Population pharmacokinetic modeling to establish the role of P-glycoprotein on ciprofloxacin distribution to lung and prostate following intravenous and intratracheal administration to Wistar rats.

Ciprofloxacin (CIP) is indicated for clinical treatment of urinary and respiratory tract infections. Poor infection site penetration and consequent insufficient exposure to the antimicrobial agent may be the reason for some therapeutic failures. Ciprofloxacin is reported as a substrate for efflux transporters, such as P-glycoprotein, which could be related to the presence of sub-therapeutic drug concentration at the infection site. In the present work we evaluated CIP pharmacokinetics (PK) in plasma and lung and prostate tissues of Wistar rats after intravenous (i.v.) and intratracheal (i.t.) dosing (7 mg/Kg) in the presence and absence of P-gp inhibitor tariquidar (TAR, 15 mg/Kg). Microdialysis was applied to determine free tissue concentration-time profiles and the obtained data were analyzed by non-compartmental and population PK (popPK) analysis. A sequential strategy was used to develop the popPK model: characterization of CIP PK in tissues (Tissue model) was performed subsequently to CIP PK modeling in plasma (Plasma model). Two and three compartmental models were used to simultaneously characterize plasma concentrations after i.t. and i.v. dosing; the distribution model was developed by separating the central compartment into venous and arterial compartment and by adding lung and prostate; TAR was identified as a significant covariate for clearance and volume of distribution of central compartment as well as for inter-compartmental clearance. Our results indicate an impact of P-gp on plasma PK, likely by acting on renal active secretion of CIP. Regarding CIP exposure in lung and prostate tissues, our results suggest a complex interplay between drug transporters; P-gp inhibition by TAR was likely counterbalanced by the activity of other efflux/influx transporters, which could not be fully characterized by our model.

Population Pharmacokinetic Modeling to Describe the Total Plasma and Free Brain Levels of Fluconazole in Healthy and Cryptococcus neoformans Infected Rats: How Does the Infection Impact the Drug's Levels on Biophase?

PURPOSE: The present work aimed to evaluate the influence of experimental meningitis caused by C. neoformans on total plasma and free brain concentrations of fluconazole (FLC) in Wistar rats. METHOD: The infection was induced by the administration of 100 µL of inoculum (1.105 CFU) through the tail vein. Free drug in the brain was assessed by microdialisys (µD). Blood and µD samples were collected at pre-determined time points up to 12 h after intravenous administration of FLC (20 mg/kg) to healthy and infected rats. The concentration-time profiles were analyzed by non-compartmental and population pharmacokinetics approaches. RESULTS: A two-compartmental popPK model was able to simultaneously describe plasma and free drug concentrations in the brain for both groups investigated. Analysis of plasma and µD samples showed a better FLC distribution on the brain of infected than healthy animals (1.04 ± 0.31 vs 0.69 ± 0.14, respectively). The probability of target attainment was calculated by Monte Carlo simulations based on the developed popPK model for 125 mg/kg dose for rats and 400-2000 mg for humans. CONCLUSIONS: FLC showed a limited use in monotherapy to the treatment of criptoccocosis in rats and humans to value of MIC >8 µg/mL.

Beyond the "Lock and Key" Paradigm: Targeting Lipid Rafts to Induce the Selective Apoptosis of Cancer Cells.

For more than 40 years, the fluid mosaic model of cellular membranes has supported our vision of an inert lipid bilayer containing membrane protein receptors that are randomly hit by extracellular molecules to trigger intracellular signaling events. However, the notion that compartmentalized cholesterol- and sphingomyelin-rich membrane microdomains (known as lipid rafts) spatially arrange receptors and effectors to promote kinetically favorable interactions necessary for the signal transduction sounds much more realistic. Despite their assumed importance for the dynamics of ligand-receptor interactions, lipid rafts and biomembranes as a whole remain less explored than the other classes of biomolecules because of the higher variability and complexity of their membrane phases, which rarely provide the detailed atomic-level structural data in X-ray crystallography assays necessary for molecular modeling studies. The fact that some alkylphospholipids (e.g. edelfosine: 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine) selectively induce the apoptotic death of cancer cells by recruiting Fas death receptors and the downstream signaling molecules into clusters of lipid rafts suggests these potential drug targets deserve a more in-depth investigation. Herein, we review the structure of lipid rafts, their role in apoptotic signaling pathways and their potential role as drug targets for the treatment of cancer.

Enantioselective analysis of etodolac in human plasma by LC-MS/MS: Application to clinical pharmacokinetics.

Etodolac is a non-steroidal anti-inflammatory drug with preferential inhibition of cyclooxigenase-2 and is widely used in the management of pain in patients with inflammatory arthritis. Etodolac is available as a racemic mixture of (-)-(R)-Etodolac and (+)-(S)-Etodolac; cyclooxigenases inhibition is attributed to (+)-(S)-Etodolac. According to our knowledge, this is the first method for determination of etodolac enantiomers in plasma using LC-MS/MS. Plasma extraction were performed with 25µL of plasma and 1mL of n-hexane:ethyl acetate (95:5); racemic ibuprofen was used as internal standard. Resolution of enantiomers were performed in a Chiralcel(®)OD-H column; deprotonated [M-H](-) and their respective ion products were monitored at transitions of 286>242 for etodolac enantiomers and 205>161 for ibuprofen. The quantitation limit was 3.2ng/mL for both enantiomers in plasma. The method was applied to study the pharmacokinetics of etodolac enantiomers after the administration of a 300 and 400mg dose of racemic drug to a healthy volunteer. Analysis of plasma samples showed higher plasma concentration of (-)-(R)-Etodolacfor both doses (300mg dose: AUC(0-∞)49.80 versus 4.55ugh/mL;400mg dose: AUC(0-∞) 63.90 versus 6.00ugh/mL) with an (R)-(+)/(S)-(-) ratio of approximately 11.

Influence of glomerular filtration rate on the pharmacokinetics of cyclophosphamide enantiomers in patients with lupus nephritis.

The pharmacokinetics of cyclophosphamide (CYC) enantiomers were evaluated in patients with lupus nephritis distributed in 2 groups according to creatinine clearance: group 1 (90.6-144.6 mL/min/1.73 m(2)) and group 2 (42.8-76.4 mL/min/1.73 m(2)). All patients were treated with 0.75 to 1.3 g of racemic CYC as a 2-hour infusion and with 1 mg intravenous midazolam as a drug-metabolizing marker. CYC enantiomers and midazolam concentrations in plasma were measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS). The following differences (Wilcoxon test, P < or = .05) were observed between the (S)-(-) and (R)-(+) enantiomers: AUC(0-infinity) 152.41 vs 129.25 microg.h/mL, CL 3.28 vs 3.89 L/h, Vd 31.38 vs 29.74 L, and t((1/2)) 6.79 vs 5.56 h for group 1 and AUC(0-infinity) 167.20 vs 139.08 microg.h/mL, CL 2.99 vs 3.59 L/h, and t((1/2)) 6.15 vs 4.99 h for group 2. No differences (Mann test, P < or = .05) were observed between groups 1 and 2 in the pharmacokinetic parameters of both enantiomers. No significant relationship was observed between midazolam clearance (2.92-16.40 mL/min.kg) and clearance of each CYC enantiomer. In conclusion, CYC kinetic disposition is enantioselective, resulting in higher exposures of the (S)-(-) enantiomer in lupus nephritis patients, and the pharmacokinetic parameters of both enantiomers are not altered by the worsening of renal condition.

Determination of cyclophosphamide enantiomers in plasma by LC-MS/MS: Application to pharmacokinetics in breast cancer and lupus nephritis patients.

This article describes the enantioselective analysis of cyclophosphamide (CPA) in human plasma using LC-MS/MS. CPA enantiomers were extracted from plasma using a mixture of ethyl acetate and chloroform (75:25, v/v). The enantiomers were separated on a Chiralcel(R) OD-R column, with the mobile phase consisting of a mixture of acetonitrile and water (75:25, v/v) plus 0.2% formic acid. The protonated ions and their respective product ions were monitored using two functions, 261 > 141 for CPA enantiomers and 189 > 104 for the internal standard (antipyrine). Recovery rates were higher than 95% and the quantification limit was 2.5-ng/ml plasma for both enantiomers. The coefficients of variation and the relative errors obtained for the validation of intra- and interassay precision and accuracy were less than 10%. The method was applied for the investigation of the enantioselective pharmacokinetics of CPA in a lupus nephritis patient treated with 1 g CPA infused over 2 h and in a breast cancer patient treated with 0.9 g infused over 1 h. No stereoselectivity in the pharmacokinetic parameters was observed for either patient. Clearance values of 2.63 and 2.93 l/h and of 3.36 and 3.61 l/h for (-)-(S) and (+)-(R)-CPA were obtained for the breast cancer and lupus nephritis patient, respectively.

Stereoselective disposition of fenoprofen in plasma and synovial fluid of patients with rheumatoid arthritis.

The simultaneous disposition of fenoprofen enantiomers in synovial fluid and plasma was studied in 11 patients with arthritis and chronic knee effusions treated with a single oral dose of 600 mg rac-fenoprofen. A plasma sample and a synovial fluid sample were collected simultaneously from each patient up to 16 h after the administration of fenoprofen. A stereospecific assay for fenoprofen using LC-MS-MS was developed and applied successfully to the analysis of the enantiomers in plasma (LOQ = 10 ng of each enantiomer/ml) and synovial fluid (LOQ = 25 ng of each enantiomer/ml). The values of the area under the curve (AUC) for the S-(+)-fenoprofen eutomer were approximately 2.5 times higher in plasma than in synovial fluid (256 vs 104 microg h/ml), while the values for the R-(-)-fenoprofen distomer were about four times higher in plasma than in synovial fluid (42.5 vs 10.5 microg h/ml). These data demonstrate accumulation of the S-(+)-fenoprofen eutomer in plasma and in synovial fluid, with concentrations versus time AUC (+)/(-) ratios of 6.0 in plasma and 9.9 in synovial fluid, suggesting a greater accumulation of the eutomer at the active site represented by synovial fluid than in plasma. This result demonstrates the importance of enantioselective methods and of analysis of synovial fluid rather than plasma in studies of the pharmacokinetics-pharmacodynamics of fenoprofen.