Rational assessment of the interaction profile of cerivastatin supports its low propensity for drug interactions

Clopidogrel Markedly Increases Plasma Concentrations of CYP2C8 Substrate Pioglitazone

The glucose-lowering drug pioglitazone undergoes hepatic CYP2C8-mediated biotransformation to its main metabolites. The antiplatelet drug clopidogrel is metabolized to clopidogrel acyl-β-d-glucuronide, which was recently found to be a strong time-dependent inhibitor of CYP2C8 in humans. Therefore, we studied the effect of clopidogrel on the pharmacokinetics of pioglitazone. In a randomized crossover study, 10 healthy volunteers ingested either 300 mg of clopidogrel on day 1, and 75 mg on days 2 and 3, or placebo. Pioglitazone 15 mg was administered 1 hour after placebo and clopidogrel on day 1. Plasma concentrations of pioglitazone, clopidogrel, and their main metabolites were measured up to 72 hours. Clopidogrel increased the area under the plasma concentration-time curve (AUC0-∞) of pioglitazone 2.1-fold [P < 0.001, 90% confidence interval (CI) 1.8-2.6] and prolonged its half-life from 6.7 to 11 hours (P = 0.002). The peak concentration of pioglitazone was unaffected but the concentration at 24 hours was increased 4.5-fold (range 1.6-9.8; P < 0.001, 90% CI 3.17-6.45) by clopidogrel. The M-IV-to-pioglitazone AUC0-∞ ratio was 49% (P < 0.001, 90% CI 0.40-0.59) of that during the control phase, indicating that clopidogrel inhibited the CYP2C8-mediated biotransformation of pioglitazone. Clopidogrel increases the exposure to pioglitazone by inhibiting its CYP2C8-mediated biotransformation. In consequence, use of clopidogrel may increase the risk of fluid retention and other concentration-related adverse effects of pioglitazone.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

Clopidogrel Has No Clinically Meaningful Effect on the Pharmacokinetics of the Organic Anion Transporting Polypeptide 1B1 and Cytochrome P450 3A4 Substrate Simvastatin

Simvastatin and clopidogrel are commonly used together in the treatment of cardiovascular diseases. Organic anion transporting polypeptide (OATP) 1B1 activity markedly affects the hepatic uptake of simvastatin acid, whereas both simvastatin and simvastatin acid are sensitive to changes in cytochrome P450 3A4 activity. Clopidogrel and its metabolites inhibit OATP1B1 and CYP3A4 in vitro. We studied the effect of clopidogrel on the pharmacokinetics of simvastatin in a randomized crossover study. Twelve healthy volunteers ingested either a dose of placebo (control) or 300 mg of clopidogrel on day 1 and 75 mg on days 2 and 3. Simvastatin 40 mg was administered 1 hour after placebo and after clopidogrel on days 1 and 3. Plasma drug concentrations were measured for up to 12 hours. Clopidogrel 300 mg (day 1) increased the concentrations of simvastatin and simvastatin acid during the absorption phase. After clopidogrel 300 mg, the area under the concentration time curve (AUC) of simvastatin from 0 to 2 hours was 156% (P = 0.02) and its AUC(0-12 hours) was 132% (P = 0.08) of that during placebo, whereas the AUC(0-2 hours) and the AUC(0-12 hours) of simvastatin acid were 148% (P = 0.04) and 112% (P = 0.52) of control. Clopidogrel 75 mg (day 3) had no significant effect on the pharmacokinetic variables of simvastatin or simvastatin acid compared with placebo. The effect of clopidogrel seemed independent of the SLCO1B1 c.521T>C genotype. In conclusion, as clopidogrel did not have significant effects on the total exposure to simvastatin or simvastatin acid, clopidogrel does not seem to inhibit OATP1B1 or CYP3A4 to a clinically relevant extent.

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

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

Chromatography–mass spectrometry methods for the quantitation of statins in biological samples

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, more commonly known as 'statins', are a novel class of drugs widely used for the treatment of hypercholesterolaemia in patients with established cardiovascular disease as well as those at high risk of developing atherosclerosis. Published chromatographic-mass spectrometric methods for the quantification of presently available seven statins, atorvastatin, simvastatin, lovastatin, pravastatin, fluvastatin, rosuvastatin and pitavastatin are reviewed. High performance liquid chromatography (HPLC) in combination with tandem mass spectrometry (MS/MS) is the analytical technique of choice for the quantification of statins in biological samples. This review envisages that most of the methods used for quantification of statins are in plasma and they are suitable for therapeutic drug monitoring of these drugs.

Functional characterization of five novel CYP2C8 variants, G171S, R186X, R186G, K247R, and K383N, found in a Japanese population

Cytochrome P450 2C8 is one of the primary enzymes responsible for the metabolism of a wide range of drugs such as paclitaxel, cerivastatin, and amiodarone. We have sequenced the CYP2C8 gene from 201 Japanese subjects and found five novel nonsynonymous single nucleotide polymorphisms (SNPs): 511G>A (G171S), 556C>T (R186X; X represents the translational stop codon), 556C>G (R186G), 740A>G (K247R), and 1149G>T (K383N), with the allele frequency of 0.0025. The CYP2C8 variants were heterologously expressed in COS-1 cells and functionally characterized in terms of expression level, paclitaxel 6alpha-hydroxylase activity, and intracellular localization. The prematurely terminated R186X variant was undetectable by Western blotting and inactive toward paclitaxel 6alpha-hydroxylation. The G171S, K247R, and K383N variants exhibited properties similar to those of the wild-type CYP2C8. Paclitaxel 6alpha-hydroxylase activity of the R186G transfectant was only 10 to 20% that of wild-type CYP2C8. Furthermore, the R186G variant displayed a lower level of protein expression in comparison to the wild type, which was restored by the addition of a proteasome inhibitor (MG-132; Z-Leu-Leu-Leu-aldehyde). The reduced CO-difference spectral analysis using recombinant proteins from an insect cell/baculovirus system revealed that the R186G variant has a minor peak at 420 nm in addition to the characteristic Soret peak at 450 nm, suggesting the existence of improperly folded protein. These results indicate that the novel CYP2C8 SNPs, 556C>T (R186X) and 556C>G (R186G), could influence the metabolism of CYP2C8 substrates such as paclitaxel and cerivastatin.

Tacrolimus and cerivastatin pharmacokinetics and adverse effects after single and multiple dosing with cerivastatin in renal transplant recipients

AIMS

In contrast to cyclosporin, only limited information exists on the interaction potential between the immunosuppressive agent tacrolimus and HMG-CoA reductase inhibitors, which are metabolized via the cytochrome P450 system. The aim of this study was to investigate the pharmacokinetics, and adverse effects of cerivastatin combined with tacrolimus in renal transplant patients.

METHODS

Ten patients with stable kidney graft functions and LDL-cholesterol serum concentrations > 110 mg dl-1 were included in the study. After an observation period of 3 months, cerivastatin (0.2 mg daily) was administered for an additional 3 months. Tacrolimus steady-state pharmacokinetics and cerivastatin single- and multiple-dose pharmacokinetics were determined. Lipid concentrations, routine laboratory parameters and adverse events were obtained and analysed throughout the study period of 6 months.

RESULTS

Blood tacrolimus trough concentrations were not affected by cerivastatin (mean +/- SD 8.6 +/- 2.1 ng ml(-1) before, and 8.7 +/- 2.4 ng ml(-1) at day 90 of cerivastatin dosing, with a 95% confidence interval on the difference = 0.97, 1.08). The mean area under the blood concentration-time curve to 24 h (AUC(0,24 h)) for cerivastatin was 14.5 +/- 2.53 micro g l(-1) h(-1) at day 1 after starting treatment and 19.02 +/- 3.55 micro g l(-1) h(-1) (3 months later), resulting in a 35% higher (AUC(0,24 h)) compared with the first dose. Total cholesterol, LDL-cholesterol and triglyceride concentrations were significantly lowered by cerivastatin whereas no significant effect of cerivastatin on serum creatininkinase concentrations was observed and no adverse effects were documented.

CONCLUSIONS

Tacrolimus increased the AUC(0, 24 h) of cerivastatin by a mean of 35% in renal transplant patients. Cerivastatin had no detectable effect on the pharmacokinetics of tacrolimus.

Hyperlipidaemia in patients with HIV-1 infection receiving highly active antiretroviral therapy: epidemiology, pathogenesis, clinical course and management

A wide range of abnormalities of lipid metabolism have been recently described in HIV-infected patients receiving a protease inhibitor (PI)-based highly active antiretroviral therapy, including hypertriglyceridaemia and hypercholesterolaemia. The increase of plasma lipid concentrations may involve up to 70-80% of HIV-positive subjects treated with a PI-containing regimen and are frequently (but not always) associated with the fat redistribution or the lipodystrophy syndrome. Multiple pathogenetic mechanisms by which antiretroviral agents lead to dyslipidaemia have been hypothesized, but they are still controversial. The potential clinicopathological consequences of HIV-associated hyperlipidaemia are not completely known, but several anecdotal observations report an increased risk of premature coronary artery diseases in young HIV-positive individuals receiving PIs, besides peripheral atherosclerosis and acute pancreatitis. A limited-to-significant improvement of increased triglyceride and cholesterol plasma levels was described in patients who replaced PIs with nevirapine, efavirenz or abacavir, but the risks of long-term toxicity and virological relapse of this treatment switching are not completely defined. A hypolipidaemic diet and regular physical exercise may act favorably on dyslipidaemia, but pharmacological therapy becomes necessary when hyperlipidaemia is severe or persists for a long time. The choice of hypolipidaemic drugs is problematic because of potential pharmacological interactions with antiretroviral compounds and other antimicrobial agents, associated with an increased risk of toxicity and intolerance. Statins are considered the first-line therapy for the PI-related hypercholesterolaemia, while fibrates are the cornerstone of drug therapy when predominant hypertriglyceridaemia is of concern.

Incidence of hyperlipidaemia in a cohort of 212 HIV-infected patients receiving a protease inhibitor-based antiretroviral therapy

Two hundred and twelve HIV-positive patients who started a new protease inhibitor (PI)-based antiretroviral regimen between January 1998 and December 2000 in our tertiary care centre were prospectively followed-up during a 12-month study period, in order to assess the incidence of hyperlipidaemia and related clinical adverse events. At the end of 1-year follow-up, PI-containing antiretroviral treatment led to a statistically significant increase in serum triglyceride levels (P<0.005) and total and LDL-cholesterol levels (P<0.05). The overall incidence of hypertriglyceridaemia and hypercholesterolaemia was 38.2 and 25%, respectively. The incidence of increased serum triglyceride levels was significantly higher in patients treated with ritonavir (66.6%) or lopinavir/ritonavir (60.7%), compared with other PIs (P<0.04). Clinical adverse events possibly related to the hyperlipidaemia (such as cardiovascular diseases or acute pancreatitis) were not observed during the entire 12 months study period. In conformity with other previously published studies, the very high incidence of hyperlipidaemia during a PI-based therapy recognised in our work raises a big concern about its potential clinico-pathological consequences and the most convenient pharmacological management of these metabolic imbalances.

Statins and fibrates for the treatment of hyperlipidaemia in HIV-infected patients receiving HAART

OBJECTIVES

The aim of our work is to evaluate the role of statins and fibrates in the management of hyperlipidaemia in HIV-infected patients receiving highly active antiretroviral therapy.

DESIGN

Open-label, randomized, prospective study of the efficacy and safety of bezafibrate, gemfibrozil, fenofibrate, pravastatin and fluvastatin as pharmacologic treatment for protease inhibitor-related dyslipidaemia.

METHODS

Plasma lipid levels of 656 HIV-infected patients who referred to our tertiary care centre and were on protease inhibitor-based antiretroviral therapy for at least 12 months have been evaluated. All patients had HIV viral load < 50 copies/ml and presented with hypertriglyceridaemia of at least 6 months duration that was unresponsive to a hypolipidaemic diet; all have been treated with bezafibrate, gemfibrozil, fenofibrate, pravastatin, or fluvastatin for 12 months.

RESULTS

Of the 656 patients observed 113 (17.2%) received pharmacological therapy, while seven patients were excluded from evaluation due to early drop-out. Of the 106 evaluable subjects, bezafibrate was used in 25 cases, gemfibrozil in 22, fenofibrate in 22, pravastatin in 19, and fluvastatin in 18. At the close of 1-year follow-up, fibrates led to a reduction of 40.7% and 21.9% versus baseline triglyceridaemia and cholesterolaemia, respectively (P < 0.001), and statins led to a reduction of 34.8% and 25.2% versus baseline triglyceride and total cholesterol levels, respectively (P < 0.001), without significant differences according to each different administered hypolipidaemic drug.

CONCLUSIONS

All administered statins and fibrates revealed a similar, significant efficacy in the treatment of diet-resistant hyperlipidaemia, and showed a favourable tolerability profile.

Effects of HMG-CoA reductase inhibitors on skeletal muscle: are all statins the same?

The 3-hydroxy-3-methyl coenzyme A (HMG-CoA) reductase inhibitors or statins, specifically inhibit the enzyme HMG-CoA in the liver, thereby inhibiting the rate limiting step in cholesterol biosynthesis and so reducing plasma cholesterol levels. Numerous studies have consistently demonstrated that cholesterol lowering with statin therapy reduces morbidity and mortality from coronary heart disease, whilst recent evidence has demonstrated that benefits of statin therapy may also extend into stroke prevention. Since hypercholesterolaemia is a chronic condition, the long-term safety and tolerability of these agents is an important issue. Numerous large-scale clinical trials have consistently demonstrated a positive safety and tolerability profile for statins. Hepatic, renal and muscular systems are rarely affected during statin therapy, with adverse reactions involving skeletal muscle being the most common, ranging from mild myopathy to myositis and occasionally to rhabdomyolysis and death. Postmarketing data supports the positive safety and tolerability profile of statins, with an overall adverse event frequency of less than 0.5% and a myotoxicity event rate of less than 0.1%. The recent withdrawal of cerivastatin from the world market due to deaths from rhabdomyolysis has, however, focused attention on the risk of adverse events and in particular myotoxicity associated with statins. Indeed, initial clinical trial data supports postmarketing data, demonstrating a higher incidence of myotoxicity associated with cerivastatin, particularly when used in combination with fibrates. The potential mechanisms underlying statin-induced myotoxicity are complex with no clear consensus of opinion. Candidate mechanisms include intracellular depletion of essential metabolites and destabilisation of cell membranes, resulting in increased cytotoxicity. Cytochrome P450 3A4 is the main isoenzyme involved in statin metabolism. Reduced activity of this enzyme due to either reduced expression or inhibition by other drugs prescribed concomitantly such as cyclosporin or itraconazole may increase drug bioavailability and the risk of myotoxicity. Such factors may partly account for the interindividual variability in susceptibility to statin-induced myotoxicity, although other as of yet unclarified, genetic factors may also be involved. The risk of rhabdomyolysis is increased with combination fibrate-statin therapy, with initial evidence suggesting that gemfibrozil-statin combination may particularly increase the risk of myotoxicity, with pharmacodynamic as well as pharmacokinetic mechanisms being involved.

Pharmacokinetic-pharmacodynamic drug interactions with HMG-CoA reductase inhibitors

The HMG-CoA reductase inhibitors (statins) are effective in both the primary and secondary prevention of ischaemic heart disease. As a group, these drugs are well tolerated apart from two uncommon but potentially serious adverse effects: elevation of liver enzymes and skeletal muscle abnormalities, which range from benign myalgias to life-threatening rhabdomyolysis. Adverse effects with statins are frequently associated with drug interactions because of their long-term use in older patients who are likely to be exposed to polypharmacy. The recent withdrawal of cerivastatin as a result of deaths from rhabdomyolysis illustrates the clinical importance of such interactions. Drug interactions involving the statins may have either a pharmacodynamic or pharmacokinetic basis, or both. As these drugs are highly extracted by the liver, displacement interactions are of limited importance. The cytochrome P450 (CYP) enzyme system plays an important part in the metabolism of the statins, leading to clinically relevant interactions with other agents, particularly cyclosporin, erythromycin, itraconazole, ketoconazole and HIV protease inhibitors, that are also metabolised by this enzyme system. An additional complicating feature is that individual statins are metabolised to differing degrees, in some cases producing active metabolites. The CYP3A family metabolises lovastatin, simvastatin, atorvastatin and cerivastatin, whereas CYP2C9 metabolises fluvastatin. Cerivastatin is also metabolised by CYP2C8. Pravastatin is not significantly metabolised by the CYP system. In addition, the statins are substrates for P-glycoprotein, a drug transporter present in the small intestine that may influence their oral bioavailability. In clinical practice, the risk of a serious interaction causing myopathy is enhanced when statin metabolism is markedly inhibited. Thus, rhabdomyolysis has occurred following the coadministration of cyclosporin, a potent CYP3A4 and P-glycoprotein inhibitor, and lovastatin. Itraconazole has been shown to increase exposure to simvastatin and its active metabolite by at least 10-fold. Pharmacodynamically, there is an increased risk of myopathy when statins are coprescribed with fibrates or nicotinic acid. This occurs relatively infrequently, but is particularly associated with the combination of cerivastatin and gemfibrozil. Statins may also alter the concentrations of other drugs, such as warfarin or digoxin, leading to alterations in effect or a requirement for clinical monitoring. Knowledge of the pharmacokinetic properties of the statins should allow the avoidance of the majority of drug interactions. If concurrent therapy with known inhibitors of statin metabolism is necessary, the patient should be monitored for signs and symptoms of myopathy or rhabdomyolysis and the statin should be discontinued if necessary.

How well tolerated are lipid-lowering drugs?

It has been clearly established that lipid-lowering treatments [such as 3-hydroxyl-3-methylglutamyl coenzyme A reductase inhibitors ('statins') or fibrates] can reduce cardiovascular events, and with one of the statins even total mortality, in high-risk populations. Intervention studies have not included the very old, but it is generally assumed that this patient group would benefit from these treatments to an extent similar to younger patients. Worries about the associations seen in observational studies between low cholesterol levels and cancer, cerebral haemorrhage or mood and behaviour change have been largely overcome by findings from the latest large drug intervention trials, which do not show any increase in these conditions with statin or fibrate treatments. The common adverse effects associated with these drugs are relatively mild and often transient in nature. Potentially more serious adverse effects, which are more clearly related to drug treatment and are probably dose-dependent, include elevations in hepatic transaminase levels and myopathy; however, these effects are uncommon and generally resolve rapidly when treatment is stopped. The risk of myopathy with fibrate treatment is increased in patients with renal impairment, and the risk of myopathy with statin treatment increases with co-administration of drugs that inhibit statin metabolism or transport. Other adverse effects are related to specific drugs, for example, clofibrate is associated with an increased risk of gallstones. Studies in elderly patients have not shown an increased risk of adverse effects with lipid-lowering drugs compared with younger patients, but in clinical practice there may be some increased risk, particularly with regards to drug interactions. Therefore, lipid-lowering drugs should be administered with extra caution to elderly patients.

Bilateral pharmacokinetic interaction between cyclosporine A and atorvastatin in renal transplant recipients

Atorvastatin is increasingly used as a cholesterol-lowering agent in solid organ transplant recipients receiving cyclosporine A (CsA). However, the potential bilateral pharmacokinetic interaction between atorvastatin and CsA in renal transplant recipients has not previously been examined. Baseline 12-h CsA pharmacokinetic investigation was performed in 21 renal transplant recipients and repeated after 4 weeks of atorvastatin treatment (10 mg/ d). At week 4, 24-h pharmacokinetics of atorvastatin was also performed. All patients received basiliximab induction followed by CsA and prednisolone immunosuppression. Compared with historic controls, CsA-treated patients showed, on average, sixfold higher plasma HMG-CoA reductase inhibitory activity after 4 weeks of atorvastatin treatment (p < 0.05). Atorvastatin had a moderate effect on the pharmacokinetics of CsA and reduced the AUC0-12 (area under curve, 0-12h) by 9.5 +/- 18% (p = 0.013) and Cmax (maximal concentration) by 13.5 +/- 24% (p =0.009), while C12 (trough level) was unchanged (p =0.42). Total and LDL cholesterol decreased by 26.8 +/- 8.4% (p < 0.0001) and 41.5 +/- 11.0% (p < 0.0001), respectively. Bilateral pharmacokinetic interaction between atorvastatin and CsA resulted in sixfold higher plasma HMG-CoA reductase inhibitory activity, but only a moderate decrease in systemic exposure of CsA.

Induction of apoptosis and inhibition of migration of inflammatory and vascular wall cells by cerivastatin

Statins are thought to play a role in directly affecting immune and mesenchymal cells. Since cerivastatin's pleiotropic effects are poorly investigated, we were interested to find out whether this drug can modulate leukocyte and vessel wall cell functions. Leukocyte migration was tested in modified Boyden microchemotaxis chambers and oxygen radical production was measured fluorometrically. Transendothelial migration experiments were performed with human umbilical vein endothelial cells and neutrophils. Neutrophil, monocyte, and vascular smooth muscle cell caspase-3 activity and annexin-V binding were quantified by FIENA and FACS, respectively. Cerivastatin [10 pM to 100 microM] decreased leukocyte chemotaxis towards interleukin-8 or RANTES. Migration of cells was completely restored by addition of mevalonic acid. In neutrophils, cerivastatin [100 microM] reduced transendothelial migration, whereas treatment of endothelial cells failed to affect transmigration. Neutrophil respiratory burst activity was unaffected by cerivastatin. At concentrations of 10 nM or higher, cerivastatin increased the rate of apoptosis in phagocytes and smooth muscle cells. Results show that cerivastatin is able to inhibit leukocyte chemotaxis, and that cerivastatin induces neutrophil, monocyte, and smooth muscle cell apoptosis. The drug's impact on transendothelial migration is due to its effects on neutrophils. In addition to its lipid-lowering effects, pharmacological properties of cerivastatin may include modulatory actions in leukocytes and mesenchymal cells.

A review of rosiglitazone in type 2 diabetes mellitus

The thiazolidinedione rosiglitazone maleate works primarily to improve insulin sensitivity in muscle and adipose tissue. It may have additional pharmacologic effects, however, as its main target is peroxisome proliferator-activated receptor-gamma. Data using the homeostasis model assessment and proinsulin:insulin ratio in patients with type 2 diabetes mellitus suggest that rosiglitazone may have the potential to sustain or improve beta-cell function. In these patients the drug reduces fasting plasma glucose, glycosylated hemoglobin, insulin, and C-peptide. In clinical trials, rosiglitazone monotherapy significantly reduced glycosylated hemoglobin by 1.5% compared with placebo and led to significant improvements in glycemic control when given in combination with metformin, sulfonylureas, or insulin. A dosage of 4 mg twice/day significantly reduced fasting plasma glucose levels and produced comparable reductions in glycosylated hemoglobin compared with glyburide. Rosiglitazone has a low risk of gastrointestinal side effects and hypoglycemia, reduced insulin demand, potential sparing effects on beta-cells, and favorable drug interaction profile. Adverse events of clinical significance are edema, anemia, and weight gain. Premarketing data indicate no significant difference in liver enzyme elevations for rosiglitazone, placebo, or active controls. Another drug in the thiazolidinedione class, troglitazone, was associated with idiosyncratic hepatotoxicity and was removed from the market. Therefore, until long-term data are available for rosiglitazone, liver enzyme monitoring is recommended.

Treatment of the elderly with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors: focus on drug interactions

With the aging of the population, death from coronary heart disease (CHD) and stroke has become more prevalent. Cardiovascular disease (CVD) risk factors, such as hypertension, obesity, and diabetes mellitus increase with age as well. Recent secondary-prevention studies have established the positive effect of statins in decreasing the risk of CHD mortality through the lowering of cholesterol. Statins have an excellent safety record, at least with users under age 65, and provide a cheaper alternative to more costly medical options. The most serious side effect associated with their use is myopathy, which is infrequent. Drug interactions have been found with drugs that compete for the same CYP450 isoenzymes as statins. Several drugs have been shown to significantly inhibit the CYP3A4 pathway; in combination with statins such as lovastatin, simvastatin, atorvastatin, and cerivastatin, they have been shown to elevate serum concentrations of these statins, or may increase the risk of myopathy. Alternatively, other drugs can inhibit the CYP2C9 pathway and may elevate serum concentration of fluvastatin. Due to the number of medications the elderly receive, an understanding of the various metabolic pathways is of vital importance to minimize the potential for drug interactions. The elderly population, while at high risk for CVD, is currently undertreated. Statins can effectively lower low-density lipoprotein cholesterol levels and lessen the risk of CVD for this population.

Cardiovascular drug-drug interactions

The drug-drug interactions discussed in this article have either documented or suspected clinical relevance for patients with cardiovascular disease and the clinician involved in the care of these patients. Oftentimes, drug-drug interactions are difficult, if not impossible, to predict because of the high degree of interpatient variability in drug disposition. Certain drug-drug interactions, however, may be avoided through knowledge and sound clinical judgment. Every clinician should maintain a working knowledge of reported drug-drug interactions and an understanding of basic pharmacokinetic and pharmacodynamic principles to help predict and minimize the incidence and severity of drug-drug interactions.

The effects of the statins lovastatin and cerivastatin on signalling by the prostanoid IP-receptor

The prostanoid-IP receptor may be unique among G protein coupled receptors in that it is isoprenylated. In this study, we investigated the effects of the statins lovastatin and cerivastatin on signalling by the mouse (m) IP and the human (h) IP receptors, over-expressed in human embryonic kidney (HEK) 293 cells and by the hIP receptor, endogenously expressed in human erythroleukaemia cells. Both statins significantly reduced IP receptor-mediated cyclic AMP generation and intracellular calcium ([Ca(2+)](i)) mobilization in a time and concentration dependent manner but had no effect on signalling by the non-isoprenylated beta(2) adrenergic receptor or by the human prostanoid-TP receptor isoforms. Cerivastatin (IC(50), 50 - 90 nM) was significantly more potent than lovastatin (IC(50), 0.80 - 4.2 microM) in inhibiting IP receptor signalling. Whereas IC(50) values indicated that the hIP receptor was significantly more sensitive than the mIP receptor to the statins, the extent of inhibition of cyclic AMP generation by the mIP receptor was significantly greater than that of the hIP receptor to either statin, even at the highest concentrations used. Pretreatment with either statin significantly reduced IP receptor mediated desensitization of signalling by the h.TPalpha, but not by the h.TPbeta, receptor isoform. These data generated in whole cells point to the possibility that statin therapy may interfere with IP receptor signalling in vivo; such interference may be extenuated under conditions where circulating statin levels are elevated and may account, in part, for some of the pleiotropic affects of the statins not attributed solely to their lipid lowering properties.

Efficacy and drug interactions of the new HMG-CoA reductase inhibitors cerivastatin and atorvastatin in CsA-treated renal transplant recipients

BACKGROUND

Hyperlipidaemia is an important risk factor for cardiovascular disease in renal transplant recipients. The aim of this study was to test the efficacy and possible drug-drug interactions of the new HMG-CoA reductase inhibitors (statins) atorvastatin and cerivastatin in cyclosporin A (CsA)-treated renal transplant patients. Subjects and methods. Thirty patients with stable graft function and LDL cholesterol of 130 mg/dl were randomly assigned to active treatment groups (10 mg atorvastatin or 0.2 mg cerivastatin), or a control group. CsA blood trough levels were controlled on a weekly basis and adapted if they changed more than 25% from baseline values (100-150 ng/ml). Lipid levels and routine laboratory parameters before and after a treatment period of 3 months were compared.

RESULTS

In the group treated with cerivastatin no significant changes in CsA blood trough levels occurred (CsA 116+/-21 ng/ml vs 110+/-20 ng/ml). In contrast, in the group treated with atorvastatin, four of 10 patients had a rise in CsA blood trough levels of more than 25% within 7-14 days of starting therapy. In the remaining patients no significant changes in CsA drug levels occurred. After therapy with atorvastatin or cerivastatin, total cholesterol, LDL cholesterol, and triglycerides were significantly lower compared with baseline conditions. No changes of CsA or lipoprotein levels were present in the control group.

CONCLUSION

In our study population both statins were very effective in lowering elevated LDL cholesterol levels. Cerivastatin did not influence CsA blood trough levels, whereas atorvastatin increased CsA levels in four of 10 patients. Further research in a larger study is necessary in order to confirm these results and to investigate the possible reasons for this drug interaction.

The xenobiotic inhibitor profile of cytochrome P4502C8

AIMS

To investigate inhibition of recombinant CYP2C8 by: (i) prototypic CYP isoform selective inhibitors (ii) imidazole/triazole antifungal agents (known inhibitors of CYP), and (iii) certain CYP3A substrates (given the apparent overlapping substrate specificity of CYP2C8 and CYP3A).

METHODS

CYP2C8 and NADPH-cytochrome P450 oxidoreductase were coexpressed in Spodoptera frugiperda (Sf21) cells using the baculovirus expression system. CYP isoform selective inhibitors, imidazole/triazole antifungal agents and CYP3A substrates were screened for their inhibitory effects on CYP2C8-catalysed torsemide tolylmethylhydroxylation and, where appropriate, the kinetics of inhibition were characterized. The conversion of torsemide to its tolylmethylhydroxy metabolite was measured using an h.p.l.c. procedure.

RESULTS

At concentrations of the CYP inhibitor 'probes' employed for isoform selectivity, only diethyldithiocarbamate and ketoconazole inhibited CYP2C8 by > 10%. Ketoconazole, at an added concentration of 10 microM, inhibited CYP2C8 by 89%. Another imidazole, clotrimazole, also potently inhibited CYP2C8. Ketoconazole and clotrimazole were both noncompetitive inhibitors of CYP2C8 with apparent Ki values of 2.5 microM. The CYP3A substrates amitriptyline, quinine, terfenadine and triazolam caused near complete inhibition (82-91% of control activity) of CYP2C8 at concentrations five-fold higher than the known CYP3A Km. Kinetic studies with selected CYP3A substrates demonstrated that most inhibited CYP2C8 noncompetitively. Apparent Ki values for midazolam, quinine, terfenadine and triazolam ranged from 5 to 25 microM.

CONCLUSIONS

Inhibition of CYP2C8 occurred at concentrations of ketoconazole and diethyldithiocarbamate normally employed for selective inhibition of CYP3A and CYP2E1, respectively. Some CYP3A substrates have the capacity to inhibit CYP2C8 activity and this may have implications for inhibitory drug interactions in vivo.

Preliminary guidelines for the evaluation and management of dyslipidemia in adults infected with human immunodeficiency virus and receiving antiretroviral therapy: Recommendations of the Adult AIDS Clinical Trial Group Cardiovascular Disease Focus Group

Dyslipidemia is a prevalent condition that affects patients infected with human immunodeficiency virus (HIV) who are receiving antiretroviral therapy. These preliminary recommendations summarize the current understanding in this area and propose guidelines for management. Existing guidelines for the management of dyslipidemia in the general population formed the general basis for our recommendations. Data on the prevalence and treatment of dyslipidemia of HIV-infected patients, implications of treatment-related dyslipidemia in other chronically ill populations, and pharmacokinetic profiles for the available hypolipidemic agents in non-HIV populations were considered. Although the implications of dyslipidemia in this population are not fully known, the frequency, type, and magnitude of lipid alterations in HIV-infected people are expected to result in increased cardiovascular morbidity. We propose that these patients undergo evaluation and treatment on the basis of existing guidelines for dyslipidemia, with the caveat that avoidance of interactions with antiretroviral agents is paramount.

Safety and efficacy of HMG-CoA reductase inhibitors for treatment of hyperlipidemia in patients with HIV infection

STUDY OBJECTIVE

To assess the efficacy and safety of HMG-CoA reductase inhibitors (statins) in patients with human immunodeficiency virus (HIV) infection and hyperlipidemia.

DESIGN

Retrospective analysis.

SETTING

HIV clinic.

PATIENTS

Twenty-six HIV-infected patients with hyperlipidemia.

INTERVENTION

Five patients received pravastatin, 13 lovastatin, 10 simvastatin, and 2 atorvastatin (total 30 courses).

MEASUREMENTS AND MAIN RESULTS

Reductions in cholesterol and triglycetides were used to assess efficacy; creatine kinase (CK), liver enzymes, and myalgia were markers of statin toxicity. After a median of 8.2 and 7.2 months of treatment, the agents collectively reduced median baseline total cholesterol 27% (354 to 263 mg/dl) and triglycerides 15% (513 to 438 mg/dl), respectively. Two patients, one with marked CK elevations, experienced myalgias with lovastatin, and two experienced transaminase elevations 3 or more times the upper limit of normal.

CONCLUSION

Statins are effective in reducing total cholesterol and triglycerides in HIV-infected patients, although lipid levels infrequently return to normal. Lovastatin should be avoided in patients receiving concomitant drugs that may potentiate skeletal muscle toxicity with this agent.

New insights into the pharmacodynamic and pharmacokinetic properties of statins

The beneficial effects of statins are assumed to result from their ability to reduce cholesterol biosynthesis. However, because mevalonic acid is the precursor not only of cholesterol, but also of many nonsteroidal isoprenoid compounds, inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase may result in pleiotropic effects. It has been shown that several statins decrease smooth muscle cell migration and proliferation and that sera from fluvastatin-treated patients interfere with its proliferation. Cholesterol accumulation in macrophages can be inhibited by different statins, while both fluvastatin and simvastatin inhibit secretion of metalloproteinases by human monocyte-derived macrophages. The antiatherosclerotic effects of statins may be achieved by modifying hypercholesterolemia and the arterial wall environment as well. Although statins rarely have severe adverse effects, interactions with other drugs deserve attention. Simvastatin, lovastatin, cerivastatin, and atorvastatin are biotransformed in the liver primarily by cytochrome P450-3A4, and are susceptible to drug interactions when co-administered with potential inhibitors of this enzyme. Indeed, pharmacokinetic interactions (e.g., increased bioavailability), myositis, and rhabdomyolysis have been reported following concurrent use of simvastatin or lovastatin and cyclosporine A, mibefradil, or nefazodone. In contrast, fluvastatin (mainly metabolized by cytochrome P450-2C9) and pravastatin (eliminated by other metabolic routes) are less subject to this interaction. Nevertheless, a 5- to 23-fold increase in pravastatin bioavailability has been reported in the presence of cyclosporine A. In summary, statins may have direct effects on the arterial wall, which may contribute to their antiatherosclerotic actions. Furthermore, some statins may have lower adverse drug interaction potential than others, which is an important determinant of safety during long-term therapy.

Fluvastatin in combination with cyclosporin in renal transplant recipients: a review of clinical and safety experience

Cardiovascular disease remains a significant cause of morbidity and mortality in patients who have undergone renal transplantation, with one of the main risk factors being post-transplantation hyperlipidaemia. To date, however, optimal management of elevated lipid levels in such patients has been hindered by the lack of both effective and safe treatments, coupled with concerns over probable interactions with immunosuppressive therapy, particularly cyclosporin. Numerous studies confirm that the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors, such as fluvastatin, are effective lipid-lowering agents in renal transplant recipients, supporting findings in other patients' groups. Moreover, based on investigations of metabolic profile and clinical observation, fluvastatin (at dosages of up to 80 mg/day) is well tolerated in renal transplant recipients receiving cyclosporin. In clinical trials to date, no instances of rhabdomyolysis have been observed during co-administration of fluvastatin and cyclosporin. The potential of fluvastatin for improving survival in renal transplant recipients, in terms of both cardiovascular mortality and graft rejection, is currently being investigated in two ongoing studies: ALERT (Assessment of Lescol [fluvastatin] in Renal Transplantation) and SOLAR (Study of Lescol [fluvastatin] in Acute Rejection). The results of these landmark studies should confirm the safe utility of fluvastatin in the renal transplantation setting.

Characterization of the cytochrome P450 enzymes involved in the in vitro metabolism of rosiglitazone

AIMS

To identify the human cytochrome P450 enzyme(s) involved in the in vitro metabolism of rosiglitazone, a potential oral antidiabetic agent for the treatment of type 2 diabetes-mellitus. Method The specific P450 enzymes involved in the metabolism of rosiglitazone were determined by a combination of three approaches; multiple regression analysis of the rates of metabolism of rosiglitazone in human liver microsomes against selective P450 substrates, the effect of selective chemical inhibitors on rosiglitazone metabolism and the capability of expressed P450 enzymes to mediate the major metabolic routes of rosiglitazone metabolism. Result The major products of metabolism following incubation of rosiglitazone with human liver microsomes were para-hydroxy and N-desmethyl rosiglitazone. The rate of formation varied over 38-fold in the 47 human livers investigated and correlated with paclitaxel 6alpha-hydroxylation (P<0.001). Formation of these metabolites was inhibited significantly (>50%) by 13-cis retinoic acid, a CYP2C8 inhibitor, but not by furafylline, quinidine or ketoconazole. In addition, both metabolites were produced by microsomes derived from a cell line transfected with human CYP2C8 cDNA. There was some evidence for CYP2C9 playing a minor role in the metabolism of rosiglitazone. Sulphaphenazole caused limited inhibition (<30%) of both pathways in human liver microsomes and microsomes from cells transfected with CYP2C9 cDNA were able to mediate the metabolism of rosiglitazone, in particular the N-demethylation pathway, albeit at a much slower rate than CYP2C8. Rosiglitazone caused moderate inhibition of paclitaxel 6alpha-hydroxylase activity (CYP2C8; IC50=18 microm ), weak inhibition of tolbutamide hydroxylase activity (CYP2C9; IC50=50 microm ), but caused no marked inhibition of the other cytochrome P450 activities investigated (CYP1A2, 2A6, 2C9, 2C19, 2D6, 2E1, 3A and 4A). Conclusion CYP2C8 is primarily responsible for the hydroxylation and N-demethylation of rosiglitazone in human liver; with minor contributions from CYP2C9.