Comparative pharmacokinetic interaction profiles of pravastatin, simvastatin, and atorvastatin when coadministered with cytochrome P450 inhibitors

Drug-drug interactions mediated by hepatic transporters

Transporters are a class of functional membrane proteins that are extensively expressed in the liver and are involved in the transport of a wide variety of compounds including endogenous and xenobiotic substances from the bloodstream into hepatocytes. And then, these parent substances are metabolized in the liver and excreted into bile. Hepatic transporters play important roles in the hepatic transport process of drugs, including the uptake of drugs from blood into hepatocytes or the efflux of drugs into bile. The uptake, metabolism and excretion of drugs in the liver are related to hepatic transporters. Decline or loss of transporting function of transporters caused by gene mutations is related with a variety of liver diseases. Drug-drug interaction may be induced when one drug (as a substrate or inhibitor of hepatic transporters) is co-administered simultaneously with another in clinical practice, such as adverse events of cerivastatin. In this paper, we review the potential drug-drug interactions mediated by hepatic transporters.

Pediatric pharmacogenomics: a systematic assessment of ontogeny and genetic variation to guide the design of statin studies in children

The dose-exposure-response relationship for drugs may differ in pediatric patients compared with adults. Many clinical studies have established drug dose-exposure relationships across the pediatric age spectrum; however, genetic variation was seldom included. This article applies a systematic approach to determine the relative contribution of development and genetic variation on drug disposition and response using HMG-CoA reductase inhibitors as a model. Application of the approach drives the collection of information relevant to understanding the potential contribution of ontogeny and genetic variation to statin dose-exposure-response in children, and identifies important knowledge deficits to be addressed through the design of future studies.

Pharmacokinetic interaction studies of co-administration of ticagrelor and atorvastatin or simvastatin in healthy volunteers

PURPOSE

Interactions between ticagrelor and atorvastatin or simvastatin were investigated in two-way crossover studies.

METHODS

Both studies were open-label for statin; the atorvastatin study was placebo-controlled for ticagrelor. For atorvastatin, volunteers (n = 24) received ticagrelor (loading dose 270 mg; 90 mg twice daily, 7 days) or placebo, plus atorvastatin calcium (80 mg; day 5). For simvastatin, volunteers (n = 24) received simvastatin 80 mg, or ticagrelor (loading dose 270 mg; 180 mg twice daily, 7 days) plus simvastatin (80 mg; day 5). In each study, volunteers received the alternate treatment after washout (≥ 7 days).

RESULTS

Ticagrelor increased mean atorvastatin maximum plasma concentration (C(max)) and area under the plasma concentration-time curve from zero to infinity (AUC) by 23 % and 36 %, respectively. Simvastatin C(max) and AUC were increased by 81 % and 56 % with ticagrelor. Ticagrelor also increased C(max) and AUC of analysed atorvastatin metabolites by 13-55 % and 32-67 %, respectively, and simvastatin acid by 64 % and 52 %, respectively. Co-administration of ticagrelor with each statin was well tolerated.

CONCLUSIONS

Exposure to ticagrelor and its active metabolite, AR-C124910XX, was generally unchanged by a single dose of either statin, except for a minor increase in ticagrelor C(max) in the presence of simvastatin. Effects of ticagrelor on atorvastatin pharmacokinetics were modest and unlikely clinically relevant, while with simvastatin, changes were slightly larger, and simvastatin doses >40 mg with ticagrelor should be avoided.

Concomitant administration of simvastatin with ivabradine in contrast to metoprolol intensifies slowing of heart rate in normo- and hypercholesterolemic rats

INTRODUCTION

β-Blockers play a significant role in therapeutic heart rate (HR) management and angina control. In patients who are unable to tolerate β-blockers ivabradine could be particularly useful. The aim of the study was to establish whether concomitant administration of simvastatin with ivabradine or metoprolol had any effect on rat HR and blood pressure (BP).

MATERIAL AND METHODS

The experiments were performed in hyper- and normocholesterolemic outbred Wistar rats. Animals were divided into 2 groups: receiving during 4 weeks normal diet (normocholesterolemic rats) or diet with 5% cholesterol and 2.5% cholic acid (hypercholesterolemic rats). Then rats received placebo (0.1% methylcellulose), 2) metoprolol 30 mg/kg bw; 3) ivabradine 10 mg/kg bw; 4) simvastatin 10 mg/kg bw; 5) simvastatin 10 mg/kg bw + metoprolol 30 mg/kg bw; 6) simvastatin 10 mg/kg bw + ivabradine 10 mg/kg bw. Drugs were given during a 4-week period. HR and BP measure were provided by an Isotec pressure transducer connected to a direct current bridge amplifier. For the further lipid profile examination, 0.25 ml of blood samples were taken.

RESULTS

After administration of ivabradine with simvastatin to normocholesterolemic and hypercholesterolemic rats the mean HR was significantly reduced as compared to rats receiving simvastatin (312.0 ±30.2 min(-1) vs. 430.7 ±27.8 min(-1), p<0.05); (329.8 ±24.2 min(-1) vs. 420.5 ±9.2 min(-1), p<0.05) or ivabradine alone (312.0 ±30.2 min(-1) vs. 350.2 ±16.0 min(-1), p<0.05); (329.8 ±24.2 min(-1) vs. 363.0 ±21.7 min(-1), p<0.05).

CONCLUSIONS

Concomitant administration of simvastatin with ivabradine intensified slowing of HR, although it did not influence BP in normo-and hypercholesterolemic rats. Statin-induced intensification of HR deceleration after metoprolol administration was not observed.

Risk assessment of mechanism-based inactivation in drug-drug interactions

Drug-drug interactions (DDIs) that occur via mechanism-based inactivation of cytochrome P450 are of serious concern. Although several predictive models have been published, early risk assessment of MBIs is still challenging. For reversible inhibitors, the DDI risk categorization using [I]/K(i) ([I], the inhibitor concentration; K(i), the inhibition constant) is widely used in drug discovery and development. Although a simple and reliable methodology such as [I]/K(i) categorization for reversible inhibitors would be useful for mechanism-based inhibitors (MBIs), comprehensive analysis of an analogous measure reflecting in vitro potency for inactivation has not been reported. The aim of this study was to evaluate whether the term λ/k(deg) (λ, first-order inactivation rate at a given MBI concentration; k(deg), enzyme degradation rate constant) would be useful in the prediction of the in vivo DDI risk of MBIs. Twenty-one MBIs with both in vivo area under the curve (AUC) change of marker substrates and in vitro inactivation parameters were identified in the literature and analyzed. The results of this analysis show that in vivo DDIs with >2-fold change of object drug AUC can be identified with the cutoff value of λ/k(deg) = 1, where unbound steady-state C(max) is used for inhibitor concentration. However, the use of total C(max) led to great overprediction of DDI risk. The risk assessment using λ/k(deg) coupled with unbound C(max) can be useful for the DDI risk evaluation of MBIs in drug discovery and development.

Classification of inhibitors of hepatic organic anion transporting polypeptides (OATPs): influence of protein expression on drug-drug interactions

The hepatic organic anion transporting polypeptides (OATPs) influence the pharmacokinetics of several drug classes and are involved in many clinical drug–drug interactions. Predicting potential interactions with OATPs is, therefore, of value. Here, we developed in vitro and in silico models for identification and prediction of specific and general inhibitors of OATP1B1, OATP1B3, and OATP2B1. The maximal transport activity (MTA) of each OATP in human liver was predicted from transport kinetics and protein quantification. We then used MTA to predict the effects of a subset of inhibitors on atorvastatin uptake in vivo. Using a data set of 225 drug-like compounds, 91 OATP inhibitors were identified. In silico models indicated that lipophilicity and polar surface area are key molecular features of OATP inhibition. MTA predictions identified OATP1B1 and OATP1B3 as major determinants of atorvastatin uptake in vivo. The relative contributions to overall hepatic uptake varied with isoform specificities of the inhibitors.

Clinical importance of the drug interaction between statins and CYP3A4 inhibitors: a retrospective cohort study in The Health Improvement Network

OBJECTIVE

To compare the relative hazard of muscle toxicity, renal dysfunction, and hepatic dysfunction associated with the drug interaction between statins and concomitant medications that inhibit the CYP3A4 isoenzyme.

BACKGROUND

Although statins provide important clinical benefits related to mitigating the risk of cardiovascular events, this class of medications also has the potential for severe adverse reactions. The risk for adverse events may be potentiated by concomitant use of medications that interfere with statin metabolism.

METHODS

Data from The Health Improvement Network (THIN) from 1990 to 2008 were used to conduct a retrospective cohort study. Cohorts were created to evaluate each outcome (muscle toxicity, renal dysfunction, and hepatic dysfunction) independently. Each cohort included new statin initiators and compared the relative hazard of the outcome. The interaction ratio (I*R) was the primary contrast of interest. The I*R represents the relative effect of each statin type (statin 3A4 substrate vs. statin non-3A4 substrate) with a CYP3A4 inhibitor, independent of the effect of the statin type without a CYP3A4 inhibitor. We adjusted for confounding variables using the multinomial propensity score.

RESULTS

The median follow-up time per cohort was 1.5 years. There were 7889 muscle toxicity events among 362,809 patients and 792,665 person-years. The adjusted muscle toxicity I*R was 1.22 (95% confidence interval [CI] = 0.90-1.66). There were 1449 renal dysfunction events among 272,099 patients and 574,584 person-years. The adjusted renal dysfunction I*R was 0.91 (95%CI = 0.58-1.44). There were 1434 hepatic dysfunction events among 367,612 patients and 815,945 person-years. The adjusted hepatic dysfunction I*R was 0.78 (95%CI = 0.45-1.31).

CONCLUSIONS

Overall, this study found no difference in the relative hazard of muscle toxicity, renal dysfunction, or hepatic dysfunction for patients prescribed a statin 3A4 substrate versus a statin non-3A4 substrate with CYP3A4 inhibitor concomitancy.

Simvastatin interactions with other drugs

INTRODUCTION

Statins, the mainstay of lipid-lowering therapy, are among the most commonly used drugs due to their beneficial effects in cardiovascular morbidity and mortality. Simvastatin, one of the most well-studied statins, is available in several generic forms both as monotherapy and with ezetimibe and is frequently prescribed worldwide. Despite its overall favorable risk profile, several previously stated concerns regarding high-dose simvastatin were recently formalized by the Food and Drug Administration (FDA).

AREAS COVERED

This paper discusses the interactions between simvastatin and other drugs and presents the latest FDA recommendations regarding the safe use of this statin. Relevant articles were identified through a PubMed search (up to December 2011). Furthermore, the latest FDA warning (June 2011) regarding simvastatin use was taken into account.

EXPERT OPINION

Simvastatin may have serious side effects particularly when used in high doses and in combination with certain drugs. Physicians need to adjust the recent recommendations made by the FDA in clinical practice in order to prevent treatment complications.

Pharmacological actions of statins: a critical appraisal in the management of cancer

Statins, among the most commonly prescribed drugs worldwide, are cholesterol-lowering agents used to manage and prevent cardiovascular and coronary heart diseases. Recently, a multifaceted action in different physiological and pathological conditions has been also proposed for statins, beyond anti-inflammation and neuroprotection. Statins have been shown to act through cholesterol-dependent and -independent mechanisms and are able to affect several tissue functions and modulate specific signal transduction pathways that could account for statin pleiotropic effects. Typically, statins are prescribed in middle-aged or elderly patients in a therapeutic regimen covering a long life span during which metabolic processes, aging, and concomitant novel diseases, including cancer, could occur. In this context, safety, toxicity, interaction with other drugs, and the state of health have to be taken into account in subjects treated with statins. Some evidence has shown a dichotomous effect of statins with either cancer-inhibiting or -promoting effects. To date, clinical trials failed to demonstrate a reduced cancer occurrence in statin users and no sufficient data are available to define the long-term effects of statin use over a period of 10 years. Moreover, results from clinical trials performed to evaluate the therapeutic efficacy of statins in cancer did not suggest statin use as chemotherapeutic or adjuvant agents. Here, we reviewed the pharmacology of the statins, providing a comprehensive update of the current knowledge of their effects on tissues, biological processes, and pathological conditions, and we dissected the disappointing evidence on the possible future use of statin-based drugs in cancer therapy.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

[Specific considerations on the prescription and therapeutic interchange of statins]

OBJECTIVE

The pharmaceutical industry currently offers six different statins in Spain and there is one more soon to be available. Choosing the most appropriate drug and dose is determined by the therapeutic target (reduction in LDL-C levels). Statin doses that decrease LDL-C at the same percentage are considered equivalent. Evaluating the pharmacokinetic characteristics of each statin can be useful when setting selection criteria, helping to determine which statin may be more appropriate for a patient based on their individual characteristics and on the other co-administered drugs.

METHODS

We reviewed the pharmacokinetics properties of each statin and its possible involvement in drug interactions.

RESULTS

CYP3A4 was responsible for the metabolism of lovastatin, simvastatin and atorvastatin; fluvastatin depends on CYP2C9; P-glycoprotein is responsible for decreased atorvastatin, pravastatin, simvastatin and lovastatin concentrations. The OATPA1B1 transporter involved in all statins' access to the hepatocyte, except for fluvastatin, is essential for rosuvastatin and pravastatin. These circumstances cause those drugs inhibiting or inducing isoenzymes or transporters' activity not to have the same effect on the different statins.

CONCLUSION

The pharmacokinetics is important when choosing the best statin and could be a limitation in the use of interchange therapeutic programmes when other drugs are present.

Cytochrome P450-mediated cardiovascular drug interactions

INTRODUCTION

There are numerous drug-drug interactions (DDIs) related to cardiovascular medications and many of these are mediated via the cytochrome P450 (CYP) system. Some of these may lead to serious adverse events and it is, therefore, essential that clinicians are aware of the important interactions that occur.

AREAS COVERED

An extensive literature search was performed to analyze the CYP-mediated cardiovascular DDIs that lead to a loss of efficacy or potential toxicity. Cardiovascular drugs may be victims or act as perpetrators of DDIs. The paper analyzes CYP-mediated drug interactions concerning anticoagulants, antiplatelet agents, antiarrhythmics, β-blockers, calcium antagonists, antihypertensive medications, lipid-lowering drugs and oral antidiabetic agents.

EXPERT OPINION

Cardiovascular DDIs involving the CYP system are numerous. Additionally, the spectrum of drugs prescribed is constantly changing, particularly with cardiovascular diseases and it is not necessarily the case that drugs that had shown safety earlier will always show safety. Clinicians are encouraged to develop their knowledge of CYP-mediated DDIs so that they can choose safe drug combination regimens, adjust drug dosages appropriately and conduct therapeutic drug monitoring for drugs with narrow therapeutic indices.

pH-sensitive interaction of HMG-CoA reductase inhibitors (statins) with organic anion transporting polypeptide 2B1

The human organic anion transporting polypeptide 2B1 (OATP2B1, SLCO2B1) is ubiquitously expressed and may play an important role in the disposition of xenobiotics. The present study aimed to examine the role of OATP2B1 in the intestinal absorption and tissue uptake of 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase inhibitors (statins). We first investigated the functional affinity of statins to the transporter as a function of extracellular pH, using OATP2B1-transfeced HEK293 cells. The results indicate that OATP2B1-mediated transport is significant for rosuvastatin, fluvastatin and atorvastatin, at neutral pH. However, OATP2B1 showed broader substrate specificity as well as enhanced transporter activity at acidic pH. Furthermore, uptake at acidic pH was diminished in the presence of proton ionophore, suggesting proton gradient as the driving force for OATP2B1 activity. Notably, passive transport rates are predominant or comparable to active transport rates for statins, except for rosuvastatin and fluvastatin. Second, we studied the effect of OATP modulators on statin uptake. At pH 6.0, OATP2B1-mediated transport of atorvastatin and cerivastatin was not inhibitable, while rosuvastatin transport was inhibited by E-3-S, rifamycin SV and cyclosporine with IC(50) values of 19.7 ± 3.3 μM, 0.53 ± 0.2 μM and 2.2 ± 0.4 μM, respectively. Rifamycin SV inhibited OATP2B1-mediated transport of E-3-S and rosuvastatin with similar IC(50) values at pH 6.0 and 7.4, suggesting that the inhibitor affinity is not pH-dependent. Finally, we noted that OATP2B1-mediated transport of E-3-S, but not rosuvastatin, is pH sensitive in intestinal epithelial (Caco-2) cells. However, uptake of E-3-S and rosuvastatin by Caco-2 cells was diminished in the presence of proton ionophore. The present results indicate that OATP2B1 may be involved in the tissue uptake of rosuvastatin and fluvastatin, while OATP2B1 may play a significant role in the intestinal absorption of several statins due to their transporter affinity at acidic pH.

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.

Atorvastatin-induced acute elevation of hepatic enzymes and the absence of cross-toxicity of pravastatin

Atorvastatin has been associated with liver injury. We reported here two cases of aminotransferases elevation within 12 h of low-dose atorvastatin therapy. Liver functions were fully recovered to the baseline level 11 days after discontinuation of atorvastatin treatment. The possible relative risk factors included advanced age, chronic and systemic diseases, and co-administration of cytochrome P450 3A (CYP3A) enzyme-dependent metabolic drugs or its inhibitors such as clopidogrel and diltiazem. No significant transaminase elevation was observed after switching to pravastatin. Thus, pravastatin might be safer than atorvastain in patients with chronic or systemic diseases, or with co-administration of CYP3A enzyme-dependent drugs.

Gender differences, polypharmacy, and potential pharmacological interactions in the elderly

OBJECTIVE

This study aims to analyze pharmacological interactions among drugs taken by elderly patients and their age and gender differences in a population from Porto Alegre, Brazil.

METHODS

We retrospectively analyzed the database provided by the Institute of Geriatric and Gerontology, Porto Alegre, Brazil. The database was composed of 438 elderly and includes information about the patients' disease, therapy regimens, utilized drugs. All drugs reported by the elderly patients were classified using the Anatomical Therapeutic and Chemical Classification System. The drug-drug interactions and their severity were assessed using the Micromedex® Healthcare Series.

RESULTS

Of the 438 elderly patients in the data base, 376 (85.8%) used pharmacotherapy, 274 were female, and 90.4% of females used drugs. The average number of drugs used by each individual younger than 80 years was 3.2±2.6. Women younger than 80 years old used more drugs than men in the same age group whereas men older than 80 years increased their use of drugs in relation to other age groups. Therefore, 32.6% of men and 49.2% of women described at least one interaction, and 8.1% of men and 10.6% of women described four or more potential drug-drug interactions. Two-thirds of drug-drug interactions were moderate in both genders, and most of them involved angiotensin-converting enzyme inhibitor, non-steroidal anti-inflammatory, loop and thiazide diuretics, and β-blockers.

CONCLUSION

Elderly patients should be closely monitored, based on drug class, gender, age group and nutritional status.

Uptake transporters of the human OATP family: molecular characteristics, substrates, their role in drug-drug interactions, and functional consequences of polymorphisms

Organic anion transporting polypeptides (OATPs, gene family: SLC21/SLCO) mediate the uptake of a broad range of substrates including several widely prescribed drugs into cells. Drug substrates for members of the human OATP family include HMG-CoA-reductase inhibitors (statins), antibiotics, anticancer agents, and cardiac glycosides. OATPs are expressed in a variety of different tissues including brain, intestine, liver, and kidney, suggesting that these uptake transporters are important for drug absorption, distribution, and excretion. Because of their wide tissue distribution and broad substrate spectrum, altered transport kinetics, for example, due to drug-drug interactions or due to the functional consequences of genetic variations (polymorphisms), can contribute to the interindividual variability of drug effects. Therefore, the molecular characteristics of human OATP family members, the role of human OATPs in drug-drug interactions, and the in vitro analysis of the functional consequences of genetic variations in SLCO genes encoding OATP proteins are the focus of this chapter.

Physiologically based predictions of the impact of inhibition of intestinal and hepatic metabolism on human pharmacokinetics of CYP3A substrates

The first objective of the present study was to predict the pharmacokinetics of selected CYP3A substrates administered at a single oral dose to human. The second objective was to predict pharmacokinetics of the selected drugs in presence of inhibitors of the intestinal and/or hepatic CYP3A activity. We developed a whole-body physiologically based pharmacokinetics (WB-PBPK) model accounting for presystemic elimination of midazolam (MDZ), alprazolam (APZ), triazolam (TRZ), and simvastatin (SMV). The model also accounted for concomitant administration of the above-mentioned drugs with CYP3A inhibitors, namely ketoconazole (KTZ), itraconazole (ITZ), diltiazem (DTZ), saquinavir (SQV), and a furanocoumarin contained in grape-fruit juice (GFJ), namely 6',7'-dihydroxybergamottin (DHB). Model predictions were compared to published clinical data. An uncertainty analysis was performed to account for the variability and uncertainty of model parameters when predicting the model outcomes. We also briefly report on the results of our efforts to develop a global sensitivity analysis and its application to the current WB-PBPK model. Considering the current criterion for a successful prediction, judged satisfied once the clinical data are captured within the 5th and 95th percentiles of the predicted concentration-time profiles, a successful prediction has been obtained for a single oral administration of MDZ and SMV. For APZ and TRZ, however, a slight deviation toward the 95th percentile was observed especially for C(max) but, overall, the in vivo profiles were well captured by the PBPK model. Moreover, the impact of DHB-mediated inhibition on the extent of intestinal pre-systemic elimination of MDZ and SMV has been accurately predicted by the proposed PBPK model. For concomitant administrations of MDZ and ITZ, APZ and KTZ, as well as SMV and DTZ, the in vivo concentration-time profiles were accurately captured by the model. A slight deviation was observed for SMV when coadministered with ITZ, whereas more important deviations have been obtained between the model predictions and in vivo concentration-time profiles of MDZ coadministered with SQV. The same observation was made for TRZ when administered with KTZ. Most of the pharmacokinetic parameters predicted by the PBPK model were successfully predicted within a two-fold error range either in the absence or presence of metabolism-based inhibition. Overall, the present study demonstrated the ability of the PBPK model to predict DDI of CYP3A substrates with promising accuracy.

Hepatic OATP and OCT uptake transporters: their role for drug-drug interactions and pharmacogenetic aspects

Uptake transporters in the basolateral membrane of hepatocytes are important for the hepatobiliary elimination of drugs. Further, since drug-metabolizing enzymes are located intracellularly, uptake into hepatocytes is a prerequisite for their subsequent metabolism. Therefore, alteration of uptake transporter function (e.g., by concomitantly administered drugs or due to functional consequences of genetic variations, leading to reduced transport function) may result in a change in drug pharmacokinetics. In this review, we focus on the hepatocellularly expressed members of the OATP and OCT family, their impact on transport-mediated drug-drug interactions, and on the functional consequences of variations in genes encoding these transporters.

Atorvastatin: safety and tolerability

IMPORTANCE OF THE FIELD

Atorvastatin is the most widely used statin administered in a variety of settings, including primary and secondary prevention of cardiovascular events, in the elderly, in patients with chronic kidney disease and in diabetic patients. Therefore, the safety and tolerability of atorvastatin is of paramount importance.

AREAS COVERED IN THIS REVIEW

We searched MEDLINE for literature published between 1997 and 2010 on the safety and tolerability of atorvastatin. We retrieved data from randomized controlled trials, meta-analyses, post-marketing studies, reports to regulatory bodies and case reports of rare adverse events.

WHAT THE READER WILL GAIN

The reader will gain insight into the incidence, severity, prevention and management of the major adverse effects of atorvastatin (i.e., liver function abnormalities and muscle-related side effects) overall and in special populations.

TAKE HOME MESSAGE

The existing data suggest that atorvastatin is generally well tolerated across the range of its therapeutic dosage (10 - 80 mg/day).

Liquid chromatography-tandem mass spectrometric assay for pravastatin and two isomeric metabolites in mouse plasma and tissue homogenates

A bioanalytical assay for pravastatin and two isomeric metabolites, 3'α-isopravastatin and 6'-epipravastatin, was developed and validated. Mouse plasma and tissue homogenates from liver, kidney, brain and heart were pre-treated using protein precipitation with acetonitrile containing deuterated internal standards of the analytes. The extract was diluted with water and injected into the chromatographic system. This system consisted of a polar embedded octadecyl silica column using isocratic elution with formic acid in a water-acetonitrile mixture. The eluate was transferred to an electrospray interface using negative ionization and the analytes were detected and quantified with the selected reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was successfully validated in a 3.4-7100ng/ml concentration range for pravastatin, 1.3-2200ng/ml for 3'α-isopravastatin and 0.5-215ng/ml for 6'-epipravastatin using only plasma for calibration. For plasma samples, subjected to full validation, within and between day precisions were 1-7% (9-18% at the LLQ level) and accuracies were between 91% and 103%. For tissue homogenates, subjected to partial validation, within and between day precisions were 2-12% (6-19% at the LLQ level) and accuracies were between 87% and 113% (81 and 113% at the LLQ level). Drug and metabolites were shown to be chemically stable under most relevant analytical conditions. Finally, the assay was successfully applied for a pilot study in mice. After intravenous administration of the drug, all isomeric compounds were found in plasma; however, in liver and kidney homogenate only the parent drug showed levels exceeding the LLQ.

Influence of genetic variation in CYP3A4 and ABCB1 on dose decrease or switching during simvastatin and atorvastatin therapy

PURPOSE

Simvastatin and atorvastatin are metabolized by the CYP3A4 enzyme and transported by the ABCB1 transporter. We studied whether the polymorphism CYP3A4*1B and the polymorphisms C1236T, G2677A/T and C3435T in the ABCB1 gene were associated with a decrease of the prescribed dose or a switch to another cholesterol lowering drug during simvastatin and atorvastatin therapy. These events may indicate that statin plasma levels were too high and resulted in an adverse drug reaction or a too strong reduction in cholesterol level.

METHODS

We identified 1239 incident simvastatin and atorvastatin users in the Rotterdam Study, a population-based cohort study. Associations between the polymorphisms in the CYP3A4 and ABCB1 gene and the time to a decrease in dose or a switch to another cholesterol lowering drug were studied using Cox proportional hazards.

RESULTS

Simvastatin and atorvastatin users with the CYP3A4*1B variant G allele had a lower risk (HR 0.46; 95%CI 0.24-0.90) for these events than users with the wild-type AA genotype. No significant associations were found for the ABCB1 polymorphisms. The association with the CYP3A4*1B polymorphism was found in women (HR 0.33; 95%CI 0.12-0.89) and was non-significant in men (HR 0.69 95%CI 0.28-1.70). This association was stronger in patients with the ABCB1 3435T variant allele versus the G allele.

CONCLUSION

In simvastatin and atorvastatin users, the CYP3A4*1B G allele is associated with a lower risk of elevated statin plasma levels, particularly in women and in users with the ABCB1 3435T variant allele.

Hepatic OATP1B transporters and nuclear receptors PXR and CAR: interplay, regulation of drug disposition genes, and single nucleotide polymorphisms

Drug uptake transporters are now increasingly recognized as clinically relevant determinants of variable drug responsiveness and unexpected drug-drug interactions. Emerging evidence strongly suggests members of the organic anion transporting polypeptide (OATP) family appear to be particularly important to the disposition of many drugs in clinical use today. Specifically, the liver-enriched OATP1B subfamily members OATP1B1 and OATP1B3 exhibit broad substrate specificity and the ability to transport drugs which are ligands for xenobiotic sensing nuclear receptors such as the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Accordingly, OATP1B transporters may indirectly regulate expression of drug metabolism genes via modulation of the intracellular concentration of PXR and CAR ligands. Moreover, a number of functionally important single nucleotide polymorphisms (SNPs) in OATP1B transporters have been described. In this review, a brief summary of known SNPs in PXR and CAR will be followed by an in-depth outline of OATP1B1 and OATP1B3 transporters particularly in relation to the known SNPs in these OATPs and the interplay between OATP1B transporters with PXR and CAR, both in vitro and in vivo.

Over 8 years experience on severe acute poisoning requiring intensive care in Hong Kong, China

In order to obtain up-to-date information on the pattern of severe acute poisoning and the characteristics and outcomes of these patients, 265 consecutive patients admitted to an intensive care unit in Hong Kong for acute poisoning from January 2000 to May 2008 were studied retrospectively. Benzodiazepine (25.3%), alcohol (23%), tricyclic antidepressant (17.4%), and carbon monoxide (15.1%) were the four commonest poisons encountered. Impaired consciousness was common and intubation was required in 67.9% of admissions, with a median duration of mechanical ventilation of less than 1 day. The overall mortality was 3.0%. Among the 257 survivors, the median lengths of stay in the intensive care unit and acute hospital (excluding days spent in psychiatric ward and convalescent hospital) were less than 1 day and 3 days, respectively. Factors associated with a longer length of stay included age of 65 or older, presence of comorbidity, Acute Physiology and Chronic Health Evaluation II score of 25 or greater, and development of shock, rhabdomyolysis, and aspiration pneumonia, while alcohol intoxication was associated with a shorter stay. This is the largest study of its kind in the Chinese population and provided information on the pattern of severe acute poisoning requiring intensive care admission and the outcomes of the patients concerned.

Fibrate/Statin initiation in warfarin users and gastrointestinal bleeding risk

PURPOSE

To evaluate whether initiation of a fibrate or statin increases the risk of hospitalization for gastrointestinal bleeding in warfarin users.

METHODS

We used Medicaid claims data (1999-2003) to perform an observational case-control study nested within person-time exposed to warfarin in those > or =18 years (n=353,489). Gastrointestinal bleeding cases were matched to 50 controls based on index date and state.

RESULTS

Chronic warfarin users had an increased odds ratio of gastrointestinal bleeding upon initiation of gemfibrozil (1.88; 95% confidence interval [CI], 1.00-3.54] for the first prescription; 1.75; 95% CI, 0.77-3.95 for the second prescription); simvastatin (1.46; 95% CI, 1.03-2.07 for the first prescription; 1.60; 95% CI, 1.07-2.39 for the second prescription); or atorvastatin (1.39; 95% CI, 1.07-1.81 for the first prescription; 1.05; 95% CI, 0.73-1.52 for the second prescription). In contrast, no increased risk was found with pravastatin initiation (0.75; 95% CI, 0.39-1.46 for the first prescription; 0.90; 95% CI, 0.43-1.91 for the second prescription).

CONCLUSIONS

Initiation of a fibrate or statin that inhibits CYP3A4 enzymes, including atorvastatin, was associated with an increased risk of hospitalization for gastrointestinal bleeding. Initiation of pravastatin, which is mainly excreted unchanged, was not associated with an increased risk.

Does Simvastatin Cause More Myotoxicity Compared with Other Statins?

Objective:

To review the literature regarding statins and myotoxicity and evaluate these data to determine whether incidence rates are higher with simvastatin.

Data Sources:

Literature was identified from a search of MEDLINE (1966–August 2009) and International Pharmaceutical Abstracts (1970–August 2009), as well as references of selected articles. Key search terms included the names of individual statins, rhabdomyolysis, myopathy, myalgia, myotoxicity, statins, and drug interactions.

Study Selection and Data Extraction:

All English-language articles discussing statin-related myotoxicity and relevant drug interactions that involved human subjects were examined.

Data Synthesis:

Simvastatin is a commonly prescribed, moderately potent statin. Recent evidence suggests that the risk of severe muscle toxicity with simvastatin may be higher than that with other statins, particularly when used in combination with cytochrome P450 isoenzyme inhibitors. However, the lack of direct comparative clinical trials assessing the risk of myotoxicity among the statins in equivalent doses precludes definitive conclusions. Data sources examining low-to-mode rate doses of simvastatin suggest that myotoxicity with this agent is infrequent, with rates similar to those seen with other statins. Conversely, findings from clinical trials using the maximum daily dose (80 mg) and a clinical trials database of varying doses of simvastatin suggest a possible increase in rates of myotoxicity with the 80-mg dose compared with lower doses and a higher incidence rate when compared with maximum doses of other statins.

Conclusions:

Overall, the rates of severe myotoxicity with all statins are low, especially with low-to-moderate doses. However, recent trials for those using simvastatin 80 mg daily suggest a higher incidence of myotoxicity compared with maximum approved doses of other statins. Practitioners should be aware of these possible risks and individualize therapy to limit myotoxicity.

Prediction of human drug-drug interactions from time-dependent inactivation of CYP3A4 in primary hepatocytes using a population-based simulator

Time-dependent inactivation (TDI) of human cytochromes P450 3A4 (CYP3A4) is a major cause of clinical drug-drug interactions (DDIs). Human liver microsomes (HLM) are commonly used as an enzyme source for evaluating the inhibition of CYP3A4 by new chemical entities. The inhibition data can then be extrapolated to assess the risk of human DDIs. Using this approach, under- and overpredictions of in vivo DDIs have been observed. In the present study, human hepatocytes were used as an alternative to HLM. Hepatocytes incorporate the effects of other mechanisms of drug metabolism and disposition (i.e., phase II enzymes and transporters) that may modulate the effects of TDI on clinical DDIs. The in vitro potency (K(I) and k(inact)) of five known CYP3A4 TDI drugs (clarithromycin, diltiazem, erythromycin, verapamil, and troleandomycin) was determined in HLM (pooled, n = 20) and hepatocytes from two donors (D1 and D2), and the results were extrapolated to predict in vivo DDIs using a Simcyp population trial-based simulator. Compared with observed DDIs, the predictions derived from HLM appeared to be overestimated. The predictions based on TDI measured in hepatocytes were better correlated with the DDIs (n = 37) observed in vivo (R(2) = 0.601 for D1 and 0.740 for D2) than those from HLM (R(2) = 0.451). In addition, with the use of hepatocytes a greater proportion of the predictions were within a 2-fold range of the clinical DDIs compared with using HLM. These results suggest that DDI predictions from CYP3A4 TDI kinetics in hepatocytes could provide an alternative approach to balance HLM-based predictions that can sometimes substantially overestimate DDIs and possibly lead to erroneous conclusions about clinical risks.

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.

In vitro evidence for the role of OATP and OCT uptake transporters in drug-drug interactions

BACKGROUND

Transport proteins, for example the drug export pump P-glycoprotein, are important for the absorption, distribution and excretion of drugs. Inhibition and induction of P-glycoprotein efflux function is a well-established mechanism of drug-drug interactions. Alteration of transporter-mediated drug uptake by concomitantly administered drugs may also result in a change in drug pharmacokinetics. These uptake transporter-mediated drug-drug interactions are the focus of this review.

OBJECTIVE

To examine the current in vitro evidence on interactions mediated by OATPs (organic anion transporting polypeptides) and OCTs (organic cation transporters).

METHODS

Comparing data of in vivo observed drug-drug interactions with in vitro analysed alterations in drug transport mediated by the hepatic expressed uptake transporters OATP1B1, OATP1B3 and OCT1 and by the renal expressed OCT2 protein.

RESULTS/CONCLUSIONS

Some of the previously in vivo described drug-drug interactions could be explained by alteration in uptake transporter function demonstrating that inhibition or induction of uptake transporters is a newly recognised mechanism of potential drug-drug interactions.

Immunomodulation by statins: mechanisms and potential impact on autoimmune diseases

Statins are inhibitors of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) and they are the most effective agents for lowering cholesterol in clinical practice for the treatment of cardiovascular diseases. However, it has become clear that statins also have pleiotropic immunomodulatory effects in addition to their lipid-lowering properties. As a result, much attention has been focused on their potential as therapeutic agents for the treatment of inflammatory autoimmune diseases. In this review the effect of statins on the expression and function of a variety of immune-relevant molecules will be discussed alongside the underlying mechanisms that contribute to the immunomodulatory effects of statins.

Computing with evidence Part II: An evidential approach to predicting metabolic drug-drug interactions

We describe a novel experiment that we conducted with the Drug Interaction Knowledge-base (DIKB) to determine which combinations of evidence enable a rule-based theory of metabolic drug-drug interactions to make the most optimal set of predictions. The focus of the experiment was a group of 16 drugs including six members of the HMG-CoA-reductase inhibitor family (statins). The experiment helped identify evidence-use strategies that enabled the DIKB to predict significantly more interactions present in a validation set than the most rigorous strategy developed by drug experts with no loss of accuracy. The best-performing strategies included evidence types that would normally be of lesser predictive value but that are often more accessible than more rigorous types. Our experimental methods represent a new approach to leveraging the available scientific evidence within a domain where important evidence is often missing or of questionable value for supporting important assertions.

Impact of cholesterol on ABC and SLC transporters expression and function and its role in disposition variability to lipid-lowering drugs

This report focuses on the effects of cholesterol on the expression and function of the ATP-binding cassette (ABCB1, ABCG2 and ABCC2) and solute-linked carrier (SLCO1B1 and SLCO2B1) drug transporters with a particular focus on the potential impact of cholesterol on lipid-lowering drug disposition. Statins are the most active agents in the treatment of hypercholesterolemia. However, considerable interindividual variation exists in the response to statin therapy. Therefore, it would be huge progress if factors were identified that reliably differentiate between responders and nonresponders. Many studies have suggested that plasma lipid concentrations can affect drug disposition of compounds, such as ciclosporin and amphotericin B. Both compounds are able to affect the expression and function of ABC transporters. Although still speculative, these effects might be owing to the regulation of drug transporters by plasma cholesterol levels. Studies with normo- and hyper-cholesterolemic individuals, before and after atorvastatin treatment, have demonstrated that plasma cholesterol levels are correlated with drug transporter expression, as well as being related to atorvastatin’s cholesterol-lowering effect. The mechanism influencing the correlation between cholesterol levels and the expression and function of drug transporters remains unclear. Some studies provide strong evidence that nuclear receptors, such as the pregnane X receptor and the constitutive androstane receptor, mediate this effect. In the near future, pharmacogenomic studies with individuals in a pathological state should be performed in order to identify whether high plasma cholesterol levels might be a factor contributing to interindividual oral drug bioavailability.

Verapamil for cluster headache. Clinical pharmacology and possible mode of action

Verapamil is used mainly in cardiovascular diseases. High-dose verapamil (360-720 mg) is, however, currently the mainstay in the prophylactic treatment of cluster headache. The oral pharmacokinetics are variable. The pharmacodynamic effect of verapamil, the effect on blood pressure, also varies considerably among subjects. The dose of verapamil used for cluster headache is approximately double the dose used in cardiovascular disease, most likely because verapamil is a substrate for the efflux transporter P-glycoprotein in the blood-brain barrier. The access of verapamil to the central nervous system is therefore limited. The clinical use of verapamil in cluster headache is reviewed and several relevant drug interactions are mentioned. Finally, its possible mode of action in cluster headache is discussed. The effect of verapamil in cluster headache most likely takes place in the hypothalamus.Verapamil is an L-type calcium channel blocker but it is also a blocker of other calcium channels (T-, P-, and possibly N- and Q-type Ca(2+) channels) and the human ether-a-go-go-related gene potassium channel. With so many different actions of verapamil, it is impossible at the present time to single out a certain mode of action of the drug in cluster headache.

Jupiter to earth: a statin helps people with normal LDL-C and high hs-CRP, but what does it mean?

The JUPITER trial (Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin) (N Engl J Med 2008; 359:2195-2207) compared rosuvastatin (Crestor) 20 mg daily vs placebo in apparently healthy people who had levels of low-density lipoprotein cholesterol (LDL-C) lower than 130 mg/dL but elevated levels (>or= 2 mg/L) of high-sensitivity C-reactive protein (hs-CRP). Rosuvastatin treatment lowered LDL-C levels by 50% and hs-CRP levels by 37%, accompanied by a 44% relative risk reduction in the composite end point of unstable angina, revascularization, and confirmed death from cardiovascular causes. In absolute terms, 95 people had to be treated over 2 years to prevent one event. There was, however, a higher incidence of diabetes in the rosuvastatin group.

Lowering low-density lipoprotein cholesterol: statins, ezetimibe, bile acid sequestrants, and combinations: comparative efficacy and safety

Statins, ezetimibe, and bile acid-binding resins can be used individually or in combination for lowering low-density lipoprotein cholesterol (LDL-C) levels. Statins are the most potent drugs for lowering LDL-C and are well tolerated in most patients. The addition of a bile acid sequestrant or ezetimibe to a statin produces additional LDL-C reduction allowing many patients to reach LDL-C targets. This article discusses the efficacy and safety of available statins, bile acid sequestrants, and ezetimibe in the treatment of hyperlipidemia.

Co-medication of statins and CYP3A4 inhibitors before and after introduction of new reimbursement policy

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

HMG-CoA reductase inhibitors (statins) are frequently used drugs in the treatment of dyslipidaemia. Co-medication with interacting drugs increases the risk of statin-induced muscular side-effects. Simvastatin exhibits particularly high interaction potential due to substantial metabolism via cytochrome P450 3A4 (CYP3A4).

WHAT THIS STUDY ADDS

In June 2005, a new reimbursement policy was introduced by the Norwegian Medicines Agency stating that simvastatin should be prescribed as first-line lipid-lowering therapy. Following introduction of the new policy, the number of patients co-medicated with simvastatin and CYP3A4 inhibitors almost doubled. A potential consequence is increased incidence of muscular side-effects in the statin-treated population.

AIMS

To assess the prevalence of co-medication of statins and CYP3A4 inhibitors before and after introduction of a new Norwegian reimbursement policy, which states that all patients should be prescribed simvastatin as first-line lipid-lowering therapy.

METHODS

Data from patients receiving simvastatin, lovastatin, pravastatin, fluvastatin or atorvastatin in 2004 and 2006, including co-medication of potent CYP3A4 inhibitors, were retrieved from the Norwegian Prescription Database covering the total population of Norway. Key measurements were prevalence of continuous statin use (two or more prescriptions on one statin) and proportions of different statin types among all patients and those co-medicated with CYP3A4 inhibitors.

RESULTS

In 2004, 5.9% (n= 272 342) of the Norwegian population received two or more prescriptions on one statin compared with 7.0% (n= 324 267) in 2006. The relative number of simvastatin users increased from 39.7% (n= 112 122) in 2004 to 63.1% (n= 226 672) in 2006. A parallel increase was observed within the subpopulation co-medicated with statins and CYP3A4 inhibitors, i.e. from 42.9% (n= 7706) in 2004 to 63.6% (n= 13 367) in 2006. For all other statins the number of overall users decreased to a similar extent to those co-medicated with CYP3A4 inhibitors.

CONCLUSIONS

In both 2004 and 2006, the choice of statin type did not depend on whether the patient used a CYP3A4 inhibitor or not. Considering the pronounced interaction potential of simvastatin with CYP3A4 inhibitors, a negative influence of the new policy on overall statin safety seems likely.

Risk management of simvastatin or atorvastatin interactions with CYP3A4 inhibitors

BACKGROUND

Co-administration of cytochrome P450 (CYP) 3A4 inhibitors with simvastatin or atorvastatin is associated with increased risk of developing myopathy or rhabdomyolysis.

OBJECTIVE

To detect co-prescriptions of CYP3A4 inhibitors with simvastatin or atorvastatin in community pharmacies and assess the risk-preventive actions taken by the prescribing physicians who were alerted about the co-prescription by the pharmacist.

METHODS

This naturalistic study was performed during four separate 6-week periods in 2004 and 2005, and involved 110 Norwegian community pharmacists (25-30 in each period). Co-prescription of the selected CYP3A4 inhibitors diltiazem, verapamil, clarithromycin, erythromycin, fluconazole, itraconazole and ketoconazole with either simvastatin or atorvastatin was detected with the aid of a simple computer programme. In instances where the pharmacist alerted the prescribing physician about the co-prescription, information on possible strategies to minimize the risk associated with the interaction was also provided. Odds ratios (ORs) were estimated to describe the associations between prescription variables and frequencies of physician information and prescription change, respectively.

RESULTS

In total, 245 co-prescriptions of CYP3A4 inhibitors with simvastatin (134 events) or atorvastatin (111) were detected. Diltiazem (86 events), verapamil (72), erythromycin (48) and clarithromycin (29) were the most commonly co-prescribed CYP3A4 inhibitors. Physicians were informed in 168 out of 245 cases (68.6%). The prescription was subsequently changed in 100 out of 168 cases (59.5%). Another 50 physicians (29.8%) responded that they would consult the patient and monitor potential adverse effects, while only 18 physicians (10.7%) replied that they had already managed the interactions or considered the issue as irrelevant. The adjusted OR for the informing of the physician was 1.89 (95% CI 0.98, 3.63) in patients receiving a daily HMG-CoA reductase inhibitor ('statin') dose of >or=40 mg compared with patients receiving a statin dose of <40 mg/day. The adjusted OR for prescription change was 4.98 (95% CI 2.36, 10.52) if co-prescription was detected prior to the initiation of concurrent use compared with if it was detected during concurrent use.

CONCLUSION

Nine out of ten physicians changed prescriptions or monitored potential adverse effects when informed by community pharmacists about the risk associated with co-prescription of CYP3A4 inhibitors with simvastatin or atorvastatin. This suggests that an important risk factor for myotoxicity due to these statins could be minimized through interdisciplinary co-operation.

Concomitant use of statins and CYP3A4 inhibitors in administrative claims and electronic medical records databases

BACKGROUND

Patients may experience increased risk of adverse drug interactions when statins are administered concomitantly with cytochrome P450 3A4 (CYP3A4) inhibitors.

OBJECTIVE

To determine patient numbers in routine clinical practice with concomitant exposure to CYP3A4-metabolized statins and CYP3A4 inhibitors and highlight potential risk for adverse drug interaction.

METHODS

Exposure to prescription medications over 1 year (2005-2006) was evaluated from patient records: US PharMetrics Integrated Patient-Centric administrative claims database and the US General Electric Medical System (GEMS) database. Rates of concomitant prescribing of statins with CYP3A4 inhibitors (listed in United States of America product labels and all identified potential inhibitors) were examined in the cohort overall, in those aged ≥65 years, and in those receiving higher doses of statins.

RESULTS

Overall, 951,166 patient records were included (PharMetrics n = 650,825; GEMS, n = 300,341). Of these, 792,081 (83%) patients used a CYP3A4-metabolized statin as opposed to a non-CYP3A4-metabolized statin (17%). Findings from both databases were consistent. Overall, 25-30% of patients given a CYP3A4-metabolized statin were concomitantly exposed to a CYP3A4 inhibitor, including approximately 9% concomitantly exposed to a labeled inhibitor, findings consistent with those in patients aged ≥65 years, and patients on higher doses of statins.

CONCLUSIONS

Clinicians frequently co-prescribe CYP3A4-metabolized statins with CYP3A4 inhibitors. Physician education regarding the impact of these inhibitors on the metabolism of lovastatin, simvastatin, and atrovastatin is needed. Further studies are also needed to determine whether concomitant administration of a non-CYP3A4-metabolized statin (such as fluvastatin, pravastatin, or rosuvastatin) with a CYP3A4 inhibitor, may reduce adverse event rates in routine clinical practice.

Effects of cyclosporin A and itraconazole on the pharmacokinetics of atorvastatin in rats

AIM

To evaluate the effects of cyclosporin A and itraconazole, which were used as inhibitors of P-glycoprotein (P-gp) and/or cytochrome P450 (CYP) 3A4 on the pharmacokinetics of atorvastatin in rats.

METHODS

The pharmacokinetic parameters of atorvastatin were measured after intravenous (2 mg/kg) and intragastric (10 mg/kg) administration of atorvastatin in rats, which were pretreated with cyclosporin A (5, 10, and 20 mg/kg) or itraconazole (5, 10, and 20 mg/kg).

RESULTS

Compared with the control rats, cyclosporin A and itraconazole altered the pharmacokinetics of atorvastatin significantly. The AUC0-t values of atorvastatin after intragastric administration, pretreated with cyclosporin A (5-20 mg/kg), increased by 32.3%, 61.8%, and 187.2%, respectively, but the CLbile values decreased (P<0.01, 5-20 mg/kg). With pretreatment of itraconazole (5-20 mg/kg), the AUC(0-t) values of atorvastatin increased by 88.2%, 102%, and 123%, respectively, but the CL(bile) values decreased (P<0.01, 5-20 mg/kg).

CONCLUSION

These data indicated that cyclosporin A could be effective in inhibiting the efflux of atorvastatin, and itraconazole could be effective in inhibiting both the metabolism and biliary excretion of atorvastatin.