Mechanistic studies on metabolic interactions between gemfibrozil and statins

Management of Cardiovascular Risk in Patients With Type 2 Diabetes Mellitus as a Component of the Cardiometabolic Syndrome

Heart disease and stroke are the most life-threatening consequences of diabetes mellitus, with mortality rates up to two to four times higher for persons with diabetes vs. those without and accounting for up to 65% of deaths. The cardiometabolic syndrome is a potent indicator of future risk of type 2 diabetes and concomitant increased potential for cardiovascular morbidity and mortality. Pharmacologic treatment is usually necessary to improve blood pressure and lipids, thereby decreasing the risk of cardiovascular disease. The reduction of cardiovascular and renal risk with type 2 diabetes and elevated blood pressure are compelling indications for thiazide diuretics, blockers, angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, and calcium channel blockers. Nevertheless, most patients with type 2 diabetes and elevated blood pressure will require two or more agents to lower blood pressure to the recommended goal of <130/80 mm Hg, and combination therapy may be beneficial. In patients with the cardiometabolic syndrome without type 2 diabetes, the present goal is to maintain BP <140/90 mm Hg, although recent data suggest potential decrease in the progression of prehypertension to hypertension with antihypertensive medication. Furthermore, blockers of the renin-angiotensin system may actually prevent newonset diabetes. It is reasonable for patients with type 2 diabetes and cardiovascular disease to achieve an optional low-density lipoprotein cholesterol (LDL-C) goal <70 mg/dL, and statin therapy should be considered regardless of baseline LDL-C level. In patients with the cardiometabolic syndrome without type 2 diabetes and calculated moderately high-risk status (two or more risk factors; 10-year risk, 10%-20%), the present goal for LDL-C is <130 mg/dL, with perhaps a therapeutic option of <100 mg/dL, and in patients with the cardiometabolic syndrome at lower risk, the LDL-C goal remains <160 mg/dL. Multifactorial management must be utilized to prevent progression of cardiovascular risk with the cardiometabolic syndrome and the ravages of cardiovascular disease in persons with type 2 diabetes, including antiplatelet therapy with aspirin.

Efficacy and safety of the coadministration of ezetimibe/simvastatin with fenofibrate in patients with mixed hyperlipidemia

BACKGROUND

Mixed hyperlipidemia is characterized by elevated low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and TG-rich lipoprotein levels.

METHODS

In a multicenter, randomized, double-blind, placebo-controlled, parallel arm trial, eligible patients were 18 to 79 years of age, with mixed hyperlipidemia (LDL-C 130-220 mg/dL, TG 150-500 mg/dL). Patients with type 2 diabetes were limited to those with LDL-C of 100 to 180 mg/dL. Patients (N = 611) were randomized in a 3:3:3:1 ratio to one of 4 treatment arms for 12 weeks: ezetimibe/simvastatin 10/20 mg (EZE/SIMVA) + fenofibrate 160 mg (FENO), EZE/SIMVA 10/20 mg, FENO 160 mg, or placebo. The primary objective was to evaluate the LDL-C-lowering efficacy of EZE/SIMVA + FENO versus FENO monotherapy.

RESULTS

Low-density lipoprotein cholesterol level was significantly (P < .05) reduced with EZE/SIMVA + FENO (-45.8%) compared with FENO (-15.7%) or placebo (-3.5%), but not when compared with EZE/SIMVA (-47.1%). High-density lipoprotein cholesterol and apolipoprotein A-I levels were significantly increased with EZE/SIMVA + FENO (18.7% and 11.1%, respectively) treatment compared with EZE/SIMVA (9.3% and 6.6%) or placebo (1.1% and 1.6%), but not when compared with FENO (18.2% and 10.8%). Triglyceride, non-high-density lipoprotein cholesterol, and apolipoprotein B levels were significantly reduced with EZE/SIMVA + FENO (-50.0%, -50.5%, and -44.7%, respectively) versus all other treatments. Treatment with EZE/SIMVA + FENO was generally well tolerated with a safety profile similar to the EZE/SIMVA and FENO therapies.

CONCLUSIONS

Coadministration of EZE/SIMVA + FENO effectively improved the overall atherogenic lipid profile of patients with mixed hyperlipidemia. Clinical trial registry number: NCT 00093899 (http://www.ClinicalTrials.gov).

Predicting the Oxidative Metabolism of Statins: An Application of the MetaSite® Algorithm

PURPOSE

This study was undertaken to examine the MetaSite algorithm by comparing its predictions with experimentally characterized metabolites of statins produced by cytochromes P450 (CYPs).

METHODS

Seven statins were investigated, namely atorvastatin, cerivastatin, fluvastatin, pitavastatin and pravastatin which are (or were) used in their active hydroxy-acid form, and lovastatin and simvastatin which are used as the lactone prodrug. But given the fast lactone-hydroxy-acid equilibrium undergone by statins, both forms were investigated for each of the seven drugs. The MetaSite version 2.5.3 used here contains the homology 3D-models of CYP1A2, CYP2C19, CYP2C9, CYP2D6 and CYP3A4. In addition, we also used the crystallographic 3D-structure of human CYP2C9 and CYP3A4. To allow a better interpretation of results, the probability function PsMi calculated by MetaSite (namely the probability of atom i to be a site of metabolism) was explicitly decomposed into its two components, namely a recognition score Ei (the accessibility of atom i) and the chemical reactivity Ri of atom i toward oxidation reactions.

RESULTS

The current version of MetaSite is known to work best with prior experimental knowledge of the cytochrome(s) P450 involved. And indeed, experimentally confirmed sites of oxidation were correctly given a high priority by MetaSite. In particular 77% of correct predictions (including false positive but, as discussed, this is not necessarily a shortcoming) were obtained when considering the first five metabolites indicated by MetaSite.

CONCLUSION

To the best of our knowledge, this is the first independent report on the software. It is expected to contribute to the development of improved versions, but above all it demonstrates that the usefulness of such softwares critically depends on human experts.

Risk and predictability of drug interactions in the elderly

The issue of drug-drug interactions is particularly relevant for geriatric patients with epilepsy because they are often treated with multiple medications for concurrent diseases such as cardiovascular disease and psychiatric disorders (e.g., dementia and depression). The antidepressants with the least potential for altering antiepileptic drug (AED) metabolism are citalopram, escitalopram, venlafaxine, duloxetine, and mirtazapine. The use of established AEDs with enzyme-inducing properties, such as carbamazepine, phenytoin, and phenobarbital, may be associated with reductions in the levels of drugs such as donepezil, galantamine, and particularly warfarin. Carbamazepine, phenytoin, and phenobarbital have been reported to decrease prothrombin time in patients taking oral anticoagulants, although with phenytoin, an increase in prothrombin time has also been reported. Drugs associated with increased risk of bleeding in patients taking oral anticoagulants include selective serotonin reuptake inhibitors (especially fluoxetine), gemfibrozil, fluvastatin, and lovastatin. Other drugs affected by enzyme inducers include cytochrome P450 3A4 substrates, such as calcium channel blockers (e.g., nimodipine, nilvadipine, nisoldipine, and felodipine) and the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors atorvastatin, lovastatin, and simvastatin. Although there have been no reports of AEDs altering ticlopidine metabolism, ticlopidine coadministration can result in carbamazepine and phenytoin toxicity. Also, there is a significant risk of elevated levels of carbamazepine when diltiazem and verapamil are administered. In addition, there are case reports of phenytoin toxicity when administered with diltiazem. Drugs with a lower potential for metabolic drug interactions include (1) cholinesterase inhibitors (although the theoretical possibility of a reduction in donepezil and galantamine levels by enzyme-inducing AEDs should be considered) and the N-methyl-D-aspartate receptor antagonist memantine and (2) antihypertensives such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, hydrophilic beta-blockers, and thiazide diuretics. There is a moderate risk that enzyme-inducing AEDs will decrease levels of lipophilic beta-blockers. Newer AEDs have a lower potential for drug interactions. In particular, levetiracetam and gabapentin have not been reported to alter enzyme activity. In summary, there is a significant potential for drug interactions between AEDs and drugs commonly prescribed in geriatric patients with epilepsy.

Fibrate therapy in patients with metabolic syndrome and diabetes mellitus

Patients with metabolic syndrome and type 2 diabetes mellitus are usually in moderately high-risk, high-risk, or very high-risk cardiovascular categories and present major therapeutic challenges. The dyslipidemia in such patients is typically a disorder of the triglyceride/high-density lipoprotein axis (TG/HDL axis) characterized by an excess of triglyceride-rich lipoproteins and a reduction of HDL. Very often, lifestyle therapy and statin monotherapy fail to achieve guideline goals, necessitating combination therapies. Fibric acids (or fibrates), are agonists of peroxisome proliferator-activated receptor alpha,which have amassed significant lipid-surrogate and clinical outcome trial data, especially in insulin-resistant patients, typical of those with metabolic syndrome or type 2 diabetes mellitus. Current guidelines advocate fibrate use as an add-on to statin therapy when TG/HDL abnormalities exist in such patients. In this paper, we review pertinent and recent trial data, mechanisms of action, and the safety of fibrate therapy.

Molecular basis of differences among statins and a comparison with antioxidant vitamins

Although all statin drugs lower levels of circulating low-density lipoprotein cholesterol by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A, molecular differences among statins affect their metabolism, solubility, and intramembrane localization, which in turn is likely to influence their efficacy and safety. In addition, these properties may have a differential impact on the pleiotropic effects of statins, including their ability to improve endothelial function and to affect proliferation and apoptosis in vascular tissues. Many pleiotropic effects of statins appear to be due to inhibition of small guanosine triphosphate-binding proteins and/or restoration of nitric oxide bioavailability, and atorvastatin metabolites may also directly protect vascular tissues from oxidative damage. The possibility of cardiovascular benefits from antioxidant effects of atorvastatin metabolites contrasts with the lack of benefits seen in most studies of antioxidant vitamins. This article reviews some of the differences in pleiotropic effects of statins and assesses the contribution of their solubility and membrane localization as the possible basis for these differences. In addition, the possibility that statin benefits on stroke reflect pleiotropic effects is reviewed. Finally, possible reasons for differences between the effects of atorvastatin metabolites and antioxidant vitamins are considered.

Translational pharmacogenetics and risk management in the cardiovascular arena: CYP3A5*3 model for gene-based drug selection

The clinical community is moving rapidly toward the prospective application of gene-based drug dosing. Specifically within the cardiovascular arena, the cytochrome P450 (CYP)3A5*3 allele may represent an optimal starting point. All CYP3A5*3 alleles contain an A6986G transition in intron 3, which reduces enzyme expression through the introduction of a premature stop codon. The current review explores four potential reasons why the clinical and scientific communities should consider including CYP3A5*3 in any panel of gene polymorphisms developed for the purpose of guiding cardiovascular pharmacotherapy: the CYP3A enzyme family metabolizes nearly half of all prescription drugs; the CYP3A enzyme family metabolizes several drugs utilized for primary and secondary risk reduction in the context of coronary artery disease; the CYP3A5*3 allele has been associated with differential outcomes related to lipid lowering therapy; and the CYP3A5*3 allele is highly prevalent in all populations studied to date.

Involvement of Multiple Cytochrome P450 and UDP-Glucuronosyltransferase Enzymes in the in Vitro Metabolism of Muraglitazar

Muraglitazar (Pargluva), a dual alpha/gamma peroxisome proliferator-activated receptor activator, has both glucose- and lipid-lowering effects in animal models and in patients with diabetes. The human major primary metabolic pathways of muraglitazar include acylglucuronidation, aliphatic/aryl hydroxylation, and O-demethylation. This study describes the identification of human cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) enzymes involved in the in vitro metabolism of muraglitazar. [(14)C]Muraglitazar was metabolized by cDNA-expressed CYP2C8, 2C9, 2C19, 2D6, and 3A4, but to a very minimal extent by CYP1A2, 2A6, 2B6, 2C18, 2E1, and 3A5. Inhibition of the in vitro metabolism of muraglitazar in human liver microsomes, at a clinically efficacious concentration, by chemical inhibitors and monoclonal antibodies further supported involvement of CYP2C8, 2C9, 2C19, 2D6, and 3A4 in its oxidation. A combination of intrinsic clearance (V(max)/K(m)) and relative concentrations of each P450 enzyme in the human liver was used to predict the contribution of CYP2C8, 2C9, 2C19, 2D6, and 3A4 to the formation of each primary oxidative metabolite and to the overall oxidative metabolism of muraglitazar. Glucuronidation of [(14)C]muraglitazar was catalyzed by cDNA-expressed UGT1A1, 1A3, and 1A9, but not by UGT1A6, 1A8, 1A10, 2B4, 2B7, and 2B15. The K(m) values for muraglitazar glucuronidation by the three active UGT enzymes were similar (2-4 muM). In summary, muraglitazar was metabolized by multiple P450 and UGT enzymes to form multiple metabolites. This characteristic predicts a low potential for the alteration of the pharmacokinetic parameters of muraglitazar via polymorphic drug metabolism enzymes responsible for clearance of the compound or by coadministration of drugs that inhibit or induce relevant metabolic enzymes.

Management of dyslipidemia in diabetes

Diabetes is associated with a high risk of cardiovascular disease. The management of dyslipidemia, a well-recognized and modifiable risk factor among patients with type 2 diabetes, is an important element in the multifactorial approach to prevent coronary heart disease. Diabetic dyslipidemia typically consists of elevated triglyceride, low high-density lipoprotein cholesterol (HDL-C), and the predominance of small dense low-density lipoprotein (LDL) particles. LDL cholesterol (LDL-C) levels in patients with diabetes are similar to those found in the rest of the population. During the past few years, clinical trials have provided evidence that lipid-lowering therapy has a similar beneficial effect on cardiovascular outcomes in diabetic and nondiabetic individuals. According to current guidelines, the primary lipid target is an LDL-C <100 mg/dL (<70 mg/dL in very high-risk patients) and, to this end, statins are the agents of choice. The appropriate management of dyslipidemia in patients with diabetes, particularly in individuals with low LDL-C, remains controversial. To achieve lipid targets, attention should be directed first toward nonpharmacologic therapeutic interventions to control dyslipidemia, such as diet, exercise, smoking cessation, weight loss, and glycemic control. Statin therapy is recommended for most subjects but, frequently, a combination of lipid-lowering agents is required. A number of combinations are possible, and several factors should be considered to improve the safety of this strategy.

RP-HPLC determination of paraoxonase 3 activity in human blood serum

The aim of the present work was to establish conditions for paraoxonase 3 (PON3) activity determination in human blood serum with simvastatin (SV) as a substrate. The activity of PON3 is considered as a good early predictor of susceptibility to premature atherosclerosis as well as of statin therapy effectiveness. The method used quantifies the SV and beta,delta-dihydroxyacid simvastatin (SVA) liberated from SV after incubation with blood serum, followed by deproteinization of the reaction mixture. Separation of SV and SVA was performed on an LC(18) column by isocratic elution with acetonitrile-K-phosphate buffer of pH 4.5 (v/v, 70:30) as a mobile phase at flow rate of 1.5 ml min(-1). Detection based on ultraviolet absorption at a wavelength of 239 nm was reliable for the simultaneous assay of SV and SVA. The applied method was sufficiently sensitive, precise and accurate for determination of low simvastatin lactone hydrolase (statinase) activity in blood serum of children (1.97-6.86 pmol min(-1) ml(-1)). The method is characterized by good linearity over the measurement range of 0.5-6 microg ml(-1) (1.194-14.3 nmol ml(-1)). Limits of detection (LOD) and quantitation (LOQ) for SV were 3.1 and 10.4 ng ml(-1), respectively. In case of SVA, LOD and LOQ were 4.7 and 14.44 ng ml(-) for a 20 microl sample, respectively. Precision and accuracy of PON3 statinase activity determination in human blood serum with SV as substrate were satisfactory and acceptable for bioanalytical methods.

Statins and myotoxicity: a therapeutic limitation

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

The interference of pharmaceuticals with endogenous and xenobiotic metabolizing enzymes in carp liver: an in-vitro study

The interactions of fibrate (clofibrate, fenofibrate, bezafibrate, gemfibrozil), antiinflammatory (ibuprofen, diclofenac, naproxen, ketoprofen), and anti-depressive (fluoxetine,fluvoxamine, paroxetine) drugs with CYP catalyzed pathways (CYP1A, CYP3A-, CYP2K-, and CYP2M-like) and Phase II activities (UDP-glucuronosyltransferases and sulfotransferases), involved in both xenobiotic and endogenous metabolism in fish, were investigated in-vitro by incubating carp liver subcellular fractions in the presence of the substrate and the selected drug. Anti-depressive drugs were strong inhibitors of CYP1A (92-94% inhibition), CYP3A-like (69-80% inhibition), and CYP2K-like (36-69% inhibition) catalyzed activities, while antiinflammatory drugs were potent CYP2M-like inhibitors (32-74% inhibition). Among the lipid regulators, gemfibrozil strongly inhibited CYP2M-catalyzed activity (91% inhibition) and other CYP isoforms (CYP1A and CYP3A-like). Additionally, glucuronidation of naphthol and testosterone were targeted by antiinflammatory drugs, and to a lesser extent, by fibrate drugs (48-78% inhibition). No significant alteration on sulfotransferase activities was observed, apart from a minor inhibitory effect of clofibrate, gemfibrozil, and fluoxetine on the sulfation of estradiol. Overall, gemfibrozil, diclofenac, and the three anti-depressive drugs appear to be the pharmaceuticals with the highest potential to interfere with fish metabolic systems.

Treating dyslipidaemia in the setting of diabetes mellitus and cardiovascular disease: a less commonly perceived therapeutic perspective in clinical practice

Diabetes mellitus and cardiovascular disease are being managed more belligerently in recent times, with multifactorial cardiovascular risk reduction being the focus of therapeutic interventions. We review some of the caveats to be exercised in the treatment of these patients that are pertinent to clinicians in daily clinical practice.

In vitro and in vivo CYP3A64 induction and inhibition studies in rhesus monkeys: a preclinical approach for CYP3A-mediated drug interaction studies

In this study, induction and inhibition of rhesus monkey CYP3A64 versus human CYP3A4 were characterized in vitro, and the corresponding pharmacokinetic consequences were evaluated in rhesus monkeys. In monkey hepatocytes, rifampin markedly induced CYP3A64 mRNA (EC50 = 0.5 microM; Emax = 6-fold) and midazolam (MDZ) 1'-hydroxylase activity (EC50 = 0.2 microM; Emax = 2-fold). Compound A (N-[2(R)-hydroxy-1(S)-indanyl-5-[2(S)-(1,1-dimethylethylaminocarbonyl)-4-[(furo[2,3-b]pyridin-5-yl)-methyl]piperazin-1-yl]-4(S)-hydroxy-2(R)-phenylmethylpentanamide), a known potent and mechanism-based inhibitor of CYP3A4, strongly inhibited the formation of 1'-hydroxy MDZ by recombinant CYP3A64 in a concentration- and time-dependent manner (KI = 0.25 microM; k(inact) = 0.4 min(-1)). Similar corresponding results also were obtained with human CYP3A4 in the presence of rifampin or compound A. In rhesus monkeys, MDZ exhibited a relatively high metabolic clearance (primarily via 1'-hydroxylation followed by glucuronidation) and a low hepatic availability (Fh = 16%). Consistent with the induction of hepatic metabolism of a high-clearance compound, pretreatment with rifampin (18 mg/kg p.o. for 5 days) did not significantly affect the i.v. kinetics of MDZ, but caused a pronounced reduction (approximately 10-fold) in the systemic exposure to MDZ and, consequently, its Fh following intrahepatic portal vein administration (i.pv.) of MDZ. A comparable extent of the pharmacokinetic interaction also was obtained after a 1.8 mg/kg rifampin dose. Also consistent with the in vitro CYP3A64 inhibition finding, compound A (6 mg/kg i.v.) markedly increased (10-fold) the i.pv. administered MDZ exposure. At the doses studied, plasma concentrations of rifampin or compound A reached or exceeded their respective in vitro EC50 or KI values. These findings suggest the potential applicability of the in vitro-in vivo relationship approach in rhesus monkeys for studying CYP3A-mediated interactions in humans.

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

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

Itraconazole, gemfibrozil and their combination markedly raise the plasma concentrations of loperamide

OBJECTIVE

Loperamide is biotransformed in vitro by the cytochromes P450 (CYP) 2C8 and 3A4 and is a substrate of the P-glycoprotein efflux transporter. Our aim was to investigate the effects of itraconazole, an inhibitor of CYP3A4 and P-glycoprotein, and gemfibrozil, an inhibitor of CYP2C8, on the pharmacokinetics of loperamide.

METHODS

In a randomized crossover study with 4 phases, 12 healthy volunteers took 100 mg itraconazole (first dose 200 mg), 600 mg gemfibrozil, both itraconazole and gemfibrozil, or placebo, twice daily for 5 days. On day 3, they ingested a single 4-mg dose of loperamide. Loperamide and N-desmethylloperamide concentrations in plasma were measured for up to 72 h and in urine for up to 48 h. Possible central nervous system effects of loperamide were assessed by the Digit Symbol Substitution Test and by subjective drowsiness.

RESULTS

Itraconazole raised the peak plasma loperamide concentration (Cmax) 2.9-fold (range, 1.2-5.0; P < 0.001) and the total area under the plasma loperamide concentration-time curve (AUC(0-infinity)) 3.8-fold (1.4-6.6; P < 0.001) and prolonged the elimination half-life (t(1/2)) of loperamide from 11.9 to 18.7 h (P < 0.001). Gemfibrozil raised the Cmax of loperamide 1.6-fold (0.9-3.2; P < 0.05) and its AUC(0-infinity) 2.2-fold (1.0-3.7; P < 0.05) and prolonged its t(1/2) to 16.7 h (P < 0.01). The combination of itraconazole and gemfibrozil raised the Cmax of loperamide 4.2-fold (1.5-8.7; P < 0.001) and its AUC(0-infinity) 12.6-fold (4.3-21.8; P < 0.001) and prolonged the t(1/2) of loperamide to 36.9 h (P < 0.001). The amount of loperamide excreted into urine within 48 h was increased 3.0-fold, 1.4-fold and 5.3-fold by itraconazole, gemfibrozil and their combination, respectively (P < 0.05). Itraconazole, gemfibrozil and their combination reduced the plasma AUC(0-72) ratio of N-desmethylloperamide to loperamide by 65%, 46% and 88%, respectively (P < 0.001). No significant differences were seen in the Digit Symbol Substitution Test or subjective drowsiness between the phases.

CONCLUSION

Itraconazole, gemfibrozil and their combination markedly raise the plasma concentrations of loperamide. Although not seen in the psychomotor tests used, an increased risk of adverse effects should be considered during concomitant use of loperamide with itraconazole, gemfibrozil and especially their combination.

Statin safety: an overview and assessment of the data--2005

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statin drugs, have been studied in numerous controlled human research trials involving hundreds of thousands of study participants. Statins have been prescribed for millions of patients. Based on this vast research and clinical experience, statins have been shown to improve lipid blood levels and reduce atherosclerotic coronary artery disease (CAD) risk, resulting in reduced CAD morbidity and mortality, and in several studies, reduced overall ("all-cause") mortality. From a safety perspective, both research trial evidence and clinical practice experience have demonstrated that statins are generally well tolerated. However, as with all pharmaceuticals, safety considerations exist with both monotherapy and combination statin therapy, mainly involving potential adverse effects on muscle, liver, kidney, and the nervous system. The evidence supporting statin-related potential adverse experiences on these organ systems is sometimes strong and based on clear clinical trial evidence (such as the increased risk of muscle enzyme elevation with higher statin doses). The evidence is at other times more speculative, being based on case reports and inconclusive clinical trial data (such as possible favorable or unfavorable effects of statins on cognition). Because the use of statins is so widespread, it is useful for the clinician to understand statin safety issues and the level of available evidence supporting the contention that various adverse effects are caused by statins. This review presents an assessment of statin safety based on an overview of the current statin safety data and their clinical implications.

Statin safety: a systematic review

A systematic review of cohort studies, randomized trials, voluntary notifications to national regulatory authorities, and published case reports was undertaken to assess the incidence and characteristics of adverse effects in patients treated with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins. For statins other than cerivastatin, the incidence of rhabdomyolysis in 2 cohort studies was 3.4 (1.6 to 6.5) per 100,000 person-years, an estimate supported by data from 20 randomized controlled trials. Case fatality was 10%. Incidence was about 10 times greater when gemfibrozil was used in combination with statins. Incidence was higher (4.2 per 100,000 person-years) with lovastatin, simvastatin, or atorvastatin (which are oxidized by cytochrome P450 3A4 [CYP3A4], which is inhibited by many drugs) than pravastatin or fluvastatin (which are not oxidized by CYP3A4). In persons taking simvastatin, lovastatin, or atorvastatin, 60% of cases involved drugs known to inhibit CYP3A4 (especially erythromycin and azole antifungals), and 19% involved fibrates, principally gemfibrozil. The incidence of myopathy in patients treated with statins, estimated from cohort studies supported by randomized trials, was 11 per 100,000 person-years. For liver disease, randomized trials reported fewer hepatobiliary disorders in patients allocated statins than in those allocated placebo. The notification rate of liver failure to regulatory authorities was about 1 per million person-years of statin use. Randomized trials show no excess of renal disease or proteinuria in statin-allocated participants, and the decline in glomerular filtration rate was smaller with statins than with placebo. Evidence from 4 cohort studies and case reports suggests that statins cause peripheral neuropathy, but the attributable risk is small (12 per 100,000 person-years). No change in cognitive function was found in randomized trials of statins in elderly patients.

Statin safety and drug interactions: clinical implications

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

An assessment of statin safety by muscle experts

The National Lipid Association's (NLA) Muscle Safety Expert Panel was charged with the duty of examining the definitions, causative factors, and management of statin myopathy. The Panel was asked to use its evidence-based findings to form recommendations in response to a series of specific questions posed by the Task Force. The panel was composed of a clinical cardiologist, an exercise physiologist and skeletal muscle expert, and an expert in preventive cardiology who also examined skeletal muscle complications of statin use.

Ezetimibe-associated myopathy in monotherapy and in combination with a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Two cases of myopathy associated with ezetimibe are reported. In the first case, a woman on ezetimibe monotherapy presented with muscle pain and an elevated concentration of creatine kinase (CK) on two occasions, with ezetimibe 10 mg and with ezetimibe 5 mg after a washout period. The recurrence of muscle pain after washout and the CK increase both supported the hypothesis that ezetimibe alone can be linked to myalgia. In the second case, a man had been treated with atorvastatin, and ezetimibe 10 mg was added to improve his lipid profile. Two months later, the patient complained of muscle pain and a CK increase was noted. The appearance of symptoms when adding ezetimibe to atorvastatin supports a potential pharmacokinetic and/or a pharmacodynamic interaction between these two drugs. These cases suggest that ezetimibe monotherapy as well as ezetimibe associated with the use of a statin may induce myalgia. The mechanism by which ezetimibe could cause muscle pain is not known.

Lipid-lowering therapy for elderly patients at risk for coronary events and stroke

Hyperlipidemia continues to be a major risk factor for cardiovascular diseases, particularly coronary heart disease, in the elderly population. Despite the fact that hyperlipidemia does not seem to be a major risk factor for stroke, therapy for hyperlipidemia, especially with statins, has clearly been demonstrated to reduce both coronary heart disease events and stroke, with the most convincing data being for the elderly population. Although we review some safety concerns with statin therapy applicable to the elderly, statins alone or with other proved therapies, including fibrates, niacin, and exercise training, have been demonstrated to reduce major cardiovascular diseases, including coronary heart disease and stroke in the elderly. In addition, this therapy can be safely administered to most elderly patients and seems to have either neutral or slightly beneficial effects on dementia. Therefore, aggressive lipid treatment, particularly with statins, is needed in the primary and secondary prevention of cardiovascular diseases in the elderly.

PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS: How Their Effects on Macrophages Can Lead to the Development of a New Drug Therapy Against Atherosclerosis

Peroxisome proliferator-activated receptors (PPARs) alpha (alpha), beta/delta (beta/delta), and gamma (gamma) are members of the nuclear receptor superfamily, which also includes the estrogen, androgen, and glucocorticoid receptors. Recent evidence suggests that PPARs regulate genes involved in lipid metabolism, glucose homeostasis, and inflammation in various tissues; however, the mechanisms involved are not completely understood. Anti-diabetic drugs, called glitazones, can selectively activate PPARgamma, and hypolipidemic drugs, called fibrates, can weakly activate PPARalpha. Both classes of drugs can decrease insulin resistance and dyslipidemias, which also makes them attractive for treating the metabolic syndrome. The metabolic syndrome exhibits a constellation of risk factors for atherosclerosis that include obesity, insulin resistance, dyslipidemias, and hypertension. Interestingly, all three PPARs are present in macrophages and can therefore have a profound effect on several disease processes, including atherosclerosis. Macrophages are key players in atherosclerotic lesion development. Currently, the first line of defense in reducing the risk of atherosclerosis is aimed at lowering low-density lipoproteins (LDL) and raising high-density lipoproteins (HDL), but a large percentage of patients on statins still succumb to coronary artery disease. However, with the development of drugs selectively activating PPARs, a new arsenal of drugs specifically targeting to the macrophage/foam cell may potentially have a profound impact on how we treat cardiovascular disease.

An open-label, crossover study of the pharmacokinetics of Insoluble Drug Delivery®-MicroParticle fenofibrate in combination with atorvastatin, simvastatin, and extended-release niacin in healthy volunteers

BACKGROUND

Fenofibrate has been prescribed concomitantly with other lipid-lowering agents as a treatment for dyslipidemia. However, combination therapy, particularly a statin-fibrate combination, may be associated with an increased risk of myopathy, although this risk appears to be less with fenofibrate than with other fibrates.

OBJECTIVE

The objective of this study was to determine the effect of administering a single dose of atorvastatin, simvastatin, or extended-release (ER) niacin on the pharmacokinetics and safety of a single dose of fenofibrate Insoluble Drug Delivery-MicroParticle (IDD-P).

METHODS

This was an open-label, single-center,randomized, 4-treatment, 4-period crossover study in healthy adult volunteers. Subjects were randomized to 1 of 4 treatment sequences, administered 1 week apart, that included all 4 of the following treatments: 1 IDD-P fenofibrate 160-mg tablet alone; 1 IDD-P fenofibrate 160-mg tablet plus 1 atorvastatin 10-mg tablet; 1 IDD-P fenofibrate 160-mg tablet plus 1 simvastatin 10-mg tablet; and 1 IDD-P fenofibrate 160-mg tablet plus 1 ER niacin 500-mg tablet. Blood samples for pharmacokinetic analysis were obtained immediately before and up to 72 hours after administration during each of the 4 treatment periods. If the 90% CI for the log-transformed parameter was between 0.80 and 1.25, and the 90% CI for the nontransformed parameter was between 0.80 and 1.20, then the absence of a clinically significant drug interaction was assumed. However, the absence of a drug interaction was not to be ruled out if one or more of the CIs exceeded the boundary, provided the CI included 1.00.

RESULTS

Twenty healthy subjects were enrolled. Sixteen (80%) of the subjects were male and 17 (85%) were black; mean (SD) age was 35 (9.3) years. The mean C(max), AUC from the time of administration to the last quantifiable concentration (AUC(0-t)), and AUC from the time of administration to infinity (AUC(0-infinity)) were 5%, 6%, and 2% lower, respectively, with IDD-P fenofibrate plus atorvastatin than with IDD-P fenofibrate alone; the mean C(max), AUC(0-t), and AUC(0-infinity) were 6% lower, and 10% and 9% higher, respectively, with IDD-P fenofibrate plus simvastatin than with IDD-P fenofibrate alone; and the mean C(max), AUC(0-t), and AUC(0-infinity) were 12%, 6%, and 5% lower, respectively, with IDD-P fenofibrate plus ER niacin than with IDD-P fenofibrate alone. The 90% CIs surrounding the mean ratios for AUC(0-infinity) and AUC(0-infinity) for all 3 comparisons were between 0.80 and 1.25, suggesting the absence of a drug interaction for these parameters. For C(max), an absence of a drug interaction was observed between concomitantly administered IDD-P fenofibrate and both atorvastatin and simvastatin; absence of drug interaction was not found for IDD-P fenofibrate plus ER niacin. All treatments were well tolerated; headache was the most common adverse event (AE) (10%). One subject with creatinine kinase levels of 1300 IU/L (>6 times the upper limit of normal) at baseline experienced a seizure approximately 12 to approximately 13 hours after administration of IDD-P fenofibrate plus atorvastatin; this serious AE was deemed to be possibly related to study drug.

CONCLUSIONS

Concomitant administration of a single dose of either atorvastatin or simvastatin had no significant effect on the pharmacokinetics of a single dose of IDD-P fenofibrate. A drug interaction between concomitantly administered single doses of IDD-P fenofibrate and ER niacin could not be ruled out.

Fenofibrate: a novel formulation (Triglide) in the treatment of lipid disorders: a review

Cardiovascular disease is the major cause of mortality worldwide and accounts for approximately 40% of all deaths. Dyslipidemia is one of the primary causes of atherosclerosis and effective interventions to correct dyslipidemia should form an integral component of any strategy aimed at preventing cardiovascular disease. Fibrates have played a major role in the treatment of hyperlipidemia for more than two decades. Fenofibrate is one of the most commonly used fibrates worldwide. Since fenofibrate was first introduced in clinical practice, a major drawback has been its low bioavailability when taken under fasting conditions. Insoluble Drug Delivery-Microparticle fenofibrate is a new formulation that has an equivalent extent of absorption under fed or fasting conditions. In this review, we will discuss the clinical pharmacology of fenofibrate, with particular emphasis on this novel formulation, as well as its lipid-modulating and pleiotropic actions. We will also analyze the major trial that evaluated fibrates for primary and secondary prevention of cardiovascular disease, the safety and efficacy profile of fibrate-statin combination treatment, and the current recommendations regarding the use of fibrates in clinical practice.

Excretion and ecotoxicity of pharmaceutical and personal care products in the environment

The presence and fate of pharmaceutical and personal care products (PPCPs) in the environment is undergoing increasing scrutiny. The existing clinical pharmacokinetics and pharmacodynamics data for 81 common compounds were examined for cues of ecotoxicity. Of these the proportions excreted were available for 60 compounds (i.e., 74%). The compounds had a low (< or =0.5%), a moderately low (6-39%), a relatively high (40-69%), or a high (> or =70%) proportion of the parent compound excreted. More than half of the compounds evaluated have low or moderately low proportions of the parent compound excreted. However, the proportions excreted were negatively but moderately correlated (r = -0.50; n = 13; P = 0.08) with the concentrations of the compounds in the aquatic environment, suggesting that the compounds that have low proportions excreted may also have inherently low degradability in the environment. Solubility, logK(ow), and pKa work well in predicting the behavior of PPCPs under clinical conditions and have been used in the environmental assessment of PPCPs prior to approval. However, these parameters did not correlate with the proportion of PPCPs excreted in the environment or their concentration in the environment, underscoring the need for research into the behavior of PPCPs in the environment. PPCPs occur in low concentrations in the environment and are unlikely to elicit acute toxicity. An ecotoxicity potential that is based on chronic toxicity, bioavailability, and duration of exposure to nontarget organisms is described as a guide in assessing the potency of these compounds in the environment.

Fibrates in combination with statins in the management of dyslipidemia

While elevated low-density lipoprotein cholesterol is the primary target of hypercholesterolemia treatment, high triglycerides and low high-density lipoprotein cholesterol are also important targets for therapy. Correcting these lipid abnormalities should be an integral part of therapy in hypertensive individuals. Medications such as the fibrates are effective and well tolerated for reducing triglycerides and increasing high-density lipoprotein cholesterol, and their use has resulted in a reduction in cardiovascular events. Fibrates are also recommended as adjunct therapy for patients receiving statins whose low-density lipoprotein cholesterol or non-high-density lipoprotein cholesterol is not reduced to goal levels. The combination of a statin and a fibrate may, however, raise the risk of myopathy and rhabdomyolysis. Gemfibrozil, one of the fibrates, but not fenofibrate, interferes with statin glucuronidation, which may increase the risk of myopathy due to elevations in statin serum levels. This may at least partially explain the lower incidence of myopathy with fenofibrate compared with gemfibrozil when combined with statins. Combination therapy with a fibrate and a statin is a potentially useful therapy for patients with atherogenic lipid profiles, for which fenofibrate appears to be a more appropriate choice due to less myopathic potential.

Statin/fibrate combination in patients with metabolic syndrome or diabetes: evaluating the risks of pharmacokinetic drug interactions

Patients with the metabolic syndrome and/or Type 2 diabetes mellitus continue to have a high risk of coronary heart disease (CHD) and progression of atherosclerotic lesions despite aggressive statin therapy. Although the National Cholesterol Education Programme Adult Treatment Panel III guidelines recommend the use of fibrates in combination with statins in patients at very high risk of CHD (e.g., patients at the low-density lipoprotein cholesterol target with high triglycerides and low high-density lipoprotein cholesterol, many physicians remain reluctant to use these combinations due to concerns of myotoxicity. Recently conducted metabolic and pharmacokinetic drug-drug interaction studies using gemfibrozil or fenofibrate in combination with five commonly used statins demonstrated a widely different drug interaction potential for these two fibrates. Gemfibrozil causes a 2- to 6-fold increase in statin area under the curve and increases the exposure to many recently approved drugs for the treatment of diabetes. Alternatively, fenofibrate does not adversely affect either the metabolism or pharmacokinetics of the statins studied. These pharmacokinetic differences appear to translate into less potential for interactions with fenofibrate/statin combination therapy compared to gemfibrozil/statin co-administration. The Action to Control Cardiovascular Risk in Diabetes (ACCORD) study in 10,000 patients with Type 2 diabetes mellitus is testing the efficacy and safety of fenofibrate/statin combination.

Relative impact of CYP3A genotype and concomitant medication on the severity of atorvastatin-induced muscle damage

Atorvastatin is metabolized through enzymes encoded by members of the cytochrome P-450 (CYP) 3A gene family. Some patients who take atorvastatin along with concomitant medications known to inhibit CYP3A enzyme activity (e.g. itraconazole) develop rhabdomyolysis secondary to a severe drug-induced myopathy. The present study aimed to characterize the relationship between CYP3A gene polymorphisms and atorvastatin-induced muscle damage in the context of concomitant medication. The study employed a retrospective case--control (n=137) design. Study subjects were recruited from the general patient population served by Marshfield Clinic, a large horizontally integrated multispecialty group practice located in central Wisconsin, and case assignment was based upon both subjective (myalgia) and objective inclusion criteria [elevated serum creatine kinase (CK) levels]. The primary outcome was the relationship between serum CK level and CYP3A genotype. CYP3A genotype was not associated with an increased risk for the development of atorvastatin-induced muscle damage. CYP3A4*1B and CYP3A5*3 allele frequencies were similar in cases (n=68) and controls (n=69). Conversely, CYP3A genotype was associated with an increased severity of atorvastatin-induced muscle damage. An association was identified between the non-functional CYP3A5*3 allele and the magnitude of serum CK elevation in case patients experiencing myalgia. Patients who were homozygous for CYP3A5*3 demonstrated greater serum CK levels than patients who were heterozygous for CYP3A5*3, when concomitant lipid-lowering agents were sequentially removed from the analysis (P=0.025 without gemfibrozil, P=0.010 without gemfibrozil and niacin). The study demonstrates that patients who develop myalgia while taking atorvastatin are more likely to experience a greater degree of muscle damage if they express two copies of CYP3A5*3.

Combinatorial pharmacogenetics

Combinatorial pharmacogenetics seeks to characterize genetic variations that affect reactions to potentially toxic agents within the complex metabolic networks of the human body. Polymorphic drug-metabolizing enzymes are likely to represent some of the most common inheritable risk factors associated with common 'disease' phenotypes, such as adverse drug reactions. The relatively high concordance between polymorphisms in drug-metabolizing enzymes and clinical phenotypes indicates that research into this class of polymorphisms could benefit patients in the near future. Characterization of other genes affecting drug disposition (absorption, distribution, metabolism and elimination) will further enhance this process. As with most questions concerning biological systems, the complexity arises out of the combinatorial magnitude of all the possible interactions and pathways. The high-dimensionality of the resulting analysis problem will often overwhelm traditional analysis methods. Novel analysis techniques, such as multifactor dimensionality reduction, offer viable options for evaluating such data.

Considerations in the treatment of dyslipidemia associated with chronic kidney failure and renal transplantation

In comparison to the general population, individuals with chronic kidney failure experience an increased risk for atherosclerotic cardiovascular disease attributed predominantly to pronounced abnormalities in lipid metabolism. The emerging consensus is that patients with chronic kidney failure should be treated aggressively for dyslipidemia. Statins reduce the risk of cardiovascular disease in a range of at-risk patients; this class of lipid-lowering drugs should be considered first-line treatment of dyslipidemia observed in renal disease patients. Although the statins share a common lipid-lowering effect, there are differences within this class of drugs. The statins differ in their pharmacokinetic effects, drug interaction profiles, and risk of myotoxicity. This article characterizes the dyslipidemia observed in the renal failure setting and reviews the therapeutic considerations involved in selecting among the statins. Lovastatin, simvastatin, pravastatin, fluvastatin, atorvastatin, and rosuvastatin are the available statins in the United States.

High-density lipoprotein as a therapeutic target: clinical evidence and treatment strategies

The clinical importance of low serum levels of high-density lipoprotein (HDL) cholesterol is often under-recognized and underappreciated as a risk factor for premature atherosclerosis as well as for cardiovascular morbidity and mortality. Low serum levels of HDL are frequently encountered, especially in patients who are obese or have the metabolic syndrome. In prospective epidemiologic studies, every 1-mg/dL increase in HDL is associated with a 2% to 3% decrease in coronary artery disease risk, independent of low-density lipoprotein (LDL) cholesterol and triglyceride (TG) levels. The primary mechanism for this protective effect is believed to be reverse cholesterol transport, but several other anti-inflammatory, antithrombotic, and antiproliferative functions for HDL have also been identified. In recognition of these antiatherogenic effects, recent guidelines have increased the threshold for defining low levels of HDL for both men and women. The first step in achieving these revised targets is therapeutic lifestyle changes. When these measures are inadequate, pharmacotherapy specific to the patient's lipid profile should be instituted. Niacin therapy, currently the most effective means for raising HDL levels, should be initiated in patients with isolated low HDL (HDL <40 mg/dL, LDL and non-HDL at or below National Cholesterol Education Program (NCEP) targets based on global cardiovascular risk evaluation). Patients who have both low HDL and elevated LDL should receive a statin or statin-niacin combination therapy, and patients with concomitant low HDL and elevated TGs should receive a fibrate initially, with a statin, niacin, or ezetimibe added thereafter as needed to help attain NCEP lipoprotein targets.

Beneficial vascular and metabolic effects of peroxisome proliferator-activated receptor-alpha activators

Fibric acid is a synthetic ligand of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-alpha that is highly expressed in skeletal muscle and heart, where it promotes beta-oxidation of fatty acids to mediate hypolipidemic actions. PPAR-alpha regulates expression of key proteins involved in atherogenesis, vascular inflammation, plaque instability, and thrombosis. Thus, PPAR-alpha may exert direct antiatherogenic actions in the vascular wall. Endothelial dysfunction associated with the metabolic syndrome and other insulin-resistant states is characterized by impaired insulin-stimulated nitric oxide production from the endothelium and decreased blood flow to skeletal muscle. Thus, improvement in insulin sensitivity leads to improved endothelial function. This may be an additional mechanism whereby fibrates decrease the incidence of coronary heart disease. Adiponectin is a protein secreted specifically by adipose cells that may couple regulation of insulin sensitivity with energy metabolism and serve to link obesity with insulin resistance. In this review, we discuss the mechanisms underlying the vascular and metabolic effects of fibrates that may act synergistically to prevent or regress atherosclerosis and coronary heart disease.

Statins and stroke

Inhibitors of HMG-CoA reductase (statins) are potent cholesterol-lowering drugs. Large clinical trials have shown that statins reduce the incidence of cerebrovascular events, which might be surprising because cholesterol is not an established risk factor for stroke. In addition to their cholesterol-lowering properties, statins exert a number of pleiotropic, vasculoprotective actions that include improvement of endothelial function, increased nitric oxide (NO) bioavailability, antioxidant properties, inhibition of inflammatory responses, immunomodulatory actions, regulation of progenitor cells, and stabilization of atherosclerotic plaques. In fact, statins augment cerebral blood flow and confer significant protection in animal models of stroke partly via mechanisms related to the upregulation of endothelial nitric oxide synthase. Retrospective clinical evidence suggests that long-term statin administration may not only reduce stroke risk but also improve outcome. Early secondary prevention trials are underway to test the hypothesis that statin treatment initiated immediately after an event improves short-term outcome. Lastly, recent evidence suggests that sudden discontinuation of statin treatment leads to a rebound effect with downregulation of NO production. Withdrawal of statin treatment may impair vascular function and increase morbidity and mortality in patients with vascular disease.

A literature search on pharmacokinetic drug interactions of statins and analysis of how such interactions are reflected in package inserts in Japan

BACKGROUND AND OBJECTIVES

Statins (HMG-CoA reductase inhibitors) are one of the most widely prescribed classes of drugs throughout the world, because of their excellent cholesterol-lowering effect and overall safety profile except for rare but fatal rhabdomyolysis arising either directly or indirectly by pharmacokinetic interactions with certain other drugs. As package inserts in pharmaceuticals are the primary source of information for health care providers, we carried out a literature search to examine how crucial information was provided in package inserts of five statins approved in Japan (simvastatin, atorvastatin, fluvastatin, pravastatin and pitavastatin).

METHODS

A MEDLINE search from 1996 to June 2004 was carried out to identify studies on clinical pharmacokinetic drug interactions for the five statins. We mainly collected information on area under plasma concentration (AUC) following co-administration of statins with other drugs. The current package inserts used in Japan were obtained from the website of the Pharmaceutical and Medical Device Agency whereas USA package inserts were obtained from the Food and Drug Administration website.

RESULTS

The majority of package inserts listed the drugs that interacted with statins with most describing the risk of rhabdomyolysis because of the possibility of increases in blood concentration. However, quantitative information such as change in AUC was provided in only a few cases. Instructions for dosage adjustment are seldom provided in the Japanese package inserts. USA package inserts list almost identical drug interactions as the Japanese package inserts, although they contain more quantitative data, especially for typical cytochrome P450 (CYP) inhibitors.

CONCLUSION

All pharmacokinetic drug interactions including relevant quantitative data for potential effectors and details on mechanisms of interaction need to be given in package inserts as soon as the information becomes available, to ensure safe and proper use of the drugs concerned. Including such information in the package insert will be an extremely valuable aid for health care providers.

Role of fibric acid derivatives in the management of risk factors for coronary heart disease

Although elevated low-density lipoprotein (LDL)-cholesterol is a well established coronary heart disease (CHD) risk factor, the ability to adequately discriminate high-risk individuals by this risk factor alone is limited and other metabolic risk variables are known to modulate CHD risk. For instance, it has been reported that the cluster of metabolic disturbances observed among individuals with abdominal obesity, the so-called metabolic syndrome, is associated with a substantially increased risk of CHD. Among the features of the dyslipidaemic profile observed in these individuals, the high triglyceride-low high-density lipoprotein (HDL)-cholesterol dyslipidaemia is predictive of an elevated risk of CHD. Fibric acid derivatives (fibrates) have been used in clinical practice for more than 2 decades as a class of agents known to decrease triglyceride levels while substantially increasing HDL-cholesterol levels, with a limited but significant additional lowering effect on LDL-cholesterol levels. Although the clinical benefits of HMG-CoA reductase inhibitors (statins) have been well documented by primary and secondary prevention trials that justify their widespread use, it was not until the publication of the VA-HIT (Veterans Affairs High-Density Lipoprotein Intervention Trial) that the relevance of identifying HDL-cholesterol as a therapeutic target to reduce the risk of recurrent CHD events was finally confirmed. The clinical benefits of fibrate therapy are especially important in the subpopulation of patients with low HDL-cholesterol levels with the metabolic syndrome, particularly in patients with type 2 diabetes mellitus or in abdominally obese, hyperinsulinaemic patients. Evidence also suggests that there is a 'fibrate effect' that mediates the reduction in CHD risk beyond the favourable impact of these agents on HDL-cholesterol levels. This last notion is consistent with the pleiotropic effects of fibrates which are known to be related to their mechanisms of action. Through peroxisome proliferator-activated alpha-receptors, fibrates have a significant impact on the synthesis of several apolipoproteins (apo) and enzymes of lipoprotein metabolism as well as on the expression of several genes involved in fibrinolysis and inflammation. Fibrate therapy has been reported to decrease apo CIII levels (a powerful inhibitor of lipoprotein lipase) and increase apo AI levels, as well as to increase lipoprotein lipase activity. Such changes contribute to improve the catabolism of triglyceride-rich lipoproteins, leading to a substantial increase in HDL-cholesterol levels accompanied by a shift in the size and density of LDL particles (from small, dense LDL particles to larger, more buoyant cholesteryl ester-rich LDL). It is proposed that some of these pleiotropic effects could explain some of the clinical benefits of fibrate therapy beyond its HDL-raising properties, particularly among patients with abdominal obesity, hyperinsulinaemia or type 2 diabetes with both low HDL- and low/normal LDL-cholesterol levels.

Therapeutic roles of peroxisome proliferator-activated receptor agonists

Peroxisome proliferator-activated receptors (PPARs) play key roles in the regulation of energy homeostasis and inflammation, and agonists of PPARalpha and -gamma are currently used therapeutically. Fibrates, first used in the 1970s for their lipid-modifying properties, were later shown to activate PPARalpha. These agents lower plasma triglycerides and VLDL particles and increase HDL cholesterol, effects that are associated with cardiovascular benefit. Thiazolidinediones, acting via PPARgamma, influence free fatty acid flux and thus reduce insulin resistance and blood glucose levels. PPARgamma agonists are therefore used to treat type 2 diabetes. PPARalpha and -gamma agonists also affect inflammation, vascular function, and vascular remodeling. As knowledge of the pleiotropic effects of these agents advances, further potential indications are being revealed, including roles in the management of cardiovascular disease (CVD) and the metabolic syndrome. Dual PPARalpha/gamma agonists (currently in development) look set to combine the properties of thiazolidinediones and fibrates, and they hold considerable promise for improving the management of type 2 diabetes and providing an effective therapeutic option for treating the multifactorial components of CVD and the metabolic syndrome. The functions of a third PPAR isoform, PPARdelta, and its potential as a therapeutic target are currently under investigation.

Cytochrome P450 gene-based drug prescribing and factors impacting translation into routine clinical practice

Pharmacogenetics represents a rapidly advancing, competitive field of investigation. Due to the potential for clinically recognizable interactions between a set of old polymorphic genes and a relatively new environmental insult (drugs), many human geneticists believe that variability in the drug-metabolizing enzyme systems will soon translate into clinical practice across entire populations. Despite this, the field has not yet received widespread clinical acceptance. This article will review the common cytochrome P450 gene polymorphisms and discuss the factors that may facilitate (or attenuate) their translation into clinical practice.

Interconversion pharmacokinetics of simvastatin and its hydroxy acid in dogs: effects of gemfibrozil

PURPOSE

To characterize the pharmacokinetics of simvastatin (SV) and simvastatin acid (SVA), a lactone-acid pair known to undergo reversible metabolism, and to better understand mechanisms underlying pharmacokinetic interactions observed between SV and gemfibrozil.

METHODS

Pharmacokinetic studies were conducted after intravenous administration of SV and SVA to dogs pretreated with a vehicle or gemfibrozil. In vitro metabolism of SVA in dog hepatocytes as well as in vitro hepatic and plasma conversion of SV/SVA were investigated in the absence and presence of gemfibrozil.

RESULTS

In control animals, the irreversible elimination clearances of SV (CL10) and SVA (CL20) were 10.5 and 18.6 ml min(-1) kg(-1), respectively. The formation clearance of SVA from SV (CL12 = 4.8 ml min(-1) kg(-1)) was 8-fold greater than that of SV from SVA (CL21 = 0.6 ml min(-1) kg(-1)), and the recycled fraction was relatively minor (0.009). In gemfibrozil-treated animals, CL10 was essentially unchanged, whereas CL12, CL20, CL21, and recycled fraction were significantly decreased to 2.9, 9, 0.14 ml min(-1) kg(-1), and 0.003, respectively. In control dogs, values for real volume of distribution at steady state (Vss,real) of SV (2.3 L kg(-1)) were much larger than the corresponding values of SVA (0.3 L kg(-1)). Gemfibrozil treatment did not affect Vss,real of either SV or SVA. In dog hepatocytes, gemfibrozil modestly affected the formation of CYP3A-mediated oxidative metabolites (IC50 > 200 microM) and beta-oxidative products (IC5) approximately 100 microM), but markedly inhibited the glucuronidation-mediated lactonization of SVA and the glucuronidation of an SVA beta-oxidation product (IC50 = 18 microM). In in vitro dog and human liver S9 and plasma, hydrolysis of SV to SVA was much faster than that of SVA to SV. Gemfibrozil (250 microM) had a minimal inhibitory effect on the hydrolysis of either SV to SVA or SVA to SV in dog and human liver S9, but had a significant ( approximately 60%) inhibitory effect on the SV to SVA hydrolysis in both dog and human plasma.

CONCLUSIONS

In dogs, the interconversion process favored the formation of SVA and was less efficient than the irreversible elimination processes of SV and SVA. Treatment with gemfibrozil did not affect the distribution of SV/SVA, but rather affected the elimination of SVA and the SV/SVA interconversion processes. Gemfibrozil decreased CL20 and CL21 likely via its inhibitory effect on the glucuronidation of SVA, and not on the CYP3A-mediated oxidative metabolism of SV or SVA, the beta-oxidation of SVA, nor the SVA to SV hydrolysis. The decrease in CL12 might be due in part to the inhibitory effect of gemfibrozil on SV to SVA hydrolysis in plasma. Similar rationales may also be applicable to studies in humans and/or other statin lactone-acid pairs.

Suboptimal choices and dosing of statins at start of therapy

AIM

To assess dosing and determinants of the choice of statins among starters of statins.

METHODS

Data were obtained from the PHARMO database comprising pharmacy and linked hospital discharge records of approximately 300 000 subjects in the Netherlands. All new users of statins in 1998 were selected. Patient characteristics and drug regimens were compared between starters of different statins. Odds ratios (OR) and 95% confidence intervals (CI) were calculated using polytomous logistic regression modelling, using the start of simvastatin therapy as reference category.

RESULTS

In 1998, 1738 patients started using simvastatin (41.1%), pravastatin (23.1%), fluvastatin (11.9%), atorvastatin (22.8%) or cerivastatin (1.0%). Compared with starters with simvastatin [mean dose 1.02 +/- 0.39 defined daily doses (DDDs)], starters with pravastatin (1.27 +/- 0.56 DDDs) and atorvastatin (1.43 +/- 0.59 DDDs) received higher doses (P < 0.001), whereas users of fluvastatin (0.78 +/- 0.37 DDDs) and cerivastatin (0.81 +/- 0.30 DDDs) received lower doses (P < 0.001). Patients already using CYP3A4 inhibitors more frequently received fluvastatin (OR = 1.80; 95% CI 1.11, 2.94), metabolized by non-CYP3A4 pathways, and atorvastatin (OR = 1.62; 95% CI 1.06, 2.47), which is metabolized by CYP3A4, than simvastatin. Statin doses were not adjusted when prescribed to patients using CYP3A4 inhibitors.

CONCLUSIONS

Many patients starting statin therapy did not receive a statin of first choice. The coadministration of potentially interacting drugs may have led to a change in statin choice, but not in dosage lowering. These findings suggest that the quality of statin therapy could be improved.

Rosuvastatin for the Treatment of Hypercholesterolemia

Rosuvastatin, a new hydrophilic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin), is approved as an adjunct to diet in patients with primary hypercholesterolemia, mixed dyslipidemia, or Fredrickson type IV hypercholesterolemia. Because of its increased affinity for the reductase, rosuvastatin reduces the low-density lipoprotein cholesterol (LDL) level more than atorvastatin, simvastatin, and pravastatin do, without additional adverse effects. In addition, cytochrome P450 isoenzymes do not extensively metabolize rosuvastatin, and inhibitors of these isoenzymes do not substantially affect it. Rosuvastatin could be a first-line option for patients requiring a reduction of 50% or more to reach the LDL goal of the National Cholesterol Education Program Adult Treatment Panel III. Rosuvastatin monotherapy may allow patients to achieve this LDL goal earlier, and it may help them avoid combination therapy or potential adverse effects of high-dose statin therapy. However, because cardiovascular disease morbidity and mortality data are lacking for rosuvastatin (but available for all other marketed statins) and because its postmarketing data are limited, rosuvastatin should be reserved for patients requiring an LDL reduction of 50% or less who cannot reach the recommended goal with other statins because of adverse effects, drug interactions, or cost.

In vitro metabolism of phenoxypropoxybiguanide analogues in human liver microsomes to potent antimalarial dihydrotriazines

Phenoxypropoxybiguanides, such as 1 (PS-15), are prodrugs analogous to the relationship of proguanil and its active metabolite cycloguanil. Unlike cycloguanil, however, 1a (WR99210), the active metabolite of 1, has retained in vitro potency against newly emerging antifolate-resistant malaria parasites. Unfortunately, manufacturing processes and gastrointestinal intolerance have prevented the clinical development of 1. In vitro antimalarial activity and in vitro metabolism studies have been performed on newly synthesized phenoxypropoxybiguanide analogues. All of the active dihydrotriazine metabolites exhibited potent antimalarial activity with in vitro IC(50) values less than 0.04 ng/mL. In vitro metabolism studies in human liver microsomes identified the production of not only the active dihydrotriazine metabolite, but also a desalkylation on the carbonyl chain, and multiple hydroxylated metabolites. The V(max) for production of the active metabolites ranged from 10.8 to 27.7 pmol/min/mg protein with the K(m) ranging from 44.8 to 221 microM. The results of these studies will be used to guide the selection of a lead candidate.

Simvastatin plus ezetimibe: combination therapy for the management of dyslipidaemia

Hyperlipidaemia is a pivotal risk factor for the development of atherosclerotic disease. A large number of studies have demonstrated that the treatment of abnormalities in lipoprotein levels reduces the risk for myocardial infarction, peripheral vascular disease, carotid artery disease, stroke, and cardiovascular mortality. Despite the development of multiple drug classes to treat dyslipidaemias and the promulgation of clearly defined guidelines for the management of lipid disorders, dyslipidaemia tends to be undertreated in the majority of patients at risk for cardiovascular disease. A part of the reluctance to treat different lipoprotein fractions to goal levels is attributable to physician- and patient-related concerns over the increasing toxicity of available therapies, as their dosages are increased. The risks of hepatotoxicity, myalgia, and rhabdomyolysis are fairly well characterised in patients receiving statins, fibrates and niacin. Another issue affecting treatment success rates is the fact that many patients with complex dyslipidaemias are inadequately responsive to single-agent therapy. As the epidemics of obesity, metabolic syndrome and diabetes mellitus continue to worsen, physicians will encounter severe, mixed dyslipidaemias more frequently. Many of these patients will require combinations of drugs to address the various metabolic derangements causing changes in multiple lipoprotein fractions. Although the need for combination therapy is well-established in the management of disorders, such as hypertension and diabetes, it is less often used for the treatment of dyslipidaemias. The development of safe, cost-effective, and efficacious combination dyslipidaemic therapy is an important goal in cardiovascular medicine. Simvastatin plus ezetimibe has recently been combined as a fixed dose therapy, which offers clinicians the opportunity to simultaneously inhibit two key pathways in cholesterol metabolism: hepatic cholesterol biosynthesis and the absorption of cholesterol at the level of the proximal jejunum. This dual mechanism of inhibition substantially increases the capacity to decrease serum levels of atherogenic low-density lipoproteins and increase high-density lipoprotein, compared with that observed when either drug is used alone. This combination increases the likelihood of therapeutic success in patients with dyslipidaemia.

Management of diabetic dyslipidemia

Identification and management of dyslipidemia is an important element in the multi-factorial approach to prevent coronary heart disease. Diabetic dyslipidemia typically consists of elevated triglyceride, low high-density lipoprotein cholesterol, predominance of small, dense low-density lipoprotein (LDL) particles, and average LDL cholesterol (LDL-C). Lipid-lowering therapy has a beneficial effect on cardiovascular outcomes. Statin treatment is beneficial in patients who are older than 40 years of age, irrespective of the LDL-C value. To achieve lipid targets, attention should be directed first toward nonpharmacologic therapeutic interventions, such as diet, exercise, smoking cessation, weight loss, and improving glycemic control. Although statin therapy is recommended for most subjects, judicious use of combination therapy should be considered in the highest risk subjects.

Rosuvastatin safety: lessons from the FDA review and post-approval surveillance

Rosuvastatin is the first statin approved by the regulatory authorities since the withdrawal of cerivastatin. Although highly efficacious, this new statin has generated considerable controversy regarding its safety. Rosuvastatin was approved for clinical use based on the largest pre-approval database for all statins prior to commercial use. In this database, rosuvastatin had a similar safety profile to other approved statins up to the highest approval dose of 40 mg. As with all statins, there is a marked increase in adverse effects when the dose is titrated from 40 to 80 mg, and rosuvastatin demonstrates a similar dose/toxicity relationship. In the pre-approval data trials on 80 mg, there was a 1.0% (n = 16) incidence of myopathy and 7 patients developed rhabdomyolysis. However the <or= 40 mg doses had a myopathy rate similar to other statins. In the post-marketing surveillance for rosuvastatin, there have been reports of rhabdomyolysis, but the incidence rate, when corrected for prescription utilisation, is similar to other statins following initial approval.

Current Drug Options for Raising HDL Cholesterol

Although circumstantial evidence supports raising high-density lipoprotein cholesterol (HDLC) in patients with low levels of HDLC, the scarcity of event-based trials has led to uncertainty with regard to the benefit of high-density lipoprotein (HDL)-raising therapy. Based on the National Cholesterol Education Program guidelines, therapy for dyslipidemia is focused initially on targeting low-density lipoprotein cholesterol (LDLC), and in patients with hypertriglyceridemia, secondarily on targeting non-HDLC. When HDLC remains low, the decision to target HDLC depends on the assessment of risk of cardiovascular events. We often consider drug therapy specifically to raise HDLC in high-risk patients, such as those with established atherosclerotic vascular disease, type 2 diabetes, or a Framingham risk score of 20% or above. The majority of high-risk patients require drug therapy, usually a statin, to achieve aggressive LDLC and non-HDLC goals, and thus many patients with low HDLC are candidates for statin therapy. However, a second drug is often required to achieve substantial HDL raising. Although no formal goals for HDLC exist, reasonable goals are HDLC greater than 40 mg/dL in men and greater than 50 mg/dL in women. We often add either niacin or a fibrate to a statin in high-risk patients with low HDLC levels. Targeting HDLC with pharmacologic therapy is a more difficult decision in moderate-risk patients, in whom therapy must be highly individualized.

Reporting rate of rhabdomyolysis with fenofibrate + statin versus gemfibrozil + any statin

There is an increasing trend among physicians to use 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) in combination with other antilipidemic agents. The complementary lipid-altering effects of statins and fibric acid derivatives (fibrates) have led to an increasing use of statin/fibrate combination therapy, particularly for patients who have mixed dyslipidemia. Clinical experience indicates that there may be an increased risk of myotoxicity associated with statin/fibrate combination therapy. However, it is not known whether there are differences in the rate of myotoxicity between the use of fenofibrate and gemfibrozil in combination with statins. To evaluate this question, data from the United States Food and Drug Administration's Adverse Event Reporting System was reviewed to determine how many adverse events were reported for patients who were being treated concomitantly with statins and fibrates. The findings suggest that the use of fenofibrate in combination with statins results in fewer reports of rhabdomyolysis per million prescriptions dispensed than does the use of gemfibrozil.