Pathogenesis of Aspergillus fumigatus and the kinetics of galactomannan in an in vitro model of early invasive pulmonary aspergillosis: implications for antifungal therapy

BACKGROUND: Little is known about the pathogenesis of invasive pulmonary aspergillosis and the relationship between the kinetics of diagnostic markers and the outcome of antifungal therapy. METHODS: An in vitro model of the human alveolus, consisting of a bilayer of human alveolar epithelial and endothelial cells, was developed. An Aspergillus fumigatus strain expressing green fluorescent protein was used. Invasion of the cell bilayer was studied using confocal and electron microscopy. The kinetics of culture, polymerase chain reaction, and galactomannan were determined. Galactomannan was used to measure the antifungal effect of macrophages and amphotericin B. A mathematical model was developed, and results were bridged to humans. RESULTS: A. fumigatus penetrated the cellular bilayer 14-16 h after inoculation. Galactomannan levels were inextricably tied to fungal invasion and were a robust measure of the antifungal effect of macrophages and amphotericin B. Neither amphotericin nor macrophages alone was able to suppress the growth of A. fumigatus; rather, the combination was required. Monte Carlo simulations showed that human dosages of amphotericin B of at least 0.6 mg/kg were required to achieve adequate drug exposure. CONCLUSIONS: This model provides a strategy by which relationships among pathogenesis, immunological effectors, and antifungal drug therapy for invasive pulmonary aspergillosis may be further understood.     

In Vitro Combination of Isavuconazole with Micafungin or Amphotericin B Deoxycholate against Medically Important Molds

Whether isavuconazole, an extended-spectrum triazole, possesses synergistic activity in combination therapy with echinocandins or amphotericin B for the treatment of invasive molds infections has not been studied. Our in vitro combination studies showed that isavuconazole and micafungin are synergistically active against Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, and Cunninghamella bertholletiae. These results suggest that isavuconazole, in combination with micafungin, may have a role in the treatment of invasive aspergillosis and warrants further investigation.     

Comparative antifungal activities and plasma pharmacokinetics of micafungin (FK463) against disseminated candidiasis and invasive pulmonary aspergillosis in persistently neutropenic rabbits

Micafungin (FK463) is an echinocandin that demonstrates potent in vitro antifungal activities against Candida and Aspergillus species. However, little is known about its comparative antifungal activities in persistently neutropenic hosts. We therefore investigated the plasma micafungin pharmacokinetics and antifungal activities of micafungin against experimental disseminated candidiasis and invasive pulmonary aspergillosis in persistently neutropenic rabbits. The groups with disseminated candidiasis studied consisted of untreated controls (UCs); rabbits treated with desoxycholate amphotericin B (DAMB) at 1 mg/kg of body weight/day; or rabbits treated with micafungin at 0.25, 0.5, 1, and 2 mg/kg/day intravenously. Compared with the UCs, rabbits treated with micafungin or DAMB showed significant dosage-dependent clearance of Candida albicans from the liver, spleen, kidney, brain, eye, lung, and vena cava. These in vivo findings correlated with the results of in vitro time-kill assays that demonstrated that micafungin has concentration-dependent fungicidal activity. The groups with invasive pulmonary aspergillosis studied consisted of UCs; rabbits treated with DAMB; rabbits treated with liposomal amphotericin B (LAMB) at 5 mg/kg/day; and rabbits treated with micafungin at 0.5, 1, and 2 mg/kg/day. In comparison to the significant micafungin dosage-dependent reduction of the residual burden (in log CFU per gram) of C. albicans in tissue, micafungin-treated rabbits with invasive pulmonary aspergillosis had no reduction in the concentration of Aspergillus fumigatus in tissue. DAMB and LAMB significantly reduced the burdens of C. albicans and A. fumigatus in tissues (P < 0.01). Persistent galactomannan antigenemia in micafungin-treated rabbits correlated with the presence of an elevated burden of A. fumigatus in pulmonary tissue. By comparison, DAMB- and LAMB-treated animals had significantly reduced circulating galactomannan antigen levels. Despite a lack of clearance of A. fumigatus from the lungs, there was a significant improvement in the rate of survival (P < 0.001) and a reduction in the level of pulmonary infarction (P < 0.05) in micafungin-treated rabbits. In summary, micafungin demonstrated concentration-dependent and dosage-dependent clearance of C. albicans from persistently neutropenic rabbits with disseminated candidiasis but not of A. fumigatus from persistently neutropenic rabbits with invasive pulmonary aspergillosis.     

Levofloxacin and ciprofloxacin decrease procainamide and N-acetylprocainamide renal clearances

Ten healthy adults participated in a randomized, crossover drug interaction study testing procainamide only, procainamide plus levofloxacin, and procainamide plus ciprofloxacin. During levofloxacin therapy, most procainamide and N-acetylprocainamide (NAPA) pharmacokinetic parameters, including decreased renal clearances and renal clearance/creatinine clearance ratios, changed (P < 0.05). During ciprofloxacin treatment, only procainamide and NAPA renal clearances decreased significantly.     

Serum caffeine levels after 24 hours of caffeine abstention: observations on clinical patients undergoing myocardial perfusion imaging with dipyridamole or adenosine

Although caffeine attenuates the vasodilatation produced by dipyridamole and adenosine, and is therefore contraindicated when these agents are used for myocardial perfusion scintigraphy, caffeine levels in clinical patients undergoing standard imaging protocols have not been studied. Eighty-six patients undergoing clinically indicated intravenous dipyridamole (n=75) or adenosine (n=11) thallium-201 myocardial perfusion scintigraphy, all of whom reported abstention from products containing caffeine for 24 h, were studied prospectively. Blood samples were drawn prior to initiation of the pharmacologic infusion, and serum caffeine levels were determined using an enzyme immunoassay technique. Results of these determinations were correlated with maximum pulse and blood pressure changes measured during and immediately after the stressor infusion, and thallium imaging findings. Detectable caffeine levels were found in 34 patients (40%), ranging from 0.1 to 5.0 mg/l. There was no significant difference in mean systolic blood pressure decrease or mean pulse increase between patients with caffeine levels > 1.0 mg/l (20.4 ± 18.2 mmHg, 11.0 ± 8.9 BPM; n=5) and those with lower (0.1 to 0.9 mg/1) (15.4 ± 9.5 mmHg, 14.4 ± 8.2 BPM; n=29) or no detectable caffeine levels (18.0 ± 11.5 mmHg, 16.6 ± 10.1 BPM; n=52). Redistribution on thallium imaging was also identified with a similar frequency in these three groups (2/5, 40%; 8/29, 28%; 22/52, 42% respectively). Correspondence to: A.F. Jacobson     

Compartmental pharmacokinetics and tissue distribution of multilamellar liposomal nystatin in rabbits

The plasma pharmacokinetics of multilamellar liposomal nystatin were studied in normal, catheterized rabbits after single and multiple daily intravenous administration of dosages of 2, 4, and 6 mg/kg of body weight, and drug levels in tissues were assessed after multiple dosing. Concentrations of liposomal nystatin were measured as those of nystatin by a validated high-performance liquid chromatography method, and plasma concentration data were fitted into a two-compartment open model. Across the investigated dosage range, liposomal nystatin demonstrated nonlinear kinetics with more than proportional increases in the AUC(0-24) and decreasing clearance, consistent with dose-dependent tissue distribution and/or a dose-dependent elimination process. After single-dose administration, the mean C(max) increased from 13.07 microg/ml at 2 mg/kg to 41.91 microg/ml at 6 mg/kg (P < 0.001); the AUC(0-24) changed from 11.65 to 67.44 microg. h/ml (P < 0.001), the V(d) changed from 0.205 to 0. 184 liters/kg (not significant), the CL(t) from 0.173 to 0.101 liters/kg. h (P < 0.05), and terminal half-life from 0.96 to 1.51 h (P < 0.05). There were no significant changes in pharmacokinetic parameters after multiple dosing over 14 days. Assessment of tissue concentrations of nystatin near peak plasma levels after multiple dosing over 15 days revealed preferential distribution to the lungs, liver, and spleen at that time point. Substantial levels were also found in the urine, raising the possibility that renal excretion may play a significant role in drug elimination. Liposomal nystatin administered to rabbits was well tolerated and displayed nonlinear pharmacokinetics, potentially therapeutic peak plasma concentrations, and substantial penetration into tissues. Pharmacokinetic parameters were very similar to those observed in patients, thus validating results derived from infection models in the rabbit and allowing inferences to be made about the treatment of invasive fungal infections in humans.     

Compartmental Pharmacokinetics and Tissue Distribution of the Antifungal Echinocandin Lipopeptide Micafungin (FK463) in Rabbits

The plasma pharmacokinetics and tissue distribution of the novel antifungal echinocandin-like lipopeptide micafungin (FK463) were investigated in healthy rabbits. Cohorts of three animals each received micafungin at 0.5, 1, and 2 mg/kg of body weight intravenously once daily for a total of 8 days. Serial plasma samples were collected on days 1 and 7, and tissue samples were obtained 30 min after the eighth dose. Drug concentrations were determined by validated high-performance liquid chromatographic methods. Plasma drug concentration data were fit to a two-compartment pharmacokinetic model, and pharmacokinetic parameters were estimated using weighted nonlinear least-square regression analysis. Micafungin demonstrated linear plasma pharmacokinetics without changes in total clearance and dose-normalized area under the concentration-time curve from 0 h to infinity. After administration of single doses to the rabbits, mean peak plasma drug concentrations ranged from 7.62 microg/ml at 0.5 mg/kg to 16.8 microg/ml at 2 mg/kg, the area under the concentration-time curve from 0 to 24 h ranged from 5.66 to 21.79 microg x h/ml, the apparent volume of distribution at steady state ranged from 0.296 to 0.343 liter/kg, and the elimination half-life ranged from 2.97 to 3.20 h, respectively. No significant changes in pharmacokinetic parameters and no accumulation was noted after multiple dosing. Mean tissue micafungin concentrations 30 min after the last of eight daily doses were highest in the lung (2.26 to 11.76 microg/g), liver (2.05 to 8.82 microg/g), spleen (1.87 to 9.05 microg/g), and kidney (1.40 to 6.12 microg/g). While micafungin was not detectable in cerebrospinal fluid, the concentration in brain tissue ranged from 0.08 to 0.18 microg/g. These findings indicate linear disposition of micafungin at dosages of 0.5 to 2 mg/kg and achievement of potentially therapeutic drug concentrations in plasma and tissues that are common sites of invasive fungal infections.