonephritis within 5 days after mixed infection, while it was not observed until 14 days after infection with P. aeruginosa P9 alone. P. aeruginosa P9 inoculated together with E. faecalis TN2005 was more resistant to eradication from the kidneys by beta-lactam antibiotics than P. aeruginosa P9 inoculated alone. These results suggest that E. faecalis TN2005 invades the renal medulla first in mixed urinary tract infection and induces histological changes which lead to aggravation of the pyelonephritis caused by P. aeruginosa P9.

Therapeutic effect of cefozopran (SCE-2787), a new parenteral cephalosporin, against experimental infections in mice

The therapeutic effect of cefozopran (SCE-2787), a new semisynthetic parenteral cephalosporin, against experimental infections in mice was examined. Cefozopran was more effective than cefpiramide and was as effective as ceftazidime and cefpirome against acute respiratory tract infections caused by Klebsiella pneumoniae DT-S. In the model of chronic respiratory tract infection caused by K. pneumoniae 27, cefozopran was as effective as ceftazidime. The therapeutic effect of cefozopran against urinary tract infections caused by Pseudomonas aeruginosa P9 was superior to that of cefpirome and was equal to those of ceftazidime and cefclidin. In addition, cefozopran was more effective than ceftazidime and was as effective as flomoxef in a thigh muscle infection caused by methicillin-sensitive Staphylococcus aureus 308A-1. Against thigh muscle infections caused by methicillin-resistant S. aureus N133, cefozopran was the most effective agent. The potent therapeutic effect of cefozopran in those experimental infections in mice suggests that it would be effective against respiratory tract, urinary tract, and soft tissue infections caused by a variety of gram-positive and gram-negative bacteria in humans.