Pharmacokinetics of clarithromycin and concentrations in body fluids and bronchoalveolar cells of foals

Physiologically based pharmacokinetic modeling to assess the drug-drug interactions of anaprazole with clarithromycin and amoxicillin in patients undergoing eradication therapy of H. pylori infection

OBJECTIVE

This study aimed to assess the pharmacokinetic (PK) interactions of anaprazole, clarithromycin, and amoxicillin using physiologically based pharmacokinetic (PBPK) models.

METHODS

The PBPK models for anaprazole, clarithromycin, and amoxicillin were constructed using the GastroPlus™ software (Version 9.7) based on the physicochemical data and PK parameters obtained from literature, then were optimized and validated in healthy subjects to predict the plasma concentration-time profiles of these three drugs and assess the predictive performance of each model. According to the analysis of the properties of each drug, the developed and validated models were applied to evaluate potential drug-drug interactions (DDIs) of anaprazole, clarithromycin, and amoxicillin.

RESULTS

The developed PBPK models properly described the pharmacokinetics of anaprazole, clarithromycin, and amoxicillin well, and all predicted PK parameters (Cmax,ss, AUC0-τ,ss) ratios were within 2.0-fold of the observed values. Furthermore, the application of these models to predict the anaprazole-clarithromycin and anaprazole-amoxicillin DDIs demonstrates their good performance, with the predicted DDI Cmax,ss ratios and DDI AUC0-τ,ss ratios within 1.25-fold of the observed values, and all predicted DDI Cmax,ss, and AUC0-τ,ss ratios within 2.0-fold. The simulated results show no need to adjust the dosage when co-administered with anaprazole in patients undergoing eradication therapy of H. pylori infection since the dose remained in the therapeutic range.

CONCLUSION

The whole-body PBPK models of anaprazole, clarithromycin, and amoxicillin were built and qualified, which can predict DDIs that are mediated by gastric pH change and inhibition of metabolic enzymes, providing a mechanistic understanding of the DDIs observed in the clinic of clarithromycin, amoxicillin with anaprazole.

Should Airway Interstitial Fluid Be Used to Evaluate the Pharmacokinetics of Macrolide Antibiotics for Dose Regimen Determination in Respiratory Infection?

Macrolide antibiotics are important drugs to combat infections. The pharmacokinetics (PK) of these drugs are essential for the determination of their optimal dose regimens, which affect antimicrobial pharmacodynamics and treatment success. For most drugs, the measurement of their concentrations in plasma/serum is the surrogate for drug concentrations in target tissues for therapy. However, for macrolides, simple reliance on total or free drug concentrations in serum/plasma might be misleading. The macrolide antibiotic concentrations of serum/plasma, interstitial fluid (ISF), and target tissue itself usually yield very different PK results. In fact, the PK of a macrolide antibiotic based on serum/plasma concentrations alone is not an ideal predictor for the in vivo efficacy against respiratory pathogens. Instead, the PK based on drug concentrations at the site of infection or ISF provide much more clinically relevant information than serum/plasma concentrations. This review aims to summarize and compare/discuss the use of drug concentrations of serum/plasma, airway ISF, and tissues for computing the PK of macrolides. A better understanding of the PK of macrolide antibiotics based on airway ISF concentrations will help optimize the antibacterial dose regimen as well as minimizing toxicity and the emergence of drug resistance in clinical practice.

Pharmacokinetics of tildipirosin in horses after intravenous and intramuscular administration and its potential muscle damage

Tildipirosin is a novel semisynthetic macrolide antibiotic exclusively used in veterinary practice to treat respiratory infections. There are no pharmacokinetic or safety information available regarding the use of tildipirosin after intramuscular administration in horses. Thus, the objective of this work was to determine the disposition kinetics of tildipirosin after intravenous (IV) and intramuscular (IM) administration in horses and its potential muscle damage and cardiotoxicity. Six mature, Spanish-breed horses were used in a crossover study with a washout period of 30 days. Tildipirosin (18%) was administered at single doses by IV (2 mg/kg) and IM (4 mg/kg) routes. Tildipirosin plasma concentrations were determined by HPLC assay with ultraviolet detection. Muscle damage and inflammation were assessed by creatine kinase (CK) and haptoglobin (Hp), respectively. Creatine kinase myocardial band (CK-MB) and troponin (Tn) were used to evaluate cardiotoxicity. Tildipirosin in horses reached peak concentrations (C_max = 1.13 μg/mL) at 0.60 h (t_max) after IM administration with an absolute bioavailability of 109.2%. Steady-state volume of distribution and clearance were 3.31 ± 0.57 L/kg and 0.22 ± 0.02 L/h/kg, respectively. Tildipirosin did not cause cardiotoxicity since CK-MB and Tn basal levels were not significantly different from those obtained after several days post-administration. Mild local reactions were observed after IM administration. This local inflammation was associated with mild myolysis (CK 239-837 UI/L), which was detectable for 48 h. In brief, tildipirosin could help to treat respiratory infections in horses because it showed extensive distribution, high bioavailability and did not provoke general adverse reactions.

Rhodococcus equi Foal Pneumonia: Update on Epidemiology, Immunity, Treatment, and Prevention

Pneumonia in foals caused by the bacterium Rhodococcus equi has a worldwide distribution and is a common cause of disease and death for foals. The purpose of this narrative review is to summarise recent developments pertaining to the epidemiology, immune responses, treatment, and prevention of rhodococcal pneumonia of foals. Screening tests have been used to implement earlier detection and treatment of foals with presumed subclinical R. equi pneumonia to reduce mortality and severity of disease. Unfortunately, this practice has been linked to the emergence of antimicrobial resistant R. equi in North America. Correlates of protective immunity for R. equi infections of foals remain elusive, but recent evidence indicates that innate immune responses are important both for mediating killing and orchestrating adaptive immune responses. A macrolide antimicrobial in combination with rifampin remains the recommended treatment for foals with R. equi pneumonia. Great need exists to identify which antimicrobial combination is most effective for treating foals with R. equi pneumonia and to limit emergence of antimicrobial-resistant strains. In the absence of an effective vaccine against R. equi, passive immunisation remains the only commercially-available method for effectively reducing the incidence of R. equi pneumonia. Because passive immunisation is expensive, labour-intensive, and carries risks for foals, great need exists to develop alternative approaches for passive and active immunisation.

Pharmacokinetic profiles of clarithromycin in freshwater crocodiles (Crocodylus siamensis)

Clarithromycin (CLA) is a new β-lactamase-resistant macrolide antibiotic with potent activity against gram-positive and some gram-negative bacteria. To the authors' best knowledge, limited pharmacokinetic information to establish suitable therapeutic plans is available for freshwater crocodiles. To assess the prudent use of antibiotic in reptiles, this study was conducted to explore the pharmacokinetic characteristics of CLA in the freshwater crocodile, Crocodylus siamensis, following either single intravenous (i.v.) or intramuscular (i.m.) administration at a dosage of 2.5 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168 h. CLA plasma samples were cleaned up using liquid-liquid extraction, and analysed by a validated liquid chromatography tandem-mass spectrometry (LC-MS/MS). CLA was quantifiable from 5 min to 72 h after i.v. administration, whereas it was detectable for 168 after i.m. administration at an identical dose rate. A non-compartmental model was used to fit the plasma concentration of CLA versus time curve for each crocodile. The t_1/2λz value, similar for both routes (20 h), indicated that the overall rate of elimination of CLA in crocodiles is relatively slow. The average i.m. F% was complete. The protein plasma bound was found to be about 30%. CLA is a time-dependent antibiotic, and the T > MIC is the best PK/PD predictor for its efficacy. The CLA dosage of 2.5 mg/kg appeared to produce an appropriate value of the PK-PD surrogate that predicts antibacterial success for disease caused by susceptible bacteria.

Evaluation by polymerase chain reaction assay of persistent shedding of pathogenic leptospires in the urine of dogs with leptospirosis

BACKGROUND

Persistent leptospiruria in naturally infected dogs occurs despite appropriate antibiotic treatment.

HYPOTHESIS/OBJECTIVES

To determine the frequency of persistent leptospiruria in naturally infected dogs and the association of persistent leptospiruria with different antibiotic treatments.

ANIMALS

Thirty-two dogs of varying age and breed diagnosed with leptospirosis via urine polymerase chain reaction assay (PCR).

METHODS

A prospective observational study of dogs diagnosed with leptospirosis was undertaken to determine the frequency of persistent leptospiruria as determined by PCR. Clinical presentation of leptospirosis, antibiotic treatment, serum creatinine concentration, and outcome were recorded.

RESULTS

Fifteen of 32 dogs had a negative urine PCR on the first submission in the study, 5 of 15 received only an aminopenicillin. The remaining 17 dogs had a negative urine PCR on the second (n = 6 dogs), third (n = 5), fourth (n = 5), and eighth (n = 1) submissions. Acute kidney injury was reported in 32/32 dogs. Two of 32 dogs developed chronic kidney disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

Persistent leptospiruria is common despite treatment with antibiotics frequently recommended for treatment. Follow-up urine PCR to confirm clearance of the organism is recommended in all dogs. In dogs with persistent leptospiruria, chronic kidney disease can develop after acute kidney injury.

Pharmacokinetics and pulmonary distribution of Draxxin® (tulathromycin) in healthy adult horses

The objective of this study was to determine the pharmacokinetics and tolerability of tulathromycin (Draxxin^® ; 2.5 mg/kg once) after intramuscular (IM), subcutaneous (SC), and slow intravenous (IV) administration to six adult horses. A three-phase design and 4-week washout period were used. Drug concentrations in blood and bronchoalveolar lavage (BAL) samples were determined by ultra-performance liquid chromatography tandem mass spectrometry and pharmacokinetic parameters calculated using noncompartmental analysis. Following SC and IM administration, all horses exhibited sweating, discomfort, and periods of recumbency. As signs were more severe after SC administration this route was only used in 3/6 horses. Intravenous administration of tulathromycin was well tolerated in all horses. Mean bioavailability was 99.4% IM and 115% SC. Mean maximum plasma concentration was 645 ng/ml IM and 373 ng/ml SC. Mean half-life was 59.8 h, 54.8 h, and 57.9 h for IV, IM, and SC administration, respectively. Mean clearance was 3.25 ml/kg/min, and mean volume of distribution was 16.8 L/kg following IV administration. Drug was detectable in plasma and BAL samples for 120 h following all routes; however, adverse effects may prevent IM use and SC use is not recommended. Tulathromycin may be a practical and affordable antimicrobial for use in adult equine patients.

Is Antimicrobial Treatment Effective During Therapeutic Plasma Exchange? Investigating the Role of Possible Interactions

Antimicrobial treatment during therapeutic plasma exchange (TPE) remains a complex issue. Recommendations based on a limited number of experimental studies should be implemented in clinical practice with caution. Effective management of infections due to plasma or albumin-related interactions, as well as impaired pharmacokinetics, in critical illness is difficult. Knowing the pharmacokinetics of the drugs concerned and the procedural aspects of plasmapheresis should be helpful in planning personalized treatment. In general, possessing a low distribution volume, a high protein-binding affinity, a low endogenous clearance rate, and long distribution and elimination half-lives make a drug more prone to elimination during TPE. A high frequency and longer duration of the procedure may also contribute to altering a drug's concentration. The safest choice would be to start and finish TPE before antimicrobial agent infusion. If this not feasible, a reasonable alternative is to avoid administering the drug just before TPE and to delay the procedure for the time of the administered drug's distributive phase. Ultimately, if plasma exchange must be performed urgently or the drug has a very narrow therapeutic index, monitoring its plasma concentration is advised.

Efficacy of liposomal gentamicin against Rhodococcus equi in a mouse infection model and colocalization with R. equi in equine alveolar macrophages

Rhodococcus equi, a facultative intracellular pathogen and an important cause of pneumonia in foals, is highly susceptible to killing by gentamicin in vitro. However, gentamicin is not effective in vivo, due to its poor cellular penetration. Encapsulation of drugs in liposomes enhances cellular uptake. The objectives of this study were to compare liposomal gentamicin and free gentamicin with respect to their uptake by equine macrophages and intracellular colocalization with R. equi and to compare the efficacies of liposomal gentamicin, free gentamicin and clarithromycin with rifampin for the reduction of R. equi CFU in a mouse model of infection. After ex vivo exposure, a significantly higher mean (±SD) percentage of equine alveolar macrophages contained liposomal gentamicin (91.9±7.6%) as opposed to free gentamicin (16.8±12.5%). Intracellular colocalization of drug and R. equi, as assessed by confocal microscopy, occurred in a significantly higher proportion of cells exposed to liposomal gentamicin (81.2±17.8%) compared to those exposed to free gentamicin (10.4±8.7%). The number of R. equi CFU in the spleen was significantly lower in mice treated with liposomal gentamicin compared to that of mice treated with free gentamicin or to untreated control mice. Treatment with liposomal gentamicin also resulted in a significantly greater reduction in the number of R. equi CFU in the liver compared to treatment with clarithromycin in combination with rifampin. These results support further investigation of liposomal gentamicin as a new treatment for infections caused by R. equi.

Penetration of anti-infective agents into pulmonary epithelial lining fluid: focus on antibacterial agents

The exposure-response relationship of anti-infective agents at the site of infection is currently being re-examined. Epithelial lining fluid (ELF) has been suggested as the site (compartment) of antimicrobial activity against lung infections caused by extracellular pathogens. There have been an extensive number of studies conducted during the past 20 years to determine drug penetration into ELF and to compare plasma and ELF concentrations of anti-infective agents. The majority of these studies estimated ELF drug concentrations by the method of urea dilution and involved either healthy adult subjects or patients undergoing diagnostic bronchoscopy. Antibacterial agents such as macrolides, ketolides, newer fluoroquinolones and oxazolidinones have ELF to plasma concentration ratios of >1. In comparison, β-lactams, aminoglycosides and glycopeptides have ELF to plasma concentration ratios of ≤1. Potential explanations (e.g. drug transporters, overestimation of the ELF volume, lysis of cells) for why these differences in ELF penetration occur among antibacterial classes need further investigation. The relationship between ELF concentrations and clinical outcomes has been under-studied. In vitro pharmacodynamic models, using simulated ELF and plasma concentrations, have been used to examine the eradication rates of resistant and susceptible pathogens and to explain why selected anti-infective agents (e.g. those with ELF to plasma concentration ratios of >1) are less likely to be associated with clinical treatment failures. Population pharmacokinetic modelling and Monte Carlo simulations have recently been used and permit ELF and plasma concentrations to be evaluated with regard to achievement of target attainment rates. These mathematical modelling techniques have also allowed further examination of drug doses and differences in the time courses of ELF and plasma concentrations as potential explanations for clinical and microbiological effects seen in clinical trials. Further studies are warranted in patients with lower respiratory tract infections to confirm and explore the relationships between ELF concentrations, clinical and microbiological outcomes, and pharmacodynamic parameters.

Diagnosis, treatment, control, and prevention of infections caused by Rhodococcus equi in foals

Rhodococcus equi, a gram-positive facultative intracellular pathogen, is one of the most common causes of pneumonia in foals. Although R. equi can be cultured from the environment of virtually all horse farms, the clinical disease in foals is endemic at some farms, sporadic at others, and unrecognized at many. On farms where the disease is endemic, costs associated with morbidity and mortality attributable to R. equi may be very high. The purpose of this consensus statement is to provide recommendations regarding the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals.

Pulmonary disposition of erythromycin, azithromycin, and clarithromycin in foals

The objectives of the present study were to determine and compare the pulmonary disposition of azithromycin, clarithromycin, and erythromycin in foals. A single dose (10 mg/kg) of azithromycin, clarithromycin, or erythromycin was administered intragastrically to six healthy 1- to 3-month-old foals using an orthogonal design. Activity of the drugs was measured in serum, pulmonary epithelial lining fluid (PELF), and bronchoalveolar lavage (BAL) cells by use of a microbiologic assay. Peak drug activity in PELF was significantly higher in foals treated with clarithromycin (48.96+/-13.26 microg/mL) than in foals treated with azithromycin (10.00+/-7.46 microg/mL). Quantifiable erythromycin activity in PELF was only found in two of six foals. Peak drug activity in BAL cells was not significantly different between azithromycin (49.92+/-26.94 microg/mL) and clarithromycin (74.20+/-45.80 microg/mL) but activity for both drugs was significantly higher than that of erythromycin (1.02+/-1.11 microg/mL). Terminal half-life of azithromycin in serum (25.7+/-15.4 h), PELF (34.8+/-30.9 h), and BAL cells (54.4+/-17.5 h) was significantly longer than that of both clarithromycin and erythromycin. Peak azithromycin and clarithromycin activity was significantly higher in BAL cells, followed by PELF, and serum. In contrast, peak erythromycin activity in BAL cells was not significantly different from that of serum.