Penetration of Anti-Infective Agents into Pulmonary Epithelial Lining Fluid
University of Illinois at Chicago, USA. Clinical Pharmacokinetics
(Impact Factor: 5.05).
10/2011; 50(10):637-64. DOI: 10.2165/11594090-000000000-00000
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.
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- "a widely used technique for collecting the ELF to determine sufficient drug concentrations achieved at the infected site. This technique has been commonly applied to antibacterial agents (Rodvold et al., 2011a) and is also recently applicable to other anti-infective agents, such as antifungal, antitubercular, antiparasitic, and antiviral agents (Rodvold et al., 2011b). In the case of LO as well, it is likely that the ELF is a relevant site to determine drug concentrations from the standpoint of pharmacokinetic/pharmacodynamic relationship, considering viral surface location of the neuraminidase enzyme. "
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ABSTRACT: Laninamivir octanoate (LO) is an ester prodrug of the neuraminidase inhibitor laninamivir. We previously reported that a prolonged high retention of laninamivir in mouse respiratory tissues was achieved by intranasal administration of LO. In this study, we evaluated intrapulmonary pharmacokinetics both in vivo and in vitro in order to investigate the potential mechanism involved in such a preferable retention. After intranasal administration of LO to mice (0.5 μmol/kg), the drug was distributed from the airway space into the lungs, and laninamivir remained in the lung at 24 h post-dose (2680 pmol/g), with a higher concentration than that in the epithelial lining fluid. The laninamivir was localized mainly on the epithelial cells of airway tracts, determined by microautoradiography using (14)C-labeled LO. In mouse airway epithelial cells, the cellular uptake and hydrolysis of LO were observed over incubation time without any apparent saturation at the highest concentration tested (1000 μM). Furthermore, after additional incubation in drug-free medium, the intracellular laninamivir was released very slowly into the medium with an estimate rate constant of 0.0707 h(-1), which was regarded as a rate-limiting step in the cellular retention. These results demonstrated that the prolonged high retention of laninamivir in the respiratory tissues was attributed to a consecutive series of three steps: uptake of LO into the airway epithelial cells, hydrolysis of LO into laninamivir by intracellular esterase(s), and limited efflux of the generated laninamivir due to its poor membrane permeability. This prodrug approach could be useful for lung-targeting drug delivery.
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ABSTRACT: The critical role of pharmacokinetics and pharmacodynamics in the selection and dosing of antimicrobial therapeutics, including
antifungal agents, has gained increasing recognition [1–4]. The study of pharmacokinetics involves understanding the interaction
of a drug with the host, including measurements of absorption, distribution, metabolism, and elimination. The study of antimicrobial
pharmacodynamics provides insight into the link between drug pharmacokinetics, in vitro susceptibility, and treatment outcome.
Knowledge of the pharmacokinetic/pharmacodynamic index and magnitude associated with efficacy can be helpful for clinicians
to predict therapeutic success/failure, guide optimal dosing levels and intervals, aid in susceptibility breakpoint development,
guide therapeutic drug monitoring, and limit potential adverse outcomes, including toxicity and the development of resistance
[5–8]. Numerous in vitro, animal, and clinical studies have been instrumental in characterizing the pharmacodynamic activity
of the clinically available antifungal drug classes, including triazoles, polyenes, flucytosine, and echinocandins [6–18].
The analyses of data with these antifungal drug classes have identified distinct pharmacodynamic characteristics that result
in different optimal dosing strategies. Accumulating clinical data have also become available with several antifungals that
allow pharmacodynamic data analyses [19–25]. Most often the results of these investigations have corroborated information
from experimental models. The following chapter outlines the pharmacodynamic characteristics of antifungals and presents evidence
of the clinical relevance of these concepts.
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ABSTRACT: Epithelial lining fluid (ELF) is often considered to be the site of extracellular pulmonary infections. During the past 25 years, a limited number of studies have evaluated the intrapulmonary penetration of antifungal, antitubercular, antiparasitic and antiviral agents. For antifungal agents, differences in drug concentrations in ELF or bronchoalveolar lavage (BAL) fluid were observed among various formulations or routes of administration, and between agents within the same class. Aerosolized doses of deoxycholate amphotericin B, liposomal amphotericin B and amphotericin B lipid complex resulted in higher concentrations in ELF or BAL fluid than after intravenous administration. The mean concentrations in ELF following intravenous administration of both anidulafungin and micafungin ranged between 0.04 and 1.38 μg/mL, and the ELF to plasma concentration ratios (based on the area under the concentration-time curve for total drug concentrations) were between 0.18 and 0.22 during the first 3 days of therapy. Among the azole agents, intravenous administration of voriconazole resulted in the highest mean ELF concentrations (range 10.1-48.3 μg/mL) and ratio of penetration (7.1). The range of mean ELF concentrations of itraconazole and posaconazole following oral administration was 0.2-1.9 μg/mL, and the ELF to plasma concentration ratios were <1. A series of studies have evaluated the intrapulmonary penetration of first- and second-line oral antitubercular agents in healthy adult subjects and patients with AIDS. The ELF to plasma concentration ratio was >1 for isoniazid, ethambutol, pyrazinamide and ethionamide. For rifampicin (rifampin) and rifapentine, the ELF to plasma concentration ratio ranged between 0.2 and 0.32, but in alveolar macrophages the concentration of rifampicin was much higher (145-738 μg/mL compared with 3.3-7.5 μg/mL in ELF). No intrapulmonary studies have been conducted for rifabutin. Sex, AIDS status or smoking history had no significant effects on the magnitude of ELF concentrations of antitubercular agents. Subjects who were slow acetylators had higher plasma and ELF concentrations of isoniazid than those who were fast acetylators. Penetration of dapsone into ELF was very good, with the range of mean ELF to plasma concentration ratios being 0.65-2.91 at individual sampling times over 48 hours. Once-daily dosing of aerosolized pentamidine resulted in higher concentrations in BAL fluid than after intravenous administration. The mean BAL concentrations at 15-32 days after once- or twice-monthly administration of aerosolized pentamidine 300 and 600 mg ranged from 6.5 to 28.4 ng/mL. No differences in pentamidine BAL concentrations were observed in symptomatic patients who developed Pneumocystis jirovecii pneumonia compared with patients who did not. Zanamivir concentrations in ELF were similar in magnitude (range 141-326 ng/mL) following administration by continuous intravenous infusion (3 mg/hour), oral inhalation (10 mg every 12 hours) and intravenous bolus (200 mg every 12 hours). Data from case reports have suggested that concentrations of nelfinavir and saquinavir in ELF are undetectable, whereas tipranavir and lopinavir had measureable ELF concentrations (2.20 μmol/L and 14.4 μg/mL, respectively) when these protease inhibitors were co-administrated with ritonavir. While the clinical significance of ELF or BAL concentrations remains unknown for this group of anti-infective agents, the knowledge of drug penetration into the extracellular space of the lung should assist in re-evaluating and designing specific dosing regimens for use against potential pathogens.
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