Microdialysis

The effect of food on plasma and tissue concentrations of linezolid after multiple doses

In the present pilot study we investigated the effect of food ingestion on target site pharmacokinetics of linezolid, the first clinically approved oxazolidinone. For this purpose we determined free concentrations of linezolid at steady state in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue under fasting and non-fasting conditions in healthy volunteers (n = 9) by means of in vivo microdialysis. Ingestion of food led to a marked delay in the time to reach the peak concentration (T(max)), whereas the area under the concentration-time curve from 0 to 24 h (AUC(0-24 h)) remained unchanged. These data suggest that the rate of linezolid absorption is decreased by food intake. However, the overall extent of linezolid absorption and the distribution of linezolid were not affected. Tissue levels of linezolid appeared sufficiently high to eradicate pathogens with a minimum inhibitory concentration of <or= 4 mg/L.

Penetration of linezolid into soft tissues of healthy volunteers after single and multiple doses

The present study tested the ability of linezolid to penetrate soft tissues in healthy volunteers. Ten healthy volunteers were subjected to linezolid drug intake at a dose of 600 mg twice a day for 3 to 5 days. The first dose was administered intravenously. All following doses were self-administered orally. The tissue penetration of linezolid was assessed by use of in vivo microdialysis. In the single-dose experiments the ratios of the area under the concentration-time curve from 0 to 8 h (AUC0-8) for tissue to the AUC0-8 for free plasma were 1.4+/-0.3 (mean+/-standard deviation) and 1.3+/-0.4 for subcutaneous adipose and muscle tissue, respectively. After multiple doses, the corresponding mean ratios were 0.9+/-0.2 and 1.0+/-0.5, respectively. The ratios of the AUC from 0 to 24 h (AUC0-24) for free linezolid in tissues to the MIC were between 50 and 100 for target pathogens with MICs between 2 and 4 mg/liter. In conclusion, the present study showed that linezolid penetrates rapidly into the interstitial space fluid of subcutaneous adipose and skeletal muscle tissues in healthy volunteers. On the basis of pharmacokinetic-pharmacodynamic calculations, we suggest that linezolid concentrations in soft tissues can be considered sufficient to inhibit the growth of many clinically relevant bacteria.

Penetration of Orally Administered Prulifloxacin Into Human Lung Tissue

OBJECTIVE

To evaluate the distribution in lung tissue of ulifloxacin, the active metabolite of prulifloxacin, a new once-daily fluoroquinolone administered orally in a single 600mg dose.

DESIGN

Open-label, randomised study.

PATIENTS

Twenty-seven patients (25 males, 2 females; mean age 65.7 years [range 49-79 years]) with a lung neoplasm requiring lobectomy or pneumonectomy.

METHODS

Patients were randomly assigned to five treatment groups and received a single oral dose of prulifloxacin 600mg at 2, 4, 6, 12 or 24 hours preoperatively. During surgery, blood and healthy lung (based on macroscopic appearance) samples were collected at the same time. Ulifloxacin concentrations in plasma and lung tissue were determined by a validated reversed-phase high-performance liquid chromatography assay. Lung tissue ulifloxacin concentrations were adjusted for blood contamination, by measuring haemoglobin in the supernatant of each tissue sample and applying a corrective equation.

RESULTS

Ulifloxacin concentration in lung tissue exceeded plasma concentration at every timepoint. Following administration of prulifloxacin 600mg, the overall mean corrected lung/plasma ratio over the 24-hour period was 6.9 (range 1.2-14.1). When sampling intervals were assessed, the corrected lung/plasma ratios were 7.5 (2 hours after dosing), 6.3 (4 hours), 4.3 (6 hours), 7.0 (12 hours) and 9.2 (24 hours). The mean corrected lung/plasma area under the concentration-time curve ratio was 6.3, demonstrating the ability of the drug to penetrate lung tissue and confirming the high exposure of this target tissue to ulifloxacin. However, the limitation of the lung tissue sampling method and the high interpatient variability should be considered. Over the 24-hour period, the concentrations of ulifloxacin in lung tissue were higher than the minimum inhibitory concentration (MIC) values for pathogens frequently involved in community-acquired respiratory tract infections.

CONCLUSION

Lung tissue penetration data may have a supportive value when considered jointly with MICs and efficacy results. The findings from this lung penetration study could explain the efficacy of once-daily prulifloxacin 600mg observed in clinical trials conducted in patients with exacerbation of chronic bronchitis.

Concentrations of gemifloxacin at the target site in healthy volunteers after a single oral dose

Free gemifloxacin concentrations in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue were measured by means of in vivo microdialysis to characterize the ability of gemifloxacin to penetrate human soft tissues. Twelve healthy volunteers received a single oral dose of 320 mg of gemifloxacin. The mean areas under the concentration-time curves from 0 to 10 h (AUC(0-10)) were significantly higher for soft tissue than for unbound gemifloxacin in plasma (P < 0.05). The ratios of the mean AUC(0-10) for tissue to the AUC(0-10) for free gemifloxacin in plasma were 1.7 +/- 0.7 (mean +/- standard deviation) for skeletal muscle and 2.4 +/- 1.0 for adipose tissue. The AUC(0-24) ratios for free gemifloxacin in tissues to the MIC at which 90% of frequently isolated bacteria are inhibited were close to or higher than 100 h. Therefore, based on pharmacokinetic and pharmacodynamic calculations, we conclude that gemifloxacin might be a useful therapeutic option for the treatment of soft tissue infections.