The effect of converting from pravastatin to simvastatin on the pharmacodynamics of warfarin

Drug-drug interaction between warfarin and statins: A Danish cohort study

Initiation of statin treatment is suggested to increase the international normalised ratio (INR) among warfarin users. However, available data is limited and conflicting. We conducted a register-based cohort study to evaluate the drug-drug interaction between warfarin and statins. By linking data on INR measurements and filled prescriptions, we identified warfarin users 2000-2015 initiating simvastatin (n = 1363), atorvastatin (n = 165) or rosuvastatin (n = 23). Simvastatin initiation led to an increase in mean INR from 2.40 to 2.71, with INRs peaking after 4 weeks, corresponding to a mean change of 0.32 (95%CI 0.25-0.38). High-dose and low-dose simvastatin led to comparable changes (mean change 0.33 vs 0.29). Initiation of atorvastatin and rosuvastatin lead to INR increases of 0.27 (95%CI 0.12-0.42) and 0.30 (95%CI -0.09-0.69). In conclusion, initiation of simvastatin, atorvastatin or rosuvastatin among warfarin users led to a minor increase in INR. The magnitude of this change is for most patients likely of limited clinical relevance.

The effect of simvastatin on warfarin anticoagulation: a Swedish register-based nationwide cohort study

PURPOSE

Some data indicate that simvastatin may increase the anticoagulative effect in patients treated with warfarin, but the evidence is scarce. The aim of the present study was to investigate how the anticoagulative effect of warfarin is affected by the initiation of simvastatin in a very large patient sample.

METHODS

In a retrospective cohort study, we included 5637 individuals on warfarin treatment initiating simvastatin. INR values and warfarin doses were calculated week-by-week during co-treatment. Data were obtained from two large Swedish warfarin registers and from the Swedish Prescribed Drug Register.

RESULTS

INR increased from 2.43 at baseline to 2.58, 4 weeks after simvastatin initiation, and did not stabilize until the last quarter of the year studied. Consequently, the proportion of patients with an INR above 3 increased from around 8 to 15%.

CONCLUSIONS

In conclusion, initiation of simvastatin resulted in moderately increased INR values and subsequent dose decreases in patients already on warfarin. In order to avoid the increased risk of bleeding, the initiation of simvastatin may be accompanied by closer INR monitoring.

Old and new oral anticoagulants: Food, herbal medicines and drug interactions

The most commonly prescribed oral anticoagulants worldwide are the vitamin K antagonists (VKAs) such as warfarin. Factors affecting the pharmacokinetics of VKAs are important because deviations from their narrow therapeutic window can result in bleedings due to over-anticoagulation or thrombosis because of under-anticoagulation. In addition to pharmacodynamic interactions (e.g., augmented bleeding risk for concomitant use of NSAIDs), interactions with drugs, foods, herbs, and over-the-counter medications may affect the risk/benefit ratio of VKAs. Direct oral anticoagulants (DOACs) including Factor Xa inhibitors (rivaroxaban, apixaban and edoxaban) and thrombin inhibitor (dabigatran) are poised to replace warfarin. Phase-3 studies and real-world evaluations have established that the safety profile of DOACs is superior to those of VKAs. However, some pharmacokinetic and pharmacodynamic interactions are expected. Herein we present a critical review of VKAs and DOACs with focus on their potential for interactions with drugs, foods, herbs and over-the-counter medications.

Probable Warfarin–Simvastatin Interaction

Objective:

To report and discuss a case of fatal cerebral hemorrhage following a switch from atorvastatin to simvastatin in a patient taking warfarin.

Case Summary:

An 82-year-old white female was admitted to the hospital because of an international normalized ratio (INR) value greater than 8, which was detected at a routine follow-up visit to monitor warfarin therapy. Four weeks earlier her lipid-lowering therapy had been switched from atorvastatin 10 mg daily to simvastatin 10 mg daily. She had been treated with 2.5 mg of warfarin daily for almost 30 years due to episodes of deep venous thrombosis and lung embolism. Her INR had been stable within the treatment range (2.0–3.5) for more than 2 years before the INR increase. Upon hospitalization, she was given 5 mg of vitamin K orally, A few hours later she lost the feeling and movement of her right arm and a computed tomography scan showed major bleeding in the left cerebral hemisphere. She died the following day.

Discussion:

One study has shown a lack of interaction between warfarin and atorvastatin. In comparison, 3 studies have shown significant increases (10–30%) in warfarin effect and/or reductions in dose requirement after starling concomitant simvastatin treatment. The interaction mechanism between simvastatin and warfarin is not known but is possibly associated with reduced elimination of warfarin. Use of the Naranjo probability scale showed that the likelihood of warfarin-induced INR increase following the switch to simvastatin was probable.

Conclusions:

Atorvastatin and simvastatin appear to differ in their potential to interact with warfarin. Clinicians should be aware of the interaction risk when starting simvastatin treatment in patients on warfarin therapy.

Drug interactions with statins

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are generally well tolerated as monotherapy. Statins are associated with two important adverse effects, asymptomatic elevation in liver enzymes and myopathy. Myopathy is most likely to occur when statins are administered with other drugs. Statins are substrates of multiple drug transporters (including OAT- -P1B1, BCRP and MDR1) and several cytochrome P450 (CYP) enzymes (including CYP3A4, CYP2C8, CYP2C19, and CYP2C9). Possible adverse effects of statins can occur due to interactions in concomitant use of drugs that substantially inhibit or induce their methabolic pathway. This review summarizes the most important interactions of statins.

Effect of Rosuvastatin on Warfarin Pharmacodynamics and Pharmacokinetics

The effect of rosuvastatin on warfarin pharmacodynamics and pharmacokinetics was assessed in 2 trials. In trial A (a randomized, double-blind, 2-period crossover study), 18 healthy volunteers were given rosuvastatin 40 mg or placebo on demand (o.d.) for 10 days with 1 dose of warfarin 25 mg on day 7. In trial B (an open-label, 2-period study), 7 patients receiving warfarin therapy with stable international normalized ratio values between 2 and 3 were coadministered rosuvastatin 10 mg o.d. for up to 14 days, which increased to rosuvastatin 80 mg if the international normalized ratio values were <3 at the end of this period. The results indicated that rosuvastatin can enhance the anticoagulant effect of warfarin. The mechanism of this drug-drug interaction is unknown. Rosuvastatin had no effect on the total plasma concentrations of the warfarin enantiomers, but the free plasma fractions of the enantiomers were not measured. Appropriate monitoring of the international normalized ratio is indicated when this drug combination is coadministered.

Identification and weighting of the most critical "real-life" drug-drug interactions with acenocoumarol in a tertiary care hospital

PURPOSE

The objective of this study was to identify the most clinically relevant drug-drug interactions (DDIs) at risk of affecting acenocoumarol safety in our tertiary care university hospital, a 2,000 bed institution.

METHODS

We identified DDIs occurring with acenocoumarol by combining two different sources of information: a 1-year retrospective analysis of acenocoumarol prescriptions and comedications from our Computerized Physician Order Entry (CPOE) system (n = 2,439 hospitalizations) and a retrospective study of clinical pharmacology consultations involving acenocoumarol over the past 14 years (1994-2007) (n = 407). We classified these DDIs using an original risk-analysis method. A criticality index was calculated for each associated drug by multiplying three scores based on mechanism of interaction, involvement in a supratherapeutic international normalized ratio (INR) (≥ 6) and involvement in a severe bleeding.

RESULTS

One hundred and twenty-six DDIs were identified and weighted. Twenty-eight drugs had a criticality index ≥ 20 and were therefore considered at high risk for interacting with acenocoumarol by increasing its effect: 75% of these drugs involved a pharmacokinetic mechanism and 14 % a pharmacodynamic mechanism. An unknown mechanism of interaction was involved in 11 % of drugs.

CONCLUSION

Twenty-eight specific drugs were identified as being at high risk for interacting with acenocoumarol in our hospital using an original risk-analysis method. Most analyzed drugs interact with acenocoumarol via a pharmacokinetic mechanism. Actions such as the implementation of alerts in our CPOE system should be specifically developed for these drugs.

A clinically significant interaction between warfarin and simvastatin is unique to carriers of the CYP2C9*3 allele

Background: Simvastatin interacts with warfarin, but the strength of the interaction varies between individual patients, indicating a genetic predisposition. Patients & methods: The influence of the CYP2C9*2 and CYP2C9*3 polymorphisms on the interaction between simvastatin and warfarin was analyzed in data from 1132 patients. Results: Simvastatin use reduced warfarin dose requirements by 29% in carriers of the CYP2C9*3 allele, compared with 5% in noncarriers. A regression model showed a significant influence of CYP2C9*3 on the drug–drug interaction, predicting a warfarin dose reduction of 25% in CYP2C9*3 heterozygotes and 43% in CYP2C9*3 homozygotes. Conclusion: Our data indicate that the CYP2C9*3 polymorphism predisposes for a pharmacologic interaction between warfarin and simvastatin.

Original submitted 5 January 2012; Revision submitted 15 February 2012

Drug and dietary interactions of warfarin and novel oral anticoagulants: an update

Clinicians and patients around the world have been intrigued by the concept of developing an oral anticoagulant with a broad therapeutic window and few drug and dietary interactions that can be administered at fixed doses with no or minimal monitoring. The recently approved oral direct thrombin inhibitor dabigatran, along with the emerging oral anti-factor Xa inhibitors, rivaroxaban, apixaban, and edoxaban, have been developed to address many of the shortcomings of warfarin therapy. As warfarin is associated with extensive food and drug interactions, there is also a need to consider such interactions with the new oral anticoagulants. While to date few drug and dietary interactions have been reported with the new oral anticoagulants, it is still early in their development and clinical use cycle. Pharmacokinetic and pharmacodynamic profiles will have to be closely accounted for when determining the likelihood of a potential drug interaction prior to therapy initiation. As the list of drugs and supplements that interact with warfarin is continuously expanding, and the knowledge on drug interactions with the novel oral anticoagulants is still in its infancy, clinicians need to be vigilant when initiating any of these agents or when any changes in the patient's medication profile occur and perform a close screening for potential drug and dietary interactions. The objective of this paper is to give an update on drug and dietary interactions with warfarin and the novel oral anticoagulants, dabigatran, rivaroxaban, apixaban, and edoxaban.

Drug-drug interaction study to assess the effects of multiple-dose pitavastatin on steady-state warfarin in healthy adult volunteers

Warfarin, an antagonist of vitamin K, which inhibits clotting factor synthesis, is prescribed for thrombosis prophylaxis and treatment and is known to have a narrow therapeutic range. Pitavastatin is a potent HMG-CoA reductase inhibitor. In this study, the influence of multiple-dose pitavastatin (4 mg once daily) on steady-state warfarin pharmacodynamic and pharmacokinetic profiles was investigated in 24 healthy male participants whose international normalized ratio (INR) was maintained by individualized doses of warfarin. The ratio of the least squares mean of prothrombin time and INR was 0.989 (90% confidence interval [CI], 0.955-1.023) and 0.993 (0.956-1.209), respectively (test: warfarin + pitavastatin; reference: warfarin only). The geometric mean ratios of C(max) and AUC were 1.034 (90% CI, 0.994-1.075) and 1.066 (1.035-1.099), respectively, for R-warfarin and 1.033 (0.995-1.073) and 1.058 (1.026-1.092), respectively, for S-warfarin. Warfarin pharmacodynamic profiles and pharmacokinetic profiles did not differ between the warfarin monotherapy and the coadministration of pitavastatin and warfarin. No drug-drug interaction between pitavastatin and warfarin was demonstrated.

Possible Amiodarone−Warfarin Interaction: A Reemphasis on a Potentially Dangerous Drug−Drug Interaction

This article reports two patients with delayed amiodarone— warfarin interaction resulting in a significant elevation in the international normalized ratio. One patient developed episodes of nosebleeds. Amiodarone is a potent inhibitor of the cytochrome P450 enzyme system. Warfarin undergoes metabolism via the same isoenzyme, potentially leading to prolongation of elevated international normalized ratio levels. A decrease in the warfarin dose is thus warranted when coadministered with amiodarone to circumvent the potential danger of this interaction, which can go unnoticed because several weeks of therapy may be necessary to discern an elevated international normalized ratio. The Naranjo probability scale indicated a possible relationship between the elevated international normalized ratio levels and the coadministration of amiodarone and warfarin. With the coadministration of warfarin and amiodarone, frequent and close monitoring of warfarin is paramount, especially in the initial weeks of therapy, in an effort to prevent supratherapeutic international normalized ratios and bleeding complications.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

The influence of co-treatment with carbamazepine, amiodarone and statins on warfarin metabolism and maintenance dose

AIMS

Warfarin is a frequently used anticoagulant drug with narrow therapeutic index and high interindividual variability in the dose requirement. We have previously shown that warfarin dose is influenced by cytochrome P450 (CYP) 2C9 genotype, age, body weight and co-treatment with drugs that interfere with warfarin metabolism. As, in many patients, drug co-treatment cannot be avoided, we investigated the effect of co-treatment with carbamazepine, amiodarone and statins on warfarin metabolism and maintenance dose.

METHODS

Caucasian patients on stable maintenance warfarin therapy with CYP2C9*1/*1 genotype (n=82) were included in the study. Plasma concentrations of (S)- and (R)-warfarin as well as warfarin hydroxylated metabolites were determined using HPLC assay and corresponding clearances of (S)- and (R)-warfarin were calculated.

RESULTS

Patients co-treated with carbamazepine (n=5) had significantly higher plasma 10-hydroxywarfarin concentrations than patients not taking any interacting drugs (n=54) (median: 0.327 microg/ml vs 0.030 microg/ml, p=0.003). (S)- and (R)-warfarin clearances were also higher in the carbamazepine co-treated group (p=0.003), as were warfarin dose requirements (median: 9.00 mg/day vs 3.86 mg/day, p=0.003). Under the conditions of this study, patients co-treated with amiodarone (n=6) did not differ significantly regarding any measured characteristic from patients with no interacting drug treatment, while patients co-treated with simvastatin or lovastatin (n=17) had lower 10-hydroxywarfarin concentration (p=0.02).

CONCLUSIONS

We confirmed important interaction between carbamazepine and warfarin metabolism which can be of major clinical importance. If treatment with carbamazepine cannot be avoided, patients taking warfarin should be frequently monitored, especially when initiating or stopping carbamazepine therapy.

Results from a rosuvastatin historical cohort study in more than 45 000 Dutch statin users, a PHARMO study

PURPOSE

Clinical benefits of statin therapy are accepted, but their safety profiles have been under scrutiny, particularly for the recently introduced statin, rosuvastatin, relating to serious adverse events involving muscle, kidney and liver. Therefore, a historical cohort study was performed to evaluate the association between rosuvastatin versus other statin use and the incidence of rhabdomyolysis, myopathy, acute renal failure and hepatic impairment.

METHODS

Incident users of rosuvastatin or other statins in 2003-2004 and a cohort of patients not prescribed statins were included from the PHARMO database of >2 million Dutch residents. Cases of hospitalisations for myopathy, rhabdomyolysis, acute renal failure or hepatic impairment were identified for these cohorts. Potential cases were validated through a multi-step process using data obtained from hospital records. Additionally, cases of all cause deaths were identified from certification alone.

RESULTS

In 2003 and 2004, 10,147 incident rosuvastatin users, 37,396 incident other statin users and 99,935 patients without statin prescriptions were included. There were 26 validated outcome events in the three cohorts including one case each of myopathy (other statin group) and rhabdomyolysis (non-treated group). There were no significant differences in the incidence of outcome events between rosuvastatin and other statin users.

CONCLUSION

This study indicated that the number of outcome events is less than 1 per 3000 person years. This study in more than 45,000 Dutch statin users suggests that rosuvastatin does not lead to an increased incidence of rhabdomyolysis, myopathy, acute renal failure or hepatic impairment compared to other statins.

Information deficits in the summary of product characteristics preclude an optimal management of drug interactions: a comparison with evidence from the literature

OBJECTIVE

To compare comprehensiveness and accuracy of drug interaction information in the German summary of product characteristics (SPC) with current evidence from the literature and to evaluate the SPC's usefulness with respect to management of drug interactions.

METHODS

Information on clinically relevant drug interactions was compared between the SPC and three standard information sources on drug interactions (DRUGDEX, Hansten/Horn's Drug Interactions Analysis and Management, Stockley's Drug Interactions) according to five consecutive criteria (inclusion, appropriateness of class labelling, effect description, management recommendation, explicit dose adjustment). Using medication data of an outpatient population (n=4,949), we determined what percentage of insufficiently characterized combinations indeed occurred in outpatients treated with combination drug therapy.

RESULTS

Only for 33% (192/579) of the evaluated combinations did SPCs provide drug interaction information equivalent to the evidence from the published literature. Of the clinically relevant drug interactions, 16% were completely missing and 51% were insufficiently characterized compared with standard sources. Explicit management recommendations were either missing or differed from standard sources in 18% of the evaluated pairs of compounds. Of these missing or insufficiently characterized combinations, 12% (47/387) were indeed prescribed to outpatients. Those drug combinations for which the interaction potential was not mentioned in the SPC were received by 0.6% (32/4,949) of patients, and 4% (192/4,949) of patients received combinations that had insufficiently characterized drug interactions.

CONCLUSIONS

If physicians only rely on SPC information for drug interactions, adverse events due to lacking management recommendations may occur. To meet the SPCs claim of being the basis of information for health professionals on how to use medicinal products safely and effectively, information on drug interactions should be thoroughly up-dated and expanded.

Rosuvastatin-acenocoumarol interaction

BACKGROUND

Previous evidence suggests that hydroxymethylglutaryl coenzyme A-reductase inhibitors (statins) might potentiate the effect of oral anticoagulants, but a MEDLINE search (key terms: stains, rosuvastatin, anticoagulants, acenocoumarol, and interaction; years: 1980-2005) revealed no reports of an interaction between rosuvastatin and acenocoumarol.

OBJECTIVE

The aim of this article was to describe a case of possible interaction between rosuvastatin and acenocoumarol.

METHODS

We report the case of a 36-year-old male patient receiving long-term oral treatment with acenocoumarol, a synthetic coumarin anticoagulant, who experienced an increase in international normalized ratio (INR) and a hematoma in the left leg approximately 45 days after the initiation of treatment with rosuvastatin.

RESULTS

After discontinuation of both drugs, an unexpectedly rapid decrease in INR was observed.

CONCLUSIONS

Based on the results of this case, a possible pharmacologic interaction between rosuvastatin and acenocoumarol should be considered. Rosuvastatin might enhance the anticoagulant effect of acenocoumarol, and a rebound effect in cases of simultaneous discontinuation of both drugs might occur. Rosuvastatin should be administered with extreme caution in patients receiving long-term acenocoumarol therapy.

Oral anticoagulant drug interactions with statins: case report of fluvastatin and review of the literature

A 67-year-old man receiving a stable maintenance dosage of warfarin experienced an increased international normalized ratio (INR) without bleeding when his atorvastatin therapy was switched to fluvastatin. His warfarin dosage was reduced and his INR stabilized. The fluvastatin was switched back to atorvastatin, and the warfarin dosage was increased to maintain the patient's goal INR. The literature supports a drug interaction between warfarin and fluvastatin due to the strong affinity of fluvastatin for the cytochrome P450 enzyme 2D6. This interaction has not been seen with atorvastatin. Lovastatin also reportedly has caused increases in INR when coadministered with warfarin. It is unclear whether simvastatin interacts with warfarin, but it may increase INRs slightly or increase serum simvastatin levels. One case report describes an interaction between simvastatin and the anticoagulant acenocoumarol, which resulted in an elevated INR. Pravastatin does not appear to interact with warfarin but has caused an increased INR when combined with the anticoagulant fluindione. Thus, until more definitive data are available, clinicians should monitor the INR closely after starting statin therapy in any patient receiving anticoagulation therapy.

Pharmacokinetic-pharmacodynamic drug interactions with HMG-CoA reductase inhibitors

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

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.

Clinically relevant differences between the statins: implications for therapeutic selection

Although the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, share a common lipid-lowering effect, there are differences within this class of drugs. The low-density lipoprotein (LDL) cholesterol-lowering efficacy, pharmacokinetic properties, drug-food interactions, and cost can vary widely, thus influencing the selection of a particular statin as a treatment option. The statins that produce the greatest percentage change in LDL cholesterol levels are atorvastatin and simvastatin. Atorvastatin and fluvastatin are least affected by alterations in renal function. Fewer pharmacokinetic drug interactions are likely to occur with pravastatin and fluvastatin, because they are not metabolized through the cytochrome P450 (3A4) system. The most cost-effective statins, based on cost per percentage change in LDL cholesterol levels, are fluvastatin, cerivastatin, and atorvastatin. Awareness of these differences may assist in the selection or substitution of an appropriate statin for a particular patient.

Warfarin therapy: a review of the literature since the Fifth American College of Chest Physicians' Consensus Conference on Antithrombotic Therapy

Evidence-based medicine is currently a fashionable term. The evidence that warfarin is safe, effective, and cost beneficial in preventing stroke in AF, DVT treatment, and DVT prophylaxis is mounting. However, the evidence that warfarin remains underutilized in these conditions is also mounting. There is new evidence that supports conservative management of overanticoagulation without bleeding. The amount of time, if any, that patients are off warfarin for various procedures is being reduced. Warfarin interactions with other agents continue to be reported so that practitioners can avoid or treat them. Even the contraindication of warfarin in pregnancy is being reexamined. Those with expertise in anticoagulation therapy have an imperative to inform colleagues about the evidence in favor of warfarin.