Cytochrome P450 drug interactions within the HMG-CoA reductase inhibitor class: are they clinically relevant?

Drug interaction potential of Ankaferd blood stopper® in human hepatocarcinoma cells

BACKGROUND

Ankaferd blood stopper® (ABS) is an herbal extract consisting of mixtures of Alpinia officinarum, Gycyrrhiza glabra, Vitis vinifera, Thymus vulgaris, and Urtica dioica plants and has been used in recent years in Turkish medicine as a hemostatic agent. Despite its extensive usage, there is no information available about the drug interaction in HepG2 cells. The current work evaluated the effect of ABS on the expression of CYP1A1-1A2, CYP2E1, and CYP3A4 isozymes that are primarily involved in drug and carcinogen metabolism.

METHODS

We selected HepG2 cells as in vitro cellular models of the human liver. The cells were treated with different concentrations of ABS [0.25%-40% (v/v)]. A crystal violet staining assay was used to determine the cytotoxicity of ABS. We examined drug-metabolizing enzymes, including 7-ethoxyresorufin O-deethylase (CYP1A1), 7-methoxyresorufin O-demethylase (CYP1A2), aniline 4-hydroxylase (CYP2E1), and erythromycin N-demethylase (CYP3A4), in vitro in HepG2 cells. The expression (mRNA, protein) levels of drug-metabolizing enzymes were analyzed by qPCR and Western blotting, respectively.

RESULTS

The EC05 and EC10 values for ABS were 0.37% and 0.52% (v/v), respectively. Therefore, 0.37% and 0.52% (v/v) doses were used for the remaining portion of this study. Investigation of the expression and activity levels revealed that CYP1A1-1A2, CYP2E1, and CYP3A4 activities were not affected by ABS significantly, with qPCR and Western blot results corroborating this result.

DISCUSSION

Our study found that the activity, mRNA, and protein expression levels of CYP isozymes did not change with the application of ABS, suggesting that when humans are exposed to ABS, there may not be any risk associated with clinical drug toxicity, cancer formation, and drug metabolism disorders in humans.

Severe Rhabdomyolysis as Complication of Interaction between Atorvastatin and Fusidic Acid in a Patient in Lifelong Antibiotic Prophylaxis: A Dangerous Combination

Atorvastatin and HMG-CoA reductase inhibitors are the most frequently used medication in the world due to very few adverse toxic side effects. One potentially life threatening adverse effect is caused by clinically significant statin induced rhabdomyolysis, either independently or in combination with fusidic acid. The patient in our case who previously had cardiac insufficiency, atrial fibrillation, and thoracic aorta aneurysm and was treated with insertion of an endovascular metallic stent in the aorta is presented in the report. He had an inoperable aortitis with an infected stent and para-aortic abscesses with no identified microorganism. The patient responded well to empirical antibiotic treatment with combination therapy of fusidic acid and moxifloxacin. This treatment was planned as a lifelong prophylactic treatment. The patient had been treated with atorvastatin for several years. He developed severe rhabdomyolysis when he was started on fusidic acid and moxifloxacin. The patient made a fast recovery after termination of treatment with atorvastatin and fusidic acid. We here report a life threatening complication of rhabdomyolysis that physicians must be aware of. This can happen either in atorvastatin monotherapy or as a complication of pharmacokinetic interaction between atorvastatin and fusidic acid.

Pharmacogenomics Implications of Using Herbal Medicinal Plants on African Populations in Health Transition

The most accessible points of call for most African populations with respect to primary health care are traditional health systems that include spiritual, religious, and herbal medicine. This review focusses only on the use of herbal medicines. Most African people accept herbal medicines as generally safe with no serious adverse effects. However, the overlap between conventional medicine and herbal medicine is a reality among countries in health systems transition. Patients often simultaneously seek treatment from both conventional and traditional health systems for the same condition. Commonly encountered conditions/diseases include malaria, HIV/AIDS, hypertension, tuberculosis, and bleeding disorders. It is therefore imperative to understand the modes of interaction between different drugs from conventional and traditional health care systems when used in treatment combinations. Both conventional and traditional drug entities are metabolized by the same enzyme systems in the human body, resulting in both pharmacokinetics and pharmacodynamics interactions, whose properties remain unknown/unquantified. Thus, it is important that profiles of interaction between different herbal and conventional medicines be evaluated. This review evaluates herbal and conventional drugs in a few African countries and their potential interaction at the pharmacogenomics level.

Reduced exposure variability of the CYP3A substrate simvastatin by dose individualization to CYP3A activity

This study aimed to demonstrate that the dose of a CYP3A substrate (simvastatin) can be adapted individually on the basis of CYP3A activity as assessed by midazolam metabolic clearance. In 18 healthy participants individual CYP3A activity was quantified using midazolam metabolic clearance both alone and during CYP3A inhibition with 40 mg ritonavir. Thereafter, simvastatin acid exposure was determined after a simvastatin standard dose (40 mg) and doses adapted to individual CYP3A activity at baseline and during CYP3A inhibition. Interindividual variability of CYP3A activity and simvastatin acid AUC0-24 was large and both correlated (r(2)  = 0.745, P < .001). The adapted simvastatin doses ranged from 25 to 80 mg and their administration reduced simvastatin variability fivefold. Despite the low adapted simvastatin dose of 12 mg during CYP3A inhibition with ritonavir, exposure increased (point estimate of 4.2 [90% CI: 3.15-5.61]) probably caused by additional OATP1B1 inhibition. CYP3A activity-based dose adaptation can be used to reduce interindividual variability in simvastatin exposure.

Rhabdomyolysis caused by an unusual interaction between azithromycin and simvastatin

Rhabdomyolysis is an uncommon but life-threatening adverse effect of simvastatin therapy. A 73-year-old male on chronic simvastatin therapy received azithromycin for acute bronchitis. He presented with weakness of all extremities with a significant increase in creatinine phosphokinase levels and acute kidney injury. Simvastatin was stopped and supportive therapy with intravenous saline and bicarbonate was initiated. The serum creatinine and creatine phosphokinase returned to baseline in the next 7 days. Two months later, simvastatin was resumed without any recurrence of symptoms. Our case report highlights the rare description of rhabdomyolysis caused by a drug interaction between simvastatin with azithromycin.

Dipeptidylpeptidase-4 inhibitors (gliptins): focus on drug-drug interactions

Patients with type 2 diabetes mellitus (T2DM) are generally treated with many pharmacological compounds and are exposed to a high risk of drug-drug interactions. Indeed, blood glucose control usually requires a combination of various glucose-lowering agents, and the recommended global approach to reduce overall cardiovascular risk generally implies administration of several protective compounds, including HMG-CoA reductase inhibitors (statins), antihypertensive compounds and antiplatelet agents. New compounds have been developed to improve glucose-induced beta-cell secretion and glucose control, without inducing hypoglycaemia or weight gain, in patients with T2DM. Dipeptidylpeptidase-4 (DPP-4) inhibitors are novel oral glucose-lowering agents, which may be used as monotherapy or in combination with other antidiabetic compounds, metformin, thiazolidinediones or even sulfonylureas. Sitagliptin, vildagliptin and saxagliptin are already on the market, either as single agents or in fixed-dose combined formulations with metformin. Other compounds, such as alogliptin and linagliptin, are in a late phase of development. This review summarizes the available data on drug-drug interactions reported in the literature for these five DDP-4 inhibitors: sitagliptin, vildagliptin, saxagliptin, alogliptin and linagliptin. Possible pharmacokinetic interferences have been investigated between each of these compounds and various pharmacological agents, which were selected because there are other glucose-lowering agents (metformin, glibenclamide [glyburide], pioglitazone/rosiglitazone) that may be prescribed in combination with DPP-4 inhibitors, other drugs that are currently used in patients with T2DM (statins, antihypertensive agents), compounds that are known to interfere with the cytochrome P450 (CYP) system (ketoconazole, diltiazem, rifampicin [rifampin]) or with P-glycoprotein transport (ciclosporin), or agents with a narrow therapeutic safety window (warfarin, digoxin). Generally speaking, almost no drug-drug interactions or only minor drug-drug interactions have been reported between DPP-4 inhibitors and any of these drugs. The gliptins do not significantly modify the pharmacokinetic profile and exposure of the other tested drugs, and the other drugs do not significantly alter the pharmacokinetic profile of the gliptins or exposure to these. The only exception concerns saxagliptin, which is metabolized to an active metabolite by CYP3A4/5. Therefore, exposure to saxagliptin and its primary metabolite may be significantly modified when saxagliptin is coadministered with specific strong inhibitors (ketoconazole, diltiazem) or inducers (rifampicin) of CYP3A4/5 isoforms. The absence of significant drug-drug interactions could be explained by the favourable pharmacokinetic characteristics of DPP-4 inhibitors, which are not inducers or inhibitors of CYP isoforms and are not bound to plasma proteins to a great extent. Therefore, according to these pharmacokinetic findings, which were generally obtained in healthy young male subjects, no dosage adjustment is recommended when gliptins are combined with other pharmacological agents in patients with T2DM, with the exception of a reduction in the daily dosage of saxagliptin when this drug is used in association with a strong inhibitor of CYP3A4/A5. It is worth noting, however, that a reduction in the dose of sulfonylureas is usually recommended when a DPP-4 inhibitor is added, because of a pharmacodynamic interaction (rather than a pharmacokinetic interaction) between the sulfonylurea and the DPP-4 inhibitor, which may result in a higher risk of hypoglycaemia. Otherwise, any gliptin may be combined with metformin or a thiazolidinedione (pioglitazone, rosiglitazone), leading to a significant improvement in glycaemic control without an increased risk of hypoglycaemia or any other adverse event in patients with T2DM. Finally, the absence of drug-drug interactions in clinical trials in healthy subjects requires further evidence from large-scale studies, including typical subjects with T2DM - in particular, multimorbid and geriatric patients receiving polypharmacy.

Statins and congestive heart failure

Despite many post hoc analyses of cardiovascular databases in recent years suggesting a benefit of statins in the prevention and treatment of congestive heart failure (HF), a prospective study of statin therapy on two clinically relevant end points--HF morbidity and survival--had not been reported until 2007. However, a large-scale prospective trial, Controlled Rosuvastatin Multinational Trial in Heart Failure (CORONA), has just reported its primary results. These results somewhat surprisingly show no survival benefit in a group of patients with ischemic systolic HF given low-dose rosuvastatin. In addition to this uncertainty generated by the results of CORONA, there remains additional uncertainty in the existing, predominantly retrospective data on statins because of the potential bias in study designs, use of post hoc subgroup analyses, and lack of mechanistic data. This review critically evaluates the recent literature in this area.

Pravastatin-induced colitis

We report an unusual case of pravastatin-induced colitis in an 80-year old lady. Onset of symptoms was noted within 48 h of starting the medication. Colonoscopy revealed diffuse ulceration throughout the colon with relative sparing of the rectum, with the biopsies showing ulceration and inflammation. The patient received a short course of steroid therapy and 5 months after stopping pravastatin, there was complete macroscopic and microscopic resolution of the colonic lesions. Drug interaction of pravastatin with amitryptiline could have resulted in this uncommon complication.

Age-related differences in the prevalence of potential drug-drug interactions in ambulatory dyslipidaemic patients treated with statins

BACKGROUND AND OBJECTIVE

Elderly patients may be at higher risk of drug-drug interactions (DDIs) because of polypharmacy. This study evaluated age-specific differences in the prevalence of clinically relevant potential DDIs (pDDIs) in ambulatory dyslipidaemic patients treated with an HMG-CoA reductase inhibitor (statin). We hypothesised that elderly patients are at higher risk for pDDIs because of the presence of more drugs and drugs with a higher potential for DDIs in this age group.

METHODS

A total of 2742 dyslipidaemic ambulatory patients treated with a statin were included in this cross-sectional study. Drug treatment was screened for clinically relevant pDDIs using an electronic drug interaction program (DRUG-REAX System).

RESULTS

The study sample consisted of 483 (17.6%) patients aged < or = 54 years, 732 (26.7%) aged 55-64 years, 924 (33.7%) aged 65-74 years and 603 (22.0%) patients aged > or = 75 years. Patients > or =75 years had significantly more pharmacologically active substances prescribed than patients aged < or =54 years (mean 5.8 vs 3.8, respectively; p < 0.001). Cardiovascular diseases such as coronary heart disease, heart failure or arrhythmias were also significantly more prevalent in patients aged > or = 75 years than in younger patients. The overall prevalence of pDDIs increased significantly from 7.9% in those aged < or = 54 years to 18.4% in patients aged > or = 75 years (p < 0.001). The frequency of both pDDIs associated with statins and non-statin pDDIs increased with age. Risk factors for pDDIs in patients aged > or = 75 years were arrhythmias, heart failure and the number of pharmacologically active substances prescribed. The more frequent prescription of cardiovascular drugs with a high potential for pDDIs (e.g. amiodarone and digoxin) in patients aged > or = 75 years was mainly responsible for the observed increases in statin and non-statin pDDIs in this age group.

CONCLUSIONS

Compared with younger patients, elderly dyslipidaemic patients are at a higher risk for clinically relevant pDDIs, mainly because of a higher number of drugs prescribed. In addition, patients aged > or = 75 years were prescribed more drugs with a high potential for DDIs, especially drugs used for the treatment of arrhythmias and heart failure. The risk for adverse reactions associated with pDDIs may often be reduced by dose adjustment, close monitoring or selection of an alternative drug.

Statins and clinical outcomes in heart failure

HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase inhibitors (statins) are well-established therapies in the prevention and treatment of cardiovascular disease, reducing all-cause mortality and cardiovascular events in many disease states. Studies have also suggested that statins given to patients after myocardial infarction improve event-free survival even in short time frames; however, evidence for the benefit of statins in established HF (heart failure) has not been demonstrated with the same rigour of a randomized clinical trial setting. In fact, clinical data examining the effect of statins in HF have been limited by the retrospective or observational nature of these analyses, examination of incompletely validated surrogate end points, small prospective studies in subgroups of HF subjects, and non-uniform doses and different statins being used. In this review, we examine the evidence for the effect of statins on mortality in HF, taking into account theoretical arguments, appropriateness of surrogate markers, animal data and analysis of the predominantly retrospective clinical data that is currently available.

Effect of polymorphic CYP3A5 genotype on the single-dose simvastatin pharmacokinetics in healthy subjects

Simvastatin, a cholesterol-lowering agent, is mainly metabolized by CYP3A4/5. The objective of this study was to investigate the effect of CYP3A5*3 genotype on the pharmacokinetics of simvastatin in humans. Twenty-two men with CYP3A5*1/*1 (n = 4), CYP3A5*1/*3 (n = 8), or CYP3A5*3/*3 (n = 10) genotypes were enrolled. Each subject ingested a 20-mg dose of simvastatin, and plasma simvastatin concentrations were measured for 12 hours after dosing. The mean (+/-SD) area under the plasma concentration-time curve for simvastatin in the CYP3A5*1/*1 carriers (4.94 +/- 2.25 ng x h/mL) was significantly lower than CYP3A5*3/*3 carriers (16.35 +/- 6.37 ng x h/mL; P = .013, Bonferroni test). The mean (+/-SD) oral clearance was also significantly different between CYP3A5*1/*1 carriers (4.80 +/- 2.35 L/h) and CYP3A5*3/*3 carriers (1.35 +/- 0.61 L/h; P < .05, Dunn's test). However, other pharmacokinetic parameters including peak plasma concentrations and half-life did not show any difference between genotype groups. These findings suggest that the polymorphic CYP3A5 gene affects the disposition of simvastatin and provides a plausible explanation for interindividual variability of simvastatin disposition.

Pharmacokinetic interactions with thiazolidinediones

Type 2 diabetes mellitus is a complex disease combining defects in insulin secretion and insulin action. New compounds called thiazolidinediones or glitazones have been developed for reducing insulin resistance. After the withdrawal of troglitazone because of liver toxicity, two compounds are currently used in clinical practice, rosiglitazone and pioglitazone. These compounds are generally used in combination with other pharmacological agents. Because they are metabolised via cytochrome P450 (CYP), glitazones are exposed to numerous pharmacokinetic interactions. CYP2C8 and CYP3A4 are the main isoenzymes catalysing biotransformation of pioglitazone (as with troglitazone), whereas rosiglitazone is metabolised by CYP2C9 and CYP2C8. For both rosiglitazone and pioglitazone, the most relevant interactions have been described in healthy volunteers with rifampicin (rifampin), which results in a significant decrease of area under the plasma concentration-time curve [AUC] (54-65% for rosiglitazone, p<0.001; 54% for pioglitazone, p<0.001), and with gemfibrozil, which results in a significant increase of AUC (130% for rosiglitazone, p<0.001; 220-240% for pioglitazone, p<0.001). The relevance of such drug-drug interactions in patients with type 2 diabetes remains to be evaluated. However, in the absence of clinical data, it is prudent to reduce the dosage of each glitazone by half in patients treated with gemfibrozil. Conversely, rosiglitazone and pioglitazone do not seem to significantly affect the pharmacokinetics of other compounds. Although some food components have also been shown to potentially interfere with drugs metabolised with the CYP system, no published study deals specifically with these possible CYP-mediated food-drug interactions with glitazones.

Pharmacokinetic drug interaction profiles of proton pump inhibitors

Proton pump inhibitors are used extensively for the treatment of gastric acid-related disorders because they produce a greater degree and longer duration of gastric acid suppression and, thus, better healing rates, than histamine H(2) receptor antagonists. The need for long-term treatment of these disorders raises the potential for clinically significant drug interactions in patients receiving proton pump inhibitors and other medications. Therefore, it is important to understand the mechanisms for drug interactions in this setting. Proton pump inhibitors can modify the intragastric release of other drugs from their dosage forms by elevating pH (e.g. reducing the antifungal activity of ketoconazole). Proton pump inhibitors also influence drug absorption and metabolism by interacting with adenosine triphosphate-dependent P-glycoprotein (e.g. inhibiting digoxin efflux) or with the cytochrome P450 (CYP) enzyme system (e.g. decreasing simvastatin metabolism), thereby affecting both intestinal first-pass metabolism and hepatic clearance. Although interactions based on the change of gastric pH are a group-specific effect and thus may occur with all proton pump inhibitors, individual proton pump inhibitors differ in their propensities to interact with other drugs and the extent to which their interaction profiles have been defined. The interaction profiles of omeprazole and pantoprazole have been studied most extensively. A number of studies have shown that omeprazole carries a considerable potential for drug interactions, since it has a high affinity for CYP2C19 and a somewhat lower affinity for CYP3A4. In contrast, pantoprazole appears to have lower potential for interactions with other medications. Although the interaction profiles of esomeprazole, lansoprazole and rabeprazole have been less extensively investigated, evidence suggests that lansoprazole and rabeprazole seem to have a weaker potential for interactions than omeprazole. Although only a few drug interactions involving proton pump inhibitors have been shown to be of clinical significance, the potential for drug interactions should be taken into account when choosing a therapy for gastric acid-related disorders, especially for elderly patients in whom polypharmacy is common, or in those receiving a concomitant medication with a narrow therapeutic index.

Endocrinology and Dialysis: Management of Lipid Abnormalities Associated with End-Stage Renal Disease

The management of lipid abnormalities in patients with end-stage renal disease (ESRD) remains controversial. Large, well-designed studies investigating the effects of dyslipidemia on cardiovascular (CV) morbidity and mortality and the role of cholesterol lowering drugs in reducing mortality in ESRD patients are lacking. While it seems reasonable to suspect that dyslipidemia and its treatment in ESRD patients will affect CV morbidity and mortality similar to that in the general population, recent studies have suggested that this may not be the case. Furthermore, the pharmacokinetics of lipid lowering drugs are altered in patients with ESRD and must be considered when treating this group of patients. This article reviews the major classes of drugs used to treat dyslipidemia, emphasizing their role in patients with ESRD.

Drug interactions of clinical importance with antihyperglycaemic agents: an update

Because management of type 2 diabetes mellitus usually involves combined pharmacological therapy to obtain adequate glucose control and treatment of concurrent pathologies (especially dyslipidaemia and arterial hypertension), drug-drug interactions must be carefully considered with antihyperglycaemic drugs. Additive glucose-lowering effects have been extensively reported when combining sulphonylureas (or the new insulin secretagogues, meglitinide derivatives, i.e. nateglinide and repaglinide) with metformin, sulphonylureas (or meglitinide derivatives) with thiazolidinediones (also called glitazones) and the biguanide compound metformin with thiazolidinediones. Interest in combining alpha-glucosidase inhibitors with either sulphonylureas (or meglitinide derivatives), metformin or thiazolidinediones has also been demonstrated. These combinations result in lower glycosylated haemoglobin (HbA(1c)), fasting glucose and postprandial glucose levels than with either monotherapy. Even if modest pharmacokinetic interferences have been reported with some combinations, they do not appear to have important clinical consequences. No significant adverse effects, except a higher risk of hypoglycaemic episodes that may be attributed to better glycaemic control, occur with any combination. Challenging the classical dual therapy with sulphonylurea plus metformin, there is a recent trend to use alternative dual combinations (sulphonylurea plus thiazolidinedione or metformin plus thiazolidinedione). In addition, triple therapy with the addition of a thiazolidinedione to the metformin-sulphonylurea combination has been recently evaluated and allows glucose targets to be reached before insulin therapy is considered. This triple therapy appears to be safe, with no deleterious drug-drug interactions being reported so far.Potential interferences may also occur between glucose-lowering agents and other drugs, and such drug-drug interactions may have important clinical implications. Relevant pharmacological agents are those that are widely coadministered in diabetic patients (e.g. lipid-lowering agents, antihypertensive agents); those that have a narrow efficacy/toxicity ratio (e.g. digoxin, warfarin); or those that are known to induce (rifampicin [rifampin]) or inhibit (fluconazole) the cytochrome P450 (CYP) system. Metformin is currently a key compound in the pharmacological management of type 2 diabetes, used either alone or in combination with other antihyperglycaemics. There are no clinically relevant metabolic interactions with metformin, because this compound is not metabolised and does not inhibit the metabolism of other drugs. In contrast, sulphonylureas, meglitinide derivatives and thiazolidinediones are extensively metabolised in the liver via the CYP system and thus, may be subject to drug-drug metabolic interactions. Many HMG-CoA reductase inhibitors (statins) are also metabolised via the CYP system. Even if modest pharmacokinetic interactions may occur, it is not clear whether drug-drug interactions between oral antihyperglycaemic agents and statins may have clinical consequences regarding both efficacy and safety. In contrast, a marked pharmacokinetic interference has been reported between gemfibrozil and repaglinide and, to a lesser extent, between gemfibrozil and rosiglitazone. This leads to a drastic increase in plasma concentrations of each antihyperglycaemic agent when they are coadministered with the fibric acid derivative, and an increased risk of adverse effects. Some antihypertensive agents may favour hypoglycaemic episodes when co-prescribed with sulphonylureas or meglitinide derivatives, especially ACE inhibitors, but this effect seems to result from a pharmacodynamic drug-drug interaction rather than from a pharmacokinetic drug-drug interaction. No, or only modest, interferences have been described with glucose-lowering agents and other pharmacological compounds such as digoxin or warfarin. The effects of inducers or inhibitors of CYP isoenzymes on the metabolism and pharmacokinetics of the glucose-lowering agents of each pharmacological class has been tested. Significantly increased (with CYP inhibitors) or decreased (with CYP inducers) plasma levels of sulphonylureas, meglitinide derivatives and thiazolidinediones have been reported in healthy volunteers, and these pharmacokinetic changes may lead to enhanced or reduced glucose-lowering action, and thus hypoglycaemia or worsening of metabolic control, respectively. In addition, some case reports have evidenced potential drug-drug interactions with various antihyperglycaemic agents that are usually associated with a higher risk of hypoglycaemia.

Statin-induced rhabdomyolysis

Simvastatin and other HMG-CoA reductase inhibitors (statins) are one of the most frequently prescribed class of medications in the United States, with over 15 million Americans taking these drugs. Relatively rare adverse effects related to the known toxic effects of these drugs are more common than generally realized. Clinically significant statin-induced rhabdomyolysis is an uncommon but life-threatening adverse effect. We describe a case of simvastatin-induced rhabdomyolysis. Current knowledge of the pharmacology of the HMG-CoA reductase inhibitors and the drug interactions that potentiate these adverse effects are discussed. The clinical features of rhabdomyolysis and current treatment recommendations are presented.

Interacciones medicamentosas. Nuevos aspectos

A drug interaction is the quantitative or qualitative modification of the effect of a drug by the simultaneous or successive administration of a different one. The simultaneous administration of several medicines to the same patient can facilitates their appearance. It is difficult to determine their incidence, but it is related to the number of drugs administered simultaneously. Although it is impossible to remember all the clinical relevant interactions, to bare in mind their existence and the possible mechanisms of production can help to identify them and to contribute to their prevention. The most frequent interactions related with clinical problems are the pharmacokinetic ones, mainly those related to the metabolism through the cytochrome P450 system or the presystemic clearance by means of the P-glycoprotein and other drug transporters. Interactions between drugs and grapefruit juice or St John's wort are frequent and it is important to bear in mind in clinical practice.

The role of transporters in drug interactions

Transport proteins play an important role in the adsorption, distribution and elimination of a wide variety of drugs. Therefore, it is not surprising that transporter-based drug interactions can occur in the clinic. These interactions can lead to changes in toxicity and/or efficacy of the affected drug. Here, we review such interactions and ask if these interactions could have been predicted from in vitro data. Conducting such in vitro-in vivo correlation is important for predicting future transporter-based drug interactions.

In vivo and in vitro characterization of skeletal muscle metabolism in patients with statin-induced adverse effects

OBJECTIVE

Statins (3-hydroxymethylglutaryl-coenzyme A reductase inhibitor) are widely used to treat hypercholesterolemia. They are generally well tolerated, but myotoxic effects have been reported and the corresponding mechanisms are still a matter of debate. The aim of the present study was to determine whether impairment of calcium homeostasis and/or mitochondrial impairment could account for the adverse effects of statins in skeletal muscle.

METHODS

Eleven patients with increased creatine kinase levels and myalgias after statin treatment were evaluated using in vitro contracture tests (IVCTs), histology, and 31P magnetic resonance spectroscopy (31P-MRS).

RESULTS

IVCT results were abnormal in 7 of the 9 patients, indicating an impaired calcium homeostasis. The 31P-MRS investigation disclosed no anomaly at rest, and the aerobic function assessed during the postexercise recovery period was normal. On the contrary, the pH recovery kinetics was significantly slowed down as indicated by a reduced proton efflux, which could be ultimately linked to a failure of calcium homeostasis. Overall, our observations indicate a normal mitochondrial function and raise the possibility that statins may unmask a latent pathology involving an impairment of calcium homeostasis such as malignant hyperthermia (MH).

CONCLUSION

In case of susceptibility to MH, statins treatment must be administered with caution, and signs of adverse effects should be checked.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.

Drug–drug interactions in oncology: Why are they important and can they be minimized?

Adverse drug-drug interactions are a major cause of morbidity and mortality. Cancer patients are at particularly high risk of such interactions because they commonly receive multiple medications, including cytotoxic chemotherapy, hormonal agents and supportive care drugs. In addition, the majority of cancer patients are elderly, and so require medications for co-morbid conditions such as cardiovascular, gastrointestinal, and rheumatological diseases. Furthermore, the age-related decline in hepatic and renal function reduces their ability to metabolize and clear drugs and so increases the potential for toxicity. Not all drug-drug interactions can be predicted, and those that are predictable are not always avoidable. However, increased awareness of the potential for these interactions will allow healthcare providers to minimize the risk by choosing appropriate drugs and also by monitoring for signs of interaction. This review considers the basic principles of drug-drug interactions, and presents specific examples that are relevant to oncology.

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.

Safety of statins: focus on clinical pharmacokinetics and drug interactions

Statin monotherapy is generally well tolerated, with a low frequency of adverse events. The most important adverse effects associated with statins are myopathy and an asymptomatic increase in hepatic transaminases, both of which occur infrequently. Because statins are prescribed on a long-term basis, however, possible interactions with other drugs deserve particular attention, as many patients will typically receive pharmacological therapy for concomitant conditions during the course of statin treatment. This review summarizes the pharmacokinetic properties of statins and emphasizes their clinically relevant drug interactions.

Rhabdomyolysis in Association with Simvastatin and Amiodarone

OBJECTIVE:

To report a case of severe myopathy associated with concomitant simvastatin and amiodarone therapy.

CASE SUMMARY:

A 63-year-old white man with underlying insulin-dependent diabetes, recent coronary artery bypass surgery, and postoperative hemiplegia was treated with aspirin, metoprolol, furosemide, nitroglycerin, and simvastatin. Due to recurrent atrial fibrillation, oral anticoagulation with phenprocoumon and antiarrhythmic treatment with amiodarone were initiated. Four weeks after starting simvastatin 40 mg/day and 2 weeks after initiating amiodarone 1 g/day for 10 days, then 200 mg/day, he developed diffuse muscle pain with generalized muscular weakness. Laboratory investigations revealed a significant increase of creatine kinase (CK) peaking at 40 392 U/L. Due to a suspected drug interaction of simvastatin with amiodarone, both drugs were stopped. CK normalized over the following 8 days, and the patient made an uneventful recovery. An objective causality assessment revealed that the myopathy was probably related to simvastatin.

DISCUSSION:

Myopathy is a rare but potentially severe adverse reaction associated with statins. Besides high statin doses, concomitant use of fibrates, defined comorbidities, and concurrent use of inhibitors of cytochrome P450 are important additional risk factors. This is especially relevant if statins predominantly metabolized by CYP3A4 are combined with inhibitors of this isoenzyme. Amiodarone is a potent inhibitor of several different CYP isoenzymes, including CYP3A4.

CONCLUSIONS:

Avoiding the concomitant use of drugs with the potential to inhibit CYP-dependent metabolism (eg, amiodarone) or elimination of statins may decrease the risk of statin-associated myopathy. Alternatively, if drug therapy with a potent CYP inhibitor is inevitable, choosing a statin without relevant CYP metabolism (eg, pravastatin) should be considered.

Metabolism, excretion, and pharmacokinetics of rosuvastatin in healthy adult male volunteers

BACKGROUND

Rosuvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A-reductase inhibitor, or statin, that has been developed for the treatment of dyslipidemia.

OBJECTIVE

This study assessed the metabolism, excretion, and pharmacokinetics of a single oral dose of radiolabeled rosuvastatin ([14C]-rosuvastatin) in healthy volunteers.

METHODS

This was a nonrandomized, open-label, single-day trial. Healthy adult male volunteers were given a single oral dose of [14C]-rosuvastatin 20 mg (20 mL [14C]-rosuvastatin solution, nominally containing 50 microCi radioactivity). Blood, urine, and fecal samples were collected up to 10 days after dosing. Tolerability assessments were made up to 10 days after dosing (trial completion) and at a follow-up visit within 14 days of trial completion.

RESULTS

Six white male volunteers aged 36 to 52 years (mean, 43.7 years) participated in the trial. The geometric mean peak plasma concentration (C(max)) of rosuvastatin was 6.06 ng/mL and was reached at a median of 5 hours after dosing. At C(max), rosuvastatin accounted for approximately 50% of the circulating radioactive material. Approximately 90% of the rosuvastatin dose was recovered in feces, with the remainder recovered in urine. The majority of the dose (approximately 70%) was recovered within 72 hours after dosing; excretion was complete by 10 days after dosing. Metabolite profiles in feces indicated that rosuvastatin was excreted largely unchanged (76.8% of the dose). Two metabolites-rosuvastatin-5S-lactone and N-desmethyl rosuvastatin-were present in excreta. [14C]-rosuvastatin was well tolerated; 2 volunteers reported 4 mild adverse events that resolved without treatment.

CONCLUSIONS

The majority of the rosuvastatin dose was excreted unchanged. Given the absolute bioavailability (20%) and estimated absorption (approximately 50%) of rosuvastatin, this finding suggests that metabolism is a minor route of clearance for this agent.

Early detection of drug interactions utilizing a computerized drug prescription handling system-focus on cerivastatin-gemfibrozil

OBJECTIVES

Based on the recent cerivastatin experience, we retrospectively evaluated the effect of notifying a drug alert utilizing a computerized drug-handling system.

METHODS

The evaluation was carried out during three periods: period I corresponded to all prescriptions issued during April, 2001 ("baseline period"), before the Spanish Drug Agency issued alerts on the concomitant therapy with cerivastatin and gemfibrozil; period II (June) corresponded to a time in which a first informative note had been released; and period III (July) after the second warning alert was issued.

RESULTS

Data collected included the reading of 2,693,656 drug prescriptions, 1,937,083 (71.9%) of which contained patient information. Forty-four patients received combined therapy with cerivastatin and gemfibrozil over the three periods, yielding 55 exposures: 27 during the baseline period, and 28 between periods II and III, when the alert bulletins had already been released. Moreover, 41.6% of doctors included in the follow-up repeated the hazardous prescription during those two periods.

CONCLUSIONS

The effect of the informative notes about the risk of prescribing cerivastatin and gemfibrozil concomitantly on doctors' prescribing habits was limited. The system for screening information from drug prescriptions presented herein allows the early detection of drug interactions by identifying the doctors who issue hazardous prescriptions as well as patients at the highest risk of adverse drug reactions, thus allowing a personal feedback with both of them.

Drug-induced and toxic myopathies

Drug-induced myopathies and, more rarely, rhabdomyolysis, are a common biological and clinical setting for clinical rheumatologists. The focus of this chapter is to review (i) the clinical presentation and management of these adverse drug reactions (ADR) according to pain and associated neurological symptoms, (ii) the common drugs prescribed by rheumatologists which may induce reactions such as ADR, with special reference to new drugs, (iii) the pathological classification associated with specific patterns, and (iv) the risk factors leading to myotoxicity (including genetic predisposition). Specific features to be reviewed include macrophage myofasciitis and biological agents of major importance when considering terrorist attacks with biological weapons. When diagnosis is suspected, discontinuation of the putative drug(s) is mandatory and should be carefully monitored.