Application of a LC-MS/MS method for evaluating lung penetration of tobramycin in rats by microdialysis.

A bioanalytical LC-MS/MS method was developed and validated to determine tobramycin in plasma and lung microdialysate samples. Tobramycin was separated using a C18 column and a mobile phase consisting of water and acetonitrile, both with 10mM of heptafluorobutyric acid, eluted as gradient. Apramycin was used as internal standard (IS) for plasma samples. Drugs were monitored using electrospray ionization operating on positive mode (ESI+) monitoring the transitions 468.2>163.3 m/z for tobramycin and 540.3>217.2 m/z for IS. The method showed linearity in the concentration range of 0.1-50µgmL-1 for microdialysate and 0.5-100µgmL-1 for plasma with coefficients of determination ≥0.991. The inter- and intra-day precision, the accuracy and the stability of the drug in different conditions were in accordance with the limits established by US Food and Drug Administration guideline. The concentrations of tobramycin in plasma and lung microdialysate, determined using CMA/20 probes and a Ringer solution at a flow rate of 1µLmin-1, were evaluated in healthy Wistar rats after a 10mgkg-1 i.v. bolus dose. Samples were harvested up to 12h post-dose. Before animal's experiments, probe recovery was determined by dialysis and retrodialysis in vitro and by retrodialysis in vivo. Probes recovery was independent of drug concentration and method of determination. In vivo recovery was 27.74±7.70%. Pharmacokinetic parameters were estimated by non-compartmental analysis using the software Phoenix®. The estimated area under the curve (AUC0-∞) was 128±19µghmL-1 and 105±12µghmL-1 for plasma and lung, respectively. Tobramycin plasma clearance was 0.07±0.01L/h/kg and the volume of distribution was 0.49±0.09L/kg. Elimination half-life in plasma was 4.4±0.7h and in lung, 4.2±0.56h. The free tissue/free plasma AUC0-∞ ratio was 0.94. This is the first study showing a validated method to quantify tobramycin in microdialysate samples and to evaluate the lung interstitial concentration of the drug.

Non specific immunity in aged healthy subjects and in patients with chronic bronchitis.

We investigated the effects of aging on some functional activities (chemotaxis, phagocytosis, nitroblue tetrazolium reduction and candidacidal activity) of peripheral polymorphonuclear and mononuclear phagocytes in 96 healthy subjects and 89 patients with chronic bronchitis, aged 40 to 100 years. The subjects were divided according to age into younger (40-65 years) and older (66-100 years) individuals. No subject was taking any drug known to affect phagocytic functions. A few abnormalities in PMN and monocyte functions were observed in aged healthy subjects, in comparison to the younger ones; in fact, only the chemotactic response to complement-derived chemotactic factors was significantly impaired in elderly healthy individuals. On the contrary, multiple alterations of phagocyte activities, i.e., chemotaxis, phagocytosis, and candidacidal activity were observed in aged subjects with chronic bronchitis, compared to healthy adults. However, the results obtained in older and younger patients with chronic bronchitis were superimposable. The present data suggest that the decline in functional activities of phagocytes in the aged could depend on the effect of the underlying chronic bronchitis on the cellular components of the non-specific host defense system, rather than a direct effect of the aging process.