Accumulation of lovastatin, but not pravastatin, in the blood of cyclosporine-treated kidney graft patients after multiple doses

Assessing Trans-Inhibition of OATP1B1 and OATP1B3 by Calcineurin and/or PPIase Inhibitors and Global Identification of OATP1B1/3-Associated Proteins

Organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are key determinants of drug-drug interactions (DDIs). Various drugs including the calcineurin inhibitor (CNI) cyclosporine A (CsA) exert preincubation-induced trans-inhibitory effects upon OATP1B1 and/or OATP1B3 (abbreviated as OATP1B1/3) by unknown mechanism(s). OATP1B1/3 are phosphoproteins; calcineurin, which dephosphorylates and regulates numerous phosphoproteins, has not previously been investigated in the context of preincubation-induced trans-inhibition of OATP1B1/3. Herein, we compare the trans-inhibitory effects exerted on OATP1B1 and OATP1B3 by CsA, the non-analogous CNI tacrolimus, and the non-CNI CsA analogue SCY-635 in transporter-overexpressing human embryonic kidney (HEK) 293 stable cell lines. Preincubation (10-60 min) with tacrolimus (1-10 µM) rapidly and significantly reduces OATP1B1- and OATP1B3-mediated transport up to 0.18 ± 0.03- and 0.20 ± 0.02-fold compared to the control, respectively. Both CsA and SCY-635 can trans-inhibit OATP1B1, with the inhibitory effects progressively increasing over a 60 min preincubation time. At each equivalent preincubation time, CsA has greater trans-inhibitory effects toward OATP1B1 than SCY-635. Preincubation with SCY-635 for 60 min yielded IC50 of 2.2 ± 1.4 µM against OATP1B1, which is ~18 fold greater than that of CsA (0.12 ± 0.04 µM). Furthermore, a proteomics-based screening for protein interactors was used to examine possible proteins and processes contributing to OATP1B1/3 regulation and preincubation-induced inhibition by CNIs and other drugs. A total of 861 and 357 proteins were identified as specifically associated with OATP1B1 and OATP1B3, respectively, including various protein kinases, ubiquitin-related enzymes, the tacrolimus (FK506)-binding proteins FKBP5 and FKBP8, and several known regulatory targets of calcineurin. The current study reports several novel findings that expand our understanding of impaired OATP1B1/3 function; these include preincubation-induced trans-inhibition of OATP1B1/3 by the CNI tacrolimus, greater preincubation-induced inhibition by CsA compared to its non-CNI analogue SCY-635, and association of OATP1B1/3 with various proteins relevant to established and candidate OATP1B1/3 regulatory processes.

Evaluation of the drug-drug interaction potential of the novel hepatitis B and D virus entry inhibitor bulevirtide at OATP1B in healthy volunteers

Introduction: Bulevirtide is a first-in-class antiviral drug to treat chronic hepatitis B/D. We investigated the drug-drug interaction potential and pharmacokinetics of high-dose subcutaneous bulevirtide (5 mg twice daily) with organic anion transporting polypeptide 1B1 (OATP1B1) and cytochrome P450 (CYP) 3A4. Methods: This was a single-center, open-label, fixed-sequence drug-drug interaction trial in 19 healthy volunteers. Before and at bulevirtide steady state, participants ingested a single 40 mg dose of pravastatin. A midazolam microdose was applied to quantify CYP3A4 activity. Results: At bulevirtide steady state, pravastatin area under the concentration-time curve (AUC_0-∞) increased 1.32-fold (90% CI 1.08-1.61). The 5 mg bulevirtide twice-daily treatment resulted in a mean AUC_0-12 of 1210 h*ng/ml (95% CI 1040-1408) and remained essentially unchanged under the influence of pravastatin. CYP3A4 activity did not change to a clinically relevant extent. As expected, total bile acids increased substantially (35-fold) compared to baseline during bulevirtide treatment. All study medication was well tolerated. Discussion: The study demonstrated that high-dose bulevirtide inhibited OATP1B-mediated hepatic uptake of the marker substrate pravastatin but the extent is considered clinically not relevant. Changes in CYP3A4 activity were also not clinically relevant. In conclusion, this study suggests that OATP1B substrate drugs as well as CYP3A4 substrates may safely be used without dose adjustment in patients treated with bulevirtide. However, in patients using high statin doses and where concomitant factors potentially further increase statin exposure, caution may be required when using bulevirtide.

Pharmacogenomics of lipid-lowering agents: the impact on efficacy and safety

Hyperlipidemia is a significant risk factor for cardiovascular disease morbidity and mortality. The lipid-lowering drugs are considered the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease. Unfortunately, the lack of efficacy and associated adverse effects, ranging from mild-to-moderate to potentially life-threatening, lead to therapy discontinuation. Numerous reports support the role of gene polymorphisms in drugs' pharmacokinetic parameters and their associated adverse reactions. Therefore, this study aims to understand the pharmacogenomics of lipid-lowering drugs and the impact of genetic variants of key genes on the drugs' efficacy and toxicity. Indeed, genetically guided lipid-lowering therapy enhances overall safety, improves drug adherence and achieves long-term therapy.

Choosing statins: a review to guide clinical practice

Statins are among the most widely prescribed medicines in the world and have proved their value in reducing cardiovascular events and mortality. Many patients report adverse effects that lead to interruption of treatment. This review aims to individualize statin treatment, considering efficacy for reducing cardiovascular risk and safety, in the setting of specific diseases, to minimize the side effects and improve compliance. We gathered evidence that may help clinicians to choose specific statins in different clinical situations, such as the risk of new diabetes, chronic kidney disease, liver disease, human immunodeficiency virus infection, organ transplant, heart failure and elderly people. Efficacy of statins is well established in a large number of clinical conditions. Therefore, main objective is to revise statin in specific clinical settings, based on pharmacokinetics, safety, drug metabolism and interactions to provide the best choice in different clinical scenarios.

Statin use and incident cardiovascular events in renal transplant recipients

BACKGROUND

Statins achieve potent LDL lowering in the general population leading to a significant cardiovascular (CV) risk reduction. In renal transplant recipients (RTR) statins are included in treatment guidelines, however, conclusive evidence of improved cardiovascular outcomes has not been uniformly provided and concerns have been raised about simultaneous use of statins and the immunosuppressant cyclosporine. This study aimed to elucidate the effect of statins on a compound CV endpoint, comprised of ischaemic CV events and CV mortality in RTR, with subgroup analysis focussing on cyclosporine users.

METHOD

622 included RTR (follow-up 5.4 years) were matched based on propensity scores and dichotomized by statin use. Survival analysis was conducted.

RESULTS

Cox regression showed that statin use was not significantly associated with the compound CV endpoint in a fully adjusted model (HR = 0.81, 95% CI = 0.53-1.24, P = .33). Subgroup analyses in RTR using cyclosporine revealed a strong positive association of statin use with the CV compound outcome in a fully adjusted model (HR = 6.60, 95% CI 1.75-24.9, P = .005). Furthermore, statin use was positively correlated with cyclosporine trough levels (correlation coefficient 0.11, P = .04).

CONCLUSION

In conclusion, statin use does not significantly decrease incident CV events in an overall RTR cohort, but is independently associated with CV-specific mortality and events in cyclosporine using RTR, possibly due to a bilateral pharmacological interaction.

Pharmacogenetics of Statin-Induced Myotoxicity

Statins, a class of lipid-lowering medications, have been a keystone treatment in cardiovascular health. However, adverse effects associated with statin use impact patient adherence, leading to statin discontinuation. Statin-induced myotoxicity (SIM) is one of the most common adverse effects, prevalent across all ages, genders, and ethnicities. Although certain demographic cohorts carry a higher risk, the impaired quality of life attributed to SIM is significant. The pathogenesis of SIM remains to be fully elucidated, but it is clear that SIM is multifactorial. These factors include drug-drug interactions, renal or liver dysfunction, and genetics. Genetic-inferred risk for SIM was first reported by a landmark genome-wide association study, which reported a higher risk of SIM with a polymorphism in the SLCO1B1 gene. Since then, research associating genetic factors with SIM has expanded widely and has become one of the foci in the field of pharmacogenomics. This review provides an update on the genetic risk factors associated with SIM.

Prediction of Cyclosporin-Mediated Drug Interaction Using Physiologically Based Pharmacokinetic Model Characterizing Interplay of Drug Transporters and Enzymes

Uptake transporter organic anion transporting polypeptides (OATPs), efflux transporters (P-gp, BCRP and MRP2) and cytochrome P450 enzymes (CYP450s) are widely expressed in the liver, intestine or kidney. They coordinately work to control drug disposition, termed as "interplay of transporters and enzymes". Cyclosporine A (CsA) is an inhibitor of OATPs, P-gp, MRP2, BCRP and CYP3As. Drug-drug interaction (DDI) of CsA with victim drugs occurs via disordering interplay of transporters and enzymes. We aimed to establish a whole-body physiologically-based pharmacokinetic (PBPK) model which predicts disposition of CsA and nine victim drugs including atorvastatin, cerivastatin, pravastatin, rosuvastatin, fluvastatin, simvastatin, lovastatin, repaglinide and bosentan, as well as drug-drug interactions (DDIs) of CsA with nine victim drugs to investigate the integrated effect of enzymes and transporters in liver, intestinal and kidney on drug disposition. Predictions were compared with observations. Most of the predictions were within 0.5-2.0 folds of observations. Atorvastatin was represented to investigate individual contributions of transporters and CYP3As to atorvastatin disposition and their integrated effect. The contributions to atorvastatin disposition were hepatic OATPs >> hepatic CYP3A > intestinal CYP3As ≈ efflux transporters (P-gp/BCRP/MRP2). The results got the conclusion that the developed PBPK model characterizing the interplay of enzymes and transporters was successfully applied to predict the pharmacokinetics of 10 OATP substrates and DDIs of CsA with 9 victim drugs.

Red Yeast Rice: A Systematic Review of the Traditional Uses, Chemistry, Pharmacology, and Quality Control of an Important Chinese Folk Medicine

Red yeast rice (RYR), a Chinese traditional folk medicine produced by the fermentation of cooked rice kernels with a Monascaceae mold, Monascus purpureus, has long been used to treat blood circulation stasis, indigestion, diarrhea, and limb weakness in East Asian countries. This article provides a systematic review of the traditional uses, chemistry, biological activities, and toxicology of RYR to highlight its future prospects in the field of medicine. The literature reviewed for this article was obtained from the Web of Science, Elsevier, SciFinder, PubMed, CNKI, ScienceDirect, and Google Scholar, as well as Ph.D. and M.Sc. dissertations, published prior to July 2019. More than 101 chemical constituents have been isolated from RYR, mainly consisting of monacolins, pigments, organic acids, sterols, decalin derivatives, flavonoids, polysaccharides, and other compounds. Crude extracts of RYR, as well as its isolated compounds, possess broad pharmacological properties with hypolipidemic, anti-atherosclerotic, anti-cancer, neurocytoprotective, anti-osteoporotic, anti-fatigue, anti-diabetic, and anti-hypertensive activities. However, further studies are needed to characterize its diverse chemical constituents and the toxicological actions of the main bioactive compounds. New pharmacological trials addressing the overlooked traditional uses of RYR, such as in the treatment of indigestion and diarrhea, are required.

Timing of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor initiation and allograft vasculopathy progression and outcomes in heart transplant recipients

Aims

Early studies from the 1990s have shown that statins improve survival and attenuate cardiac allograft vasculopathy (CAV). However, little contemporary data are available on the incremental benefit of statins with the current use of new‐generation immunosuppressive agents and the use of coronary intravascular ultrasound for assessment of CAV. We sought to investigate the effect of early statin (ES) as compared with late statin (LS) initiation after heart transplantation (HT) on long‐term CAV progression and clinical outcomes in a large contemporary HT cohort.

Methods and results

We analysed a cohort of 409 adult HT recipients. CAV progression was assessed by serial coronary intravascular ultrasound volumetric measurements of the differences between baseline and last follow‐up plaque volume (PV) and plaque index (PV/vessel volume ratio). CAV progression and clinical outcomes were compared between the ES (<2 years after HT) and the LS (>2 years after HT) groups. During a median follow‐up of 8.2 years, ES resulted in significantly lower change (Δ) of plaque index (+3.8% ± 1.7% vs. +8.2% ± 3.6%; P = 0.0008) and PV (+0.8 ± 0.3 vs. +1.9 ± 1.2; P = 0.045) compared with LS group. In a Cox proportional hazards regression model and after adjustment for baseline characteristics, ES was associated with a 52% decreased risk of CAV‐associated events (hazard ratio 0.48, 95% confidence interval: 0.27–0.91; P = 0.025) and a 42% decreased risk of the composite endpoint of all‐cause mortality and CAV‐associated events (hazard ratio 0.58, 95% confidence interval: 0.38–0.91; P = 0.019).

Conclusions

Early initiation of statin therapy after HT results in attenuated CAV progression as well as in decreased CAV‐related events and mortality.

Statin-Associated Side Effects

Hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors or statins are well tolerated, but associated with various statin-associated symptoms (SAS), including statin-associated muscle symptoms (SAMS), diabetes mellitus (DM), and central nervous system complaints. These are "statin-associated symptoms" because they are rare in clinical trials, making their causative relationship to statins unclear. SAS are, nevertheless, important because they prompt dose reduction or discontinuation of these life-saving mediations. SAMS is the most frequent SAS, and mild myalgia may affect 5% to 10% of statin users. Clinically important muscle symptoms, including rhabdomyolysis and statin-induced necrotizing autoimmune myopathy (SINAM), are rare. Antibodies against HMG-CoA reductase apparently provoke SINAM. Good evidence links statins to DM, but evidence linking statins to other SAS is largely anecdotal. Management of SAS requires making the possible diagnosis, altering or discontinuing the statin treatment, and using alternative lipid-lowering therapy.

Pediatric Statin Administration: Navigating a Frontier with Limited Data

Increasingly, children and adolescents with dyslipidemia qualify for pharmacologic intervention. As they are for adults, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins) are the mainstay of pediatric dyslipidemia treatment when lifestyle modifications have failed. Despite the overall success of these drugs, the magnitude of variability in dose-exposure-response profiles contributes to adverse events and treatment failure. In children, the cause of treatment failures remains unclear. This review describes the updated guidelines for screening and management of pediatric dyslipidemia and statin disposition pathway to assist the provider in recognizing scenarios where alterations in dosage may be warranted to meet patients' specific needs.

Translational insight into statin-induced muscle toxicity: from cell culture to clinical studies

Statins are lipid-lowering drugs used widely to prevent and treat cardiovascular and coronary heart diseases. These drugs are among the most commonly prescribed medicines intended for long-term use. In general, statins are well tolerated. However, muscular adverse effects appear to be the most common obstacle that limits their use, resulting in poor patient compliance or even drug discontinuation. In addition, rare but potentially fatal cases of rhabdomyolysis have been reported with the use of these drugs, especially in the presence of certain risk factors. Previous reports have investigated statin-induced myotoxicity in vivo and in vitro using a number of cell lines, muscle tissues, and laboratory animals, in addition to randomized clinical trials, observational studies, and case reports. None of them have compared directly results from laboratory investigations with clinical observations of statin-related muscular adverse effects. To the best of our knowledge this is the first review article that combines laboratory investigation with clinical aspects of statin-induced myotoxicity. By reviewing published literature of in vivo, in vitro, and clinically relevant studies of statin myotoxicity, we aim to translate this important drug-related problem to establish a clear picture of proposed mechanisms that explain the risk factors and describe the diagnostic approaches currently used for evaluating the degree of muscle damage induced by these agents. This review provides baseline novel translational insight that can be used to enhance the safety profile, to minimize the chance of progression of these adverse effects to more severe and potentially fatal rhabdomyolysis, and to improve the overall patient compliance and adherence to long-term statin therapy.

HMG CoA reductase inhibitors (statins) for kidney transplant recipients

BACKGROUND

People with chronic kidney disease (CKD) have higher risks of cardiovascular disease compared to the general population. Specifically, cardiovascular deaths account most deaths in kidney transplant recipients. Statins are a potentially beneficial intervention for kidney transplant patients given their established benefits in patients at risk of cardiovascular disease in the general population. This is an update of a review first published in 2009.

OBJECTIVES

We aimed to evaluate the benefits (reductions in all-cause and cardiovascular mortality, major cardiovascular events, myocardial infarction and stroke, and progression of CKD to requiring dialysis) and harms (muscle or liver dysfunction, withdrawal, cancer) of statins compared to placebo, no treatment, standard care, or another statin in adults with CKD who have a functioning kidney transplant.

SEARCH METHODS

We searched the Cochrane Renal Group's Specialised Register to 29 February 2012 through contact with the Trials Search Co-ordinator using search terms relevant to this review.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs that compared the effects of statins with placebo, no treatment, standard care, or statins on mortality, cardiovascular events, kidney function and toxicity in kidney transplant recipients.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed risk of bias. Treatment effects were expressed as mean difference (MD) for continuous outcomes (lipids, glomerular filtration rate (GFR), proteinuria) and relative risk (RR) for dichotomous outcomes (major cardiovascular events, mortality, fatal or non-fatal myocardial infarction, fatal or non-fatal stroke, elevated muscle or liver enzymes, withdrawal due to adverse events, cancer, end-stage kidney disease (ESKD), acute allograft rejection) together with 95% confidence intervals (CI).

MAIN RESULTS

We identified 22 studies (3465 participants); 17 studies (3282 participants) compared statin with placebo or no treatment, and five studies (183 participants) compared two different statin regimens.From data generally derived from a single high-quality study, it was found that statins may reduce major cardiovascular events (1 study, 2102 participants: RR 0.84, CI 0.66 to 1.06), cardiovascular mortality (4 studies, 2322 participants: RR 0.68, CI 0.45 to 1.01), and fatal or non-fatal myocardial infarction (1 study, 2102 participants: RR 0.70, CI 0.48 to 1.01); although effect estimates lack precision and include the possibility of no effect.Statins had uncertain effects on all-cause mortality (6 studies, 2760 participants: RR 1.08, CI 0.63 to 1.83); fatal or non-fatal stroke (1 study, 2102 participants: RR 1.18, CI 0.85 to 1.63); creatine kinase elevation (3 studies, 2233 participants: RR 0.86, CI 0.39 to 1.89); liver enzyme elevation (4 studies, 608 participants: RR 0.62, CI 0.33 to 1.19); withdrawal due to adverse events (9 studies, 2810 participants: RR 0.89, CI 0.74 to 1.06); and cancer (1 study, 2094 participants: RR 0.94, CI 0.82 to 1.07).Statins significantly reduced serum total cholesterol (12 studies, 3070 participants: MD -42.43 mg/dL, CI -51.22 to -33.65); low-density lipoprotein cholesterol (11 studies, 3004 participants: MD -43.19 mg/dL, CI -52.59 to -33.78); serum triglycerides (11 studies, 3012 participants: MD -27.28 mg/dL, CI -34.29 to -20.27); and lowered high-density lipoprotein cholesterol (11 studies, 3005 participants: MD -5.69 mg/dL, CI -10.35 to -1.03).Statins had uncertain effects on kidney function: ESKD (6 studies, 2740 participants: RR 1.14, CI 0.94 to 1.37); proteinuria (2 studies, 136 participants: MD -0.04 g/24 h, CI -0.17 to 0.25); acute allograft rejection (4 studies, 582 participants: RR 0.88, CI 0.61 to 1.28); and GFR (1 study, 62 participants: MD -1.00 mL/min, CI -9.96 to 7.96).Due to heterogeneity in comparisons, data directly comparing differing statin regimens could not be meta-analysed. Evidence for statins in people who have had a kidney transplant were sparse and lower quality due to imprecise effect estimates and provided limited systematic evaluation of treatment harm.

AUTHORS' CONCLUSIONS

Statins may reduce cardiovascular events in kidney transplant recipients, although treatment effects are imprecise. Statin treatment has uncertain effects on overall mortality, stroke, kidney function, and toxicity outcomes in kidney transplant recipients. Additional studies would improve our confidence in the treatment benefits and harms of statins on cardiovascular events in this clinical setting.

Evaluation of the pharmacokinetics and drug interactions of the two recently developed statins, rosuvastatin and pitavastatin

INTRODUCTION

Statins are the cornerstone of lipid-lowering therapy to reduce the risk of coronary heart disease. Rosuvastatin and pitavastatin are the two recently developed statins with less potential for drug interaction resulting in improved safety profiles.

AREAS COVERED

This review summarizes the pharmacokinetics and drug interactions of rosuvastatin and pitavastatin. The materials reviewed were identified by searching PubMed for publications using 'rosuvastatin', 'pitavastatin', 'statins', 'pharmacokinetics' and 'drug interaction' as the search terms.

EXPERT OPINION

Rosuvastatin and pitavastatin have favorable pharmacokinetic and safety profiles as their disposition does not depend on or is only marginally influenced by cytochrome P450 (CYP) enzymes, thus potentially reducing the risk of drug-drug interactions of these two statins with other drugs known to inhibit CYP enzymes. However, drug transporters play a significant role in the disposition of rosuvastatin and pitavastatin and drug interactions may occur through these. Genetic polymorphisms in drug transporters may also affect the pharmacokinetics, drug interactions and/or the lipid-lowering effect of these statins to a different extent.

A common rejection module (CRM) for acute rejection across multiple organs identifies novel therapeutics for organ transplantation

A set of 11 genes, termed the common rejection module, predicts acute graft rejection in solid organ transplant patients and may help to identify novel drug targets in transplantation.

Using meta-analysis of eight independent transplant datasets (236 graft biopsy samples) from four organs, we identified a common rejection module (CRM) consisting of 11 genes that were significantly overexpressed in acute rejection (AR) across all transplanted organs. The CRM genes could diagnose AR with high specificity and sensitivity in three additional independent cohorts (794 samples). In another two independent cohorts (151 renal transplant biopsies), the CRM genes correlated with the extent of graft injury and predicted future injury to a graft using protocol biopsies. Inferred drug mechanisms from the literature suggested that two FDA-approved drugs (atorvastatin and dasatinib), approved for nontransplant indications, could regulate specific CRM genes and reduce the number of graft-infiltrating cells during AR. We treated mice with HLA-mismatched mouse cardiac transplant with atorvastatin and dasatinib and showed reduction of the CRM genes, significant reduction of graft-infiltrating cells, and extended graft survival. We further validated the beneficial effect of atorvastatin on graft survival by retrospective analysis of electronic medical records of a single-center cohort of 2,515 renal transplant patients followed for up to 22 yr. In conclusion, we identified a CRM in transplantation that provides new opportunities for diagnosis, drug repositioning, and rational drug design.

Transporters and drug-drug interactions: important determinants of drug disposition and effects

Uptake and efflux transporters determine plasma and tissue concentrations of a broad variety of drugs. They are localized in organs such as small intestine, liver, and kidney, which are critical for drug absorption and elimination. Moreover, they can be found in important blood-tissue barriers such as the blood-brain barrier. Inhibition or induction of drug transporters by coadministered drugs can alter pharmacokinetics and pharmacodynamics of the victim drugs. This review will summarize in particular clinically observed drug-drug interactions attributable to inhibition or induction of intestinal export transporters [P-glycoprotein (P-gp), breast cancer resistance protein (BCRP)], to inhibition of hepatic uptake transporters [organic anion transporting polypeptides (OATPs)], or to inhibition of transporter-mediated [organic anion transporters (OATs), organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATEs), P-gp] renal secretion of xenobiotics. Available data on the impact of nutrition on transport processes as well as genotype-dependent, transporter-mediated drug-drug interactions will be discussed. We will also present and discuss data on the variable extent to which information on the impact of transporters on drug disposition is included in summaries of product characteristics of selected countries (SPCs). Further work is required regarding a better understanding of the role of the drug metabolism-drug transport interplay for drug-drug interactions and on the extrapolation of in vitro findings to the in vivo (human) situation.

Transporter-mediated drug-drug interactions

Drug-drug interactions are a serious clinical issue. An important mechanism underlying drug-drug interactions is induction or inhibition of drug transporters that mediate the cellular uptake and efflux of xenobiotics. Especially drug transporters of the small intestine, liver and kidney are major determinants of the pharmacokinetic profile of drugs. Transporter-mediated drug-drug interactions in these three organs can considerably influence the pharmacokinetics and clinical effects of drugs. In this article, we focus on probe drugs lacking significant metabolism to highlight mechanisms of interactions of selected intestinal, hepatic and renal drug transporters (e.g., organic anion transporting polypeptide [OATP] 1A2, OATP2B1, OATP1B1, OATP1B3, P-gp, organic anion transporter [OAT] 1, OAT3, breast cancer resistance protein [BCRP], organic cation transporter [OCT] 2 and multidrug and toxin extrusion protein [MATE] 1). Genotype-dependent drug-drug interactions are also discussed.

The evolution of the OATP hepatic uptake transport protein family in DMPK sciences: from obscure liver transporters to key determinants of hepatobiliary clearance

Over the last two decades the impact on drug pharmacokinetics of the organic anion transporting polypeptides (OATPs: OATP-1B1, 1B3 and 2B1), expressed on the sinusoidal membrane of the hepatocyte, has been increasingly recognized. OATP-mediated uptake into the hepatocyte coupled with subsequent excretion into bile via efflux proteins, such as MRP2, is often referred to as hepatobiliary excretion. OATP transporter proteins can impact some drugs in several ways including pharmacokinetic variability, pharmacodynamic response and drug-drug interactions (DDIs). The impact of transporter mediated hepatic clearance is illustrated with case examples, from the literature and also from the Pfizer portfolio. The currently available in vitro techniques to study the hepatic transporter proteins involved in the hepatobiliary clearance of drugs are reviewed herein along with recent advances in using these in vitro data to predict the human clearance of compounds recognized by hepatic uptake transporters.

In vivo CYP3A activity is significantly lower in cyclosporine-treated as compared with tacrolimus-treated renal allograft recipients

In vitro studies have identified cyclosporine and tacrolimus as CYP3A inhibitors. In the current study in renal allograft recipients, we used intravenously and orally administered midazolam as a drug probe to assess whether the study drugs at doses that are generally used in clinical practice have differential effects on in vivo hepatic and first-pass CYP3A activities. Systemic and apparent oral midazolam clearance were 24% (269 ± 73 vs. 354 ± 102 ml/min, P = 0.022) and 31% (479 ± 190 vs. 688 ± 265 ml/min, P = 0.013), respectively, lower in cyclosporine-treated patients (n = 20) than in matched tacrolimus-treated patients (n = 20). The latter displayed midazolam clearances similar to those in two larger cohorts of nonmatched tacrolimus-treated patients (n = 58 and n = 80) and to those receiving a calcineurin inhibitor-free regimen (n = 6). This implies that in vivo hepatic and first-pass CYP3A activities are significantly lower in patients receiving cyclosporine than in those receiving tacrolimus, indicating that, at the doses generally used in clinical practice, cyclosporine is the stronger of the two with respect to CYP3A inhibition. This observation has important implications in the context of drug-drug interactions in transplant recipients.

Influence of non-steroidal anti-inflammatory drugs on organic anion transporting polypeptide (OATP) 1B1- and OATP1B3-mediated drug transport

The transporter-mediated uptake of drugs from blood into hepatocytes is a prerequisite for intrahepatic drug action or intracellular drug metabolism before excretion. Therefore, uptake transporters, e.g., members of the organic anion transporting polypeptide (OATP) family are important determinants of drug pharmacokinetics. Highly and almost exclusively expressed in hepatocytes are the OATP family members OATP1B1 (SLCO1B1) and OATP1B3 (SLCO1B3). Drug substrates of OATP1B1 and OATP1B3 include antibiotics and HMG-CoA reductase inhibitors (statins). It has been demonstrated that administration of two or more drugs that are substrates for these hepatic uptake transporters may lead to transporter-mediated drug-drug interactions, resulting in altered transport kinetics for drug substrates. In this study we investigated whether non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol interact with OATP1B1 and OATP1B3 using the standard substrate BSP and the drug substrate pravastatin. Using human embryonic kidney cells stably expressing OATP1B1 or OATP1B3, we demonstrated that bromosulfophthalein uptake was inhibited by diclofenac, ibuprofen. and lumiracoxib. Of interest, pravastatin uptake was stimulated by these NSAIDs, and for ibuprofen we determined activation constants (EC₅₀ values) of 64.0 and 93.1 μM for OATP1B1- and OATP1B3-mediated uptake, respectively. Furthermore, we investigated whether NSAIDs were also substrates for OATP1B1 and OATP1B3 and demonstrated that only diclofenac was significantly transported by OATP1B3, whereas all other NSAIDs investigated were not substrates for these uptake transporters. These results demonstrated that drugs may interact with transport proteins by allosteric mechanisms without being substrates and, therefore, not only uptake inhibition but also allosteric-induced modulation of transport function may be an important mechanism in transporter-mediated drug-drug interactions.

Organic anion transporting polypeptide 1B1: a genetically polymorphic transporter of major importance for hepatic drug uptake

The importance of membrane transporters for drug pharmacokinetics has been increasingly recognized during the last decade. Organic anion transporting polypeptide 1B1 (OATP1B1) is a genetically polymorphic influx transporter expressed on the sinusoidal membrane of human hepatocytes, and it mediates the hepatic uptake of many endogenous compounds and xenobiotics. Recent studies have demonstrated that OATP1B1 plays a major, clinically important role in the hepatic uptake of many drugs. A common single-nucleotide variation (coding DNA c.521T>C, protein p.V174A, rs4149056) in the SLCO1B1 gene encoding OATP1B1 decreases the transporting activity of OATP1B1, resulting in markedly increased plasma concentrations of, for example, many statins, particularly of active simvastatin acid. The variant thereby enhances the risk of statin-induced myopathy and decreases the therapeutic indexes of statins. However, the effect of the SLCO1B1 c.521T>C variant is different on different statins. The same variant also markedly affects the pharmacokinetics of several other drugs. Furthermore, certain SLCO1B1 variants associated with an enhanced clearance of methotrexate increase the risk of gastrointestinal toxicity by methotrexate in the treatment of children with acute lymphoblastic leukemia. Certain drugs (e.g., cyclosporine) potently inhibit OATP1B1, causing clinically significant drug interactions. Thus, OATP1B1 plays a major role in the hepatic uptake of drugs, and genetic variants and drug interactions affecting OATP1B1 activity are important determinants of individual drug responses. In this article, we review the current knowledge about the expression, function, substrate characteristics, and pharmacogenetics of OATP1B1 as well as its role in drug interactions, in parts comparing with those of other hepatocyte-expressed organic anion transporting polypeptides, OATP1B3 and OATP2B1.

Impact of statins on cardiovascular outcomes in renal transplant recipients: a systematic review

Patients with chronic kidney disease including renal transplant recipients (RTRs) have a markedly higher prevalence of cardiovascular disease than the general population. Many trials have established the role of statins in the prevention of cardiovascular mortality, not only by decreasing the low density lipoprotein-cholesterol levels but also by their pleotropic effects. These data from the general population may not be applicable to RTRs as these patients have different cardiovascular risk profiles. Till date, only a few prospective, randomized trials have assessed the use of statins in RTRs with regards to cardiovascular outcomes. The Assessment of Lescol in Renal Transplant trial, the largest trial so far, suggested that dyslipidemia management with statins in RTRs is associated with a significant reduction in the incidence of cardiac death and nonfatal myocardial infarction (although differences in the combined primary end point were not statistically significant). The current guidelines from National Kidney Foundation for managing dyslipidemia in RTRs recommend managing all chronic kidney disease patients as a coronary heart disease equivalent. The task group for drafting these guidelines concluded that based on the currently available evidence, additional studies may be needed in RTRs to confirm and extend the results of Assessment of Lescol in Renal Transplant trial.

Drug interactions in transplant patients: what everyone should know

PURPOSE OF REVIEW

Adverse events due to drug-drug interactions remain a challenge in the postsurgical care of transplant recipients. A combination of potent and selective immunosuppressive drugs, which have a narrow therapeutic index, with medications for the treatment of comorbidities such as dyslipidemia, infection, psychiatric conditions, and hypertension, can lead to life-threatening drug-drug interactions.

RECENT FINDINGS

There are a number of important drug-drug interactions which are important for physicians to consider. It is critical to understand the pharmacodynamics and pharmacokinetics of drug-drug interactions, their potential impact on patient care, and the management strategies.

SUMMARY

Close therapeutic drug monitoring and evaluation of drug-specific side effects continue to be an important key to minimize adverse events due to drug-drug interactions.

Impact of OATP transporters on pharmacokinetics

Membrane transporters are now recognized as important determinants of the transmembrane passage of drugs. Organic anion transporting polypeptides (OATP) form a family of influx transporters expressed in various tissues important for pharmacokinetics. Of the 11 human OATP transporters, OATP1B1, OATP1B3 and OATP2B1 are expressed on the sinusoidal membrane of hepatocytes and can facilitate the liver uptake of their substrate drugs. OATP1A2 is expressed on the luminal membrane of small intestinal enterocytes and at the blood-brain barrier, potentially mediating drug transport at these sites. Several clinically used drugs have been identified as substrates of OATP transporters (e.g. many statins are substrates of OATP1B1). Some drugs may inhibit OATP transporters (e.g. cyclosporine) causing pharmacokinetic drug-drug interactions. Moreover, genetic variability in genes encoding OATP transporters can result in marked inter-individual differences in pharmacokinetics. For example, a single nucleotide polymorphism (c.521T > C, p.Val174Ala) in the SLCO1B1 gene encoding OATP1B1 decreases the ability of OATP1B1 to transport active simvastatin acid from portal circulation into the liver, resulting in markedly increased plasma concentrations of simvastatin acid and an enhanced risk of simvastatin-induced myopathy. SLCO1B1 polymorphism also affects the pharmacokinetics of many other, but not all (fluvastatin), statins and that of the antidiabetic drug repaglinide, the antihistamine fexofenadine and the endothelin A receptor antagonist atrasentan. This review compiles the current knowledge about the expression and function of human OATP transporters, their substrate and inhibitor specificities, as well as pharmacogenetics.

Successful strategy to improve the specificity of electronic statin-drug interaction alerts

PURPOSE

A considerable weakness of current clinical decision support systems managing drug-drug interactions (DDI) is the high incidence of inappropriate alerts. Because DDI-induced, dose-dependent adverse events can be prevented by dosage adjustment, corresponding DDI alerts should only be issued if dosages exceed safe limits. We have designed a logical framework for a DDI alert-system that considers prescribed dosage and retrospectively evaluates the impact on the frequency of statin-drug interaction alerts.

METHODS

Upper statin dose limits were extracted from the drug label (SPC) (20 statin-drug combinations) or clinical trials specifying the extent of the pharmacokinetic interaction (43 statin-drug combinations). We retrospectively assessed electronic DDI alerts and compared the number of standard alerts to alerts that took dosage into account.

RESULTS

From among 2457 electronic prescriptions, we identified 73 high-risk statin-drug pairs. Of these, SPC dosage information classified 19 warnings as inappropriate. Data from pharmacokinetic trials took quantitative dosage information more often into consideration and classified 40 warnings as inappropriate. This is a significant reduction in the number of alerts by 55% compared to SPC-based information (26%; p < 0.001).

CONCLUSION

This retrospective study of pharmacokinetic statin interactions demonstrates that more than half of the DDI alerts that presented in a clinical decision support system were inappropriate if DDI-specific upper dose limits are not considered.

The use of ciclosporin in psoriasis

Ciclosporin is a cyclic undecapeptide discovered in the 1970s to possess a potent inhibitory action on T lymphocytes. The subsequent discovery, in 1979, that it was remarkably effective in treatment of psoriasis transformed thinking about the nature of the disease, which subsequently became generally recognized as autoimmune in nature. Ciclosporin remains one of the most effective and rapidly acting treatments currently available for psoriasis. Virtually all the diverse manifestations of this disease can respond. The main side effects are nephrotoxicity and hypertension. There is considerable variation between individuals in susceptibility to these so careful monitoring is required. Ciclosporin should be used in single or intermittent short courses for all except the most severe cases as this is safer than continuous treatment. The rate of improvement depends very much on the dose, which ranges from 2 to 5.0 mg/kg/day. Ciclosporin can be combined with any topical treatment and a useful dose-sparing effect can be achieved in this way if patients are compliant. In severe cases ciclosporin is often used in combination with other systemic antipsoriatic drugs in order to spare the dose of each agent and reduce toxicity. Concurrent or intercurrent use of ultraviolet therapy is discouraged due to the increased risk of non-melanoma skin cancer. This article reviews the mode of action, pharmacokinetics, indications, contraindications, side effects, dosage regimens, pretreatment screening and monitoring, drug interactions, and use of treatment combinations with ciclosporin in the management of psoriasis.

Rhabdomyolysis reports show interaction between simvastatin and CYP3A4 inhibitors

PURPOSE

To assess spontaneous reports of rhabdomyolysis associated with simvastatin (SV) and pravastatin (PV) for evidence of CYP3A4 interaction. Clinical trial results advocate cholesterol lowering in high-risk patients including diabetics and the elderly. Given the association between advancing age, metabolic, and cardiovascular disease, many patients are treated with concomitant medications upon statin initiation. Although statins are generally safe, minor and severe adverse reactions arise, especially when given to patients taking concomitant medications that inhibit the statin clearance and lead to increased statin plasma concentration.

METHODS

We conducted a comparative case series of rhabdomyolysis reports associated with SV and PV. Domestic spontaneous reports were obtained from the FDA's Adverse Event Reporting System (AERS). Drug utilization data were obtained from IMS HEALTH and the National Ambulatory Medical Care Survey (NAMCS). Adverse event reporting rates (AER) and ratios (AERR) of rhabdomyolysis associated with SV and PV-with and without stratification by CYP3A4 inhibitor concomitancy were determined.

RESULTS

Stratification by CYP3A4 inhibitor concomitancy did not change the rhabdomyolysis AER for PV with or without a CYP3A4 inhibitor (2.4 cases and 3.1 cases per 10 million Rx, respectively). However, stratification of SV reports with or without a concomitant CYP3A4 inhibitor resulted in a rhabdomyolysis AER (38.4 and 6.0 cases per 10 million Rx, respectively). The corresponding AERR with or without a CYP3A4 inhibitor were 0.77 for PV and 6.43 for SV.

CONCLUSIONS

Spontaneous adverse event reports provide evidence of increased risk for rhabdomyolysis based on interaction between SV and selected CYP3A4 inhibitors.

Adverse drug reactions in patients with cardiovascular disease

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

Drug/Drug interaction between lopinavir/ritonavir and rosuvastatin in healthy volunteers

OBJECTIVES

This open-label, single-arm, pharmacokinetic (PK) study in HIV-seronegative volunteers evaluated the bioequivalence of rosuvastatin and lopinavir/ritonavir when administered alone and in combination. Tolerability and lipid changes were also assessed.

METHODS

Subjects took 20 mg of rosuvastatin alone for 7 days, then lopinavir/ritonavir alone for 10 days, and then the combination for 7 days. Intensive PK sampling was performed on days 7, 17, and 24.

RESULTS

Twenty subjects enrolled, and PK data were available for 15 subjects. Geometric mean (+/-SD) rosuvastatin area under the concentration time curve (AUC)[0,tau] and maximum concentration (Cmax) were 47.6 ng.h/mL (+/-15.3) and 4.34 ng/mL (+/-1.8), respectively, when given alone versus 98.8 ng.h/mL (+/-65.5) and 20.2 ng/mL (+/-16.9) when combined with lopinavir/ritonavir (P < 0.0001). The geometric mean ratio was 2.1 (90% confidence interval [CI]: 1.7 to 2.6) for rosuvastatin AUC[0,tau] and 4.7 (90% CI: 3.4 to 6.4) for rosuvastatin Cmax with lopinavir/ritonavir versus rosuvastatin alone (P < 0.0001). There was 1 asymptomatic creatine phosphokinase elevation 17 times the upper limit of normal (ULN) and 1 liver function test elevation between 1.1 and 2.5 times the ULN with the combination.

CONCLUSIONS

Rosuvastatin low-density lipoprotein reduction was attenuated with lopinavir/ritonavir. Rosuvastatin AUC and Cmax were unexpectedly increased 2.1- and 4.7-fold in combination with lopinavir/ritonavir. Rosuvastatin and lopinavir/ritonavir should be used with caution until the safety, efficacy, and appropriate dosing of this combination have been demonstrated in larger populations.

Role of OATP transporters in the disposition of drugs

During recent years, it has become increasingly recognized that drug transporters play important roles in drug absorption and disposition. Organic anion transporting polypeptides (OATPs) are membrane transporters critically involved in the cellular uptake of drugs in tissues important for pharmacokinetics, such as the intestine, liver and kidneys. Recent advances in the pharmacogenomics of OATP1B1 have revealed that OATP transporters can play important roles in explaining interindividual variability in drug pharmacokinetics, and thus contribute to interindividual as well as interethnic variability in drug response. This article will provide an up-to-date review of human OATPs and their substrates, and a current compilation of their DNA sequence variations.

Multiple Inhibition Mechanisms and Prediction of Drug–Drug Interactions: Status of Metabolism and Transporter Models as Exemplified by Gemfibrozil–Drug Interactions

PURPOSE

To assess the consequences of multiple inhibitors and differential inhibition mechanisms on the prediction of 12 gemfibrozil drug-drug interactions (DDIs). In addition, qualitative zoning of transporter-related gemfibrozil and cyclosporine DDIs was investigated.

METHODS

The effect of gemfibrozil and its acyl-glucuronide on different enzymes was incorporated into a metabolic prediction model. The impact of CYP2C8 time-dependent inhibition by gemfibrozil acyl-glucuronide was assessed using repaglinide, cerivastatin, loperamide, rosiglitazone and pioglitazone DDIs. Gemfibrozil and cyclosporine inhibition data obtained in human embryonic kidney cells expressing OATP1B1 and hepatic input concentration ([I]in) were used for qualitative zoning of 14 transporter-mediated DDIs.

RESULTS

Incorporation of time-dependent inhibition by gemfibrozil glucuronide showed no significant improvement in the prediction, as CYP2C8 contributed <65% to the overall elimination of the victim drugs investigated. Qualitative zoning of OATP1B1 DDIs resulted in no false negative predictions; yet the magnitude of observed interactions was significantly over-predicted.

CONCLUSIONS

Time-dependent inhibition by gemfibrozil glucuronide is only important for victim drugs eliminated predominantly (>80%) via CYP2C8. Qualitative zoning of OATP1B1 inhibitors based on [I]in/K (i) is valid in drug screening to avoid false negatives. Refinement of the transporter model by incorporating the fraction of drug transported by a particular transporter is recommended.

The unique character of cardiovascular disease in chronic kidney disease and its implications for treatment with lipid-lowering drugs

Although the risk for cardiovascular disease (CVD) is high in individuals with chronic kidney disease (CKD), there are very limited data to guide the use of lipid-lowering drugs (LLDs) in this population because the major trials of LLDs in the general population have included very few individuals with CKD. The pathophysiologic and epidemiologic differences of CVD in the CKD population suggest that the study findings derived in the general population may not be directly applicable to those with CKD, and the few trials that have been directed at patients with kidney disease have not shown clear clinical benefits of LLDs. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) Work Group has provided consensus-based guidelines for managing dyslipidemias in individuals with CKD and after renal transplantation. Since the publication of these statements, further data have emerged and multiple studies are ongoing to define better the role of LLDs in patients with CKD. In this article, the data that are pertinent to the CKD population are reviewed, and updated recommendations for use of LLD in the CKD population are provided.

Effect of cyclosporine and tacrolimus on cytochrome p450 activities in human liver microsomes

The effects of cyclosporine and tacrolimus on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated debrisoquine 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, CYP3A4-mediated nifedipine oxidation, and CYP3A4-mediated testosterone 6beta-hydroxylation activities in human liver microsomes were compared. Cyclosporine and tacrolimus, at concentrations of 0.2 or 2 muM, neither inhibited nor stimulated any of the metabolic activities except for those of CYP3A4. On the other hand, cyclosporine and tacrolimus competitively inhibited CYP3A4-mediated nifedipine oxidation activity, with inhibition constants (K(i)) of 1.42 and 0.36 muM, respectively. In addition, 20 muM cyclosporine inhibited CYP2C19 and CYP2D6 activities by 29% and 30%, respectively. These results suggest that tacrolimus would not cause clinically significant interactions with other drugs, which are metabolized by CYPs, via the inhibition of hepatic metabolism and that the reason why cyclosporine, but not tacrolimus, has a pharmacokinetic inhibitory effect might be that the dosage and/or the unbound concentrations around its metabolic enzymes are higher than those of tacrolimus, rather than the differences in the inhibition potential. Obvious substrate-dependent effects on CYP3A4-inhibition potential were not observed.

Pharmacokinetics and response to pravastatin in paediatric patients with familial hypercholesterolaemia and in paediatric cardiac transplant recipients in relation to polymorphisms of the SLCO1B1 and ABCB1 genes

AIMS

Our aim was to investigate associations between the single nucleotide polymorphisms (SNPs) in the SLCO1B1 (encoding OATP1B1) and ABCB1 (encoding P-glycoprotein) genes with the pharmacokinetics and efficacy of pravastatin in children with heterozygous familial hypercholesterolaemia (HeFH) and in paediatric cardiac transplant recipients.

METHODS

Twenty children with HeFH (aged 4.9-15.6 years) and 12 cardiac transplant recipients (aged 4.4-18.7 years and receiving triple immunosuppressive medication) who had participated in previous pharmacokinetic and pharmacodynamic studies with pravastatin were genotyped for the -11187G > A and 521T > C SNPs in the SLCO1B1 gene and for the 2677G > T/A and 3435C > T SNPs in the ABCB1 gene.

RESULTS

Two HeFH patients with the -11187GA genotype had a 81% lower peak plasma pravastatin concentration (Cmax) (difference in means -13.9 ng ml(-1), 95% CI -21.1, -6.7; P < 0.001) and a 74% smaller area under the plasma concentration-time curve (AUC0, infinity) (-25.3 ng ml(-1) h, 95% CI -35.6, -15.0; P < 0.0001) and significantly greater increase in high density lipoprotein (HDL) cholesterol after 2 months treatment with pravastatin than patients with the reference genotype. No significant differences were seen in the pharmacokinetics or effects of pravastatin between HeFH patients with the SLCO1B1 521TC and 521TT genotypes. The cardiac transplant recipients with the SLCO1B1 521TC genotype (n = 3) had a 46% lower Cmax (-67.7 ng ml(-1), 95% CI -135.7, 0.3; P = 0.055) and 62% lower AUC(0,24 h) (-228.5 ng ml(-1) h, 95% CI -402.7, -54.3; P = 0.016) and a shorter half-life (t1/2) (0.9 +/- 0.1 vs. 1.3 +/- 0.4 h, P = 0.015) of pravastatin than those with the reference genotype. Decreases in total and low-density lipoprotein cholesterol by pravastatin were significantly smaller, and the increase in HDL-cholesterol was greater in the transplant recipients with the 521TC genotype compared with patients with the 521TT reference genotype.

CONCLUSIONS

In children with HeFH and in paediatric cardiac transplant recipients receiving immunosuppressive medication, the -11187G > A and SLCO1B1 521T > C SNPs were associated with decreased plasma concentrations of pravastatin. These differences are opposite to those seen previously in healthy adults. The mechanisms underlying these phenomena are unclear and warrant further study.

Statins and myotoxicity: a therapeutic limitation

Hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors represent the most successful class of drugs for the treatment of hypercholesterolaemia and dyslipidaemia implicated in the pathogenesis of coronary heart disease and atherosclerosis. However, the popular profile of statins in terms of efficacy has been maligned by its adverse events. The myotoxicity, ranging from mild myopathy to serious rhabdomyolysis, associated with HMG-CoA reductase inhibitors, during treatment of hypercholesterolaemia is of paramount importance. Rhabdomyolysis is a rare but idiosyncratic muscle wasting disorder of different etiologies. Statin-associated rhabdomyolysis causes skeletal muscle injury by self-perpetuating events leading to fatal irreversible renal damage through a series of biochemical reactions. Preferential distribution and action of statins in liver could be the key to minimise myotoxicity concerns. Hepato-specific distribution of statins is governed by various factors such as physicochemical properties, pharmacokinetic properties and selective transporter-mediated uptake in liver rather in extrahepatic cells. The interactions of statins with concomitant drugs of different classes merit attention for their safety profile. Although pharmacokinetic as well as pharmacodynamic interactions have been implicated in pathophysiology of statin-induced muscle wasting, the underlying mechanism is not clearly understood. Besides, pharmacokinetic and phramcodynamic factors, statin-associated myotoxcity may also implicate pharmacogenomic factors. The pharmacogenomics characterised by CYP polymorphism and other genetic factors is responsible for inter-individual variations to efficacy and tolerability of statins. The pathophysiological mechanisms may include statin-induced differences in cholesterol:phospholipid ratio, isoprenoid levels, small GTP binding proteins and apoptosis. However, the present understanding of pathophysiological mechanisms, does not offer a reliable approach to address the same at preclinical level. Although statin-associated myotoxicity affects compliance, quality of life of patient and discontinuation rate, yet the low incidence of myotoxicty including rhabdomyolysis and less severity of commonly occurring myopathy and myalgia do not raise doubts about the clinical efficacy and tolerability of statins. Medical management of myotoxicity seems to be pivotal for the proper compliance of patients with statin treatment. The appropriate and judicious use of drugs would substantially reduce the likelihood of developing clinically important myopathy.

Statin-induced rhabdomyolysis

Simvastatin and other HMG-CoA reductase inhibitors (statins) are one of the most frequently prescribed class of medications in the United States, with over 15 million Americans taking these drugs. Relatively rare adverse effects related to the known toxic effects of these drugs are more common than generally realized. Clinically significant statin-induced rhabdomyolysis is an uncommon but life-threatening adverse effect. We describe a case of simvastatin-induced rhabdomyolysis. Current knowledge of the pharmacology of the HMG-CoA reductase inhibitors and the drug interactions that potentiate these adverse effects are discussed. The clinical features of rhabdomyolysis and current treatment recommendations are presented.

Drug-drug interaction between pitavastatin and various drugs via OATP1B1

It has already been demonstrated that pitavastatin, a novel potent HMG-coenzyme A reductase inhibitor, is taken up into human hepatocytes mainly by organic anion transporting polypeptide (OATP) 1B1. Because OATP2B1 is also localized in the basolateral membrane of human liver, we took two approaches to further confirm the minor contribution of OATP2B1 to the hepatic uptake of pitavastatin. Western blot analysis revealed that the ratio of the band density of OATP2B1 in human hepatocytes to that in our expression system is at least 6-fold lower compared with OATP1B1 and OATP1B3. The uptake of pitavastatin in human hepatocytes could be inhibited by both estrone-3-sulfate (OATP1B1/OATP2B1 inhibitor) and estradiol-17beta-D-glucuronide (OATP1B1/OATP1B3 inhibitor). These results further supported the idea that OATP1B1 is a predominant transporter for the hepatic uptake of pitavastatin. Then, to explore the possibility of OATP1B1-mediated drug-drug interaction, we checked the inhibitory effects of various drugs on the pitavastatin uptake in OATP1B1-expressing cells and evaluated whether the in vitro inhibition was clinically significant or not. As we previously reported, we used the methodology for estimating the maximum unbound concentration of inhibitors at the inlet to the liver (I(u,in,max)). Judging from I(u,in,max) and inhibition constant (K(i)) for OATP1B1, several drugs (especially cyclosporin A, rifampicin, rifamycin SV, clarithromycin, and indinavir) have potentials for interacting with OATP1B1-mediated uptake of pitavastatin. The in vitro experiments could support the clinically observed drug-drug interaction between pitavastatin and cyclosporin A. These results suggest that we should pay attention to the concomitant use of some drugs with pitavastatin.

Pharmacokinetic and pharmacodynamic alterations of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors: drug-drug interactions and interindividual differences in transporter and metabolic enzyme functions

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are widely used for the treatment of hypercholesterolemia. Their efficacy in preventing cardiovascular events has been shown by a large number of clinical trials. However, myotoxic side effects, sometimes severe, including myopathy or rhabdomyolysis, are associated with the use of statins. In some cases, such toxicity is associated with pharmacokinetic alterations. In this review, the pharmacokinetic aspects and physicochemical properties of statins are reviewed in order to understand the mechanism governing their pharmacokinetic alterations. Among the statins, simvastatin, lovastatin and atorvastatin are metabolized by cytochrome P450 3A4 (CYP3A4) while fluvastatin is metabolized by CYP2C9. Cerivastatin is subjected to 2 metabolic pathways mediated by CYP2C8 and 3A4. Pravastatin, rosuvastatin and pitavastatin undergo little metabolism. Their plasma clearances are governed by the transporters involved in the hepatic uptake and biliary excretion. Also for other statins, which are orally administered as open acid forms (i.e. fluvastatin, cerivastatin and atorvastatin), hepatic uptake transporter(s) play important roles in their clearances. Based on such information, pharmacokinetic alterations of statins can be predicted following coadministration of other drugs or in patients with lowered activities in drug metabolism and/or transport. We also present a quantitative analysis of the effect of some factors on the pharmacokinetics of statins based on a physiologically based pharmacokinetic model. To avoid a pharmacokinetic alteration, we need to have information about the metabolizing enzyme(s) and transporter(s) involved in the pharmacokinetics of statins and, along with such information, model-based prediction is also useful.

Simvastatin: a review

Simvastatin is a long-established hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, first introduced in 1988. At the maximal recommended dose of 80 mg/day, it produces an average reduction in low-density lipoprotein cholesterol (LDL-C) of 47%, accompanied by reductions in very LDL-C, triglycerides and apolipoprotein B, and a modest increase in high-density lipoprotein cholesterol. The only important, although rare, adverse effect of simvastatin is myopathy, an effect shared by all members of the class; when severe, this can take the form of rhabdomyolysis, which may lead to acute renal failure. The mechanism of the myopathy is not understood. The risk is increased by certain concomitant drugs, including gemfibrozil and potent inhibitors of cytochrome P450 3A4. Simvastatin has been studied in two large outcome trials, the Scandinavian Simvastatin Survival Study (4S), and the Heart Protection Study (HPS), both of which demonstrated strikingly beneficial effects on a variety of cardiovascular outcomes, with minimal adverse effects. 4S was the first study with a cholesterol-lowering agent to demonstrate an unequivocal reduction in all-cause mortality (30%; p = 0.0003). HPS showed that the beneficial effects of simvastatin were obtainable in a broad array of patients with, or at high risk of, coronary heart disease (CHD) in categories previously little studied, including women, the elderly, patients with diabetes without known CHD, and, perhaps most importantly, patients with LDL-C well below the UK population average. Simvastatin has recently become available in many countries as a combination product with the cholesterol absorption inhibitor, ezetimibe. Because of its long record of safety and demonstrated ability to reduce cardiovascular risk, simvastatin has recently become available without a prescription in the UK at the 10 mg dosage level.

Statin safety and drug interactions: clinical implications

The risks of muscle adverse events related to use of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, increase significantly with the addition of interacting drugs to a patient's therapy. The mechanism for most statin drug interactions involves the cytochrome P-450 system, which provides an indication of which drugs may interact. However, it is difficult to predict the probability of a drug interaction in a given patient because there are individual differences in sensitivity to increased statin drug levels. Drug metabolism studies show simvastatin and lovastatin to be especially sensitive to the inhibiting effects of other drugs on the cytochrome P-450 3A4 (CYP3A4) isoenzyme. Atorvastatin metabolism is less affected by inhibitors of this isoenzyme. Case reports, postmarketing surveillance, and clinical trial data demonstrate the clinical effect of CYP3A4 inhibitors on statins. Also, through possible inhibition of statin biliary excretion and glucuronidation, gemfibrozil given concomitantly with rosuvastatin, lovastatin, and simvastatin significantly increases the risk of myopathy and rhabdomyolysis, a potentially life-threatening consequence of statin drug interactions.

The role of transporters in drug interactions

Transport proteins play an important role in the adsorption, distribution and elimination of a wide variety of drugs. Therefore, it is not surprising that transporter-based drug interactions can occur in the clinic. These interactions can lead to changes in toxicity and/or efficacy of the affected drug. Here, we review such interactions and ask if these interactions could have been predicted from in vitro data. Conducting such in vitro-in vivo correlation is important for predicting future transporter-based drug interactions.

Ezetimibe in Renal Transplant Patients with Hyperlipidemia Resistant to HMG-CoA Reductase Inhibitors

Hyperlipidemia affects the majority of renal transplant patients. Multiple risk factors contribute to elevated serum cholesterol including the use of certain immunosuppressant agents. HMG-Co A reductase inhibitors have become the preferred class of cholesterol-lowering medication with an increasing body of evidence to support their safety, efficacy, and outcomes in both the normal and renal transplant populations. New guidelines recommend lowering previous LDL-c goals as outcomes appears to continually improve. As a result, ezetimibe has been added to patients with persistently elevated triglycerides and/or LDL-c in individuals who possessed a renal transplant and were deemed to be on a maximum safe dose of statin agent. After the addition of ezetimibe, total cholesterol, LDL-c, and triglycerides fell by 21%, 31%, and 13%, respectively. Creatinine phosphokinase, liver enzyme serum levels, and renal function were not affected to any level of clinical significance with the addition of ezetimibe. Large interpatient variability of measurable immunosuppressant levels was seen but no serious adverse events were attributed to a change in levels.