Drug-drug interaction mediated by inhibition and induction of P-glycoprotein

Discovery of potent antimycobacterial agents targeting lumazine synthase (RibH) of Mycobacterium tuberculosis

Tuberculosis (TB) continues to be a global health crisis, necessitating urgent interventions to address drug resistance and improve treatment efficacy. In this study, we validate lumazine synthase (RibH), a vital enzyme in the riboflavin biosynthetic pathway, as a potential drug target against Mycobacterium tuberculosis (M. tb) using a CRISPRi-based conditional gene knockdown strategy. We employ a high-throughput molecular docking approach to screen ~ 600,000 compounds targeting RibH. Through in vitro screening of 55 shortlisted compounds, we discover 3 compounds that exhibit potent antimycobacterial activity. These compounds also reduce intracellular burden of M. tb during macrophage infection and prevent the resuscitation of the nutrient-starved persister bacteria. Moreover, these three compounds enhance the bactericidal effect of first-line anti-TB drugs, isoniazid and rifampicin. Corroborating with the in silico predicted high docking scores along with favourable ADME and toxicity profiles, all three compounds demonstrate binding affinity towards purified lumazine synthase enzyme in vitro, in addition these compounds exhibit riboflavin displacement in an in vitro assay with purified lumazine synthase indicative of specificity of these compounds to the active site. Further, treatment of M. tb with these compounds indicate reduced production of flavin adenine dinucleotide (FAD), the ultimate end product of the riboflavin biosynthetic pathway suggesting the action of these drugs on riboflavin biosynthesis. These compounds also show acceptable safety profile in mammalian cells, with a high selective index. Hence, our study validates RibH as an important drug target against M. tb and identifies potent antimycobacterial agents.

Impact of P-Glycoprotein-Mediated Drug-Endogenous Substrate Interactions on Androgen and Blood-Brain Barrier Permeability

This report focuses on pharmacokinetic drug-endogenous substrate interactions (DEIs). We hypothesized that P-glycoprotein (P-gp)-mediated DEI might affect androgen kinetics, especially its blood-brain barrier (BBB) permeability. The intracellular accumulation of the endogenous substrates of P-gp, testosterone (TES) and androstenedione (ADO) was increased by several tested drugs in uptake studies using P-gp overexpressing cells, indicating that these drugs inhibit P-gp-mediated efflux of TES of ADO from the cells. In a transport study using rat BBB kit, we found that the BBB limited the penetration of TES and ADO into the central nervous system. In addition, tested drugs that cause DEI were found to increase BBB permeability of TES and ADO via P-gp inhibition. In short, this study provides new findings regarding the possibility that DEI may affect the kinetics of endogenous substrates of P-gp.

Comprehensive in vitro analysis evaluating the variable drug-drug interaction risk of rifampicin compared to rifabutin

Compared to rifampicin (600 mg/day), standard doses of rifabutin (300 mg/day) have a lower risk of drug-drug interactions due to induction of cytochrome P450 3A4 (CYP3A4) or P-glycoprotein (Pgp/ABCB1) mediated by the pregnane X receptor (PXR). However, clinical comparisons with equal rifamycin doses or in vitro experiments respecting actual intracellular concentrations are lacking. Thus, the genuine pharmacological differences and the potential molecular mechanisms of the discordant perpetrator effects are unknown. Consequently, the cellular uptake kinetics (mass spectrometry), PXR activation (luciferase reporter gene assays), and impact on CYP3A4 and Pgp/ABCB1 expression and activity (polymerase chain reaction, enzymatic assays, flow cytometry) were evaluated in LS180 cells after treatment with different rifampicin or rifabutin concentrations for variable exposure times and eventually normalized to actual intracellular concentrations. In addition, inhibitory effects on CYP3A4 and Pgp activities were investigated. While rifampicin is poorly taken up by LS180 cells, it strongly activates PXR and leads to enhanced expression and activity of CYP3A4 and Pgp. In contrast, rifabutin is a significantly less potent and less efficient PXR activator and gene inducer, despite sixfold to eightfold higher intracellular accumulation. Finally, rifabutin is a potent inhibitor of Pgp (IC50 = 0.3 µM) compared to rifampicin (IC50 = 12.9 µM). Together, rifampicin and rifabutin significantly differ by their effects on the regulation and function of CYP3A4 and Pgp, even when controlled for intracellular concentrations. Rifabutin's concurrent Pgp inhibitory action might partly compensate the inducing effects, explaining its weaker clinical perpetrator characteristics.

Refinement of safety and efficacy of anti-cancer chemotherapeutics by tailoring their site-specific intracellular bioavailability through transporter modulation

Low intracellular bioavailability, off-site toxicities, and multi drug resistance (MDR) are the major constraints involved in cancer chemotherapy. Many anticancer molecules fail to become a good lead in drug discovery because of their poor site-specific bioavailability. Concentration of a molecule at target sites is largely varied because of the wavering expression of transporters. Recent anticancer drug discovery strategies are paying high attention to enhance target site bioavailability by modulating drug transporters. The level of genetic expression of transporters is an important determinant to understand their ability to facilitate drug transport across the cellular membrane. Solid carrier (SLC) transporters are the major influx transporters involved in the transportation of most anti-cancer drugs. In contrast, ATP-binding cassette (ABC) superfamily is the most studied class of efflux transporters concerning cancer and is significantly involved in efflux of chemotherapeutics resulting in MDR. Balancing SLC and ABC transporters is essential to avoid therapeutic failure and minimize MDR in chemotherapy. Unfortunately, comprehensive literature on the possible approaches of tailoring site-specific bioavailability of anticancer drugs through transporter modulation is not available till date. This review critically discussed the role of different specific transporter proteins in deciding the intracellular bioavailability of anticancer molecules. Different strategies for reversal of MDR in chemotherapy by incorporation of chemosensitizers have been proposed in this review. Targeted strategies for administration of the chemotherapeutics to the intracellular site of action through clinically relevant transporters employing newer nanotechnology-based formulation platforms have been explained. The discussion embedded in this review is timely considering the current need of addressing the ambiguity observed in pharmacokinetic and clinical outcomes of the chemotherapeutics in anti-cancer treatment regimens.

Naringenin alters the pharmacokinetics of ranolazine in part through the inhibition of cytochrome P450 (3A4) and P-glycoprotein

Background

This study set out to look at how naringenin affected the pharmacokinetics of ranolazine in rats. The pharmacokinetic investigation of ranolazine in rats following oral administration of ranolazine with or without coadministration of naringenin was successfully conducted using the established technique. Animals were administered the same medications for 7 days as part of a multiple dosage study (MDS), and the amount of ranolazine in plasma was calculated on 18 days. The intestinal transit of ranolazine in the presence and absence of naringenin and verapamil was examined in an in vitro experiment using the intestinal sacs of rats and chickens (P-glycoprotein inhibitor).

Results

Naringenin raised the maximal level (Cmax) of ranolazine from 231 ± 10.16 to 303.67 ± 9.46 and 325.67 ± 21.81 ng/mL in SDS and MDS, respectively. Moreover, naringenin elevated the area under the curve (AUC) of ranolazine from 1293.54 ± 37.18 to 1505.38 ± 100.30 and 1575.42 ± 76.98 ng/mL/h in SDS and MDS. In the presence of naringenin, there was an increase in the transfer of ranolazine from the mucosal side to the serosal side. Naringenin inhibits the enzymes Cytochrome P450 (3A4) or (CYP3A4) and P-glycoprotein (P-gp). The findings showed that naringenin might have a considerable impact on ranolazine pharmacokinetics, including extending its t1/2 and raising its AUC.

Conclusions

The findings of the study showed that naringenin inhibits the enzymes CYP3A4 and P-gp. Therefore, naringenin might have a considerable impact on ranolazine pharmacokinetics, including extending its t1/2 and raising its AUC.

Graphical abstract

Findings on In Vitro Transporter-Mediated Drug Interactions and Their Follow-Up Actions for Labeling: Analysis of Drugs Approved by US FDA between 2017 and 2021

Understanding possible follow-up actions on in vitro findings helps determine the necessity of labeling for drug interactions. We analyzed information for in vitro findings on transporter-mediated interactions of drugs approved by the U.S. Food and Drug Administration’s Center for Drug Evaluation and Research for the last five years (i.e., 2017–2021) and their follow-up actions for labeling. Higher R values than the pre-defined cut-off were observed with 3.7–39.1% inhibitor drugs in a simple prediction. Among these drugs, 16–41.7% were labeled with their potential drug interactions, while results of supporting studies or scientific rationales were submitted for the other drugs leading to no interaction labeling. In vitro transporter substrates were reported with 1.7–67.6% of drugs. The interaction labels for these substrate drugs were observed in up to 40% of drugs, while the other drugs were not labeled on the drug interactions with claims for their low interaction potential, evidenced by clinical studies or scientific rationales. The systematic and comprehensive analysis in this study will provide insight into the management of in vitro findings for transporter substrate or inhibitor drugs.

Iatrogenic doramectin overdosing causes toxicity in sheep: A case report

Macrocyclic lactones are widely used endectocides in ruminants, with a high margin of safety for labeled indications. No previous report of iatrogenic doramectin overdosing has been published. We report an outbreak in a sheep flock in Northeast Patagonia, Argentina. Toxicity signs were observed in more than 10% and 59% of ewes and lambs, respectively, particularly those with low body condition, treated with doramectin 3.5% long-acting injectable formulation, presumably at the indicated dose of 700 μg/kg. Clinical signs included lethargy, mydriasis and coma. Doramectin concentration in blood samples was 826.8 (±119.3) ng/ml. Cerebrospinal fluid (CSF) and liver doramectin concentration in euthanized lambs were 3.26-4.28 ng/ml and 8506-8772 ng/g, respectively. Epidemiological and clinical information, and high doramectin concentration were sufficient to confirm the neurotoxicity. Scarce fat deposition could have altered doramectin pharmacokinetic which may have accounted for the observed neurotoxicity. Special care should be taken when animals under similar nutritional conditions are treated with macrocyclic lactones.

Implication of metabolomics and transporter modulation based strategies to minimize multidrug resistance and enhance site-specific bioavailability: a needful consideration toward modern anticancer drug discovery

Induction of drug-metabolizing enzymes and efflux transporters (DMET) through activation of pregnane x receptor (PXR) is the primary factor involved in almost all bioavailability and drug resistance-related problems of anticancer drugs. PXR is a transcriptional regulator of many metabolizing enzymes and efflux transporters proteins like p-glycoprotein (p-gp), multidrug resistant protein 1 and 2 (MRP 1 and 2), and breast cancer resistant protein (BCRP), etc. Several anticancer drugs are potent activators of PXR receptors and can modulate the gene expression of DMET proteins. Involvement of anticancer drugs in transcriptional regulation of DMET can prompt increased metabolism and efflux of their own or other co-administered drugs, which leads to poor site-specific bioavailability and increased drug resistance. In this review, we have discussed several novel strategies to evade drug-induced PXR activation and p-gp efflux including assessment of PXR ligand and p-gp substrate at early stages of drug discovery. Additionally, we have critically discussed the chemical structure and drug delivery-based approaches to avoid PXR binding and inhibit the p-gp activity of the drugs at their target sites.

Approaches to minimize the effects of P-glycoprotein in drug transport: A review

P-glycoprotein (P-gp) is a transporter protein that is come under the ATP binding cassette family of proteins. It is situated on the surface of the intestine epithelium, where P-gp substrate binds to the transporter and is pumped into the intestine lumen by the ATP-driven energy-dependent process. In this review, we summarize the role of the P-gp efflux transporter situated on the intestine, the clinical importance of P-gp related drug interactions, and approaches to minimize the effect of P-gp in drug transport. This review also focuses on the impact of P-gp on the bioavailability of the orally administered drug. Many drug's oral bioavailabilities can improve by concomitant use of P-gp inhibitors. Multidrug resistance are reduced by using some naturally occurring compounds obtained from plants and several synthetic P-gp inhibitors. Formulation strategies, one of the most important approaches to mimic the P-gp transporter's action, finally enhancing the oral bioavailability of the drug by inhibiting its P-gp efflux. Vitamin E TPGS, Gelucire 44/14 and other pharmaceutical/formulation excipients inhibit the P-gp efflux. A prodrug approach might be a useful strategy to overcome drug resistance. Prodrug helps to enhance the solubility or alter the pharmacokinetic properties but does not diminish the pharmacological action.

In Vitro Evaluation of P-gp-Mediated Drug-Drug Interactions Using the RPTEC/TERT1 Human Renal Cell Model

BACKGROUND AND OBJECTIVES

In vitro evaluation of the P-glycoprotein (P-gp) inhibitory potential is an important issue when predicting clinically relevant drug-drug interactions (DDIs). Located within all physiological barriers, including intestine, liver, and kidneys, P-gp plays a major role in the pharmacokinetics of various therapeutic classes. However, few data are available about DDIs involving renal transporters during the active tubular secretion of drugs. In this context, the present study was designed to investigate the application of the human renal cell line RPTEC/TERT1 to study drug interactions mediated by P-gp.

METHODS

The P-gp inhibitory potentials of a panel of drugs were first determined by measuring the intracellular accumulation of rhodamine 123 in RPTEC/TERT1 cells. Then four drugs were selected to assess the half-maximal inhibitor concentration (IC50) values by measuring the intracellular accumulation of two P-gp-substrate drugs, apixaban and rivaroxaban. Finally, according to the FDA guidelines, the [I₁]/IC50 ratio was calculated for each combination of drugs to assess the clinical relevance of the DDIs.

RESULTS

The data showed that drugs which are known P-gp inhibitors, including cyclosporin A, ketoconazole, and verapamil, caused great increases in rhodamine 123 retention, whereas noninhibitors did not affect the intracellular accumulation of the P-gp substrate. The determined IC50 values were in accordance with the inhibition profiles observed in the rhodamine 123 accumulation assays, confirming the reliability of the RPTEC/TERT1 model.

CONCLUSIONS

Taken together, the data demonstrate the feasibility of the application of the RPTEC/TERT1 model for evaluating the P-gp inhibitory potentials of drugs and consequently predicting renal drug interactions.

Association of ABCB1 polymorphisms with carbamazepine metabolism and resistance in epilepsy: A meta-analysis

OBJECTIVE

ABCB1 polymorphisms were previously demonstrated to be associated with the metabolism and resistance of carbamazepine (CBZ) in epilepsy, but the results still remained controversial. Therefore, we performed this meta-analysis to further evaluate the impacts of ABCB1 polymorphisms on CBZ metabolism and resistance.

METHODS

The PubMed, EMBASE, Cochrane library, Chinese National Knowledge Infrastructure, Chinese Science and Technique Journals Database and Wan Fang Database were searched for eligible publications up to 5 July 2021. The mean difference (MD), Odds ratio (OR) and 95 % confidence interval (CI) were calculated by Review Manager 5.3 software to assess the strength of the association.

RESULTS

Twelve studies involving 2126 epilepsy patients were included in this meta-analysis. We found that the TC genotype (heterozygous model: TC vs. CC) of rs1045642 polymorphism was significantly connected with decreased CBZ concentration. Furthermore, this polymorphism was indicated to be associated with concentrations of carbamazepine-10, 11-epoxide (homozygote model: TT vs. CC; heterozygous model: TC vs CC; dominant model: TT + TC vs. CC; over-dominant model: TC vs. TT + CC) and carbamazepine-10, 11-trans dihydrodiol (heterozygous model: TC vs. CC; dominant model: TT + TC vs. CC). Moreover, the AG genotype of rs2032582 polymorphism was related to increased CBZ concentration in heterozygous (AG vs. GG), dominant (AA + AG vs. GG) and over-dominant (AG vs. AA + GG) models. Additionally, rs1128503 was associated with CBZ resistance in heterozygous model (TC vs. CC).

CONCLUSIONS

ABCB1 rs1045642 and rs2032582 polymorphisms were associated with CBZ metabolism for epilepsy, and rs1128503 was related to CBZ resistance. These findings would contribute to improving individualized therapy of epileptic patients.

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.

The influence of P-glycoprotein expression in the standard treatment of Helicobacter pylori infection in Sprague Dawley rats

BACKGROUND

P-glycoprotein (P-gp) is an Adenosine triphosphate (ATP) dependent drug-efflux pump which is located abundantly in the stomach and protects the gut mucosa from xenobiotic.

OBJECTIVE

The purpose of this study was to investigate the influence of P-gp modulation on the efficacy of treatment regimen.

METHOD

P-gp modulation in rats was performed by using P-gp inducer (150 mg/kg rifampicin) and P-gp inhibitor (10 mg/kg cyclosporine A) for 14 days prior to be infected with Helicobacter pylori (H. pylori). The rats were further divided into groups, which were normal control, vehicle control, antibiotics and omeprazole, antibiotics only and omeprazole only for another 2 weeks of treatment. The ulcer formation and P-gp expression were determined by using macroscopic evaluation and western blot analysis, respectively.

RESULTS

The highest P-gp expression was shown in the induced P-gp rats (2.00 ± 0.68) while the lowest P-gp expression was shown in the inhibited P-gp rats (0.45 ± 0.36) compared to the normal P-gp rats. In all groups, the rats which were infected with H. pylori, had a significant increase (p < 0.05) in P-gp expression level and a more severe ulcer formation compared to the healthy rats. The ulcer developed at different levels in the rats with inhibited, induced, or normal P-gp expression. After receiving the standard therapy for H. pylori, it was observed that the healing rate for ulcer was increased to 91% (rats with inhibited P-gp expression), 82% (rats with induced P-gp expression) and 75% in rats with normal P-gp. The use of rifampicin to induce P-gp level was also shown to be effective in eradicating the H. pylori infection.

CONCLUSION

The synergism in the standard therapy by using two antibiotics (clarithromycin and amoxicillin) and proton pump inhibitor (omeprazole) have shown to effectively eradicate the H. pylori infection. Thus, P-gp expression influenced the effectiveness of the treatment.

Development of UPLC-MS/MS Method for Studying the Pharmacokinetic Interaction Between Dasatinib and Posaconazole in Rats

Background and Aim

Dasatinib is approved for the treatment of leukaemia worldwide. Triazole agents such as posaconazole may be used for the control of secondary fungal infection with leukaemia. This work aimed to develop a bioanalytical method to study the potential interaction between dasatinib and posaconazole.

Methods

An ultrahigh-performance liquid chromatography-tandem mass spectrometry method was established to measure the plasma concentrations of dasatinib and posaconazole in rats simultaneously. Simple protein precipitation with acetonitrile was applied to extract dasatinib and posaconazole in samples. The chromatographic separation of analytes was conducted on an UPLC BEH C18 column using a mobile phase consisting of 0.1% aqueous formic acid and acetonitrile. Dasatinib and posaconazole were monitored in positive ion mode with the following mass transition pairs: m/z 488.2→401.1 for dasatinib and m/z 701.3→683.4 for posaconazole. The method was successfully applied for pharmacokinetic interaction between dasatinib and posaconazole.

Results

The established method expressed good linearity in 1–1000 ng/mL of dasatinib and 5–5000 ng/mL of posaconazole, with limit of detection was 1 ng/mL and 5 ng/mL, respectively. Methodology validations, including accuracy, precision, matrix effect, recovery, and stability, met the US Food and Drug Administration (FDA) acceptance criteria for bioanalytical method validation. Dasatinib strongly inhibited the clearance of posaconazole in vivo, while posaconazole expressed no significant effect on the pharmacokinetics of dasatinib.

Conclusion

Dasatinib alters the pharmacokinetics of posaconazole. Attention should be paid to the unexpected risk of adverse clinical outcomes when posaconazole is co-administered with dasatinib.

Characterization of P-Glycoprotein Inhibitors for Evaluating the Effect of P-Glycoprotein on the Intestinal Absorption of Drugs

For developing oral drugs, it is necessary to predict the oral absorption of new chemical entities accurately. However, it is difficult because of the involvement of efflux transporters, including P-glycoprotein (P-gp), in their absorption process. In this study, we conducted a comparative analysis on the inhibitory activities of seven P-gp inhibitors (cyclosporin A, GF120918, LY335979, XR9576, WK-X-34, VX-710, and OC144-093) to evaluate the effect of P-gp on drug absorption. GF120918, LY335979, and XR9576 significantly decreased the basal-to-apical transport of paclitaxel, a P-gp substrate, across Caco-2 cell monolayers. GF120918 also inhibited the basal-to-apical transport of mitoxantrone, a breast cancer resistance protein (BCRP) substrate, in Caco-2 cells, whereas LY335979 hardly affected the mitoxantrone transport. In addition, the absorption rate of paclitaxel after oral administration in wild-type mice was significantly increased by pretreatment with LY335979, and it was similar to that in mdr1a/1b knockout mice. Moreover, the absorption rate of topotecan, a BCRP substrate, in wild-type mice pretreated with LY335979 was similar to that in mdr1a/1b knockout mice but significantly lower than that in bcrp knockout mice. These results indicate that LY335979 has a selective inhibitory activity for P-gp, and would be useful for evaluating the contribution of P-gp to drug absorption.

Drug-drug interaction database for safe prescribing of systemic antifungal agents

INTRODUCTION

A drug-drug interaction (DDI) describes the influence of one drug upon another or the change in a drug's effect on the body when the drug is taken together with a second drug. A DDI can delay, decrease or enhance absorption or metabolism of either drug. Several antifungal agents have a large number of potentially deleterious DDIs.

METHODS

The antifungal drug interactions database https://antifungalinteractions.org/was first launched in 2012 and is updated regularly. It is available as web and app versions to allow information on potential drug interactions with antifungals with a version for patients and another for health professionals. A new and updated database and interface with apps was created in 2019. This allows clinicians and patients to rapidly check for DDIs. The database is fully referenced to allow the user to access further information if needed. Currently DDIs for fluconazole, itraconazole, voriconazole, posaconazole, isavuconazole, terbinafine, amphotericin B, caspofungin, micafungin and anidulafungin are cross-referenced against 2398 other licensed drugs, a total of nearly 17,000 potential DDIs.

RESULTS

The database records 541 potentially severe DDIs, 1129 moderate and 1015 mild DDIs, a total of 2685 (15.9%).

CONCLUSION

As the online database and apps are free to use, we hope that widespread acceptance and usage will reduce medical misadventure and iatrogenic harm from unconsidered DDIs.

Interaction Toxicity Study between P-glycoprotein Inhibitor (Captopril) and Inducer (Spironolactone) with Their Substrate (Lovastatin) in Male Rats

An interaction toxicity study was performed to evaluate and compare the effect of P-glycoprotein (P-gp) inhibitor (captopril) and inducer (spironolactone) on their common substrate (lovastatin) that were done by comparing LD50 of the acute study with their chronic form then with those combined therapeutic doses administered for 90 days. Therefore, isobolographic analysis and chronicity index were used as the parameters for this study. Forty rats were allocated into five groups according to the used treatment into: captopril, spironolactone, lovastatin, captopril + lovastatin and spironolactone + lovastatin using up and down method to determine their acute exposure LD50 while ninety rats were used to perform the chronic stage of the study divided equally into six groups according to daily dosing regimen as following G1- control group administered distilled water orally; G2 administered captopril 0.7 mg/kg BW orally; G3-administered spironolactone 1.4 mg/kg BW orally; G4- administered lovastatin 0.57 mg/kg BW orally; G5-administered spironolactone1.4 mg/kg BW orally and lovastatin 0.57 mg/kg BW, G6- administered captopril 0.7 mg/kg BW and lovastatin 0.57 mg/kg BW orally. The results of isobolographic analysis showed that the sort of interaction between P-gp inhibitor (captopril) and lovastatin alone and as combined administration showed to be antagonistic after acute administration while it was synergistic after chronic administration; for P-gp inducer, spironolactone and lovastatin were additive after acute administration and antagonistic after chronic administration. Chronicity index results showed that both captopril and lovastatin accumulated after administered each alone and showed more accumulation after their combined administration while the chronicity index for P-gp inducer (spironolactone) and lovastatin showed less total concentration in the body burden after their combined administration than alone one. In conclusion, it seems that P-gp inhibitor (captopril) causes accumulation of itself and substrate (lovastatin), while P-gp inducer (spironolactone) causes reduction on the body burden of itself as well as lovastatin possibly due to their effects on the kinetics of the body and this may affect the efficacy and safety of drugs.

Efflux mechanism and pathway of verapamil pumping by human P-glycoprotein

Multidrug resistance (MDR) caused by overexpressed permeability-glycoprotein (P-gp) in cancer cells is the main barrier for the cure of cancers. P-gp can pump many chemotherapeutic drugs, which is a viable target to overcome P-gp-mediated MDR by efficient inhibitors of P-gp. However, limited understanding of the efflux mechanism by human P-gp hinders the development of efficient inhibitors. Herein, the transport of a P-gp inhibitor, verapamil, by human P-gp has been investigated using targeted molecular dynamics simulations and energetics analysis based on our previous research on the transport of a drug (doxorubicin). The energetics analysis identifies that the driving forces for the transport of verapamil are electrostatic repulsions contributed by the positively charged residues in the initial stage and then hydrophobic interactions contributed by the important residues in the later stage. This scenario is generally consistent with that in the transport of doxorubicin. However, the positively charged residues and the important residues for the transport of verapamil are incompletely consistent with the relative residues for the transport of doxorubicin. Moreover, the binding free energy contributions of the positively charged residues for the transport of verapamil are generally higher than them for the transport of doxorubicin, while the important residues constitute significantly different binding free energy compositions in the transports of the two substrates. Consequently, the pathway for the transport of verapamil is identified, which shares only two residues (F336 and M986) with the pathway of doxorubicin. This may imply the weak competitiveness of verapamil with doxorubicin in the substrate efflux. Taken together, this work provided new insights into the efflux mechanisms by human P-gp and would be beneficial in the design of potent P-gp inhibitors.

Differential Impacts of Azole Antifungal Drugs on the Pharmacokinetic Profiles of Dasatinib in Rats by LC-MS-MS

BACKGROUND

Dasatinib, as an oral multi-targeted inhibitor of BCR-ABL and SRC family kinases, has been widely used for the treatment of Philadelphia Chromosome Positive Leukemias in imatinib-acquired resistance and intolerance. The study aimed to develop and validate a simple and robust assay with a small volume of plasma based on liquid chromatography coupled with tandem mass spectrometry to determine the concentration of dasatinib and to investigate the impact of the cytochrome 3A4 inhibitors, including ketoconazole, voriconazole, itraconazole and posaconazole, on the pharmacokinetics of dasatinib in rats.

METHODS

Thirty rats were divided randomly into five groups, control group (0.5% carboxymethylcellulose sodium), ketoconazole (30 mg/kg) group, voriconazole group (30 mg/kg), itraconazole group (30 mg/kg) and posaconazole group (30 mg/kg). After 150 μL blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, and 48 h and precipitated with acetonitrile, the plasma concentration of dasatinib was determined through Fluoro- Phenyl column (150 mm×2.1 mm, 3 μm) in a positive ionization mode.

RESULTS

The results suggested that ketoconazole, voriconazole, and posaconazole could increase the AUC0-t of dasatinib to varying degrees while significantly reducing its clearance. However, there was no significant impact on the pharmacokinetics of dasatinib, co-administered with itraconazole except for the CL and MRT0-t of dasatinib. Additionally, voriconazole could significantly increase Cmax of dasatinib by approximately 4.12 fold.

CONCLUSION

These data indicated that ketoconazole, posaconazole and voriconazole should be cautiously co-administered with dasatinib or close therapeutic drug monitoring of dasatinib concentration, which might cause the drug-drug interaction.

Potential of B-cell-targeting therapy in overcoming multidrug resistance and tissue invasiveness associated with P-glycoprotein expressing-B cell compartments

Rheumatoid arthritis (RA) is a systemic autoimmune mediated inflammatory disease characterized by progressive joint damage and extra-articular organ manifestations. Among the effector pathways and cells involved in the development of RA, activated B cells play a pivotal role in the pathological process of RA. P-glycoprotein (P-gp), a member of ATP-binding cassette transporters, is induced on the cell membrane by certain stimuli. P-gp transports various drugs from the cytoplasm to the cell exterior, resulting in the development of drug resistance. P-gp expression on B cells appears in patients with RA as the disease activity increases, and treatment of these patients' results in modification of over-expression of P-gp on activated B cells. Evidence suggests that P-gp expressing-activated B cells play important roles in the pathogenesis and treatment resistance in RA through the efflux of intracellular drugs and progression of infiltration in inflammatory lesions. Therapies designed to target activated B cells might overcome refractory RA. Identification of the subsets of peripheral activated B cells that express P-gp in RA patients might help the selection of suitable treatment strategy.

Predictors of tacrolimus pharmacokinetic variability: current evidences and future perspectives

INTRODUCTION

In kidney transplantation, tacrolimus (TAC) is at the cornerstone of current immunosuppressive strategies. Though because of its narrow therapeutic index, it is critical to ensure that TAC levels are maintained within this sharp window through reactive adjustments. This would allow maximizing efficiency while limiting drug-associated toxicity. However, TAC high intra- and inter-patient pharmacokinetic (PK) variability makes it more laborious to accurately predict the appropriate dosage required for a given patient.

AREAS COVERED

This review summarizes the state-of-the-art knowledge regarding drug interactions, demographic and pharmacogenetics factors as predictors of TAC PK. We provide a scoring index for each association to grade its relevance and we present practical recommendations, when possible for clinical practice.

EXPERT OPINION

The management of TAC concentration in transplanted kidney patients is as critical as it is challenging. Recommendations based on rigorous scientific evidences are lacking as knowledge of potential predictors remains limited outside of DDIs. Awareness of these limitations should pave the way for studies looking at demographic and pharmacogenetic factors as well as gut microbiota composition in order to promote tailored treatment plans. Therapeutic approaches considering patients' clinical singularities may help allowing to maintain appropriate concentration of TAC.

Considerations for interactions of drugs used for the treatment of COVID-19 with anti-cancer treatments

SARS-CoV2 infection is an emerging issue worldwide. Cancer patient are at increased risk of infection compared to general population. On the other hand, these patients are at major risk of drug interactions caused by renal and hepatic impairment background. Because of the long-term use of chemotherapy drugs, drug interactions are important in these patients especially with SARS-CoV2 treatments now. This paper is review of reported drug interactions of current treatments for COVID-19 and anticancer agents.

Inter-individual variations and modulators of MDR1 transport activity in human placenta

INTRODUCTION

ATP binding cassette (ABC) membrane transporter multidrug resistance 1 (MDR1) is one of the most important efflux transporters in the human placenta protecting the fetus from exposure to xenobiotic toxicity. Recent studies have focused on placental MDR1 expression, but few studies have analyzed placental MDR1 transport activity. The purpose of this study was to investigate placental MDR1 transport activity using a relatively large sample size of human placentas. Furthermore, the effect of ABCB1 gene polymorphisms were investigated along with physiological factors including maternal age, times of pregnancy, BMI, delivery mode or pregnancy complications on placental MDR1 transport activity.

METHODS

A total of 252 human placentas were obtained after delivery. MDR1 transport activity was detected by N-methyl quinidine uptake in placental microvillus membrane vesicles (MVMVs). Nine common single nucleotide polymorphisms (SNPs) in ABCB1 genes were determined by Snapshot. The association between ABCB1 gene polymorphisms, maternal age, times of pregnancy, BMI, delivery mode or pregnancy complications, and transporter activity was investigated.

RESULTS

Inter-individual variations of MDR1 transport activity were observed among 252 subjects. The per unit protein activity was ranged from 0.05 to 0.15/mg. Nine SNPs in ABCB1 gene didn't exhibit significant association with transporter activity of MDR1. Likewise, neither age, times of pregnancy, delivery mode nor pregnancy complications showed any significant effect of placental MDR1 transport activity. But placental MDR1 transport activity in obese pregnant women was lower than those in non-obese pregnant women.

CONCLUSION

Inter-individual variations of MDR1 transport activity existed in human placentas. This may contribute to variations in drug exposure to the fetus affecting clinical outcomes. Maternal age, times of pregnancy, delivery mode nor pregnancy complications included in this study maybe not significantly impact placental MDR1 transport activity, but maternal obese could inhibit placental MDR1 activity.

Peripheral Opioid Receptor Antagonists for Opioid-Induced Constipation: A Primer on Pharmacokinetic Variabilities with a Focus on Drug Interactions

Opioid analgesics remain a treatment option for refractory acute and chronic pain, despite their potential risk for abuse and adverse events (AEs). Opioids are associated with several common AEs, but the most bothersome is opioid-induced constipation (OIC). OIC is often overlooked but has the potential to affect patient quality of life, increase associated symptom burden, and impede long-term opioid compliance. The peripherally acting µ-receptor antagonists (PAMORAs) are a class of drugs that include methylnaltrexone, naloxegol, and naldemedine. Collectively, each is approved for the treatment of OIC. PAMORAs work peripherally in the gastrointestinal tract, without impacting the central analgesic effects of opioids. However, each has unique pharmacokinetic properties that may be impacted by coadministered drugs or food. This review focuses on important metabolic and pharmacokinetic principals that are pertinent to drug interactions involving µ-opioid receptor antagonists prescribed for OIC. It highlights subtle differences among the PAMORAs that may have clinical significance. For example, unlike naloxegol or naldemedine, methylnaltrexone is not a substrate for CYP3A4 or p-glycoprotein; therefore, its plasma concentration is not altered when coadministered with concomitant medications that are CYP3A4 or p-glycoprotein inducers or inhibitors. With a better understanding of pharmacokinetic nuances of each PAMORA, clinicians will be better equipped to identify potential safety and efficacy considerations that may arise when PAMORAs are coadministered with other medications.

Contributions of Drug Transporters to Blood-Placental Barrier

The placenta is the only organ linking two different individuals, mother and fetus, termed as blood-placental barrier. The functions of the blood-placental barrier are to regulate material transfer between the maternal and fetal circulation. The main functional units are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. A series of drug transporters such as P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), multidrug resistance-associated proteins (MRP1, MRP2, MRP3, MRP4, and MRP5), organic anion-transporting polypeptides (OATP4A1, OATP1A2, OATP1B3, and OATP3A1), organic anion transporter 4 (OAT4), organic cation transporter 3 (OCT3), organic cation/carnitine transporters (OCTN1 and OCTN2), multidrug and toxin extrusion 1 (MATE1), and equilibrative nucleoside transporters (ENT1 and ENT2) have been demonstrated on the apical membrane of syncytiotrophoblast, some of which also expressed on the basolateral membrane of syncytiotrophoblast or fetal capillary endothelium. These transporters are involved in transport of most drugs in the placenta, in turn, affecting drug distribution in fetus. Moreover, expressions of these transporters in the placenta often vary along with the gestational ages and are also affected by pathophysiological factor. This chapter will mainly illustrate function and expression of these transporters in placentas, their contribution to drug distribution in fetus, and their clinical significance.

Computational Systems Pharmacology-Target Mapping for Fentanyl-Laced Cocaine Overdose

The United States of America is fighting against one of its worst-ever drug crises. Over 900 people a week die from opioid- or heroin-related overdoses, while millions more suffer from opioid prescription addiction. Recently, drug overdoses caused by fentanyl-laced cocaine specifically are on the rise. Due to drug synergy and an increase in side effects, polydrug addiction can cause more risk than addiction to a single drug. In the present work, we systematically analyzed the overdose and addiction mechanism of cocaine and fentanyl. First, we applied our established chemogenomics knowledgebase and machine-learning-based methods to map out the potential and known proteins, transporters, and metabolic enzymes and the potential therapeutic target(s) for cocaine and fentanyl. Sequentially, we looked into the detail of (1) the addiction to cocaine and fentanyl by binding to the dopamine transporter and the μ opioid receptor (DAT and μOR, respectively), (2) the potential drug-drug interaction of cocaine and fentanyl via p-glycoprotein (P-gp) efflux, (3) the metabolism of cocaine and fentanyl in CYP3A4, and (4) the physiologically based pharmacokinetic (PBPK) model for two drugs and their drug-drug interaction at the absorption, distribution, metabolism, and excretion (ADME) level. Finally, we looked into the detail of JWH133, an agonist of cannabinoid 2-receptor (CB2) with potential as a therapy for cocaine and fentanyl overdose. All these results provide a better understanding of fentanyl and cocaine polydrug addiction and future drug abuse prevention.

Baicalin reduces ciclosporin bioavailability by inducing intestinal p-glycoprotein in rats

Objectives

To investigate the effects of multiple doses of baicalin (BG) on the pharmacokinetics of ciclosporin (CsA) in rats and the potential mechanisms.

Methods

Pharmacokinetic parameters of CsA were determined in male rats after administration of CsA (3 mg/kg, i.g. or i.v.) to rats in the presence and absence of BG (80 mg/kg, i.g. or i.v.) for 7 days. The livers and intestines of rats were isolated and the CYP3A and p-glycoprotein (P-gp) expression were analysed. The effect of BG on the intestinal absorptive behaviour of CsA was also investigated using in-vitro everted rat gut sac model.

Key findings

Baicalin (80 mg/kg, i.v., 7 days) had no effect on the intravenously administered CsA. However, BG (80 mg/kg, i.g., 7 days) significantly decreased the Cmax, AUC0–t and AUC0–∞ of orally administered CsA by 38, 26 and 25%, respectively (P &lt; 0.01 or P &lt; 0.05). Further study revealed that the expression of P-gp in intestine increased in oral multiple doses of BG-treated rats. The in-vitro everted rat gut sac model demonstrated BG (10 μm) significantly decreased the absorption of CsA (10 μm) in intestine (P &lt; 0.05).

Conclusions

Multiple doses of BG decreased the oral bioavailability of CsA in rats significantly, which may be mainly attributable to inhibition of absorption of CsA in intestine and induction of P-gp. The interaction between BG and CsA may occur when BG and CsA were co-administered for long-term use. The dosage adjustment and blood concentration monitoring of CsA may be required in clinic.

Different structures of berberine and five other protoberberine alkaloids that affect P-glycoprotein-mediated efflux capacity

Berberine, berberrubine, thalifendine, demethyleneberberine, jatrorrhizine, and columbamine are six natural protoberberine alkaloid (PA) compounds that display extensive pharmacological properties and share the same protoberberine molecular skeleton with only slight substitution differences. The oral delivery of most PAs is hindered by their poor bioavailability, which is largely caused by P-glycoprotein (P-gp)-mediated drug efflux. Meanwhile, P-gp undergoes large-scale conformational changes (from an inward-facing to an outward-facing state) when transporting substrates, and these changes might strongly affect the P-gp-binding specificity. To confirm whether these six compounds are substrates of P-gp, to investigate the differences in efflux capacity caused by their trivial structural differences and to reveal the key to increasing their binding affinity to P-gp, we conducted a series of in vivo, in vitro, and in silico assays. Here, we first confirmed that all six compounds were substrates of P-gp by comparing the drug concentrations in wild-type and P-gp-knockout mice in vivo. The efflux capacity (net efflux) ranked as berberrubine > berberine > columbamine ~ jatrorrhizine > thalifendine > demethyleneberberine based on in vitro transport studies in Caco-2 monolayers. Using molecular dynamics simulation and molecular docking techniques, we determined the transport pathways of the six compounds and their binding affinities to P-gp. The results suggested that at the early binding stage, different hydrophobic and electrostatic interactions collectively differentiate the binding affinities of the compounds to P-gp, whereas electrostatic interactions are the main determinant at the late release stage. In addition to hydrophobic interactions, hydrogen bonds play an important role in discriminating the binding affinities.

Epimagnolin A, a tetrahydrofurofuranoid lignan from Magnolia fargesii, reverses ABCB1-mediated drug resistance

BACKGROUND

Epimagnolin A is an ingredient of the Chinese crude drug Shin-i, derived from the dried flower buds of Magnolia fargesii and Magnolia flos, which has been traditionally used for the treatment of allergic rhinitis and nasal congestion, empyema, and sinusitis. The pharmacokinetic activity of epimagnolin A remains to be evaluated.

PURPOSE

In this study, we examined the possible interactions of epimagnolin A with human ATP-binding cassette (ABC) transporter ABCB1, a membrane protein vital in regulating the pharmacokinetics of drugs and xenobiotics.

STUDY DESIGN/METHODS

The interaction of epimagnolin A with ABCB1 was evaluated in calcein, ATPase, and MTT assays by using Flp-In-293/ABCB1 cells and purified ABCB1 and simulated in molecular docking studies.

RESULTS

Epimagnolin A inhibited calcein export by Flp-In-293/ABCB1 cells in a concentration-dependent manner in a calcein assay. ATPase assay revealed a concentration-dependent stimulation of the ATPase activity of ABCB1 by epimagnolin A. Epimagnolin A also showed saturation kinetics in the relationship between the compound-stimulated ATPase activity and the compound concentration, suggesting Michaelis-Menten kinetics similar to those of the control drug, verapamil. K_m and V_max values were calculated from Hanes-Woolf plots of (compound concentration) × (compound-stimulated ATPase activity)^-1 vs. (compound concentration); the K_m of epimagnolin and verapamil was 42.9 ± 7.53  μM and 12.3 ± 4.79  μM, respectively, and the corresponding V_max values were 156 ± 15.0  μM and 109 ± 3.18  μM. Molecular docking studies on human ABCB1 showed that epimagnolin A docked to the same binding pocket as verapamil, and 3-(4,5-dimethyl-2-thiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays showed that the sensitivities of Flp-In-293/ABCB1 cells against anti-cancer drugs were enhanced upon exposure to 10  μM epimagnolin A.

CONCLUSION

These results strongly suggest that epimagnolin A affects the transport activity of ABCB1 as a substrate.

Racemic vs. enantiopure inert Ti(iv) complex of a single diaminotetrakis(phenolato) ligand in anticancer activity toward human drug-sensitive and -resistant cancer cell lines

A tetrakis(phenolato) Ti(iv) complex was synthesized in racemic and optically pure form, exhibiting high hydrolytic stability, and similar cytotoxicity for all stereochemical forms on HT-29 and A2780 cancer cells. Higher activity of the racemate on drug-resistant A2780cp and A2780adr lines implies a beneficial activity of both enantiomers rendering enantiomeric resolution unnecessary.

Posaconazole–digoxin drug–drug interaction mediated by inhibition of P-glycoprotein

Drug–drug interactions between digoxin and the triazole antifungal agents, mediated via various cytochrome P450 isozymes, have been described in the literature. Posaconazole is not extensively metabolized by these isozymes but is both a p-glycoprotein (P-gp) substrate and inhibitor. To our knowledge, there have been no published cases of clinically significant posaconazole-digoxin drug–drug interactions. We report an interaction between posaconazole (300 mg by mouth daily) and digoxin (0.25 mg by mouth daily, Monday through Friday) resulting in atrial fibrillation with slow ventricular response and degenerating into polymorphic ventricular tachycardia.

Overview of Transporters in Pharmacokinetics and Drug Discovery

Transporters play important roles in absorption, distribution, metabolism, and elimination (ADME) processes, as well as drug pharmacokinetics (PK) and pharmacodynamics (PD). They are also important in maintaining the homeostasis of endogenous compounds and nutrients in the body. Increasing evidences also suggest that they are important in mediating drug-drug interactions (DDIs). While the significance of transporters in drug pharmacodynamics and DDIs are beyond the scope of this overview, the basic concepts of transporters, their contributions in membrane permeation processes, and their roles in influencing drug ADME pathway and PK will be discussed. © 2018 by John Wiley & Sons, Inc.

No pharmacokinetic interactions between candesartan and amlodipine following multiple oral administrations in healthy subjects

PURPOSE

To evaluate the pharmacokinetics and pharmacodynamics of candesartan and amlodipine in the absence and presence of each other in healthy subjects.

METHODS

This study consisted of two parts: part 1, the effect of amlodipine on candesartan; part 2, the effect of candesartan on amlodipine. Each part was designed as a randomized, open-label, two-sequence, two-period, two-intervention crossover study with 20 subjects and performed separately in different populations. Pharmacokinetic assessments were performed over 48 hours for candesartan in part 1 and 72 hours for amlodipine in part 2 after drug administration on Day 10. Safety data included the results of physical examinations, clinical laboratory tests, vital signs, an electrocardiogram, and adverse events.

RESULTS

For both candesartan and amlodipine, the 90% confidence intervals for the geometric mean ratios of area under the concentration-time curve from time zero to the time of dosing interval of 24 hours and maximum concentration after drug administration fell within the bioequivalence acceptance criteria. Although this study was conducted in normotensive subjects, blood pressure lowering effects were observed in all intervention groups and co-administration of candesartan and amlodipine reduced blood pressure more than amlodipine alone, but similar to candesartan alone. No serious adverse event was reported throughout the study, and all treatment emergent adverse events were mild to moderate in severity and were recovered without sequelae.

CONCLUSION

Co-administration of candesartan and amlodipine did not change the systemic exposure of each drug alone in healthy subjects. The administration of candesartan 32 mg alone, amlodipine 10 mg alone, and co-administration of candesartan and amlodipine were well tolerated during the study.

New insights in the in vitro characterisation and molecular modelling of the P-glycoprotein inhibitory promiscuity

The presence of several binding sites for both substrates and inhibitors is yet a poorly explored thematic concerning the assessment of the drug-drug interactions risk due to interactions of multiple drugs with the human transport protein P-glycoprotein (P-gp or MDR1, gene ABCB1). In this study we measured the inhibitory behaviour of a set of known drugs towards P-gp by using three different probe substrates (digoxin, Hoechst 33,342 and rhodamine 123). A structure-based model was built to unravel the different substrates binding sites and to rationalize the cases where drugs were not inhibiting all the substrates. A separate set of experiments was used to validate the model and confirmed its suitability to either detect the substrate-dependent P-gp inhibition and to anticipate proper substrates for in vitro experiments case by case. The modelling strategy described can be applied for either design safer drugs (P-gp as antitarget) or to target specific sub-site inhibitors towards other drugs (P-gp as target).

Boeravinone B, A Novel Dual Inhibitor of NorA Bacterial Efflux Pump of Staphylococcus aureus and Human P-Glycoprotein, Reduces the Biofilm Formation and Intracellular Invasion of Bacteria

This study elucidated the role of boeravinone B, a NorA multidrug efflux pump inhibitor, in biofilm inhibition. The effects of boeravinone B plus ciprofloxacin, a NorA substrate, were evaluated in NorA-overexpressing, wild-type, and knocked-out Staphylococcus aureus (SA-1199B, SA-1199, and SA-K1758, respectively). The mechanism of action was confirmed using the ethidium bromide accumulation and efflux assay. The role of boeravinone B as a human P-glycoprotein (P-gp) inhibitor was examined in the LS-180 (colon cancer) cell line. Moreover, its role in the inhibition of biofilm formation and intracellular invasion of S. aureus in macrophages was studied. Boeravinone B reduced the minimum inhibitory concentration (MIC) of ciprofloxacin against S. aureus and its methicillin-resistant strains; the effect was stronger in SA-1199B. Furthermore, time–kill kinetics revealed that boeravinone B plus ciprofloxacin, at subinhibitory concentration (0.25 × MIC), is as equipotent as that at the MIC level. This combination also had a reduced mutation prevention concentration. Boeravinone B reduced the efflux of ethidium bromide and increased the accumulation, thus strengthening the role as a NorA inhibitor. Biofilm formation was reduced by four–eightfold of the minimal biofilm inhibitory concentration of ciprofloxacin, effectively preventing bacterial entry into macrophages. Boeravinone B effectively inhibited P-gp with half maximal inhibitory concentration (IC₅₀) of 64.85 μM. The study concluded that boeravinone B not only inhibits the NorA-mediated efflux of fluoroquinolones but also considerably inhibits the biofilm formation of S. aureus. Its P-gp inhibition activity demonstrates its potential as a bioavailability and bioefficacy enhancer.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Rhabdomyolysis in a Patient Treated with Colchicine and Atorvastatin

Objective:

To report a case of severe rhabdomyolysis that developed after administration of atorvastatin to a patient receiving regular colchicine treatment.

Case Summary:

A 45-year-old man with nephrotic syndrome and amyloidosis presented with dyspnea, altered mentation, and severe fatigue. He had been taking colchicine 1.5 mg/day for amyloidosis for 3 years without adverse effects. Atorvastatin 10 mg/day was prescribed for hypercholesterolemia one month prior to admission. After 2 weeks of atorvastatin treatment, he began to experience myalgia and reduced muscle strength. The creatinine and creatine kinase concentrations on admission were 8.1 mg/dL and 9035 U/L, respectively. The patient was diagnosed with rhabdomyolysis with the findings of myoglobinuric, oliguric acute renal failure, and more than 50–fold elevated creatine kinase concentration. His muscle strength improved after withdrawal of atorvastatin and colchicine. However, he died because of nosocomial pneumonia that developed during his hospital stay. The Naranjo probability scale indicated that atorvastatin and colchicine were probable causes of rhabdomyolysis.

Discussion:

Atorvastatin and colchicine have well-known myotoxic adverse effects. Despite atorvastatin's proven safety, its use with certain drugs, such as colchicine, makes it a potential myotoxic drug. This might be because concomitant administration of P-glycoprotein substrates, such as statins, and colchicine, which is a P-glycoprotein inhibitor, modifies pharmacokinetics by increasing bioavailability and organ uptake of the substrates, leading to more adverse reactions and toxicities.

Conclusions:

We recommend checking the creatine kinase level one week after prescribing 2 or more potentially myotoxic drugs concomitantly, after dose increase of a myotoxic drug, or after prescribing a new drug to a patient already using other myotoxic agents.

Association between statin use and ischemic stroke or major hemorrhage in patients taking dabigatran for atrial fibrillation

BACKGROUND

Dabigatran etexilate is a prodrug whose absorption is opposed by intestinal P-glycoprotein and which is converted by carboxylesterase to its active form, dabigatran. Unlike other statins, simvastatin and lovastatin are potent inhibitors of P-glycoprotein and carboxylesterase, and might either increase the risk of hemorrhage with dabigatran etexilate or decrease its effectiveness.

METHODS

We conducted 2 population-based, nested case-control studies involving Ontario residents 66 years of age and older who started dabigatran etexilate between May 1, 2012, and Mar. 31, 2014. In the first study, cases were patients with ischemic stroke; in the second, cases were patients with major hemorrhage. Each case was matched with up to 4 controls by age and sex. All cases and controls received a single statin in the 60 days preceding the index date. We determined the association between each outcome and the use of simvastatin or lovastatin, relative to other statins.

RESULTS

Among 45 991 patients taking dabigatran etexilate, we identified 397 cases with ischemic stroke and 1117 cases with major hemorrhage. After multivariable adjustment, use of simvastatin or lovastatin was not associated with an increased risk of stroke (adjusted odds ratio [OR] 1.33, 95% confidence interval [CI] 0.88 to 2.01). In contrast, use of simvastatin and lovastatin were associated with a higher risk of major hemorrhage (adjusted OR 1.46, 95% CI 1.17 to 1.82).

INTERPRETATION

In patients receiving dabigatran etexilate, simvastatin and lovastatin were associated with a higher risk of major hemorrhage relative to other statins. Preferential use of the other statins should be considered in these patients.

The Interactions of P-Glycoprotein with Antimalarial Drugs, Including Substrate Affinity, Inhibition and Regulation

The combination of passive drug permeability, affinity for uptake and efflux transporters as well as gastrointestinal metabolism defines net drug absorption. Efflux mechanisms are often overlooked when examining the absorption phase of drug bioavailability. Knowing the affinity of antimalarials for efflux transporters such as P-glycoprotein (P-gp) may assist in the determination of drug absorption and pharmacokinetic drug interactions during oral absorption in drug combination therapies. Concurrent administration of P-gp inhibitors and P-gp substrate drugs may also result in alterations in the bioavailability of some antimalarials. In-vitro Caco-2 cell monolayers were used here as a model for potential drug absorption related problems and P-gp mediated transport of drugs. Artemisone had the highest permeability at around 50 x 10(-6) cm/sec, followed by amodiaquine around 20 x 10(-6) cm/sec; both mefloquine and artesunate were around 10 x 10(-6) cm/sec. Methylene blue was between 2 and 6 x 10(-6) cm/sec depending on the direction of transport. This 3 fold difference was able to be halved by use of P-gp inhibition. MRP inhibition also assisted the consolidation of the methylene blue transport. Mefloquine was shown to be a P-gp inhibitor affecting our P-gp substrate, Rhodamine 123, although none of the other drugs impacted upon rhodamine123 transport rates. In conclusion, mefloquine is a P-gp inhibitor and methylene blue is a partial substrate; methylene blue may have increased absorption if co-administered with such P-gp inhibitors. An upregulation of P-gp was observed when artemisone and dihydroartemisinin were co-incubated with mefloquine and amodiaquine.

Gaining Insights Into the Pharmacology of Anthelmintics Using Haemonchus contortus as a Model Nematode

Progress made in understanding pharmacokinetic behaviour and pharmacodynamic mechanisms of drug action/resistance has allowed deep insights into the pharmacology of the main chemical classes, including some of the few recently discovered anthelmintics. The integration of pharmaco-parasitological research approaches has contributed considerably to the optimization of drug activity, which is relevant to preserve existing and novel active compounds for parasite control in livestock. A remarkable amount of pharmacology-based knowledge has been generated using the sheep abomasal nematode Haemonchus contortus as a model. Relevant fundamental information on the relationship among drug influx/efflux balance (accumulation), biotransformation/detoxification and pharmacological effects in parasitic nematodes for the most traditional anthelmintic chemical families has been obtained by exploiting the advantages of working with H. contortus under in vitro, ex vivo and in vivo experimental conditions. The scientific contributions to the pharmacology of anthelmintic drugs based on the use of H. contortus as a model nematode are summarized in the present chapter.

Pharmacokinetic and Metabolic Characteristics of Herb-Derived Khellactone Derivatives, A Class of Anti-HIV and Anti-Hypertensive: A Review

A vast number of structural modifications have been performed for khellactone derivatives (KDs) that have been widely concerned owing to their diverse biological properties, including anti-hypertension, anti-HIV, reversing P-glycoprotein (P-gp) mediated multidrug resistance, and anti-inflammation effects, to find the most active entity. However, extensive metabolism of KDs results in poor oral bioavailability, thus hindering the clinical trial performance of those components. The primary metabolic pathways have been revealed as hydrolysis, oxidation, acyl migration, and glucuronidation, while carboxylesterases and cytochrome P450 3A (CPY3A), as well as UDP-glucuronosyltransferases (UGTs) primarily mediate these metabolic pathways. Attention was mainly paid to the pharmacological features, therapeutic mechanisms and structure-activity relationships of KDs in previous reviews, whereas their pharmacokinetic and metabolic characteristics have seldom been discussed. In the present review, KDs' metabolism and their pharmacokinetic properties are summarized. In addition, the structure-metabolism relationships of KDs and the potential drug-drug interactions (DDIs) induced by KDs were also extensively discussed. The polarity, the acyl groups substituted at C-3' and C-4' positions, the configuration of C-3' and C-4', and the moieties substituted at C-3 and C-4 positions play the determinant roles for the metabolic profiles of KDs. Contributions from CYP3A4, UGT1A1, P-gp, and multidrug resistance-associated protein 2 have been disclosed to be primary for the potential DDIs. The review is expected to provide meaningful information and helpful guidelines for the further development of KDs.

High-Dose Verapamil in Episodic and Chronic Cluster Headaches and Cardiac Adverse Events: Is It as Safe as We Think?

Cluster headache (CH) is a primary headache disorder with relatively effective treatments. Although few sufficiently controlled trials are available, verapamil is recommended as the first-line prophylactic drug for CH by the French Headache Society (with a low level of evidence, level B) and by the EFNS (European Federation of Neurological Societies, level A). Daily doses of more than 480 mg (and up to 1200 mg daily) are frequently used off-label, while 360 mg daily is the only dosage to have demonstrated its effectiveness in a double-blind trial against placebo, and the usual label posology used by cardiologists is 240 mg daily in hypertension. We report the case of a 19-year-old man who was self-reported to our cardiology consultation for dyspnea and asthenia for 18 months. His medical history consisted of CH crisis for 4 years treated by verapamil 720 mg/day for 18 months with relatively good efficiency. His electrocardiogram (ECG) showed a sinus bradycardia at 40 bpm with a first-degree atrio-ventricular block. Evolution was favorable after progressive verapamil discontinuation. Analysis performed on the French Pharmacovigilance Database between July 1, 2000 and December 1, 2014 found four other cases of cardiac adverse events related to high-dose verapamil used in CH prevention (two cases of syncope with complete atrio-ventricular block with verapamil 1200 and 240 mg daily, respectively, one syncope related to sick sinus syndrome with verapamil 360 mg daily, and one case of sinus bradycardia with verapamil 720 mg daily). Although available studies seem to demonstrate an apparent good tolerance, this off-label practice should not be considered as standard of care and requires strict cardiac monitoring, as suggested by the Agence Nationale de Sécurité du Médicament (ANSM) in a recent re-evaluation of the benefit/risk ratio of high-dose verapamil used in CH prevention.

Selection of resistant acute myeloid leukemia SKM-1 and MOLM-13 cells by vincristine-, mitoxantrone- and lenalidomide-induced upregulation of P-glycoprotein activity and downregulation of CD33 cell surface exposure

Bone marrow cells and peripheral blood mononuclear cells obtained from both acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) patients contain upregulated levels of cell surface antigen CD33 compared with healthy controls. This difference enables the use of humanized anti-CD33 antibody conjugated to cytotoxic agents for CD33 targeted immunotherapy. However, the expression of the membrane-bound drug transporter P-glycoprotein (P-gp) has been shown to be critical for resistance against the cytotoxicity of a humanized anti-CD33 antibody conjugated to maytansine-derivative DM4. The aim of the present study was to examine whether the expression of P-gp in AML cell lines is associated with changes in CD33 expression. For this purpose, we established drug resistant variants of SKM-1 and MOLM-13 AML cell lines via the selection of parental cells for resistance to vincristine, mitoxantrone and lenalidomide. All three substances induced a multidrug resistance (MDR) phenotype in SKM-1 cells associated with strong upregulation of P-gp and downregulation of CD33. However, in MOLM-13 cells, the upregulation of P-gp and downregulation of CD33 were present only in cells selected for resistance to vincristine and mitoxantrone but not lenalidomide. Inverse expression of P-gp and CD33 were observed in all resistant variants of SKM-1 and MOLM-13 cells. The MDR phenotype of resistant variants of SKM-1 and MOLM-13 cells was associated with alterations in apoptotic regulatory proteins and downregulation of the multidrug resistance associated protein 1 and breast cancer resistance protein.