P-glycoprotein system as a determinant of drug interactions: the case of digoxin-verapamil

Evaluation of the Effect of Lorlatinib on CYP2B6, CYP2C9, UGT, and P-Glycoprotein Substrates in Patients with Advanced Non-Small Cell Lung Cancer

BACKGROUND AND OBJECTIVE

Lorlatinib is a tyrosine kinase inhibitor approved for the treatment of advanced anaplastic lymphoma kinase-positive non-small cell lung cancer. This study assessed the effect of steady-state lorlatinib on the metabolic enzymes cytochrome P450 (CYP) 2B6, CYP2C9, and uridine 5'-diphospho-glucuronosyltransferase (UGT) and the P-glycoprotein (P-gp) transporter.

METHODS

Thirty-two patients received a single oral dose of a probe drug on Day - 2 to determine the pharmacokinetics of the probe drug alone. Starting on Day 1, patients received 100 mg oral lorlatinib daily. On Day 15, a single oral dose of the probe drug was administered concurrently with lorlatinib. Pharmacokinetic parameters for these probe substrates were assessed.

RESULTS

Plasma exposures of all probe substrates were reduced by lorlatinib compared with the probe alone. The greatest reduction in area under the plasma concentration-time curve from time zero to infinity (AUC∞) and maximum (peak) plasma drug concentration (Cmax) (67% and 63% decrease, respectively) was observed with the P-gp probe substrate fexofenadine. Lorlatinib coadministration also decreased the AUC∞ and Cmax of bupropion (CYP2B6 probe substrate) by 25% and 27%, tolbutamide (CYP2C9 probe substrate) by 43% and 15%, and acetaminophen (UGT probe substrate) by 45% and 28%, respectively.

CONCLUSIONS

Lorlatinib is a net moderate inducer of P-gp and a weak inducer of CYP2B6, CYP2C9, and UGT after steady state is achieved with daily dosing. Medications that are P-gp substrates with a narrow therapeutic window should be avoided in patients taking lorlatinib; no dose modifications are needed with substrates of CYP2B6, CYP2C9, or UGT.

CLINICALTRIALS

gov: NCT01970865.

Drug Interactions Affecting Antiarrhythmic Drug Use

Antiarrhythmic drugs (AAD) play an important role in the management of arrhythmias. Drug interactions involving AAD are common in clinical practice. As AADs have a narrow therapeutic window, both pharmacokinetic as well as pharmacodynamic interactions involving AAD can result in serious adverse drug reactions ranging from arrhythmia recurrence, failure of device-based therapy, and heart failure, to death. Pharmacokinetic drug interactions frequently involve the inhibition of key metabolic pathways, resulting in accumulation of a substrate drug. Additionally, over the past 2 decades, the P-gp (permeability glycoprotein) has been increasingly cited as a significant source of drug interactions. Pharmacodynamic drug interactions involving AADs commonly involve additive QT prolongation. Amiodarone, quinidine, and dofetilide are AADs with numerous and clinically significant drug interactions. Recent studies have also demonstrated increased morbidity and mortality with the use of digoxin and other AAD which interact with P-gp. QT prolongation is an important pharmacodynamic interaction involving mainly Vaughan-Williams class III AAD as many commonly used drug classes, such as macrolide antibiotics, fluoroquinolone antibiotics, antipsychotics, and antiemetics prolong the QT interval. Whenever possible, serious drug-drug interactions involving AAD should be avoided. If unavoidable, patients will require closer monitoring and the concomitant use of interacting agents should be minimized. Increasing awareness of drug interactions among clinicians will significantly improve patient safety for patients with arrhythmias.

Pediatric Drug-Drug Interaction Evaluation: Drug, Patient Population, and Methodological Considerations

Hospitalized pediatric patients and those with complex or chronic conditions treated on an outpatient basis are commonly prescribed multiple drugs, resulting in increased risk for drug-drug interactions (DDIs). Although dedicated DDI evaluations are routinely performed in healthy adult volunteers during drug development, they are rarely performed in pediatric patients because of ethical, logistical, and methodological challenges. In the absence of pediatric DDI evaluations, adult DDI data are often extrapolated to pediatric patients. However, the magnitude of a DDI in pediatric patients may differ from adults because of age-dependent physiological changes that can impact drug disposition or response and because of other factors related to the drug (eg, dose, formulation) and the patient population (eg, disease state, obesity). Therefore, the DDI magnitude needs to be assessed in children separately from adults, although a lack of clinical DDI data in pediatric populations makes this evaluation challenging. As a result, pediatric DDI assessment relies on the predictive performance of the pharmacometric approaches used, such as population and physiologically based pharmacokinetic modeling. Therefore, careful consideration needs to be given to adequately account for the age-dependent physiological changes in these models to build high confidence for such untested DDI scenarios. This review article summarizes the key considerations related to the drug, patient population, and methodology, and how they can impact DDI evaluation in the pediatric population.

Pharmacokinetic drug–drug interactions: an insight into recent US FDA-approved drugs for prostate cancer

Pharmacokinetic drug–drug interaction is a significant safety and efficiency concern as it results in considerable concentration changes. Drug–drug interactions are a substantial concern in anticancer drugs that possess a narrow therapeutic index. These interactions remain as the principal regulatory obstacle that can lead to termination in the preclinical stage, restrictions in the prescription, dosage adjustments or withdrawal of the drugs from the market. Drug metabolizing enzymes or transporters mediate the majority of clinically relevant drug interactions. Cancer diagnosed aged patients use multiple medications and are more prone to significant drug–drug interactions. This review provides detailed information on clinically relevant drug–drug interactions resulting from drug metabolism by enzymes and transporters with a particular emphasis on recent FDA approved antiprostate cancer drugs.

A Mechanistic, Enantioselective, Physiologically Based Pharmacokinetic Model of Verapamil and Norverapamil, Built and Evaluated for Drug-Drug Interaction Studies

The calcium channel blocker and antiarrhythmic agent verapamil is recommended by the FDA for drug–drug interaction (DDI) studies as a moderate clinical CYP3A4 index inhibitor and as a clinical Pgp inhibitor. The purpose of the presented work was to develop a mechanistic whole-body physiologically based pharmacokinetic (PBPK) model to investigate and predict DDIs with verapamil. The model was established in PK-Sim^®, using 45 clinical studies (dosing range 0.1–250 mg), including literature as well as unpublished Boehringer Ingelheim data. The verapamil R- and S-enantiomers and their main metabolites R- and S-norverapamil are represented in the model. The processes implemented to describe the pharmacokinetics of verapamil and norverapamil include enantioselective plasma protein binding, enantioselective metabolism by CYP3A4, non-stereospecific Pgp transport, and passive glomerular filtration. To describe the auto-inhibitory and DDI potential, mechanism-based inactivation of CYP3A4 and non-competitive inhibition of Pgp by the verapamil and norverapamil enantiomers were incorporated based on in vitro literature. The resulting DDI performance was demonstrated by prediction of DDIs with midazolam, digoxin, rifampicin, and cimetidine, with 21/22 predicted DDI AUC ratios or C_trough ratios within 1.5-fold of the observed values. The thoroughly built and qualified model will be freely available in the Open Systems Pharmacology model repository to support model-informed drug discovery and development.

Interactions of human organic anion transporters 1-4 and human organic cation transporters 1-3 with the stimulant drug methamphetamine and amphetamine

Drug membrane transport system proteins, namely, drug transporters, are expressed in the kidney and liver and play a crucial role in the excretion process. This study aimed to elucidate the interactions of the drug transporters human organic anion transporters 1, 2, 3, 4 (hOAT1, 2, 3, 4) and human organic cation transporters 1, 2, 3 (hOCT1, 2, 3), which are expressed primarily in human kidney, liver, and brain, with the stimulants methamphetamine (METH) and amphetamine (AMP). The results of an inhibition study using representative substrates of hOATs and hOCTs showed that METH and AMP significantly inhibited (by >50%) uptake of the hOCT1 and hOCT3 representative substrate 1-methy1-4-phenylpyridinium ion (MPP+) and hOCT2 representative substrate tetraethyl ammonium (TEA). However, METH and AMP did not inhibit uptake of the representative substrates of hOAT1, hOAT2, hOAT3, and hOAT4, (i.e., p-aminohippuric (PAH) acid, prostaglandin F2α (PGF2α), estron sulfate (ES), and ES respectively). Kinetic analyses revealed that METH competitively inhibited hOCT1-mediated MPP+ and hOCT2-mediated TEA uptake (Ki, 16.9 and 78.6 µM, respectively). Similarly, AMP exhibited competitive inhibition, with Ki values of 78.6 and 42.8 µM, respectively. In contrast, hOCT3 exhibited mixed inhibition of representative substrate uptake; hence, calculating Ki values was not possible. Herein, we reveal that hOCTs mediate the inhibition of METH and AMP. The results of this uptake study suggest that METH and AMP bind specifically to hOCT1 and hOCT2 without passing through the cell membrane, with subsequent passage of METH and AMP via hOCT3.

Regulation of P-glycoprotein by Bajijiasu in vitro and in vivo by activating the Nrf2-mediated signalling pathway

CONTEXT

Bajijiasu (BJJS), a main bioactive compound from Morinda officinalis F.C. How. (Rubiaceae), is widely administered concomitantly with other drugs for treating male impotence, female infertility, fatigue, chronic rheumatism, depression, etc. Objective: This study investigates the regulation of P-glycoprotein (P-gp) by BJJS in vitro and in vivo.

MATERIAL AND METHODS

HepG2 cells were incubated with BJJS (10, 20 or 40 μM) for 48 h. C57 mice were orally treated with BJJS (25, 50 or 100 mg/kg) for 2 weeks. The protein and mRNA levels of P-gp were measured by using Western blot and real-time PCR, respectively. siNrf2 RNA was used to explore the mediation effects of Nrf2 on the P-gp expression. The efflux activity of P-gp was tested via a flow cytometry.

RESULTS

Incubation of HepG2 cells with BJJS at 10, 20, and 40 μM up-regulated the P-gp protein expression by 12.3%, 82.9%, and 134.3%, respectively. Treatment of C57 mice with BJJS at 25, 50 and 100 mg/kg increased the P-gp protein expression by 49.3%, 75.8% and 106.0%, respectively. Incubation of the cells with BJJS at 10, 20 and 40 μM up-regulated the total Nrf2 protein levels by 34.3%, 93.1% and 118.6%, respectively, and also increased the nuclear Nrf2 protein levels by 14.8%, 44.4% and 59.25%, respectively. The total Nrf2 protein levels were increased by 46.3%, 66.5%, and 87.4%, respectively, in the mice exposed to BJJS at 25, 50, and 100 mg/kg. Inhibition of Nrf2 by siRNA diminished the P-gp induction by 25.0%, 33.4%, and 38.7%, respectively, in the cells. In addition, BJJS enhanced the efflux activity of P-gp by 9.6%, 37.1%, and 48.1%, respectively, in the cells.

CONCLUSIONS

BJJS activates Nrf2 to induce P-gp expression, and enhanced the efflux activity of P-gp. The possibility of potential herb-drug interactions when BJJS is co-administered with other P-gp substrate drugs should be carefully monitored.

Interspecies comparison of putative ligand binding sites of human, rat and mouse P-glycoprotein

Prior to the clinical phases of testing, safety, efficacy and pharmacokinetic profiles of lead compounds are evaluated in animal studies. These tests are primarily performed in rodents, such as mouse and rats. In order to reduce the number of animal experiments, computational models that predict the outcome of these studies and thus aid in prioritization of preclinical candidates are heavily needed. However, although computational models for human off-target interactions with decent quality are available, they cannot easily be transferred to rodents due to lack of respective data. In this study, we assess the transferability of human P-glycoprotein activity data for development of in silico models to predict in vivo effects in rats and mouse using a structure-based approach. P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that transports xenobiotic compounds such as toxins and drugs out of cells and has a broad substrate and inhibitor specificity. Being mostly expressed at barriers, it influences the bioavailability of drugs and thus contributes also to toxicity. Comparison of the binding site interaction profiles of human, rat and mouse P-gp derived from docking studies with a set of common inhibitors suggests that the inhibitors share potentially similar binding modes. These findings encourage the use of in vitro human P-gp data for predicting in vivo effects in rodents and thus contributes to the 3Rs (Replace, Reduce and Refine) of animal experiments.

Mdr1a plays a crucial role in regulating the analgesic effect and toxicity of aconitine by altering its pharmacokinetic characteristics

Aconitine (AC) is the primary bioactive/toxic alkaloid in plants of the Aconitum species. Our previous study demonstrated that Mdr1 was involved in efflux of AC. However, the mechanism by which Mdr1 regulates the efficacy/toxicity of AC in vivo remains unclear. The present study aimed to determine the effects of Mdr1a on the efficacy/toxicity and pharmacokinetics of AC in wild-type and Mdr1a^-/- FVB mice. After oral administration of AC, significantly higher analgesic effect was observed in Mdr1a^-/- mice (49% to 105%) compared to wild-type mice (P<0.05). The levels of s100-β protein and creatine kinase, which indicate cerebral and myocardial damage, respectively, were also significantly increased (P<0.05) in Mdr1a^-/- mice. Histopathological examination revealed that the Mdr1a^-/- mice suffered from evident cerebral and myocardial damages, but the wild-type mice did not. These findings suggested that Mdr1a deficiency significantly promoted the analgesic effect of AC and exacerbated its toxicity. Pharmacokinetic experiments showed that T_1/2 of AC in the Mdr1a^-/- mice was significantly higher (from 87% to 300%) than that in wild-type mice (P<0.05). The distribution of AC in the brain of Mdr1a^-/- mice was 2- to 32-fold higher than that in the brains of wild-type mice (P<0.05). Toxic reactions were more severe in Mdr1a^-/- mice compared to wild-type mice. In conclusion, Mdr1a deficiency significantly enhanced the analgesic effect of AC and exacerbated its toxicity by upregulating its distribution to the brain and decreasing its plasma elimination rate. Thus, Mdr1a dysfunction may cause severe AC poisoning.

Spica prunellae and its marker compound rosmarinic acid induced the expression of efflux transporters through activation of Nrf2-mediated signaling pathway in HepG2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Spica prunellae (SP) is a well-known traditional Chinese medicinal herb with properties of antihypertensive, antihyperglycemic, antiviral, anti-inflammatory, and antitumor activities. This herb is also popularly consumed as a food additive in some drinks or other food forms for treating pyreticosis. Rosmarinic acid (RA) is the marker compound from SP, which possesses anti-oxidative and anti-inflammatory functions.

AIM OF THE STUDY

This study aims to investigate the regulatory effect of the water extract of SP (WESP) and RA on efflux transports (ETs), including P-glycoprotein (p-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP) in HepG2 cell line. Results would provide beneficial information for the proper application of SP in clinics.

MATERIALS AND METHODS

HepG2 cells were treated with different doses of the tested drugs for 24 or 96h. MTT assay was used to examine cell viability. The protein and mRNA levels of the ETs were measured by using Western blot and real-time PCR, respectively. Reporter assay was used to study the antioxidant response element (ARE)-luciferin activity by using HepG2-C8 cells, which were generated by transfecting plasmid containing ARE-luciferin gene into HepG2 cells. The transport activities of ETs were tested by using substrate probes.

RESULTS

WESP significantly (p<0.05) increased the expression of ETs in a dose-dependent manner. The increase caused by WESP was stronger than RA alone. Both WESP and RA promoted the translocation of nuclear factor E2-related factor-2 (Nrf2) from cytoplasm to the nucleus as well as significantly (p<0.05) enhanced the ARE-luciferin activity. WESP and RA also enhanced the efflux activity of P-gp and MRP2, accompanied by marked increase (p<0.05) in the intracellular ATP levels.

CONCLUSIONS

WESP could significantly induce the expression of ETs through the activation of Nrf2-mediated signaling pathway in HepG2 cells. RA could be one of the active compounds responsible for the induction. WESP and RA also enhanced the efflux activity of P-gp and MRP2, and the increased intracellular ATP levels were likely involved in this induction. Results of this study provide a better understanding of the regulation of SP on ETs and the underlying molecular mechanism. Results indicated that potential drug-drug interactions may exist when SP is co-administered with other substrate drugs that are transported via the ETs, especially P-gp and MRP2, thereby providing beneficial information for appropriate use of SP for clinical therapy.

Pharmacogenomics of Drug Metabolizing Enzymes and Transporters: Relevance to Precision Medicine

The interindividual genetic variations in drug metabolizing enzymes and transporters influence the efficacy and toxicity of numerous drugs. As a fundamental element in precision medicine, pharmacogenomics, the study of responses of individuals to medication based on their genomic information, enables the evaluation of some specific genetic variants responsible for an individual’s particular drug response. In this article, we review the contributions of genetic polymorphisms to major individual variations in drug pharmacotherapy, focusing specifically on the pharmacogenomics of phase-I drug metabolizing enzymes and transporters. Substantial frequency differences in key variants of drug metabolizing enzymes and transporters, as well as their possible functional consequences, have also been discussed across geographic regions. The current effort illustrates the common presence of variability in drug responses among individuals and across all geographic regions. This information will aid health-care professionals in prescribing the most appropriate treatment aimed at achieving the best possible beneficial outcomes while avoiding unwanted effects for a particular patient.

Toxicity of beauvericin on porcine oocyte maturation and preimplantation embryo development

Beauvericin (BEA) is one of many toxins produced by Fusarium species that contaminate feed materials. The aim of this study was to assess its effects on porcine oocyte maturation and preimplantation embryo development. Cumulus-oocyte-complexes and developing embryos were exposed to BEA and cultured until the blastocyst stage. Cumulus cells, oocytes and embryos were examined for viability, progesterone synthesis, multidrug resistance protein (MDR1), ATP content and gene expression related to MDR1 function, oxidative phosphorylation, steroidogenesis and apoptosis. BEA was toxic in embryos, oocytes and cumulus cells at concentrations exceeding 0.5μM, and embryos were most vulnerable after the four-cell stage. Since BEA exerted different effects in embryos, oocytes and cumulus cells, the toxic mechanism is suggested to involve different pathways. Currently there are no consistent data on adverse effects of BEA in pig farms.

Induction of P-glycoprotein expression and activity by Aconitum alkaloids: Implication for clinical drug-drug interactions

The Aconitum species, which mainly contain bioactive Aconitum alkaloids, are frequently administered concomitantly with other herbal medicines or chemical drugs in clinics. The potential risk of drug–drug interactions (DDIs) arising from co-administration of Aconitum alkaloids and other drugs against specific targets such as P-glycoprotein (P-gp) must be evaluated. This study focused on the effects of three representative Aconitum alkaloids: aconitine (AC), benzoylaconine (BAC), and aconine, on the expression and activity of P-gp. We observed that Aconitum alkaloids increased P-gp expression in LS174T and Caco-2 cells in the order AC > BAC > aconine. Nuclear receptors were involved in the induction of P-gp. AC and BAC increased the P-gp transport activity. Strikingly, intracellular ATP levels and mitochondrial mass also increased. Furthermore, exposure to AC decreased the toxicity of vincristine and doxorubicin towards the cells. In vivo, AC significantly up-regulated the P-gp protein levels in the jejunum, ileum, and colon of FVB mice, and protected them against acute AC toxicity. Taken together, the findings of our in vitro and in vivo experiments indicate that AC can induce P-gp expression, and that co-administration of AC with P-gp substrate drugs may cause DDIs. Our findings have important implications for Aconitum therapy in clinics.

Unravelling the complex drug-drug interactions of the cardiovascular drugs, verapamil and digoxin, with P-glycoprotein

P-glycoprotein (Pgp) plays a major role in promoting drug–drug interactions (DDIs) with verapamil and digoxin. In the present study, we present a comprehensive molecular and mechanistic model of Pgp DDIs encompassing drug binding, ATP hydrolysis, transport and conformational changes.

Drug–drug interactions (DDIs) and associated toxicity from cardiovascular drugs represents a major problem for effective co-administration of cardiovascular therapeutics. A significant amount of drug toxicity from DDIs occurs because of drug interactions and multiple cardiovascular drug binding to the efflux transporter P-glycoprotein (Pgp), which is particularly problematic for cardiovascular drugs because of their relatively low therapeutic indexes. The calcium channel antagonist, verapamil and the cardiac glycoside, digoxin, exhibit DDIs with Pgp through non-competitive inhibition of digoxin transport, which leads to elevated digoxin plasma concentrations and digoxin toxicity. In the present study, verapamil-induced ATPase activation kinetics were biphasic implying at least two verapamil-binding sites on Pgp, whereas monophasic digoxin activation of Pgp-coupled ATPase kinetics suggested a single digoxin-binding site. Using intrinsic protein fluorescence and the saturation transfer double difference (STDD) NMR techniques to probe drug–Pgp interactions, verapamil was found to have little effect on digoxin–Pgp interactions at low concentrations of verapamil, which is consistent with simultaneous binding of the drugs and non-competitive inhibition. Higher concentrations of verapamil caused significant disruption of digoxin–Pgp interactions that suggested overlapping and competing drug-binding sites. These interactions correlated to drug-induced conformational changes deduced from acrylamide quenching of Pgp tryptophan fluorescence. Also, Pgp-coupled ATPase activity kinetics measured with a range of verapamil and digoxin concentrations fit well to a DDI model encompassing non-competitive and competitive inhibition of digoxin by verapamil. The results and previous transport studies were combined into a comprehensive model of verapamil–digoxin DDIs encompassing drug binding, ATP hydrolysis, transport and conformational changes.

Frog intestinal perfusion to evaluate drug permeability: application to p-gp and cyp3a4 substrates

To evaluate the reliability of using in situ frog intestinal perfusion technique for permeability assessment of carrier transported drugs which are also substrates for CYP enzymes. Single Pass Intestinal Perfusion (SPIP) studies were performed in frogs of the species Rana tigrina using established method for rats with some modifications after inducing anesthesia. Effective permeability coefficient (P_eff) of losartan and midazolam was calculated in the presence and absence of inhibitors using the parallel-tube model. P_eff of losartan when perfused alone was found to be 0.427 ± 0.27 × 10^-4cm/s and when it was co-perfused with inhibitors, significant change in P_eff was observed. P_eff of midazolam when perfused alone was found to be 2.03 ± 0.07 × 10^-4cm/s and when it was co-perfused with inhibitors, no significant change in P_eff was observed. Comparison of P_eff calculated in frog with that of other available models and also humans suggested that the P_eff-values are comparable and reflected well with human intestinal permeability. It is possible to determine the P_eff-value for compounds which are dual substrates of P-glycoprotein and CYP3A4 using in situ frog intestinal perfusion technique. The calculated P_eff-values correlated well with reported P_eff-values of probe drugs. comparison of the P_eff-value of losartan obtained with that of reported human’s P_eff and Caco 2 cell data, and comparison of the P_eff-value of midazolam with that of reported rat’s P_eff, we could conclude that SPIP from model can be reliably used in preclinical studies for permeability estimation. This model may represent a valuable alternative to the low speed and high cost of conventional animal models (typically rodents) for the assessment of intestinal permeability.

Long-term complete remission in a patient with intravascular large B-cell lymphoma with central nervous system involvement

This report describes a patient with intravascular large B-cell lymphoma (IVLBCL) with central nervous system involvement at the time of diagnosis who achieved complete remission for over 5 years in response to therapy. The patient, a 71 year-old woman, was previously healthy with the exception of taking verapamil for paroxysmal supraventricular tachycardia. She had presented with pyrexia and gradually progressive anemia. Brain magnetic resonance imaging revealed an infarct-like lesion in the pons, although no paralysis was observed. She was diagnosed with IVLBCL on the basis of random skin biopsy. After eight cycles of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone therapy, abnormal laboratory data had normalized, and no pontine lesion was evident on magnetic resonance imaging without receiving any intrathecal chemotherapy. IVLBCL is associated with poor prognosis, particularly in patients with central nervous system involvement. Early initiation of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone therapy and drug interactions between anticancer agents and verapamil as a p-glycoprotein inhibitor were considered the possible reasons for favorable outcome in the present case.

Is there more to learn about cytochrome P450 enzymes?

The cytochrome P450 system is a group of enzymes, found mainly in the liver and gut mucosa, that plays a crucial role in controlling the concentrations of many endogenous substances and drugs.1 The activity of the individual enzymes can vary over time and from person to person in response to diet, medicines or exposure to environmental pollutants. It has been almost 15 years since DTB reviewed the significance of the cytochrome P450 system and its relevance to prescribing (Why bother about cytochrome p450 enzymes?).1 A lot has changed in healthcare over that time, but has our understanding of this important aspect of drug metabolism altered significantly? Here we provide a brief overview of the function of cytochrome P450 enzymes and look at some of the concepts that have become established, or have begun to emerge, since the publication of our previous article.

The P-glycoprotein transport system and cardiovascular drugs

Permeability glycoprotein (P-gp) mediates the export of drugs from cells located in the small intestine, blood-brain barrier, hepatocytes, and kidney proximal tubule, serving a protective function for the body against foreign substances. Intestinal absorption, biliary excretion, and urinary excretion of P-gp substrates can therefore be altered by either the inhibition or induction of P-gp. A wide spectrum of drugs, such as anticancer agents and steroids, are known P-gp substrates and/or inhibitors, and many cardiovascular drugs have recently been observed to have clinically relevant interactions as well. We review the interactions among commonly prescribed cardiovascular drugs that are P-gp substrates and observe interactions involving P-gp that may be relevant to clinical practice. Cardiovascular drugs with narrow therapeutic indexes (e.g., antiarrhythmic agents, anticoagulant agents) have demonstrated large increases in concentrations when coadministered with potent P-gp inhibitors, thus increasing the risk for drug toxicity. Therefore, dose adjustment or use of alternative agents should be considered when strong P-gp-mediated drug-drug interactions are present. Finally, interactions between novel drugs and known P-gp inhibitors are now being systematically evaluated during drug development, and recommended guidelines for the administration of P-gp substrate drugs will be expanded.

Berberine analogue IMB-Y53 improves glucose-lowering efficacy by averting cellular efflux especially P-glycoprotein efflux

OBJECTIVE

Cellular efflux transporters, especially P-glycoprotein (P-gp), impel berberine (BBR) out of cells, and therefore reduce bioavailability of the compound. This study was designed to overcome efflux of BBR using P-gp as a target.

MATERIALS/METHODS

Molecular docking study was done to identify BBR analogues that were with low affinity to P-gp. Flow cytometry was used to determine cellular efflux of chemicals. Pharmacokinetic study was performed in Wistar rats, following oral administration of the study compounds. The efficacies of chemicals on glucose homeostasis were determined both in cultured cells and diabetic KK-Ay and db/db mice.

RESULTS

In the molecular docking study, we found that among BBR analogues pseudo-berberine (IMB-Y53) has low affinity to P-gp. IMB-Y53 was retained in Caco-2, HL-7702 and C2C12 cells for a significantly longer period of time than BBR did. P-gp inhibitor tetrandrine (Tet) abolished the efflux of BBR at different extent depending on the expression level of P-gp; however, Tet had no impact on IMB-Y53 efflux. BBR increased P-gp expression dose-dependently in intestinal and liver cells; IMB-Y53 also up-regulated P-gp but at a much lower level as compared with BBR. Administered at equal dose in rats, the maximum plasma concentration (C(max)) and area under concentration-time curve (AUC(0-24)) of IMB-Y53 were 1.61 and 2.27-fold of those of BBR, respectively, indicating an improved bioavailability. IMB-Y53 stimulated glucose utility in cultured cells with a degree similar to that of BBR, but exhibited enhanced glucose-lowering efficacy in KK-Ay and db/db diabetic mice.

CONCLUSIONS

These results suggest that overcoming cellular efflux especially P-gp's function improves bioavailability and hypoglycemic effect of BBR.

Psychotropic drug-drug interactions involving P-glycoprotein

Multidrug resistance P-glycoprotein (P-gp; also known as MDR1 and ABCB1) is expressed in the luminal membrane of the small intestine and blood-brain barrier, and the apical membranes of excretory cells such as hepatocytes and kidney proximal tubule epithelia. P-gp regulates the absorption and elimination of a wide range of compounds, such as digoxin, paclitaxel, HIV protease inhibitors and psychotropic drugs. Its substrate specificity is as broad as that of cytochrome P450 (CYP) 3A4, which encompasses up to 50 % of the currently marketed drugs. There has been considerable interest in variations in the ABCB1 gene as predictors of the pharmacokinetics and/or treatment outcomes of several drug classes, including antidepressants and antipsychotics. Moreover, P-gp-mediated transport activity is saturable, and is subject to modulation by inhibition and induction, which can affect the pharmacokinetics, efficacy or safety of P-gp substrates. In addition, many of the P-gp substrates overlap with CYP3A4 substrates, and several psychotropic drugs that are P-gp substrates are also CYP3A4 substrates. Therefore, psychotropic drugs that are P-gp substrates may cause a drug interaction when P-gp inhibitors and inducers are coadministered, or when psychotropic drugs or other medicines that are P-gp substrates are added to a prescription. Hence, it is clinically important to accumulate data about drug interactions through studies on P-gp, in addition to CYP3A4, to assist in the selection of appropriate psychotropic medications and in avoiding inappropriate combinations of therapeutic agents. There is currently insufficient information available on the psychotropic drug interactions related to P-gp, and therefore we summarize the recent clinical data in this review.

Interaction of digitalis-like compounds with p-glycoprotein

Digitalis-like compounds (DLCs), or cardiac glycosides, are produced and sequestered by certain plants and animals as a protective mechanism against herbivores or predators. Currently, the DLCs digoxin and digitoxin are used in the treatment of cardiac congestion and some types of cardiac arrhythmia, despite a very narrow therapeutic index. P-glycoprotein (P-gp; ABCB1) is the only known ATP-dependent efflux transporter that handles digoxin as a substrate. Ten alanine mutants of human P-gp drug-binding amino acids-Leu(65), Ile(306), Phe(336), Ile(340), Phe(343), Phe(728), Phe(942), Thr(945), Leu(975), and Val(982)-were generated and expressed in HEK293 cells with a mammalian baculovirus system. The uptake of [(3)H]-N-methyl-quinidine (NMQ), the P-gp substrate in vesicular transport assays, was determined. The mutations I306A, F343A, F728A, T945A, and L975A abolished NMQ transport activity of P-gp. For the other mutants, the apparent affinities for six DLCs (cymarin, digitoxin, digoxin, peruvoside, proscillaridin A, and strophanthidol) were determined. The affinities of digoxin, proscillaridin A, peruvoside, and cymarin for mutants F336A and I340A were decreased two- to fourfold compared with wild type, whereas that of digitoxin and strophanthidol did not change. In addition, the presence of a hydroxyl group at position 12β seems to reduce the apparent affinity when the side chain of Phe(336) and Phe(942) is absent. Our results showed that a δ-lactone ring and a sugar moiety at 3β of the steroid body are favorable for DLC binding to P-gp. Moreover, DLC inhibition is increased by hydroxyl groups at positions 5β and 19, whereas inhibition is decreased by those at positions 1β, 11α, 12β, and 16β. The understanding of the P-gp-DLC interaction improves our insight into DLCs toxicity and might enhance the replacement of digoxin with other DLCs that have less adverse drug effects.

Absence of Clinically Relevant Interactions between Rivaroxaban - an Oral, Direct Factor Xa Inhibitor - and Digoxin or Atorvastatin in Healthy Subjects

Objective:

To investigate potential interactions between rivaroxaban, an oral direct Factor Xa inhibitor approved for the management of thromboembolic disorders, and digoxin or atorvastatin.

Methods:

Two randomized, phase 1 clinical trials were undertaken in healthy men to assess pharmacokinetic and pharmacodynamic interactions between rivaroxaban and digoxin or atorvastatin, and the safety of these drug combinations.

Results:

Steady-state rivaroxaban did not affect the pharmacokinetic profile of steady-state digoxin ( n = 17). Digoxin did not significantly influence the pharmacokinetic profile of single-dose rivaroxaban and had minimal effects on rivaroxaban-induced inhibition of Factor Xa activity and prolongation of clotting time. Similarly, steady-state atorvastatin did not affect the pharmacokinetic profile or the pharmacodynamics of rivaroxaban and vice versa ( n = 19). All drugs (alone or in combination) were well tolerated.

Conclusions:

There were no clinically relevant pharmacokinetic or pharmaco - dynamic interactions between rivaroxaban and digoxin, or between rivaroxaban and atorvastatin, suggesting that rivaroxaban can be coadministered with either drug. This study also confirmed that rivaroxaban does not interact with substrates for permeability (P)-glycoprotein alone (digoxin) or P-glycoprotein and cytochrome P450(CYP)3A4 (atorvastatin).

Cardiac side population cells: moving toward the center stage in cardiac regeneration

Over the past decade, extensive work in animal models and humans has identified the presence of adult cardiac progenitor cells, capable of cardiomyogenic differentiation and likely contributors to cardiomyocyte turnover during normal development and disease. Among cardiac progenitor cells, there is a distinct subpopulation, termed "side population" (SP) progenitor cells, identified by their unique ability to efflux DNA binding dyes through an ATP-binding cassette transporter. This review highlights the literature on the isolation, characterization, and functional relevance of cardiac SP cells. We review the initial discovery of cardiac SP cells in adult myocardium as well as their capacity for functional cardiomyogenic differentiation and role in cardiac regeneration after myocardial injury. Finally, we discuss recent advances in understanding the molecular regulators of cardiac SP cell proliferation and differentiation, as well as likely future areas of investigation required to realize the goal of effective cardiac regeneration.

Digitalis toxicity: a fading but crucial complication to recognize

Digoxin usage has decreased in the treatment of congestive heart failure and atrial fibrillation as a result of its inferiority to beta-adrenergic inhibitors and agents that interfere with the deleterious effects of the activated renin-angiotensin-aldosterone system. As a result of reduction of usage and dosage, glycoside toxicity has become an uncommon occurrence but may be overlooked when it does occur. Older age, female sex, low lean body mass, and renal insufficiency contribute to higher serum levels and enhanced risk for toxicity. Arrhythmias suggesting digoxin toxicity led to its recognition in the case presented here.

Different effects of the selective serotonin reuptake inhibitors fluvoxamine, paroxetine, and sertraline on the pharmacokinetics of fexofenadine in healthy volunteers

Although the interaction between selective serotonin reuptake inhibitors (SSRIs) and other drugs is important in the treatment of depression, there have been few studies of SSRIs concerning transporter-mediated interactions in humans. The objective of this study was to evaluate the in vivo effects of commonly used SSRIs on the pharmacokinetics of fexofenadine, a P-glycoprotein substrate.Twelve healthy volunteers (3 females and 9 males) were enrolled in this study. Each subject received a 60-mg dose of fexofenadine orally at baseline. Afterward, they were randomly assigned to receive 3 treatments with a 60-mg dose of fexofenadine after a 7-day treatment with fluvoxamine (50 mg/d), paroxetine (20 mg/d), or sertraline (50 mg/d), with 2-week intervals between the agents.Fluvoxamine pretreatment significantly increased the maximum plasma concentration, the area under the concentration time curves, and the 24-hour urinary fexofenadine excretion by 66% (P = 0.004), 78% (P = 0.029), and 78% (P < 0.001), respectively, without prolonging its elimination half-life. Paroxetine extended the elimination half-life of fexofenadine by 45% (P = 0.042), and it increased the 24-hour urinary fexofenadine excretion by 55% (P = 0.002). Sertraline did not alter any of the pharmacokinetic parameters of fexofenadine.This is the first report of the different effects of 3 commonly used SSRIs on fexofenadine pharmacokinetics in humans. Our 7-day, repeated-dose clinical study in healthy volunteers indicates that fluvoxamine and paroxetine, but not sertraline, may impact the patient exposure to fexofenadine, which is likely the result of P-glycoprotein inhibition in the small intestine and/or the liver.

Interactions between verapamil and digoxin in Langendorff-perfused rat hearts: the role of inhibition of P-glycoprotein in the heart

P-glycoprotein (P-gp) is expressed in tumour cells as well as normal tissues including heart. Modulation of P-gp transport in vivo may lead to increased drug penetrance to tissues with resulting increases in toxicity. We aimed to investigate the effects of P-gp on the isolated heart by digoxin infusion in the absence and presence of verapamil. The study was performed in Langendorff isolated perfused rat hearts. After a 20 min. stabilisation period with Tyrode Buffer, digoxin (125 μg/5 mL) was infused for 10 min. in the control group (n = 7). The same dose of digoxin was infused during perfusion with verapamil (1 nm) containing Tyrode Buffer (n = 8) in the study group. Outflow concentration and cardiac parameters of digoxin were measured at frequent intervals for 40 min. AUEC((0-40 min)) for left ventricular developed pressure was significantly increased in the presence of verapamil (4260 ± 39.37 mmHg min versus 4607 ± 98.09 mmHg min; 95% CI -587.7 to -105.8; p = 0.0083). The significant increases in left ventricular developed pressure were at 20, 25, 30, 35 and 40 min. AUC((0-40 min)) value for outflow digoxin concentration-time curve was significantly lower in the presence of verapamil. Verapamil increased the positive inotropic effect of digoxin, probably through the inhibition of P-gp, which effluxes digoxin out of cardiac cells.

Pharmacokinetics/Pharmacodynamics of Antiarrhythmic Drugs

This article describes the pharmacology of antiarrhythmic medications. Although these medications are broadly considered in terms of their blockade of either sodium or potassium channels, they act by a variety of pharmacodynamic mechanisms. Elimination may be via hepatic metabolism or renal mechanisms, or a combination. In particular, interactions between antiarrhythmic medications and other drugs that interfere with hepatic metabolism by P450 enzymes is a source for toxicity.

Population pharmacokinetic model of digoxin in older Chinese patients and its application in clinical practice

AIM

To establish a population pharmacokinetic (PPK) model of digoxin in older Chinese patients to provide a reference for individual medication in clinical practice.

METHODS

Serum concentrations of digoxin and clinically related data including gender, age, weight (WT), serum creatinine (Cr), alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), albumin (ALB), and co-administration were retrospectively collected from 119 older patients taking digoxin orally for more than 7 d. NONMEM software was used to get PPK parameter values, to set up a final model, and to assess the models in clinical practice.

RESULTS

Spironolactone (SPI), WT, and Cr markedly affected the clearance rate of digoxin. The final model formula is Cl/F=5.9x[1-0.412 x SPI] x [1-0.0101x(WT-62.9)] x [1-0.0012x(Cr-126.8)] (L/h); Ka=1.63 (h(-1)); V(d)/F=550 (L). The population estimates for Cl/F and V(d)/F were 5.9 L/h and 550 L, respectively. The interindividual variabilities (CV) were 49.0% for Cl/F and 94.3% for V(d)/F. The residual variability (SD) between observed and predicted concentrations was 0.365 microg/L. The difference between the objective function value and the primitive function value was less than 3.84 (P>0.05) by intra-validation. Clinical applications indicated that the percent of difference between the predicted concentrations estimated by the PPK final model and the observed concentrations were -4.3%-+25%. Correlation analysis displayed that there was a linear correlation between observed and predicted values (y=1.35x+0.39, r=0.9639, P<0.0001).

CONCLUSION

The PPK final model of digoxin in older Chinese patients can be established using the NONMEM software, which can be applied in clinical practice.

Modulation of the activity of ABC transporters (P-glycoprotein, MRP2, BCRP) by flavonoids and drug response

The present article aims to review the up-to-date information on the most recent studies of the interaction of flavonoids with ABC transporters, in particular the drug pharmacokinetic consequences of such a relationship. In addition, the modulation of the expression of the ABC transporters by flavonoids is also illustrated. Flavonoids are a large group of plant polyphenols present extensively in our daily diets and herbal products. High intake of isoflavones has been associated with a variety of beneficial effects on several common diseases. These polyphenols interact with ABC drug transporters involved in drug resistance and drug absorption, distribution and excretion. A number of studies have demonstrated inhibition of drug transporters by flavonoids. This flavonoid-ABC-transporter interaction could be beneficial for poorly absorbed drugs but could also result in severe drug intoxication, especially drugs with a narrow therapeutic window. On the other hand, flavonoids are themselves substrates of ABC transporters. These proteins can affect the oral availability and tissue distribution of these compounds, modifying their beneficial effects. The challenge is to find a suitable way to predict harmful drug-flavonoid interactions mediated by these transporters.

Brain permeability of inhaled corticosteroids

The aim of this study was to evaluate if the permeability of inhaled corticosteroids entering the brain is reduced and if P-glycoprotein (P-gp) transporters are involved. Currently employed inhaled corticosteroids were given intravenously and intratracheally to rats at a dose of 100 μg kg−1. An ex-vivo receptor binding assay was used to monitor over 12 h the glucocorticoid receptor occupancy in the brain and a systemic reference organ (kidney). The involvement of P-gp in the brain permeability of triamcinolone acetonide was assessed in wild-type mice and mdr1a(-/-) knockout mice (mice lacking the gene for expressing P-gp). After both forms of administration, the average brain receptor occupancies were 20–56% of those of the reference organ, with the more lipophilic drugs showing a more pronounced receptor occupation. While the receptor occupancies in the liver of wild-type and mdr1a(-/-) mice were similar after administration of triamcinolone acetonide, brain receptor occupancies in mdr1a(-/-) mice were significantly greater (mdr1a(-/-): 47.6%, 40.2–55.0%, n = 2; wild-type: 11.5±33.0%, n = 3). Penetration into the brain for inhaled corticosteroids (especially those of lower lipophilicity) is reduced. Experiments in mdr1a(-/-) mice confirmed the involvement of P-gp transporters. Further studies are needed to assess whether potential drug interactions at the transporter level are of pharmacological significance.

Effect of P-glycoprotein inhibition on methadone analgesia and brain distribution in the rat

Methadone is an opiate drug that has been identified as an in-vitro substrate of the efflux pump P-glycoprotein (P-gp), active in the intestinal epithelium and in the blood–brain barrier (BBB), among other sites. The objective of this study was to test in vivo, in the rat model, the role of P-gp modulation on the analgesic effect and brain uptake of methadone, as well as identify the most relevant site via dual oral and intravenous (i.v.) experiments. The P-gp specific inhibitor (valspodar or PSC833) was preadministered (10 mg kg−1 i.v.) to test groups. Analgesia was measured using the tailflick test. The ED50 for oral methadone (2, 3, 6 and 8 mg kg−1) decreased three-fold in valspodar groups compared with controls (2.23 + 0.002 mg kg−1 and 6.07 + 0.07 mg kg−1; P &lt; 0.0001). The overall analgesic effect (% antinociception) was elevated 3.1 times in pretreated compared with control rats (90.65% + 0.22 vs 29.23% + 14.0; P &lt; 0.01) after 6 mg kg−1 oral methadone and 2.8 times after i.v. (0.35 mg kg−1) administration (91.75% + 4.27 vs 32.45% + 9.0; P &lt; 0.01). The brain:plasma distribution ratio was higher in pretreated animals and AUCbrain (overall brain concentration) was 6 times higher after oral methadone and 4 times higher after i.v. compared with controls, disproportionally increased relative to plasma, implying an active process at the BBB. P-gp, and hence substrate comedication, plays a critical role in the evolution of the methadone analgesic effect and in its brain uptake, independent of the administration route.

Effects of non-steroidal anti-inflammatory drugs on the pharmacokinetics and elimination of aciclovir in rats

This study aims to investigate the effect of commonly used non-steroidal anti-inflammatory drugs (NSAIDs) on the pharmacokinetics and the renal elimination of aciclovir in rats. Pharmacokinetic parameters were determined following an intravenous administration of aciclovir (5 mg kg−1) to rats in the presence and absence of ketoprofen or naproxen (25 mg kg−1). Compared with the control (given aciclovir alone), pre-treatment with ketoprofen or naproxen 30 min before aciclovir administration significantly altered the pharmacokinetics of aciclovir. Renal clearance of aciclovir was reduced by approximately two fold in the presence of ketoprofen or naproxen. Consequently, the systemic exposure (AUC) to aciclovir in the rats pre-treated with ketoprofen or naproxen was significantly (P &lt; 0.05) higher than that from the control group given aciclovir alone. Furthermore, the mean terminal plasma half-life of aciclovir was enhanced by 4–5 fold by pre-treatment with ketoprofen or naproxen. These results suggest that NSAIDs, such as ketoprofen and naproxen, are effective in altering the pharmacokinetics of aciclovir by inhibiting the organic anion transporter-mediated tubular secretion of aciclovir. Therefore, concomitant use of ketoprofen or naproxen with aciclovir should require close monitoring for clinical consequence of potential drug interaction.

Clinical utility of desvenlafaxine 50 mg/d for treating MDD: a review of two randomized placebo-controlled trials for the practicing physician

BACKGROUND

Major depressive disorder (MDD) is a common, seriously impairing illness. Desvenlafaxine (administered as desvenlafaxine succinate) is the third serotonin-norepinephrine reuptake inhibitor (SNRI) approved in the United States for the treatment of MDD. Short-term clinical studies have demonstrated the efficacy and safety of 50 to 400 mg/d doses, with no evidence that doses greater than 50 mg/d confer additional benefit.

OBJECTIVE

This paper summarizes published data on the efficacy, safety, and tolerability of the desvenlafaxine 50-mg/d recommended therapeutic dose for MDD and discusses clinical practice considerations.

METHODS

A systematic review of MEDLINE, PsycINFO, and PubMed (all years through June 2009) was performed using the terms desvenlafaxine, DVS, and ODV. The criteria for inclusion in the review were a double-blind design, a placebo control or active comparator group, the 50-mg desvenlafaxine dose group, and enrollment of patients with a diagnosis of MDD. Posters were included if they reported on a study that was subsequently published in a manuscript.

RESULTS

Overall results of two randomized, placebo-controlled, 8-week clinical trials demonstrated the efficacy of desvenlafaxine 50 mg/d for MDD. Statistically significant improvements compared with placebo were observed on the primary efficacy measure (17-item Hamilton Rating Scale for Depression [HAM-D(17)] total score; P < 0.05). Significant differences were observed on several secondary measures (Montgomery Asberg Depression Rating Scale scores in both trials [P < 0.05]; Clinical Global Impressions-Improvement scores [P < or = 0.01], Clinical Global Impressions-Severity scores [P < or = 0.01], HAM-D(17) response [P < or = 0.01] and remission [P < 0.05] in one trial each). Functional outcomes measures (Sheehan Disability Scale total and World Health Organization 5-Item Well-Being Index scores) were significant in both trials (P < 0.05). Safety results indicate desvenlafaxine treatment was safe and well tolerated; findings were consistent with the SNRI class. The generalizability of these findings is limited by the study protocols, which excluded patients with unstable comorbid medical conditions and also those with other Axis 1 and 2 psychiatric illnesses. Additionally, comparisons with other SNRIs are challenging given differences in study design. Desvenlafaxine can be initiated with the 50-mg/d therapeutic dose without titration and provides efficacy with rates of discontinuation due to treatment-emergent adverse events similar to placebo. In vitro data indicate desvenlafaxine has minimal inhibitory effects on cytochrome P450 (CYP) 2D6 and clinical studies show desvenlafaxine does not have a clinically relevant effect on CYP2D6 metabolism. In vitro data also indicate desvenlafaxine is not a substrate or inhibitor of the p-glycoprotein transporter. Plasma protein binding of desvenlafaxine is low (30%) and independent of drug concentration. Bioavailability is high at 80% after oral administration and is not affected by food.

CONCLUSIONS

Desvenlafaxine 50 mg/d has demonstrated efficacy, safety, and tolerability for the treatment of MDD in two placebo-controlled trials. The metabolic profile of desvenlafaxine suggests a low risk of drug-drug interactions owing to minimal inhibitory effects on CYP2D6, lack of interaction with p-glycoprotein, and low protein binding.

Synthesis and preclinical evaluation of novel PET probes for P-glycoprotein function and expression

P-glycoprotein (P-gp) is an ATP-dependent efflux pump protecting the body against xenobiotics. A P-gp substrate (7) and an inhibitor (6) were labeled with (11)C, resulting in potential tracers of P-gp function and expression.

METHODS

6 and 7 were labeled using (11)CH(3)I. (11)C-verapamil was prepared as published previously, using (11)C-methyl triflate. MicroPET scans (with arterial sampling) and biodistribution studies were performed in rats pretreated with saline, cyclosporin A (CsA, 50 mg/kg), or cold 6 (15 mg/kg).

RESULTS

The radiochemical yields of (11)C-6 and (11)C-7 were approximately 30% with a total synthesis time of 45 min. Cerebral distribution volumes (DV) of (11)C-6 (2.35 +/- 0.11) and (11)C-7 (1.86 +/- 0.15) in saline-treated rats were higher than of (11)C-verapamil (0.64 +/- 0.12). DVs of (11)C-7 and (11)C-verapamil were significantly increased by CsA (to 5.26 +/- 0.14 and 5.85 +/- 0.32, respectively). The DV of (11)C-6 was reduced by cold 6 (to 1.65 +/- 0.03). Its uptake was also reduced (up to 67%) in several peripheral organs that express P-gp.

CONCLUSIONS

(11)C-7 is a novel tracer of P-gp function with higher baseline uptake than (11)C-verapamil. Upregulation of P-gp function in response to treatment (which is hard to detect with (11)C-verapamil) may be detectable using (11)C-7 and PET. Because (11)C-6 shows specific binding in target organs, this compound is the first PET tracer allowing measurement of P-gp expression.

Adverse drug reactions in patients with cardiovascular disease

Adverse drug reactions (ADRs) occur frequently in modern medical practice, increasing morbidity and mortality and inflating the cost of care. Patients with cardiovascular disease are particularly vulnerable to ADRs due to their advanced age, polypharmacy, and the influence of heart disease on drug metabolism. The ADR potential for a particular cardiovascular drug varies with the individual, the disease being treated, and the extent of exposure to other drugs. Knowledge of this complex interplay between patient, drug, and disease is a critical component of safe and effective cardiovascular disease management. The majority of significant ADRs involving cardiovascular drugs are predictable and therefore preventable. Better patient education, avoidance of polypharmacy, and clear communication between physicians, pharmacists, and patients, particularly during the transition between the inpatient to outpatient settings, can substantially reduce ADR risk.

Inhibition of P-glycoprotein in Caco-2 cells: effects of herbal remedies frequently used by cancer patients

1. The herbal products Natto K2, Agaricus, mistletoe, noni juice, green tea and garlic were investigated for in vitro inhibitory potential on P-glycoprotein (P-gp)-mediated transport of digoxin (30 nM) in differentiated and polarized Caco-2 cells. 2. Satisfactory cell functionality was demonstrated through measurements of assay linearity, transepithelial electric resistance (TEER), cytotoxicity, mannitol permeability, and inclusion of the positive inhibition control verapamil. 3. The most potent inhibitors of the net digoxin flux (IC(50)) were mistletoe > Natto K2 > Agaricus > green tea (0.022, 0.62, 3.81, >4.5 mg ml(-1), respectively). Mistletoe also showed the lowest IC(25) value, close to that obtained by verapamil (1.0 and 0.5 microg ml(-1), respectively). The IC(50)/IC(25) ratio was found to be a good parameter for the determination of inhibition profiles. Garlic and noni juice were classified as non-inhibitors. 4. This study shows that mistletoe, Natto K2, Agaricus and green tea inhibit P-gp in vitro. Special attention should be paid to mistletoe due to very low IC(50) and IC(25) values and to Natto K2 due to a low IC(50) value and a low IC(50)/IC(25) ratio.

P-glycoprotein efflux transporter activity often displays biphasic dose-response relationships

The occurrence of P-glycoprotein efflux transporter systems is recognized as playing critical roles in chemotherapy, drug pharmacokinetics, and the bioavailability of environmental toxins. This article reveals that P-glycoprotein efflux transporter activity commonly displays a biphasic dose response, with low doses being stimulatory and high doses inhibiting. The quantitative features of these biphasic dose responses are consistent with the hormetic dose-response model and are independent of biological model and chemical class. These findings provide further support for the generalizability of the hormetic dose-response model while having important biological and clinical implications, including transport through the blood-brain barrier.

Prevalence of adverse drug combinations in a large post-mortem toxicology database

The prevalence of important adverse drug combinations was studied among the 37,367 cases included in the Finnish post-mortem toxicology database during 2000-2006. The new SFINX interaction database (Swedish, Finnish, INteraction X-referencing) was utilised to identify adverse drug combinations. Consequently, the 24 drugs chosen for the study generated 96 two-compound combinations possessing potentially severe interactions. The total number of hits for the combinations found in the post-mortem database was 267, which accounts for approximately 0.71% of all cases. The potential role of adverse drug interaction (ADI) in these cases was evaluated from the background information and death certificate. The possible ADI cases comprised 23% of all hits and 0.17% of all cases analysed. In cases with a pharmacodynamic mechanism, the most prominent combinations were medicines causing serotonin syndrome or a beta(1)-blocker with verapamil or diltiazem. In cases with a pharmacokinetic mechanism, half of the cases involved digoxin in combination with verapamil. In one third of the possible ADI cases, a forensic pathologist had noted the studied compounds as an underlying or contributing cause of death, although the agents' specific role in ADIs was rarely recognised.

Dietary salt does not influence the disposition of verapamil enantiomers in relation to efflux transporter ABCB1 genetic polymorphism in healthy Korean subjects

To evaluate the effects of dietary salt on the stereoselective disposition of verapamil enantiomers in relation to the transporter ABCB1 2677GG/3435CC and 2677TT/3435TT haplotypes, ten healthy subjects were asked to take diets of three different salt levels for 7 days in a randomized, three-way crossover manner. The plasma concentrations of verapamil and norverapamil enantiomers were determined after a single oral dose of 240 mg verapamil on the last day of each phase. Pharmacokinetic parameters were calculated by non-compartmental analysis techniques and compared among the three different dietary salt phases. Compared with the medium salt diet, the high and low salt diets had no significant effect on the disposition of verapamil enantiomers. Moreover, the ABCB1 haplotypes did not alter the impact of dietary salt, although ABCB1 2677TT/3435TT subjects had slightly, but not significantly, higher C(max) and area under the curve (AUC) and lower T(max) for the verapamil enantiomers than did 2677GG/3435CC subjects in each salt phase.