Population pharmacokinetics and bioavailability of tacrolimus in kidney transplant patients

AIMS

The use of tacrolimus is complicated by its narrow therapeutic index and wide intra- and interpatient variability. Tacrolimus population pharmacokinetics, including bioavailability, were investigated in an adult kidney transplant cohort to identify patient characteristics that influence pharmacokinetics.

METHODS

The database (drug monitoring data) included 83 adult kidney transplant recipients and analysis was performed by a population approach with NONMEM. Data were collected during the first months after transplantation. Patients were administered oral or intravenous tacrolimus as part of a triple immunosuppressive regimen that also included mycophenolate mofetil and corticosteroids. Subsequent doses were adjusted on the basis of clinical evidence of efficacy and toxicity as in routine therapeutic drug monitoring.

RESULTS

A one compartment open model with linear absorption and elimination adequately described the data. The typical value of minimal clearance was 1.8 +/- 0.2 l h(-1). Clearance increased with time post transplantation to reach 50% of maximal value after 3.8 +/- 0.5 days, with a maximal value of 5.6 l h(-1). Moreover clearance increased by approximately 1.6 fold (range 0.5-1.6) if the dose of prednisone was >25 mg. The typical value for volume of distribution, V, (98 +/- 13 l kg(-1)) was similar to reported values in kidney transplant patients. The oral bioavailability of tacrolimus was poor and ranged from 11.2 to 19.1%. No covariates significantly influenced V or F.

CONCLUSIONS

The number of days postoperation and corticosteroid dose were significant covariates influencing tacrolimus clearance.

Cell cycle arrest by oxaliplatin on cancer cells

Oxaliplatin (L-OHP) is the only platinum compound to show activity in colorectal cancer. We evaluated the cytotoxicity of L-OHP on four human cancer cell lines and its influence on the cell cycle, when treated during long exposure (72 h) and different post-incubation times (24 or 72 h). We used a panel of cell lines: HT29 (colon cancer), MCF7 (breast cancer), Hela (uterine cervix) and A549 (lung adenocarcinoma). Inhibition concentration (IC)(50) was assessed by MTT assay. Cell cycle modifications were determined using dual parameter bromodeoxyuridine and propidium iodide. L-OHP yielded a superior cytotoxicity on HT29 and MCF7 relative to Hela and A549 after treatment, the post-incubations demonstrate that growth inhibition was irreversible for HT29 and Hela cell lines contrary to MCF7 and A549. The main effects of L-OHP are G2/M cell cycle arrest and transient S phase delay. Taken together, L-OHP treatment results on HT29, MCF7 and Hela, are in favor of lengthening the infusion duration to patients during further clinical trials.

[New insights and perspectives in the management of dyslipidemia]

PURPOSE

Recent end point trials of lipid-lowering drugs have shown that patients at very high-risk for coronary disease benefit from treatments that lowers low density lipoprotein cholesterol (LDL cholesterol) plasma levels< or =70 mg/dl and that patients with at least 2 risk factors benefit from LDL cholesterol levels< or =100 mg/dl. Epidemiologic studies have shown that the concentration of high density lipoprotein cholesterol (HDL cholesterol) is a strong, independent, inverse predictor of coronary disease risk. Innovative pharmacological approaches to raise low HDL cholesterol levels are currently of considerable interest, especially for patients with type 2 diabetes or metabolic syndrome.

RESULTS

Rosuvastatin has shown superior efficacy in lowering LDL cholesterol, although evidence of clinical benefit is actually lacking. Ezetimibe is a lipid-lowering drug that inhibits absorption of dietary and biliary cholesterol. Its co-administration with statin has given very interesting results. Niacin is the most effective of currently available options for raising HDL cholesterol, although tolerability can be an issue, with serious side effects such as loss of glucose control and liver toxicity. Flushing may occur in 80% of treated patients. Two CETP inhibitors have shown therapeutical efficacy to raise HDL cholesterol, but clinical benefit remains uncertain.

Very low blood hydroxychloroquine concentration as an objective marker of poor adherence to treatment of systemic lupus erythematosus

BACKGROUND

Poor adherence to treatment is difficult to diagnose accurately. Hydroxychloroquine (HCQ) has a long elimination half-life and its concentration in whole blood can be measured easily.

OBJECTIVE

To evaluate the utility of a very low blood HCQ concentration as a marker of poor compliance in patients with systemic lupus erythematosus (SLE).

METHODS

HCQ concentrations were determined on a blinded basis in 203 unselected patients with SLE. At the end of the study, the patients were informed of the results and retrospectively interviewed about their adherence to treatment.

RESULTS

14 (7%) patients said that they had stopped taking HCQ (n = 8) or had taken it no more than once or twice a week (n = 6). Their mean (SD) HCQ concentration was 26 (46) ng/ml. range (0-129 ng/ml) By contrast, the other patients had a mean HCQ concentration of 1079 ng/ml range (205-2629 ng/ml). The principal barriers to adherence were related to HCQ treatment characteristics. Adherence subsequently improved in 10 of the 12 patients whose blood HCQ concentrations were remeasured.

CONCLUSIONS

Very low whole-blood HCQ concentrations are an objective marker of prolonged poor compliance in patients with SLE. Regular drug assays might help doctors in detect non-compliance and serve as a basis for counselling and supporting these patients.

Prevention of atrial fibrillation onset by beta-blocker treatment in heart failure: a meta-analysis

AIMS

Atrial fibrillation (AF) is an important morbidity-mortality risk factor, especially in patients with heart failure (HF). Beta-blockers reduce morbidity and mortality in HF. The study was designed to estimate the preventive efficacy of beta-blocker treatment on AF occurrence in patients with HF.

METHODS AND RESULTS

A systematic review of the literature was performed to identify all clinical trials evaluating beta-blockers' efficacy in HF. Eligible studies had to be randomized, placebo-controlled and providing information on the incidence of AF during follow-up among those with sinus rhythm at baseline. A total of seven studies which included 11 952 patients receiving a background treatment with angiotensin-converting enzyme-inhibitors could be found. Overall, beta-blockers significantly reduced incidence of onset of AF from 39 to 28 per 1000 patient-years: relative risk reduction=27% (95% confidence interval 14-38, P<0.001); heterogeneity test: P=0.096. A same trend of efficacy was observed in all trials except the SENIORS study. In this trial which included aged patients (>70 years) with systolic or diastolic HF, a higher prevalence of AF at baseline (35%) was observed compared with the mean baseline prevalence (13%).

CONCLUSION

Beta-blockers appear to effectively prevent occurrence of AF in patients with systolic HF.

Heart conduction disorders related to antimalarials toxicity: an analysis of electrocardiograms in 85 patients treated with hydroxychloroquine for connective tissue diseases

OBJECTIVE

The antimalarial agents chloroquine (CQ) and hydroxychloroquine (HCQ) are used in long-term treatment of connective tissue diseases (CTDs). A high incidence of heart conduction disorders, including bundle-branch block and incomplete or complete atrioventricular block, has been observed among patients treated with CQ. Since no data were available for HCQ, we studied electrocardiograms (ECGs) in 85 unselected patients with CTD treated with HCQ as the sole antimalarial.

METHODS

Eighty-five unselected out-patients treated with HCQ for a minimum of 1 yr, and without established cardiac diseases had standard 12-lead ECGs.

RESULTS

Two incomplete right bundle-branch blocks and one left bundle-branch block were observed. No atrioventricular block was observed. The mean PR interval was 137 +/- 20 ms (range 99-188). The mean QTc interval was 410 ms (range 349-464). The mean heart rate was 73 beats/min (range 53-102).

CONCLUSION

PR interval, QTc interval and heart rate were not different from normal values. The rate of heart conduction disorders was similar to what is expected in the general population, and contrasted with prior results in CQ-treated patients. Our results add further evidence on the safety of HCQ compared with CQ.

Association between ABCC2 gene haplotypes and tenofovir-induced proximal tubulopathy

BACKGROUND

Tenofovir disoproxil fumarate (TDF) may induce renal proximal tubulopathy (rPT). There are no data on pharmacogenomic predictors of rPT in the genes encoding the multidrug-resistance protein (MRP) 2 and MRP4 transporters.

METHODS

Mutational screening of the genes for MRP2 (ABCC2) and MRP4 (ABCC4) was performed using genomic DNA from 13 human immunodeficiency virus type 1 (HIV-1)-infected patients (group 1) presenting with TDF-induced rPT. Concomitantly, 17 unrelated HIV-1-infected patients who had received TDF therapy and who did not have rPT (group 2) were included in a case-control analysis, to assess the influence of single-nucleotide polymorphisms (SNPs) identified in ABCC2 and ABCC4.

RESULTS

Six SNPs were identified in ABCC2. A significant allelic association between the 1249 G-->A SNP and TDF-induced rPT was observed (odds ratio, 6.11 [95% confidence interval, 1.19-31.15]; P<.02). ABCC2 haplotypes were significantly associated with the onset of TDF-induced rPT--CATC appeared to be a predisposing haplotype, as it was found in 40.9% of the group 1 case patients and in 13.7% of the group 2 control subjects (P<.01), whereas CGAC appeared to be a protective haplotype, as it was not observed in the group 1 case patients but was present in 20.2% of the group 2 control subjects (P<.01). No association was observed between ABCC4 polymorphism and TDF-induced rPT in the present study.

CONCLUSION

ABCC2 haplotypes are associated with rPT induced by TDF in HIV-1-infected patients.

Low blood concentration of hydroxychloroquine is a marker for and predictor of disease exacerbations in patients with systemic lupus erythematosus

OBJECTIVE

To study the possible relationship between whole-blood hydroxychloroquine (HCQ) concentrations and clinical efficacy of HCQ in patients with systemic lupus erythematosus (SLE).

METHODS

Whole-blood HCQ concentrations were measured, under blinded conditions, in 143 unselected patients with SLE who had been receiving HCQ 400 mg daily for at least 6 months. The relationship of these concentrations to current disease activity and to subsequent exacerbations during 6 months of followup was investigated.

RESULTS

At baseline, 23 patients had active disease (mean +/- SD SLE Disease Activity Index 12.4 +/- 7.5). The mean whole-blood HCQ concentration in this group was significantly lower than that in the 120 patients with inactive disease (694 +/- 448 ng/ml versus 1,079 +/- 526 ng/ml; P = 0.001). Among the 120 patients who had inactive disease at baseline, the mean HCQ concentration at baseline in the 14 (12%) who had disease exacerbations during followup was significantly lower than that in the patients whose disease remained inactive. Multivariate logistic regression showed that the HCQ concentration was the only predictor of exacerbation (odds ratio 0.4 [95% confidence interval 0.18-0.85], P = 0.01). Receiver operating characteristic curve analysis showed that a whole-blood HCQ concentration cutoff of 1,000 ng/ml had a negative predictive value of 96% for exacerbation during followup.

CONCLUSION

Low whole-blood HCQ concentrations are associated with SLE disease activity and are a strong predictor of disease exacerbation. Regular drug assaying and individual tailoring of treatment might help to improve the efficacy of HCQ treatment in patients with SLE.

Anti-factor Xa kinetics after intravenous enoxaparin in patients undergoing percutaneous coronary intervention: a population model analysis

AIM

Recent studies have suggested that intravenous (i.v.) enoxaparin could be used as antithrombotic therapy in patients ongoing percutaneous coronary intervention (PCI). However, anti-Xa pharmacokinetics following different i.v. dosing regimens is not clearly established.

METHODS

A population pharmacokinetic analysis was developed using anti-Xa activities measured in 546 patients who received a single 0.5 mg kg(-1) i.v. dose of enoxaparin immediately before PCI. Effects of higher doses (0.75 mg kg(-1) and 1 mg kg(-1)) and/or additional bolus after the initial administration were similarly simulated.

RESULTS

Enoxaparin anti-Xa time profiles were best described by a one-compartment model with zero-order kinetics. Mean population parameters (intersubject variability, %) were CL 1.2 l h(-1) (33), V 2.9 l (30) and zero-order input 0.25 h (24). With a single bolus of 0.5 mg kg(-1), the totality of the patients reached an effective anticoagulation level (anti-Xa >0.5 IU ml(-1)) and only 2.5% reached levels above 1.5 IU ml(-1). Simulations showed that greater doses (0.75 mg kg(-1) and 1 mg kg(-1)) prolonged the duration of anticoagulation (3.4 and 4.1 h, respectively) compared with the 0.5 mg kg(-1) bolus (2.7 h) and markedly increased the proportion (48% and 79%, respectively) of patients with anti-Xa levels >1.5 IU ml(-1). For delayed and/or prolonged procedures, patients could be administered a second bolus of half the initial dose in a time interval between 90 min to 2 h after in order to maintain similar anticoagulation profile levels.

CONCLUSIONS

A single 0.5 mg kg(-1) i.v. dose of enoxaparin reached anticoagulation levels adequately and should be safer compared with greater doses for anticoagulation in patients undergoing an elective PCI. An additional second bolus could be proposed in patients with delayed or prolonged procedures.

Left bundle branch block as a risk factor for progression to heart failure

The prevalence of conduction disturbances, particularly left bundle branch block (LBBB), is strongly correlated with age and with the presence of cardiovascular disease. LBBB has been reported to affect approximately 25% of the heart failure (HF) population and it is likely that the deleterious role of such conduction disorders in the progression to HF has been underestimated. The purpose of this article is to review the data from the literature indicating that LBBB may have a causative role, mediated through the resulting intra-ventricular asynchrony, in the deterioration of cardiac function and the development of cardiac remodelling and HF. It also aims to address the potential for future clinical therapies for this conduction disorder.

Prevention of cardiovascular events in end-stage renal disease: results of a randomized trial of fosinopril and implications for future studies

Cardiovascular events (CVEs) are the leading cause of death in chronic hemodialysis patients. Results of trials in non-end-stage renal disease (ESRD) patients cannot be extrapolated to patients with ESRD. It is critical to test cardiovascular therapies in these high-risk patients who are usually excluded from major cardiovascular trials. The study objective was to evaluate the effect of fosinopril on CVEs in patients with ESRD. Eligible patients were randomized to fosinopril 5 mg titrated to 20 mg daily (n=196) or placebo (n=201) plus conventional therapy for 24 months. The primary end point was combined fatal and nonfatal first major CVEs (cardiovascular death, resuscitated death, nonfatal stroke, heart failure, myocardial infarction, or revascularization). No significant benefit for fosinopril was observed in the intent to treat analysis (n=397) after adjusting for independent predictors of CVEs (RR=0.93, 95% confidence interval (CI) 0.68-1.26, P=0.35). The per protocol secondary supportive analysis (n=380) found a trend towards benefit for fosinopril (adjusted RR=0.79 (95% CI 0.59-1.1, P=0.099)). In the patients who were hypertensive at baseline, systolic and diastolic blood pressures were significantly decreased in the fosinopril as compared to the placebo group. After adjustment for risk factors, trends were observed suggesting fosinopril may be associated with a lower risk of CVEs. These trends may have become statistically significant had the sample size been larger, and these findings warrant further study.

Prévention des évènements ischémiques majeurs au cours de l’artériopathie oblitérante des membres inférieurs : l’aspirine a-t-elle un rôle ?

OBJECTIVE

To determine the effect of aspirin among patients with lower limb occlusive arterial disease.

DESIGN

Meta-analysis of trials issuing from a collaborative meta-analysis of randomized trials of anti-platelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients. Five trials were identified as comparing aspirin (with or without dipyridamole) to placebo, in 1 029 patients with lower limb occlusive arterial disease. There was no new publication found comparing aspirin and placebo in lower limb occlusive arterial disease.

MAIN OUTCOME MEASURE

As in the main meta-analysis, "serious vascular event": non fatal myocardial infarction, non fatal stroke or vascular death.

RESULTS

Among these 1 029 patients, allocation to aspirin did not reduce the outcome of serious vascular event, nor of any of the individual events. This result, as opposed to the enhancement of 23% +/- 8% announced in the main meta-analysis, clearly demonstrate that the beneficial effect cannot be attributable to aspirin.

DISCUSSION

In the collaborative meta-analysis, aspirin was the most widely used product (75% of the trials) and it showed its beneficial effect when administered at doses ranging from 75 to 150 mg/day, as compared to placebo. Among the other anti-platelet treatments analyzed, clopidogrel was the only product for which large scale randomized evidence versus aspirin was available. Various national health institutions, in the United States as well as in Europe, show a major concern regarding the use of anti-platelet treatments, in peripheral arterial occlusive disease as well as in other manifestations of cardiovascular disease. Their guidelines take of course the patient's health into account but the economical aspect of this prevention is increasingly hard to circumvent. Based on the results of the collaborative meta-analysis, these guidelines all recommend a lifetime use of low doses of aspirin, reserving clopidogrel for patients intolerant to aspirin, mainly because they do not consider the additional benefit recognized with clopidogrel as important enough to counterbalance the cost of the treatment. While aspirin as a first choice antiplatelet therapy cannot be discussed in coronary disease, after a myocardial infarction, or in cerebrovascular disease, its use in lower limb occlusive arterial disease does not enable a reduction in morbi-mortality. From an economical point of view, the use of a cheap but inefficient preventive treatment could also lead to an increased cost for curing the complications expected with an uncontrolled widely spread disease as chronic lower limb ischemia.

Cardiomyopathy Related to Antimalarial Therapy with Illustrative Case Report

The antimalarial agents, chloroquine (CQ) and hydroxychloroquine (HCQ) are used in long-term treatment of connective tissue diseases and dermatological disorders and are generally regarded as safe. We present one case of cardiotoxicity in a 59-year-old woman treated with antimalarials during 13 years for a discoid lupus erythematosus. She progressively developed conduction disturbances and congestive heart failure (CHF). When the diagnosis of antimalarials toxicity was suspected, CQ was withdrawn. However, heart transplantation had to be performed in the following 4 months for severe CHF. Indeed, rare but severe cardiotoxicity may develop following prolonged use of antimalarials with both conduction disturbances (45 patients) and CHF (25 patients). These cardiac toxic effects have been reported with CQ and less frequently with HCQ use alone. Diagnoses are often delayed since the toxicity of the drug might be misattributed to other factors in these patients. The endomyocardial biopsy, or in some cases the muscle biopsy, are essential to confirm the antimalarials toxicity. Antimalarials have been stopped in 12 cases of CHF, leading to improvement in 8 cases (within 3 months to 5 years) and to deaths or to heart transplantation in 4 cases (within 1 week to 3 months). In the latter cases, as in our patient, the lack of improvement may have been explained by the severity of the cardiomyopathy at diagnosis and the short delay since withdrawal. As a consequence, the potential for reversibility and the severity in undiagnosed cases of these toxic cardiomyopathies emphasize the importance of recognizing early signs of toxicity in order to withdraw antimalarials before the occurrence of life-threatening CHF.

Cytochrome P450 2C19 loss-of-function polymorphism is a major determinant of clopidogrel responsiveness in healthy subjects

The capacity of clopidogrel to inhibit ADP-induced platelet aggregation shows wide intersubject variability. To determine whether frequent functional variants of genes coding for candidate cytochrome P450 (CYP) isoenzymes involved in clopidogrel metabolic activation (CYP2C19*2, CYP2B6*5, CYP1A2*1F, and CYP3A5*3 variants) influence the platelet responsiveness to clopidogrel, we conducted a prospective pharmacogenetic study in 28 healthy white male volunteers treated for 7 days with clopidogrel 75 mg/d. We observed that pharmacodynamic response to clopidogrel was significantly associated with the CYP2C19 genotype. Twenty of the subjects were wild-type CYP2C19 (*1/*1) homozygotes, while the other 8 subjects were heterozygous for the loss-of-function polymorphism CYP2C19*2 (*1/*2). Baseline platelet activity was not influenced by the CYP2C19 genotype. In contrast, platelet aggregation in the presence of 10 muM ADP decreased gradually during treatment with clopidogrel 75 mg once daily in *1/*1 subjects, reaching 48.9% +/- 14.9% on day 7 (P < .001 vs baseline), whereas it did not change in *1/*2 subjects (71.8% +/- 14.6% on day 7, P = .22 vs baseline, and P < .003 vs *1/*1 subjects). Similar results were found with VASP phosphorylation. The CYP2C19*2 loss-of-function allele is associated with a marked decrease in platelet responsiveness to clopidogrel in young healthy male volunteers and may therefore be an important genetic contributor to clopidogrel resistance in the clinical setting.

Use of an indirect effect model to describe the LDL cholesterol-lowering effect by statins in hypercholesterolaemic patients

Statins are the most commonly prescribed agents for the treatment of hypercholesterolaemia. This is due to their efficacy in reducing low-density lipoprotein cholesterol (LDL) level which is the primary goal of the treatment especially for patients with multiple risk factors or with established coronary heart diseases. The purpose of this study was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model that describes the LDL-lowering process in patients with hypercholesterolaemia treated with atorvastatin, fluvastatin or simvastatin. A total of 100 patients were studied retrospectively. They received atorvastatin (n = 57), fluvastatin (n = 26) or simvastatin (n = 17). As no pharmacokinetic data were available, the absorption rate was fixed to 1/h and atorvastatin, simvastatin and fluvastatin elimination half-lives were fixed to 14, 2 and 2.5 h respectively. A total of 309 LDL levels were measured and the data were analysed by nonmem v. The time course of the LDL-lowering effect of statins was described by an indirect-response model with precursor (LDL synthesis, input rate K(in)) and response (circulating LDL, input and output rates K) compartments. The following parameters were estimated: LDL input rate (K(in)) 0.14 +/- 0.015 g/L/day (mean +/- SD); inhibition fraction of K(in) (INH) 0.21 +/- 0.017; and dose producing 50% increase of LDL removal (D50), 26 +/- 7.8, 1.3 +/- 0.48 and 15 +/- 5.25 mg for atorvastatin, simvastatin and fluvastatin, respectively. Gender, bodyweight, age, calories/day, sugar/day, lipids/day, hyperlipidaemia types and waist/hip circumference, renal and hepatic functions had no effect on the pharmacodynamic parameters. The pharmacodynamic parameters for the three statins were accurately estimated. The PK/PD model developed successfully predicted the time course of the LDL-lowering effect of statins.

Tubular transporters 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 mutant transport-deficient (TR-) rats, in which MRP2 is lacking. After treatment by probenecid or placebo, pharmacokinetics of adefovir 10mg/kg was studied via population nonlinear mixed effect modeling. 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+/-0.02l/h) than in normal control (0.09+/-0.05l/h), in normal probenecid (0.10+/-0.07l/h) and in TR- control rats (0.13+/-0.07l/h). 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.

Cell cycle arrest and apoptosis induced by oxaliplatin (L-OHP) on four human cancer cell lines

BACKGROUND

The effects of oxaliplatin (L-OHP) on cell cycle and apoptosis were examined.

MATERIALS AND METHODS

The HT29, MCF7, Hela and A549 cell lines were treated and dual parameter flow cytometry BrdU/PI was then performed to monitor cell cycle modifications. Annexin V-FITC and PI probes were used for the detection of apoptosis.

RESULTS

The cells were treated for 3 h followed or not by 24 and 72 h of post-incubation. No changes were observed after 3 h of treatment, while after 24 h of post-incubation, all the cells except A549 were predominantly accumulated in the G2/M-phase; this accumulation was time-dependent. Apoptosis induction was late and moderate and was observed only after 12 h of treatment and 24 h of post-incubation.

CONCLUSION

L-OHP induced cell cycle arrest and moderate apoptosis; these two activities were time-dependent. These findings warrant further investigation into the potential antitumour activity of L-OHP in MCF7 and Hela cells and in lengthening the infusion duration in order to achieve the acquired cellular modifications.

Population pharmacokinetic study of methotrexate in patients with lymphoid malignancy

PURPOSE

A population pharmacokinetic model was developed to describe dose-exposure relationships of methotrexate (MTX) in adults with lymphoid malignancy; this is in order to explore the interindividual variability in relationship with the different physiopathological variables. The final model was applied to the Bayesian estimation of MTX concentrations using two blood samples.

METHODS

Fifty-one patients receiving 136 courses of MTX (1-6 per patient) were included in this study. The data was analysed using NONMEM software. A linear two-compartment model with linear elimination best described the data. Setting mean parameters values and variabilities to population values, we obtained Bayesian prediction of MTX pharmacokinetic parameters and concentrations. The predictive performance was evaluated by comparing the Bayesian estimated and observed concentrations and the Bayesian estimated parameters with the individual final model estimated parameters.

RESULTS

The population pharmacokinetic parameters and the inter-subject variablities expressed as coefficient of variation were: the total body clearance CL, 7.1 l h-1 (22%), the volume of the central and peripheral compartments V1, 25.1 l (22.5%), V2, 2.7 l (64%), respectively, and the transfer constant Q, 2.7 (51%) l h-1. Inter-course variability was only significant on CL. Age and serum creatinine had significant effects on CL and was included in the final model. A good correlation was obtained between Bayesian estimated and experimental concentrations (r2=0.85).

Deficiency of the 5-Hydroxytryptamine Transporter Gene Leads to Cardiac Fibrosis and Valvulopathy in Mice

Background— Serotonin (5-hydroxytryptamine; 5-HT) overproduction is responsible for cardiac valvular disease in patients with carcinoid tumors. Reduced 5-HT inactivation is one proposed mechanism of the valvulopathy observed in individuals treated with the appetite suppressants fenfluramine and phentermine. One key protein limiting systemic availability of 5-HT is the 5-HT transporter (5-HTT) expressed by platelets and pulmonary vascular cells; 5-HTT is responsible for 5-HT uptake and subsequent inactivation of the amine passing through the lung. Here we investigated whether 5-HTT–deficient (5-HTT-KO) mice developed structural and/or functional cardiac abnormalities and valvulopathy.

Methods and Results— Cardiac endothelial cells expressed large amounts of 5-HTT in wild-type mice. 5-HTT deficiency appeared to be associated with marked interstitial, perivascular, and valvular fibrosis as evidenced by staining of cardiac collagen in 5-HTT-KO mice. Histological analysis provided evidence for valvulopathy characterized by valvular hyperplasia and prominent fibrosis at the attachment site and base of the leaflets. Echocardiography revealed an increase in left ventricular lumen diameter and a decrease in left ventricular diameter fractional shortening. Although 5-HT 1B receptors mediated the 5-HT–induced collagen secretion by human cardiac myofibroblasts, the contribution of this receptor type to valvulopathy was ruled out because double-KO mice deficient in both 5-HTT and 5-HT 1B receptors showed the same cardiac alterations as 5-HTT-KO mice.

Conclusions— The present results establish a link between 5-HTT and the development of cardiac fibrosis and valvulopathy in vivo. 5-HTT-KO mice represent an especially relevant model for studying the mechanisms by which 5-HT induces valvulopathy.