Acute muscular syndrome associated with administration of clofibrate

The Interaction Between Rosuvastatin and Ticagrelor Leading to Rhabdomyolysis: A Case Report and Narrative Review

Objective

Drug interactions are a common cause of morbidity and mortality and may require prompt discontinuation of therapeutic regimens due to harmful side effects. Patients with acute coronary syndromes are likely to be prescribed multiple medications that are metabolized through the cytochrome P450 system, increasing the probability for drug interaction. Atorvastatin and simvastatin are both well known to interact with the oral P2Y12 agent ticagrelor. The purpose of this paper is to describe the interaction of ticagrelor with rosuvastatin leading to rhabdomyolysis, which is less clearly defined in the literature.

Method

We report a case of a 74-year-old male who presented with bilateral lower extremity weakness and difficulty ambulating for one month after being prescribed ticagrelor for a drug eluting stent, in the setting of already being on rosuvastatin. His clinical picture and laboratory findings were consistent with a diagnosis of rhabdomyolysis. His medications were adjusted to a regimen of clopidogrel and alirocumab. One month later, he returned to his baseline status.

Results

The mechanism of interaction between rosuvastatin and ticagrelor appears to be multifactorial. It may be caused by CYP450-mediated metabolism from a small amount of crossover between isoenzymes. Ticagrelor may also cause acute kidney injury, increasing the concentration of rosuvastatin. Other mechanisms of interaction include genetic differences in the organic anion transporter polypeptides and transportation through p-glycoprotein.

Conclusion

Future pharmacokinetic studies are warranted to better understand the interaction.

Life Threatening Hyperkalemia Associated with Clofibrate-Induced Myopathy in a CAPD Patient

A man being treated with CAPD developed severe hyperkalemia associated with clofibrate-induced rhabdomyolysis. A total intake of 9.5 9 of clofibrate was complicated by a 100fold increase of CPK, a dramatic increase in muscular enzymes and a life-threatening serum K level of 7.9 mEq/l. Despite a significant peritoneal elimination of clofibrate, this man exhibited a supranormal serum level of free drug.

Rhabdomyolysis precipitated by possible interaction of ticagrelor with high-dose atorvastatin

OBJECTIVE

To report a case of rhabdomyolysis possibly caused by interaction of ticagrelor with high-dose atorvastatin.

SUMMARY

A 62-year-old woman originally from India underwent uncomplicated percutaneous coronary intervention following ST-elevation myocardial infarction. The patient was discharged on a secondary prevention drug regimen that included ticagrelor 90 mg twice daily, atorvastatin 80 mg once daily, metoprolol 25 mg twice daily, and aspirin 81 mg daily. Two months later, the patient was readmitted with complaints of muscle pain, nausea, vomiting, and poor oral intake. The patient was diagnosed with rhabdomyolysis based on her symptoms combined with elevated creatine kinase, urine myoglobin, and serum creatinine. Intravenous fluids were initiated and atorvastatin held. Throughout the second hospital stay, serial laboratory values revealed a decrease in creatine kinase and resolution of acute kidney injury and muscle pain. The patient was discharged on aspirin and clopidogrel. Low-dose statin therapy was started at a follow-up appointment with close monitoring without recurrence of rhabdomyolysis.

RESULTS

A drug interaction between the cytochrome P450 3A4 inhibitor ticagrelor and substrate atorvastatin 80 mg may have precipitated development of rhabdomyolysis in this patient. The probability of this drug interaction is rated as "possible" on both the Naranjo Adverse Drug Reaction Probability Scale and the Drug Interaction Probability Scale.

CONCLUSION

Rhabdomyolysis was observed possibly because of a drug interaction between once-daily ticagrelor and atorvastatin 80 mg. Clinicians need to be aware of this possible drug interaction via CYP3A4 and potential complications.

Necrotizing myopathies: an update

Necrotizing myopathy is defined by the predominant pathological feature of necrosis of muscle fibers in the absence of substantial lymphocytic inflammatory infiltrates. Most commonly necrotizing myopathies are divided into immune mediated (IMNM) and nonimmune mediated (NIMNM). IMNM has been associated with anti-signal recognition particle antibodies, connective tissue diseases, cancer, post-statin exposure with 3-hydroxy-3-methylglutaryl-coenzyme A antibodies, and viral infections including HIV and hepatitis C. NIMNM is linked to medications and toxic exposures. Both IMNM and NIMNM are typically characterized by proximal weakness, although the severity can vary substantially. Myalgias are reported by some, but not all, patients. Pathological findings on muscle biopsy include predominant fiber necrosis with little or no inflammatory infiltrate. In IMNM, there is variable evidence for the deposition of membrane attack complex on capillaries and muscle fibers, although membrane attack complex deposition on capillaries is typically less than is seen in dermatomyositis; class I major histocompatibility complex expression on muscle fibers is variable but typically less than is seen in polymyositis. Immunohistochemical abnormalities are not typically seen in NIMNM. Treatment of IMNM involves immunosuppressive therapy, although there are no controlled trials to guide particular treatment choices. Treatment of NIMNM involves removal of the toxic exposure.

A Clinical Review of Statin-Associated Myopathy

Objective: To review the epidemiology, clinical features, proposed mechanisms, risk factors, and management of statin-associated myopathy. Data Sources: Literature searches were conducted in PubMed (1948 to April 2013), TOXLINE, International Pharmaceutical Abstracts (1970 to April 2013), and Google Scholar using the terms statin, hydroxymethylglutaryl-coenzyme A reductase inhibitors, myopathy, myalgia, safety, and rhabdomyolysis. Results were limited to English publications. Study Selection and Data Extraction: All relevant original studies, guidelines, meta-analyses, and reviews of statin-associated myopathy and safety of statins were assessed for inclusion. References from selected articles were reviewed to identify additional citations. Data Synthesis: The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors remain one of the most effective medications for reducing low-density-lipoprotein cholesterol. Statins are well tolerated by most patients; however, it is estimated that 10% to 15% of patients develop statin-related muscle adverse effects known as statin-associated myopathy. Although clinicians may be aware of statin-associated myopathy, they may not be aware of its clinical presentation. Providers should assess individual patient risk factors before choosing the appropriate statin. A variety of skeletal muscle aches that may not present as a danger to the patient, may affect patient adherence and quality of life. There are several steps that providers can take to properly treat and manage patients with myalgia complaints. Conclusions: Statin-associated myopathy is a clinical problem that contributes to statin therapy discontinuation. Patients who are statin intolerant may be treated with alternative treatment options such as low-dose statins, switching statins, using alternative dosing strategies in statins with longer half-lives, non-statin lipid-lowering agents, and complementary therapies.

The Role of PPARα Activation in Liver and Muscle

PPARα is one of three members of the soluble nuclear receptor family called peroxisome proliferator-activated receptor (PPAR). It is a sensor for changes in levels of fatty acids and their derivatives that responds to ligand binding with PPAR target gene transcription, inasmuch as it can influence physiological homeostasis, including lipid and carbohydrate metabolism in various tissues. In this paper we summarize the involvement of PPARα in the metabolically active tissues liver and skeletal muscle and provide an overview of the risks and benefits of ligand activation of PPARα, with particular consideration to interspecies differences.

Statin therapy and the expression of genes that regulate calcium homeostasis and membrane repair in skeletal muscle

In skeletal muscle of patients with clinically diagnosed statin-associated myopathy, discrete signs of structural damage predominantly localize to the T-tubular region and are suggestive of a calcium leak. The impact of statins on skeletal muscle of non-myopathic patients is not known. We analyzed the expression of selected genes implicated in the molecular regulation of calcium and membrane repair, in lipid homeostasis, myocyte remodeling and mitochondrial function. Microscopic and gene expression analyses were performed using validated TaqMan custom arrays on skeletal muscle biopsies of 72 age-matched subjects who were receiving statin therapy (n = 38), who had discontinued therapy due to statin-associated myopathy (n = 14), and who had never undergone statin treatment (n = 20). In skeletal muscle, obtained from statin-treated, non-myopathic patients, statins caused extensive changes in the expression of genes of the calcium regulatory and the membrane repair machinery, whereas the expression of genes responsible for mitochondrial function or myocyte remodeling was unaffected. Discontinuation of treatment due to myopathic symptoms led to a normalization of gene expression levels, the genes encoding the ryanodine receptor 3, calpain 3, and dystrophin being the most notable exceptions. Hence, even in clinically asymptomatic (non-myopathic) patients, statin therapy leads to an upregulation in the expression of genes that are concerned with skeletal muscle regulation and membrane repair.

New 2-aryloxy-3-phenyl-propanoic acids as peroxisome proliferator-activated receptors alpha/gamma dual agonists with improved potency and reduced adverse effects on skeletal muscle function

The preparation of a new series of 2-aryloxy-3-phenyl-propanoic acids, resulting from the introduction of a linker into the diphenyl system of the previously reported PPARalpha/gamma dual agonist 1, allowed the identification of new ligands with improved potency on PPARalpha and unchanged activity on PPARgamma. For the most interesting stereoisomers S-2 and S-4, X-ray studies in PPARgamma and docking experiments in PPARalpha provided a molecular explanation for their different behavior as full and partial agonists of PPARalpha and PPARgamma, respectively. Due to the adverse effects provoked by hypolipidemic drugs on skeletal muscle function, we also investigated the blocking activity of S-2 and S-4 on skeletal muscle membrane chloride channel conductance and found that these ligands have a pharmacological profile more beneficial compared to fibrates currently used in therapy.

Myotoxic reactions to lipid-lowering therapy are associated with altered oxidation of fatty acids

Despite exceptional efficacy and safety, fear of muscle toxicity remains a major reason statins are underutilized. Evidence suggests that statin muscle toxicity may be mediated by abnormalities in lipid metabolism. To test the hypothesis that myotubes from patients intolerant of lipid-lowering therapies have abnormal fatty acid oxidation (FAO) responses we compared muscle from 11 subjects with statin intolerance (Intolerant) with muscle from seven statin-naive volunteers undergoing knee arthroplasty (Comparator). Gross muscle pathology was graded and skeletal muscle cell cultures were produced from each subject. FAO was assessed following treatment with increasing statin concentrations. There was no difference in muscle biopsy myopathy scores between the groups. Basal octanoate oxidation was greater in Intolerant than in Comparator subjects (P = 0.03). Lovastatin-stimulated palmitate oxidation tended to be greater for Intolerant compared to Control subjects' myotubes (P = 0.07 for 5 microM and P = 0.06 for 20 microM lovastatin). In conclusion abnormalities in FAO of Intolerant subjects appear to be an intrinsic characteristic of these subjects that can be measured in their cultured myotubes.

The Guinea pig as a preclinical model for demonstrating the efficacy and safety of statins

Statins, because of their excellent efficacy and manageable safety profile, represent a key component in the current armamentarium for the treatment of hypercholesterolemia. Nonetheless, myopathy remains a safety concern for this important drug class. Cerivastatin was withdrawn from the market for myotoxicity safety concerns. BMS-423526 [{(3R,5S)-7-[4-(4-fluorophenyl)-6,7-dihydro-2-(1-methylethyl)-5H-benzo[6,7]cyclohepta[1,2-b]pyridin-3-yl]-3,5-dihydroxy-heptenoic acid} sodium salt], similar to cerivastatin in potency and lipophilicity, was terminated in early clinical development due to an unacceptable myotoxicity profile. In this report, we describe the guinea pig as a model of statin-induced cholesterol lowering and myotoxicity and show that this model can distinguish statins with unacceptable myotoxicity profiles from statins with acceptable safety profiles. In our guinea pig model, both cerivastatin and BMS-423526 induced myotoxicity at doses near the ED(50) for total cholesterol (TC) lowering in plasma. In contrast, wide differences between myotoxic and TC-lowering doses were established for the currently marketed, more hydrophilic statins, pravastatin, rosuvastatin, and atorvastatin. This in vivo model compared favorably to an in vitro model, which used statin inhibition of cholesterol synthesis in rat hepatocytes and L6 myoblasts as surrogates of potential efficacy and toxicity, respectively. Our conclusion is that the guinea pig is a useful preclinical in vivo model for demonstrating whether a statin is likely to have an acceptable therapeutic safety margin.

Acute renal failure and myalgia in a transplant patient

A 64-yr-old man with kidney transplant for ESRD as a result of diabetic nephropathy presented with acute renal failure, weakness, myalgia, and pigmented urine. His medications included mycophenolate, cyclosporine, prednisone, furosemide, diltiazem, aspirin, simvastatin, an angiotensin receptor blocker, and insulin. A renal biopsy was performed. Pathologic findings and differential diagnosis are discussed, and the literature is reviewed.

Statin therapy depresses total body fat oxidation in the absence of genetic limitations to fat oxidation

Cholesterol lowering drugs are associated with myopathic side effects in 7% of those on therapy, which is reversible in most, but not all patients. This study tested the hypothesis that total body fat oxidation (TBFO) is reduced by statins in patients with genetic deficiencies in FO, determined by white blood cells (FOwbc) and by molecular analysis of common deficiencies, and would cause intolerance in some patients. Six patients on statin therapy without myopathic side effects (tolerant) and 7 patients who had previously developed statin-induced myopathic symptoms (intolerant) (age = 58 +/- 8.25 yrs, ht. = 169 +/- 11 cm, and wt. = 75.4 +/- 14.2 kg) were tested for TBFO (Respiratory Exchange Ratio, RER) pre- and during exercise. FOwbc was not significantly different between tolerant and intolerant (0.261 +/- 0.078 vs. 0.296 +/- 0.042 nmol/h per 10(9) wbc), or normals (0.27 +/- 0.09 nmol/h per 10(9) wbc) and no common molecular abnormalities were found. Pre-exercise RER (0.73 +/- 0.05 vs. 0.84 +/- 0.05) was significantly lower in the intolerant group and the VO2 at RER = 1.0 (1.27 +/- 0.32 vs. 1.87 +/- 0.60 L/min) greater than the tolerant. Post-exercise lactates were not different between groups. Although dietary fat intake was not different, blood lipoprotein levels, particularly triglycerides were 35% lower in tolerant than previously intolerant. TBFO and blood lipoproteins were reduced in tolerant patients in spite of the absence of genetic limitations, but not in the intolerant group as hypothesized. Although not conclusive, these data suggest the need for a prospective study of the effects of statins on fat oxidation.

Expert commentary: the safety of fibrates in lipid-lowering therapy

The use of fibrates in the management of lipoprotein disorders has a history dating back to the mid-1960s. This group of drugs has now been tested in several large long-term trials with cardiovascular end points. Overall, there is good evidence for the reduction of cardiovascular disease in primary prevention studies and in those of subjects with manifest disease. More recent trials have suffered from high interference due to 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) introduction, particularly in their placebo control groups. However, there is very good evidence for overall safety from a combined study of >20,000 patients in these controlled clinical trials lasting approximately 5 years. Abdominal pain has been observed more frequently in the statin vs placebo group. Myopathy, liver enzyme elevations, and cholecystitis have been potential adverse reactions of interest. However, these have occurred at a very low rate and are rarely found to be statistically more frequent in the active-treatment group compared with the subjects taking placebo. The recent Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study found a slightly higher incidence of pancreatitis, deep venous thrombosis, and pulmonary embolism. Small creatinine and homocysteine elevations are observed in many patients taking fibrates, and the effect of this on long-term outcomes is under study. The FIELD study also described a significant reduction in the rates of progression of proteinuria and vascular retinopathy with fibrate therapy. To date, there has been no study exclusive to patients with elevated triglycerides, raising the question of the potential benefit of these drugs in patients with the lipid abnormalities most effectively treated with fibrates.

Changes of blood biochemical values in ponies recovering from hyperlipemia in Japan

Hyperlipemia in horses is a disorder of lipid metabolism peculiar to ponies. This study reports changes of blood biochemical values from the acute to the postconvalescent phases in 3 Shetland ponies with hyperlipemia in Japan. Diseased ponies (all 7 to 9 years old, in late pregnancy, and obese) were fed in the same farm. The periods of their hospitalizations ranged from 30 to 45 days. Twelve well-conditioned ponies (3 to 13 years old) around parturition were used to establish baseline values for blood test results. Main clinical findings in the affected ponies were depression, dysphagia, anorexia, ventral edema and milky-appearing plasma. Hypertriglyceridemia (40- to 70-fold rise of controls) was found in the acute phase of the disease in the affected ponies, and was derived from increased very-low density lipoproteins. Aspartate transaminase and gamma-glutamyl transpeptidase activities, blood urea nitrogen, and creatinin concentrations were increased in acute ponies compared to controls, suggesting impairment of liver and kidney functions. However, these values gradually recovered until the end of postconvalescent phase. Hyperinsulinemia was observed in the acute phase of the hyperlipemia of all affected ponies. And an exaggerated insulin response to intravenous glucose was observed in the 2 ponies given intravenous glucose tolerance tests. These findings suggest decreased insulin sensitivity in hyperlipemic ponies.

Clinical perspectives of statin-induced rhabdomyolysis

Fear of muscle toxicity remains a major reason that patients with hyperlipidemia are undertreated. Recent evaluations of statin-induced rhabdomyolysis offer new insights on the clinical management of both muscle symptoms and hyperlipidemia after rhabdomyolysis. The incidence of statin-induced rhabdomyolysis is higher in practice than in controlled trials in which high-risk subjects are excluded. Accepted risks include age; renal, hepatic, and thyroid dysfunction; and hypertriglyceridemia. New findings suggest that exercise, Asian race, and perioperative status also may increase the risk of statin muscle toxicity. The proposed causes and the relationship of drug levels to statin rhabdomyolysis are briefly reviewed along with the problems with the pharmacokinetic theory. Data suggesting that patients with certain metabolic abnormalities are predisposed to statin rhabdomyolysis are presented. The evaluation and treatment of patients' muscle symptoms and hyperlipidemia after statin rhabdomyolysis are presented. Patients whose symptoms are related to other disorders need to be identified. Lipid management of those whose symptoms are statin-related is reviewed including treatment suggestions.

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.

Statin therapy induces ultrastructural damage in skeletal muscle in patients without myalgia

Muscle pain and weakness are frequent complaints in patients receiving 3-hydroxymethylglutaryl coenzymeA (HMG CoA) reductase inhibitors (statins). Many patients with myalgia have creatine kinase levels that are either normal or only marginally elevated, and no obvious structural defects have been reported in patients with myalgia only. To investigate further the mechanism that mediates statin-induced skeletal muscle damage, skeletal muscle biopsies from statin-treated and non-statin-treated patients were examined using both electron microscopy and biochemical approaches. The present paper reports clear evidence of skeletal muscle damage in statin-treated patients, despite their being asymptomatic. Though the degree of overall damage is slight, it has a characteristic pattern that includes breakdown of the T-tubular system and subsarcolemmal rupture. These characteristic structural abnormalities observed in the statin-treated patients were reproduced by extraction of cholesterol from skeletal muscle fibres in vitro. These findings support the hypothesis that statin-induced cholesterol lowering per se contributes to myocyte damage and suggest further that it is the specific lipid/protein organization of the skeletal muscle cell itself that renders it particularly vulnerable.

The Toxicology of Ligands for Peroxisome Proliferator-Activated Receptors (PPAR)

Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that modulate target gene expression in response to endogenous and exogenous ligands. Ligands for the PPARs have been widely developed for the treatment of various diseases including dyslipidemias and diabetes. While targeting selective receptor activation is an established therapeutic approach for the treatment of various diseases, a variety of toxicities are known to occur in response to ligand administration. Whether PPAR ligands produce toxicity via a receptor-dependent and/or off-target-mediated mechanism(s) is not always known. Extrapolation of data derived from animal models and/or in vitro models, to humans, is also questionable. The different toxicities and mechanisms associated with administration of ligands for the three PPARs will be discussed, and important data gaps that could increase our current understanding of how PPAR ligands lead to toxicity will be highlighted.

Toxic Myopathies

Muscle tissue is highly sensitive to drugs and toxins because ot its high metabolic activity and potential sites for disruption of energy-producing pathways. Early recognition of toxic myopathies is important, as they potentially are reversible on removal of the offending toxin, with greater likelihood of complete resolution the sooner this is achieved. Clinical features range from mild muscle pain and cramps to severe weakness with rhabdomyolysis, renal failure, and even death. The pathogenic bases can be multifactorial. This article reviews drugs responsible for common types of toxic myopathy and their clinical and histopathologic features and illustrates possible underlying cellular mechanisms.

Rhabdomyolysis and Renal Failure Associated with Gemfibrozil Monotherapy

OBJECTIVE

To report a case of rhabdomyolysis and acute renal failure associated with gemfibrozil monotherapy of hyperlipidemia.

CASE SUMMARY

A 30-year-old white man with hypertension, type 1 diabetes mellitus, and hyperlipidemia was hospitalized due to myalgias, nausea, and vomiting that began after he started working as a jackhammer operator 4 days previously. His medications were lisinopril, aspirin, insulin, and gemfibrozil. Creatine kinase and creatinine, which previously had been mildly elevated and normal, respectively, were markedly elevated, consistent with rhabdomyolysis with acute renal failure.

DISCUSSION

As of December 8, 2003, this is the only report of a patient with normal baseline creatinine level who developed rhabdomyolysis with acute renal failure associated with gemfibrozil monotherapy. Strenuous exertion, hypovolemia, and lisinopril use may have contributed to the severity of illness. An objective causality assessment revealed that an adverse drug reaction to gemfibrozil was possible.

CONCLUSIONS

Gemfibrozil monotherapy of hyperlipidemia may predispose to rhabdomyolysis with acute renal failure. Patients using gemfibrozil should be cautioned regarding strenuous exertion, dehydration, and the need for prompt evaluation of myalgias.

Conservation of chloride channel structure revealed by an inhibitor binding site in ClC-1

Crystal structures of bacterial CLC proteins were solved recently, but it is unclear to which level of detail they can be extrapolated to mammalian chloride channels. Exploiting the difference in inhibition by 9-anthracene carboxylic acid (9-AC) between ClC-0, -1, and -2, we identified a serine between helices O and P as crucial for 9-AC binding. Mutagenesis based on the crystal structure identified further residues affecting inhibitor binding. They surround a partially hydrophobic pocket close to the chloride binding site that is accessible from the cytoplasm, consistent with the observed intracellular block by 9-AC. Mutations in presumably Cl--coordinating residues yield additional insights into the structure and function of ClC-1. Our work shows that the structure of bacterial CLCs can be extrapolated with fidelity to mammalian Cl- channels.

Iatrogenic and toxic myopathies

There has been increasing awareness of the adverse effects of therapeutic agents and exogenous toxins on the structure and function of muscle. The resulting clinical syndrome varies from one characterized by muscle pain to profound myalgia, paralysis, and myoglobinuria. Because toxic myopathies are potentially reversible, their prompt recognition may reduce their damaging effects or prevent a fatal outcome. Interest in the toxic myopathies, however, derives not only from their clinical importance but also from the fact that they serve as useful experimental models in muscle research. Morphological and biochemical studies have increased our understanding of the basic cellular mechanisms of myotoxicity. Toxins may produce, for instance, necrotizing, lysosomal-related, inflammatory, anti-microtubular, mitochondrial, hypokalemia-related, or protein synthesis-related muscle damage.

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.

Myopathy and rhabdomyolysis with lipid-lowering drugs

Drug-induced myopathy and rhabdomyolysis are rare adverse drug reactions (ADR). They have been seen after the introduction of modern lipid-lowering drugs more regularly. The first description after medication with clofibrate dates back to 1968. Apparently, all fibrates can induce myopathy. It usually starts after a few days of medication, or after prolonged use, showing muscle weakness and/or pain. Concomitantly, the enzyme creatininephosphokinase (CPK) is raised dramatically. Muscular necrosis can follow leading secondarily to kidney failure, and eventually to death. For the class of statins, myopathy was more often seen after their introduction, and it became their most feared adverse effect, especially in combination of statins with other drugs (mibefradil, gemfibrozil, cyclosporin). In animal models the evolution of the disease and the mechanism of action may be elucidated. Though strong epidemiological data are lacking, the incidence of myopathy is probably similar for all lipid-lowering drugs and is in the range of 0.1-0.5% with monotherapy, increasing to 0.5-2.5% with combination therapy. Severe cases of rhabdomyolysis are rarer, but may have a significant mortality. The market success of cerivastatin within a short period has led to 100s of myopathies and some dozens of deaths. Though interactions on metabolism and ensuing high plasma levels can partially explain myopathy as intoxication, there are strong indications that other (endocrine, metabolic, genetic) factors might play a role in the pathophysiology. The patient population at risk should better be defined and withheld from myopathy-inducing drugs.

Fast and slow gating of CLC-1: differential effects of 2-(4-chlorophenoxy) propionic acid and dominant negative mutations

Our knowledge about ClC-1 muscle chloride channel gating, previously gained from single-channel recording and noise analysis, provides a theoretical basis for further analysis of macroscopic currents. In the present study, we propose a simple method of calculation of open probabilities (P(o)) of fast and slow gates from the relative amplitudes of ClC-1 inward current components. With this method, we investigated the effects of 2-(4-chlorophenoxy) propionic acid (CPP), a drug known to produce myotonia in animals, and dominant negative myotonic mutations, F307S and A313T, on fast and slow gating of ClC-1. We have shown that these mutations affected the P(o) of the slow gate, as expected from their mode of inheritance, and that CPP predominantly affected the fast gating process. CPP's action on the fast gating of mutant channels was similar to its effect in wild-type channels. Comparison of the effects of CPP and the mutations on fast and slow gating with the effects produced by reduction of external Cl(-) concentration suggested that CPP and mutations exert their action by affecting the transition of the channel from its closed to open state after Cl(-) binding to the gating site.

HMG-CoA reductase inhibitors and myotoxicity

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors specifically inhibit HMG-CoA reductase in the liver, thereby inhibiting the biosynthesis of cholesterol. These drugs significantly reduce plasma cholesterol level and long term treatment reduces morbidity and mortality associated with coronary heart disease. The tolerability of these drugs during long term administration is an important issue. Adverse reactions involving skeletal muscle are not uncommon, and sometimes serious adverse reactions involving skeletal muscle such as myopathy and rhabdomyolysis may occur, requiring discontinuation of the drug. Occasionally, arthralgia, alone or in association with myalgia, has been reported. In this article we review scientific data provided via Medline, adverse drug reaction case reports from the Swedish Drug Information System (SWEDIS) and the World Health Organization's International Drug Information System (INTDIS) database, focusing on HMG-CoA reductase inhibitor-related musculoskeletal system events. Cytochrome P450 (CYP) 3A4 is the main isoenzyme involved in the metabolic transformation of HMG-CoA reductase inhibitors. Individuals with both low hepatic and low gastrointestinal tract levels of CYP3A4 expression may be at in increased risk of myotoxicity due to potentially higher HMG-CoA reductase inhibitor plasma concentrations. The reported incidence of myotoxic reactions in patients treated with this drug class varies from 1 to 7% and varies between different agents. The risk of these serious adverse reactions is dose-dependent and may increase when HMG-CoA reductase inhibitors are prescribed concomitantly with drugs that inhibit their metabolism, such as itraconazole, cyclosporin, erythromycin and nefazodone. Electrolyte disturbances, infections, major trauma, hypoxia as well as drugs of abuse may increase the risk of myotoxicity. It is important that the potentially serious adverse reactions are recognised and correctly diagnosed so that the HMG-CoA reductase inhibitor may at once be withdrawn to prevent further muscular damage.

Modulation of the gating of CIC-1 by S-(-) 2-(4-chlorophenoxy) propionic acid

1. Using whole-cell patch-clamping and Sf-9 cells expressing the rat skeletal muscle chloride channel, rCIC-1, the cellular mechanism responsible for the myotonic side effects of clofibrate derivatives was examined. 2. RS-(+/-) 2-(4-chlorophenoxy)propionic acid (RS-(+/-) CPP) and its S-(-) enantiomer produced pronounced effects on CIC-1 gating. Both compounds caused the channels to deactivate more rapidly at hyperpolarizing potentials, which showed as a decrease in the time constants of both the fast and slow deactivating components of the whole cell currents. Both compounds also produced a concentration-dependent shift in the voltage dependence of channel apparent open probability to more depolarizing potentials, with an EC50 of 0.79 and 0.21 mM for the racemate and S-(-) enantiomer respectively. R-(+) CPP at similar concentrations had no effect on gating. RS-(+/-) CPP did not block the passage of Cl- through the pore of rCIC-1. 3. CIC-1 is gated by Cl- binding to a site within an access channel and S-(-) CPP alters gating of the channel by decreasing the affinity of this binding site for Cl-. Comparison of the EC50 for RS-(+/-) CPP and S-(-) CPP indicates that R-(+) CPP can compete with the S-(-) enantiomer for the site but that it is without biological activity. 4. RS-(+/-) CPP produced the same effect on rCIC-1 gating when added to the interior of the cell and in the extracellular solution. 5. S-(-) CPP modulates the gating of CIC-1 to decrease the membrane Cl- conductance (GCl), which would account for the myotonic side effects of clofibrate and its derivatives.

Toxic myopathies

Toxic myopathies may occur with a variety of prescribed medications, illicit drug abuse, or other toxins. The article discusses an overview of some of the compounds that may cause myopathy, the clinical and laboratory features, histology, mechanisms of action, and potential risk factors of myopathy. The ability to recognize these syndromes is essential to avoid unnecessary tests and to avoid delay in treatment, especially in critically ill patients or patients with other neuromuscular diseases.

On the molecular etiology of decreased arachidonic (20:4n-6), docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) acids in Zellweger syndrome and other peroxisomal disorders

Alterations in the metabolism of arachidonic (20:4n-6), docosapentaenoic (22:5n-6), and docosahexaenoic (22:6n-3) acids and other polyunsaturated fatty acids in Zellweger syndrome and other peroxisomal disorders are reviewed. Previous proposals that peroxisomes are necessary for the synthesis of 22:6n-3 and 22:5n-6 are critically examined. The data suggest that 22:6n-3 is biosynthesized in mitochondria via a channelled carnitine-dependent pathway involving an n-3-specific delta-4 desaturase, while 20:4n-6, 20:5n-3 and 22:5n-6 are synthesized by both mitochondrial and microsomal systems; these pathways are postulated to be interregulated as compensatory-redundant systems. Present evidence suggests that 22:6n-3-containing phospholipids may be required for the biochemical events involved in successful neuronal migration and developmental morphogenesis, and as structural cofactors for the functional assembly and integration of a variety of membrane enzymes, receptors, and other proteins in peroxisomes and other subcellular organelles. A defect in the mitochondrial desaturation pathway is proposed to be a primary etiologic factor in the clinicopathology of Zellweger syndrome and other related disorders. Several implications of this proposal are examined relating to effects of pharmacological agents which appear to inhibit steps in this pathway, such as some hypolipidemics (fibrates), neuroleptics (phenothiazines and phenytoin) and prenatal alcohol exposure.

Choosing the right lipid-regulating agent. A guide to selection

If dietary therapy and other lifestyle changes do not adequately normalise blood lipid levels, lipid-regulating drugs, as single-drug or combination-drug therapy, may be prescribed to supplement lifestyle changes. Evaluation of the individual patient's health and risk status, determination of the dyslipidaemia, definition of treatment goals and a clear understanding of the mechanisms and effects of lipid-regulating agents are necessary for optimisation of treatment. Although all the available lipid-regulating agents lower low density lipoprotein (LDL) cholesterol, the agents with the greatest LDL cholesterol-lowering effect are the bile acid sequestrants, which up-regulate the LDL receptor by the decrease in intrahepatic cholesterol caused by the interruption of enterohepatic circulation of cholesterol-rich bile acids, and the HMG-CoA reductase inhibitors, which partially inhibit HMG-CoA reductase. The agents with the greatest triglyceride-lowering effect are nicotinic acid, which decreases the production of very low density lipoprotein (VLDL) cholesterol and reduces the availability of free fatty acids in the circulation, and the fibric acid derivatives, which increase lipoprotein lipase activity and may also decrease the release of free fatty acids. Although the safety profile of the available lipid-regulating drugs has been established, patients should be monitored for potential adverse effects and interactions with concomitantly administered agents. When used correctly, lipid-regulating drug therapy is highly effective in the treatment of a variety of dyslipidaemias.

Muscle-specific overexpression of lipoprotein lipase causes a severe myopathy characterized by proliferation of mitochondria and peroxisomes in transgenic mice

In extrahepatic tissues lipoprotein lipase (LPL) hydrolyzes triglycerides thereby generating FFA for tissue uptake and metabolism. To study the effects of increased FFA uptake in muscle tissue, transgenic mouse lines were generated with a human LPL minigene driven by the promoter of the muscle creatine kinase gene. In these mice human LPL was expressed in skeletal muscle and cardiac muscle, but not in other tissues. In proportion to the level of LPL overexpression, decreased plasma triglyceride levels, elevated FFA uptake by muscle tissue, weight loss, and premature death were observed in three independent transgenic mouse lines. The animals developed a severe myopathy characterized by muscle fiber degeneration, fiber atrophy, glycogen storage, and extensive proliferation of mitochondria and peroxisomes. This degree of proliferation suggests that FFA play an important role in the biogenesis of these organelles. Our experiments indicate that LPL is rate limiting for the supply of muscle tissue with triglyceride-derived FFA. Improper regulation of muscle LPL can lead to major pathological changes and may be important in the pathogenesis of some human myopathies. Muscle-specific LPL transgenic mouse lines will serve as a useful animal model for the investigation of myopathies and the biogenesis of mitochondria and peroxisomes.

Electrical myotonia of rabbit skeletal muscles by HMG-CoA reductase inhibitors

HMG-CoA reductase (HCR) inhibitors are effective cholesterol-lowering agents in the treatment of hypercholesterolemia. Using intracellular microelectrodes, we studied the pathomechanism of myotonia experimentally induced in rabbits by HCR inhibitors, simvastatin, and pravastatin. The external intercostal muscle of rabbits showed some electrophysiologic characteristics of myotonia including repetitive firing after administration of simvastatin (50 mg/kg per day, for 4 weeks). The relative chloride conductance, though reduced in both, was more affected in simvastatin-administered muscles. In normal muscles perfused with a solution containing the inhibitors, both simvastatin and pravastatin produced membrane hyperexcitability with repetitive firing similar to that seen in simvastatin-administered rabbits. The minimum concentrations required to cause repetitive firing was 0.3 mg/L for simvastatin and 30 mg/L for pravastatin. These results indicate that HCR inhibitors induce some characteristics of myotonia by blocking the chloride channel in the muscle membrane.

Lipid-lowering effect and safety of acipimox in hemodialysis patients and renal transplant recipients

The efficacy and safety of acipimox, an antilipolytic agent, were studied in 10 uremic patients under hemodialysis (group A) and in 8 renal transplant recipients with adequate renal function (group B). The medication was given for 20 weeks at a dose of 250 mg daily in both groups. Total serum cholesterol decreased significantly from 218.1 +/- 17.4 to 175.2 +/- 15.2 mg/dL (-19.7%) in group A and from 261.2 +/- 16.5 to 215.3 +/- 26.9 mg/dL (-17.6%) in group B; as did serum triglycerides, from 206.7 +/- 26.9 to 146.9 +/- 17.6 mg/dL (-29%) in group A and from 168.2 +/- 20.6 to 111.3 +/- 12.4 mg/dL (-33.8%) in group B. Low-density lipoprotein (LDL)-cholesterol and very low-density lipoprotein (VLDL)-cholesterol were also decreased significantly (LDL-C by -27% and -25%, and VLDL-C by -29.2% and -33.8% in groups A and B, respectively). Furthermore, the high-density lipoprotein (HDL)-cholesterol was increased significantly, by +29.6% in group A and +18% in group B. The apolipoproteins Apo-A1 and Apo-A2 were decreased in Group A but not in group B. The Apo-B was decreased in group B. Serum CPK (total and muscle fraction), total bilirubin, SGPT, SGOT, alkaline phosphatase, gamma GT, LDL, a-Fp, and creatinine remained unchanged in both groups. Acipimox seems to be effective in the regulation of atherogenic lipid disorders in hemodialysis patients and renal transplant recipients, without any muscular damage or alteration of kidney and liver function.

Acute compartment syndrome: an unusual presentation of gemfibrozil induced myositis

OBJECTIVE

To present a case of gemfibrozil-induced myositis which precipitated an acute compartment syndrome.

CLINICAL FEATURES

A 49-year-old woman with chronic renal failure was given gemfibrozil for hyperlipidaemia. She developed myositis in the sixth week of therapy. Her symptoms initially persisted despite withdrawal of gemfibrozil and she developed an acute compartment syndrome.

INTERVENTION AND OUTCOME

Emergency fasciotomy was performed. She gradually improved and complete recovery occurred eight weeks after cessation of gemfibrozil therapy.

CONCLUSION

Gemfibrozil may induce a local myositis which, in our patient, precipitated an acute compartment syndrome. One should be alert to symptoms of possible drug-induced myositis in patients receiving gemfibrozil. Extreme caution should be exercised in its use in patients with impaired renal function.

Experimental simvastatin-induced myopathy in rabbits

We induced experimental myopathy in rabbits by giving simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor. After oral administration of simvastatin (50 mg/kg/day) for 2 weeks, serum CK was elevated in 5 of 7 rabbits; degenerating or necrotic fibers were seen in 3 rabbits. Using electromyography, myotonic discharges were found in the 2 rabbits examined. The combination of myotonic discharges, necrosis and raised serum CK levels suggests that the myopathy was induced by lesions of the muscle surface membrane.

Tolerability of fibric acids. Comparative data and biochemical bases

Fibric acids are an established class of drugs for the treatment of hyperlipoproteinaemias. Although they have been in use for 30 years or longer, some doubts remain as to their relative tolerability, both as a class and as single agents. Some side effects, e.g. lithogenicity, may be related to their mode of action, while others, e.g. the acute muscular syndrome, may be linked to the spatial conformation of the molecule. These disadvantages should, however, be weighed against the additional, potentially therapeutic properties shown by these compounds. In particular, effects on maturity onset diabetes and hyperuricaemia, as well as a very interesting fibrinolytic potential, have been described for some of them. A painstaking comparative analysis of the major literature data pertaining to the clinical toxicological profile of these agents allow to conclude that, while belonging to a chemical class, fibric acids show dramatic differences from one another, in terms of side effects and of additional pharmacodynamic activities. Moreover, in the case of lithogenicity for example, considerable differences exist between normo- and hyperlipidaemic subjects. Overall, newer molecules of more sophisticated design have a significantly improved tolerability profile vs the old clofibrate.

Effects of clofibric acid on the activity and activity state of the hepatic branched-chain 2-oxo acid dehydrogenase complex

Feeding clofibric acid to rats caused little or no change in total activity of the liver branched-chain 2-oxo acid dehydrogenase complex (BCODC). No change in mass of liver BCODC was detected by immunoblot analysis in response to dietary clofibric acid. No changes in abundance of mRNAs for the BCODC E1 alpha, E1 beta and E2 subunits were detected by Northern-blot analysis. Likewise, dietary clofibric acid had no effect on the activity state of liver BCODC (percentage of enzyme in the dephosphorylated, active, form) of rats fed on a chow diet. However, dietary clofibric acid greatly increased the activity state of liver BCODC of rats fed on a diet deficient in protein. No stable change in liver BCODC kinase activity was found in response to clofibric acid in either chow-fed or low-protein-fed rats. Clofibric acid had a biphasic effect on flux through BCODC in hepatocytes prepared from low-protein-fed rats. Stimulation of BCODC flux at low concentrations was due to clofibric acid inhibition of BCODC kinase, which in turn allowed activation of BCODC by BCODC phosphatase. Inhibition of BCODC flux at high concentrations was due to direct inhibition of BCODC by clofibric acid. The results suggest that the effects of clofibric acid in vivo on branched-chain amino acid metabolism can be explained by the inhibitory effects of this drug on BCODC kinase.

Bezafibrate induced rhabdomyolysis

The case is presented of a 70 year old woman with mild hypercholesterolaemia and hypertension who was readmitted to hospital six months after a previous admission for angina pectoris. The patient was treated with verapamil, nifedipine, and aspirin, and had been receiving bezafibrate (400 mg every 12 hours) for the previous 40 days. Twenty four hours after admission she developed podagra, which was treated with indomethacin (100 mg daily). Eight days after admission myocardial infarction was suspected, and the next day she presented with symptoms of rhabdomyolysis, which was confirmed by laboratory tests. Bezafibrate was withdrawn and the patient became asymptomatic after seven days. It is recommended that doctors should be aware of the possibility of patients, especially those with impaired renal function, developing rhabdomyolysis while being treated with bezafibrate.

[Iatrogeny. The importance of clinical diagnosis. Myopathies induced by clofibrate]

The authors describe the neurological manifestations of a female patient with hypercholesterolemia who developed myopathy in the course of her treatment with clofibrate. After the drug was tapered off, the neurological signs and symptoms disappeared. Therefore, attention is called for the importance of the differential diagnosis of iatrogenic myopathies with polymyositis.

Purification, characterization, regulation and molecular cloning of mitochondrial protein kinases

The mitochondrial kinases responsible for the phosphorylation and inactivation of rat heart pyruvate dehydrogenase complex and the rat liver and heart branched-chain alpha-ketoacid dehydrogenase complexes have been purified to homogeneity. The branched-chain alpha-ketoacid dehydrogenase kinase is composed of one subunit with a molecular weight of 44 kDa; pyruvate dehydrogenase kinase has two subunits with molecular weights of 48 (alpha) and 45 kDa (beta). Proteolysis maps of branched-chain alpha-ketoacid dehydrogenase kinase and the two subunits of pyruvate dehydrogenase kinase are different, suggesting that all subunits are different entities. The alpha subunit of the rat heart pyruvate dehydrogenase kinase was selectively cleaved by chymotrypsin with concomitant loss of kinase activity, as previously shown for the bovine kidney enzyme, suggesting that the catalytic activity of pyruvate dehydrogenase kinase resides in this subunit. Polyclonal antibodies against branched-chain alpha-ketoacid dehydrogenase kinase, purified by an epitope selection method, bound only to the 44 kDa polypeptide of the branched-chain alpha-ketoacid dehydrogenase complex, substantiating that the 44 kDa protein corresponds to the kinase for this complex. Both kinases exhibited strong substrate specificity toward their respective complexes and would not inactivate heterologous complexes. The kinases possessed slightly different substrate specificities toward histones. Phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase complex by its purified kinase was inhibited by alpha-chloroisocaproate and dichloroacetate, established inhibitors of the phosphorylation of the complex. cDNAs encoding the branched-chain alpha-ketoacid dehydrogenase kinase have been isolated from rat heart and rat liver lambda gt11 libraries. This represents the first successful cloning of a mitochondrial protein kinase. Preliminary data suggest that two different isoforms of the kinase may exist in different ratios in various tissues. No evidence was found for induction of the branched-chain alpha-ketoacid dehydrogenase complex nor its kinase by clofibric acid. Rather, clofibric acid is a potent inhibitor of the activity of the branched-chain alpha-ketoacid dehydrogenase kinase and this may be the molecular mechanism responsible for the myotonic effects of clofibric acid in man.