Statins and risk of polyneuropathy: a case-control study

Risks and benefits of continued aggressive statin therapy

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, are a well-tolerated, effective class of medications for the reduction of low-density lipoprotein cholesterol (LDL-C) and total cholesterol levels. Extensive data from clinical trials demonstrate that these agents reduce fatal and nonfatal cardiovascular risk in primary and secondary prevention patients, including women and the elderly. A threshold value for LDL-C reduction below which there is no further clinical benefit has not yet been identified. In the Heart Protection Study (HPS), significant relative risk reduction occurred even among patients with LDL-C levels < 2.6 mmol/l (100 mg/dl). Statin therapy also produced reductions in cardiovascular disease in a wide range of high-risk patients regardless of baseline cholesterol levels. Rhabdomyolysis, typically defined as muscle pain or weakness associated with creatine kinase levels higher than 10 times the upper limit of normal and the presence of myoglobulinuria, is a rare but potentially serious complication of statins. Although dose-dependent transaminase elevations occur in 0.5 to 2% of cases, it has not been determined whether these elevations qualify as true drug-related hepatotoxicity. Management of myopathy and elevated transaminases is addressed in a joint publication from the American College of Cardiology (ACC), the American Heart Association (AHA), and the National Heart, Lung, and Blood Institute (NHLBI). Because statins have significant potential benefits and a low risk for serious adverse effects, aggressive therapy should be considered in patients at high risk for coronary heart disease.

Association of HMG-CoA reductase inhibitors with neuropathy

OBJECTIVE

To review the possible association between statins and peripheral neuropathy.

DATA SOURCES

Literature was obtained from MEDLINE (1984-September 2002) and International Pharmaceutical Abstracts (1970-June 2002). Key search terms included statin, neuropathy, and HMG-CoA reductase inhibitor.

DATA SYNTHESIS

Epidemiologic studies and case reports suggest an increased risk of peripheral neuropathy with statin drugs. Most patients were receiving long-term therapy, although the onset was highly variable. The majority of cases were at least partially reversible with drug cessation. Specific risk factors or mechanisms have not been identified.

CONCLUSIONS

Observational data suggest a link between chronic statin use and increased risk of peripheral neuropathy. However, the risk appears to be small relative to the significant cardioprotective benefits.

Medication-induced peripheral neuropathy

Although not very common, medication-induced neuropathy is a treatable condition and, therefore, is important to identify. Medications continue to grow in number and expand in usage; consequently, toxic neuropathy continues to be relevant to neurologists. Many agents have toxicities that are tolerated because the treatments are necessary, such as therapies for HIV and malignancy. Additional agents to prevent or ameliorate the toxic neuropathy are being sought and trials are ongoing. Certain patients, however, may be at high risk for peripheral nerve toxicity due to genetic factors or another underlying neuropathy. Newer drug-delivery methods, such as viral transfection, may produce less toxicity in the future. The underlying pathomechanisms remain incompletely elucidated; however, apoptosis is emerging as an important final pathway in some forms of toxic neuropathy. Although most cases demonstrate acute or subacute onset after exposure, recent experiences with statin drugs raise the possibility of occult toxic causes of chronic idiopathic neuropathy.

[Adverse effects of statins]

The safety of the hydroxymethyl glutaryl-coenzyme A reductase inhibitors (statins) has been called into question following the recent withdrawal from the market of one of the class, cerivastatin. The withdrawal of cerivastatin highlighted concerns regarding the safety of the entire class. According to data from several large clinical trials, the statins (except cerivastatin) are well tolerated. The most important and clinically relevant adverse effect reported with statins is myopathy. Myopathy is a clinical diagnosis of elevated creatine phosphokinase and/or myalgia along with fatigue. However, the severe from (i.e. statin-associated rhabdomyolysis) is an uncommon syndrome and occurs at a rate of approximately 1/100,000 patients/years. Statin-associated myopathy is related to statin doses, and often to drug/drug interactions. Other clinically relevant adverse effects associated with statin therapy include liver transminases elevation, which is relatively mild and often self-limiting There is no evidence from clinical trials of a significant alteration of ophthalmological function with statins. The issue of statin-induced cancer remains inconclusive. Overall, the statins seem to exhibit a favourable risk/benefit ratio, and this undoubtedly justifies life-long clinical use of statins for cardiovascular prevention.

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.