A mutation in the drug transporter gene ABCC2 associated with impaired methotrexate elimination

Human multidrug resistance protein 2 (MRP2, encoded by ABCC2) is involved in active efflux of anionic drugs such as methotrexate. MRP2 is expressed on the luminal side of hepatocytes and renal proximal tubular cells, indicating an important role in drug elimination. We postulated that loss-of-function mutations in ABCC2, which are involved in the Dubin-Johnson syndrome, may be associated with impaired methotrexate elimination and an increased risk of toxicity. We studied the biological phenotype and ABCC2 coding sequence in a patient receiving a high-dose methotrexate infusion for large B-cell lymphoma and who had an unusual pharmacokinetic profile, mainly characterized by a three-fold reduction in the methotrexate elimination rate. This resulted in severe methotrexate over-dosing and reversible nephrotoxicity. An inversion of the urinary coproporphyrin isomer I/III ratio (a specific biological marker of the Dubin-Johnson syndrome) was observed in this patient. Genetic analysis of ABCC2 identified a heterozygous mutation replacing a highly conserved arginine by glycine in the cytoplasmic part of the second membrane-spanning domain (position 412 of MRP2), a region associated with substrate affinity. This genetic variant was not found in a control population. Functional analysis in transiently transfected Chinese hamster ovary cells revealed a loss of transport activity of the G412 MRP2 mutant protein. An ABCC2 mutation altering MRP2-mediated methotrexate transport and resulting in impaired drug elimination and subsequent renal toxicity was identified. Candidates for methotrexate therapy should be considered for MRP2 functional testing.

[Tubular transporters OAT1 and MRP2 and clearance of adefovir]

Adefovir is transported by the organic anion transporter (OAT1) and the multidrug resistant protein (MRP2, 4 and 5). We studied adefovir clearance in rat after inhibition of transporters by probenecid and in TR- rats, in which MRP2 is lacking. After treatment by probenecid or placebo, pharmacokinetics of adefovir 10 mg/kg was studied via population modeling (NONMEM). The fraction of drug excreted in the urine was low. Renal clearance of adefovir was significantly lower (P < 0.05) in probenecid TR- rats (0.03 +/- 0.02 l/hour) than in normal control (0.09 +/- 0.05 l/hour), in normal probenecid (0.10 +/- 0.07 l/hour) and in TR- control rats (0.13 +/- 0.07 l/hour). In vivo in rats MRP2 mutation alone did not affect adefovir clearance suggesting that MRP2 does not play a critical role in the secretion of adefovir. Additional pharmacological inhibition of transporters decreased renal clearance, which may reflect inhibition of compensating transport mechanisms activated when MRP2 is lacking.

Drug eluting stents: an updated meta-analysis of randomised controlled trials

OBJECTIVE

To confirm the overall benefit of drug eluting stents (DES), to evaluate the effect of different DES, and to assess the global safety of DES compared with bare stents through a meta-analysis of randomised controlled trials.

METHODS

Randomised controlled trials comparing sirolimus and derivates or paclitaxel and derivates eluting stents versus bare stents. Binary restenosis and major adverse cardiac events (MACE) were chosen as primary end points. Death, Q wave myocardial infarction (MI), and stent thrombosis up to 12 months' follow up were also analysed.

RESULTS

MACE overall occurrence was highly reduced with DES from 19.9% to 10.1% (odds ratio (OR) 0.46, 95% confidence interval (CI) 0.41 to 0.52, p < 0.001). A significant heterogeneity (p < 0.001) was found between subgroups according to the drug: MACE OR was 0.28 (95% CI 0.22 to 0.35) in the sirolimus subgroup and 0.62 (95% CI 0.53 to 0.73) in the paclitaxel subgroup. Restenosis was also highly reduced from 31.7% with bare stents to 10.5% with DES (OR 0.25, 95% CI 0.22 to 0.29, p < 0.001) with a similar heterogeneity between subgroups. Mortality, Q wave MI, and stent thrombosis were not significantly different between DES and control group, whereas Q wave MI and stent thrombosis tended to be more frequent with paclitaxel.

CONCLUSION

This meta-analysis confirms the overall benefit of DES on restenosis and MACE with significant heterogeneity between drugs, suggesting higher efficacy of sirolimus eluting stents. Additional data with longer follow up and in high risk populations are needed to clarify issues on stent thrombosis.

Effect on survival and hospitalization of initiating treatment for chronic heart failure with bisoprolol followed by enalapril, as compared with the opposite sequence: results of the randomized Cardiac Insufficiency Bisoprolol Study (CIBIS) III

BACKGROUND

In patients with chronic heart failure (CHF), a beta-blocker is generally added to a regimen containing an angiotensin-converting-enzyme (ACE) inhibitor. It is unknown whether beta-blockade as initial therapy may be as useful.

METHODS AND RESULTS

We randomized 1010 patients with mild to moderate CHF and left ventricular ejection fraction < or =35%, who were not receiving ACE inhibitor, beta-blocker, or angiotensin receptor blocker therapy, to open-label monotherapy with either bisoprolol (target dose 10 mg QD; n=505) or enalapril (target dose 10 mg BID; n=505) for 6 months, followed by their combination for 6 to 24 months. The 2 strategies were blindly compared with regard to the combined primary end point of all-cause mortality or hospitalization and with regard to each of these end point components individually. Bisoprolol-first treatment was noninferior to enalapril-first treatment if the upper limit of the 95% confidence interval (CI) for the absolute between-group difference was <5%, corresponding to a hazard ratio (HR) of 1.17. In the intention-to-treat sample, the primary end point occurred in 178 patients allocated to bisoprolol-first treatment versus 186 allocated to enalapril-first treatment (absolute difference -1.6%, 95% CI -7.6 to 4.4%, HR 0.94; 95% CI 0.77 to 1.16). In the per-protocol sample, 163 patients allocated to bisoprolol-first treatment had a primary end point, versus 165 allocated to enalapril-first treatment (absolute difference -0.7%, 95% CI -6.6 to 5.1%, HR 0.97; 95% CI 0.78 to 1.21). With bisoprolol-first treatment, 65 patients died, versus 73 with enalapril-first treatment (HR 0.88; 95% CI 0.63 to 1.22), and 151 versus 157 patients were hospitalized (HR 0.95; 95% CI 0.76 to 1.19).

CONCLUSIONS

Although noninferiority of bisoprolol-first versus enalapril-first treatment was not proven in the per-protocol analysis, our results indicate that it may be as safe and efficacious to initiate treatment for CHF with bisoprolol as with enalapril.

Captopril-furosemide survival study in experimental heart failure

The strategy of diuretic drug administration remains to be defined in heart failure as experimental and clinical evidence have clearly established the benefit of neurohormonal blockade. The impact of addition of diuretic treatment to angiotensin-converting enzyme inhibition on survival remains to be demonstrated. The objectives of the study were to evaluate cardiovascular and renal effects of addition of diuretic treatment to captopril (2 g/L, in drinking water), on survival, on the experimental model of heart failure. Rats were followed for 10 months after coronary ligation. Echocardiographic, hemodynamic, morphometry and renal function investigations were then performed on surviving rats. Survival (from 34 to 61%), diuresis and natriuresis were significantly improved compared to control group only in animals treated with a combination of captopril + furosemide. In treated group: cardiac dimensions were reduced with left ventricular fractional shortening significantly increased in combination group (from 22.4 to 28%); captopril + furosemide animals had highest heart rate and lowest systolic and diastolic blood pressures; body and heart weight were reduced, but kidney weight was significantly increased with furosemide (1.7 g in control vs. 2 g in capto + furo); plasma renin activity and angiotensin 1 were greatly increased, and moderately stimulated in control. In conclusion, this combination of drugs significantly improved cardiac remodeling and survival of animals, increased diuresis and natriuresis despite stimulation of plasma renin activity and kidney hypertrophy.

Prognostic benefit of beta-blockers in patients not receiving ACE-Inhibitors

AIMS

Beta-blockers (BBs) confer significant prognostic benefit in patients (pts) with systolic chronic heart failure (CHF). However, major trials have thus far studied BBs mainly in addition to ACE-Inhibitors or angiotensin receptor blockers (ARBs) as background therapy. The magnitude of the prognostic benefit of BBs in the absence of ACE-I or ARB has not as yet been determined.

METHODS AND RESULTS

We performed a meta-analysis of all placebo-controlled BB studies in patients with CHF (n>200). Trials were identified via Medline literature searches, meeting abstracts, and contact with study organizations. Results for all-cause mortality and death or heart failure hospitalization were pooled using the Mantel-Haenszel (fixed effects) method. The impact of BB therapy on all-cause mortality in CHF, in the absence (4.8%) and presence (95.2%) of ACE-I (or ARB), was determined from six trials of 13 370 patients. The risk ratio (RR) for BBs vs. placebo was 0.73 [95% confidence interval (CI) 0.53-1.02] in the absence of ACE-I or ARB at baseline, compared with a RR of 0.76 (95% CI 0.71-0.83) in the presence of these agents. When ACE-Inhibitors were analysed in the same way (pre-BB), a RR of 0.89 (0.80-0.99) vs. placebo was observed in studies of >90 days. The impact of BB therapy on death or HF hospitalization in systolic CHF, in the absence and presence of ACE-I, was determined from three trials of 8988 patients. The RR for BBs vs. placebo was 0.81 (95% CI 0.61-1.08) in the absence of ACE-I or ARB at baseline, compared with a RR of 0.78 (95% CI 0.74-0.83) in the presence of these agents. When ACE-Is were analysed in the same way (pre-BB), a RR of 0.85 (95% CI 0.78-0.93) vs. placebo was observed in studies of >90 days.

CONCLUSION

The magnitude of the prognostic benefit conferred by BBs in the absence of ACE-I appears to be similar to those of ACE-Is in systolic CHF. These data therefore suggest that either ACE-Is or BBs could be used as first-line neurohormonal therapy in patients with systolic CHF. Prospective studies directly comparing these agents are required to definitively address this issue.

Population pharmacokinetics of tacrolimus in full liver transplant patients: modelling of the post-operative clearance

OBJECTIVE

To investigate the population pharmacokinetics of tacrolimus in an adult liver transplant cohort using routine drug monitoring data and to identify patient characteristics that influence pharmacokinetic parameters.

METHODS

Tacrolimus pharmacokinetics was studied in 37 adult patients using a population approach performed with NONMEM.

RESULTS

A one-compartment open model with linear absorption and elimination adequately described the data. The apparent clearance (CL) was approximately zero in the immediate post-operative days (PODs) and then rapidly increased as a function of POD to reach a plateau. This was modelled as a sigmoid relationship with the characteristic parameters CL(max) (plateau), TCL(50) (time to obtain 50% of the plateau) and gamma (coefficient of sigmoidicity). This clearance model was thought to describe the hepatic function regeneration after transplantation. Typical population estimates (percentage inter-individual variability) of CL(max), TCL50, and gamma and apparent distribution volumes (V) were 36 l/h (43%), 6.3 days (33%), and 4.9 l and 1870 l (49%), respectively. The CL(max) was negatively related to plasma albumin, and TCL50 was positively related to aspartate amino transferase (ASAT). Bayesian estimations performed at different POD times indicated that acceptable precisions in individual pharmacokinetic predictions could be obtained after the 15th POD.

CONCLUSION

Tacrolimus clearance modelling showed that there was a large variation in individual CL estimates up to the 15th day post-surgery. After this period, the mean error resulting from the Bayesian estimation was strongly decreased and this estimation method could be applicable and should limit tacrolimus monitoring.

Inhibition of catecholamine-induced cardiac fibrosis by an aldosterone antagonist

In heart failure, the renin-angiotensin-aldosterone and the sympathetic systems are overactivated and lead to formation of cardiac fibrosis, which contributes to the aggravation of cardiac function. The aim of the present study was to evaluate the role of aldosterone and angiotensin II on formation of left ventricular fibrosis induced by chronic beta-adrenergic stimulation with isoproterenol (iso) in the rat heart failure model induced by myocardial infarction (MI). Rats were submitted to chronic treatment with either the aldosterone receptor antagonist potassium canrenoate (pc, 20 mg/kg/d) or both aldosterone and angiotensin II receptor antagonists with addition of losartan (los, 10 mg/kg/d). Isoproterenol induced cardiac hypertrophy, which was completely inhibited by potassium canrenoate alone in atria and by potassium canrenoate plus losartan in infarcted ventricles. Isoproterenol also induced cardiac fibrosis, which was completely inhibited in infarcted rats by potassium canrenoate alone in right and left ventricles. In left ventricle, extent of fibrosis was, for control MI, 1.30 +/- 0.34%; MI + iso, 2.50 +/- 0.27%; MI + iso + pc, 0.82 +/- 0.11%; and MI + iso + pc + los, 1.47 +/- 0.31%. The deleterious effects of beta-adrenoceptor stimulation on cardiac fibrosis seem therefore to involve aldosterone action. These results suggest a transregulation between the adrenergic and mineralocorticoid pathways, most likely at the nucleus level, with activation of profibrotic genes.

Dosing strategy in patients with renal failure receiving enoxaparin for the treatment of non-ST-segment elevation acute coronary syndrome

BACKGROUND

Enoxaparin therapy is recommended for the initial treatment of patients with non-ST-segment elevation acute coronary syndrome. However, little dosing information is available regarding the use of enoxaparin in patients with renal impairment.

METHODS

We conducted a population pharmacokinetic analysis using anti-Xa activities measured in 532 patients (normal renal function in 34%, mild renal impairment in 36%, moderate renal impairment in 20%, and severe renal impairment in 10%) receiving subcutaneous enoxaparin (mean weight-corrected dose [+/-SD], 0.83 +/- 0.19 mg x kg(-1) x 12 h(-1) for an acute coronary syndrome. Simulations were then performed to develop a dosing strategy for patients with renal impairment.

RESULTS

A 1-compartment model with first-order kinetics best fit the data. The covariate analysis showed that enoxaparin clearance was related to renal function and volume of distribution to total body weight. Enoxaparin clearance was decreased by 31% in patients with moderate renal impairment and by 44% in patients with severe renal impairment, resulting in a significant accumulation with the use of the standard 1 mg . kg(-1) x 12 h(-1) dosing regimen. Simulations showed that a first unadjusted dose of 1 mg/kg followed by a regimen of 0.8 mg . kg(-1) x 12 h(-1) in patients with moderate renal impairment or 0.66 mg . kg(-1) x 12 h(-)1 in patients with severe renal impairment should avoid accumulation of enoxaparin and keep peak anti-Xa activities between 0.5 and 1.2 IU/mL for a large majority of patients.

CONCLUSIONS

An enoxaparin dosage reduction should be considered in acute coronary syndrome patients with creatinine clearance lower than 50 mL/min. A simple dosing protocol for enoxaparin to avoid significant accumulation in patients with moderate or severe renal impairment is proposed.

Low-molecular-weight heparin vs. unfractionated heparin in percutaneous coronary intervention: A combined analysis

This meta-analysis assessed the rates of the efficacy and safety endpoints with intravenous low-molecular-weight heparin (LMWH) compared with unfractionated heparin (UFH) in patients undergoing percutaneous coronary intervention (PCI). Subcutaneous LMWH has compared favorably with UFH, but limited experience exists with intravenous LMWH for immediate anticoagulation in PCI. The meta-analysis included data from eight randomized trials in which patients received LMWH (n = 1,037) or UFH (n = 978) during PCI. Seven additional nonrandomized studies/registries were analyzed to assess the efficacy and safety of LMWH during PCI. Efficacy endpoints were ischemic events (usually a composite of death, myocardial infarction, and urgent revascularization) and the safety endpoint was bleeding (major, minor, or all bleeding). In the randomized studies, LMWH was comparable with UFH in terms of efficacy (6.2% vs. 7.5%) and major bleeding (0.9% vs. 1.8%). The analysis of pooled data, randomized or not, suggests potential improved efficacy (5.8% vs. 7.6%) and reduced major bleeding (0.6% vs. 1.8%) with LMWH (n = 3,787) compared with UFH (n = 978). During PCI, intravenous LMWH without coagulation monitoring has the potential to be at least as safe and efficacious as intravenous UFH. Further studies of LMWHs in PCI are therefore required.

Bisoprolol and hydrochlorothiazide effects on cardiovascular remodeling in spontaneously hypertensive rats

Anti-hypertensive agents may differently stimulate compensatory neuro-hormonal mechanisms and induce different effects on the cardiovascular remodeling and function. The combination of low doses of the two synergistic drugs may lead to a lesser activation of counter regulatory mechanisms and could provide optimal therapeutic benefit. We evaluated on spontaneously hypertensive rats the effect of 3-week period of anti-hypertensive treatment. Rats were divided into four groups: control, bisoprolol (100 mg kg-1), hydrochlorothiazide (10 mg kg-1), and their combination with low doses (10 and 1 mg kg-1, respectively). The effects of treatment were evaluated on neuro-hormonal stimulation, cardiac and vascular structure and function. The combination had synergistic anti-hypertensive effects and significantly reduced heart rate and blood pressure but to a lower extent compared with bisoprolol 100 mg kg-1. Combination therapy was associated with a lower renin activation compared to hydrochlorothiazide alone and improved endothelial function. Cardiovascular remodeling differed between the groups: with bisoprolol, cardiac hypertrophy was reduced; with the combination therapy, the aortic media/lumen ratio was most increased. The consequent shear stress reduction may explain the associated endothelial function improvement. Such favourable cardiovascular remodeling with diuretic-beta-blockade combination may participate to the long-term cardiovascular protection during anti-hypertensive treatment.

Safety of hydroxychloroquine in pregnant patients with connective tissue diseases. Review of the literature

Hydroxychloroquine (HCQ) is widely used in the treatment of systemic lupus erythematosus (SLE). Even if it is generally agreed that pregnancy per se increases disease activity in patients with SLE and that withdrawal of HCQ at the onset of pregnancy may result in exacerbation of SLE, use of HCQ during pregnancy has remained controversial for a long time. Parke was the first to propose continuation of HCQ throughout gestation. Currently, more than 250 pregnancies resulting in live births have been reported and no increase in the rate of birth defects have been demonstrated. When studied, no retinal toxicity and ototoxicity have been found. Data concerning lactation and HCQ treatment are rare. However, the amount of HCQ received by children through lactation seems very low. In conclusion, HCQ should probably be maintained throughout pregnancy in patients with SLE and it does not seem necessary to advise against breastfeeding.

[From ischaemia to heart failure: heart rate--actor or stamper?]

The heart rate in sinus rhythm depends on If current-induced automaticity of sinus node cells. Such a current is activated by hyperpolarisation and is modulated by influences from sympathetic and para-sympathetic tones. There are established prognostic values for the baseline heart rate and its variability in coronary heart disease and heart failure. However, heart rate per se directly modulates myocardial oxygen consumption and cardiac contractility by interfering with the excitation-contraction coupling. The therapeutic implications of pharmacological modulation of the heart rate are important mainly for slowing the heart rate, as illustrated by the use of calcium antagonists in coronary heart disease and beta-blockers in both coronary heart disease and heart failure. The possibility of a direct action on sinusal automaticity by drugs such as ivabradine, an If channel blocker, reveals new therapeutic perspectives. Indeed, a benefit of combination therapy with these drugs and beta-blockers should be lower heart rate values than can be attained with maximally tolerated doses of beta-blockers.

[Clinical trials of beta-blockers in heart failure: history, overview and future prospects]

Although beta-blockers have been classically contraindicated in heart failure patients, their administration at progressively increasing doses provides long-term benefit in such patients with altered left ventricular function, and prevents the direct and indirect deleterious cardiac effects of catecholamines. By improving left ventricular function and preventing severe arrhythmias, beta-blockade improves survival, reduces the occurrence of sudden death and hospital admissions for worsening heart failure. The degree of benefit is dose dependent, although few prospective data confirm this fact. Among tested compounds, bisoprolol, metoprolol and carvedilol have produced similar improvements in survival with a 34% reduction in mortality in large-scale clinical trials. Bucindolol, however, did not significantly improve survival in the BEST trial. Different hypotheses may explain such results. In terms of therapeutic strategy, beta-blocker treatment must be initiated in stabilised patients already receiving diuretics and an angiotensin-converting enzyme inhibitor. Ongoing studies are evaluating the potential benefit of starting treatment first with beta-blockers in order to better prevent sudden death, particularly as this most often occurs in the early stages of the disease.

Randomized trial to determine the effect of nebivolol on mortality and cardiovascular hospital admission in elderly patients with heart failure (SENIORS)

AIMS

Large randomized trials have shown that beta-blockers reduce mortality and hospital admissions in patients with heart failure. The effects of beta-blockers in elderly patients with a broad range of left ventricular ejection fraction are uncertain. The SENIORS study was performed to assess effects of the beta-blocker, nebivolol, in patients >/=70 years, regardless of ejection fraction.

METHODS AND RESULTS

We randomly assigned 2128 patients aged >/=70 years with a history of heart failure (hospital admission for heart failure within the previous year or known ejection fraction </=35%), 1067 to nebivolol (titrated from 1.25 mg once daily to 10 mg once daily), and 1061 to placebo. The primary outcome was a composite of all cause mortality or cardiovascular hospital admission (time to first event). Analysis was by intention to treat. Mean duration of follow-up was 21 months. Mean age was 76 years (SD 4.7), 37% were female, mean ejection fraction was 36% (with 35% having ejection fraction >35%), and 68% had a prior history of coronary heart disease. The mean maintenance dose of nebivolol was 7.7 mg and of placebo 8.5 mg. The primary outcome occurred in 332 patients (31.1%) on nebivolol compared with 375 (35.3%) on placebo [hazard ratio (HR) 0.86, 95% CI 0.74-0.99; P=0.039]. There was no significant influence of age, gender, or ejection fraction on the effect of nebivolol on the primary outcome. Death (all causes) occurred in 169 (15.8%) on nebivolol and 192 (18.1%) on placebo (HR 0.88, 95% CI 0.71-1.08; P=0.21).

CONCLUSION

Nebivolol, a beta-blocker with vasodilating properties, is an effective and well-tolerated treatment for heart failure in the elderly.

Revascularization strategies in acute myocardial infarction: a meta-analysis

OBJECTIVE

Many treatments and procedures have been tested to reduce complications after myocardial infarction. Our objective was to assess in this clinical situation the best evidence-based medicine revascularization strategy including the most recently developed interventions such as thrombolysis, angioplasty, stent implantation and glycoprotein IIb/IIIa (GpIIb/IIIa) antagonists.

MATERIAL AND METHODS

We performed the meta-analyses of randomized controlled trials by testing the addition of a stent to primary angioplasty, the addition of GpIIb/IIIa antagonists to primary angioplasty, the addition of GpIIb/IIa antagonists to primary angioplasty + stent and finally addition of GpIIb/IIIa antagonists to thrombolytics. The primary outcome was the combined endpoint of death or myocardial infarction or urgent revascularization at 1 month.

RESULTS

The combined endpoint was significantly reduced by 31% (95% CI: 11% - 47%) at 30 days when stent was added to primary angioplasty. GpIIb/IIIa blockers provided an additional benefit by reducing the combined criteria by 50% (95% CI: 27% - 66%) in patients who underwent primary angioplasty, and by 42% (95% CI: 16% - 60%) when associated with angioplasty and stent implantation. Administration of GpIIb/IIIa in addition to thrombolytics, aspirin and heparin was associated with a significant reduction in the combined criteria by 17% (95% CI: 10% - 23%) and a significant excess of major bleeding by 69% (95% CI: 38% - 109%). However, the risk/benefit ratio indicates that patients with this association should be treated with the corresponding doses used in these trials.

CONCLUSION

In acute myocardial infarction, stent implantation provides therapeutic benefit when added to primary angioplasty. The addition of GpIIb/IIIa blockers appears to provide further benefit if bleeding complications are minimized.

Pharmacokinetic and pharmacodynamic interactions between metoprolol and dronedarone in extensive and poor CYP2D6 metabolizers healthy subjects

As dronedarone a new noniodinated antiarrhythmic agent structurally related to amiodarone could inhibit CYP2D6 and is planned to be associated with beta-blockers, interactions with CYP2D6 metabolized beta-blockers such as metoprolol, have to be studied. Forty-nine healthy male subjects genotyped for CYP2D6 were included in a randomized, double-blind, placebo-controlled study. Metoprolol was administrated during 13 days (200 mg/day). After the initial 5 days, subjects received placebo (n = 12), 800 mg (n = 6), 1200 mg (n = 9), or 1600 mg (n = 17) of dronedarone daily during eight additional days. Pharmacokinetic parameters of metoprolol were investigated at day 5 and at day 13 in 44 subjects, 39 extensive metabolizers and five poor metabolizers for CYP2D6. Cardiac contractility function was evaluated by the rate-corrected electromechanical systole duration (QS2i) and the mean velocity of endocardial circumferential fiber shortening (Vcfmean). Cmax and AUC0--24 h of metoprolol increased from days 5 to 13 in proportion to dronedarone dose only in CYP2D6 extensive metabolizers genotyped subjects (P < 0.001). In all subjects, from days 5 to 13, Vcfmean decreased and QS2i significantly increased in dronedarone groups. The Vcfmean changes were however significant only with the 1600 mg dronedarone dose compared with placebo while QS2i changes induced by addition of dronedarone were significant compared with placebo at all dose levels. Between days 5 and 13, QS2i and Vcfmean changes were significantly correlated with both dronedarone concentrations at day 13 and with metoprolol concentration changes between days 5 and 13. Plasma metoprolol concentrations were highest in poor metabolizer subjects and dronedarone did not further increase their level but increased QS2i in the two subjects receiving the 1600 mg dose. Addition of dronedarone (800-1600 mg daily) to metoprolol (200 mg daily) increases bioavailability of metoprolol in CYP2D6 extensive metabolizers and induces an additive dronedarone dose-dependent negative inotropic effect. Nevertheless at 800 mg daily (anticipated therapeutic dose) these effects were modest.