Intrapulmonary Concentrations of Telithromycin: Clinical Implications for Respiratory Tract Infections due to Streptococcus pneumoniae

Pharmacokinetic modelling of serum and bronchial concentrations for clarithromycin and telithromycin, and site-specific pharmacodynamic simulation for their dosages

WHAT IS KNOWN AND OBJECTIVE

Clinical pharmacokinetic profiles of clarithromycin and telithromycin in bronchopulmonary sites have not been fully characterized. This study aimed to describe in more detail the pharmacokinetics of the two macrolides in epithelial lining fluid (ELF) of human bronchi and to evaluate their pharmacodynamic target attainment at this site.

METHODS

Previously reported drug concentration data for serum and ELF were simultaneously fitted to a three-compartment pharmacokinetic model using nonmem program. The model parameter estimates were used for site-specific pharmacodynamic simulation.

RESULTS AND DISCUSSION

Population mean parameters for clarithromycin were as follows: distribution volumes of central, peripheral and ELF compartments (V1 /F, V2 /F and V3 /F) = 204·7, 168·9 and 67·1 L; clearance (CL/F) = 34·4 L/h; absorption rate constant (Ka ) = 0·680 1/h; transfer rate constants connecting compartments (K12 , K21 , K13 and K31  = 0·0193, 0·434, 0·667 and 0·260 1/h, respectively). Mean parameters for telithromycin were as follows: V1 /F, V2 /F and V3 /F = 370·3, 290·3 and 213·8 L; CL/F = 89·5 L/h; Ka  = 0·740 1/h; K12 , K21 , K13 and K31  = 0·0026, 1·044, 0·758 and 0·158 1/h, respectively. Using these parameters, the mean ELF/serum ratio in the area under drug concentration-time curve (AUC) was 7·80 for clarithromycin and 8·05 for telithromycin. Clarithromycin achieved a ≥ 90% probability of attaining a pharmacodynamic target [AUC/minimum inhibitory concentration (MIC) = 100] in ELF against bacterial isolates for which MICs were ≤0·5 and ≤1 mg/L for twice-daily doses of 250 and 500 mg, respectively. For telithromycin, once-daily doses of 600 and 800 mg achieved a ≥90% probability in ELF against Streptococcus pneumoniae, Staphylococcus aureus and Moraxella catarrhalis isolates but not Haemophilus influenzae isolates.

WHAT IS NEW AND CONCLUSION

These results should provide a better understanding of the bronchial pharmacokinetics of clarithromycin and telithromycin, while also providing useful information about their dosages for respiratory tract infections based on site-specific pharmacodynamic evaluation. Further studies in a large number of patients are needed to confirm our findings and clarify their therapeutic implications.

Pulmonary disposition of tedizolid following administration of once-daily oral 200-milligram tedizolid phosphate in healthy adult volunteers

This study assessed the pulmonary disposition of tedizolid, an oxazolidinone, in adult volunteers receiving 200 mg of the prodrug tedizolid phosphate orally every 24 h for 3 days to steady state. Plasma samples were collected over the dosing interval, and participants were randomized to undergo bronchoalveolar lavage (BAL) at 2, 6, 12, or 24 h after the last dose. Drug concentrations in plasma, BAL fluid, and alveolar macrophages (AM) were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the urea correction method was used to calculate epithelial lining fluid (ELF) concentrations. Pharmacokinetic parameters were estimated by noncompartmental methods followed by compartmental population pharmacokinetics. Penetration was calculated as the area under the concentration-time curve during the dosing interval (AUC(0-24)) for ELF and AM relative to the free AUC(0-24) (fAUC(0-24)) in plasma. The half-life and volume of distribution in plasma were 9.23 ± 2.04 h and 108.25 ± 20.53 liters (means ± standard deviations), respectively. Total AUC(0-24) in plasma was 25.13 ± 5.78 μg · h/ml. Protein binding was 89.44% ± 1.58%, resulting in a mean fAUC(0-24) of 2.65 ± 0.72 μg · h/ml in plasma. Mean concentrations (μg/ml) at 2, 6, 12, and 24 h were 9.05 ± 3.83, 4.45 ± 2.18, 5.62 ± 1.99, and 1.33 ± 0.59 in ELF and 3.67 ± 1.02, 4.38 ± 2.18, 1.42 ± 0.63, and 1.04 ± 0.52 in AM. ELF and AM penetration ratios were 41.2 and 20.0. The mean ELF penetration ratio after population analyses was 39.7. This study demonstrates that tedizolid penetrates into ELF and AM to levels approximately 40-fold and 20-fold, respectively, higher than free-drug exposures in plasma.

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.

Antibiotics in acute exacerbations of chronic bronchitis

Acute exacerbations of chronic bronchitis (AECB) are a major contributor to morbidity and mortality in patients with chronic obstructive pulmonary disease, accounting for more than 16 million physician office visits and over 500,000 hospitalizations in the USA each year. Antimicrobials have been recognized by clinical guidelines as an important component in the management of AECB with a bacterial etiology. The challenge of identifying patients most likely to benefit from antimicrobial therapy is difficult in the clinical setting. However, appropriate risk stratification of patients, and the use of antimicrobials within the correct spectrum and for a suitable duration, can improve clinical outcomes while minimizing induction of antimicrobial resistance. With an improved design in pharmacologic and clinical studies, differences can be appreciated among the various antimicrobial agents available to treat AECB. Factors to be considered in antimicrobial agent selection include local tissue penetration, effects on bacteriological eradication, duration of therapy, speed of resolution and prevention or delay of recurrences.

Intrapulmonary pharmacokinetics of S-013420, a novel bicyclolide antibacterial, in healthy Japanese subjects

S-013420 (EDP-420) is a novel bicyclolide (bridged bicyclic macrolide) antibacterial currently under development for the treatment of respiratory tract infections. The objective of the present study was to determine the plasma and intrapulmonary pharmacokinetic parameters of orally administered S-013420 in healthy volunteers. Twenty-eight healthy Japanese male subjects who never smoked were randomly allocated to seven groups of four subjects each who underwent bronchoalveolar lavage (BAL) at different times after dosing (2, 4, 6, 8, 10, 12, or 24 h). Blood samples were also taken at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, 48, and 72 h after dosing. The S-013420 concentrations in plasma, epithelial lining fluid (ELF), and alveolar macrophages (AMs) were measured by using a combined high-performance liquid chromatography-mass spectrometric technique. A pharmacokinetic analysis of the plasma, ELF, and AM S-013420 concentration profiles was performed. S-013420 was rapidly absorbed in plasma, and the mean time to the maximum concentration in plasma was 2.27 h. S-013420 was rapidly distributed to the ELF and was slowly distributed to AMs. The areas under the concentration-time curves from time zero to 24 h (AUC0-24) for S-013420 were 20.3 times higher in ELF than in plasma and 244.6 times higher in AMs than in plasma. The mean maximum concentration in plasma was higher in ELF than in plasma and was much higher in AM than in plasma. Furthermore, pharmacodynamic calculations were done by using the AUC0-24/MIC90 ratio for common pneumonia pathogens (Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis). The AUC0-24 for plasma/MIC90s for these four organisms were 41.8, 83.6, 1.3, and 20.9, respectively. The AUC0-24 for ELF/MIC90s were 849.6, 1,699.2, 26.6, and 424.8, respectively. Considering the good efficacy shown in a subsequent phase 2 study (S. Kohno, K. Yamaguchi, Y. Tanigawara, A. Watanabe, A. Aoki, Y. Niki, and J. Fujita, Abstr. 47th Intersci. Conf. Antimicrob. Agents Chemother., abstr. L-485), the good distribution of S-013420 in AMs and ELF observed in the present study is predictive of the good efficacy of S-013420 against respiratory pathogens.

Bronchopulmonary disposition of intravenous voriconazole and anidulafungin given in combination to healthy adults

Voriconazole and anidulafungin in combination are being investigated for use for the treatment of pulmonary aspergillosis. We determined the pulmonary disposition of these agents. Twenty healthy participants received intravenous voriconazole (at 6 mg/kg of body weight every 12 h [q12h] on day 1 and then at 4 mg/kg q12h) and anidulafungin (200 mg on day 1 and then 100 mg every 24 h) for 3 days. Five participants each were randomized for collection of bronchoalveolar lavage samples at times of 4, 8, 12, and 24 h. Drug penetration was determined by the ratio of the total drug area under the concentration-time curve during the dosing interval (AUC(0-tau)) for epithelial lining fluid (ELF) and alveolar macrophages (AM) to the total drug AUC(0-tau) in plasma. The mean (standard deviation) half-life and AUC(0-tau) were 6.9 (2.1) h and 39.5 (19.8) microg h/ml, respectively, for voriconazole and 20.8 (3.1) h and 101 (21.8) microg h/ml, respectively, for anidulafungin. The AUC(0-tau) values for ELF and AM were 282 and 178 microg h/ml, respectively, for voriconazole, and 21.9 and 1,430 microg h/ml, respectively, for anidulafungin. This resulted in penetration ratios into ELF and AM of 7.1 and 4.5, respectively, for voriconazole and 0.22 and 14.2, respectively, for anidulafungin. The mean total concentrations of both drugs in ELF and AM at 4, 8, 12, and 24 h remained above the MIC(90)/90% minimum effective concentration for most Aspergillus species. In healthy adult volunteers, voriconazole achieved high levels of exposure in both ELF and AM, while anidulafungin predominantly concentrated in AM.

Identifying exposure targets for treatment of staphylococcal pneumonia with ceftobiprole

Ceftobiprole is a cephalosporin with potent activity against methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). In order to treat patients with severe staphylococcal pneumonia, it is important to understand the drug exposure required to mediate the killing of multiple log(10) cells in a preclinical-infection model. We measured drug exposure in terms of the percentage of penetration of the drug into epithelial lining fluid (ELF) and in terms of the time for which the drug concentration was above the MIC (time>MIC) in plasma and ELF. In a murine model of staphylococcal pneumonia, we demonstrated that ceftobiprole penetrated into ELF from the plasma at a median level of nearly 69% (25th to 75th percentile range, 25 to 187%), as indexed to the ratio of values for the area under the concentration-time curve in ELF and plasma. The total-drug times>MIC in ELF that were required to kill 1 log(10) and 2 log(10) CFU/g of lung tissue were 15% and 25% of the dosing interval. We also examined the penetration of ELF by ceftobiprole in volunteers, demonstrating mean and median penetration percentages of 25.5% and 15.3%, respectively (25th to 75th percentile range, 8 to 30%). Attainment rates were calculated for kill targets of 1 log(10) and 2 log(10) CFU/g, taken from the murine model, but using the volunteer ceftobiprole ELF penetration data. The standard dose for ceftobiprole is 0.5 g every 8 h as a 2-h infusion. The attainment rates remained above 90% for 1-log(10) and 2-log(10) CFU/g kill targets at MICs of 1 and 0.5 mg/liter, respectively. Taking the expectation over the distribution of ceftobiprole MICs for 4,958 MRSA isolates showed an overall target attainment of 85.6% for a 1-log(10) CFU/g kill and 79.7% for a 2-log(10) CFU/g kill. It is important to derive exposure targets in preclinical-infection models of the infection site so that these targets can be explored in clinical trials in order to optimize the probability of a good clinical outcome.

Pharmacodynamics of levofloxacin in a murine pneumonia model of Pseudomonas aeruginosa infection: determination of epithelial lining fluid targets

The dose choice for Pseudomonas aeruginosa remains a matter of debate. The actual exposure targets required for multilog killing of organisms at the primary infection site have not been delineated. We studied Pseudomonas aeruginosa PAO1 using a murine model of pneumonia. We employed a large mathematical model to fit all the concentration-time data in plasma and epithelial lining fluid (ELF) as well as colony counts in lung simultaneously for all drug doses. Penetration into ELF was calculated to be approximately 77.7%, as indexed to the ratio of the area under the concentration-time curve for ELF (AUC(ELF)) to the AUC(plasma). We determined the ELF concentration-time profile required to drive a stasis response as well as 1-, 2-, or 3-log(10)(CFU/g) kill. AUC/MIC ratios of 12.4, 31.2, 62.8, and 127.6 were required to drive these bacterial responses. Emergence of resistance was seen only at the two lowest doses (three of five animals at 50 mg/kg [body weight] and one of five animals at 100 mg/kg). The low exposure targets were likely driven by a low mutational frequency to resistance. Bridging to humans was performed using Monte Carlo simulation. With a 750-mg levofloxacin dose, target attainment rates fell below 90% at 4 mg/liter, 1 mg/liter, and 0.5 mg/liter for 1-, 2-, and 3-log kills, respectively. Given the low exposure targets seen with this strain, we conclude that levofloxacin at a 750-mg dose is not adequate for serious Pseudomonas aeruginosa pneumonia as a single agent. More isolates need to be studied to make these observations more robust.

In vitro activity of telithromycin against Haemophilus influenzae at epithelial lining fluid concentrations

BACKGROUND

Haemophilus influenzae is one of the main aetiological agents of community-acquired respiratory tract infections. The primary aim of this study was to evaluate the antibacterial activity of telithromycin against H. influenzae clinical isolates showing different pattern of resistance in comparison with azithromycin and clarithromycin at 1/4 x, 1/2 x, 1 x, 2 x, 4 x minimum inhibitory concentration (MIC) and to peak concentrations in epithelial lining fluid (ELF). The secondary aim was to determine the influence of CO2 enriched atmosphere on bacterial susceptibility.

RESULTS

Telithromycin showed high activity against H. influenzae, including strains susceptible to beta-lactams (n = 200), beta-lactamase producer (n = 50) and beta-lactamase negative ampicillin resistant (BLNAR) (n = 10), with MIC from < or =0.03 to 4 mg/L, and MIC50/MIC90 of 1/2 mg/L with susceptibility rate of 100%, and minimum bactericidal concentrations (MBC) from 2 to 4-fold higher than the MIC. Azithromycin was the most active tested macrolide (range: 0.25 - 4 mg/L; MIC50/MIC90: 1/2 mg/L), comparable to telithromycin, while clarithromycin showed the highest MICs and MBCs (range: 0.25 - 8 mg/L; MIC50/MIC90: 2/8 mg/L). In time-kill studies, telithromycin showed a bactericidal activity at the higher concentrations (4 - 2 x MIC and ELF) against all the strains, being complete after 12 - 24 hours from drug exposition. At MIC concentrations, at ambient air, bactericidal activity of telithromycin and azithromycin was quite similar at 12 hours, and better than that of clarithromycin. Besides, telithromycin and clarithromycin at ELF concentrations were bactericidal after 12 hours of incubation for most strains, while 24 hours were needed to azithromycin to be bactericidal. Incubation in CO2 significantly influenced the MICs and MBCs, and only slightly the in vitro killing curves.

CONCLUSION

Telithromycin showed an in-vitro potency against H. influenzae comparable to azithromycin, with an in-vitro killing rate more rapid and superior to clarithromycin at 2X-MIC against beta-lactamase producers and BLNAR strains, and to azithromycin at ELF concentrations against beta-lactamase negative strains. Against all strains, MICs and MBCs were lower in the absence of CO2 for the tested antibiotics, showing an adverse effect of incubation in a CO2 environment. The in-vitro potency together with the tissue concentrations of the antimicrobial, should be considered in predicting efficacy.

Telithromycin in lower respiratory tract infections

Telithromycin is a ketolide, a semisynthetic derivative of the 14-membered ring macrolide antibiotics, with an expanded spectrum of activity relative to macrolides. Its good tissue pharmacokinetic characteristics allows once-daily administration, and it has been successfully employed in lower respiratory tract infections. Recent data indicate that telithromycin may exert anti-inflammatory/immunomodulatory effects that may be of use in the treatment of both acute and chronic airway diseases. This review examines the role of telithromycin in lower respiratory tract infections, analyzing published data on exacerbations of chronic bronchitis, community-acquired pneumonia and asthma in adults. In addition, pharmacokinetic and pharmacodynamic properties of the drug are considered.

Antibacterial dosage in intensive-care-unit patients based on pharmacokinetic/pharmacodynamic principles

PURPOSE OF REVIEW

Selection of the best antibiotic dosage regimen in intensive-care-unit patients is a critical factor for decreasing morbidity and mortality rates. The integration of pharmacokinetics and pharmacodynamics is essential to establishing an adequate therapy. Many studies on this issue have been published in recent years due to its relevance, some of which are commented upon in this review.

RECENT FINDINGS

Several studies have shown that it is feasible to theoretically forecast pharmacodynamic outcomes and select the most adequate antibiotic therapy with Monte Carlo simulations. Moreover, new strategies such as the use of continuous or extended intravenous beta-lactam infusions may considerably improve therapeutic efficacy.

SUMMARY

Future studies are needed in patients to assess the influence of selecting antibiotic therapy based on the impact of pharmacokinetic/pharmacodynamic on mortality, morbidity, cost, etc. It would be of special interest to evaluate this impact on patients with infections caused by multiresistant pathogens, whose mortality rates are even higher. Moreover, although studies such as this would not be easy, mainly due to the large number of patients required to obtain statistically significant results, they should be strongly encouraged because of the possible clinical and economic benefits.

Use of Pharmacodynamic Principles to Optimise Dosage Regimens for Antibacterial Agents in the Elderly

Throughout most of the world we are witnessing an ever increasing number of aged people as a percentage of the general population. In the coming years, the unique spectrum of infections presented by an elderly population, particularly those in long-term care facilities, will challenge our ability to maintain an effective battery of antibacterials. The pharmacokinetic parameters of most antibacterial agents are altered when assessed in the elderly due in part to non-pathological physiological changes. The inability to clear a drug from the body due to declining lung, kidney/bladder, gastrointestinal and circulatory efficiency can cause accumulation in the body of drugs given in standard dosages. While this may have the potential benefit of achieving therapeutic concentrations at a lower dose, there is also a heightened risk of attaining toxic drug concentrations and an increased chance of unfavourable interactions with other medications. Pharmacodynamic issues in the elderly are related to problems that arise from treating elderly patients who may have a history of previous antibacterial treatment and exposure to resistant organisms from multiple hospitalisations. Furthermore, the elderly often acquire infections in tandem with other common disease states such as diabetes mellitus and heart disease. Thus, it is essential that optimised dosage strategies be designed specifically for this population using pharmacodynamic principles that take into account the unique circumstances of the elderly. Rational and effective dosage and administration strategies based on pharmacodynamic breakpoints and detailed understanding of the pharmacokinetics of antibacterials in the elderly increase the chances of achieving complete eradication of an infection in a timely manner. In addition, this strategy helps prevent selection of drug-resistant bacteria and minimises the toxic effects of antibacterial therapy in the elderly patient.