Prolongation and enhancement of serum methotrexate concentrations by probenecid

Matrix Approach Assessment of Cabotegravir Drug-Drug Interactions with OAT1/OAT3 Substrates and UGT1A1/UGT1A9 Inhibitors Using Physiologically-Based Pharmacokinetic Modeling

Background/Objective: Cabotegravir (CAB), available as an oral tablet and as a long-acting (LA) nanosuspension for intramuscular injection, is approved as a combination therapy for the treatment, and as a monotherapy for the prevention, of HIV-1 infection. People living with HIV may receive multiple concomitant medications, with the associated risk of drug-drug interactions (DDIs). CAB is an inhibitor of OAT1/OAT3 renal transporters and a substrate of the UDP-glucuronosyltransferase enzymes UGT1A1 and 1A9, in vitro. While the effect of induction of UGT1A1/UGT1A9 on CAB exposure had been investigated in the clinic, the effect of the risk of DDIs with CAB via inhibition of these enzymes, or as an inhibitor of OAT1/OAT3 transporters, had not been evaluated. Methods: A physiologically-based pharmacokinetic (PBPK) model was developed and verified for orally dosed CAB to investigate the DDI risks associated with CAB, using a matrix approach to extensively qualify the PBPK platform and the substrates and/or inhibitors of either OAT1/OAT3 or UGT1A1/UGT1A9. The effect of uncertainties in in vitro inhibition values for OAT1/OAT3 was assessed via sensitivity analysis. Results: A mean increase of less than 25% in systemic exposure for OAT1/OAT3 substrates was predicted, with the potential for an increase of up to 80% based on the sensitivity analysis. On co-dosing with UGT1A1/UGT1A9 inhibitors, the predicted mean increase in CAB exposure was within 11%. Conclusions: PBPK modelling indicated that clinically relevant DDIs are not anticipated with OAT1/3 substrates or UGT1A1/1A9 inhibitors and CAB. With maximal exposure of the LA formulation of CAB being lower than the oral, the results of these simulations can be extrapolated to LA injectable dosing.

Methotrexate for inflammatory skin disease in pediatric patients: Consensus treatment guidelines

Methotrexate (MTX) is a readily accessible drug, first used in 1948 and employed for a wide variety of indications since then. However, despite widespread off-label use, FDA labeling does not include approved indications for the use of MTX for many inflammatory skin diseases in pediatric patients, including morphea, psoriasis, atopic dermatitis, and alopecia areata, among others. Without published treatment guidelines, some clinicians may be hesitant to use MTX off-label, or uncomfortable prescribing MTX in this population. To address this unmet need, an expert consensus committee was convened to develop evidence- and consensus-based guidelines for use of MTX to treat pediatric inflammatory skin disease. Clinicians with experience and expertise in clinical research, drug development, and treating inflammatory skin disease in pediatric patients with MTX were recruited. Five committees were created based on major topic areas: (1) indications and contraindications, (2) dosing, (3) interactions with immunizations and medications, (4) adverse effects (potential for and management of), and (5) monitoring needs. Pertinent questions were generated and addressed by the relevant committee. The entire group participated in a modified Delphi process to establish agreement on recommendations for each question. The committee developed 46 evidence- and consensus-based recommendations, each with >70% agreement among members, across all five topics. These are presented in tables and text, along with a discussion of supporting literature, and level of evidence. These evidence- and consensus-based recommendations will support safe and effective use of MTX for the underserved population of pediatric patients who may benefit from this valuable, time-honored medication.

A critical review of methotrexate clinical interactions: role of transporters

INTRODUCTION

Methotrexate (MTX) is an anti-folate and immunosuppressive drug prescribed for various malignancies and immune diseases. However, delayed elimination of MTX associated with concomitant use of some medications can lead to severe and life-threatening adverse effects.

AREAS COVERED

This paper investigated drug-MTX interactions that lead to elevated MTX levels and related adverse effects due to the role of transporters. Methotrexate toxicity occurs at both low and high doses administrations. According to the studies we reviewed in this paper, most interaction records with methotrexate occurred with co-administration of indomethacin, ketoprofen, omeprazole, piperacillin/tazobactam, ciprofloxacin, co-trimoxazole, probenecid, and imatinib, mainly due to the role of transporters. However, most studies were performed as case reports or series, and confirming the exact drug-methotrexate interaction still needs further clinical investigations.

EXPERT OPINION

Our findings showed no firm evidence of interactions of proton pump inhibitors (PPIs), levetiracetam, and NSAIDS with MTX. Moreover, patients' risk factors, hypoalbuminemia, renal failure, third space fluid retention, the elderly, polypharmacy, and transport inhibition are the most critical factors for MTX toxicity. If substitution or temporary discontinuation is not possible, healthcare providers should be aware of interactions, especially in patients with risk factors for MTX toxicity.

Studying the right transporter at the right time: an in vitro strategy for assessing drug-drug interaction risk during drug discovery and development

INTRODUCTION

Transporters are significant in dictating drug pharmacokinetics, thus inhibition of transporter function can alter drug concentrations resulting in drug-drug interactions (DDIs). Because they can impact drug toxicity, transporter DDIs are a regulatory concern for which prediction of clinical effect from in vitro data is critical to understanding risk.

AREA COVERED

The authors propose in vitro strategies to assist mitigating/removing transporter DDI risk during development by frontloading specific studies, or managing patient risk in the clinic. An overview of clinically relevant drug transporters and observed DDIs are provided, alongside presentation of key considerations/recommendations for in vitro study design evaluating drugs as inhibitors or substrates. Guidance on identifying critical co-medications, clinically relevant disposition pathways and using mechanistic static equations for quantitative prediction of DDI is compiled.

EXPERT OPINION

The strategies provided will facilitate project teams to study the right transporter at the right time to minimise development risks associated with DDIs. To truly alleviate or manage clinical risk, the industry will benefit from moving away from current qualitative basic static equation approaches to transporter DDI hazard assessment towards adopting the use of mechanistic models to enable quantitative DDI prediction, thereby contextualising risk to ascertain whether a transporter DDI is simply pharmacokinetic or clinically significant requiring intervention.

A Simple and Rapid Bioluminescence-Based Functional Assay of Organic Anion Transporter 1 as a D-Luciferin Transporter

Organic anion transporter 1 (SLC22A6/OAT1) plays a key role in renal tubular excretion of endo- and exogenous anionic substances including drugs. Since the inhibition of OAT1 function by a concomitant drug may cause pharmacokinetic drug-drug interactions (DDIs) in clinical practice, an in vitro uptake study to evaluate the inhibition potency of OAT1 is useful for the prediction and avoidance of DDIs and recommended for drug candidates in drug development. In this chapter, we describe a rapid and highly sensitive functional assay of OAT1 based on bioluminescence (BL) detection using D-luciferin as a substrate in living cells. The principle of measurement simply relies on the biochemical feature of D-luciferin to be recognized as a substrate of OAT1, and the BL intensity depending on intracellular D-luciferin level and luciferase activity, thereby allowing the quantitative analysis of OAT1-mediated D-luciferin transport. The BL measurement can be completed within 1 min without experimental procedures for removing extracellular uptake solution and washing cells, both of which involve in the conventional uptake studies using isotope-labeled or fluorescent compounds. The present method is applicable to high-throughput screening to identify and avoid potential OAT1 inhibitors in drug development.

Multidrug resistance proteins (MRPs): Structure, function and the overcoming of cancer multidrug resistance

ATP-binding cassette (ABC) transporters mediate the ATP-driven translocation of structurally and mechanistically distinct substrates against steep concentration gradients. Among the seven human ABC subfamilies namely ABCA-ABCG, ABCC is the largest subfamily with 13 members. In this respect, 9 of the ABCC members are termed "multidrug resistance proteins" (MRPs1-9) due to their ability to mediate cancer multidrug resistance (MDR) by extruding various chemotherapeutic agents or their metabolites from tumor cells. Furthermore, MRPs are also responsible for the ATP-driven efflux of physiologically important organic anions such as leukotriene C₄, folic acid, bile acids and cAMP. Thus, MRPs are involved in important regulatory pathways. Blocking the anticancer drug efflux function of MRPs has shown promising results in overcoming cancer MDR. As a result, many novel MRP modulators have been developed in the past decade. In the current review, we summarize the structure, tissue distribution, biological and pharmacological functions as well as clinical insights of MRPs. Furthermore, recent updates in MRP modulators and their therapeutic applications in clinical trials are also discussed.

Uptake Transporters of the SLC21, SLC22A, and SLC15A Families in Anticancer Therapy-Modulators of Cellular Entry or Pharmacokinetics?

Solute carrier transporters comprise a large family of uptake transporters involved in the transmembrane transport of a wide array of endogenous substrates such as hormones, nutrients, and metabolites as well as of clinically important drugs. Several cancer therapeutics, ranging from chemotherapeutics such as topoisomerase inhibitors, DNA-intercalating drugs, and microtubule binders to targeted therapeutics such as tyrosine kinase inhibitors are substrates of solute carrier (SLC) transporters. Given that SLC transporters are expressed both in organs pivotal to drug absorption, distribution, metabolism, and elimination and in tumors, these transporters constitute determinants of cellular drug accumulation influencing intracellular drug concentration required for efficacy of the cancer treatment in tumor cells. In this review, we explore the current understanding of members of three SLC families, namely SLC21 (organic anion transporting polypeptides, OATPs), SLC22A (organic cation transporters, OCTs; organic cation/carnitine transporters, OCTNs; and organic anion transporters OATs), and SLC15A (peptide transporters, PEPTs) in the etiology of cancer, in transport of chemotherapeutic drugs, and their influence on efficacy or toxicity of pharmacotherapy. We further explore the idea to exploit the function of SLC transporters to enhance cancer cell accumulation of chemotherapeutics, which would be expected to reduce toxic side effects in healthy tissue and to improve efficacy.

Two cases of severe neutropenia in patients on low-dose methotrexate and ceftriaxone

PURPOSE

There are limited data on the effect of ceftriaxone on methotrexate clearance, with results of some studies indicating altered methotrexate pharmacokinetics with the administration of ceftriaxone. We describe 2 possible cases demonstrating an interaction between methotrexate and ceftriaxone, resulting in profound neutropenia.

SUMMARY

The decision to continue methotrexate therapy in the setting of surgery or during treatment of an active infection continues to be a topic of debate due to perceived negative effects on the healing process. Methotrexate is typically administered at a lower dose for inflammatory arthritis than for hematologic indications, thus having less immunosuppression potential. However, if methotrexate is continued during treatment of infection, drug interactions along with effects on the healing process should be considered. Ceftriaxone is commonly considered safe for long-term therapy due to its favorable adverse effect and drug interaction profile. Ceftriaxone is partially eliminated via organic anion transporters in the kidneys, leading to potential competition with methotrexate clearance in the renal tubules. Clinicians using these drugs concurrently should be aware of the potential for development of neutropenia and monitor patients receiving this combination closely.

CONCLUSION

Two patients receiving ceftriaxone therapy in the setting of a joint infection developed profound neutropenia after resuming oral methotrexate therapy for inflammatory arthritis.

Transporter-Mediated Drug-Drug Interactions and Their Significance

Drug transporters are considered to be determinants of drug disposition and effects/toxicities by affecting the absorption, distribution, and excretion of drugs. Drug transporters are generally divided into solute carrier (SLC) family and ATP binding cassette (ABC) family. Widely studied ABC family transporters include P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance proteins (MRPs). SLC family transporters related to drug transport mainly include organic anion-transporting polypeptides (OATPs), organic anion transporters (OATs), organic cation transporters (OCTs), organic cation/carnitine transporters (OCTNs), peptide transporters (PEPTs), and multidrug/toxin extrusions (MATEs). These transporters are often expressed in tissues related to drug disposition, such as the small intestine, liver, and kidney, implicating intestinal absorption of drugs, uptake of drugs into hepatocytes, and renal/bile excretion of drugs. Most of therapeutic drugs are their substrates or inhibitors. When they are comedicated, serious drug-drug interactions (DDIs) may occur due to alterations in intestinal absorption, hepatic uptake, or renal/bile secretion of drugs, leading to enhancement of their activities or toxicities or therapeutic failure. This chapter will illustrate transporter-mediated DDIs (including food drug interaction) in human and their clinical significances.

Roles of Renal Drug Transporter in Drug Disposition and Renal Toxicity

The kidney plays an important role in maintaining total body homeostasis and eliminating toxic xenobiotics and metabolites. Numerous drugs and their metabolites are ultimately eliminated in the urine. The reabsorption and secretion functions of the nephron are mediated by a variety of transporters located in the basolateral and luminal membranes of the tubular cells. In the past decade, many studies indicated that transporters play important roles in drug pharmacokinetics and demonstrated the impact of renal transporters on the disposition of drugs, drug-drug interactions, and nephrotoxicities. Here, we focus on several important renal transporters and their roles in drug elimination and disposition, drug-induced nephrotoxicities and potential clinical solutions.

Effects of proton pump inhibitors and famotidine on elimination of plasma methotrexate: Evaluation of drug-drug interactions mediated by organic anion transporter 3

Methotrexate (MTX) is an antifolate agent used in the treatment of numerous types of cancer, and eliminated by active tubular secretion via organic anion transporter 3 (OAT3). Gastric antisecretory drugs, such as proton pump inhibitors (PPIs) and histamine H₂ receptor antagonists, are widely used among patients with cancer in clinical practice. The aim of the present study was to analyse the potential drug-drug interactions between MTX and gastric antisecretory drugs in high-dose MTX (HD-MTX) therapy. The impact of PPIs on the plasma MTX concentration on 73 cycles of HD-MTX therapy was analysed retrospectively in 43 patients. Also investigated was the involvement of OAT3 in PPI-MTX drug interaction in an in vitro study using human OAT3 expressing HEK293 cells. In a retrospective study, patients who received a PPI had significantly higher MTX levels at 48 h (0.38 vs. 0.15 μmol l^-1 , respectively, p = 0.000018) and 72 h (0.13 vs. 0.05 μmol l^-1 , respectively, p = 0.0002) compared with patients who did not receive a PPI (but received famotidine). Moreover, in vitro experiments demonstrated that PPIs (esomeprazole, lansoprazole, omeprazole and rabeprazole) inhibited hOAT3-mediated uptake of MTX in a concentration-dependent manner (IC₅₀ values of 0.40-5.5 μ m), with a rank order of lansoprazole > esomeprazole > rabeprazole > omeprazole. In contrast to PPIs, famotidine showed little inhibitory effect on hOAT3-mediated MTX uptake. These results demonstrated that co-administration of PPI, but not famotidine, could result in a pharmacokinetic interaction that increases the plasma MTX levels, at least in part, via hOAT3 inhibition.

Delayed methotrexate elimination: Incidence, interaction with antacid drugs, and clinical consequences?

The aim of this retrospective cohort study was to investigate the incidence of delayed methotrexate elimination in patients treated with high-dose methotrexate (≥1 g/m² ) for haematological malignancy and to identify the impact of interacting drugs, especially proton-pump inhibitors (PPIs) and ranitidine. All patients treated with high-dose methotrexate over a 6 year period in the haematology department of the Lyon Sud University Hospital (Hospices Civils de Lyon, France) were included. Potential risk factors for delayed methotrexate elimination were tested in a generalized linear model by univariate analysis: patient age, gender, methotrexate dose, administration of PPI or ranitidine, and concomitant nephrotoxic drugs. A total of 412 cycles of methotrexate were administered to 179 patients. Proton-pump inhibitors were co-administered with methotrexate in 127 cycles and ranitidine in 192 cycles. Ninety-three cycles included no antacid drugs. A total of 918 plasma methotrexate assays were performed. Methotrexate concentrations were checked at 24 hours in 92% of cycles. Delayed methotrexate elimination was observed in 20.9% of cycles. A total of 63 cycles with delayed methotrexate elimination were only identified on plasma methotrexate measures at 72 hours: ie, plasma methotrexate was in the normal range at 24 and 48 hour post injection. Use of PPI/ranitidine or no antacid drugs did not increase risk of delayed elimination, with respectively delayed methotrexate elimination in 20.5%, 21.9%, and 19.4% of cycles (P = .89). Impaired baseline creatinine clearance showed significant association in univariate analysis. Fifteen patients showed grade 1 acute kidney injury, 1 grade 2, 2 grade 3, and none grade 4. For half of these cases, delayed methotrexate elimination was observed and the 2 grade 3 events appeared in patients treated with PPIs. This retrospective study suggests that there is no association between concomitant use of proton-pump inhibitors (pantoprazole and esomeprazole) or ranitidine and delayed methotrexate elimination.

Renal Transporter-Mediated Drug-Drug Interactions: Are They Clinically Relevant?

The kidney, through the distinct processes of passive glomerular filtration and active tubular secretion, plays an important role in the elimination of numerous endobiotics (eg, hormones, metabolites), toxins, nutrients, and drugs. Renal transport pathways mediating active tubular secretion and reabsorption in the proximal tubule are complex, involving apical and basolateral transporters acting in concert. Detailed studies of the molecular mechanisms of net active tubular secretion have established the involvement of multiple transporters with overlapping substrate specificity mediating competing secretion and reabsorption pathways. Although drug interactions arising from inhibition of renal transporters are rare relative to other mechanisms, they can involve commonly administered drugs (eg, cimetidine, metformin), may be underappreciated due to muted effects on plasma pharmacokinetics relative to tissue levels, can affect narrow-therapeutic-index medications (eg, antiarrhythmic, oncology medications), and may disproportionately affect sensitive populations where polypharmacy is common (eg, the elderly, diabetics). In particular, there is the potential for larger-magnitude interactions in subjects with reduced glomerular filtration rates due to the increased relative contribution of tubular secretion. The assessment of additional endpoints in drug-drug interaction studies including pharmacodynamics, positron emission tomography imaging, and metabolomics promises to expand our understanding of the clinical relevance of renal drug interactions.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Quantitative Prediction of Human Renal Clearance and Drug-Drug Interactions of Organic Anion Transporter Substrates Using In Vitro Transport Data: A Relative Activity Factor Approach

Organic anion transporters (OATs) are important in the renal secretion, and thus, the clearance, of many drugs; and their functional change can result in pharmacokinetic variability. In this study, we applied transport rates measured in vitro using OAT-transfected human embryonic kidney cells to predict human renal secretory and total renal clearance of 31 diverse drugs. Selective substrates to OAT1 (tenofovir), OAT2 (acyclovir and ganciclovir), and OAT3 (benzylpenicillin, oseltamivir acid) were used to obtain relative activity factors (RAFs) for these individual transporters by relating in vitro transport clearance (after physiologic scaling) to in vivo secretory clearance. Using the estimated RAFs (0.64, 7.3, and 4.1, respectively, for OAT1, OAT2, and OAT3, respectively) and the in vitro active clearances, renal secretory clearance and total renal clearance were predicted with average fold errors (AFEs) of 1.89 and 1.40, respectively. The results show that OAT3-mediated transport play a predominant role in renal secretion for 22 of the 31 drugs evaluated. This mechanistic static approach was further applied to quantitatively predict renal drug-drug interactions (AFE ∼1.6) of the substrate drugs with probenecid, a clinical probe OAT inhibitor. In conclusion, the proposed in vitro-in vivo extrapolation approach is the first comprehensive attempt toward mechanistic modeling of renal secretory clearance based on routinely employed in vitro cell models.

Inhibitory Interaction Potential of 22 Antituberculosis Drugs on Organic Anion and Cation Transporters of the SLC22A Family

Twenty-two currently marketed antituberculosis drugs were comprehensively evaluated for their inhibitory effect on organic anionic transporter (OAT)- and organic cation transporter (OCT)-mediated uptake using stably transfected HEK293 cells in vitro We observed moderate to strong inhibitory effects on OAT1- and OAT3-mediated para-aminohippurate (PAH) uptake and OCT1- and OCT2-mediated N-methyl-4-phenylpylidinium acetate (MPP+) uptake. Ciprofloxacin, linezolid, para-aminosalicylic acid (PAS), and rifampin were observed to have strong inhibitory effects, with the concentrations for a 50% inhibitory effect (IC50s) being 35.1, 31.1, 37.6, and 48.1 μM, respectively, for OAT1 and >100, 21.9, 24.6, and 30.2 μM, respectively, for OAT3. Similarly, pyrazinamide, rifabutin, and levofloxacin were observed to have inhibitory effects, with IC50 values being 36.5, 42.7, and 30.3 μM, respectively, for OCT1 and with the IC50 value for PAS being 94.2 μM for OCT2. In addition, we used zidovudine and metformin as clinically prescribed substrates of OATs and OCTs, respectively, and zidovudine and metformin uptake was also strongly inhibited by the antituberculosis drugs. Among the tested drugs, the highest drug-drug interaction (DDI) indexes were found for PAS, which were 9.3 to 13.9 for OAT1 and 12.0 to 17.7 for OAT3, and linezolid, which were 1.18 to 2.15 for OAT1 and 1.7 to 3.01 for OAT3. Similarly, the DDI indexes of pyrazinamide and levofloxacin were 0.57 and 0.30, respectively, for OCT1, and the DDI index of PAS was 3.8 for OCT2, suggesting a stronger possibility (DDI index value cutoff, >0.1) of in vivo DDIs. This is the first comprehensive report of the inhibitory potential of anti-TB drugs on OAT- and OCT-mediated uptake of prototype and clinically prescribed substrate drugs in vitro, providing an ability to predict DDIs between anti-TB drugs and other coprescribed drugs in clinical studies in vivo.

A guide to clinically relevant drug interactions in oncology

This paper presents an overview of new information on clinically relevant drug-drug interactions, particular focuses on negative drug interactions in oncology. We have generated a concise table of drug-drug interactions that provides a synopsis of the clinical outcome of the interaction along with a recommendation for management. We have also generated other tables that describe specific interactions with methotrexate and dosing guidelines for cytotoxic drugs in the presence of renal or hepatic dysfunction. Since warfarin is one of the non-anticancer drugs that is commonly used in cancer patients for the treatment and prevention of venous thromboembolism, its interactions with other anticancer drugs that have been reported in literatures were also reviewed in this paper. In general, drug interactions observed in cancer patients may be categorized into pharmacokinetic, pharmacodynamic and pharmaceutic interactions. Pharmacokinetic interactions involve one drug altering the absorption, distribution, metabolism, or excretion of another drug. Interpatient variability in the pharmacokinetic profile of many anticancer agents often complicates the predictability of the antitumor response and toxicities. Among four pharmacokinetic characteristics, drug interactions involving hepatic metabolism is probably the most common and important mechanism responsible for oncologic drug interactions. For example, several anticancer drugs including taxanes, vinca alkaloids, and irinotecan are known to be metabolized by cytochrome CYP3A4. Enzyme-inducing anticonvulsants have been shown to significantly decrease the plasma levels of these anticancer drugs, thereby compromising the anti-tumor effects. N ephrotoxicity or changes in hepatic function caused by some anticancer drugs (e.g., cisplatin, asparaginase) may also have an impact on the pharmacokinetics of the interacting agents. Pharmacodynamic interactions may occur when two or more drugs acting at a common receptor-binding site impact on the pharmacologic action of the object drug, without influencing the pharmacokinetics of each interacting agent. In clinical setting, a decrease of antitumor efficacy was observed in breast cell lines when gemcitabine or vinorelbine were used in combination with paclitaxel. On the other hand, a decreased incidence of thrombocytopenia was seen in patients receiving combination of carboplatin and palcitaxel compared to those receiving carboplatin alone. The third type of drug-drug interaction is known as pharmaceutic interaction. When one drug may alter the physical or chemical compatibility of another drug that utlimately leads to a change in appearance of the solution or a decrease of effectiveness of the drug due to drug inactivation or degradation.

Effect of ceftriaxone and cefepime on high-dose methotrexate clearance

Numerous drug interactions with methotrexate have been identified, which can lead to serious life-threatening effects. Up to 90% of methotrexate is excreted unchanged in the urine with primary excretion dependent on organic anion transport in the renal proximal tubule. The two pathways responsible for methotrexate secretion are organic anion transport 1 and primarily organic anion transport 3. Penicillins undergo tubular secretion via organic anion transport, and cephalosporins are believed to also possess a similar risk when administered with methotrexate; however, there are no human studies observing this interaction with cephalosporins and methotrexate. Ceftriaxone undergoes biliary clearance and has low affinity for the same organic anion transports as methotrexate; therefore, ceftriaxone has a low potential to interact with methotrexate. Cefepime is primarily secreted by organic cation transport N2, and also has a low potential to interact with methotrexate. This case report describes the pharmacokinetic effect of concomitant beta-lactam therapy in a patient receiving high-dose methotrexate.

Stereoselective Inhibition of Methotrexate Excretion by Glucuronides of Nonsteroidal Anti-inflammatory Drugs via Multidrug Resistance Proteins 2 and 4

Combined administration of methotrexate (MTX) and nonsteroidal anti-inflammatory drugs (NSAIDs) can result in a decreased systemic clearance of MTX. To date, inhibition of renal uptake via organic anion transporters and efflux via multidrug resistance-associated protein (MRPs) by NSAIDs has been recognized as possible sites of drug interaction between MTX and NSAIDs. Although most NSAIDs are glucuronidated in kidney tissue and excreted mainly as glucuronide conjugates, it is not fully known whether the glucuronides of NSAIDs (NSAIDs-Glu) inhibit MTX excretion via MRP2 and MRP4. The purpose of this study was to investigate the inhibitory effects of the glucuronides of several NSAIDs (diclofenac, R- and S-ibuprofen, R- and S-flurbiprofen, and R- and S-naproxen), as well as the parent NSAIDs on MTX uptake using human MRP2- and MRP4-expressing inside-out vesicles. Results confirm that all NSAIDs and NSAIDs-Glu examined exhibited stereoselective and concentration-dependent inhibitory effects on MTX uptake via MRP2 and MRP4. Notably, NSAIDs-Glu potently inhibited MTX uptake via MRP2 and MRP4 compared with the corresponding parent NSAIDs except for naproxen in MRP2 and S-flurbiprofen in MRP4. The present results support that the glucuronides of NSAIDs, as well as the parent NSAIDs, are involved in the inhibition of urinary excretion of MTX via MRP2 and MRP4.

Drug interaction profile of the HIV integrase inhibitor cabotegravir: assessment from in vitro studies and a clinical investigation with midazolam

1. Cabotegravir (CAB; GSK1265744) is a potent HIV integrase inhibitor in clinical development as an oral lead-in tablet and long-acting injectable for the treatment and prevention of HIV infection. 2. This work investigated if CAB was a substrate for efflux transporters, the potential for CAB to interact with drug-metabolizing enzymes and transporters to cause clinical drug interactions, and the effect of CAB on the pharmacokinetics of midazolam, a CYP3A4 probe substrate, in humans. 3. CAB is a substrate for Pgp and BCRP; however, its high intrinsic membrane permeability limits the impact of these transporters on its intestinal absorption. 4. At clinically relevant concentrations, CAB did not inhibit or induce any of the CYP or UGT enzymes evaluated in vitro and had no effect on the clinical pharmacokinetics of midazolam. 5. CAB is an inhibitor of OAT1 (IC50 0.81 µM) and OAT3 (IC50 0.41 µM) but did not or only weakly inhibited Pgp, BCRP, MRP2, MRP4, MATE1, MATE2-K, OATP1B1, OATP1B3, OCT1, OCT2 or BSEP. 6. Based on regulatory guidelines and quantitative extrapolations, CAB has a low propensity to cause clinically significant drug interactions, except for coadministration with OAT1 or OAT3 substrates.

Proton pump inhibitors inhibit methotrexate transport by renal basolateral organic anion transporter hOAT3

The coadministration of methotrexate (MTX) and proton pump inhibitors (PPIs) can result in a pharmacokinetic interaction that delays MTX elimination and subsequently increases the MTX blood concentrations. Human organic anion transporters (hOATs) are responsible for the renal tubular secretion of MTX and are thought to be involved in this drug interaction. The aim of this study was to evaluate the inhibitory potencies of PPIs on hOAT1 and hOAT3, which are the two isoforms of OATs predominantly expressed in kidney proximal tubules. Using stably transfected cell systems that express the uptake transporters human embryonic kidney (HEK)-hOAT1 and HEK-hOAT3, we analyzed the inhibitory potencies of omeprazole, lansoprazole, and pantoprazole on OAT-mediated [(3)H]estrone sulfate (ES), [(3)H]p-aminohippuric acid (PAH), and [(3)H]MTX uptake in vitro. hOAT3 is a high affinity transporter for MTX (Km = 21.17 ± 5.65 µM). Omeprazole, lansoprazole, and pantoprazole inhibited [(3)H]MTX uptake in HEK-hOAT3 cells with an IC50 of 6.8 ± 1.16, 1.14 ± 0.26, and 4.45 ± 1.62 µM, respectively, and inhibited the [(3)H]ES uptake in HEK-hOAT3 cells with an IC50 of 20.59 ± 4.07, 3.96 ± 0.96, and 7.89 ± 2.31 µM, respectively. Furthermore, omeprazole, lansoprazole, and pantoprazole exhibited inhibited PAH uptake on hOAT1 in a concentration-dependent manner (IC50 = 4.32 ± 1.26, 7.58 ± 1.06, and 63.21 ± 4.74 µM, respectively). These in vitro results suggest that PPIs inhibit [(3)H]MTX transport via hOAT3 inhibition, which most likely explains the drug-drug interactions between MTX and PPIs and should be considered for other OATs substrates.

Flavonoids are inhibitors of human organic anion transporter 1 (OAT1)-mediated transport

Organic anion transporter 1 (OAT1) has been reported to be involved in the nephrotoxicity of many anionic xenobiotics. As current clinically used OAT1 inhibitors are often associated with safety issues, identifying potent OAT1 inhibitors with little toxicity is of great value in reducing OAT1-mediated drug nephrotoxicity. Flavonoids are a class of polyphenolic compounds with exceptional safety records. Our objective was to evaluate the effects of 18 naturally occurring flavonoids, and some of their glycosides, on the uptake of para-aminohippuric acid (PAH) in both OAT1-expressing and OAT1-negative LLC-PK1 cells. Most flavonoid aglycones produced substantial decreases in PAH uptake in OAT1-expressing cells. Among the flavonoids screened, fisetin, luteolin, morin, and quercetin exhibited the strongest effect and produced complete inhibition of OAT1-mediated PAH uptake at a concentration of 50 μM. Further concentration-dependent studies revealed that both morin and luteolin are potent OAT1 inhibitors, with IC50 values of <0.3 and 0.47 μM, respectively. In contrast to the tested flavonoid aglycones, all flavonoid glycosides had negligible or small effects on OAT1. In addition, the role of OAT1 in the uptake of fisetin, luteolin, morin, and quercetin was investigated and fisetin was found to be a substrate of OAT1. Taken together, our results indicate that flavonoids are a novel class of OAT1 modulators. Considering the high consumption of flavonoids in the diet and in herbal products, OAT1-mediated flavonoid-drug interactions may be clinically relevant. Further investigation is warranted to evaluate the nephroprotective role of flavonoids in relation to drug-induced nephrotoxicity mediated by the OAT1 pathway.

Pharmacokinetic interaction between methotrexate and chloral hydrate

We report the case of a drug interaction between methotrexate (MTX) and chloral hydrate (CH) observed in a child treated for acute leukemia. Significantly slower MTX clearance and increased MTX exposure occurred on the first three courses of a high-dose chemotherapy when co-administered with CH despite normal renal function, adequate hydration, and alkalinization. Mean MTX area under the curve associated with CH administration was 1,134 µmol hours/L, compared to 608 µmol hours/L after discontinuation of CH. This interaction possibly resulted from a competition between anionic CH metabolites and MTX for renal tubular excretion.

Pharmacologic modulation strategies to reduce dose requirements of anticancer therapy while preserving clinical efficacy

Drug interactions may be exploited to overcome pharmacokinetic issues in order to improve the therapeutic index of a drug, with clinical goals of reducing the dose of the active drug while preserving efficacy or reducing toxicity. This strategy has been used in infectious disease and transplant medicine, and, more recently, in oncology. Pharmacologic modulation strategies range from coadministration of either a drug that inhibits a metabolizing enzyme that would inactivate the drug of interest, a drug that induces an enzyme that activates the drug of interest or a drug that inhibits transporters that affect the uptake or elimination of the drug of interest. This review will discuss pharmacologic modulation strategies that have been tested clinically in order to increase systemic drug exposure. Important examples include ketoconazole inhibition of hepatic CYP3A4 in order to increase systemic exposure to docetaxel, irinotecan and etoposide, and cyclosporine inhibition of intestinal ATP-binding cassette transporters in order to decrease the toxicity of irinotecan and increase the bioavailability of oral docetaxel, paclitaxel and topotecan.

OATPs, OATs and OCTs: the organic anion and cation transporters of the SLCO and SLC22A gene superfamilies

The human organic anion and cation transporters are classified within two SLC superfamilies. Superfamily SLCO (formerly SLC21A) consists of organic anion transporting polypeptides (OATPs), while the organic anion transporters (OATs) and the organic cation transporters (OCTs) are classified in the SLC22A superfamily. Individual members of each superfamily are expressed in essentially every epithelium throughout the body, where they play a significant role in drug absorption, distribution and elimination. Substrates of OATPs are mainly large hydrophobic organic anions, while OATs transport smaller and more hydrophilic organic anions and OCTs transport organic cations. In addition to endogenous substrates, such as steroids, hormones and neurotransmitters, numerous drugs and other xenobiotics are transported by these proteins, including statins, antivirals, antibiotics and anticancer drugs. Expression of OATPs, OATs and OCTs can be regulated at the protein or transcriptional level and appears to vary within each family by both protein and tissue type. All three superfamilies consist of 12 transmembrane domain proteins that have intracellular termini. Although no crystal structures have yet been determined, combinations of homology modelling and mutation experiments have been used to explore the mechanism of substrate recognition and transport. Several polymorphisms identified in members of these superfamilies have been shown to affect pharmacokinetics of their drug substrates, confirming the importance of these drug transporters for efficient pharmacological therapy. This review, unlike other reviews that focus on a single transporter family, briefly summarizes the current knowledge of all the functionally characterized human organic anion and cation drug uptake transporters of the SLCO and the SLC22A superfamilies.

Critical role of organic anion transporters 1 and 3 in kidney accumulation and toxicity of aristolochic acid I

Ingestion of aristolochic acid (AA), especially its major constituent aristolochic acid I (AAI), results in severe kidney injury known as aristolochic acid nephropathy (AAN). Although hepatic cytochrome P450s metabolize AAI to reduce its kidney toxicity in mice, the mechanism by which AAI is uptaken by renal cells to induce renal toxicity is largely unknown. In this study, we found that organic anion transporters (OATs) 1 and 3, proteins known to transport drugs from the blood into the tubular epithelium, are responsible for the transportation of AAI into renal tubular cells and the subsequent nephrotoxicity. AAI uptake in HEK 293 cells stably transfected with human OAT1 or OAT3 was greatly increased compared to that in the control cells, and this uptake was dependent on the AAI concentration. Administration of probenecid, a well-known OAT inhibitor, to the mice reduced AAI renal accumulation and its urinary excretion and protected mice from AAI-induced acute tubular necrosis. Further, AAI renal accumulation and severe kidney lesions induced by AAl in Oat1 and Oat3 gene knockout mice all were markedly suppressed compared to those in the wild-type mice. Together, our results suggest that OAT1 and OAT3 have a critical role in AAl renal accumulation and toxicity. These transporters may serve as a potential therapeutic target against AAN.

Toward a systems level understanding of organic anion and other multispecific drug transporters: a remote sensing and signaling hypothesis

Organic anion transporters (Oats) are located in the barrier epithelia of diverse organs, where they mediate the absorption and excretion of a wide range of metabolites, signaling molecules, and xenobiotics. Although their interactions with a broad group of substrates have been extensively studied and described, the primary physiological role of Oats remains elusive. The presence of overlapping substrate specificities among the different Oat isoforms, together with recent metabolomic data from the Oat1, Oat3, and renal-specific transporter (RST/URAT1) knockout mice, suggests a possible role in remote signaling wherein substrates excreted through one Oat isoform in one organ are taken up by another Oat isoform located in a different organ, thereby mediating communication between different organ systems, or even between different organisms. Here we further develop this "remote sensing and signaling hypothesis" and suggest how the regulation of SLC22 subfamily members (including those of the organic cation, organic carnitine, and unknown substrate transporter subfamilies) can be better understood by considering the organism's broader need to communicate between epithelial and other tissues by simultaneous regulation of transport of metabolites, signaling molecules, drugs, and toxins. This systems biology perspective of remote signaling (sensing) could help reconcile an enormous array of tissue-specific data for various SLC22 family genes and, possibly, other multispecific transporters, such as those of the organic anion transporting polypeptide (OATP, SLC21) and multidrug resistance-associated protein (MRP) families.

Clinically Significant Drug–Drug Interactions Between Oral Anticancer Agents and Nonanticancer Agents: Profiling and Comparison of Two Drug Compendia

Background:

Use of oral anticancer agents is gaining wide acceptance in the treatment of cancer. However, patients receiving oral therapy are at high risk for drug–drug interactions (DDIs).

Objective:

To create a drug profile for each clinically significant DDI involving selected oral anticancer agents and evaluate the agreement between 2 commonly used DDI compendia: Drug Interaction Facts (DIF) 2008 and Micromedex DRUGDEX.

Methods:

DDI profiles were developed based on primary and tertiary literature reviews. DIF 2008 and Micromedex DRUGDEX were compared to assess the consistency of listings, severity, and scientific evidence ratings of DDIs involving the oral anticancer agents that were selected. The Spearman correlation test was used to assess the correlation of the severity ratings between the 2 compendia.

Results:

A total of 184 DDIs were identified. A DDI profile was created for 40 of these that met the predetermined criteria for clinically significant interactions. The comparative assessment showed inconsistency in DDI listings (15.2% of those identified were listed in DIF only and 46.7% were listed in Micromedex only), severity ratings (Spearman correlation coefficient 0.49), and scientific evidence ratings (disagreement 25.8%).

Conclusions:

The discrepancies in DDI listing and rating systems between the compendia evaluated here reflect the need for more studies to standardize the definitions and classifications of DDIs.

Species difference in the inhibitory effect of nonsteroidal anti-inflammatory drugs on the uptake of methotrexate by human kidney slices

Simultaneous use of nonsteroidal anti-inflammatory drugs (NSAIDs), probenecid, and other drugs has been reported to delay the plasma elimination of methotrexate in patients. Previously, we have reported that inhibition of the uptake process cannot explain such drug-drug interactions using rats. The present study quantitatively evaluated the possible role of the transporters in such drug-drug interactions using human kidney slices and membrane vesicles expressing human ATP-binding cassette (ABC) transporters. The uptake of methotrexate by human kidney slices was saturable with a K(m) of 45 to 49 microM. Saturable uptake of methotrexate by human kidney slices was markedly inhibited by p-aminohippurate and benzylpenicillin, but only weakly by 5-methyltetrahydrofolate. These transport characteristics are similar to those of a basolateral organic anion transporter (OAT) 3/SLC22A8. NSAIDs and probenecid inhibited the uptake of methotrexate by human kidney slices, and, in particular, salicylate, indomethacin, phenylbutazone, and probenecid were predicted to exhibit significant inhibition at clinically observed plasma concentrations. Among ABC transporters, such as BCRP/ABCG2, multidrug resistance-associated protein (MRP) 2/ABCC2, and MRP4/ABCC4, which are candidates for the luminal efflux of methotrexate, ATP-dependent uptake of methotrexate by MRP4-expressing membrane vesicles was most potently inhibited by NSAIDs. Salicylate and indomethacin were predicted to inhibit MRP4 at clinical plasma concentrations. Diclofenac-glucuronide significantly inhibited MRP2-mediated transport of methotrexate in a concentration-dependent manner, whereas naproxen-glucuronide had no effect. Inhibition of renal uptake (via OAT3) and efflux processes (via MRP2 and MRP4) explains the possible sites of drug-drug interaction for methotrexate with probenecid and some NSAIDs, including their glucuronides.

Recommendations for the use of methotrexate in juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is one of the most common rheumatic diseases in childhood. In a significant number of JIA cases the disease is resistant to therapy with NSAIDs, intra-articular corticosteroid injections, and physiotherapy, and methotrexate is used as a second-line agent. The efficacy of methotrexate therapy in children with JIA has been demonstrated in prospective controlled trials and this agent appears to have slightly superior efficacy compared with leflunomide. Data from randomized studies indicate a starting dose of 10-15 mg/m(2)/week orally. The dose of parenteral methotrexate can be increased to 15-20 mg/m(2)/week. Combination therapy with methotrexate and an NSAID is recommended. However, there are still no data on when to initiate methotrexate in JIA and how long children should be treated. The most common adverse effects are aversion to the drug and nausea. In the case of minor adverse effects the use of folic acid at a dosage of 1 mg/day is feasible. In JIA, daily folate supplementation has only been studied in one small heterogeneous cohort with a very short observation period and, at present, a general recommendation on daily folate supplementation cannot be made. In summary, methotrexate is seen by many pediatric rheumatologists as the first-choice, second-line drug; there is good evidence of its efficacy in JIA. However, in light of the recent introduction of biologic agents, the place of methotrexate in the treatment of JIA may have to be redefined in the coming years.

A phase I clinical pharmacologic study of pralatrexate in combination with probenecid in adults with advanced solid tumors

PURPOSE

The antifolate pralatrexate (10-propargyl-10-deazaaminopterin, PDX) demonstrates greater in vitro and in vivo antitumor efficacy than methotrexate. Preclinical models indicated that the efficacy of pralatrexate may be enhanced by coadministration with probenecid. The aim of this phase I study was to determine the maximum-tolerated dose of pralatrexate when combined with probenecid given every 2 weeks in humans.

METHODS

The starting dose was pralatrexate 40 mg/m(2) intravenously and probenecid 70 mg/m(2) intravenously administered every 14 days, where one cycle of treatment was every 28 days. The pralatrexate dose was initially fixed while probenecid dose escalation was explored. The pralatrexate area under the curve (AUC), terminal-half life (t1/2), and maximum plasma concentration (Cmax) were determined in cycle 1.

RESULTS

Seventeen patients with advanced solid tumors were treated with a median of two prior chemotherapy regimens. Stomatitis was dose-limiting with pralatrexate 40 mg/m(2) and probenecid 233 mg/m(2). Mean pralatrexate AUC and half life (t1/2) increased with increasing doses of probenecid. No objective responses were seen.

CONCLUSION

For patients with advanced solid tumors, the maximum-tolerated dose of this drug combination was pralatrexate 40 mg/m(2) and probenecid 140 mg/m(2). Vitamin B(12) and folate supplementation may allow for further dose escalation of pralatrexate and probenecid. This is a suitable question for a future study.

Organic anion transporter (Slc22a) family members as mediators of toxicity

Exposure of the body to toxic organic anions is unavoidable and occurs from both intentional and unintentional sources. Many hormones, neurotransmitters, and waste products of cellular metabolism, or their metabolites, are organic anions. The same is true for a wide variety of medications, herbicides, pesticides, plant and animal toxins, and industrial chemicals and solvents. Rapid and efficient elimination of these substances is often the body's best defense for limiting both systemic exposure and the duration of their pharmacological or toxicological effects. For organic anions, active transepithelial transport across the renal proximal tubule followed by elimination via the urine is a major pathway in this detoxification process. Accordingly, a large number of organic anion transport proteins belonging to several different gene families have been identified and found to be expressed in the proximal nephron. The function of these transporters, in combination with the high volume of renal blood flow, predisposes the kidney to increased toxic susceptibility. Understanding how the kidney mediates the transport of organic anions is integral to achieving desired therapeutic outcomes in response to drug interactions and chemical exposures, to understanding the progression of some disease states, and to predicting the influence of genetic variation upon these processes. This review will focus on the organic anion transporter (OAT) family and discuss the known members, their mechanisms of action, subcellular localization, and current evidence implicating their function as a determinant of the toxicity of certain endogenous and xenobiotic agents.

Evidence-based use of methotrexate in children with rheumatic diseases: a consensus statement of the Working Groups Pediatric Rheumatology Germany (AGKJR) and Pediatric Rheumatology Austria

Juvenile idiopathic arthritis (JIA) is the most common diagnosis in children and adolescents with rheumatic disorders. In many children and adolescents, JIA is successfully treated with non-steroidal anti-inflammatory drugs (NSAID) and physiotherapy. However, in a significant number of cases the disease is resistant to this therapy, and treatment with "second line" disease-modifying antirheumatic drugs (DMARDs) is required. Methotrexate (MTX) is frequently referred to as "first-choice second-line agent" for the treatment of JIA. To increase drug safety, the Working Groups for Children and Adolescents with Rheumatic Diseases in Germany (AGKJR) and Pediatric Rheumatology Austria have initiated the formulation of evidence-based recommendations. Evidence is based on consensus expert meetings, a MEDLINE search with the key words "Methotrexate" and "juvenile arthritis" limited to age 0-18 years, standard textbooks and review articles, data from the central registry of the German Research Center for Rheumatic Diseases (Deutsches Rheumaforschungszentrum Berlin DRFZ), experience with MTX in adults with rheumatoid arthritis (RA), and recommendations of the German Society of Rheumatology (DGRh). Based on these data, evidence and recommendations are graded, and evidence-based recommendations for the use of MTX in children and adolescents with rheumatic disease are presented.

Inhibition of the human organic anion transporter 1 by the caffeine metabolite 1-methylxanthine

Caffeine (1,3,7-trimethylxanthine) is daily and widely consumed in beverages and food and is mainly metabolized to 1,7-dimethylxanthine and 1-methylxanthine. Indirect clinical evidence suggests that 1-methylxanthine interacts with the organic anion transport system in the human kidney. In this study the effect of caffeine and its main metabolites on the human organic anion transporter 1 (hOAT1) was investigated using CHO cells overexpressing hOAT1. The uptake of 6-carboxyfluorescein into CHO(hOAT) cells was significantly inhibited by > or = 100 microM of 1-methylxanthine. Five hundred micromolar 1-methylxanthine was equieffective to 100 microM probenecid. In contrast, caffeine and 1,7-dimethylxanthine did not inhibit the transport of 6-carboxyfluorescein at concentrations up to 500 microM. In conclusion, the caffeine metabolite 1-methylxanthine inhibits the transport activity of hOAT1 in vitro. The central involvement of hOAT1 in the renal excretion of numerous drugs suggests that this inhibition may alter the pharmacokinetics of a series of clinically important drugs in humans.

EFFECTS OF MORPHINE ON METHOTREXATE DISPOSITION IN MICE

1. Morphine has been shown to slow the renal excretion of other drugs. The present study in mice evaluated the effects of morphine on the disposition of methotrexate (MTX), an antimetabolite eliminated by the kidneys. 2. Mice were injected with morphine (20 mg/kg) or saline s.c. After 30 min, 20-80 mg/kg MTX was injected i.v. Blood and urine samples were assayed for MTX by HPLC. 3. Morphine reduced plasma clearance (CL) of MTX from 0.147 +/- 0.015 to 0.061 +/- 0.009 mL/min per g bodyweight (P < 0.01). The area under the plasma concentration-time curve (AUC(0- infinity )) was raised by morphine from 151 +/- 18 to 369 +/- 36 micro g.mL per min (P < 0.01). Without morphine administration, 22-27% of an MTX dose was excreted into the urine in 30 min. The corresponding fractions excreted into the urine after morphine were reduced to 15-18% (P < 0.01). 4. Plasma levels of MTX administered intravenously to mice are elevated by the concomitant administration of morphine, which reduces renal elimination of MTX.

Quantitative evaluation of the drug-drug interactions between methotrexate and nonsteroidal anti-inflammatory drugs in the renal uptake process based on the contribution of organic anion transporters and reduced folate carrier

The present study examined the possible role of transporters in the drug-drug interactions between methotrexate (MTX) and nonsteroidal anti-inflammatory drugs (NSAIDs) in the renal uptake process of MTX. MTX is recognized by reduced folate carrier (RFC-1) and rat organic anion transporters (rOat1 and rOat3) as a substrate. Uptake of MTX by kidney slices was saturable and inhibited potently by dibromosulfophthalein. Folate and benzylpenicillin (PCG) inhibited the uptake by 30 to 40% and 40 to 50% of the total saturable uptake of MTX by kidney slices, respectively, whereas the effect of p-aminohippurate (PAH) was minimal at the concentration selective for rOat1. In contrast, the uptake of 5-methyltetrahydrofolate by the kidney slices was inhibited by MTX, folate, and dibromosulfophthalein, but not by PAH and PCG. These results suggest that rOat3 and RFC-1 are almost equally involved in the uptake of MTX by the kidney slices, whereas RFC-1 is responsible for the renal uptake of 5-methyltetrahydrofolate. NSAIDs, except salicylate, were potent inhibitors of rOat3 (K(i) of 1.3-19 microM), but weak inhibitors of RFC-1 (K(i) of 70-310 microM). This is in a good agreement with the biphasic inhibition profiles of NSAIDs for the uptake of MTX by kidney slices. These results suggest that the renal uptake of MTX is not so greatly affected by NSAIDs as expected from the inhibition of rOat3-mediated transport.

Novel quinolinone-phosphonic acid AMPA antagonists devoid of nephrotoxicity

We reported previously the synthesis and structure-activity relationships (SAR) in a series of 2-(1H)-oxoquinolines bearing different acidic functions in the 3-position. Exploiting these SAR, we were able to identify 6,7-dichloro-2-(1H)-oxoquinoline-3-phosphonic acid compound 3 (S 17625) as a potent, in vivo active AMPA antagonist. Unfortunately, during the course of the development, nephrotoxicity was manifest at therapeutically effective doses. Considering that some similitude exists between S 17625 and probenecid, a compound known to protect against the nephrotoxicity and/or slow the clearance of different drugs, we decided to synthesise some new analogues of S 17625 incorporating some of the salient features of probenecid. Replacement of the chlorine in position 6 by a sulfonylamine led to very potent AMPA antagonists endowed with good in vivo activity and lacking nephrotoxicity potential. Amongst the compounds evaluated, derivatives 7a and 7s appear to be the most promising and are currently evaluated in therapeutically relevant stroke models.

Clinically relevant drug-drug interactions in oncology

Although anticancer agents are one of the most toxic classes of medication prescribed today, there is relatively little information available about clinically relevant drug-drug interactions. Pharmacokinetic drug interactions have been described, including alterations in absorption, catabolism, and excretion. For example, an increased bioavailability of 6-mercaptopurine has been observed when combined with either allopurinol or methotrexate, leading to increased toxicity in some patients. Induction of etoposide or teniposide clearance by anticonvulsants has also been described, resulting in a lower systemic exposure and risk for lower anticancer activity. Alterations in elimination of methotrexate has been observed with probenecid, presumably through competition for renal secretion. There are also several examples of pharmacodynamic interactions. The combination of 5-fluorouracil plus folinic acid results in more efficient inhibition of thymidylate synthase, a finding which is now utilized routinely in the treatment of colorectal cancer. Improvements in the in vitro and early clinical testing now allow a relatively high degree of prediction of potential clinical drug interactions, prior to observations of untoward drug effects. In conclusion, drug interactions among commonly used anticancer agents have been identified. Their clinical significance can have more impact than many other classes of medications due to the narrow therapeutic index of antineoplastic agents and the potential for lethal side-effects. It is only through prospective, preclinical and early clinical evaluation that the presence of clinically significant drug interactions can be identified and the information used to provide better therapy for this significant health problem.

Pharmacology and pharmacokinetics of methotrexate in rheumatic disease. Practical issues in treatment and design

Methotrexate (MTX) is among the most effective drugs for treatment of rheumatoid arthritis and has been proven valuable in the treatment of multiple other disorders of immune regulation. MTX has been administered at a wide range of doses and dose intervals, in conjunction with multiple other drugs, and in patients with a broad range of concomitant disorders. To design a safe and effective MTX treatment plan for an individual patient, the provider must have knowledge of the pharmacology and drug interactions of this effective but potentially dangerous medication. The first section of the article reviews MTX structure, pharmacology pharmacokinetics, and mechanisms of action in rheumatic disease. The second section examines factors that can be used to increase MTX efficacy and decrease toxicity.

Antineoplastic agents. Drug interactions of clinical significance

With the use of numerous drugs in the treatment of cancer, the potential for drug interactions is considerable. Because of the limited therapeutic indices of anticancer drugs, one should be aware that even small alterations in pharmacokinetics or pharmacodynamics may result in serious adverse effects. Pharmacokinetic drug interactions may alter absorption, bioavailability, distribution, metabolism and elimination patterns. For example, allopurinol inhibits the enzyme xanthine oxidase, thereby blocking the first-pass metabolism of mercaptopurine. Due to this drug interaction, plasma concentrations of mercaptopurine can increase up to 5-fold. Pharmacodynamic drug interactions are characterised by a similar or opposing pharmacological effect of both drugs upon the same biological system. For example, cotrimoxazole (trimethoprim-sulfamethoxazole) inhibits folic acid metabolism through direct binding to dihydrofolate reductase, an enzyme which is also inhibited by methotrexate. More pharmacological investigations are needed to understand the mechanisms and clinical implications of drug interactions with antineoplastic agents.

The effect of probenecid on paracetamol metabolism and pharmacokinetics

The influence of probenecid on the pharmacokinetics of paracetamol was investigated in a group of healthy volunteers. Pretreatment with probenecid caused a significant decrease in paracetamol clearance (6.23 to 3.42 ml.min-1.kg-1). The urinary excretion of paracetamol sulphate (243 to 193 mg); and paracetamol glucuronide (348 to 74.5 mg) were significantly reduced, whereas that of paracetamol was unchanged. Probenecid was shown to be an uncompetitive inhibitor of paracetamol glucuronidation in vitro, using rat liver microsomes.