Intrapulmonary Pharmacokinetics of Antibacterial Agents

Treatment of Drug-Susceptible Tuberculosis

Mycobacterium tuberculosis is a major public health concern and requires prompt treatment. Goals of treatment include curing the individual patient and protecting the community from ongoing tuberculosis transmission. To achieve durable cure, regimens must include multiple agents given concurrently and in a manner to ensure completion of therapy. This article focuses on preferred regimens of drug-susceptible tuberculosis under current guidelines by the American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America and World Health Organization. In addition, topics including patient centered care, poor treatment outcomes, and adverse effects are also discussed.

Intrapulmonary concentrations of meropenem administered by continuous infusion in critically ill patients with nosocomial pneumonia: a randomized pharmacokinetic trial

Background

Optimal antimicrobial drug exposure in the lung is required for successful treatment outcomes for nosocomial pneumonia. Little is known about the intrapulmonary pharmacokinetics (PK) of meropenem when administered by continuous infusion (CI). The aim of this study was to evaluate the PK of two dosages of meropenem (3 g vs 6 g/day by CI) in the plasma and epithelial lining fluid (ELF) in critically ill patients with nosocomial pneumonia.

Methods

Thirty-one patients (81% male, median (IQR) age 72 (22) years) were enrolled in a prospective, randomized, clinical trial. Sixteen patients received 1 g/8 h and 15 2 g/8 h by CI (8 h infusion). Plasma and ELF meropenem concentrations were modeled using a population methodology, and Monte Carlo simulations were performed to estimate the probability of attaining (PTA) a free ELF concentration of 50% of time above MIC (50% fT>MIC), which results in logarithmic killing and the suppression of resistance in experimental models of pneumonia.

Results

The median (IQR) of meropenem AUC_0–24 h in the plasma and ELF was 287.6 (190.2) and 84.1 (78.8) mg h/L in the 1 g/8 h group vs 448.1 (231.8) and 163.0 (201.8) mg h/L in the 2 g/8 h group, respectively. The penetration ratio was approximately 30% and was comparable between the dosage groups. In the Monte Carlo simulations, only the highest approved dose of meropenem of 2 g/8 h by CI allowed to achieve an optimal PTA for all isolates with a MIC < 4 mg/L.

Conclusions

An increase in the dose of meropenem administered by CI achieved a higher exposure in the plasma and ELF. The use of the highest licensed dose of 6 g/day may be necessary to achieve an optimal coverage in ELF for all susceptible isolates (MIC ≤ 2 mg/L) in patients with conserved renal function. An alternative therapy should be considered when the presence of microorganisms with a MIC greater than 2 mg/L is suspected.

Trial registration

The trial was registered in the European Union Drug Regulating Authorities Clinical Trials Database (EudraCT-no. 2016-002796-10). Registered on 27 December 2016.

Patient-specific modeling of regional antibiotic concentration levels in airways of patients with cystic fibrosis: are we dosing high enough?

Background

Pseudomonas aeruginosa (Pa) infection is an important contributor to the progression of cystic fibrosis (CF) lung disease. The cornerstone treatment for Pa infection is the use of inhaled antibiotics. However, there is substantial lung disease heterogeneity within and between patients that likely impacts deposition patterns of inhaled antibiotics. Therefore, this may result in airways below the minimal inhibitory concentration of the inhaled agent. Very little is known about antibiotic concentrations in small airways, in particular the effect of structural lung abnormalities. We therefore aimed to develop a patient-specific airway model to predict concentrations of inhaled antibiotics and to study the impact of structural lung changes and breathing profile on local concentrations in airways of patients with CF.

Methods

In- and expiratory CT-scans of children with CF (5–17 years) were scored (CF-CT score), segmented and reconstructed into 3D airway models. Computational fluid dynamic (CFD) simulations were performed on 40 airway models to predict local Aztreonam lysine for inhalation (AZLI) concentrations. Patient-specific lobar flow distribution and nebulization of 75 mg AZLI through a digital Pari eFlow model with mass median aerodynamic diameter range were used at the inlet of the airway model. AZLI concentrations for central and small airways were computed for different breathing patterns and airway surface liquid thicknesses.

Results

In most simulated conditions, concentrations in both central and small airways were well above the minimal inhibitory concentration. However, small airways in more diseased lobes were likely to receive suboptimal AZLI. Structural lung disease and increased tidal volumes, respiratory rates and larger particle sizes greatly reduced small airway concentrations.

Conclusions

CFD modeling showed that concentrations of inhaled antibiotic delivered to the small airways are highly patient specific and vary throughout the bronchial tree. These results suggest that anti-Pa treatment of especially the small airways can be improved.

Subtherapeutic linezolid concentrations in a patient with morbid obesity and methicillin-resistant Staphylococcus aureus pneumonia: case report and review of the literature

OBJECTIVE

To report a case of subtherapeutic linezolid concentrations in a patient with morbid obesity.

CASE SUMMARY

A 34-year-old male with morbid obesity (265 kg, body mass index 82 kg/m(2)) was admitted for severe sepsis due to respiratory failure requiring emergent intubation and treatment of community-acquired pneumonia. Admission tracheal aspirate culture revealed methicillin-resistant Staphylococcus aureus (MRSA) for which vancomycin was prescribed. Therapy subsequently was changed to linezolid, because the patient's clinical status worsened, with significant hypoxia (partial pressure of arterial oxygen/fraction of inspired oxygen [PaO2/FiO2] ratio 145), increasing leukocytosis (white blood cell count from 10,800/μL on admission to 15,400/μL on hospital day 6), and persistent fever (38.3 °C). After 48 hours of linezolid monotherapy, the patient remained febrile with continued leukocytosis, worsening hypoxemia, and a persistently positive MRSA culture from a repeat endotracheal aspirate. Linezolid serum concentrations were obtained and vancomycin was reinstituted, after which the patient began to improve (afebrile, improving PaO2/FiO2 ratio, decreasing leukocytosis). On hospital day 12, the patient removed his endotracheal tube, and a sputum sample was obtained for culture. The patient's clinical status subsequently declined, prompting addition of cefepime to his antibiotic regimen. This sputum culture revealed not only MRSA, but also quinolone-resistant Escherichia coli. After completing treatment for both organisms the patient was discharged home.

DISCUSSION

Limited data on linezolid dosing in the morbidly obese population show lower serum drug concentrations than those in nonobese patients, but no clinical failure has been reported when treating MRSA skin and soft tissue infections or MRSA tracheitis. In our patient, low steady-state linezolid serum concentrations (peak 4.13 μg/mL [reference 15-27] and trough 1.27 μg/mL [reference 2-9]) were thought to contribute to his poor clinical response.

CONCLUSIONS

To our knowledge, this is the first report of subtherapeutic linezolid concentrations correlated with decreased clinical effectiveness when during treatment of MRSA pneumonia in a patient with morbid obesity.

The importance of tissue penetration in achieving successful antimicrobial treatment of nosocomial pneumonia and complicated skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus: vancomycin and linezolid

BACKGROUND

The rising prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) and the recent emergence of community-associated MRSA are major clinical, public health, and economic challenges. MRSA is a leading cause of nosocomial pneumonia and complicated skin and soft-tissue infections (cSSTI). Vancomycin and linezolid are two commonly used antimicrobial agents with activity against Gram-positive pathogens, particularly MRSA, that are used to treat both nosocomial pneumonia and cSSTI. Recently, the therapeutic efficacy of vancomycin in the treatment of hospitalized patients with MRSA infections has been questioned due to the emergence of MRSA strains with reduced susceptibility to vancomycin together with concerns related to inadequate dosing and poor tissue penetration of the drug.

SCOPE

A literature review was conducted to investigate the pharmacokinetics and pulmonary and tissue penetration of vancomycin and linezolid. Using MEDLINE and EMBASE, the most relevant articles in English published over the past 25 years (up to October 2008) were identified and summarized. Studies in human volunteers and adult patients that measured concentrations of antibiotic in serum, epithelial lining fluid (ELF), and tissue were selected for further review.

FINDINGS

For both drugs, pharmacokinetic studies were conducted in diverse patient populations and employed varying techniques to measure tissue concentrations. Vancomycin concentrations in ELF ranged from 5 to 25% of simultaneous plasma levels, while concentrations in whole homogenized lung tissue were slightly higher (24-41%). Distribution of vancomycin into soft tissue was variable. For linezolid, overall mean concentrations in ELF and in soft tissue were generally similar or higher than simultaneous plasma levels, although variability in tissue penetration across studies in healthy volunteers and patients was seen.

LIMITATIONS

The studies included in this review vary greatly in their designs and patient populations; this, together with methodologic difficulties, limits the interpretation of the data.

CONCLUSIONS

In the absence of clinical data correlating ELF concentrations and clinical outcome, the clinical significance of differences in pulmonary penetration of vancomycin and linezolid is unknown. Higher vancomycin serum concentrations may be necessary to achieve appropriate lung concentrations to optimize treatment outcomes. Linezolid demonstrates adequate penetration into lung and other soft issues with sustained concentrations above the minimum inhibitory concentrations for susceptible pathogens, including MRSA, for the majority of the dosing interval. Examination of the pharmacokinetic data adds insights not provided by the clinical trial data and together provides clinicians with a more comprehensive basis for selecting appropriate antimicrobial therapy for the treatment of serious MRSA infections.

Alveolar concentrations of piperacillin/tazobactam administered in continuous infusion to patients with ventilator-associated pneumonia

OBJECTIVES

To determine the steady-state serum and alveolar concentrations of piperacillin/tazobactam administered in continuous infusion to critically ill patients with ventilator-associated pneumonia and various degrees of renal failure.

DESIGN

Prospective comparative study.

SETTING

An intensive care unit and research ward in a university hospital.

PATIENTS

Forty patients with microbiologically documented ventilator-associated pneumonia.

INTERVENTIONS

Patients were randomized to receive piperacillin/tazobactam daily continuous infusions of 12/1.5 g or 16/2 g after a loading dose of 4/0.5 g. The serum and alveolar piperacillin/tazobactam concentrations were determined at steady-state with high performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

The median (interquartile) serum and alveolar piperacillin concentrations were respectively 25.3 mg/L (23.1-32.6) and 12.7 mg/L (6.7-18.0) for 12/1.5 g/day, and 38.9 mg/L (32.9-59.6) and 19.1 mg/L (14.0-21.5), respectively, for 16/2 g/day in patients with no/mild renal failure. In patients with moderate/advance renal failure, the median (interquartile) serum and alveolar piperacillin concentrations were 102.4 mg/L (97.4-112.6) and 44.1 mg/L (33.4-48.3), respectively, for 12/1.5 g/day, and 135.3 mg/L (119.5-146.2) and 54.9 mg/L (45.2-110.3), respectively, for 16/2 g/day. Our results show great variability in piperacillin/tazobactam concentrations, with an alveolar percentage penetration of 40-50% for piperacillin and 65-85% for tazobactam and a negative association between serum or alveolar concentrations and creatinine clearance.

CONCLUSIONS

A target piperacillin serum concentration of at least 35-40 mg/L is probably required to provide alveolar concentrations exceeding the susceptibility breakpoint for gram-negative bacteria (16 mg/L) during ventilator-associated pneumonia. In patients with no/mild renal failure, a continuous daily dose of piperacillin/tazobactam 16/2 g allows reaching this target concentration, which might be not observed with 12/1.5 g/day. In patients with moderate/advanced renal failure, both dosages achieve serum concentrations far above the 35-40 mg/L threshold, suggesting that in that case, therapeutic drug monitoring should be performed in order to adjust the daily dose.

Reliability of mini-bronchoalveolar lavage for the measurement of epithelial lining fluid concentrations of tobramycin in critically ill patients

OBJECTIVE

To evaluate the reliability of mini-bronchoalveolar lavage (mini-BAL) for the measurement of tobramycin concentrations in epithelial lining fluid (ELF) in comparison with conventional bronchoscopic bronchoalveolar lavage (BAL).

DESIGN

Prospective, open-label study.

SETTING

An intensive care unit and research ward in a university hospital.

PATIENTS

Twelve critically ill adult patients with ventilator-associated pneumonia (VAP).

INTERVENTIONS

All subjects received intravenous infusions of tobramycin 7-10 mg/kg once daily. After 2 days of therapy, the steady-state serum and ELF concentrations (obtained from BAL and mini-BAL) of tobramycin were determined by means of high-performance liquid chromatography.

MEASUREMENTS AND RESULTS

We observed poor penetration of tobramycin in ELF of approximately approximately 12% with ELF peak concentrations of approximately approximately 3 mg/l with both methods. Good agreement in Bland-Altman analysis (mean +/- SD bias = 0.04 +/- 0.38 mg/l) was observed between the two methods of sampling.

CONCLUSION

Our results suggest that tobramycin 7-10 mg/kg once daily in critically ill patients with VAP might provide insufficient lung concentrations in the case of difficult-to-treat pathogens. Besides, mini-BAL, which is simple, non-invasive and easily repeatable at the bedside, appears to be a reliable method for the measurement of antibiotic concentrations in ELF in comparison with bronchoscopic BAL in critically ill patients with VAP.

Pharmacokinetics and lung tissue concentrations of tulathromycin in swine

The absolute bioavailability and lung tissue distribution of the triamilide antimicrobial, tulathromycin, were investigated in swine. Fifty-six pigs received 2.5 mg/kg of tulathromycin 10% formulation by either intramuscular (i.m.) or intravenous (i.v.) route in two studies: study A (10 pigs, i.m. and 10 pigs, i.v.) and study B (36 pigs, i.m.). After i.m. administration the mean maximum plasma concentration (C(max)) was 616 ng/mL, which was reached by 0.25 h postinjection (t(max)). The mean apparent elimination half-life (t(1/2)) in plasma was 75.6 h. After i.v. injection plasma clearance (Cl) was 181 mL/kg.h, the volume of distribution at steady-state (V(ss)) was 13.2 L/kg and the elimination t(1/2) was 67.5 h. The systemic bioavailability following i.m. administration was >87% and the ratio of lung drug concentration for i.m. vs. i.v. injection was > or =0.96. Following i.m. administration, a mean tulathromycin concentration of 2840 ng/g was detected in lung tissue at 12 h postdosing. The mean lung C(max) of 3470 ng/g was reached by 24 h postdose (t(max)). Mean lung drug concentrations after 6 and 10 days were 1700 and 1240 ng/g, respectively. The AUC(inf) was 61.4 times greater for the lung than for plasma. The apparent elimination t(1/2) for tulathromycin in the lung was 142 h (6 days). Following i.m. administration to pigs at 2.5 mg/kg body weight, tulathromycin was rapidly absorbed and highly bioavailable. The high distribution to lung and slow elimination following a single dose of tulathromycin, are desirable pharmacokinetic attributes for an antimicrobial drug indicated for the treatment of respiratory disease in swine.