Pharmacocinétique des antibiotiques dans les voies respiratoires inférieures. Limites de l'apport de cette information

[An example of simulation for a better understanding of PK/PD relationship of antibiotics]

The interpretation of PK/PD indices is specific to each class of antibiotics. In order to illustrate this, we developed a multidisciplinary tutorial program based on simulation of clinical cases. Three drugs were included in this software: tobramycin, vancomycin and azithromycin. From the dosage regimen proposed by the user, the model simulates a plotting of antibiotic plasma concentrations vs. time (tobramycin, vancomycin and azithromycin) and tissue concentrations (azithromycin). Peak and trough concentrations are calculated at steady-state. A commentary is provided to evaluate the efficacy of treatment and to assist the user in improving his prescription of tobramycin or vancomycin. T(> MIC) (time the concentration remains above the MIC) and AUC(24) (area under the concentration-time curve) are calculated in plasma and tissues for azithromycin. In order to create a link between theoretical pharmacokinetics and clinical practice, we propose this model as a simulation of antibiotic monitoring. We put the emphasis on interactivity and simulation, leading to applied reasoning and decision making. It illustrates (i) the influence of pharmacokinetic parameters, location of infection and bactericidal kinetics on the use of three different classes of antibiotics, (ii) the role of route of administration, dosing and intervals between administrations on therapeutic response and (iii) the influence of erratic administrations on clinical efficacy.

Une modélisation informatique pour une meilleure compréhension de la relation PK/PD : application à l’azithromycine dans le traitement de l’angine aiguë streptococcique et des exacerbations aiguës de la bronchite chronique

In order to illustrate the significance of pharmacokinetic/pharmacodynamic (PK/PD) parameters of azithromycin (AZM) in tonsillar and respiratory tract infections, we developed original simulation software. As area under the curve over 24 hours divided by the minimum inhibitory concentration (AUC24/MIC) and time over a 24-hour period that the drug concentration exceeds the MIC (t > MIC) are important predictors of the clinical efficacy of macrolides, our software calculates these indices for plasma, tonsil, epithelial lining fluid (ELF), lung tissue (LT) and alveolar macrophages (AM). For an MIC of 0.5 microgram.mL-1, after administration of AZM 500 mg daily for 3 days (tonsillitis) or AZM 500 mg on day 1 and 250 mg daily for the next 4 days (respiratory tract infections) to a 70 kg subject, PK/PD parameters are as follows: AUC24/MIC (h): 9.5 (plasma); 439 (tonsil); 57.5 (ELF); 439 (LT); 1354 (AM); t > MIC is 24 hours in all tissues. Our simulation model illustrates the following: (i) AUC24/MIC values are above the 25-30-hour threshold in S. pneumoniae infection; and (ii) tissue concentrations exceed the MIC for 6 days after the last dose in ELF and for more than 2 weeks in tonsils, LT and AM.

Uptake of quinolones by in-vitro human monocyte derived macrophages

We have developed an in-vitro model of monocyte-derived macrophage (MDMphi) to compare fluoroquinolone uptake in monocytes and derived macrophages. Monocyte-derived macrophages were obtained in-vitro by cultivating freshly isolated monocytes for seven days in RPMI 1640 medium, containing foetal calf serum and Rhu granulocyte-macrophage colony stimulating factor. Final suspensions contained 95% viable cells and 63% macrophages. Intramacrophagic accumulation of ciprofloxacin, ofloxacin or sparfloxacin was measured at equilibrium after 30-min incubation in the presence of 16-18 microg mL(-1) antibiotic. The results revealed low intracellular accumulation of ofloxacin in MDMphi (intracellular/extracellular ratio: IC/EC = 1.7). Ciprofloxacin and sparfloxacin uptake was significantly higher. The IC/EC ratios were only slightly increased in macrophages when compared with monocytes under the same experimental conditions. These results suggest that maturation of monocyte to macrophage has only a limited effect on basal quinolone uptake. Monocytic maturation cannot explain the important differences between fluoroquinolone accumulation in monocytes and tissue macrophages. Cell activation may be a greater determinant.

[Pulmonary diffusion of antibiotics. Critical analysis of the literature]

OBJECTIVES

Collect exhaustive data from the literature concerning the diffusion of antibiotics into lung tissue and calculate their inhibitory quotient towards the germs most frequently encountered in pulmonary infections.

DATA SOURCES

Review of the literature. Data collected from the Medline database with the key words: lung, diffusion, disposition, antibiotics. Inhibitory quotients calculated from these data.

RESULTS

The results were relatively similar for the different types of samples, though some differences existed between the studies. These differences were caused in particular by methodological difficulties for the tissue dosage of antibiotics.

CONCLUSION

Further standardized studies, measuring in particular the antibiotic concentration in the epithelial lining fluid and in the alveolar macrophages, are necessary to obtain more reliable results in terms of inhibitory quotients. Only clinical studies, perhaps with the help of these data, could establish the real efficiency of antibiotics in lung infections.