Helena Colom

The bioavailability and distribution of trans-resveratrol are constrained by ABC transporters

The ABC proteins are a family of membrane transporters that mediates the extrusion from cells of a wide variety of structurally unrelated substrates. The current review focuses on the role of these efflux pumps located in the intestine on the low oral bioavailability of trans-resveratrol. The enterocytes hold in the apical membrane three transporters, namely, P-glycoprotein (P-gp), multidrug resistance associated protein 2 (MRP2) and breast cancer resistance protein (BCRP), whereas the basolateral membrane contains multidrug resistance associated protein 3 (MRP3). The use of different specific inhibitors of these transporters as well as knockout mice enabled us to conclude that MRP2 and BCRP are involved in the extrusion of trans-resveratrol glucuronide and sulfate to the intestinal lumen without the participation of P-gp. The role of these transporters as a bottleneck in the absorption of trans-resveratrol cannot be undervalued affecting not only the bioavailability of its glucuronide and sulfate but also their distribution in the different organs.

Population Pharmacokinetics of Ganciclovir after Intravenous Ganciclovir and Oral Valganciclovir Administration in Solid Organ Transplant Patients Infected with Cytomegalovirus

ABSTRACT A population pharmacokinetics analysis was performed after intravenous ganciclovir and oral valganciclovir in solid organ transplant patients with cytomegalovirus. Patients received ganciclovir at 5 mg/kg of body weight (5 days) and then 900 mg of valganciclovir (16 days), both twice daily with dose adjustment for renal function. A total of 382 serum concentrations from days 5 and 15 were analyzed with NONMEM VI. Renal function given by creatinine clearance (CLCR) was the most influential covariate in CL. The final pharmacokinetic parameters were as follows: ganciclovir clearance (CL) was 7.49·(CLCR/57) liter/h (57 was the mean population value of CLCR); the central and peripheral distribution volumes were 31.9 liters and 32.0 liters, respectively; intercompartmental clearance was 10.2 liter/h; the first-order absorption rate constant was 0.895 h−1; bioavailability was 0.825; and lag time was 0.382 h. The CLCR was the best predictor of CL, making dose adjustment by this covariate important to achieve the most efficacious ganciclovir exposure.

Sequential treatment of cytomegalovirus infection or disease with a short course of intravenous ganciclovir followed by oral valganciclovir: efficacy, safety, and pharmacokinetics.

A. Caldés, S. Gil‐Vernet, Y. Armendariz, H. Colom, L. Pou, J. Niubó, L. Lladó, J. Torras, N. Manito, G. Rufí, J.M. Grinyó. Sequential treatment of cytomegalovirus infection or disease with a short course of intravenous ganciclovir followed by oral valganciclovir: efficacy, safety, and pharmacokinetics
Transpl Infect Dis 2010: 12: 204–212. All rights reserved

Do drug transporter (ABCB1) SNPs and P‐glycoprotein function influence cyclosporine and macrolides exposure in renal transplant patients? Results of the pharmacogenomic substudy within the symphony study

The function of the efflux pump P‐glycoprotein (Pgp) and ABCB1 single nucleotide polymorphisms (SNPs) should be considered as important tools to deepen knowledge of drug nephrotoxicity and disposition mechanisms. The aim of this study is to investigate the association of C3435T, G2677T, C1236T, and T129C ABCB1 SNPs with Pgp activity and exposure to different immunosuppressive drugs in renal transplant patients. Patients included in the Symphony Pharmacogenomic substudy were genotyped for ABCB1 SNPs. According to the design, patients were randomized into four immunosuppressive regimens: low and standard dose of cyclosporine (n = 30), tacrolimus (n = 13), and sirolimus (n = 23) concomitantly with mycophenolate and steroids. Pgp activity was evaluated in PBMC using the Rhodamine 123 efflux assay. TT carrier patients on C3435T, G2677T, and C1236T SNPs (Pgp‐low pumpers) showed lower Pgp activity than noncarriers. Pgp‐high pumpers treated with cyclosporine showed lower values of Pgp function than macrolides. There was a negative correlation between cyclosporine AUC and Pgp activity at 3 months. Results did not show any correlation between tacrolimus and sirolimus AUC and Pgp activity at 3 months. We found an important role of the ABCB1 SNPs Pgp function in CD3+ peripheral blood lymphocytes from renal transplant recipients. Pgp activity was influenced by cyclosporine but not macrolides exposure.

Quality by Design approach to understand the physicochemical phenomena involved in controlled release of captopril SR matrix tablets.

The aim of this study is to obtain swelling controlled release matrix tablets of captopril using the Quality by Design methodology (ICH Q8) and to know the transport mechanisms involved in captopril release. To obtain the area of knowledge, the design of experiments studying the effect of two components (HPMC K15M and ethylcellulose) at different levels has been applied, with the captopril dissolution profile as the products most important critical quality attribute (CQA). Different dissolution profiles have been obtained with the design of experiments performed, which is a key factor in the development of controlled release matrix tablets. Kinetic analysis according to the equations of Higuchi and Korsmeyer-Peppas demonstrates that the release mechanism is a mechanism of erosion when the whole percentage of the polymer is ethylcellulose, and a diffusion mechanism when the whole percentage of the polymer is HPMC K15M. The physico-chemical characteristics of the gel layer determine the release rate of captopril. The thickness of the gel layer, the porosity which is formed in the matrix upon contact with water, pore size, the swelling rate, the erosion rate of the matrix, and the physico-chemical characteristics of captopril, are factors related to the kinetic equations described and that allow us to predict the release mechanism of captopril. A new relationship of the kinetic equations governing the in vitro behavior with the physical characteristics of the gel layer of the different formulations has been established. This study shows that the size of water-filled pores and the degree of crosslinking between the chains of HPMC K15M of the matrix are related to the exponent n of the Korsmeyer-Peppas equation and the type of transport of the captopril from within the matrix to the dissolution medium, that is, if the transport is only through water-filled pores, or if a combination of diffusion occurs through water-filled pores with a transport through continuous polymeric networks.

Phase I study and preclinical efficacy evaluation of the mTOR inhibitor sirolimus plus gemcitabine in patients with advanced solid tumours

Background:We conducted a phase I study in patients with advanced solid tumours to identify the recommended dose, assess pharmacokinetics (PK), pharmacodynamic activity and preclinical antitumour efficacy of the combination of sirolimus and gemcitabine.Methods:Nineteen patients were treated with sirolimus 2 or 5 mg daily and gemcitabine 800 or 1000 mg m−2 on days 1 and 8. Dose escalation depended on dose-limiting toxicity (DLT) rate during the first 3-week period. Paired skin biopsies were evaluated for phosphorylated S6 (pS6) as marker of mTOR (mammalian target of rapamycin) inhibition. Pharmacokinetics and preclinical evaluation of efficacy using two different sarcoma cell lines and leiomyosarcoma xenografts were also conducted.Results:Three DLTs were observed: grade 3 transaminitis, grade 3 thrombocytopenia and grade 4 thrombocytopenia. Common treatment-related adverse events included anaemia, neutropenia, thrombocytopenia and transaminitis. Pharmacodynamic analyses demonstrated mTOR inhibition with sirolimus 5 mg and PK showed no influence of sirolimus concentrations on gemcitabine clearance. In vitro and in vivo studies suggested mTOR pathway hyperactivation by gemcitabine that was reversed by sirolimus. Tumour growth in leiomyosarcoma xenografts was dramatically inhibited by the treatment.Conclusions:Recommended dose was sirolimus 5 mg per 24 h plus gemcitabine 800 mg m−2. Antitumour activity in preclinical sarcoma models and mTOR signalling inhibition were observed. A phase II study is currently ongoing.

Population pharmacokinetics of high-dose methotrexate after intravenous administration in pediatric patients with osteosarcoma.

The goal of this study was to establish the population pharmacokinetics (PK) of high-dose methotrexate (HD-MTX) treatment in children with osteosarcoma and to explore the influence of patient covariates and between-occasion variability on drug disposition. Patient covariates and concentration-time data were collected. PK data analysis from 209 HD-MTX cycles from 14 patients was performed using the population approach (NONMEM V). Internal and external validations were performed to confirm the model. PK of methotrexate was best described by a 2-compartment open PK model with first-order elimination from the central compartment. Between-subject variability (BSV) was included in total plasma clearance (CL) and in central compartment distribution volume (V1) [coefficient of variation (CV) 11.9% and 8.9%, respectively]. The CV of BSV in the residual error was 25.5%. Between-occasion variability was only retained for CL (CV 8.2%). RE consisted of a proportional error of 41.6%. Age and body weight in CL and body weight in V1 were identified as the appropriate covariates. The final estimates of total CL and V1 were given by the equations CL = 88.5·(AGE/15) + 27.4·(WGT/50) L/d and V1 = 11.0 + 5.6·(WGT/50) L, respectively. Internal validation results showed that the 95% confidence interval covered all the observed MTX concentrations. Mean bias and precision of the individual predicted concentrations, calculated in a validation dataset, resulted in −1.36% and 19.71%, respectively. A population PK model was developed for HD-MTX in children with osteosarcoma. Validation studies confirmed the suitability of the model for further dose individualization by means of a Bayesian approach.

An improved cryopreservation method for porcine buccal mucosa in ex vivo drug permeation studies using Franz diffusion cells

The use of isolated animal models to assess percutaneous absorption of molecules is frequently reported. The porcine buccal mucosa has been proposed as a substitute for the buccal mucosa barrier on ex vivo permeability studies avoiding unnecessary sacrifice of animals. But it is not always easy to obtain fresh buccal mucosa. Consequently, human and porcine buccal mucosa is sometimes frozen and stored in liquid nitrogen, but this procedure is not always feasible. One cheaper and simpler alternative is to freeze the buccal mucosa of freshly slaughtered pigs in a mechanical freezer, using DMSO and albumin as cryoprotective agents. This study compared the ex vivo permeability parameters of propranolol hydrochloride through porcine buccal mucosa using a Franz diffusion cell system and HPLC as detection method. The freezing effects on drug permeability parameters were evaluated. Equally histological studies were performed. Furthermore, the use of the parameter transmucosal water loss (TMWL) as an indicator of the buccal mucosa integrity was evaluated just as transepidermal water loss (TEWL) is utilized for skin integrity. The results showed no difference between fresh and frozen mucosal flux, permeability coefficient or lag time of propranolol. However, statistical significant difference in TMWL between fresh and frozen mucosa was observed.

Determination of ganciclovir in human plasma by ultra performance liquid chromatography-UV detection

OBJECTIVES Implement a sensitive UHPLC method for the assay of ganciclovir in human plasma. DESIGN AND METHODS We developed and validated a chromatographic method coupled to ultraviolet detection for quantification of ganciclovir, with a short run time using a small volume of human plasma. Comparison of system performance was made with respect to analysis time, efficiency and sensitivity. RESULTS Correlation coefficients (r) of the calibration curves ranged from 0.999744 to 0.999784. Within-day and between-day imprecision and inaccuracy, specificity and recovery were also evaluated for validation. The method was precise and accurate and the retention time was 0.7 min. The calibration curves were linear between 0.5 and 30 μg/mL. There was a good correlation between HPLC and UHPLC techniques. CONCLUSIONS We developed a method that is currently applied in a clinical study assessing GCV plasma concentration variability after ganciclovir and valganciclovir administration.

Pharmacokinetic modeling of enterohepatic circulation of mycophenolic acid in renal transplant recipients

Several factors contribute to mycophenolic acid (MPA) between-patient variability. Here we characterize the metabolic pathways of MPA and quantify the effect of combining genetic polymorphism of multidrug-resistant-associated protein-2, demographics, biochemical covariates, co-medication (cyclosporine (CsA) vs. macrolides), and renal function on MPA, 7-O-MPA-glucuronide (MPAG), and acyl-glucuronide (AcMPAG) disposition, in renal transplant recipients, after mycophenolate mofetil. Complete pharmacokinetic profiles from 56 patients (five occasions) were analyzed. Enterohepatic circulation was modeled by transport of MPAG to the absorption site. This transport significantly decreased with increasing CsA trough concentrations (CtroughCsA). MPAG and AcMPAG plasma clearances significantly decreased with renal function. No significant influence of multidrug-resistant-associated protein-2 C24T single-nucleotide polymorphism was found. The model adequately predicted the increase in MPAG/AcMPAG exposures in CsA and macrolide patients with decreased renal function. This resulted in higher MPA exposures in macrolide patients versus CsA patients, and increased MPA exposures with renal function from 25 to 10 ml/min, in macrolide patients, owing to enhanced MPAG enterohepatic circulation. Lower-percentage enterohepatic circulation occurred with higher CtroughCsA and renal function values. The lack of MPA protein-binding modeling did not permit evaluation of the impact of renal function and CtroughCsA on MPA exposures in CsA patients. Thus, dose tailoring of covariates is recommended for target MPA exposure.