Measurement of tobramycin in bronchoalveolar lavage fluid by a modified fluorescence polarization immunoassay

Pharmacokinetics and safety of an 8 week continuous treatment with once-daily versus twice-daily inhalation of tobramycin in cystic fibrosis patients

OBJECTIVES

We evaluated the pharmacokinetics, safety and tolerability of two different continuous treatment regimens of tobramycin inhalation solution (TIS) in 29 cystic fibrosis (CF) patients chronically infected with Pseudomonas aeruginosa.

PATIENTS AND METHODS

In this randomized, multicentre, open-label, two-period crossover study, TIS (300 mg/5 mL) was administered via PARI eFlow(®) rapid once daily and twice daily each for 8 weeks. Serum pharmacokinetics of these two regimens was analysed. Tobramycin levels were determined before the morning dose and at 30, 60 and 90 min after the end of nebulization in the middle and at the end of each 8 week cycle. At these timepoints, trough and peak serum tobramycin concentrations (Cmax, mg/L) as well as the area under the curve for 0-90 min of tobramycin (AUC0-90min) were assessed in order to evaluate the risk of systemic toxicity. Safety parameters and forced expiratory volume in 1 s (FEV1) were assessed.

RESULTS

For once-daily treatment, tobramycin levels were 10% higher after 8 weeks compared with 4 weeks (AUC0-90min ratio = 1.096, 90% CI = 0.860-1.396, P = 0.5237). For twice-daily treatment, tobramycin levels after 8 weeks showed a 40% decrease compared with 4 weeks (AUC0-90min ratio = 0.608, 90% CI = 0.461-0.802, P = 0.0055). The AUC0-90min ratio at 8 weeks (once daily versus twice daily) did not differ significantly (AUC0-90min ratio = 0.749, 90% CI = 0.514-1.092, P = 0.2009). The mean FEV1 did not differ markedly compared between treatment periods or with baseline. No audiological or nephrotoxic side effects were noted.

CONCLUSIONS

Continuous treatment with TIS (once daily or twice daily) over 8 weeks appears to be safe and tolerable.

Pharmacokinetics and safety of tobramycin administered by the PARI eFlow rapid nebulizer in cystic fibrosis

BACKGROUND

Nebulization times have been identified as an issue in patient compliance with tobramycin solution for inhalation (TSI) therapy in cystic fibrosis (CF).

METHODS

In this randomized, open-label, multicentre, two-period, crossover study, patients (n=25) with CF and chronic pulmonary pseudomonal infection received TSI for 15 days via eFlow rapid or LC PLUS nebulizer. Nebulization times and sputum/serum tobramycin concentrations were determined, and safety evaluated.

RESULTS

Nebulization times were significantly shorter for eFlow rapid versus LC PLUS on Day 1 (least squares mean estimate of the difference -10.5 min, 95% confidence intervals [CI] -12.6, -8.3, p<0.0001) and Day 15 (difference -7.7 min, 95% CI -9.0, -6.5, p<0.0001). Broadly comparable sputum/systemic exposure to tobramycin was observed and the incidence of adverse events was similar for both nebulizers.

CONCLUSION

Use of the eFlow rapid nebulizer reduced TSI nebulization time. The systemic exposure to tobramycin appeared to be broadly similar in this exploratory study.

Penetration of gentamicin into the alveolar lining fluid of critically ill patients with ventilator-associated pneumonia

STUDY OBJECTIVES

To estimate the penetration of gentamicin into lung tissue by measuring its concentrations in alveolar lining fluid (ALF) and blood in critically ill patients with ventilator-associated pneumonia (VAP).

PATIENTS AND INTERVENTIONS

The study population consisted of 24 patients who were admitted to an ICU for respiratory failure and developed VAP. Patients were scheduled to undergo bronchoscopy with BAL after IV administration of a once-daily, 240-mg schedule of gentamicin for the treatment of VAP. Patients were assigned at random to one of four groups of six patients each according to the scheduled time for bronchoscopy (1, 2, 4, or 6 h, respectively). A serum sample was obtained at 0.5 h (n = 24), and both serum and ALF samples (n = 6) were collected at each of the above specified times for measurement of antibiotic concentrations.

MEASUREMENTS AND RESULTS

Mean +/- SEM gentamicin concentrations in the ALF were 2.95 +/- 0.37, 4.24 +/- 0.42, 3.10 +/- 0.39, and 2.65 +/- 0.35 microg/mL at 1, 2, 4, and 6 h, respectively, after the start of antibiotic infusion. Maximum gentamicin concentrations in serum (13.39 +/- 0.91 mug/mL, n = 24) and ALF (4.24 +/- 0.42 microg/mL, n = 6) were achieved at 0.5 h and 2 h, respectively, giving a penetration ratio of 0.32. The mean ratios of ALF/serum concentrations between 1 h and 6 h ranged from 0.30 to 1.14. After completion of the distribution phase, a significant positive correlation (p = 0.02) was found between gentamicin concentrations in the serum and ALF.

CONCLUSIONS

Once-daily IV administration of 240-mg gentamicin achieved average peak antibiotic concentrations of 4.24 microg/mL in the ALF 2 h after administration, and an ALF/serum penetration ratio of 32%. Higher gentamicin doses to produce higher peak blood levels than those found with the study dose are necessary to obtain active alveolar concentrations against less sensitive microorganisms in the treatment of VAP in ICU patients.

Gentamicin enzyme-linked immunosorbent assay for microdialysis samples

The authors investigated the use of a commercially available gentamicin enzyme-linked immunosorbent assay (ELISA) for the quantitative analysis of gentamicin concentrations in microdialysis samples. The assay demonstrated good accuracy and precision in the concentration range of 100 to 967 pg/mL. The developed quantitative ELISA is a highly sensitive and valid method for measuring gentamicin concentrations in microdialysis samples. This assay may be a useful alternative to other assay methodologies where analysis may be restricted by sample volume requirements and limited sensitivity.

Current methodologies for the analysis of aminoglycosides

The aminoglycosides are a large and diverse class of antibiotics that characteristically contain two or more aminosugars linked by glycosidic bonds to an aminocyclitol component. Structures are presented for over 30 of the most important members of this family of compounds. The use of aminoglycosides in clinical and veterinary medicine and in agriculture is described. Qualitative methods for aminoglycoside analysis include X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The major part of this article comprises a comprehensive review of quantitative methods for the determination of aminoglycosides. These are microbiological assay, radiochemical assay, radioimmunoassay, enzyme immunoassay, fluoroimmunoassay and other immunoassays, spectrophotometric and other non-separative methods, gas chromatography (GC), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Simple spectrophotometric methods may be adequate for the assay of bulk pharmaceuticals and their formulations. Microbiological assays make useful semi-quantitative screening tests for the analysis of veterinary drug residues in food, but rapid enzyme immunoassays are more suitable for accurate measurements of aminoglycosides in complex matrices. Automated immunoassays are the most appropriate methods for serum aminoglycoside determinations during therapeutic drug monitoring. HPLC techniques provide the specificity and sensitivity required for pharmacokinetic and other research studies, while HPLC-MS is employed for the confirmation of veterinary drug residues. The potential for further development of chromatographic and CE methods for the analysis of biological samples is outlined.