Amiodarone Interacts with Simvastatin but not with Pravastatin Disposition Kinetics

Amiodarone Therapy: Updated Practical Insights

Amiodarone, a bi-iodinated benzofuran derivative, is among the most commonly used antiarrhythmic drugs due to its high level of effectiveness. Though initially categorized as a class III agent, amiodarone exhibits antiarrhythmic properties across all four classes of antiarrhythmic drugs. Amiodarone is highly effective in maintaining sinus rhythm in patients with paroxysmal atrial fibrillation while also playing a crucial role in preventing a range of ventricular arrhythmias. Amiodarone has a complex pharmacokinetic profile, characterized by a large volume of distribution and a long half-life, which can range from several weeks to months, resulting in prolonged effects even after discontinuation. Side effects may include thyroid dysfunction, pulmonary fibrosis, and hepatic injury, necessitating regular follow-ups. Additionally, amiodarone interacts with several drugs, including anticoagulants, which must be managed to prevent adverse effects. Therefore, a deep understanding of both oral and intravenous formulations, as well as proper dosage adjustments, is essential. The aim of this paper is to provide a comprehensive and updated review on amiodarone's indications, contraindications, recommended dosages, drug interactions, side effects, and monitoring protocols.

Risk for Bleeding-Related Hospitalizations During Use of Amiodarone With Apixaban or Rivaroxaban in Patients With Atrial Fibrillation : A Retrospective Cohort Study

BACKGROUND

Amiodarone, the most effective antiarrhythmic drug in atrial fibrillation, inhibits apixaban and rivaroxaban elimination, thus possibly increasing anticoagulant-related risk for bleeding.

OBJECTIVE

For patients receiving apixaban or rivaroxaban, to compare risk for bleeding-related hospitalizations during treatment with amiodarone versus flecainide or sotalol, antiarrhythmic drugs that do not inhibit these anticoagulants' elimination.

DESIGN

Retrospective cohort study.

SETTING

U.S. Medicare beneficiaries aged 65 years or older.

PATIENTS

Patients with atrial fibrillation began anticoagulant use between 1 January 2012 and 30 November 2018 and subsequently initiated treatment with study antiarrhythmic drugs.

MEASUREMENTS

Time to event for bleeding-related hospitalizations (primary outcome) and ischemic stroke, systemic embolism, and death with or without recent (past 30 days) evidence of bleeding (secondary outcomes), adjusted with propensity score overlap weighting.

RESULTS

There were 91 590 patients (mean age, 76.3 years; 52.5% female) initiating use of study anticoagulants and antiarrhythmic drugs, 54 977 with amiodarone and 36 613 with flecainide or sotalol. Risk for bleeding-related hospitalizations increased with amiodarone use (rate difference [RD], 17.5 events [95% CI, 12.0 to 23.0 events] per 1000 person-years; hazard ratio [HR], 1.44 [CI, 1.27 to 1.63]). Incidence of ischemic stroke or systemic embolism did not increase (RD, -2.1 events [CI, -4.7 to 0.4 events] per 1000 person-years; HR, 0.80 [CI, 0.62 to 1.03]). The risk for death with recent evidence of bleeding (RD, 9.1 events [CI, 5.8 to 12.3 events] per 1000 person-years; HR, 1.66 [CI, 1.35 to 2.03]) was greater than that for other deaths (RD, 5.6 events [CI, 0.5 to 10.6 events] per 1000 person-years; HR, 1.15 [CI, 1.00 to 1.31]) (HR comparison: P = 0.003). The increased incidence of bleeding-related hospitalizations for rivaroxaban (RD, 28.0 events [CI, 18.4 to 37.6 events] per 1000 person-years) was greater than that for apixaban (RD, 9.1 events [CI, 2.8 to 15.3 events] per 1000 person-years) (P = 0.001).

LIMITATION

Possible residual confounding.

CONCLUSION

In this retrospective cohort study, patients aged 65 years or older with atrial fibrillation treated with amiodarone during apixaban or rivaroxaban use had greater risk for bleeding-related hospitalizations than those treated with flecainide or sotalol.

PRIMARY FUNDING SOURCE

National Heart, Lung, and Blood Institute.

Potential Pharmacokinetic Interactions of Common Cardiovascular Drugs and Selected European and Latin American Herbal Medicines: A Scoping Review

BACKGROUND

Herb-drug interactions are nowadays an important decision factor in many healthcare interventions. Patients with cardiovascular risk factors such as hyperlipidemia and hypertension are usually prescribed long-term treatments. We need more informed decision tools to direct future clinical research and decision making to avoid HDI occurrences in this group.

METHODS

A scoping review was conducted using data from online databases such as PUBMED, the National Library of Medicine, and the electronic Medicines Compendium. Included studies consisted of the reported effects on Phase 1/2 and P-glycoprotein of herbal medicines listed in the medicines agencies of Latin America and Europe and drugs used for cardiovascular conditions (statins, diuretics, beta blockers, calcium channel blockers, and ACE inhibitors). The cross tabulation of the results allowed for finding potential HDI.

RESULTS AND CONCLUSIONS

as per the preclinical data reviewed here, we encourage more clinical research on whether drugs with apparently very low interaction risk, such as pravastatin, nadolol, and nimodipine/nitrendipine, may help prevent HDI when statins, beta blockers, and calcium channel blockers, respectively, are prescribed for long-term treatments.

Association between statin use and physical performance in home-dwelling older patients receiving polypharmacy: cross-sectional study

Background

In older patients with polypharmacy and multiple comorbidities, even low grades of statin-associated muscle symptoms may have clinical implications. The aim of this study was therefore to investigate the potential associations between statin use and measures of physical performance and muscle function.

Methods

Participants were aged 70+, treated with at least seven regular systemic medications, and not expected to die or become institutionalized within 6 months. Physical performance measured as gait speed and Short Physical Performance Battery (SPPB) score, and muscle function measured as grip strength, were compared between users and non-users of statins. In the subgroup of statin users, the dose-response relationship was assessed using harmonized simvastatin equivalents adjusted for statin potency, pharmacokinetic interactions and SLCO1B1 c.521 T > C genotype. Multiple linear regression analyses were applied to investigate potential associations between stain use and exposure as independent variables, and physical performance and muscle function as outcomes, adjusted for age, gender, body mass, comorbidity, disability and dementia.

Results

174 patients (87 users and 87 non-users of statins) with a mean (SD) age of 83.3 (7.3) years were included. In analyses adjusted only for gender, grip strength was significantly higher in users than in non-users of statins [regression coefficient (B) 2.7, 95% confidence interval (CI) 1.0 to 4.4]. When adjusted for confounders, the association was no longer statistically significant (B 1.1, 95% CI − 0.5 to 2.7). SPPB and gait speed was also better in statin users than in non-users, but the differences were not statistically significant. In dose-response analyses adjusted for confounders, we found a statistically significant increase in SPPB score (B 0.01, 95% CI 0.00 to 0.02) and gait speed (B 0.001, 95% CI 0.000 to 0.002) per mg increase in simvastatin equivalents.

Conclusions

In contrast to our hypothesis, statin use and exposure was associated with better measures of physical performance and muscle function in older patients with complex drug treatment. The unexpected findings of this cross-sectional, observational study should be further investigated by comparing physical performance before and after statin initiation or statin withdrawal in prospective studies.

Trial registration

ClinicalTrials.gov identifier: NCT02379455, registered March 5, 2015.

Cytochrome P450 3A Time-Dependent Inhibition Assays Are Too Sensitive for Identification of Drugs Causing Clinically Significant Drug-Drug Interactions: A Comparison of Human Liver Microsomes and Hepatocytes and Definition of Boundaries for Inactivation Rate Constants

Time-dependent inhibition (TDI) of CYP3A is an important mechanism underlying numerous drug-drug interactions (DDIs), and assays to measure this are done to support early drug research efforts. However, measuring TDI of CYP3A in human liver microsomes (HLMs) frequently yields overestimations of clinical DDIs and thus can lead to the erroneous elimination of many viable drug candidates from further development. In this investigation, 50 drugs were evaluated for TDI in HLMs and suspended human hepatocytes (HHEPs) to define appropriate boundary lines for the TDI parameter rate constant for inhibition (k_obs) at a concentration of 30 µM. In HLMs, a k_obs value of 0.002 minute^-1 was statistically distinguishable from control; however, many drugs show k_obs greater than this but do not cause DDI. A boundary line defined by the drug with the lowest k_obs that causes a DDI (diltiazem) was established at 0.01 minute^-1 Even with this boundary, of the 33 drugs above this value, only 61% cause a DDI (true positive rate). A corresponding analysis was done using HHEPs; k_obs of 0.0015 minute^-1 was statistically distinguishable from control, and the boundary was established at 0.006 minute^-1 Values of k_obs in HHEPs were almost always lower than those in HLMs. These findings offer a practical guide to the use of TDI data for CYP3A in early drug-discovery research. SIGNIFICANCE STATEMENT: Time-dependent inhibition of CYP3A is responsible for many drug interactions. In vitro assays are employed in early drug research to identify and remove CYP3A time-dependent inhibitors from further consideration. This analysis demonstrates suitable boundaries for inactivation rates to better delineate drug candidates for their potential to cause clinically significant drug interactions.

Amiodarone: A Comprehensive Guide for Clinicians

Amiodarone is an effective antiarrhythmic medication frequently used in practice for both ventricular and atrial arrhythmias. Though classified as a class III antiarrhythmic, it affects all phases of the cardiac action potential. However, the drug has several side effects, including thyroid abnormalities, pulmonary fibrosis, and transaminitis, for which routine monitoring is recommended. It also interacts with several medications, such as warfarin, simvastatin, and atorvastatin, and many HIV antiretroviral medications. Given the common use of this medication in medical practice, it is vital that clinicians understand the indications, contraindications, dosing, side effects, and interactions of this medication. A thorough understanding of these topics is essential for clinicians to ensure safe and effective use of amiodarone.

Drug interactions and pharmacogenetic factors contribute to variation in apixaban concentration in atrial fibrillation patients in routine care

Factor Xa-inhibitor apixaban is an oral anticoagulant prescribed in atrial fibrillation (AF) for stroke prevention. Its pharmacokinetic profile is known to be affected by cytochrome P450 (CYP)3A metabolism, while it is also a substrate of the efflux transporters ATP-binding cassette (ABC)B1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein, BCRP). In this study, we assessed the impact of interacting medication and pharmacogenetic variation to better explain apixaban concentration differences among 358 Caucasian AF patients. Genotyping (ABCG2, ABCB1, CYP3A4*22, CYP3A5*3) was performed by TaqMan assays, and apixaban quantified by mass spectrometry. The typical patient was on average 77.2 years old, 85.5 kg, and had a serum creatinine of 103.1 µmol/L. Concomitant amiodarone, an antiarrhythmic agent and moderate CYP3A/ABCB1 inhibitor, the impaired-function variant ABCG2 c.421C > A, and sex predicted higher apixaban concentrations when controlling for age, weight and serum creatinine (multivariate regression; R² = 0.34). Our findings suggest that amiodarone and ABCG2 genotype contribute to interpatient apixaban variability beyond known clinical factors.

Clinical Aspects of Transporter-Mediated Drug-Drug Interactions

Drug transporters play an essential role in disposition and effects of multiple drugs. Plasma concentrations of the victim drug can be modified by drug-drug interactions occurring in enterocytes (e.g., P-glycoprotein), hepatocytes (e.g., organic anion-transporting polypeptide 1B1 (OATP1B1)), and/or renal proximal tubular cells (e.g., organic cation transporter 2 (OCT2)/multidrug and toxin extrusion 1 and 2-K (MATE1/MATE2-K)). In addition, transporter-mediated drug-drug interactions can cause altered local tissue concentrations and possibly altered effects/toxicity (e.g., in liver and kidneys). During drug development, there is now an intensive in vitro screening of new molecular entities as transporter substrates and inhibitors, followed if necessary by drug-drug interaction studies in healthy volunteers. Nevertheless, there are still unresolved issues, which will also be discussed in this review article (e.g., the clinical significance of transporter-mediated drug-drug interactions of particular relevance to the elderly who are prescribed multiple drugs, with additional impaired liver or kidney function, and the extent to which medication safety in real life could be improved by a reduction of those interactions).

Rosuvastatin-Induced Rhabdomyolysis - Possible Role of Ticagrelor and Patients' Pharmacogenetic Profile

Up to the beginning of 2018, a total of eight cases describing rare but clinically important drug interactions between rosuvastatin and ticagrelor which resulted in rhabdomyolysis have been noted in the Global World Health Organization (WHO) adverse drug reaction (ADR) database (VigiBase) as well as in available literature. There are several possible factors which could contribute to the onset of rhabdomyolysis: old age, initially excessive rosuvastatin dose, drug-drug interactions (DDI) on metabolic enzymes (CYPs and UGTs) and drug transporter levels (ABCB1, ABCG2, OATP1B1) and pharmacogenetic predisposition. We reviewed all available cases plus the case of an 87-year-old female Croatian/Caucasian patient who developed rhabdomyolysis following concomitant treatment with rosuvastatin and ticagrelor. The results of the pharmacogenetic analysis indicated that the patient was a carrier of inactivating alleles CYP2C9*1/*3, CYP3A4*1/*22, CYP3A5*3/*3, CYP2D6*1/*4, UGT1A1*28/*28, UGT2B7 -161C/T, ABCB1 3435C/T and ABCB1 1237C/T which could have added to the interactions not only between ticagrelor and rosuvastatin but also other concomitantly prescribed medicines, such as amiodarone and proton pump inhibitors. In this case report, the possible multifactorial causes for rhabdomyolysis following concomitant use of rosuvastatin and ticagrelor such as old age, polypharmacy, renal impairment, along with pharmacogenetics will be discussed.

Pravastatin-Induced Eczematous Eruption Mimicking Psoriasis

BACKGROUND

Statins, an example of the most commonly prescribed medications to the elderly, are not without side effects. Dermatologic events are often overlooked as arising from medications, particularly those which are taken chronically. Moreover, elderly patients are prone to pharmacologic interactions due to multiple medications. In this report, we describe a case of a statin-induced eczematous dermatitis with a psoriasis-like clinical presentation and review the skin manifestations that may arise from statin therapy.

CASE PRESENTATION

An 82-year-old man with gout and hypercholesterolemia presented to dermatology clinic with new onset of pruritic, scaly erythematous plaques bilaterally on the extensor surfaces of his arms. He had never had similar lesions before. Despite various topical and systemic treatments over several months, the rash continued to evolve. The patient was then advised to discontinue his long-term statin, which led to gradual resolution of his symptoms. He was subsequently diagnosed with statin-induced eczematous dermatitis.

CONCLUSIONS

This case report describes an adverse cutaneous reaction to statins that is rarely reported in the literature. Medications, including longstanding therapies, should be suspected in cases of refractory dermatologic lesions.

Quantitative Prediction of Drug-Drug Interactions Involving Inhibitory Metabolites in Drug Development: How Can Physiologically Based Pharmacokinetic Modeling Help?

This subteam under the Drug Metabolism Leadership Group (Innovation and Quality Consortium) investigated the quantitative role of circulating inhibitory metabolites in drug-drug interactions using physiologically based pharmacokinetic (PBPK) modeling. Three drugs with major circulating inhibitory metabolites (amiodarone, gemfibrozil, and sertraline) were systematically evaluated in addition to the literature review of recent examples. The application of PBPK modeling in drug interactions by inhibitory parent-metabolite pairs is described and guidance on strategic application is provided.

Mechanism of Drug-Drug Interactions Between Warfarin and Statins

The anticoagulant drug warfarin and the lipid-lowering statin drugs are commonly co-administered to patients with cardiovascular diseases. Clinically significant drug-drug interactions (DDIs) between these drugs have been recognized through case studies for many years, but the biochemical mechanisms causing these interactions have not been explained fully. Previous theories include kinetic alterations in cytochrome P-450-mediated drug metabolism or disturbances of drug-protein binding, leading to anticoagulant activity of warfarin; however, neither the enantioselective effects on warfarin metabolism nor the potential disruption of drug transporter function have been well investigated. This study investigated the etiology of the DDIs between warfarin and statins. Liquid chromatography-mass spectrometry methods were developed and validated to quantify racemic warfarin, 6 of its hydroxylated metabolites, and pure enantiomers of warfarin; these methods were applied to study the role of different absorption, distribution, metabolism, and excretion properties, leading to DDIs. Plasma protein binding displacement of warfarin was performed in the presence of statins using equilibrium dialysis method. Substrate kinetics of warfarin and pure enantiomers were performed with human liver microsomes to determine the kinetic parameters (Km and Vmax) for the formation of all 6 hydroxywarfarin metabolites, inhibition of warfarin metabolism in the presence of statins, was determined. Uptake transport studies of warfarin were performed using overexpressing HEK cell lines and efflux transport using human adenocarcinoma colonic cell line cells. Fluvastatin significantly displaced plasma protein binding of warfarin and pure enantiomers; no other statin resulted in significant displacement of warfarin. All the statins that inhibited the formation of 10-hydroxywarfarin, atorvastatin, pitavastatin, and simvastatin were highly potent compared to other statins; in contrast, only fluvastatin was found to be a potent inhibitor of formation of 7-hydroxy warfarin. Uptake and efflux drug transporters do not play any role in these DDIs. The results showed that DDIs between warfarin and statins are primarily caused by cytochrome P-450 inhibition.

Long-term pretreatment with desethylamiodarone (DEA) or amiodarone (AMIO) protects against coronary artery occlusion induced ventricular arrhythmias in conscious rats

The aim of this investigation was to compare the effectiveness of long-term pretreatment with amiodarone (AMIO) and its active metabolite desethylamiodarone (DEA) on arrhythmias induced by acute myocardial infarction in rats. Acute myocardial infarction was induced in conscious, male, Sprague–Dawley rats by pulling a previously inserted loose silk loop around the left main coronary artery. Long-term oral pretreatment with AMIO (30 or 100 mg·(kg body mass)−1·day−1, loading dose 100 or 300 mg·kg−1 for 3 days) or DEA (15 or 50 mg·kg−1·day−1, loading dose 100 or 300 mg·kg−1 for 3 days), was applied for 1 month before the coronary artery occlusion. Chronic oral treatment with DEA (50 mg·kg−1·day−1) resulted in a similar myocardial DEA concentration as chronic AMIO treatment (100 mg·kg−1·day−1) in rats (7.4 ± 0.7 μg·g−1 and 8.9 ± 2.2 μg·g−1). Both pretreatments in the larger doses significantly improved the survival rate during the acute phase of experimental myocardial infarction (82% and 64% by AMIO and DEA, respectively, vs. 31% in controls). Our results demonstrate that chronic oral treatment with DEA resulted in similar cardiac tissue levels to that of chronic AMIO treatment, and offered an equivalent degree of antiarrhythmic effect against acute coronary artery ligation induced ventricular arrhythmias in conscious rats.

P450-Based Drug-Drug Interactions of Amiodarone and its Metabolites: Diversity of Inhibitory Mechanisms

In this study, IC50 shift and time-dependent inhibition (TDI) experiments were carried out to measure the ability of amiodarone (AMIO), and its circulating human metabolites, to reversibly and irreversibly inhibit CYP1A2, CYP2C9, CYP2D6, and CYP3A4 activities in human liver microsomes. The [I]u/Ki,u values were calculated and used to predict in vivo AMIO drug-drug interactions (DDIs) for pharmaceuticals metabolized by these four enzymes. Based on these values, the minor metabolite N,N-didesethylamiodarone (DDEA) is predicted to be the major cause of DDIs with xenobiotics primarily metabolized by CYP1A2, CYP2C9, or CYP3A4, while AMIO and its N-monodesethylamiodarone (MDEA) derivative are the most likely cause of interactions involving inhibition of CYP2D6 metabolism. AMIO drug interactions predicted from the reversible inhibition of the four P450 activities were found to be in good agreement with the magnitude of reported clinical DDIs with lidocaine, warfarin, metoprolol, and simvastatin. The TDI experiments showed DDEA to be a potent inactivator of CYP1A2 (KI = 0.46 μM, kinact = 0.030 minute(-1)), while MDEA was a moderate inactivator of both CYP2D6 (KI = 2.7 μM, kinact = 0.018 minute(-1)) and CYP3A4 (KI = 2.6 μM, kinact = 0.016 minute(-1)). For DDEA and MDEA, mechanism-based inactivation appears to occur through formation of a metabolic intermediate complex. Additional metabolic studies strongly suggest that CYP3A4 is the primary microsomal enzyme involved in the metabolism of AMIO to both MDEA and DDEA. In summary, these studies demonstrate both the diversity of inhibitory mechanisms with AMIO and the need to consider metabolites as the culprit in inhibitory P450-based DDIs.

Potential statin-drug interactions: prevalence and clinical significance

Background

Statins are cholesterol-lowering drugs widely used for cardiovascular prevention. Although safe when used alone, in combination with other drugs the likelihood of adverse drug reactions increases significantly. The exposure of the Bulgarian population to coprescriptions leading to potential statin-drug interactions is currently unknown.

Objective

The aim of this study was to investigate the incidence of coprescriptions involving statins and to compare the exposure of outpatients and inpatients to potential statin-drug interactions.

Setting

A cardiology clinic of the teaching University hospital in Varna, Bulgaria.

Method

This observational retrospective study examined the medical records of hospitalized patients prescribed a statin in combination with potentially interacting drugs. Patients who entered the hospital with a statin coprescription (considered outpatients) were compared with those coprescribed a statin at discharge from hospital (considered inpatients). Potentially interacting drugs included inhibitors and inducers of cytochrome P450 (CYP) enzymes and drugs of narrow safety margin (coumarin anticoagulants, digitalis).

Main outcome measure

The proportion of patients exposed to statin coprescriptions with potentially interacting drugs at hospital admission and discharge. Secondary outcome measures: laboratory evidence supporting possible statin-drug interactions.

Results

Out of 1641 hospitalized patients examined, 572 were prescribed a statin, either at hospital admission or discharge. Simvastatin was most commonly prescribed and simvastatin-drug coprescription predominated, especially at discharge. The exposure to all potential statin-drug interactions was similar at hospital admission (26.1%) and discharge (24.4%), as was the exposure to statin combinations with CYP inhibitors, 6.4% and 4%, correspondingly. Overall, more coprescriptions were generated, than were eliminated by hospital physicians. Amiodarone was the CYP inhibitor most frequently coprescribed. Of all interacting drugs acenocoumarol was the most commonly found, the proportions of statin-acenocoumarol coprescriptions being roughly the same at hospital entry (11.5%) and discharge (12.4%). In 7 patients out of 69 exposed to the combination, INR was found to be higher than 3, indicating a risk of over-anticoagulation.

Conclusions

Potential statin-drug interactions are common. Although they do not differ between outpatient and inpatient settings, new hazardous coprescriptions are more frequently generated in hospital. Caution is required when acenocoumarol is coprescribed with statins, especially simvastatin.

Impact of pharmacists' interventions and simvastatin dose restrictions

BACKGROUND

On June 8, 2011, the United States Food and Drug Administration (FDA) reported safety concerns regarding statin-related myopathies and advised further restrictions on simvastatin dosing. These restrictions reduced the maximum dose for specific patient characteristics, primarily certain concomitant medications.

OBJECTIVE

The purpose of this study was to compare the effectiveness of 2 different pharmacist-conducted educational interventions on appropriate simvastatin use in the primary care setting.

METHODS

This retrospective cohort analysis was conducted in 2 academic medical center clinics. Patients prescribed simvastatin before June 8, 2011, requiring dosage adjustment based on labeling changes were evaluated for study inclusion. The pharmacists' interventions included: 30-minute didactic session for prescribers or patient-specific recommendation communicated with the physician during the patient's follow-up visit. Primary outcomes were the number of patients prescribed FDA-recommended simvastatin doses after pharmacist intervention and the intervention's impact on low-density lipoprotein (LDL).

RESULTS

Medical record review identified 1173 patients prescribed simvastatin prior to June 8, 2011; 126 patients qualified for study inclusion. After controlling for baseline characteristics, the likelihood of patients being prescribed an appropriate dose postintervention increased if they were in the patient-specific recommendation group (odds ratio [OR] = 10.59; 95% CI = 3.43-32.69; P < .0001). LDL change occurred at a similar rate between intervention groups (P = .652).

CONCLUSION

Following FDA labeling changes for simvastatin, patient-specific recommendations made by pharmacists correlated with a greater likelihood of appropriate simvastatin dosing compared with a one-time didactic education session. Patient-specific recommendations positively affect prescribing habits and making steps to improve patient safety.

Statin myotoxicity: a review of genetic susceptibility factors

The 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase inhibitors (statins) are among the most common medications prescribed worldwide, but their efficacy and toxicity vary between individuals. One of the major factors contributing to intolerance and non-compliance are the muscle side-effects, which range from mild myalgia through to severe life-threatening rhabdomyolysis. One way to address this is pharmacogenomic screening, which aims to individualize therapy to maximize efficacy whilst avoiding toxicity. Genes encoding proteins involved in the metabolism of statins as well as genes known to cause inherited muscle disorders have been investigated. To-date only polymorphisms in the SLCO1B1 gene, which encodes the protein responsible for hepatic uptake of statins, and the COQ2 gene, important in the synthesis of coenzyme Q10, have been validated as being strongly associated with statin-induced myopathy. The aim of this review is to summarize studies investigating genetic factors predisposing to statin myopathy and myalgia, as the first step towards pharmacogenomic screening to identify at risk individuals.

Impact of genetic polymorphism on drug-drug interactions mediated by cytochromes: a general approach

Currently, quantitative prediction of the impact of genetic polymorphism and drug-drug interactions mediated by cytochromes, based on in vivo data, is made by two separate methods and restricted to a single cytochrome. We propose a unified approach for describing the combined impact of drug-drug interactions and genetic polymorphism on drug exposure. It relies on in vivo data and uses the following three characteristic parameters: one for the victim drug, one for the interacting drug, and another for the genotype. These parameters are known for a wide range of drugs and genotypes. The metrics of interest are the ratio of victim drug area under the curve (AUC) in patients with genetic variants taking both drugs, to the AUC in patients with either variant or wild-type genotype taking the victim drug alone. The approach was evaluated by external validation, comparing predicted and observed AUC ratios found in the literature. Data were found for 22 substrates, 30 interacting drugs, and 38 substrate-interacting drug couples. The mean prediction error of AUC ratios was 0.02, and the mean prediction absolute error was 0.38 and 1.34, respectively. The model may be used to predict the variations in exposure resulting from a number of drug-drug-genotype combinations. The proposed approach will help (1) to identify comedications and population at risk, (2) to adapt dosing regimens, and (3) to prioritize the clinical pharmacokinetic studies to be done.

Safety of statins

Statins are an established class of drugs with proven efficacy in cardiovascular risk reduction. The concern over statin safety was first raised with the revelation of myopathy and rhabdomyolysis with the use of now withdrawn cerivastatin. Enhanced understanding of the mechanisms behind adverse effects of statins including an insight into the pharmacokinetic properties have minimised fear of statin use among clinicians. Studies reveal that occurrence of myopathy and rhabdomyolysis are rare 1/100000 patient-years. The risk of myopathy/rhabdomyolysis varies between statins due to varying pharmacokinetic profiles. This explains the differing abilities of statins to adverse effects and drug interaction potentials that precipitate adverse effects. Higher dose of rosuvastatin (80 mg/day) was associated with proteinuria and hematuria while lower doses were devoid of such effects. Awareness of drugs interacting with statins and knowledge of certain combinations such as statin and fibrates together with monitoring of altered creatine kinase activity may greatly minimise associated adverse effects. Statins also asymptomatically raise levels of hepatic transaminases but are not correlated with hepatotoxicity. Statins are safe and well tolerated including more recent potent statins such as, rosuvastatin. The benefits of intensive statin use in cardiovascular risk reduction greatly outweigh risks. The present review discusses underlying causes of statin-associated adverse effects including management in high risk groups.

Herb-drug interaction of Fucus vesiculosus extract and amiodarone in rats: a potential risk for reduced bioavailability of amiodarone in clinical practice

Fucus vesiculosus is a seaweed claimed to be useful for obesity management. Therefore, considering the relationship between obesity and cardiovascular diseases, this work aimed to assess the potential for an herb-drug interaction among a standardized F. vesiculosus extract (GMP certificate) and amiodarone (a narrow therapeutic index drug) in rats. In a first pharmacokinetic study, rats were simultaneously co-administered with a single-dose of F. vesiculosus (575 mg/kg, p.o.) and amiodarone (50 mg/kg, p.o.); in a second study, rats were pre-treated during 14 days with F. vesiculosus (575 mg/kg/day, p.o.) and received amiodarone (50 mg/kg, p.o.) on the 15th day. Rats of the control groups received the corresponding volume of vehicle. After analysis of the pharmacokinetic data it deserves to be highlighted the significant decrease in the peak plasma concentration of amiodarone (55.4%) as well as the reduction of systemic exposure to the parent drug (~30%) following the simultaneous co-administration of F. vesiculosus extract and amiodarone. This paper reports, for the first time, the herb-drug interaction between F. vesiculosus and amiodarone, which determined a considerable decrease on amiodarone bioavailability in rats. Therefore, the therapeutic efficacy of amiodarone may be compromised by the concurrent administration of herbal slimming medicines/dietary supplements containing F. vesiculosus.

Importance of multi-p450 inhibition in drug-drug interactions: evaluation of incidence, inhibition magnitude, and prediction from in vitro data

Drugs that are mainly cleared by a single enzyme are considered more sensitive to drug-drug interactions (DDIs) than drugs cleared by multiple pathways. However, whether this is true when a drug cleared by multiple pathways is coadministered with an inhibitor of multiple P450 enzymes (multi-P450 inhibition) is not known. Mathematically, simultaneous equipotent inhibition of two elimination pathways that each contribute half of the drug clearance is equal to equipotent inhibition of a single pathway that clears the drug. However, simultaneous strong or moderate inhibition of two pathways by a single inhibitor is perceived as an unlikely scenario. The aim of this study was (i) to identify P450 inhibitors currently in clinical use that can inhibit more than one clearance pathway of an object drug in vivo and (ii) to evaluate the magnitude and predictability of DDIs caused by these multi-P450 inhibitors. Multi-P450 inhibitors were identified using the Metabolism and Transport Drug Interaction Database. A total of 38 multi-P450 inhibitors, defined as inhibitors that increased the AUC or decreased the clearance of probes of two or more P450s, were identified. Seventeen (45%) multi-P450 inhibitors were strong inhibitors of at least one P450, and an additional 12 (32%) were moderate inhibitors of one or more P450s. Only one inhibitor (fluvoxamine) was a strong inhibitor of more than one enzyme. Fifteen of the multi-P450 inhibitors also inhibit drug transporters in vivo, but such data are lacking on many of the inhibitors. Inhibition of multiple P450 enzymes by a single inhibitor resulted in significant (>2-fold) clinical DDIs with drugs that are cleared by multiple pathways such as imipramine and diazepam, while strong P450 inhibitors resulted in only weak DDIs with these object drugs. The magnitude of the DDIs between multi-P450 inhibitors and diazepam, imipramine, and omeprazole could be predicted using in vitro data with similar accuracy as probe substrate studies with the same inhibitors. The results of this study suggest that inhibition of multiple clearance pathways in vivo is clinically relevant, and the risk of DDIs with object drugs may be best evaluated in studies using multi-P450 inhibitors.

Potential drug-drug interactions in prescriptions to patients over 45 years of age in primary care, southern Brazil

BACKGROUND

Few cross-sectional studies involving adults and elderly patients with major DDIs have been conducted in the primary care setting. The study aimed to investigate the prevalence of potential drug-drug interactions (DDIs) in patients treated in primary care.

METHODOLOGY/PRINCIPAL FINDINGS

A cross-sectional study involving patients aged 45 years or older was conducted at 25 Basic Health Units in the city of Maringá (southern Brazil) from May to December 2010. The data were collected from prescriptions at the pharmacy of the health unit at the time of the delivery of medication to the patient. After delivery, the researcher checked the electronic medical records of the patient. A total of 827 patients were investigated (mean age: 64.1; mean number of medications: 4.4). DDIs were identified in the Micromedex® database. The prevalence of potential DDIs and major DDIs was 63.0% and 12.1%, respectively. In both the univariate and multivariate analyses, the number of drugs prescribed was significantly associated with potential DDIs, with an increasing risk from three to five drugs (OR = 4.74; 95% CI: 2.90-7.73) to six or more drugs (OR = 23.03; 95% CI: 10.42-50.91). Forty drugs accounted for 122 pairs of major DDIs, the most frequent of which involved simvastatin (23.8%), captopril/enalapril (16.4%) and fluoxetine (16.4%).

CONCLUSIONS/SIGNIFICANCE

This is the first large-scale study on primary care carried out in Latin America. Based on the findings, the estimated prevalence of potential DDIs was high, whereas clinically significant DDIs occurred in a smaller proportion. Exposing patients to a greater number of prescription drugs, especially three or more, proved to be a significant predictor of DDIs. Prescribers should be more aware of potential DDIs. Future studies should assess potential DDIs in primary care over a longer period of time.

Emphasizing statin safety in the hospitalized patient: a review

This review examines the safe use of statin therapy in the hospitalized patient. Available data support initiation of statin therapy during hospitalization in patients with acute coronary syndromes or established cardiovascular disease and in high-risk patients with diabetes mellitus and chronic kidney disease (except for those on maintenance hemodialysis). Because of the increased risk of cardiovascular disease, statins are given to solid-organ transplant survivors and those treated with protease inhibitors for human immunodeficiency virus. However, in the multidrug, acute illness hospital environment, safety considerations become paramount. We review the essentials of statin metabolism and drug-drug interactions to provide the hospital physician with information to minimize potentially serious adverse statin effects.

Risk assessment of mechanism-based inactivation in drug-drug interactions

Drug-drug interactions (DDIs) that occur via mechanism-based inactivation of cytochrome P450 are of serious concern. Although several predictive models have been published, early risk assessment of MBIs is still challenging. For reversible inhibitors, the DDI risk categorization using [I]/K(i) ([I], the inhibitor concentration; K(i), the inhibition constant) is widely used in drug discovery and development. Although a simple and reliable methodology such as [I]/K(i) categorization for reversible inhibitors would be useful for mechanism-based inhibitors (MBIs), comprehensive analysis of an analogous measure reflecting in vitro potency for inactivation has not been reported. The aim of this study was to evaluate whether the term λ/k(deg) (λ, first-order inactivation rate at a given MBI concentration; k(deg), enzyme degradation rate constant) would be useful in the prediction of the in vivo DDI risk of MBIs. Twenty-one MBIs with both in vivo area under the curve (AUC) change of marker substrates and in vitro inactivation parameters were identified in the literature and analyzed. The results of this analysis show that in vivo DDIs with >2-fold change of object drug AUC can be identified with the cutoff value of λ/k(deg) = 1, where unbound steady-state C(max) is used for inhibitor concentration. However, the use of total C(max) led to great overprediction of DDI risk. The risk assessment using λ/k(deg) coupled with unbound C(max) can be useful for the DDI risk evaluation of MBIs in drug discovery and development.

[Specific considerations on the prescription and therapeutic interchange of statins]

OBJECTIVE

The pharmaceutical industry currently offers six different statins in Spain and there is one more soon to be available. Choosing the most appropriate drug and dose is determined by the therapeutic target (reduction in LDL-C levels). Statin doses that decrease LDL-C at the same percentage are considered equivalent. Evaluating the pharmacokinetic characteristics of each statin can be useful when setting selection criteria, helping to determine which statin may be more appropriate for a patient based on their individual characteristics and on the other co-administered drugs.

METHODS

We reviewed the pharmacokinetics properties of each statin and its possible involvement in drug interactions.

RESULTS

CYP3A4 was responsible for the metabolism of lovastatin, simvastatin and atorvastatin; fluvastatin depends on CYP2C9; P-glycoprotein is responsible for decreased atorvastatin, pravastatin, simvastatin and lovastatin concentrations. The OATPA1B1 transporter involved in all statins' access to the hepatocyte, except for fluvastatin, is essential for rosuvastatin and pravastatin. These circumstances cause those drugs inhibiting or inducing isoenzymes or transporters' activity not to have the same effect on the different statins.

CONCLUSION

The pharmacokinetics is important when choosing the best statin and could be a limitation in the use of interchange therapeutic programmes when other drugs are present.

Statin-induced myopathy: a review and update

INTRODUCTION

Statin-induced myopathy is an important cause of statin intolerance and the most common cause of statin discontinuation. Observational studies estimate that 10 - 15% of statin users develop statin-related muscle side effects ranging from mild myalgia to more severe muscle symptoms with significant CPK elevations.

AREAS COVERED

This article reviews the epidemiology, clinical features, risk factors and mechanisms of statin-induced myopathy and provides an evidence-based algorithm for managing patients with statin myopathy.

EXPERT OPINION

There are multiple risk factors for statin-induced myopathy that are both patient-related (age, genetics, co-morbidities) and drug-related (statin metabolism via the CYP system, drug-drug interactions and statin drug transport). Management options for statin-intolerant patients include statin switching, especially to low-dose, non-daily doses of long-acting statins, such as rosuvastatin and atorvastatin, and other non-statin lipid-lowering agents, such as ezetimibe and colesevelam, and possibly red yeast rice. In conclusion, statin-induced myopathy is a significant clinical problem that contributes considerably to statin therapy discontinuation. However, there exist multiple and effective management options for statin intolerant patients.

Organic anion transporting polypeptide 1B1: a genetically polymorphic transporter of major importance for hepatic drug uptake

The importance of membrane transporters for drug pharmacokinetics has been increasingly recognized during the last decade. Organic anion transporting polypeptide 1B1 (OATP1B1) is a genetically polymorphic influx transporter expressed on the sinusoidal membrane of human hepatocytes, and it mediates the hepatic uptake of many endogenous compounds and xenobiotics. Recent studies have demonstrated that OATP1B1 plays a major, clinically important role in the hepatic uptake of many drugs. A common single-nucleotide variation (coding DNA c.521T>C, protein p.V174A, rs4149056) in the SLCO1B1 gene encoding OATP1B1 decreases the transporting activity of OATP1B1, resulting in markedly increased plasma concentrations of, for example, many statins, particularly of active simvastatin acid. The variant thereby enhances the risk of statin-induced myopathy and decreases the therapeutic indexes of statins. However, the effect of the SLCO1B1 c.521T>C variant is different on different statins. The same variant also markedly affects the pharmacokinetics of several other drugs. Furthermore, certain SLCO1B1 variants associated with an enhanced clearance of methotrexate increase the risk of gastrointestinal toxicity by methotrexate in the treatment of children with acute lymphoblastic leukemia. Certain drugs (e.g., cyclosporine) potently inhibit OATP1B1, causing clinically significant drug interactions. Thus, OATP1B1 plays a major role in the hepatic uptake of drugs, and genetic variants and drug interactions affecting OATP1B1 activity are important determinants of individual drug responses. In this article, we review the current knowledge about the expression, function, substrate characteristics, and pharmacogenetics of OATP1B1 as well as its role in drug interactions, in parts comparing with those of other hepatocyte-expressed organic anion transporting polypeptides, OATP1B3 and OATP2B1.

Clinical Pharmacology of Dronedarone: Implications for the Therapy of Atrial Fibrillation

Dronedarone, a recently approved antiarrhythmic agent, is a chemical analog of amiodarone. It has an approximately 15% bioavailability, with plasma concentrations markedly increasing after a high-fat meal; it is recommended to be taken with food. The primary metabolic clearance pathway for dronedarone is via the hepatic enzyme system (primarily cytochrome P450 3A4 [CYP3A4]); the half-life of dronedarone is 27 to 31 hours. Strong CYP3A4 inhibitors, such as ketoconazole, are associated with a marked increase in dronedarone maximum concentration and are thus contraindicated; inducers of CYP3A4 will conversely decrease dronedarone exposure. Dronedarone is a substrate for P-glycoprotein (P-gp) and will lead to an increase in concentration of P-gp substrates such as digoxin. Dronedarone will cause a small increase in creatinine concentrations, without a change in glomerular filtration rate (GFR). Gender, renal dysfunction, weight, and age have little effect on the pharmacokinetics of dronedarone, and dose adjustment for these variables is not required.

Does Simvastatin Cause More Myotoxicity Compared with Other Statins?

Objective:

To review the literature regarding statins and myotoxicity and evaluate these data to determine whether incidence rates are higher with simvastatin.

Data Sources:

Literature was identified from a search of MEDLINE (1966–August 2009) and International Pharmaceutical Abstracts (1970–August 2009), as well as references of selected articles. Key search terms included the names of individual statins, rhabdomyolysis, myopathy, myalgia, myotoxicity, statins, and drug interactions.

Study Selection and Data Extraction:

All English-language articles discussing statin-related myotoxicity and relevant drug interactions that involved human subjects were examined.

Data Synthesis:

Simvastatin is a commonly prescribed, moderately potent statin. Recent evidence suggests that the risk of severe muscle toxicity with simvastatin may be higher than that with other statins, particularly when used in combination with cytochrome P450 isoenzyme inhibitors. However, the lack of direct comparative clinical trials assessing the risk of myotoxicity among the statins in equivalent doses precludes definitive conclusions. Data sources examining low-to-mode rate doses of simvastatin suggest that myotoxicity with this agent is infrequent, with rates similar to those seen with other statins. Conversely, findings from clinical trials using the maximum daily dose (80 mg) and a clinical trials database of varying doses of simvastatin suggest a possible increase in rates of myotoxicity with the 80-mg dose compared with lower doses and a higher incidence rate when compared with maximum doses of other statins.

Conclusions:

Overall, the rates of severe myotoxicity with all statins are low, especially with low-to-moderate doses. However, recent trials for those using simvastatin 80 mg daily suggest a higher incidence of myotoxicity compared with maximum approved doses of other statins. Practitioners should be aware of these possible risks and individualize therapy to limit myotoxicity.

Towards companion diagnostics for the management of statin therapy

BACKGROUND

Statins are the most commonly prescribed drugs in the world and are established first-line therapy for cardiovascular disease. Statin toxicity is related to dose, age, gender, ethnicity, body mass, renal and endocrine function and also to concomitant medications - particularly those that inhibit cytochrome P450 3A4.

OBJECTIVE/METHOD

This review describes the tests used before initiation of statin therapy, to establish their efficacy and to monitor their principal side effects. Lipids and apolipoproteins are used to measure efficacy and compliance, whereas transaminases and creatine kinase are used to measure toxicity. Guidelines agree in general, but differ in the details of measurement of baseline levels, action limits and management strategies for statin toxicity. Genetic factors are relevant to both the efficacy and the toxicity of statin therapy, with efficacy being associated with polymorphisms in lipid-related genes, whereas a function-related polymorphism in the organic anion transporting polypeptide 1B1 (OATP1B1; SLCO1B1) is associated with 60% of the cases of myopathy with high-dose simvastatin.

CONCLUSIONS

Although basic efficacy and safety panels for the initiation and monitoring of statin therapy are well established, controversy remains about the need for ancillary diagnostics in patients and to which patient groups these should be applied.

Successful strategy to improve the specificity of electronic statin-drug interaction alerts

PURPOSE

A considerable weakness of current clinical decision support systems managing drug-drug interactions (DDI) is the high incidence of inappropriate alerts. Because DDI-induced, dose-dependent adverse events can be prevented by dosage adjustment, corresponding DDI alerts should only be issued if dosages exceed safe limits. We have designed a logical framework for a DDI alert-system that considers prescribed dosage and retrospectively evaluates the impact on the frequency of statin-drug interaction alerts.

METHODS

Upper statin dose limits were extracted from the drug label (SPC) (20 statin-drug combinations) or clinical trials specifying the extent of the pharmacokinetic interaction (43 statin-drug combinations). We retrospectively assessed electronic DDI alerts and compared the number of standard alerts to alerts that took dosage into account.

RESULTS

From among 2457 electronic prescriptions, we identified 73 high-risk statin-drug pairs. Of these, SPC dosage information classified 19 warnings as inappropriate. Data from pharmacokinetic trials took quantitative dosage information more often into consideration and classified 40 warnings as inappropriate. This is a significant reduction in the number of alerts by 55% compared to SPC-based information (26%; p < 0.001).

CONCLUSION

This retrospective study of pharmacokinetic statin interactions demonstrates that more than half of the DDI alerts that presented in a clinical decision support system were inappropriate if DDI-specific upper dose limits are not considered.

Simvastatin and Amiodarone: Emergence of a Potentially Toxic Interaction

This continuing feature updates readers on recent developments in cardiovascular pharmacotherapy. Cardiovascular disease remains the number 1 killer in the United States, and more clinical outcome trials have been conducted in cardiology than in any other field of medicine. Given this rapidly expanding knowledge base, if pharmacists stay current with developments in drug therapy, they can have a significant impact on prevention and treatment.

Risk management of simvastatin or atorvastatin interactions with CYP3A4 inhibitors

BACKGROUND

Co-administration of cytochrome P450 (CYP) 3A4 inhibitors with simvastatin or atorvastatin is associated with increased risk of developing myopathy or rhabdomyolysis.

OBJECTIVE

To detect co-prescriptions of CYP3A4 inhibitors with simvastatin or atorvastatin in community pharmacies and assess the risk-preventive actions taken by the prescribing physicians who were alerted about the co-prescription by the pharmacist.

METHODS

This naturalistic study was performed during four separate 6-week periods in 2004 and 2005, and involved 110 Norwegian community pharmacists (25-30 in each period). Co-prescription of the selected CYP3A4 inhibitors diltiazem, verapamil, clarithromycin, erythromycin, fluconazole, itraconazole and ketoconazole with either simvastatin or atorvastatin was detected with the aid of a simple computer programme. In instances where the pharmacist alerted the prescribing physician about the co-prescription, information on possible strategies to minimize the risk associated with the interaction was also provided. Odds ratios (ORs) were estimated to describe the associations between prescription variables and frequencies of physician information and prescription change, respectively.

RESULTS

In total, 245 co-prescriptions of CYP3A4 inhibitors with simvastatin (134 events) or atorvastatin (111) were detected. Diltiazem (86 events), verapamil (72), erythromycin (48) and clarithromycin (29) were the most commonly co-prescribed CYP3A4 inhibitors. Physicians were informed in 168 out of 245 cases (68.6%). The prescription was subsequently changed in 100 out of 168 cases (59.5%). Another 50 physicians (29.8%) responded that they would consult the patient and monitor potential adverse effects, while only 18 physicians (10.7%) replied that they had already managed the interactions or considered the issue as irrelevant. The adjusted OR for the informing of the physician was 1.89 (95% CI 0.98, 3.63) in patients receiving a daily HMG-CoA reductase inhibitor ('statin') dose of >or=40 mg compared with patients receiving a statin dose of <40 mg/day. The adjusted OR for prescription change was 4.98 (95% CI 2.36, 10.52) if co-prescription was detected prior to the initiation of concurrent use compared with if it was detected during concurrent use.

CONCLUSION

Nine out of ten physicians changed prescriptions or monitored potential adverse effects when informed by community pharmacists about the risk associated with co-prescription of CYP3A4 inhibitors with simvastatin or atorvastatin. This suggests that an important risk factor for myotoxicity due to these statins could be minimized through interdisciplinary co-operation.

Simvastatin: present and future perspectives

Simvastatin is lipophilic statin with a short half-life that is primarily metabolized by CYP450 3A4. At doses of 5 - 80 mg, simvastatin lowers LDL cholesterol by 25 - 50%. Simvastatin has been shown to reduce the risk of cardiovascular disease by 35% and overall mortality by up to 30% over 5 years. The recommended starting dose of simvastatin 40 mg is approved as a lipid-lowering agent and for all high-risk patients, including those with cardiovascular disease and diabetes, regardless of the baseline LDL level. Simvastatin dose should be adjusted in those receiving CYP3A4 inhibitors, gemfibrozil, or ciclosporin, amiodarone, or in those with severe renal insufficiency. Coformulation of simvastatin with ezetimibe is now available, and coformulation with extended release niacin is under development.