Mechanistic studies on metabolic interactions between gemfibrozil and statins

Pitavastatin for the treatment of primary hyperlipidemia and mixed dyslipidemia

Pitavastatin is a new, synthetic member of the statin class of lipid-lowering drugs. Compared with other available statins, it has a unique cyclopropyl group on its base structure that is believed to increase 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition by a factor of five and to significantly increase the transcription and activity of LDL receptors. Pitavastatin is primarily metabolized via glucuronidation and is not a substrate for the cytochrome P450 3A4 enzyme, thus avoiding the potential for cytochrome P450-mediated drug-drug interactions. Clinical trials have shown that pitavastatin is comparable to atorvastatin and simvastatin in improving lipid measures, and more potent than pravastatin. Pitavastatin is effective in reducing triglycerides and increasing HDL-cholesterol, so it will be particularly beneficial in treating patients with mixed dyslipidemia. Its safety and adverse event profile is similar to that of other available statins, and it has an established history of use in Asia indicating tolerability and safety for treatment lasting up to 7 years.

Drug treatment of hyperlipidaemia: a guide to the rational use of lipid-lowering drugs

Mammalian sterol and lipid metabolism depends on a large number of highly evolved biochemical and histological processes responsible for the absorption, distribution and steady-state anabolic/catabolic handling of these substances. Lipoproteins are complex polymolecular assemblies comprising phospholipids, cholesterol and cholesterol esters, triglycerides and a variety of apolipoproteins. The primary function of lipoproteins is to facilitate the systemic distribution of sterols and lipids. Abnormalities in lipoprotein metabolism are quite common and are attributable to a large number of genetic mutations, metabolic derangements such as insulin resistance or thyroid dysfunction, and excess availability of cholesterol and fat from dietary sources. Dyslipidaemic states facilitate endothelial dysfunction and atherogenesis. Dyslipidaemia is recognized as a risk factor for cardiovascular disease in both men and women, and people of all racial and ethnic groups throughout the world. Dyslipidaemia is modifiable with dietary change and the use of medications that impact on lipid metabolism through a variety of mechanisms. Reducing atherogenic lipoprotein burden in serum is associated with significant and meaningful reductions in risk for a variety of cardiovascular endpoints, including myocardial infarction, ischaemic stroke, development of peripheral arterial disease and mortality. This review provides an overview on how to best position lipid-lowering drugs when attempting to normalize serum lipid profiles and reduce risk for cardiovascular disease. HMG-CoA reductase inhibitors (statins) are widely accepted to be the agents of choice for reducing serum levels of low-density lipoprotein cholesterol (LDL-C) in both the primary and secondary prevention settings. Ezetimibe and bile acid sequestrants are both effective agents for reducing LDL-C, either used alone or in combination with statins. The statins, fibric acid derivatives (fibrates) and niacin raise high-density lipoprotein cholesterol to different extents depending upon genetic and metabolic background. Fibrates, niacin and omega-3 fish oils are efficacious therapies for reducing serum triglycerides. Combinations of these drugs are frequently required for normalizing mixed forms of dyslipidaemia.

Severe statin-induced rhabdomyolysis mimicking Guillain-Barré syndrome in four patients with diabetes mellitus treated with fusidic acid

BACKGROUND

An interaction between fusidic acid and HMG coenzyme A reductase inhibitors (statins), resulting in rhabdomyolysis, has been described. Pain and mild weakness are common presenting symptoms.

CASE REPORT

We report four patients with Type 2 diabetes prescribed long-term statin treatment who, following treatment with fusidic acid, presented atypically with painless, severe flaccid paralysis suggestive of Guillain-Barré syndrome. This, together with nerve conduction studies consistent with Guillain-Barré syndrome, resulted in the delayed recognition of rhabdomyolysis in these cases.

CONCLUSIONS

The addition of fusidic acid can precipitate rhabdomyolysis in patients with diabetes already taking a statin. This can present with rapidly progressive weakness resembling Guillain-Barré syndrome. We recommend that creatine kinase is checked in patients with diabetes on statin therapy who present with profound weakness and routinely in those commenced on prolonged courses of fusidic acid.

Human skeletal muscle drug transporters determine local exposure and toxicity of statins

RATIONALE

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, are important drugs used in the treatment and prevention of cardiovascular disease. Although statins are well tolerated, many patients develop myopathy manifesting as muscle aches and pain. Rhabdomyolysis is a rare but severe toxicity of statins. Interindividual differences in the activities of hepatic membrane drug transporters and metabolic enzymes are known to influence statin plasma pharmacokinetics and risk for myopathy. Interestingly, little is known regarding the molecular determinants of statin distribution into skeletal muscle and its relevance to toxicity.

OBJECTIVE

We sought to identify statin transporters in human skeletal muscle and determine their impact on statin toxicity in vitro.

METHODS AND RESULTS

We demonstrate that the uptake transporter OATP2B1 (human organic anion transporting polypeptide 2B1) and the efflux transporters, multidrug resistance-associated protein (MRP)1, MRP4, and MRP5 are expressed on the sarcolemmal membrane of human skeletal muscle fibers and that atorvastatin and rosuvastatin are substrates of these transporters when assessed using a heterologous expression system. In an in vitro model of differentiated, primary human skeletal muscle myoblast cells, we demonstrate basal membrane expression and drug efflux activity of MRP1, which contributes to reducing intracellular statin accumulation. Furthermore, we show that expression of human OATP2B1 in human skeletal muscle myoblast cells by adenoviral vectors increases intracellular accumulation and toxicity of statins and such effects were abrogated when cells overexpressed MRP1.

CONCLUSIONS

These results identify key membrane transporters as modulators of skeletal muscle statin exposure and toxicity.

Myopathy with statin-fibrate combination therapy: clinical considerations

Many patients who receive statin therapy for hyperlipidemia-such as patients with diabetes mellitus and metabolic syndrome--have residual cardiovascular risk. These patients often have dyslipidemia, including low levels of HDL cholesterol and elevated levels of triglycerides and small, dense LDL. For such patients, combination treatment with statins and fibrates is a potentially useful strategy to improve lipid and lipoprotein profiles and reduce cardiovascular risk. However, statin-fibrate combination regimens have potential adverse effects on skeletal muscle, including myopathy. To date, no large-scale, prospective, randomized, controlled trial has evaluated the safety and efficacy of statin-fibrate combination therapy; one such trial is underway but will not report data until 2010. Until then, clinicians need to consider pharmacokinetic, pharmacodynamic, metabolic, pathophysiologic and other factors that can increase the systemic exposure of statins and/or fibrates and hence heighten the risk of toxic effects on muscles, as well as data from clinical trials and recommendations of consensus panels to optimize the safety of such combination regimens. On the basis of currently available data, fenofibrate or fenofibric acid is the fibrate of choice when used in combination with a statin because each is, in theory, associated with a lower risk of myopathy than gemfibrozil.

Regulation of sulfotransferase and UDP-glucuronosyltransferase gene expression by the PPARs

During phase II metabolism, a substrate is rendered more hydrophilic through the covalent attachment of an endogenous molecule. The cytosolic sulfotransferase (SULT) and UDP-glucuronosyltransferase (UGT) families of enzymes account for the majority of phase II metabolism in humans and animals. In general, phase II metabolism is considered to be a detoxication process, as sulfate and glucuronide conjugates are more amenable to excretion and elimination than are the parent substrates. However, certain products of phase II metabolism (e.g., unstable sulfate conjugates) are genotoxic. Members of the nuclear receptor superfamily are particularly important regulators of SULT and UGT gene transcription. In metabolically active tissues, increasing evidence supports a major role for lipid-sensing transcription factors, such as peroxisome proliferator-activated receptors (PPARs), in the regulation of rodent and human SULT and UGT gene expression. This review summarizes current information regarding the regulation of these two major classes of phase II metabolizing enzyme by PPARs.

Management of complex lipid abnormalities with a fixed dose combination of simvastatin and extended release niacin

ER niacin combined with simvastatin provides an additional option for achieving LDL-C and non-HDL-C goals for cardiovascular prevention, with greater efficacy in those with triglyceride levels >200 mg/dL. ER niacin 1000 mg combined with simvastatin 20 mg reduced LDL-C by 6%, non-HDL-C by 7%, and triglycerides by 13%, and raised HDL-C by 11% compared to simvastatin 20 mg alone. The 2000 mg dose combined with simvastatin 20 to 40 mg raised reduced LDL-C by 7% to 24%, non-HDL-C by 16% to 28%, and triglycerides by 23% to 34%, and increased HDL-C by 18% to 22% compared to similar dose simvastatin therapy. While cardiovascular risk is reduced in proportion to the magnitude of LDL-C lowering, the additive benefit of raising HDL-C and lowering triglycerides remains to be determined. ER niacin-simvastatin is reasonably well tolerated, with a <7% discontinuation rate due to flushing in patients who used aspirin or non-steroidal anti-inflammatory medications as needed. However, drop-out rates were high in both the simvastatin and ER niacin-simvastatin treatment groups in both the 24- and 52-week studies. The safety profile of the combination appears to be similar to that of niacin and simvastatin used as monotherapies. Results of ongoing morbidity/mortality trials of ER niacin added to statin therapy are eagerly awaited.

Managing statin myopathy

Approximately 10% of patients treated with statins experience some form of muscle-related side effects in clinical practice. These can range from asymptomatic creatine kinase (CK) elevation, to muscle pain, weakness, and its most severe form, rhabdomyolysis. Higher risk patients for statin myopathy are those older than 80, with a small body frame, on higher statin doses, on other medications, or with other systemic diseases including hepatic or renal diseases, diabetes mellitus, or hypothyroidism. The cause of statin myopathy is presumed to be the same for its variable presentation but has not been defined. In patients with myopathic symptoms, their symptoms and CK levels determine whether statin therapy can be continued or must be stopped.

Fenofibrate metabolism in the cynomolgus monkey using ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry-based metabolomics

Fenofibrate, widely used for the treatment of dyslipidemia, activates the nuclear receptor, peroxisome proliferator-activated receptor alpha. However, liver toxicity, including liver cancer, occurs in rodents treated with fibrate drugs. Marked species differences occur in response to fibrate drugs, especially between rodents and humans, the latter of which are resistant to fibrate-induced cancer. Fenofibrate metabolism, which also shows species differences, has not been fully determined in humans and surrogate primates. In the present study, the metabolism of fenofibrate was investigated in cynomolgus monkeys by ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOFMS)-based metabolomics. Urine samples were collected before and after oral doses of fenofibrate. The samples were analyzed in both positive-ion and negative-ion modes by UPLC-QTOFMS, and after data deconvolution, the resulting data matrices were subjected to multivariate data analysis. Pattern recognition was performed on the retention time, mass/charge ratio, and other metabolite-related variables. Synthesized or purchased authentic compounds were used for metabolite identification and structure elucidation by liquid chromatographytandem mass spectrometry. Several metabolites were identified, including fenofibric acid, reduced fenofibric acid, fenofibric acid ester glucuronide, reduced fenofibric acid ester glucuronide, and compound X. Another two metabolites (compound B and compound AR), not previously reported in other species, were characterized in cynomolgus monkeys. More importantly, previously unknown metabolites, fenofibric acid taurine conjugate and reduced fenofibric acid taurine conjugate were identified, revealing a previously unrecognized conjugation pathway for fenofibrate.

Treatment of hyperlipidaemia with fenofibrate and related fibrates

BACKGROUND

Fenofibrate is the most widely used fibrate. Its efficacy and tolerability in the treatment of hypertriglyceridaemia and combined hyperlipidaemia have been demonstrated in several clinical trials.

OBJECTIVE

To review the pharmacology, lipid-lowering and extra-lipid effects of fenofibrate and to preview ABT-335, an investigational new fenofibric acid molecule.

RESULTS

The effects of fenofibrate are mediated through the active metabolite fenofibric acid, and are described in detail in the paper. ABT-335 is a salt of fenofibric acid and, unlike fenofibrate, does not require first pass metabolism to the active moiety. ABT-335 is being developed for combination use with statins, and has recently completed three large Phase III randomised controlled trials in which the efficacy and safety of ABT-335 in combination with the three most commonly prescribed statins, atorvastatin, simvastatin and rosuvastatin, was evaluated in patients with mixed dyslipidaemia.

CONCLUSION

ABT-335 in combination with statins may provide a safe and efficacious treatment modality that enables achievement of several therapeutic goals in patients with mixed dyslipidaemia who have high cardiovascular risk.

Safety of statins

PURPOSE OF REVIEW

To examine the evidence for the adverse effects that have been reported during the use of statins.

RECENT FINDINGS

We now have over twenty years of prescription use and many large well controlled trials with statin therapy for hypercholesterolemia. There is only one significant and well documented adverse effect with this group of drugs, rhabdomyolysis. Significant muscle damage is very rare when statin therapy is used in patients carefully screened for concomitant use of other drugs which may interfere with statin catabolism and excretion. Patients with severely impaired liver function are also at risk due to the importance of hepatic excretion of all statins. Chronic myalgias or other pain syndromes have not been confirmed by blinded placebo controlled trials. A significant and reproducible rise in liver enzymes (alanine and aspartate aminotransferases) is observed in 1 to 3% of patients but actual liver damage may not occur at all. Benign and transient proteinuria occurs without evidence of altered renal function. Creatinine clearance is usually increased by statins. Peripheral neuropathy may be a rare adverse effect and this needs further study.

SUMMARY

Statins are very effective at reducing the incidence of myocardial infarction, stroke and other manifestations of vascular disease. The adverse event rates are very uncommon and the benefit risk ratio is extremely high.

Lipid lowering in the patients with prediabetes/metabolic syndrome: what is the evidence?

PURPOSE OF REVIEW

Both the metabolic syndrome and prediabetes are associated with increased coronary risk. Lipoprotein abnormalities are among the many factors that may contribute to this. The present review focuses on these abnormalities and the evidence indicating that correcting them may reduce the risk.

RECENT FINDINGS

Many drugs, both old and in development, may be able to correct lipoprotein abnormalities. No clinical trials are specifically designed to examine the effects of lipid intervention on coronary risk in the metabolic syndrome. Data from subgroup analyses and extrapolation from studies in those with and without diabetes have led to recommendations about the benefits and the targets for lipoprotein treatment.

SUMMARY

The primary goal of lipoprotein treatment is to bring the LDL-C to target levels. Thereafter, if plasma triglycerides are high and HDL-C is low, these should be corrected.

Combination therapy with an HMG-CoA reductase inhibitor and a fibric acid derivative: a critical review of potential benefits and drawbacks

It has been clearly shown that lowering low density lipoprotein-cholesterol (LDL-C) [most often with an HMG-CoA reductase inhibitor] decreases the risk of a cardiovascular event. However, this risk reduction was, at most, 35% in clinical trials, meaning that many events could not be prevented. Moreover, reaching target lipid values as recommended by the current guidelines is often difficult, mainly in high-risk situations such as secondary prevention or type 2 diabetes mellitus. As the two main classes of lipid-lowering drugs (HMG-CoA reductase inhibitors and fibric acid derivatives) have complementary effects on lipid parameters, it seems logical to combine both treatments particularly in patients with combined hyperlipidemia. In fact, combination therapy with an HMG-CoA reductase inhibitor and a fibric acid derivative induces a further decrease in LDL-C levels compared with monotherapy and improves other lipid values such as high density lipoprotein-cholesterol (HDL-C) and triglyceride (TG) levels. Unfortunately, there are currently no available randomized, prospective clinical data on the reduction of the incidence of cardiovascular events with such a combination. This is mainly because the use of HMG-CoA reductase inhibitor and fibric acid derivative combinations was initially described as dangerous. It is true that such a combination increases the risk of muscle toxicity that already exists with monotherapy. Muscle toxicity can eventually lead to life-threatening rhabdomyolysis and some precautions of use are required; however, the risk seems actually lower than what has been initially reported. The use of combined therapy with an HMG-CoA reductase inhibitor and a fibric acid derivative requires the respect of some rules such as avoiding the prescription in patients with concomitant conditions like renal failure and avoiding the use of gemfibrozil as a fibric acid derivative in such a combination. It is now imperative to design clinical trials to determine the clinical efficacy and precise safety of this combined treatment especially in patients with abnormalities in every parameter of the lipid triad (LDL, HDL and TG) and a high vascular risk such as patients with type 2 diabetes mellitus.

Gemfibrozil and its glucuronide inhibit the hepatic uptake of pravastatin mediated by OATP1B1

When pravastatin (40 mg/day) was co-administered with gemfibrozil (600 mg, b.i.d., 3 days) to man, the AUC of pravastatin increased approximately 2-fold. We have clarified that OATP1B1 is a key determinant of the hepatic uptake of pravastatin in humans. Thus, we hypothesized that gemfibrozil and the main plasma metabolites, a glucuronide (gem-glu) and a carboxylic acid metabolite (gem-M3), might inhibit the hepatic uptake of pravastatin and lead to the elevation of the plasma concentration of pravastatin. Gemfibrozil and gem-glu inhibited the uptake of (14)C-pravastatin by human hepatocytes with K(i) values of 31.7 microM and 15.7 microM, respectively and also inhibited pravastatin uptake by OATP1B1-expressing Xenopus laevis oocytes with K(i) values of 15.1 microM and 7.6 microM. Additionally, we examined the biliary transport of pravastatin and demonstrated that pravastatin was transported by MRP2 using both human canalicular membrane vesicles (hCMVs) and human MRP2-expressing vesicles. However, gemfibrozil, gem-glu and gem-M3 did not affect the biliary transport of pravastatin by MRP2. Considering the plasma concentrations of gemfibrozil and gem-glu in humans, the inhibition of OATP1B1-mediated hepatic uptake of pravastatin by gem-glu would contribute, at least in part, to the elevation of plasma concentration of pravastatin by the concomitant use of gemfibrozil.

Inhibition of human organic anion transporter 3 mediated pravastatin transport by gemfibrozil and the metabolites in humans

Coadministration of gemfibrozil (600 mg, b.i.d., 3 days) with pravastatin (40 mg/day) decreased the renal clearance of pravastatin by approximately 40% in healthy volunteers. To investigate the mechanism of this drug-drug interaction in the renal excretion process, we undertook an uptake study of pravastatin using human organic anion transporters (hOATs)-expressing S2 cells. hOAT3 and hOAT4 transported pravastatin in a saturatable manner with Michaelis--Menten constants of 27.7 microM and 257 microM respectively. On the other hand, hOAT1 and hOAT2 did not transport pravastatin. Gemfibrozil and its glucuronide and carboxylic metabolite forms inhibited the uptake of pravastatin by hOAT3 with IC(50) values of 6.8 microM, 19.7 microM and 5.4 microM, respectively. Considering the plasma concentrations of gemfibrozil and its metabolites in humans, the inhibition of hOAT3-mediated pravastatin transport by gemfibrozil and its metabolites would lead to a decrease in the renal clearance of pravastatin in clinical settings.

Effects of fibrates on human organic anion-transporting polypeptide 1B1-, multidrug resistance protein 2- and P-glycoprotein-mediated transport

The effects of different fibric acid derivatives (bezafibrate, clofibrate, clofibric acid, fenofibrate, fenofibric acid and gemfibrozil) on human organic anion transporting-polypeptide 1B1 (OATP2, OATP-C, SLC21A6), multidrug resistance protein 2 (MRP2/ABCC2) and MDR1-type P-glycoprotein (P-gp/ABCB1) were examined in vitro. Cyclosporin A (a known inhibitor of OATP1B1 and P-gp), MK-571 (a known inhibitor of MRP2) and cimetidine (an organic cation) were also tested. Bezafibrate, fenofibrate, fenofibric acid and gemfibrozil showed concentration-dependent inhibition of estradiol 17-beta-D-glucuronide uptake by OATP1B1-stably transfected HEK cells, whereas clofibrate and clofibric acid did not show any significant effects up to 100 microM. Inhibition kinetics of gemfibrozil, which exhibited the most significant inhibition on OATP1B1, was shown to be competitive with a Ki = 12.5 microM. None of the fibrates showed any significant inhibition of MRP2-mediated transport, which was evaluated by measuring the uptake of ethacrynic acid glutathione into MRP2-expressing Sf9 membrane vesicles. Only fenofibrate showed moderate P-gp inhibition as assessed by measuring cellular accumulation of vinblastine in a P-gp overexpressing cell-line. Cyclosporin A significantly inhibited OATP1B1 and P-gp, whereas only moderate inhibition was observed on MRP2. The rank order of inhibitory potency of MK-571 was determined as OATP1B1 (IC50: 0.3 microM) > MRP2 (4 microM) > P-gp (25 microM). Cimetidine did not show any effects on these transporters. In conclusion, neither MRP2- nor P-gp-mediated transport is inhibited significantly by the fibrates tested. Considering the plasma protein binding and IC50 values for OATP1B1, only gemfibrozil appeared to have a potential to cause drug-drug interactions by inhibiting OATP1B1 at clinically relevant concentrations.

Therapies to increase high-density lipoprotein cholesterol and their effect on cardiovascular outcomes and regression of atherosclerosis

Epidemiological studies have shown that decreased level of high-density lipoprotein (HDL) cholesterol (C) is an independent inverse predictor of coronary artery disease (CAD) even in patients with normal levels of low-density lipoprotein (LDL)-C. There is an abundance of evidence in favor of statins and aggressive LDL-C lowering therapy for both primary and secondary prevention of CAD. In contrast, the evidence for reduction of CAD risk with HDL-C raising therapy is relatively thin, partly due to the paucity of effective and safe drugs for increasing HDL-C level. However, there are emerging new therapies for raising HDL-C level and growing evidence in favor of pharmacologic therapies to raise HDL-C level. We present in this article a review of pharmacologic therapies that are currently available to increase HDL-C level, their safety and efficacy in relation to cardiovascular endpoints.

Toward "pain-free" statin prescribing: clinical algorithm for diagnosis and management of myalgia

Myalgia, which often manifests as pain or soreness in skeletal muscles, is among the most salient adverse events associated with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Clinical issues related to statin-associated myotoxicity include (1) incidence in randomized controlled trials and occurrence in postmarketing surveillance databases; (2) potential differences between statins in their associations with such adverse events; and (3) diagnostic and treatment strategies to prevent, recognize, and manage these events. Data from systematic reviews, meta-analyses, clinical and observational trials, and post-marketing surveillance indicate that statin-associated myalgia typically affects approximately 5.0% of patients, as myopathy in 0.1% and as rhabdomyolysis in 0.01%. However, studies also suggest that myalgia is among the leading reasons patients discontinue statins (particularly high-dose statin monotherapy) and that treatment with certain statins (eg, fluvastatin) is unlikely to result in such adverse events. This review presents a clinical algorithm for monitoring and managing statin-associated myotoxicity. The algorithm highlights risk factors for muscle toxicity and provides recommendations for (1) creatine kinase measurements and monitoring; (2) statin dosage reduction, discontinuation, and rechallenge; and (3) treatment alternatives, such as extended-release fluvastatin with or without ezetimibe, low-dose or alternate-day rosuvastatin, or ezetimibe with or without colesevelam. The algorithm should help to inform and enhance patient care and reduce the risk of myalgia and other potentially treatment-limiting muscle effects that might undermine patient adherence and compromise the overall cardioprotective benefits of statins.

Does the addition of fibrates to statin therapy have a favorable risk to benefit ratio?

Statins effectively lower low-density lipoprotein cholesterol levels and the risk of cardiovascular disease (CVD) events, and because of this they have become a standard treatment for dyslipidemia and atheroprevention. Unfortunately, statin monotherapy may fail to normalize high triglycerides and low high-density lipoprotein cholesterol, and it prevents only a minority of CVD events. Further treatment of lipid disorders that remain after statin monotherapy should help reduce the residual CVD risk. Fibrate monotherapy lowers high triglyceride levels, raises low high-density lipoprotein cholesterol, and reduces CVD risk; therefore, fibrates are recommended as an adjunct to statins for treatment of residual dyslipidemia and residual CVD risk. This review provides an update on the benefits and risks of fibrate monotherapy and addresses the benefits and risks of adding fibrates to statins.

Vascular and metabolic effects of treatment of combined hyperlipidemia: focus on statins and fibrates

Combined hyperlipidemia results from overproduction of hepatically synthesized apolipoprotein B in very low-density lipoproteins in association with reduced lipoprotein lipase activity. Thus, this condition is typically characterized by concurrent elevations in total cholesterol and triglycerides with decreased high-density lipoprotein cholesterol. High levels of apolipoprotein B-containing lipoproteins, most prominently carried by low-density lipoprotein (LDL) particles, are an important risk factor for coronary heart disease. Statin therapy is highly effective at lowering LDL cholesterol. Despite the benefits of statin treatment for lowering total and LDL cholesterol, many statin-treated patients still have initial or recurrent coronary heart disease events. In this regard, combined therapy with statins and fibrates is more effective in controlling atherogenic dyslipidemia in patients with combined hyperlipidemia than either drug alone. Furthermore, statins and fibrates activate PPARalpha in a synergistic manner providing a molecular rationale for combination treatment in coronary heart disease. Endothelial dysfunction associated with cardiovascular diseases may contribute to insulin resistance so that there may also be additional beneficial metabolic effects of combined statin/fibrates therapy. However, there has been little published evidence that combined therapy is synergistic or even better than monotherapy alone in clinical studies. Therefore, there is a great need to study the effects of combination therapy in patients. When statins are combined with gemfibrozil therapy, this is more likely to be accompanied by myopathy. However, this limitation is not observed when fenofibrate, bezafibrate, or ciprofibrate are used in combination therapy.

Atorvastatin and cardiovascular risk in the elderly--patient considerations

Elderly individuals are at increased risk of coronary heart disease (CHD) and account for a majority of CHD deaths. Several clinical trials have assessed the beneficial effects of statins in individuals with, or at risk of developing, CHD. These trials provide evidence that statins reduce risk and improve clinical outcomes even in older patients; however, statin therapy remains under-utilized among the aged. Atorvastatin has been widely investigated among the older subjects and has the greatest magnitude of favorable effects on clinical outcomes of CHD. The pharmacokinetic properties of atorvastatin allow it to be used every other day, a factor which may decrease adverse events and be especially important in the elderly. The purpose of this article is to review the evidence available from randomized clinical trials regarding the safety and efficacy of atorvastatin in primary and secondary prevention of CHD and stroke in older patients and to discuss issues such as drug interactions, patient compliance and cost-effectiveness, which affect prescription of lipid-lowering therapy among older patients.

The safety of statins in clinical practice

Statins are effective cholesterol-lowering drugs that reduce the risk of cardiovascular disease events (heart attacks, strokes, and the need for arterial revascularisation). Adverse effects from some statins on muscle, such as myopathy and rhabdomyolysis, are rare at standard doses, and on the liver, in increasing levels of transaminases, are unusual. Myopathy--muscle pain or weakness with blood creatine kinase levels more than ten times the upper limit of the normal range--typically occurs in fewer than one in 10,000 patients on standard statin doses. However, this risk varies between statins, and increases with use of higher doses and interacting drugs. Rhabdomyolysis is a rarer and more severe form of myopathy, with myoglobin release into the circulation and risk of renal failure. Stopping statin use reverses these side-effects, usually leading to a full recovery. Asymptomatic increases in concentrations of liver transaminases are recorded with all statins, but are not clearly associated with an increased risk of liver disease. For most people, statins are safe and well-tolerated, and their widespread use has the potential to have a major effect on the global burden of cardiovascular disease.

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss three specific SADRs with an emphasis on genetic risk factors. These SADRs, selected based on wide-sweeping clinical interest, are drug-induced liver injury, statin-induced myotoxicity and drug-induced long QT and torsades de pointes. Key challenges for the discovery of predictive risk alleles for these SADRs are also considered.

P-glycoprotein has differential effects on the disposition of statin acid and lactone forms in mdr1a/b knockout and wild-type mice

In the present study we examined the disposition of atorvastatin, lovastatin, and simvastatin in acid and lactone forms and pravastatin in acid form in multidrug-resistant gene (mdr1a/b) knockout (KO), and wild-type (WT) mice. Each statin was administered s.c. to mdr1a/b KO and WT mice at 3.0 mg/kg (n > or = 3 mice/time point). Blood, brain, and liver samples were harvested at 0, 0.5, 1.5, and 3 h postdose. Plasma and tissue concentrations of the acid and lactone (only the acid form was determined for pravastatin) were determined using a liquid chromatography-mass spectrometry method. Both lactone and acid were observed in plasma when lactones were administered, but only acids were detected when the acid forms were administered. The plasma and liver concentrations of acid or lactone were similar between the KO and WT mice. Two- to 23-fold higher concentrations were observed in liver than in plasma, suggesting potential uptake transporters involved. A significantly higher (p < 0.05) brain penetration in the KO compared with the WT mice was observed for lovastatin acid (but the brain/plasma ratio was low for both KO and WT mice) and lactone and simvastatin lactone but not for atorvastatin or pravastatin. The present results suggest that mouse P-glycoprotein does not affect the lactone-acid interconversion or liver-plasma distribution. Furthermore, P-glycoprotein plays a limited role in restricting the brain penetration of the acid forms of atorvastatin, pravastatin, simvastatin, lovastatin, and atorvastatin lactone but may limit the brain availability of the lactone forms of simvastatin and lovastatin.

Hypertriglyceridemia and cardiovascular risk reduction

BACKGROUND

Elevated triglyceride (TG) levels are prevalent among the US population, often occurring in persons who are overweight or obese, or who have type 2 diabetes or the metabolic syndrome. There is evidence that elevated TG levels may be a significant independent risk factor for coronary heart disease (CHD), particularly in women.

OBJECTIVE

This article reviews data on the epidemiology, associated risks, treatment, and prevention of hypertriglyceridemia, including recommended TG goals and available TG-lowering agents.

METHODS

MEDLINE was searched for articles published from 1990 through 2006 using the terms hypertriglyceridemia, dyslipidemia, and coronary heart disease, with subheadings for risk, statins, niacin, fibrates, thiazolidinediones, and omega-3 fatty acids. The reference lists of relevant articles were examined for additional citations. Publications discussing the epidemiology of hypertriglyceridemia, CHD risk, treatment guidelines for lipid management, clinical trials involving TG-lowering drugs, and outcomes for lipid-modifying therapies were selected for review.

RESULTS

Concern over the increasing rate of hypertriglyceridemia and its deleterious health consequences is reflected in the most recent National Cholesterol Education Program guidelines. Several lipid-lowering agents are available, including statins, fibrates, niacin, thiazolidinediones, and prescription omega-3 fatty acids. Clinical trials of these drugs have reported lowering of TG by 7% to 50%. Along with lifestyle changes, the use of combination pharmacotherapy to reduce lipid levels (including TG) may be an effective strategy in patients with dyslipidemia.

CONCLUSION

Use of strategies to manage TG levels, along with low-density lipoprotein cholesterol levels, is warranted to help reduce the risk of CHD.

Simvastatin: present and future perspectives

Simvastatin is lipophilic statin with a short half-life that is primarily metabolized by CYP450 3A4. At doses of 5 - 80 mg, simvastatin lowers LDL cholesterol by 25 - 50%. Simvastatin has been shown to reduce the risk of cardiovascular disease by 35% and overall mortality by up to 30% over 5 years. The recommended starting dose of simvastatin 40 mg is approved as a lipid-lowering agent and for all high-risk patients, including those with cardiovascular disease and diabetes, regardless of the baseline LDL level. Simvastatin dose should be adjusted in those receiving CYP3A4 inhibitors, gemfibrozil, or ciclosporin, amiodarone, or in those with severe renal insufficiency. Coformulation of simvastatin with ezetimibe is now available, and coformulation with extended release niacin is under development.

The UDP-Glucuronosyltransferase 2B7 Isozyme Is Responsible for Gemfibrozil Glucuronidation in the Human Liver

Gemfibrozil, a fibrate hypolipidemic agent, is eliminated in humans by glucuronidation. A gemfibrozil glucuronide has been reported to show time-dependent inhibition of cytochrome P450 2C8. Comprehensive assessment of the drug interaction between gemfibrozil and cytochrome P450 2C8 substrates requires a clear understanding of gemfibrozil glucuronidation. However, the primary UDP-glucuronosyltransferase (UGT) isozymes responsible for gemfibrozil glucuronidation remain to be determined. Here, we identified the main UGT isozymes involved in gemfibrozil glucuronidation. Evaluation of 12 recombinant human UGT isozymes shows gemfibrozil glucuronidation activity in UGT1A1, UGT1A3, UGT1A9, UGT2B4, UGT2B7, and UGT2B17, with UGT2B7 showing the highest activity. The kinetics of gemfibrozil glucuronidation in pooled human liver microsomes (HLMs) follows Michaelis-Menten kinetics with high and low affinity components. The high affinity K(m) value was 2.5 microM, which is similar to the K(m) value of gemfibrozil glucuronidation in recombinant UGT2B7 (2.2 microM). In 16 HLMs, a significant correlation was observed between gemfibrozil glucuronidation and both morphine 3-OH glucuronidation (r = 0.966, p < 0.0001) and flurbiprofen glucuronidation (r = 0.937, p < 0.0001), two reactions mainly catalyzed by UGT2B7, whereas no significant correlation was observed between gemfibrozil glucuronidation and either estradiol 3beta-glucuronidation and propofol glucuronidation, two reactions catalyzed by UGT1A1 and UGT1A9, respectively. Flurbiprofen and mefenamic acid inhibited gemfibrozil glucuronidation in HLMs with similar IC(50) values to those reported in recombinant UGT2B7. These results suggest that UGT2B7 is the main isozyme responsible for gemfibrozil glucuronidation in humans.

Dyslipidemia in type 2 diabetes mellitus

Cardiovascular disease is a significant cause of morbidity and mortality in patients with diabetes mellitus (DM). DM is now recognized as a risk equivalent for coronary heart disease. The lipid profile in patients with type 2 DM is characterized by elevated triglycerides, low levels of high-density lipoprotein cholesterol, and small dense low-density lipoprotein cholesterol (LDLC) particles and is believed to be a key factor promoting atherosclerosis in these patients. Both primary and secondary prevention studies have provided ample evidence that aggressive statin therapy reduces cardiovascular end points in patients with DM. In all persons with DM, current treatment guidelines recommend reduction of LDLC to less than 100 mg/dL, regardless of baseline lipid levels. Lowering LDLC to less than 70 mg/dL may provide even greater benefits, particularly in very high risk patients with DM and coronary heart disease.

Atorvastatin glucuronidation is minimally and nonselectively inhibited by the fibrates gemfibrozil, fenofibrate, and fenofibric acid

Gemfibrozil coadministration generally results in plasma statin area under the curve (AUC) increases, ranging from moderate (2- to 3-fold) with simvastatin, lovastatin, and pravastatin to most significant with cerivastatin (5.6-fold). Inhibition of statin glucuronidation has been postulated as a potential mechanism of interaction (Drug Metab Dispos 30:1280-1287, 2002). This study was conducted to determine the in vitro inhibitory potential of fibrates toward atorvastatin glucuronidation. [(3)H]Atorvastatin, atorvastatin, and atorvastatin lactone were incubated with human liver microsomes or human recombinant UDP-glucuronosyltransferases (UGTs) and characterized using liquid chromatography (LC)/tandem mass spectrometry and LC/UV/beta-radioactivity monitor/mass spectrometry. [(3)H]Atorvastatin yields a minor ether glucuronide (G1) and a major acyl glucuronide (G2) with subsequent pH-dependent lactonization of G2 to yield atorvastatin lactone. Atorvastatin lactonization best fit substrate inhibition kinetics (K(m) = 12 microM, V(max) = 74 pmol/min/mg, K(i) = 75 microM). Atorvastatin lactone yields a single ether glucuronide (G3). G3 formation best fit Michaelis-Menten kinetics (K(m) = 2.6 microM, V(max) = 10.6 pmol/min/mg). Six UGT enzymes contribute to atorvastatin glucuronidation with G2 and G3 formation catalyzed by UGTs 1A1, 1A3, 1A4, 1A8, and 2B7, whereas G1 formation was catalyzed by UGTs 1A3, 1A4, and 1A9. Gemfibrozil, fenofibrate, and fenofibric acid inhibited atorvastatin lactonization with IC(50) values of 346, 320, and 291 microM, respectively. Based on unbound fibrate concentrations at the inlet to the liver, these data predict a small increase in atorvastatin AUC (approximately 1.2-fold) after gemfibrozil coadministration and no interaction with fenofibrate. This result is consistent with recent clinical reports indicating minimal atorvastatin AUC increases ( approximately 1.2- to 1.4-fold) with gemfibrozil.

Pharmacogenetics and pharmacogenomics of cholesterol-lowering therapy

PURPOSE OF REVIEW

To summarize recent findings on pharmacokinetics, pharmacodynamics, drug-drug interactions and influence of lifestyle heterogeneity on adverse events in cholesterol-lowering therapy

RECENT FINDINGS

The prevention of cardiovascular disease is critically dependent on lipid-lowery therapy, including statins, cholesterol absorption inhibitors, fibrates and nicotinic acid. Statins are the most prescribed drugs in lipid lowering therapy with variability in response and almost one third of the patients do not meet their treatment goals. The severe adverse effects of treatment with cerivastatin stimulated the search for new genes and gene variations affecting pharmacokinetics, drug-drug interactions and pharmacodynamics. Moreover, instead of monotherapy, combined therapy of statins with ezetemibe and niacin was considered. This led to the identification of CD13, NPC1L1 and HM74A as new targets and CYP2C8 and glucuronidation enzymes as potential targets for drug-drug interactions. Moreover multiple polymorphic sites and pleiotrophic gene targets were reinvestigated in larger cohorts and the relevant pathogenetic factors start to evolve.

SUMMARY

Statin therapy is widely used and well tolerated by the majority of patients. To further reduce potential adverse effects and to increase efficacy, combined therapy concepts with ezetimibe or niacin are underway.

Safety considerations with gastrointestinally active lipid-lowering drugs

Gastrointestinally active agents such as cholesterol absorption inhibitors (CAIs) (eg, ezetimibe) and bile acid sequestrants (BAS) (the resins cholestyramine and colestipol, or colesevelam, a nonabsorbable polymer) offer important options for lipid-lowering therapy. Ezetimibe is a novel CAI that inhibits the absorption of dietary and biliary cholesterol without affecting the absorption of triglycerides or fat-soluble vitamins. In clinical trials, there has been no evidence of increased rates of myopathy or rhabdomyolysis associated with ezetimibe, whether in use as monotherapy or in a combination with statin therapy, although there exist case reports of possible ezetimibe-associated myopathy. Ezetimibe alone does not appear to increase liver transaminase levels significantly, but the coadministration of a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) with ezetimibe marginally increases this risk. However, reported increases in liver enzymes have not been associated with clinically meaningful symptoms and often return to baseline levels after the discontinuation of therapy or with continued treatment. To date, no cases of liver failure, liver transplantation, or death have been reported. BAS have been used clinically since the 1960s for lowering low-density lipoprotein cholesterol. Because they are not absorbed from the gastrointestinal tract into the blood, these agents do not contact most body organs and are therefore systemically safe. However, case reports and pharmacokinetic data disclose 3 kinds of adverse effects: (1) the decreased absorption of concomitant medications and sometimes of certain vitamins; (2) the physicochemical alteration of intestinal contents leading to constipation and, very rarely, intestinal obstruction; and (3) modest increases in plasma triglyceride levels due to the alteration of hepatic lipid metabolism. The newest BAS, colesevelam, has greater specificity for bile acids compared with the older agents cholestyramine and colestipol, eliminating most drug interactions and reducing the tendency for constipation. Overall, CAIs and BAS have excellent systemic safety profiles when used alone or in combination with other lipid-lowering drugs.

Safety considerations with fibrate therapy

Fibrates are an important class of drugs for the management of dyslipidemia. This class of drugs is generally well tolerated but is infrequently associated with several safety issues. Fibrates, most likely by an effect mediated by peroxisome proliferator-activated receptor-alpha, may reversibly increase creatinine and homocysteine but are not associated with an increased risk for renal failure in clinical trials. Fibrates are associated with a slightly increased risk (<1.0%) for myopathy, cholelithiasis, and venous thrombosis. In clinical trials, patients without elevated triglycerides and/or low high-density lipoprotein cholesterol (HDL) levels, fibrates are associated with an increase in noncardiovascular mortality. In combination with statins, gemfibrozil generally should be avoided. The preferred option is fenofibrate, which is not associated with an inhibition of statin metabolism. Clinicians are advised to measure serum creatinine before fibrate use and adjust the dose accordingly for renal impairment. Routine monitoring of creatinine is not required, but if a patient has a clinically important increase in creatinine, and other potential causes of creatinine increase have been excluded, consideration should be given to discontinuing fibrate therapy or reducing the dose.

Myotoxicity associated with lipid-lowering drugs

PURPOSE OF REVIEW

Lipid-lowering drugs are associated with myotoxicity, which ranges in severity from myalgias to rhabdomyolysis resulting in renal failure and death. Although rhabdomyolysis is rare, muscle symptoms and serum creatine kinase elevations are sufficiently frequent during the course of lipid-lowering drug therapy to pose diagnostic challenges for the clinician. Progress in our understanding of this form of myotoxicity is reviewed.

RECENT FINDINGS

Muscle pain and weakness are the cardinal symptoms and often interfere with vigorous exercise. These symptoms may occur with or without serum creatine kinase elevations. The risk of myotoxicity is increased by combination statin-fibrate therapy as well as by factors that elevate tissue levels of the lipid-lowering drug, including the dose, drug-drug interactions, and host factors. Underlying neuromuscular diseases may become clinically apparent during statin therapy and may predispose to myotoxicity. The pathophysiology of myotoxicity most probably involves metabolic effects of the statins on the isoprenoid pool and on mitochondrial function.

SUMMARY

Management of myotoxicity requires an evaluation of risk factors prior to prescribing lipid-lowering drugs, attention to muscle symptoms, and withdrawal of drug in the event of significant abnormalities.

Fibrates: What Have We Learned in the Past 40 Years?

The prominent use of fibric acid derivatives has lessened over the years because of unimpressive results in major clinical trials, safety concerns, and the emergence of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Clofibrate was widely used in the 1970s, but after publication of results from two major trials demonstrating only modest reductions in the rate of coronary heart disease (CHD) and concerns regarding an increase in the frequency of gallstones and overall mortality, its use subsided dramatically. With the introduction of gemfibrozil in the 1980s came a renewed interest in the class, which was also supported by the published results of the Helsinki Heart Study; however, despite a significant reduction in CHD events and a sound safety profile, overall mortality was comparable to that with placebo. Again, in the 1990s, awareness of the fibrates was heightened with the availability of fenofibrate and the findings of another major trial using gemfibrozil, the Veterans Affairs High-Density Lipoprotein Cholesterol Intervention Trial (VA-HIT), which demonstrated impressive results in reducing cardiovascular events. To further strengthen the VA-HIT results, numerous post hoc analyses were performed on the data of major trials of fibrate therapy among patients with mixed dyslipidemia, with similar findings. Recently, however, data from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study were published, indicating mixed results. Nearly 40 years after the introduction of the fibrates, practitioners are still contemplating the role of these agents in the treatment of CHD.