Mechanistic studies on metabolic interactions between gemfibrozil and statins

Comparative Effects of Fibrates on Drug Metabolizing Enzymes in Human Hepatocytes

PURPOSE

The induction potential of different fibric acid derivatives on human drug metabolizing enzymes was evaluated to help assess the role of enzyme induction on pharmacokinetic drug interactions.

METHODS

Effects of gemfibrozil, fenofibric acid, and clofibric acid on expression levels of cytochromes P450 (CYPs) 3A4 and 2C8 and UDP-glucuronyltransferase (UGT) 1A1 were evaluated in primary human hepatocyte cultures. The potential for these fibrates to activate human pregnane X receptor (PXR) also was studied in a cell-based PXR reporter gene assay.

RESULTS

All three fibrates caused increases in mRNA levels of CYP3A4 (2- to 5-fold), CYP2C8 (2- to 6-fold), and UGT1A1 (2- to 3-fold). On average, the effects on CYP3A4 were less than (< or =30% of rifampin), while those on CYP2C8 and UGT1A1 were comparable to or slightly higher than (up to 200% of rifampin) the corresponding effects observed with rifampin (10 microM). Consistent with the mRNA results, all fibrates caused moderate (approximately 2- to 3-fold) increases in CYP3A4 activity (measured by testosterone 6beta hydroxylase), as compared to about a 10-fold increase by rifampin. Significant increases (3- to 6-fold) in amodiaquine N-deethylase (a functional probe for CYP2C8 activity) also were observed with clofibric acid, fenofibric acid, and rifampin, in agreement with the mRNA finding. However, in contrast to the mRNA induction, marked decreases (>60%) in CYP2C8 activity were obtained with gemfibrozil treatment. Consistent with this finding, co-incubation of amodiaquine with gemfibrozil, but not with fenofibric acid, clofibric acid, or rifampin, in human liver microsomes or hepatocytes resulted in significantly decreased amodiaquine N-deethylase activity (IC50 = 80 microM for gemfibrozil, >500 microM for fenofibric or clofibric acid, and >50 microM for rifampin). Similar to rifampin, all three fibrates caused a modest change in the glucuronidation of chrysin, a nonspecific substrate of UGTs. No significant activation on human pregnane X receptor (PXR) was observed with the three fibrates in a PXR reporter gene assay.

CONCLUSIONS

In human hepatocytes, both fenofibric acid and clofibric acid are inducers of CYP3A4 and CYP2C8. Gemfibrozil is also an inducer of CYP3A4, but acts as both an inducer and an inhibitor of CYP2C8. In this system, all fibrates are weak inducers of UGT1A1. The enzyme inducing effects of fibrates appear to be mediated via a mechanism(s) other than PXR activation. These results suggest that fibrates may have potential to cause various pharmacokinetic drug interactions via their differential effects on enzyme induction and/or inhibition.

Differential interaction of 3-hydroxy-3-methylglutaryl-coa reductase inhibitors with ABCB1, ABCC2, and OATP1B1

The present study examined the interaction of four 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (atorvastatin, lovastatin, and simvastatin in acid and lactone forms, and pravastatin in acid form only) with multidrug resistance gene 1 (MDR1, ABCB1) P-glycoprotein, multidrug resistance-associated protein 2 (MRP2, ABCC2), and organic anion-transporting polypeptide 1B1 (OATP1B1, SLCO21A6). P-glycoprotein substrate assays were performed using Madin-Darby canine kidney (MDCK) cells expressing MDR1, and the efflux ratios [the ratio of the ratio of basolateral-to-apical apparent permeability and apical-to-basolateral permeability between MDR1 and MDCK] were 1.87, 2.32/4.46, 2.17/3.17, and 0.93/2.00 for pravastatin, atorvastatin (lactone/acid), lovastatin (lactone/acid), and simvastatin (lactone/acid), respectively, indicating that these compounds are weak or moderate substrates of P-glycoprotein. In the inhibition assays (MDR1, MRP2, Mrp2, and OATP1B1), the IC50 values for efflux transporters (MDR1, MRP2, and Mrp2) were >100 microM for all statins in acid form except lovastatin acid (>33 microM), and the IC50 values were up to 10-fold lower for the corresponding lactone forms. In contrast, the IC50 values for the uptake transporter OATP1B1 were 3- to 7-fold lower for statins in the acid form compared with the corresponding lactone form. These data demonstrate that lactone and acid forms of statins exhibit differential substrate and inhibitor activities toward efflux and uptake transporters. The interconversion between the lactone and acid forms of most statins exists in the body and will potentially influence drug-transporter interactions, and may ultimately contribute to the differences in pharmacokinetic profiles observed between statins.

Simvastatin does not have a clinically significant pharmacokinetic interaction with fenofibrate in humans

Simvastatin and fenofibrate are both commonly used lipid-regulating agents with distinct mechanisms of action, and their coadministration may be an attractive treatment for some patients with dyslipidemia. A 2-period, randomized, open-label, crossover study was conducted in 12 subjects to determine if fenofibrate and simvastatin are subject to a clinically relevant pharmacokinetic interaction at steady state. In treatment A, subjects received an 80-mg simvastatin tablet in the morning for 7 days. In treatment B, subjects received a 160-mg micronized fenofibrate capsule in the morning for 7 days, followed by a 160-mg micronized fenofibrate capsule dosed together with an 80-mg simvastatin tablet on days 8 to 14. Because food increases the bioavailability of fenofibrate, each dose was administered with food to maximize the exposure of fenofibric acid. The steady-state pharmacokinetics (AUC(0-24h), C(max), and t(max)) of active and total HMG-CoA reductase inhibitors, simvastatin acid, and simvastatin were determined following simvastatin administration with and without fenofibrate. Also, fenofibric acid steady-state pharmacokinetics were evaluated with and without simvastatin. The geometric mean ratios (GMRs) for AUC(0-24h) (80 mg simvastatin [SV] + 160 mg fenofibrate)/(80 mg simvastatin alone) and 90% confidence intervals (CIs) were 0.88 (0.80, 0.95) and 0.92 (0.82, 1.03) for active and total HMG-CoA reductase inhibitors. The GMRs and 90% CIs for fenofibric acid (80 mg SV + 160 mg fenofibrate/160 mg fenofibrate alone) AUC(0-24h) and C(max) were 0.95 (0.88, 1.04) and 0.89 (0.77, 1.02), respectively. Because both the active inhibitor and fenofibric acid AUC GMR 90% confidence intervals fell within the prespecified bounds of (0.70, 1.43), no clinically significant pharmacokinetic drug interaction between fenofibrate and simvastatin was concluded in humans. The coadministration of simvastatin and fenofibrate in this study was well tolerated.

Consumer behavior in the setting of over-the-counter statin availability: lessons from the consumer use study of OTC Mevacor

Despite the proven benefits of statins, large numbers of patients meeting guideline criteria for therapy are not receiving these drugs. It has been suggested that over-the-counter (OTC) availability of statins would allow more consumers to use statins and achieve cardiovascular risk reduction. However, concerns have been raised as to the consumers' ability to self-manage hyperlipidemia and use statins safely. The Consumer Use Study of OTC Mevacor (CUSTOM) was designed to define consumer behaviors in the setting of OTC statin availability. The study was conducted in a simulated OTC setting and allowed consumers to purchase once-daily lovastatin 20 mg. The CUSTOM dataset includes >3,300 consumers who evaluated OTC lovastatin for potential purchase at study sites and follow-up information on purchasers for up to 6 months of self-managed therapy. These data have been analyzed to address consumers' knowledge of their cholesterol concentrations as well as their ability to make OTC use decisions based on their cardiovascular risk, avoid drug-drug interactions, self-manage their cholesterol treatment after deciding to use the OTC product, and maintain interactions with physicians while using lovastatin OTC. The results showed that most study participants appropriately self-selected OTC statin therapy and managed their treatment. Use of OTC statins by consumers needing more intensive statin therapy or facing the risk of potential drug-drug interactions remains an area of concern but occurred infrequently in CUSTOM. These data are important for making an informed risk-benefit decision concerning OTC statin availability.

Fluvastatin and fluvastatin extended release: a clinical and safety profile

Cardiovascular diseases due to atherosclerosis are the leading causes of mortality in the Western world. Cholesterol-lowering therapy with 3-hydroxy-3-methylglutaryl coenzyme Areductase inhibitors (statins) has demonstrated a reduction in cardiovascular morbidity and mortality in diverse populations. Fluvastatin (Lescol, Novartis Pharmaceuticals) was the first totally synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor on the market and has recently become available in an extended-release formulation (Lescol XL, Novartis Pharmaceuticals). Data from several clinical outcome trials have shown substantial benefits from fluvastatin treatment in diverse populations. Fluvastatin exists primarily in its acid form and as inactive metabolites in vivo, while active metabolites as well as the lactone form are only present in small amounts. The demonstration of the safe use of fluvastatin in a wide range of patients may be associated with the predominant acid form of the drug in vivo, as well as its predominant metabolism via the cytochrome P450 2C9 pathway.

Fluvastatin: clinical and safety profile

Therapy with HMG-CoA reductase inhibitors (statins) has been shown to significantly reduce major coronary events and death in a wide range of individuals at risk for these events. In addition, recent observations suggest that some of the clinical benefits associated with statin therapy may be pleiotropic; that is, independent of their cholesterol-inhibiting action. It is clear that the clinical benefits associated with statin therapy far outweigh the risks; however, there may be important clinical differences among agents within the class, related to both benefits and drug safety. Evaluation of the benefit-to-risk profile for each available statin should include considering the results of randomised clinical outcome trials, the safety record of each agent, effect on lipoproteins and evidence of beneficial pleiotropic properties.Recently, data from several clinical outcome trials have shown that substantial benefits are associated with treatment with fluvastatin in diverse populations. In particular, data from two large, randomised clinical trials have demonstrated that fluvastatin is effective for secondary prevention of cardiac events in patients following coronary intervention procedures, and for primary prevention of cardiac events in renal transplant recipients. Pleiotropic benefits for fluvastatin have been shown in experimental and clinical studies as well. Fluvastatin was the first statin available as an extended-release product (fluvastatin XL 80mg); both formulations have demonstrated efficacy and safety in a wide range of patients. Taken together, these clinical outcomes and safety data suggest a strong benefit-to-risk profile for fluvastatin.

Risk of adverse events with fibrates

An increased risk for adverse events was observed with gemfibrozil relative to fenofibrate, predominantly driven by an increased rate of rhabdomyolysis. This difference was especially noticeable in patients taking the combination of gemfibrozil and a statin, particularly cerivastatin.

The influence of statin characteristics on their safety and tolerability

The efficacy of the statins for both primary and secondary prevention has now been clearly established in patients across the spectrum of cardiovascular risk. In addition to their primary effect in reducing plasma cholesterol, the statins possess various 'pleiotropic' effects that may contribute to their clinical effectiveness in reducing cardiovascular events, e.g. improvement of endothelial function, reduction of low-density lipoprotein-cholesterol oxidation and stabilisation of atheromatous plaques. Although statins share similar chemical characteristics, they differ significantly in terms of their molecular synthesis, solubility and pharmacokinetic behaviour and metabolism. Side-effects secondary to longterm statin therapy are rare, but rhabdomyolysis may occur when statins are administered together with other drugs that have a direct toxic effect on muscle or which inhibit statin metabolism. Among the various statins, it would appear that fluvastatin has the lowest propensity to interact with other drugs and the least potential to induce myotoxicity.

Genomic and non-genomic interactions of PPARalpha with xenobiotic-metabolizing enzymes

The hypolipidemic properties of fibrates, synthetic activators of the nuclear receptor, peroxisome proliferator-activated receptor alpha (PPARalpha), have been studied extensively. Recent observations indicate, however, that PPARalpha also functions as a regulator of endobiotic and xenobiotic metabolism in rodents and humans. Activators of PPARalpha affect xenobiotic-metabolizing enzymes (XMEs) at different levels. At the genomic level, the expression of numerous cytochrome P450 (CYP) and phase II conjugating genes is altered in a species-distinct manner on treatment with PPARalpha activators. As a result of such regulatory processes, PPARalpha affects the homeostasis of both its own natural ligands and other compounds including bile acids. At the non-genomic level, PPARalpha activators can act as competitive inhibitors for inactivating other molecules, leading to drug-drug interactions. These global effects of PPARalpha activators on the activity of XMEs are of physiological and pharmaceutical importance, and demonstrate that thorough studies of the actions on XMEs of each novel PPARalpha agonist are warranted.

Comparative effects of lipid-lowering therapies

The pharmacologic regulation of lipid metabolism in patients with dyslipidemia is unequivocally associated with significant reductions in risk for cardiovascular morbidity and mortality. A number of therapeutic drug classes have been developed in an effort to ever more precisely and intensively modulate lipid metabolism. Statins, fibrates, ezetimibe, and niacin exert their effects via different mechanisms and afford physicians the opportunity to beneficially impact multiple pathways in patients. When used alone or in combination, these drugs decrease risk for the development and progression of atherosclerotic disease. There are strong clinical trial data to support of the use of lipid-lowering therapies in the settings of both primary and secondary prevention. This article (1) discusses the mechanisms of action of antilipidemic medications, (2) reviews dosing regimens and the pharmacokinetic differences among drugs of the same class, (3) assesses risk for drug interactions, and (4) reviews the clinical trial evidence used to support the use of particular antilipidemic medications in specific physiologic settings. The incidence of dyslipidemia is rising worldwide. This trend portends an ever-growing need for the aggressive and judicious use of different antilipidemic medication(s) in patients at risk for all forms of atherosclerotic vascular disease.

DRUG-DRUG INTERACTIONS FOR UDP-GLUCURONOSYLTRANSFERASE SUBSTRATES: A PHARMACOKINETIC EXPLANATION FOR TYPICALLY OBSERVED LOW EXPOSURE (AUCI/AUC) RATIOS

Glucuronidation is a listed clearance mechanism for 1 in 10 of the top 200 prescribed drugs. The objective of this article is to encourage those studying ligand interactions with UDP-glucuronosyltransferases (UGTs) to adequately consider the potential consequences of in vitro UGT inhibition in humans. Spurred on by interest in developing potent and selective inhibitors for improved confidence around UGT reaction phenotyping, and the increased availability of recombinant forms of human UGTs, several recent studies have reported in vitro inhibition of UGT enzymes. In some cases, the observed potency of UGT inhibitors in vitro has been interpreted as having potential relevance in humans via pharmacokinetic drug-drug interactions. Although there are reported examples of clinically relevant drug-drug interactions for UGT substrates, exposure increases of the aglycone are rarely greater than 100% in the presence of an inhibitor relative to its absence (i.e., AUCi/AUC < or = 2). This small magnitude in change is in contrast to drugs primarily cleared by cytochrome P450 enzymes, where exposures have been reported to increase as much as 35-fold on coadministration with an inhibitor (e.g., ketoconazole inhibition of CYP3A4-catalyzed terfenadine metabolism). In this article the evidence for purported clinical relevance of potent in vitro inhibition of UGT enzymes will be assessed, taking the following into account: in vitro data on the enzymology of glucuronide formation from aglycone, pharmacokinetic principles based on empirical data for inhibition of metabolism, and clinical data on the pharmacokinetic drug-drug interactions of drugs primarily cleared by glucuronidation.

Treatment of hyperlipidemia in cardiac transplant recipients

Of the 60,000 patients receiving heart transplants between 1982 and 2001, approximately 12,000 are currently alive. The high incidence of hyperlipidemia and coronary disease (also known as accelerated graft atherosclerosis, or AGA) in these patients warrants early prophylaxis soon after transplantation with 3-hydroxy-3-methylglutaryl (HMG) Co-A reductase inhibitors (statins). Immunosuppressive agents such as prednisone, cyclosporine, mycophenylate mofetil, and sirolimus are associated with hyperlipidemia. Statins, in addition to lowering cholesterol levels, also benefit cardiac transplant recipients via effects on the immune system and endothelial function. Recent data have demonstrated that statins decrease AGA and mortality rates. Furthermore, greater benefits are seen when statins are started early. The 2 statins shown to decrease mortality in patients after cardiac transplantation are pravastatin and simvastatin, which differ in their metabolism (pravastatin is the only statin with non-cytochrome metabolism) and lipophilicity (pravastatin is less lipophilic). Although the benefit of simvastatin has been shown to extend to 8 years after transplantation, increased adverse effects in other studies with higher doses of simvastatin have resulted in new prescribing recommendations, which state that the dose of simvastatin should probably not exceed 10 mg with cyclosporine or gemfibrozil and 20 mg with amiodarone or verapamil. The evidence for potential benefits, interactions, and adverse effects of other potential lipid-lowering drugs for this patient population, such as fibrates, niacin, fish oil, cholestyramine, and ezetimibe, are also discussed. A summary algorithm is proposed, including approaches to patients with statin-associated musculoskeletal symptoms and patients with inadequate results after initial statin therapy.

Combination therapy in the management of complex dyslipidemias

PURPOSE OF REVIEW

Patients with dyslipidemias continue to be undertreated in both the primary and secondary prevention settings. Many patients have therapeutic needs that exceed simple reductions in low-density lipoprotein levels using statins. This review discusses the need for comprehensive management of all abnormalities in a given patient's lipoprotein profile and for the use of combinations of anti-lipidemic medications, when indicated.

RECENT FINDINGS

The majority of high-risk patients with manifestations of atherosclerotic disease or who have a coronary artery disease risk equivalent are not meeting their various lipoprotein targets. There is considerable reluctance to titrate statins and to use combinations of anti-lipidemic medications in patients not reaching their various lipoprotein targets. Combinations of anti-lipidemic medications can be specifically tailored to address abnormalities in multiple lipoprotein fractions. Recent clinical trials clearly demonstrate that combination therapy is well tolerated and facilitates lipoprotein goal attainment.

SUMMARY

Therapeutic approaches that incorporate the use of multiple anti-lipidemic medications should be more widely adopted in order to increase the number of patients able to meet their lipoprotein goals and to produce more substantially reduced risks for acute cardiovascular events.

Metabolism and disposition of gemfibrozil in Wistar and multidrug resistance-associated protein 2-deficient TR- rats

1. The roles of multidrug resistance-associated protein (Mrp) 2 deficiency and Mrp3 up-regulation were evaluated on the metabolism and disposition of gemfibrozil. 2. Results from in vitro studies in microsomes showed that the hepatic intrinsic clearance (CLint) for the oxidative metabolism of gemfibrozil was slightly higher (1.5-fold) in male TR- rats, which are deficient in Mrp2, than in wild-type Wistar rats, whereas CLint for glucuronidation was similar in both strains. 3. The biliary excretion of intravenously administered [14C]gemfibrozil was significantly impaired in TR-) rats compared with Wistar rats (22 versus 93% of the dose excreted as the acyl glucuronides over 72 h). Additionally, the extent of urinary excretion of radioactivity was much higher in TR- than in Wistar rats (78 versus 2.6% of the dose). 4. There were complex time-dependent changes in the total radioactivity levels and metabolite profiles in plasma, liver and kidney, some of which appeared to be related to the up-regulation of Mrp3. 5. Overall, it was demonstrated that alterations in the expression of the transporters Mrp2 and Mrp3 significantly affected the excretion as well as the secondary metabolism and distribution of [14C]gemfibrozil.

Statins as the cornerstone of drug therapy for dyslipidemia: monotherapy and combination therapy options

Low-density lipoprotein (LDL) cholesterol reduction with statin treatment remains the cornerstone of lipid-lowering therapy to reduce risk of coronary heart disease. Combination therapy with a statin poses advantages in certain settings and may allow use of lower doses of multiple drugs rather than maximum doses of a single drug. Bile-acid sequestrants or the cholesterol-absorption inhibitor ezetimibe can be added to a statin to achieve greater LDL cholesterol reductions. Niacin or fenofibrate can be added to a statin for treatment of mixed dyslipidemia. Differences in statin efficacy in reducing LDL cholesterol and meeting recommended LDL cholesterol targets as well as differences among these agents in beneficial effects on other lipid parameters can affect whether and how these agents are prescribed in monotherapy and combination therapy.

Gemfibrozil and its glucuronide inhibit the organic anion transporting polypeptide 2 (OATP2/OATP1B1:SLC21A6)-mediated hepatic uptake and CYP2C8-mediated metabolism of cerivastatin: analysis of the mechanism of the clinically relevant drug-drug interaction between cerivastatin and gemfibrozil

A serious pharmacokinetic interaction between cerivastatin (CER) and gemfibrozil (GEM) has been reported. In the present study, we examined the inhibitory effects of GEM and its metabolites, M3 and gemfibrozil 1-O-beta-glucuronide (GEM-1-O-glu), on the uptake of CER by human organic anion transporting polypeptide 2 (OATP2)-expressing cells and its metabolism in cytochrome P450 expression systems. Uptake studies showed that GEM and GEM-1-O-glu significantly inhibited the OATP2-mediated uptake of CER with IC(50) values of 72 and 24 microM, respectively. They also inhibited the CYP2C8-mediated metabolism of CER with IC(50) values of 28 and 4 microM, respectively, whereas M3 had no effects. GEM and GEM-1-O-glu minimally inhibited the CYP3A4-mediated metabolism of CER. The IC(50) values of GEM and GEM-1-O-glu for the uptake and the metabolism of CER obtained in the present study were lower than their total, and not unbound, plasma concentrations. However, considering the possibly concentrated high unbound concentrations of GEM-1-O-glu in the liver and its relatively larger plasma unbound fraction compared with GEM itself, the glucuronide inhibition of the CYP2C8-mediated metabolism of CER appears to be the main mechanism for the clinically relevant drug-drug interaction. Previously reported clinical drug interaction studies showing that coadministration of GEM with pravastatin or pitavastatin, both of which are known to be cleared from the plasma by the uptake transporters in the liver, only minimally (less than 2-fold) increased the area under the plasma concentration-time curve of these statins, also supported our present conclusion.

Emerging therapeutic strategies for the management of dyslipidemia in patients with the metabolic syndrome

The benefits of lipid-lowering therapy in significantly reducing cardiovascular events has been established in many at-risk populations. However, patients with the metabolic syndrome (MS) pose a challenge for clinical management. A high degree of residual risk exists in patients with the MS or diabetes mellitus, and this is of growing importance because of the increasing prevalence of obesity and its associated comorbidities in the world. As the MS has emerged as a major risk factor for both cardiovascular disease and diabetes, targeting treatment to achieve aggressive goals becomes paramount. This article reviews emerging therapeutic strategies for the management of dyslipidemia in patients with the MS.

CYTOCHROME P450 2C8 (CYP2C8)-MEDIATED HYDROXYLATION OF AN ENDOTHELIN ETA RECEPTOR ANTAGONIST IN HUMAN LIVER MICROSOMES

In vitro studies were performed to identify the human cytochrome P450 enzyme(s) involved in the hydroxylation (isopropyl moiety) of a previously reported endothelin ET(A) receptor antagonist, compound A [(+)-(5S,6R,7R)-2-isopropylamino-7-(4-methoxy-2-[(2R)-3-methoxy-2-methylpropyl])-5-(3,4-methylenedioxyphenyl)cyclopenteno(1,2-b) pyridine 6-carboxylic acid]. Several lines of evidence indicated that the reaction was mainly catalyzed by CYP2C8. Of the 10 recombinant cytochrome P450 isoforms tested, only CYP2C8 exhibited hydroxylase activity. In agreement, inhibitory antibodies selective for CYP2C8 attenuated (>95%) the hydroxylase activity in human liver microsomes, whereas antibodies and chemical inhibitors selective for other cytochrome P450 isoforms had a minor or no effect on the reaction. In addition, the formation of the hydroxy metabolite correlated well with CYP2C8-selective paclitaxel 6alpha-hydroxylation (r(2) approximately 0.92; p < 0.0001) and amodiaquine N-de-ethylation (r(2) approximately 0.91; p < 0.0001) in a bank of human liver microsomes (n = 15 organ donors). Finally, compound A hydroxylase activity conformed to Michaelis-Menten kinetics, and the K(m) (Michaelis constant) in human liver microsomes was similar to that of CYP2C8 ( approximately 10 microM). It is concluded that the hydroxylation of compound A is mainly catalyzed by CYP2C8, and thus the reaction can possibly serve as an alternative marker assay for CYP2C8 in human liver microsomes.

Clinical pharmacokinetics of atorvastatin

Hypercholesterolaemia is a risk factor for the development of atherosclerotic disease. Atorvastatin lowers plasma low-density lipoprotein (LDL) cholesterol levels by inhibition of HMG-CoA reductase. The mean dose-response relationship has been shown to be log-linear for atorvastatin, but plasma concentrations of atorvastatin acid and its metabolites do not correlate with LDL-cholesterol reduction at a given dose. The clinical dosage range for atorvastatin is 10-80 mg/day, and it is given in the acid form. Atorvastatin acid is highly soluble and permeable, and the drug is completely absorbed after oral administration. However, atorvastatin acid is subject to extensive first-pass metabolism in the gut wall as well as in the liver, as oral bioavailability is 14%. The volume of distribution of atorvastatin acid is 381L, and plasma protein binding exceeds 98%. Atorvastatin acid is extensively metabolised in both the gut and liver by oxidation, lactonisation and glucuronidation, and the metabolites are eliminated by biliary secretion and direct secretion from blood to the intestine. In vitro, atorvastatin acid is a substrate for P-glycoprotein, organic anion-transporting polypeptide (OATP) C and H+-monocarboxylic acid cotransporter. The total plasma clearance of atorvastatin acid is 625 mL/min and the half-life is about 7 hours. The renal route is of minor importance (<1%) for the elimination of atorvastatin acid. In vivo, cytochrome P450 (CYP) 3A4 is responsible for the formation of two active metabolites from the acid and the lactone forms of atorvastatin. Atorvastatin acid and its metabolites undergo glucuronidation mediated by uridinediphosphoglucuronyltransferases 1A1 and 1A3. Atorvastatin can be given either in the morning or in the evening. Food decreases the absorption rate of atorvastatin acid after oral administration, as indicated by decreased peak concentration and increased time to peak concentration. Women appear to have a slightly lower plasma exposure to atorvastatin for a given dose. Atorvastatin is subject to metabolism by CYP3A4 and cellular membrane transport by OATP C and P-glycoprotein, and drug-drug interactions with potent inhibitors of these systems, such as itraconazole, nelfinavir, ritonavir, cyclosporin, fibrates, erythromycin and grapefruit juice, have been demonstrated. An interaction with gemfibrozil seems to be mediated by inhibition of glucuronidation. A few case studies have reported rhabdomyolysis when the pharmacokinetics of atorvastatin have been affected by interacting drugs. Atorvastatin increases the bioavailability of digoxin, most probably by inhibition of P-glycoprotein, but does not affect the pharmacokinetics of ritonavir, nelfinavir or terfenadine.

The role of fibrates in managing hyperlipidemia: Mechanisms of action and clinical efficacy

At a time when the lipid management guidelines give more and more emphasis to the identification and treatment of high-risk patients with the metabolic syndrome and diabetes, there is an obvious need to balance the known effects of low-density lipoprotein (LDL) lowering with the new evidence of clinical efficacy derived from the adjustment of high-density lipoprotein (HDL) and triglyceride levels. Whereas the statins remain the drug of choice for patients who need to reach the LDL goal, fibrate therapy may represent the best intervention for subjects with atherogenic dyslipidemia and an LDL already close to goal. In addition, the concomitant use of fibrates may significantly reduce cardiovascular risk in patients whose LDL is controlled by statin therapy. In this review, we evaluate the pharmacologic properties of the fibrate drugs, with particular attention to the effects of peroxisome proliferator activated receptor a activation in the control of dyslipidemia as well as in the attenuation of arterial inflammation. Clinical trials of fibrates, such as the Helsinki Heart Study, Veterans Affairs High-density lipoprotein Intervention Trial, Diabetes Atherosclerosis Intervention Study, and Bezafibrate Infarction Prevention trial, have conjured up a scenario for the clinical utility of fibrates and their possible superiority to statins in the management of obese, insulin-resistant, and diabetic patients presenting with near-goal LDL and inappropriate HDL and triglyceride levels.

Pitavastatin: efficacy and safety profiles of a novel synthetic HMG-CoA reductase inhibitor

The use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, statins, has been shown to reduce major cardiovascular events in both primary and secondary prevention, and statins became one of the most widely prescribed classes of drugs throughout the world. Previously, statins have been well tolerated and have shown favorable safety profiles. However, the voluntary withdrawal of cerivastatin from the market because of a disproportionate number of reports of rhabdomyolysis-associated deaths drew attention to the pharmacokinetic profile of statins, which may possibly have been related to serious drug-drug interactions. Pitavastatin (NK-104, previously called itavastatin or nisvastatin, Kowa Company Ltd., Tokyo) is a novel, fully synthetic statin, which has a potent cholesterol-lowering action. The short-term and long-term lipid-modifying effects of pitavastatin have already been investigated in subjects with primary hypercholesterolemia, heterozygous familial hypercholesterolemia, hypertriglyceridemia, and type-2 diabetes mellitus accompanied by hyperlipidemia. Within the range of daily doses from 1 to 4 mg, the efficacy of pitavastatin as a lipid-lowering drug seems to be similar, or potentially superior, to that of atorvastatin. According to the results of pharmacokinetic studies, pitavastatin showed favorable and promising safety profile; it was only slightly metabolized by the cytochrome P450 (CYP) system, its lactone form had no inhibitory effects on the CYP3A4-mediated metabolism of concomitantly administered drugs; P-glycoprotein-mediated transport did not play a major role in its disposition, and pitavastatin did not inhibit P-glycoprotein activity. It could be concluded that pitavastatin could provide a new and potentially better therapeutic choice for lipid-modifying therapy than do the currently available statins. The efficacy and safety of higher dose treatment, as well as its long-term effects in the prevention of coronary artery disease, should be further investigated.

Effect of Gemfibrozil on the Metabolism of Pitavastatin - Determining the Best Animal Model for Human CYP And UGT Activities

A series of studies was conducted to determine the best animal model for human CYP and UGT activities. The investigation focused primarily on the interactions occurring in the CYP- or UGT-mediated metabolism of pitavastatin, and involved in vitro and in vivo experiments. We found that the best animal models for human CYP-mediated hydroxylation and UGT-mediated lactonization of pitavastatin were rats and dogs, respectively. In addition, a large difference in the metabolic properties of pitavastatin was found between monkeys and humans. In the presence of gemfibrozil, the CYP- or UGT-mediated metabolism of pitavastatin was inhibited in vitro. However, gemfibrozil treatment had no inhibitory effect on the AUC of pitavastatin and its lactone form in rats and dogs. We conclude that the plasma level of pitavastatin would not be increased by co-administration of gemfibrozil in humans.

Effects of baseline level of triglycerides on changes in lipid levels from combined fluvastatin + fibrate (bezafibrate, fenofibrate, or gemfibrozil)

This analysis was conducted to evaluate the effect of baseline triglyceride levels on lipid and lipoprotein changes after treatment with the combination of fluvastatin and fibrates. The analysis involved pooling data from 10 studies that included 1,018 patients with either mixed hyperlipidemia or primary hypercholesterolemia. Patients received a combination of fluvastatin and a fibrate (bezafibrate, fenofibrate, or gemfibrozil) from 16 to 108 weeks. The combination of fluvastatin and a fibrate improved lipid profiles, with reductions in triglycerides, low-density lipoprotein (LDL) cholesterol, and non-high-density lipoprotein (non-HDL) cholesterol that were dependent on baseline triglyceride levels. The greatest triglyceride reductions were observed in patients with high baseline triglyceride levels (> or =400 mg/dl) (41%, p <0.0001). The greatest LDL cholesterol and non-HDL cholesterol reductions occurred in patients with normal baseline triglyceride levels (<150 mg/dl) (35% and 33%, respectively; p <0.0001). The combined fluvastatin-fibrate therapy was well tolerated. Two patients (0.2%) (1 patient on fluvastatin 80 mg + gemfibrozil 1,200 mg and 1 patient on fluvastatin 20 mg + fenofibrate 200 mg) had creatine kinase levels > or =10 times the upper limit of normal, 11 patients (1.1%) had an elevation in alanine transaminase >3 times the upper limit of normal, and 7 patients (0.7%) had elevations in aspartate transaminase >3 times the upper limit of normal. Combined fluvastatin-fibrate therapy takes advantage of the complementary effects of the 2 agents, with the extent of triglyceride, LDL cholesterol, and non-HDL cholesterol lowering dependent on baseline triglyceride levels. The combination of fluvastatin and fibrates was well tolerated with no major safety concerns.

SOLVENT EFFECT ON cDNA-EXPRESSED HUMAN SULFOTRANSFERASE (SULT) ACTIVITIES IN VITRO

Sulfation is an important reaction in the biotransformation of steroid hormones, neurotransmitters, drugs, and other xenobiotics, yet little is known about the effects of organic solvents on sulfotransferase (SULT) activities in vitro. Initial experiments found that surprisingly low levels of solvent had dramatic effects on sulfotransferase activity. Consequently, we evaluated the effects of five commonly used solvents (methanol, ethanol, acetonitrile, dimethyl sulfoxide, and dimethyl formamide) on activities of cDNA-expressed sulfotransferase isozymes 1A1 (4-nitrophenol sulfation), 1A3 (dopamine sulfation), 1E1 (ethynylestradiol sulfation), and 2A1 (dehydroepiandrosterone sulfation). In addition, 1-hydroxypyrene was used as a general fluorescent probe for all four sulfotransferase isoforms examined. When substrates were present at their respective isoform-specific Km values, methanol and ethanol (0.4%, v/v) generally had less effect than acetonitrile, dimethyl sulfoxide, and dimethyl formamide on sulfotransferase activities. Acetonitrile, a commonly used solvent in cytochrome P450 studies, inhibited SULT1A1 activities (approximately 40%) at 0.4% (v/v), but activated SULT1E1-mediated 1-hydroxypyrene sulfation approximately 2.6-fold. Assuming a two-site kinetic model, studies revealed that solvent affected Vmax1, Vmax2, and the Ki value of 1-hydroxypyrene sulfation mediated by SULT1E1. In contrast, the Km value was not affected, suggesting that solvent may potentially alter binding interactions of the second substrate molecule, but not the first. Additional experiments with expressed SULT1A1, supplemented with control protein, revealed that the inhibitory effect of solvent (0.4%, v/v) was reduced to <15% for all solvents examined. Thus, it is recommended that ethanol is used as the preferred solvent vehicle and that incubations with expressed enzyme contain >12 microg/ml total protein.

The human hepatic metabolism of simvastatin hydroxy acid is mediated primarily by CYP3A, and not CYP2D6

AIMS

To identify the cytochrome P450 (CYP) isoforms responsible for the metabolism of simvastatin hydroxy acid (SVA), the most potent metabolite of simvastatin (SV).

METHODS

The metabolism of SVA was characterized in vitro using human liver microsomes and recombinant CYPs. The effects of selective chemical inhibitors and CYP antibodies on SVA metabolism were assessed in human liver microsomes.

RESULTS

In human liver microsomes, SVA underwent oxidative metabolism to three major oxidative products, with values for Km and Vmax ranging from about 50 to 80 microM and 0.6 to 1.9 nmol x min(-1) x mg(-1) protein, respectively. Recombinant CYP3A4, CYP3A5 and CYP2C8 all catalysed the formation of the three SVA metabolites, but CYP3A4 was the most active. CYP2D6 as well as CYP2C19, CYP2C9, CYP2A6, CYP1A2 did not metabolize SVA. Whereas inhibitors that are selective for CYP2D6, CYP2C9 or CYP1A2 did not significantly inhibit the oxidative metabolism of SVA, the CYP3A4/5 inhibitor troleandomycin markedly (about 90%) inhibited SVA metabolism. Quercetin, a known inhibitor of CYP2C8, inhibited the microsomal formation of SVA metabolites by about 25-30%. Immunoinhibition studies revealed 80-95% inhibition by anti-CYP3A antibody, less than 20% inhibition by anti-CYP2C19 antibody, which cross-reacted with CYP2C8 and CYP2C9, and no inhibition by anti-CYP2D6 antibody.

CONCLUSIONS

The metabolism of SVA in human liver microsomes is catalysed primarily (> or = 80%) by CYP3A4/5, with a minor contribution (< or = 20%) from CYP2C8. CYP2D6 and other major CYP isoforms are not involved in the hepatic metabolism of SVA.

Combination lipid-lowering therapy in diabetes

Owing to the National Cholesterol Education Program Adult Treatment Panel III recommendations that patients with diabetes require a low-density lipoprotein (LDL) less than 100 mg/dL and a non-high-density lipoprotein (HDL) less than 130 mg/dL, frequently, combination lipid-lowering therapy is required. However, diabetic patients are commonly on multiple medications and have renal impairment. Therefore, the risk of myopathy with statin therapy is markedly increased. The safety of lipid-lowering therapy can be significantly improved by avoiding high-dose statins in combination with fibrates, especially gemfibrozil. To achieve non-HDL goals combining fenofibrate, or if glucose is well controlled, niacin, with a statin (not to exceed 40 mg), may significantly reduce the risk of myopathy. For diabetic patients who require additional LDL lowering, ezetimibe may provide a safe combination to a statin to achieve the LDL goal of less than 100 mg/dL.

Cytochrome P450 drug interactions within the HMG-CoA reductase inhibitor class: are they clinically relevant?

The present review outlines the clinical relevance of pharmacokinetic drug interactions within the HMG-CoA reductase inhibitor class. These interactions can result in markedly increased or decreased plasma concentrations of some drugs within this class. However, the relationship between altered plasma concentrations and adverse effects or toxicity may not be linear. It is likely that other variables affect this concentration-effect relationship including: rapid changes in the concentration, concomitant lipid-lowering therapy or host genetic factors that code for different forms or amounts of metabolising enzymes and drug receptors. It is not currently possible to predict which patients will manifest clinically important drug-drug interactions, nor what concentration of an HMG-CoA reductase inhibitor will cause rhabdomyolysis. Thus, until prescribers have better scientific information from which to develop a 'therapeutic range' for each agent, caution should be exercised. In particular, patients taking a CYP3A4-metabolised agent, e.g. atorvastatin, simvastatin and lovastatin, should not be started on a CYP3A4 inhibitor or inducer without close monitoring.

Combination lipid-lowering therapy with statins: safety issues in the postcerivastatin era

Combination lipid-altering regimens represent an emerging clinical paradigm to meet increasingly stringent consensus lipoprotein targets for coronary prevention. This practice, together with escalating prevalences of coronary artery disease in certain ageing (western industrial) populations, polypharmacy in the elderly and the recent voluntary market withdrawal of cerivastatin, warrants a re-examination of the safety profiles of 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitors (i.e., statins). These agents are exceedingly well-tolerated in the vast majority of patients, very infrequently precipitating musculoskeletal symptoms and/or signs. Statins vary in their pharmacological profiles, leading to distinct levels of systemic exposure and capacities to penetrate skeletal myocytes. Pharmacokinetic interactions with certain agents increase the likelihood of statin-induced myopathy and, in exceedingly rare instances, potentially fatal rhabdomyolysis with myoglobinuria and renal failure. As with other medical decisions, the anticipated benefits of long-term statin therapy, with or without other lipid-altering agents, need to be weighed against the prospects of clinically significant drug interactions. In clinical trials and postmarketing surveillance, the two statins that are not metabolised by the cytochrome P450 3A4 system (fluvastatin and pravastatin) have exhibited very low propensities to elicit myopathy when combined with other agents. These agents should be considered initially when contemplating combination lipid-lowering regimens for coronary prevention.

The UDP-glucuronosyltransferase 1A9 enzyme is a peroxisome proliferator-activated receptor alpha and gamma target gene

Peroxisome proliferator-activated receptor (PPAR) alpha and gamma are ligand-activated transcription factors belonging to the nuclear receptor family. PPAR alpha mediates the hypolipidemic action of the fibrates, whereas PPAR gamma is a receptor for the antidiabetic glitazones. In the present study, the UDP-glucuronosyltransferase (UGT) 1A9 enzyme is identified as a PPAR alpha and PPAR gamma target gene. UGTs catalyze the glucuronidation reaction, which is a major pathway in the catabolism and elimination of numerous endo- and xenobiotics. Among the UGT1A family enzymes, UGT1A9 metabolizes endogenous compounds, including catecholestrogens, and xenobiotics, such as fibrates and to a lesser extent troglitazone. Treatment of human hepatocytes and macrophages and murine adipocytes with activators of PPAR alpha or PPAR gamma resulted in an enhanced UGT1A9 expression and activity. In addition, disruption of the PPAR alpha gene in mice completely abolished the PPAR alpha agonist-induced UGT1A9 mRNA and activity levels. A PPAR response element was identified in the promoter of UGT1A9 at positions -719 to -706 bp by transient transfection and electromobility shift assays. Considering the role of UGT1A9 in catecholestrogen metabolism, PPAR alpha and PPAR gamma activation may contribute to the protection against genotoxic catecholestrogens by stimulating their inactivation in glucuronide derivatives. Furthermore, since UGT1A9 is involved in the catabolism of fibrates, these results suggest that PPAR alpha and PPAR gamma may control the intracellular level of active fibrates.

Effects of adding fenofibrate (200 mg/day) to simvastatin (10 mg/day) in patients with combined hyperlipidemia and metabolic syndrome

Combined hyperlipidemia predisposes subjects to coronary heart disease. Two lipid abnormalities--increased cholesterol and atherogenic dyslipidemia--are potential targets of lipid-lowering therapy. Successful management of both may require combined drug therapy. Statins are effective low-density lipoprotein (LDL) cholesterol-lowering drugs. For atherogenic dyslipidemia (high triglycerides, small LDL, and low high-density lipoprotein [HDL]), fibrates are potentially beneficial. The present study was designed to examine the safety and efficacy of a combination of low-dose simvastatin and fenofibrate in the treatment of combined hyperlipidemia. It was a randomized, placebo-controlled trial with a crossover design. Three randomized phases were employed (double placebo, simvastatin 10 mg/day and placebo, and simvastatin 10 mg/day plus fenofibrate 200 mg/day). Each phase lasted 3 months, and in the last week of each phase, measurements were made of plasma lipids, lipoprotein cholesterol, plasma apolipoproteins B, C-II, and C-III and LDL speciation on 3 consecutive days. Simvastatin therapy decreased total cholesterol by 27%, non-HDL cholesterol by 30%, total apolipoprotein B by 31%, very low-density lipoprotein (VLDL) + intermediate-density lipoprotein (IDL) cholesterol by 37%, VLDL + IDL apolipoprotein B by 14%, LDL cholesterol by 28%, and LDL apolipoprotein B by 21%. The addition of fenofibrate caused an additional decrease in VLDL + IDL cholesterol and VLDL + IDL apolipoprotein B by 36% and 32%, respectively. Simvastatin alone caused a small increase in the ratio of large-to-small LDL, whereas the addition of fenofibrate to simvastatin therapy caused a marked increase in the ratio of large-to-small LDL species. Simvastatin alone produced a small (6%) and insignificant increase in HDL cholesterol concentrations. When fenofibrate was added to simvastatin therapy, HDL cholesterol increased significantly by 23%. No significant side effects were observed with either simvastatin alone or with combined drug therapy. Therefore, a combination of simvastatin 10 mg/day and fenofibrate 200 mg/day appears to be effective and safe for the treatment of atherogenic dyslipidemia in combined hyperlipidemia.

Effects of gemfibrozil, itraconazole, and their combination on the pharmacokinetics and pharmacodynamics of repaglinide: potentially hazardous interaction between gemfibrozil and repaglinide

AIMS/HYPOTHESIS

Our aim was to investigate possible interactions of gemfibrozil, itraconazole, and their combination with repaglinide.

METHODS

In a randomised crossover study, 12 healthy volunteers received twice daily for 3 days either 600 mg gemfibrozil, 100 mg itraconazole (first dose 200 mg), both gemfibrozil and itraconazole, or placebo. On day 3 they ingested a 0.25 mg dose of repaglinide. Plasma drug and blood glucose concentrations were followed for 7 h and serum insulin and C-peptide concentrations for 3 h postdose.

RESULTS

Gemfibrozil raised the area under the plasma concentration-time curve (AUC) of repaglinide 8.1-fold (range 5.5- to 15.0-fold; p<0.001) and prolonged its half-life (t(1/2)) from 1.3 to 3.7 h (p<0.001). Although itraconazole alone raised repaglinide AUC only 1.4-fold (1.1- to 1.9-fold; p<0.001), the gemfibrozil-itraconazole combination raised it 19.4-fold (12.9- to 24.7-fold) and prolonged the t(1/2) of repaglinide to 6.1 h (p<0.001). Plasma repaglinide concentration at 7 h was increased 28.6-fold by gemfibrozil and 70.4-fold by the gemfibrozil-itraconazole combination (p<0.001). Gemfibrozil alone and in combination with itraconazole considerably enhanced and prolonged the blood glucose-lowering effect of repaglinide; i.e., repaglinide became a long-acting and stronger antidiabetic.

CONCLUSION/INTERPRETATION

Clinicians should be aware of this previously unrecognised and potentially hazardous interaction between gemfibrozil and repaglinide. Concomitant use of gemfibrozil and repaglinide is best avoided. If the combination is considered necessary, repaglinide dosage should be greatly reduced and blood glucose concentrations carefully monitored.

Comparative pharmacology of rosuvastatin

The major therapeutic action of statin drugs is reduction in levels of circulating atherogenic lipoproteins as a result of inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase mainly in the liver. The magnitude of reduction of atherogenic lipoproteins differs among various statins. It is suggested that an ideal statin would maximize the pharmacodynamic activity in the liver and minimize the inhibitory activity outside the liver, particularly in some vulnerable tissues, such as skeletal muscle. An additional advantage would be a low risk of undesirable interactions with other drugs. Compared with other statins, rosuvastatin has been found to be a relatively potent inhibitor of HMG-CoA reductase and to have a high degree of selectivity for effect in liver cells compared with a range of non-hepatic cells, including cultured human skeletal muscle cells. In addition, rosuvastatin undergoes relatively little metabolism by the hepatic CYP system; it has a moderate degree of systemic bioavailability and a relatively long elimination half-life. On the basis of these criteria, rosuvastatin represents a step forward in efforts to optimize the pharmacologic properties of the statin class.

Hypercholesterolemia and Dyslipidemia: Issues for the Clinician

The current state of the art in the diagnosis and treatment of lipoprotein disorders has progressed beyond the standard "lipid profile," which includes total low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol, along with fasting triglycerides. Incorporating aspects of the atherogenic lipoprotein profile (ALP) (ALP and LDL subclass distribution), HDL subclass distribution, apolipoprotein E isoforms, lipoprotein (a), homocysteine, and high-sensitivity C-reactive protein provides the clinician with the tools to create a more detailed, accurate, and personalized diagnosis of disorders contributing to coronary artery disease in their patients. Sophisticated laboratory tests are available to clinicians through technology transfer programs as exemplified by the Lawrence Berkeley National Laboratory/Berkeley HeartLab, Berkeley, CA, collaboration and allow clinicians access to research quality laboratory tools. This has significant clinical relevance because the presence of these disorders guides treatment that is specific to the disorder(s). Appropriate treatment has been shown to have significantly greater clinical benefit in patient subgroups exhibiting the disorder the therapy is most likely to correct. A single drug or lifestyle therapy plan is no longer appropriate for all patients. The treatment must match the individual disorder(s).

Inhibition of transporter-mediated hepatic uptake as a mechanism for drug-drug interaction between cerivastatin and cyclosporin A

The mechanism involved in the clinically relevant drug-drug interaction (DDI) between cerivastatin (CER) and cyclosporin A (CsA) has not yet been clarified. In the present study, we examined the possible roles of transporter-mediated hepatic uptake in this DDI. The uptake of [(14)C]CER into human hepatocytes prepared from three different donors was examined. Kinetic analyses revealed K(m) values for the uptake of [(14)C]CER within the range of 3 to 18 microM, suggesting that more than 70% of the total uptake at therapeutic CER concentrations was accounted for by a saturable process, i.e., transporter-mediated uptake. This uptake was inhibited by CsA with K(i) values of 0.3 to 0.7 microM. The uptake of [(14)C]CER was also examined in human organic anion transporting polypeptide-2 (OATP2)-expressing Madin-Darby canine kidney cells (MDCKII). Saturable OATP2-mediated uptake of [(14)C]CER was observed and was also inhibited by CsA, with a K(i) value of 0.2 microM. These results suggest that the DDI between CER and CsA involves the inhibition of transporter-mediated uptake of CER and, at least in part, its OATP2-mediated uptake. The effect of CsA on the in vitro metabolism of [(14)C]CER was also examined. The metabolism of [(14)C]CER was inhibited by CsA with an IC(50) value of more than 30 microM. From these results, we conclude that the DDI between CER and CsA is mainly due to the inhibition of transporter (at least partly OATP2)-mediated uptake in the liver.

[Drug interactions with antilipemics]

The HMG-CoA reductase inhibitors (statins) and fibrates have been associated with myotoxicity, which, in some cases, has been fatal. Rhabdomyolysis is frequently observed during drug interactions with elevated plasma concentrations. Statins have a low oral bioavailability because of their intense first-pass extraction. Cytochrome P450 3A4 (CYP3A4) is responsible for the metabolism of atorvastatin and simvastatin which present the highest risk of drug interactions with CYP3A4 inhibitors, such as macrolides, antifungal agents, protease inhibitors, calcium channel blockers, amiodarone, and grapefruit juice. Fluvastatin has a low potential for drug interactions due to its CYP2C9-dependant metabolism. Pravastatin liver extraction does not involve CYPs and presents a low potential for drug interactions. Fibrates have a high oral bioavailability (approximately 100%), and this minimises the risk of drug interactions. However, fibrates alter the pharmacokinetics of some drugs, possibly via CYP2C9 and UDP-glucuronyltransferase (UGT) inhibition. Only three cholesterol-reducing agents have demonstrated their ability to reduce the incidence of cardiovascular death in long-term follow-up randomised trials among patients with atherosclerosis. Simvastatin exhibits the highest potential for drug interactions, pravastatin and gemfibrozil the lowest.

Statin-fibrate combination: therapy for hyperlipidemia: a review

Statins and fibrates are well-established treatments for hyperlipidaemias and the prevention of vascular events. However, fibrate + statin therapy has been restricted following early reports of rhabdomyolysis that mainly involved gemfibrozil, originally with bovastatin, and recently, with cerivastatin. Despite this limitation, several reports describing combination therapy have been published. This review considers these studies and the relevant indications and contraindications. Statin + fibrate therapy should be considered if monotherapy or adding other drugs (e.g. cholesterol absorption inhibitors, omega-3 fatty acids ornicotinic acid) did not achieve lipid targets or is impractical. Combination therapy should be hospital-based and reserved for high-risk patients with a mixed hyperlipidaemia characterised by low density lipoprotein cholesterol (LDL) >2.6 mmol/l(100 mg/dl, high density lipoprotein cholesterol (HDL) <1.0 mmol/l (40 mg/dl) and/or triglycerides> 5.6 mmol/l (500 mg/dl. These three 'goals' are individually mentioned in guidelines. Patients should have normal renal, liver and thyroid function tests and should not be receiving therapy with cyclosporine, protease inhibitors or drugs metabolised through cytochrome P450 (especially 3A4). Combination therapy is probably best conducted using drugs with short plasma half-lives; fibrates should be prescribed in the morning and statins at night to minimise peak dose interactions. Both drug classes should be progressively titated from low doses. Regular (3-monthly) monitoring of liver function and creatine kinase is required. In conclusion, fibrate + statin therapy remains an option in high-risk patents. However, long-term studies involving safety monitoring and vascular endpoints are required to demonstrate the efficacy of this regimen.

Safety considerations for statins

PURPOSE OF REVIEW

The hydroxymethyl glutaryl coenzyme A reductase inhibitors or statins offer important benefits for the large populations of individuals at high risk for coronary heart disease. These drugs have a good safety profile. Nevertheless, differences in physicochemical and pharmacokinetic properties between statins may translate into significant differences in long-term safety. This review focuses on long-term adverse effects related to statin use, namely hepatotoxicity and myopathy. Moreover, the most common drugs used in combination with statins in long-term therapies are analyzed in terms of possible drug/drug interactions affecting the safety of statins.

RECENT FINDINGS

The withdrawal of cerivastatin from the global market in 2001, because of severe cases of rhabdomyolysis, highlighted concerns regarding the safety of the entire class. Afterwards, the role of statins and their interactions with other drugs in precipitating this condition have been carefully reviewed. In approximately 60% of the total number of cases, statin-related rhabdomyolysis was found to be related to drug/drug interactions. Recently, all cases of fatal rhabdomyolysis associated with statin use have been reported to the US Food and Drug Administration. This has shown that fatal rhabdomyolysis among statin users is a rare event, the reporting rates being much less than one death per million prescriptions in the case of all statins except cerivastatin.

SUMMARY

The safety and tolerability of the available statins support their use as the first-line treatment of patients at high risk for coronary heart disease, since the clinical benefits greatly outweigh the small risk of myopathy. Nevertheless, clinicians should be aware of the adverse effects possibly related to statin therapy, particularly in patients at high risk for coronary heart disease and requiring long-term multiple-drug therapies.

Gemfibrozil inhibits CYP2C8-mediated cerivastatin metabolism in human liver microsomes

To explore the mechanism of the interaction between gemfibrozil and cerivastatin, the enzyme mapping of the oxidative metabolism of cerivastatin and the effect of gemfibrozil on cerivastatin metabolism were studied using human liver microsomes and expressed cytochrome p450 (p450) CYP2C8 and 3A4 isoforms. Based on studies with isoform-selective chemical inhibitors and expressed enzymes, CYP2C8 and CYP3A4 were equally important in the formation of desmethylcerivastatin (M-1), whereas the formation of the quantitatively most important hydroxy metabolite (M-23) was predominantly mediated via CYP2C8; other p450 isoforms played a negligible role. In human liver microsomes, gemfibrozil markedly inhibited M-23 formation, with a K(i) (IC(50)) value of 69 (95) micro M, whereas inhibition of M-1 formation was weaker with a K(i) (IC(50)) value of 273 (>250) micro M. The inhibitory effect of gemfibrozil was attributable to inhibition of CYP2C8 rather than CYP3A4, as evidenced by potent inhibition of the formation of M-23 (IC(50) = 68 micro M) and M-1 (IC(50) = 78 micro M) in recombinant CYP2C8 but not in recombinant CYP3A4. Additionally, gemfibrozil inhibited paclitaxel 6 alpha-hydroxylation [K(i) (IC(50)) = 75 micro M (91 micro M)], a CYP2C8 marker reaction, but did not inhibit testosterone 6 beta-hydroxylation (CYP3A4). The present in vitro findings suggest that inhibition of CYP2C8 activity by gemfibrozil at least partially explains the interaction between gemfibrozil and cerivastatin. The formation of M-23 acid from cerivastatin is mediated mainly by CYP2C8 and thus may be a suitable CYP2C8 probe reaction. Inhibition of CYP2C8-mediated metabolism by gemfibrozil warrants further in vivo exploration.

Existing and investigational combination drug therapy for high-density lipoprotein cholesterol

For the past 3 to 4 decades, clinical outcomes trials have shown that drugs that favorably alter serum lipid levels reduce the risk of coronary artery disease (CAD) events. However, despite these successes, the reduction in serum low-density lipoprotein (LDL) cholesterol levels with monotherapy lipid-altering drugs does not "cure" CAD to the same degree that antibiotics "cure" many infections, nor do they "prevent" CAD in the same way that childhood immunizations "prevent" the onset of such conditions as measles, mumps, and rubella. Clinical outcome trials of monotherapy lipid-altering drugs have demonstrated a reduction in the relative risk of CAD in only a minority of patients. Thus, although safe and very effective in lowering serum LDL cholesterol levels, drugs that predominantly lower cholesterol do not "cure" atherosclerotic disease, nor have they been shown to "prevent" most CAD events in numerous clinical outcome trials. The reason for the suboptimal CAD outcomes benefits of monotherapy lipid-altering drugs is likely because atherosclerosis is a complex pathologic process with many important risk factors involved in the initiation and progression of atherosclerotic lesions and involved in the onset of the CAD event itself. An elevated serum LDL cholesterol level is an important CAD risk factor, but it is not the only lipid risk factor. A decreased serum high-density lipoprotein (HDL) cholesterol level is another important risk factor for CAD. Combination therapy through existing drugs (or possibly, in the future, through investigational lipid-altering drugs) may not only improve LDL cholesterol but also improve serum HDL cholesterol levels. This more global, multidimensional approach to lipid-altering drug treatment may provide the best chance to prevent CAD.

Combination therapy for dyslipidemia: safety and regulatory considerations

The use of combination therapy is an effective way to manage dyslipidemia in patients with coronary artery disease (CAD). However, combination therapy is not a frequently used strategy in the treatment of CAD. Aggressive lipid-altering therapy often requires the use of combination therapy involving statins in conjunction with niacin, fibric-acid derivatives, ezetimibe, or bile acid resins. Yet, safety concerns regarding the combination of statins with other lipid-altering drugs and patient acceptance of combination therapy have influenced its application in the treatment of CAD. This article discusses several safety and regulatory considerations for the use of combination therapy for dyslipidemia.

Effects of fibrates on metabolism of statins in human hepatocytes

This study investigated the metabolic interaction between fibrates and statin hydroxy acids in human hepatocytes. Gemfibrozil (GFZ) modestly affected the formation of beta-oxidative products and CYP3A4-mediated oxidative metabolites of simvastatin hydroxy acid (SVA) but markedly inhibited the glucuronidation-mediated lactonization of SVA and the glucuronidation of a beta-oxidation product (IC(50) approximately 50 and 15 microM, respectively). In contrast, fenofibrate had a minimal effect on all the metabolic pathways of SVA. GFZ also significantly inhibited (IC(50) approximately 50-60 microM) the oxidation of cerivastatin (CVA) and rosuvastatin (RVA), but not of atorvastatin (AVA), while effectively decreasing (IC(50) approximately 30 to 60 microM) the lactonization of all three statins. As was observed previously with other statin hydroxy acids, RVA underwent significant glucuronidation to form an acyl glucuronide conjugate and lactonization to form RVA lactone in human liver microsomes and by UGT 1A1 and 1A3. While GFZ is not an inhibitor of CYP3A4, it is a competitive inhibitor (K(i) = 87 microM) of CYP2C8, a major catalyzing enzyme for CVA oxidation. These results suggest that 1) the pharmacokinetic interaction observed between GFZ and statins was not likely mediated by the inhibitory effect of GFZ on the beta-oxidation, but rather by its effect primarily on the glucuronidation and non-CYP3A-mediated oxidation of statin hydroxy acids, and 2) there is a potential difference between fibrates in their ability to affect the pharmacokinetics of statins, and among statins in their susceptibility to metabolic interactions with GFZ in humans.