The effects of milk thistle (Silybum marianum) on human cytochrome P450 activity.

Milk thistle (Silybum marianum) extracts are widely used as a complementary and alternative treatment of various hepatic conditions and a host of other diseases/disorders. The active constituents of milk thistle supplements are believed to be the flavonolignans contained within the extracts. In vitro studies have suggested that some milk thistle components may significantly inhibit specific cytochrome P450 (P450) enzymes. However, determining the potential for clinically significant drug interactions with milk thistle products has been complicated by inconsistencies between in vitro and in vivo study results. The aim of the present study was to determine the effect of a standardized milk thistle supplement on major P450 drug-metabolizing enzymes after a 14-day exposure period. CYP1A2, CYP2C9, CYP2D6, and CYP3A4/5 activities were measured by simultaneously administering the four probe drugs, caffeine, tolbutamide, dextromethorphan, and midazolam, to nine healthy volunteers before and after exposure to a standardized milk thistle extract given thrice daily for 14 days. The three most abundant falvonolignans found in plasma, following exposure to milk thistle extracts, were silybin A, silybin B, and isosilybin B. The concentrations of these three major constituents were individually measured in study subjects as potential perpetrators. The peak concentrations and areas under the time-concentration curves of the four probe drugs were determined with the milk thistle administration. Exposure to milk thistle extract produced no significant influence on CYP1A2, CYP2C9, CYP2D6, or CYP3A4/5 activities.

Carboxylesterase 1 as a determinant of clopidogrel metabolism and activation.

Clopidogrel pharmacotherapy is associated with substantial interindividual variability in clinical response, which can translate into an increased risk of adverse outcomes. Clopidogrel, a recognized substrate of hepatic carboxylesterase 1 (CES1), undergoes extensive hydrolytic metabolism in the liver. Significant interindividual variability in the expression and activity of CES1 exists, which is attributed to both genetic and environmental factors. We determined whether CES1 inhibition and CES1 genetic polymorphisms would significantly influence the biotransformation of clopidogrel and alter the formation of the active metabolite. Coincubation of clopidogrel with the CES1 inhibitor bis(4-nitrophenyl) phosphate in human liver s9 fractions significantly increased the concentrations of clopidogrel, 2-oxo-clopidogrel, and clopidogrel active metabolite, while the concentrations of all formed carboxylate metabolites were significantly decreased. As anticipated, clopidogrel and 2-oxo-clopidogrel were efficiently hydrolyzed by the cell s9 fractions prepared from wild-type CES1 transfected cells. The enzymatic activity of the CES1 variants G143E and D260fs were completely impaired in terms of catalyzing the hydrolysis of clopidogrel and 2-oxo-clopidogrel. However, the natural variants G18V, S82L, and A269S failed to produce any significant effect on CES1-mediated hydrolysis of clopidogrel or 2-oxo-clopidogrel. In summary, deficient CES1 catalytic activity resulting from CES1 inhibition or CES1 genetic variation may be associated with higher plasma concentrations of clopidogrel-active metabolite, and hence may enhance antiplatelet activity. Additionally, CES1 genetic variants have the potential to serve as a biomarker to predict clopidogrel response and individualize clopidogrel dosing regimens in clinical practice.

An assessment of pharmacokinetics and antioxidant activity of free silymarin flavonolignans in healthy volunteers: a dose escalation study.

Milk thistle (Silybum marianum) extracts, one of the most widely used dietary supplements, contain a mixture of six major flavonolignans (silybin A, silybin B, isosilybin A, isosilybin B, silychristin, and silydianin) and other components. However, the pharmacokinetics of the free individual flavonolignans have been only partially investigated in humans. Furthermore, antioxidant effects of the extract, which may underlie the basis of many therapeutic effects, have not been thoroughly assessed. The present study evaluated the pharmacokinetics of the six major flavonolignans in healthy volunteers receiving single doses of either one (175 mg), two (350 mg), or three (525 mg) milk thistle capsule(s) on three separate study visits. Additionally, the steady-state pharmacokinetic parameters were determined after the subjects were administered one capsule three times daily for 28 consecutive days. Our results demonstrated that all six flavonolignans were rapidly absorbed and eliminated. In order of abundance, the exposure to free flavonolignans was greatest for silybin A followed by silybin B, isosilybin B, isosilybin A, silychristin, and silydianin. The systemic exposure to these compounds appeared linear and dose proportional. The disposition of flavonolignans was stereoselective, as evidenced by the apparent clearance of silybin B, which was significantly greater than silybin A, whereas the apparent clearance of isosilybin B was significantly lower than isosilybin A. The concentrations of urinary 8-epi-prostaglandin F2α, a commonly used biomarker of oxidative status in humans, were considerably decreased in study subjects after a 28-day exposure to the extract (1.3 ± 0.9 versus 0.8 ± 0.9 ng/mg creatinine) but failed to reach statistical significance (P = 0.076).

Effect of Sirolimus levels between days 11 and 20 after allogeneic stem cell transplantation on the risk of hepatic sinusoidal obstruction syndrome.

Sinusoidal obstruction syndrome (SOS) is a serious complication of hematopoietic stem cell transplantation (HSCT). Sirolimus plus tacrolimus is an accepted regimen for graft-versus-host disease (GVHD) prophylaxis, with both agents implicated as risk factors for SOS. We analyzed 260 consecutive patients who underwent allogeneic HSCT following myeloablative conditioning using total body irradiation (TBI)-based (n = 151) or chemotherapy only (n = 109) regimens, with sirolimus plus tacrolimus for GVHD prophylaxis. SOS occurred in 28 patients at a median of 22 (range, 12-58) days. Mean sirolimus trough levels were higher between days 11 and 20 following transplant in patients who developed SOS (10.3 vs. 8.5 ng/ml, P = 0.008), with no significant difference in mean trough levels between days 0 and 10 (P = 0.67) and days 21-30 (P = 0.37). No differences in mean tacrolimus trough levels during the same time intervals were observed between those developing SOS and others. On multivariable analysis, a mean sirolimus trough level ≥ 9 ng/ml between days 11 and 20 increased the risk of SOS (hazard ratio 3.68, 95% CI: 1.57-8.67, P = 0.003), together with a longer time from diagnosis to transplant (P = 0.004) and use of TBI (P = 0.006). Our results suggest that mean trough sirolimus levels ≥ 9 ng/mL between days 11 and 20 post transplant may increase the risk of SOS and should be avoided.

Histoplasma capsulatum Infection in an Allogeneic Hematopoietic Stem Cell Transplant Patient Receiving Voriconazole Prophylaxis.

Histoplasma capsulatum infection is a rare complication in the allogeneic stem cell transplant patients. Minimal guidance exists on how to appropriately manage histoplasmosis in these patients. We report a patient who developed Histoplasma pneumonia while receiving voriconazole prophylaxis at a therapeutic trough level. The patient experienced significant clinical improvement after initiation of itraconazole pharmacotherapy. We recommend a lower threshold for evaluation for histoplasmosis in allogeneic hematopoietic stem cell transplant recipients who live in endemic regions, regardless of their antifungal prophylactic regimen.

Pharmacokinetics of Basiliximab for the Prevention of Graft-versus-Host Disease in Patients Undergoing Hematopoietic Cell Transplantation with Minimal-Intensity Cyclophosphamide and Fludarabine.

STUDY OBJECTIVE: Basiliximab is an immunosuppressive monoclonal antibody used for rejection prevention following solid organ transplantation; the pharmacokinetics (PK) of basiliximab in this setting are known. Basiliximab may also be used for prophylaxis and treatment of graft-versus-host disease (GVHD) in patients undergoing allogeneic hematopoietic cell transplantation (HCT); however, the PK of basiliximab in this setting are not known. Clinical transplant providers expect variation in the volume of distribution and clearance after nonmyeloablative allogeneic transplantation (NMAT) compared with solid organ transplantation. Blood loss, organ site-specific antibody accumulation, and differences in blood product use during the two transplantation approaches may generate differences in basiliximab PK. Therefore, the objective of this study was to describe the PK of basiliximab after its addition to a minimally intense NMAT regimen, in conjunction with cyclosporine, for GVHD prophylaxis in patients with hematologic malignancies. DESIGN: Population PK analysis of a single-center, single-arm, phase II clinical trial. SETTING: Academic cancer research center. PATIENTS: Fourteen adults with hematologic malignancies (acute myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, myelodysplastic syndrome, non-Hodgkin's lymphoma, Hodgkin's lymphoma, myelofibrosis, or severe aplastic anemia) and undergoing NMAT with a fully HLA-matched (10 of 10 antigen matched) related or unrelated donor. MEASUREMENTS AND MAIN RESULTS: Basiliximab was used in conjunction with cyclosporine to deplete activated T cells in vivo as GVHD prophylaxis. We developed a novel competitive enzyme-linked immunosorbent assay (ELISA) method using recombinant interleukin-2 receptor alpha-chain (IL-2Ra) and a commercially available soluble sIL-2R ELISA kit to permit the quantification of serum basiliximab concentrations and characterization of the PK properties of the drug in this patient population. Using a nonlinear mixed effects model with NONMEM software, a one-compartment model with first-order elimination best described the PK, as covariate analysis using stepwise covariate modeling did not improve the base model. CONCLUSION: We suggest a one-compartment population model with first-order elimination to capture the PK profile for basiliximab for this patient population.

Anti-VEGF-Induced Hypertension: a Review of Pathophysiology and Treatment Options.

OPINION STATEMENT: Abnormal intracellular signaling has been implicated in the development of many different types of cancer. Therapies targeting these abnormal pathways have revolutionized the treatment of many malignancies leading to significantly improved outcomes and survival. Despite these advances, cardiovascular toxicity is a frequently reported complication. Angiogenesis is the physiologic process of new blood vessel development and can be dysregulated in some forms of cancer. VEGF inhibitors are the pharmaceutical agents targeting this pathway; however hypertension is a commonly observed toxicity which can have significant adverse consequences including premature cessation of therapy if adequate blood pressure control cannot be achieved. This review will provide a comprehensive discussion about hypertension due to VEGF inhibition, focusing on pathophysiology, frequently used agents, and available treatment options for VEGF-induced hypertension.

A pharmacokinetic evaluation of oral edivoxetine hydrochloride for the treatment of attention deficit-hyperactivity disorder.

INTRODUCTION: The majority of available therapeutics to treat attention-deficit/hyperactivity disorder (ADHD) are formulations of either methylphenidate or amphetamine. However, psychostimulants may not be suitable options for many patients. The availability of novel pharmacological agents to treat ADHD is highly desirable. Edivoxetine hydrochloride (LY2216684) is a highly selective and potent norepinephrine reuptake inhibitor under clinical development for ADHD. AREAS COVERED: This paper provides an overview of what is presently known of the pharmacokinetics (PK) of edivoxetine based on available studies in healthy volunteers, in subjects with compromised renal and hepatic functioning and in children and adolescents. EXPERT OPINION: Available data suggest edivoxetine is safe and well tolerated. Edivoxetine is readily absorbed with metabolism proceeding through the CYP hepatic enzyme pathway, with CYP2D6 and CYP3A4 playing the most prominent roles. The tmax is ∼ 2 h post-dose, and the plasma t1/2 is ∼ 4 - 6 h irrespective of the dose. Pharmacokinetic parameters are not substantially different between children and adults. Edivoxetine may be a promising non-stimulant therapeutic agent. However, at present, there is insufficient data available to permit a thorough analysis of its potential place in ADHD pharmacotherapy, or how its PK and pharmacodynamics may differ in clinically meaningful ways from existing agents.

A sensitive LC-MS/MS assay for the simultaneous analysis of the major active components of silymarin in human plasma.

Silymarin, an extract of crushed achenes of the milk thistle plant Silybum marianum is a multi-constituent mixture, 70-80% of which consists of a complex assortment containing the flavonolignans silybin A and B, isosilybin A and B, silydianin, and silychristin, and the flavonoid taxifolin. To date, numerous pharmacological actions of the silymarin extract have been documented in the biomedical literature, including hepatoprotective, anti-inflammatory, anti-tumor, and anti-fibrotic activities. The present study describes a novel liquid chromatographic-tandem mass spectrometric method for simultaneous analysis of silychristin, silydianin, silybin A and silybin B, isosilybin A and isosilybin B, and taxifolin in human plasma employing liquid-liquid extraction. This assay provides excellent resolution of the individual silymarin constituents via utilization of a 100 A 250 mm × 2 mm, 5 µm C(18) column with the mobile phase consisting of 51% methanol, 0.1% formic acid, and 10mM ammonium acetate. The lower limit of quantification was 2 ng/ml for each constituent. Calibration curves were linear over the range from 2 ng/ml to 100 ng/ml for all analytes (r(2)>0.99). The intra- and inter-day accuracies were 91-106.5% and 95.1-111.9%, respectively. The intra- and inter-day precision was within 10.5%. Additionally, recovery, stability, and matrix effects were fully validated as well. This method was successfully applied to human plasma samples from subjects treated with the milk thistle extract Legalon(®).