The role of cytochrome P450-mediated drug-drug interactions in determining the safety of statins

Pathophysiological mechanisms of statin-associated myopathies: possible role of the ubiquitin-proteasome system

BACKGROUND

Statins are the cornerstone of pharmacotherapy for atherosclerotic cardiovascular disease. While these drugs are generally safe, treatment adherence is not optimal in a considerable proportion of patients because of the adverse effects on skeletal muscles in the forms of myopathy, myalgia, muscular pain, nocturnal muscle cramping, weakness, and rare rhabdomyolysis.

METHODS

For the purpose of this narrative review, we searched for the literature suggesting the involvement of the ubiquitin-proteasome system in the development of statin-induced myopathy.

RESULTS

Statins have been shown to up-regulate the expression of the muscle-specific ubiquitin-proteasome system as the major non-lysosomal intracellular protein degradation system. It has been postulated that statins may provoke instability in the myocyte cell membrane when subjected to eccentric exercise stress, triggering activation of intracellular proteolytic cascades and changes in protein degradation machinery. This is accompanied by the up-regulation of a series of genes implicated in protein catabolism, in addition to those of the ubiquitin-proteasome system.

CONCLUSIONS

Based on the available literature, it seems that the involvement of ubiquitin-proteasome system is potentially implicated in the pathophysiology of statin-induced myopathy.

The cytochrome P450 metabolic profiling of SMU-B in vitro, a novel small molecule tyrosine kinase inhibitor

A novel small molecule tyrosine kinase inhibitor 6-[6-Amino-5-[(1R)-1-(2,6-dichloro-3-fluorophenyl)ethoxy]-3-pyridyl]-1'-methylspiro[indoline-3,4'-piperidine]-2-one (SMU-B) had good activity against ALK (anaplastic lymphoma kinase) and ROS1 (c-ros oncogene 1) targets in non-small-cell lung cancer. The excellent bioactivity of SMU-B highlights the importance of determining its metabolic traits, which could provide meaningful information for further pharmacokinetic studies of SMU-B. In this work, we studied the metabolism of SMU-B in human liver microsomes. Three metabolites of SMU-B were identified by a quadrupole-time of flight tandem mass spectrometer (Q-TOF-MS), and the metabolic pathways of SMU-B were demethylation, dehydrogenation and oxidation. CYP3A4/5 was the principal isoform involved in SMU-B metabolism, as shown by chemical inhibition and recombination human enzyme studies. Additionally, a predication with a molecular docking model confirmed that SMU-B could interact with the active sites of CYP3A4 and CYP3A5. This study illuminates the metabolic profile of the anti-tumor drug SMU-B, which will accelerate its clinical use.

Safety assessment of concurrent statin treatment and evaluation of drug interactions in China

Objectives

Acute muscle injury and potentially fatal rhabdomyolysis may occur with the use of statins and certain enzyme inhibitors, but data on this topic from China are quite limited. This study aimed to measure the concomitant exposure of patients to different statins and their enzyme inhibitors or interacting medications in 76 hospitals in six Chinese cities.

Methods

Prescription database was retrieved from Hospital Prescription Analysis Cooperation Project from January 2015 to December 2015, covering 76 tertiary facilities in six cities in China. Every evidence-based enzyme inhibitor was included, and labeled enzyme inhibitors and other relevant information were identified and obtained using the Drug Safety Update from the UK Medicines and Healthcare Products Regulatory Agency. The proportions of different statin types among all patients and those co-medicated with their inhibitors were examined.

Results

A total of 296,765 patients exposed to statins were included in this study. 80% of patients (n = 144,863, 80.5%) were concomitantly prescribed a CYP3A4-metabolized statin with an interacting drug during the study period. Among those prescribed a non-CYP3A4-metabolized statin, 40.0% of patients were concomitantly given an interacting drug, and approximately 20% of patients were concomitantly given a labeled inhibitor, predominantly calcium channel blockers, other statins, and fibrates. Rates of co-prescription were higher in patients aged over 65 years and in patients taking high-dose statins.

Conclusion

Statins were frequently co-prescribed with metabolic inhibitors in China, where drug safety strategy on highlighting warnings and contraindications of statins are still lacking. For high-dose statins patients who are over 65 years and co-administered with any metabolic inhibitors, prescribers and pharmacists should be more concerned in order to prevent adverse drug reactions.

Oxidative metabolism of koumine is mainly catalyzed by microsomal CYP3A4/3A5

1. Gelsemium elegans Benth (Loganiaceae) is a toxic plant that can be used for committing suicide besides alleviating pains. Its anti-inflammatory and analgesic effect mainly come from its active ingredient, namely koumine. Koumine, an indole alkaloid, possesses widely pharmacological effects especially inhibition of neuropathic pain. 2. This study aimed to investigate the metabolic profile of koumine using human liver microsomes (HLMs), selective chemical inhibitors and recombinant human CYP isoforms. Ultra-performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS) was used to detect and identify metabolites. 3. Four major metabolites of koumine were found after incubation with HLMs or individual CYP isoforms. The metabolic pathways of koumine included demethylation, dehydrogenation, oxidation and demethyl-dehydrogenation. Chemical inhibition study showed that the inhibitor of CYP3A4/3A5 significantly decreased (93%) the formation of koumine metabolites. Further, CYP3A4/3A5 was shown as the most efficient isoform in biotransformation of koumine, among a series of CYP isoforms tested. 4. In conclusion, koumine was metabolized into four oxidative metabolites in HLMs. And CYP3A4/3A5 was probably the main contributor to the hepatic oxidative metabolism of koumine.

Statin-Induced Myopathy: The Two Faces of Janus

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) have been shown to be effective at lowering low-density lipoprotein cholesterol and decreasing the risk of coronary heart disease. Although safe and well tolerated by most patients, statins have also been associated with muscle-related adverse events. This article reviews statin-associated myotoxicity to clarify the definitions of muscle-related adverse events and discusses their incidences in major statin trials, case reports, and review articles through January 2006. Milder complaints (ie, myalgia) are reported by approximately 5% to 7% of patients who take statins. More severe myotoxicity, namely rhabdomyolysis, is extremely rare for all statins save cerivastatin, and most recent estimates of its incidence are between 0.44 and 0.54 cases per 10 000 person-years. The mechanism of statin-associated myotoxicity has not been satisfactorily defined and is likely due to multiple factors, including membrane instability, mitochondrial dysfunction, and defects in myocyte duplication

Co-administration of statins with cytochrome P450 3A4 inhibitors in a UK primary care population

PURPOSE

The co-administration of cytochrome P450 3A4 (CYP3A4) inhibitors with simvastatin or atorvastatin (CYP3A4-metabolised statins) is associated with increased statin exposure and can increase the risk of adverse drug reactions. The aim of this study was to measure the concomitant exposure of patients to CYP3A4-metabolised statins and CYP3A4 inhibitors in the UK primary care population.

METHODS

The co-administration of statins and CYP3A4 inhibitors during 2008 was examined in the General Practice Research Database, a large nationally representative UK primary care database. All known inhibitors were included with labelled inhibitors identified using the Medicines and Healthcare products Regulatory Agency Drug Safety Update and UK summary of product characteristics for statins. Exposure was examined in patients overall, patients 65 years and older and those prescribed higher doses of statins.

RESULTS

There were 364,574 patients included in the analyses. Ninety-three percent of the patients were prescribed CYP3A4-metabolised statins, most whom received simvastatin (72%) and atorvastatin (24%). Approximately one third (30%) of the patients prescribed a CYP3A4-metabolised statin had also been prescribed a concomitant CYP3A4 inhibitor during the study period, including 11% prescribed a concomitant labelled inhibitor, with an annualised median days of concomitant use of 173 days, predominantly involving macrolide antibiotics and calcium channel blockers co-prescriptions. Rates were higher in the subgroup aged 65 and over and in those on high dose statins.

CONCLUSIONS

The co-prescription of CYP3A4-metabolised statins and CYP3A4 inhibitors is common in UK primary care. This co-prescription suggests the limited appreciation of potential interactions and Medicines and Healthcare products Regulatory Agency safety advice, with the potential to increase likelihood for side effects amongst patients. Strategies to reduce drug interactions with potential adverse effects should be targeted at prescribers and pharmacists.

Statin Therapy Associated with Fatal Rhabdomyolysis

A 54-year-old man was admitted to the intensive care unit six weeks after a myocardial infarction suffering from metabolic derangement secondary to rhabdomyolysis. There was no obvious precipitant for his condition, though he had recently had his atorvastatin dose increased from 10 mg to 80 mg and a number of new medications commenced. Extensive investigations failed to identify other causes of rhabdomyolysis and it was concluded that his condition related to a combination of statin therapy with other medications, namely the anti-staphylococcal agent fucidic acid. Despite discontinuation of his statin therapy, rhabdomyolysis persisted and the patient died from sepsis related to a prolonged ICU stay. This case highlights the potential risks of statin therapy, particularly in the critically ill patient population, where there may be significant interactions between statins and other co-prescribed medications. Such interactions can lead to impaired statin metabolism, potentially increasing the risks of rhabdomyolysis and other serious side effects.

Concomitant use of statins and CYP3A4 inhibitors in administrative claims and electronic medical records databases

BACKGROUND

Patients may experience increased risk of adverse drug interactions when statins are administered concomitantly with cytochrome P450 3A4 (CYP3A4) inhibitors.

OBJECTIVE

To determine patient numbers in routine clinical practice with concomitant exposure to CYP3A4-metabolized statins and CYP3A4 inhibitors and highlight potential risk for adverse drug interaction.

METHODS

Exposure to prescription medications over 1 year (2005-2006) was evaluated from patient records: US PharMetrics Integrated Patient-Centric administrative claims database and the US General Electric Medical System (GEMS) database. Rates of concomitant prescribing of statins with CYP3A4 inhibitors (listed in United States of America product labels and all identified potential inhibitors) were examined in the cohort overall, in those aged ≥65 years, and in those receiving higher doses of statins.

RESULTS

Overall, 951,166 patient records were included (PharMetrics n = 650,825; GEMS, n = 300,341). Of these, 792,081 (83%) patients used a CYP3A4-metabolized statin as opposed to a non-CYP3A4-metabolized statin (17%). Findings from both databases were consistent. Overall, 25-30% of patients given a CYP3A4-metabolized statin were concomitantly exposed to a CYP3A4 inhibitor, including approximately 9% concomitantly exposed to a labeled inhibitor, findings consistent with those in patients aged ≥65 years, and patients on higher doses of statins.

CONCLUSIONS

Clinicians frequently co-prescribe CYP3A4-metabolized statins with CYP3A4 inhibitors. Physician education regarding the impact of these inhibitors on the metabolism of lovastatin, simvastatin, and atrovastatin is needed. Further studies are also needed to determine whether concomitant administration of a non-CYP3A4-metabolized statin (such as fluvastatin, pravastatin, or rosuvastatin) with a CYP3A4 inhibitor, may reduce adverse event rates in routine clinical practice.

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss three specific SADRs with an emphasis on genetic risk factors. These SADRs, selected based on wide-sweeping clinical interest, are drug-induced liver injury, statin-induced myotoxicity and drug-induced long QT and torsades de pointes. Key challenges for the discovery of predictive risk alleles for these SADRs are also considered.

Statins for the primary prevention of cardiovascular events in older adults: a review of the evidence

BACKGROUND

Although statins have been demonstrated to be beneficial for secondary prevention in the elderly, their use for primary prevention has not been well described.

OBJECTIVE

In this review, we summarize data regarding the efficacy, safety, and current recommendations for statins for the primary prevention of cardiovascular events in older adults.

METHODS

This review is based on a computerized literature search of the PubMed database for articles published in the English language from January 1980 to June 2006. Key words searched individually and cross-referenced included: statins, HMG-CoA reductase inhibitors, cholesterol, elderly, aged, cardiovascular disease, primary prevention, risk stratification, and C-reactive protein. This search produced 445 citations; reference lists revealed an additional 12 citations, all of which were screened for relevance to the topic.

RESULTS

The existing evidence suggests, but does not confirm, benefit from the use of statins for primary prevention in the elderly subgroup (ie, those aged >65 years). Of the 6 published trials of statins for primary prevention, only 3 included subjects aged >75 years, and subgroup results in older adults are unavailable. Current guidelines recommend statins for individuals based on their assessed cardiovascular risk.

CONCLUSIONS

Extension of treatment guidelines should consider an individual's global risk of coronary heart disease. However, due to the prevalence of subclinical disease in older adults, risk may be higher or otherwise differ with age. In addition, tolerance for and barriers to adherence with long-term medical therapy are important treatment considerations in older adults. Prospective, randomized controlled trials that better define the tolerability, safety, and efficacy of statin therapy in older adults with elevated cholesterol levels and intermediate cardiovascular risk are needed.

Modulation by simvastatin of iberiotoxin-sensitive, Ca2+-activated K+ channels of porcine coronary artery smooth muscle cells

BACKGROUND AND PURPOSE

Statins (3-hydroxy-3-methyl-glutaryl coenzyme A (HMG CoA) reductase inhibitors) have been demonstrated to reduce cardiovascular mortality. It is unclear how the expression level of HMG CoA reductase in cardiovascular tissues compares with that in cells derived from the liver. We hypothesized that this enzyme exists in different cardiovascular tissues, and simvastatin modulates the vascular iberiotoxin-sensitive Ca2+-activated K(+) (BK(Ca)) channels.

EXPERIMENTAL APPROACHES

Expression of HMG CoA reductase in different cardiovascular preparations was measured. Effects of simvastatin on BK(Ca) channel gatings of porcine coronary artery smooth muscle cells were evaluated.

KEY RESULTS

Western immunoblots revealed the biochemical existence of HMG CoA reductase in human cardiovascular tissues and porcine coronary artery. In porcine coronary artery smooth muscle cells, extracellular simvastatin (1, 3 and 10 microM) (hydrophobic), but not simvastatin Na+ (hydrophilic), inhibited the BK(Ca) channels with a minimal recovery upon washout. Isopimaric acid (10 microM)-mediated enhancement of the BK(Ca) amplitude was reversed by external simvastatin. Simvastatin Na+ (10 microM, applied internally), markedly attenuated isopimaric acid (10 microM)-induced enhancement of the BK(Ca) amplitude. Reduced glutathione (5 mM; in the pipette solution) abolished simvastatin -elicited inhibition. Mevalonolactone (500 microM) and geranylgeranyl pyrophosphate (20 microM) only prevented simvastatin (1 and 3 microM)-induced responses. simvastatin (10 microM ) caused a rottlerin (1 microM)-sensitive (cycloheximide (10 microM)-insensitive) increase of PKC-delta protein expression.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrated the biochemical presence of HMG CoA reductase in different cardiovascular tissues, and that simvastatin inhibited the BK(Ca) channels of the arterial smooth muscle cells through multiple intracellular pathways.

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

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

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

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

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors and rhabdomyolysis: considerations in the renal failure patient

An intense debate has developed as to the risk-benefit ratio of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) following the withdrawal of cerivastatin. The development of rhabdomyolysis in cerivastatin-treated patients should have surprised few since myotoxicity is an accepted class effect of statins. What has sprung from the cerivastatin experience though is a concern for other members of this class. Such misgivings, although understandable, are ill advised. Without question, differences exist in the risk of rhabdomyolysis occurrence amongst the various statins. In this regard, pravastatin and fluvastatin are least likely to produce rhabdomyolysis, which, in part, relates to the fact they are not metabolized by the cytochrome P450 3A4 pathway. When muscle damage occurs with statins it is most often the result of a drug-drug interaction rather than a specific adverse response to statin monotherapy. Such drug-drug interactions increase plasma concentrations of a statin and thereby increase the risk of myotoxicity. A growing consensus exists which supports an expanded use of statins in a range of patient groups including the renal failure patient. Polypharmacy and altered drug metabolism increase the risk of myotoxicity, albeit to an ill-defined degree, in this population. Many factors should enter into the choice of a statin in the multiply medicated renal failure patient.

Rhabdomyolysis and statin therapy: relevance to the elderly

A recent debate has emerged as to the risk-benefit ratio of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins). This debate has centered on the withdrawal of the HMG-CoA reductase inhibitor cerivastatin (Baycol). Its withdrawal was prompted by an unacceptably high rate of rhabdomyolysis associated with its use. The development of rhabdomyolysis in cerivastatin-treated patients surprised few, since myotoxicity is a class effect with HMG-CoA reductase inhibitors. What has sprung from the cerivastatin experience, though, is the concept of "guilt by association"; thus, other members of this class are now viewed in a similarly negative light. Such misgivings are understandable, but to a degree may be ill-advised, since differences exist in the risk and therefore the rate of rhabdomyolysis occurrence among the various HMG-CoA reductase inhibitors. In this regard, pravastatin and fluvastatin are least likely to provoke muscle cell damage, which, at least in part, relates to their not being metabolized by the cytochrome P-450 (CYP) 3A4 pathway. When muscle damage does occur with HMG-CoA reductase inhibitors, it is commonly the result of drug-drug interactions rather than a specific adverse response to HMG-CoA reductase inhibitor monotherapy. Such drug-drug interactions inevitably result in higher plasma concentrations of an HMG-CoA reductase inhibitor and thereby an increased risk of myotoxicity. A growing consensus supports an expanded use of HMG-CoA reductase inhibitors in elderly patients. Polypharmacy and altered drug metabolism both put the elderly patient at increased risk of myotoxicity when drugs in the HMG-CoA reductase inhibitor class are administered. Physicians must take many factors into account when selecting a member of the HMG-CoA reductase inhibitor class, particularly as relates to their use in the multiply medicated elderly patient.