A pharmacokinetic simulation model for ivabradine in healthy volunteers

Ivabradine is a novel bradycardic agent that has been developed for the prevention of angina. Ivabradine has an active metabolite S-18982. The aim of this study is to develop a pharmacokinetic simulation model. Pharmacokinetic data from two studies were pooled and included data from a total of 66 healthy male volunteers. The data were collected following single dose intravenous and multiple dose oral administration of ivabradine. The multiple dose regimens were administered every 12 h and there were seven active dosing levels. The modelling was performed using the NONMEM software. The model was assessed in terms of its ability to describe the original data set used in its construction and also data arising from a different clinical pharmacology study involving 12 additional subjects. The pharmacokinetics of ivabradine and S-18982 were best described by two linked two compartment intravenous bolus and first-order input, with first-pass loss, and first-order output model. When the model was used for simulation it produced an adequate description of both the original data and data arising from a different clinical pharmacology study.

Population pharmacokinetics of doxorubicin, etoposide and ifosfamide in small cell lung cancer patients: results of a multicentre study

AIMS

To determine the population pharmacokinetic (PK) parameters of doxorubicin (Dox), etoposide (Eto) and ifosfamide (Ifo) in small cell lung cancer (SCLC) patients, to assess the potential relationship between those parameters and to estimate the impact of individual morphological and biological covariates on patients' PK parameters.

METHODS

Twenty-four patients with either SCLC limited to the thorax or extensive SCLC entered the study. All but one received at least two 3 day courses of the standard AVI (Dox 50 mg m-2 day 1, Eto 120 mg m-2 day 1,2,3, Ifo 2000 mg m-2 day 1,2) regimen. Individual blood samples were collected during each course and data on 47 courses were available. Data were analysed with the NONMEM program. Dox, Eto and Ifo plasma concentrations were studied with multicompartment (3, 2 and 2, respectively) models. Inter-individual and interoccasion (course-to-course) variabilities were estimated. The influence of individual covariates (age, sex, stage of the disease, weight, height, body-surface area, serum creatinine, total protein, LDH, ASAT, ALAT, alkaline phosphatase, gamma-GT, bilirubin) on PK parameters was also assessed. Correlations between individual PK parameters of Dox, Eto and Ifo were explored by using Pearson's correlation coefficient.

RESULTS

Multiple data were available for each patient. Dox clearance (CL) and volume of distribution (Vd) were 32.0 l h-1 and 9.3 l (Inter-individual variability: 17.2% and 19.2%). Eto CL (l h-1) and Vd were, respectively, 3.34-0.0083* serum creatinine (micromol l-1) and 6.38 l (interindividual variability: 15.6% and 18.7%). Ifo CL and Vd at day 1 were 5.6 l h-1 and 26.0 l (interindividual variability: 10.1% and 17.2%, respectively). Estimation of course-to-course variability improved the precision of PK models in some cases. No correlation was observed between the respective PK parameters of each drug. Of individual covariates tested, only serum creatinine correlated with Eto CL (r = -0.37, P < 0.001). Self-induction of the metabolism of Ifo was apparent (mean CL increase from day 1 to day 2 : 42%) and individually correlated with the CL value at day 1 (r = -0.61, P < 0.001).

CONCLUSIONS

Assessment of potential relationships between individual systemic exposure of chemotherapy and therapeutic endpoints (tumour response, toxicity and survival) will be required to adjust drugs dosages based on individual PK parameters rather than questionable body-surface area. However, all three drugs in the AVI regimen should be monitored simultaneously.

Inferior vena cava interruption: how and when?

Interruption of the inferior vena cava (IVC) to prevent pulmonary embolism arising from venous thrombi in the lower extremities has become widely used since IVC filters became available about 30 years ago. However, reliable data regarding efficacy and safety of IVC filters are still lacking. The first controlled clinical trial of IVC filters demonstrated their effectiveness, but filters had no detectable impact on mortality and were associated with an increased risk of recurrent deep venous thrombosis. On the basis of the literature, indications for IVC interruption can be classified as accepted, debated, and debatable. The relevance of debated indications, more accurate identification of patients who remain "very high-risk" despite preventive or curative anticoagulant treatment, and selection of the most appropriate filter should be looked at in prospective clinical studies.

[Detection of asymptomatic venous thrombosis after lower limb prosthetic surgery. Retrospective evaluation of a systematic approach using Doppler ultrasonography: 400 cases]

OBJECTIVES

The purpose of this study was to evaluate a pragmatic approach using duplex ultrasonography (US) for detecting deep vein thrombosis (DVT) after total hip (THA) and total knee (TKA) replacement.

METHODS

Venous B-mode and color duplex US examination of both legs including a systematic evaluation of calf veins was performed twice during hospital stay (Between day 1 and day 4 for the first exam and between day 7 and day 11 for the second) in 400 consecutive patients.

RESULTS

Deep vein thrombosis was diagnosed in 53 patients (13.5%) including 7 patients with proximal DVT. Thrombosis was asymptomatic in 46 patients (85%), and was bilateral or concerned the non-operated leg in 8 patients (14.5%). No clinical pulmonary embolism (PE) occurred during hospital stay (mean hospital stay: 12.3). Prior phlebitis and age over 70 were identified as a statistically significant risk-factor for post-operative DVT (p = 0.001 and p < 0.01 respectively) concerning the whole series and the THA series (p < 0.02 and p < 0.04 respectively). No statistically significant risk factor was founded for the TKA series (p < 0.2 and p < 0.2 respectively). All patients were seen at three months. Four patients (1.16%) developed DVT between hospital discharge and the 3-month follow-up visit. One patient with coronary disease died suddenly on post-operative day 24, without clinical signs or symptoms of PE or DVT.

CONCLUSION

Venous US performed twice after total hip replacement detected asymptomatic DVT in 85% of patients. This approach might explain the absence of PE in our series and thus justify systematic ultrasonographic evaluation of lower limb veins after prosthetic replacement.

Inter-study variability in population pharmacokinetic meta-analysis: when and how to estimate it?

Population pharmacokinetic analysis is being increasingly applied to individual data collected in different studies and pooled in a single database. However, individual pharmacokinetic parameters may change randomly from one study to another. In this article, we show by simulation that neglecting inter-study variability (ISV) does not introduce any bias for the fixed parameters or for the residual variability but may result in an overestimation of inter-individual (IIV) variability, depending on the magnitude of the ISV. Two random study-effect (RSE) estimation methods were investigated: (i) estimation, in a single step, of the three-nested random effects (inter-study, inter-individual and residual variability); (ii) estimation of residual variability and a mixture of ISV and IIV in the first step, then separation of ISV from IIV in the second. The one-stage RSE model performed well for population parameter assessment, whereas, the two-stage model yielded good estimates of IIV only with a rich sampling design. Finally, irrespective of the method used, ISV estimates were valid only when a large number of studies was pooled. The analysis of one real data set illustrated the use of an ISV model. It showed that the fixed parameter estimates were not modified, whether an RSE model was used or not, probably because of the homogeneity of the experimental designs of the studies, and suggest no study-effect in this example.

[Should plasma prolactin assay be routinely performed in the assessment of erectile dysfunction? Report of a series of 445 patients. Review of the literature]

OBJECTIVE

To define the value of plasma prolactin assay in the assessment of erectile insufficiency.

MATERIAL AND METHODS

Plasma prolactin assay (radioimmunoassay) was performed in 445 patients presenting with erectile insufficiency (mean age 52.5 years).

RESULTS

9 patients (2%) presented plasma prolactin levels greater than 25 ng/ml and 4 (0.9%) of them had levels higher than 35 ng/ml. Eight of these 9 patients were taking hyperprolactinaemic drugs. The aetiology remained unclear in 1 patient, but the pituitary gland was normal on CT scan.

REVIEW OF THE LITERATURE

In the population of men with erectile insufficiency, 2.7% of subjects have plasma prolactin levels greater than 20 or 25 ng/ml. 1.3% have levels greater than 35 or 40 ng/ml and 0.6% present pituitary tumours. In the case of pituitary tumours responsible hyperprolactinaemia and erectile insufficiency: 1) plasma prolactin is greater than 30 ng/ml in 90% of cases and greater than 50 ng/ml in 83% of cases; 2) total plasma testosterone is less than 3 ng/ml in 88% of cases and less than 4 ng/ml in 96% of cases; 3) libido is decreased in 90% of cases.

CONCLUSION

The prevalence of hyperprolactinemia and pituitary tumours in the population of men with erectile insufficiency is low. Moreover, certain criteria are suggestive of hyperprolactinemia, especially when it is secondary to a pituitary tumour. Consequently, routine plasma prolactin assay is not justified. This assay should only be performed when libido is impaired, total plasma testosterone is decreased or when the patient presents certain signs such as headache, gynaecomastia or visual disturbances.

[Surgery of retinal detachment without giant tears, macular hole or advanced proliferative vitreoretinopathy]

PURPOSE

To evaluate surgical results in usual detachment cases.

MATERIAL AND METHODS

This retrospective study covered 704 non-referred cases treated by the same surgeon. A follow-up duration of at least 6 months was obtained for all the successful cases.

RESULTS

In 617 cases (87.6%) permanent reattachment was obtained with the first operation. The two main causes of initial failure were new or non-sealed breaks in 39 cases, 9 of them treated without a buckle, and postoperative PVR in 36 cases. After repeat surgery 48 additional cases were reattached, finally 665 cases (94.5%) were successfully treated. In all, postoperative PVR occurred in 39 cases, 22 of these were reoperated on, successfully for 16; thus PVR caused 23 of the 39 terminal failures. In 13 other failed cases there were no obvious unsealed break or severe postoperative PVR. A final visual acuity of 20/40 or more was attained in 443 cases.

CONCLUSION

PVR although infrequent (5.5%), was the main cause of failure. In 13 cases the reason for non reattachment remained uncertain, these failures may have involved an excessive vitreous traction and perhaps in this situation a vitrectomy with a wide angle viewing system might have been helpful.

[Inferior vena cava interruption. How and when?]

Caval interruption has been, historically, the first "treatment" of venous thromboembolic disease. Following ligation, plication, then clips, and finally intracaval filters constituted the successive improvements of this procedure, which can now be considered reasonably safe. However, reliable and clinically relevant data regarding long-term safety are lacking; recent data suggest that caval filters might increase the risk of recurrent deep venous thrombosis. As almost no controlled trials are available, indications for caval interruption are based on fragile grounds: contraindications to and failure of anticoagulant treatment in patients with recent proximal deep venous thrombosis remain the only two widely accepted indications. Although the PREPIC study, first prospective controlled trial on caval filters, confirmed their efficacy for preventing pulmonary embolism, the addition of caval filters to preventive or curative anticoagulant treatment in high-risk patients is still a matter of debate, because "very high-risk" settings despite anticoagulant treatment remain poorly defined. Finally, the risk-benefit ratio of caval interruption in addition to medical thrombolysis, or as an alternative to preventive or curative anticoagulant treatment appears unfavorable. The relevance of debatable indications, the precise identification of "very high-risk" patients, and the determination of the "best" filter should be assessed in specific prospective clinical trials.

High prevalence of detectable deep venous thrombosis in patients with acute pulmonary embolism

STUDY OBJECTIVES

Because specific studies are unavailable, the exact prevalence of detectable "residual" deep venous thrombosis (DVT) in patients with acute pulmonary embolism (PE) is unknown.

DESIGN

Review of clinical records and radiologic documents of consecutive patients.

SETTING

Pulmonary diseases and radiology departments at a university hospital.

PATIENTS

All patients hospitalized in the Department of Pulmonary Diseases with a diagnosis of acute PE during a 5-year period (1984 to 1988). During this period, the diagnosis of PE was based exclusively on pulmonary angiography, and bilateral lower limb venography was routine in patients with proven acute PE.

MEASUREMENTS AND RESULTS

Among 228 consecutive patients with angiography-proven PE, 213 underwent bilateral lower limb venography within 48 h of the diagnosis. Venography demonstrated DVT in 174 patients (81.7%; 95% confidence interval, 76.5 to 86.9%), including 128 patients (60%) with proximal DVT. Signs or symptoms of DVT were present in only 72 patients (42%) with DVT. The prevalence of detectable DVT was significantly lower in patients with recent pelvic surgery or delivery (6 of 12, 50%) than in the other patients, whatever their individual risk factors (p < 0.05). The mean pulmonary vascular obstruction was significantly lower in patients with normal venography than in patients with detectable DVT (37.6 +/- 20.9% vs 48.4 +/- 21.7%; p = 0.007).

CONCLUSIONS

Lower limb venography demonstrates a high prevalence (82%) of residual DVT in patients with angiography-proven PE. These data should be taken into account in the diagnostic and therapeutic management of patients with suspected or proven PE.

Chernobyl post-accident management: the ETHOS project

ETHOS is a pilot research project supported by the radiation protection research program of the European Commission (DG XII). The project provides an alternative approach to the rehabilitation of living conditions in the contaminated territories of the CIS in the post-accident context of Chernobyl. Initiated at the beginning of 1996, this 3-y project is currently being implemented in the Republic of Belarus. The ETHOS project involves an interdisciplinary team of European researchers from the following institutions: the Centre d'etude sur l'Evaluation de la Protection dans le domaine Nucleaire CEPN (radiological protection, economics), the Institute National d'Agronomie de Paris-Grignon INAPG (agronomy, nature & life management), the Compiegne University of Technology (technological and industrial safety, social trust), and the Mutadis Research Group (sociology, social risk management), which is in charge of the scientific co-ordination of the project. The Belarussian partners in the ETHOS project include the Ministry of Emergencies of Belarus as well as the various local authorities involved with the implementation site. The ETHOS project relies on a strong involvement of the local population in the rehabilitation process. Its main goal is to create conditions for the inhabitants of the contaminated territories to reconstruct their overall quality of life. This reconstruction deals with all the day-to-day aspects that have been affected or threatened by the contamination. The project aims at creating a dynamic process whereby acceptable living conditions can be rebuilt. Radiological security is developed in the ETHOS project as part of a general improvement in the quality of life. The approach does not dissociate the social and the technical dimensions of post-accident management. This is so as to avoid radiological risk assessment and management being reduced purely to a problem for scientific experts, from which local people are excluded, and to take into consideration the problems of acceptability of decisions and the distrust of the population towards experts. These cannot be solved merely by a better communication strategy. This paper presents the main features of the methodological approach of the ETHOS project. It also explains how it is being implemented in the village of Olmany in the district of Stolyn (Brest region) in Belarus since March 1996, as well as its initial achievements.

[Resection of lung metastases: long-term results and prognostic analysis based on 5206 cases--the International Registry of Lung Metastases]

The International Registry of Lung Metastases was established in 1991 to asses the long-term results of pulmonary metastasectomy. The Registry has accrued 5206 cases of lung metastasectomy, from 18 departments of thoracic surgery in Europe (n = 13), USA (n = 4) and Canada (n = 1). Of these patients 4572 (88%) underwent complete surgical resection. The primary tumor was epithelial in 2260 (43%), sarcoma in 2173 (42%), germ cell in 363 (7%), and melanoma in 328 (6%) patients. The disease-free interval was 0 to 11 months in 1729 (33%) cases, 12 to 35 months in 1857 (36%) and more than 36 months in 1620 (31%). Single metastases accounted for 2383 (46%) cases and multiple lesions for 2726 (52%). Mean follow up was 46 months. Analysis was performed by Kaplan-Meier estimates of survival, relative risk of death and multivariate Cox model. The actuarial survival after complete metastasectomy was 36% at 5 years, 26% at 10 years and 22% at 15 years (median 35 months); the corresponding values for incomplete resection were 13% at 5 years and 7% at 10 years (median 15 months). Among complete resections, the 5-year survival was 33% for patients with a disease free-interval of 0 to 11 months and 45% for those with a disease-free interval of more than 36 months; 43% for single lesions and 27 for four or more lesions. Multivariate analysis showed a better prognosis for patients with germ cell tumors, disease-free interval of 36 months and more and single metastases. These results confirm that lung metastasectomy is a safe and potentially curative procedure.

Clinical evaluation of the modified Brostrom-Evans procedure to restore ankle stability

The modified Brostrom procedure has become the standard for anatomic repair of symptomatic chronic lateral instability. However, it was our perception that this local tissue repair may fail eventually, particularly in patients that are overweight, hyperflexible, or are involved in strenuous work or athletic activity. This is a retrospective review of 21 lateral ankle reconstructions (20 patients) in which the modified Brostrom technique was augmented with a portion of the peroneus brevis tendon. All patients were interviewed at an average of 29.5 months (range, 14-56 months postsurgery). Fourteen patients also agreed to be evaluated by a physical therapist. No surgical complications were identified. American Orthopaedic Foot and Ankle Society ankle-hindfoot scores averaged 98.2. There was no significant difference in passive or active range of motion of plantarflexion or dorsiflexion when compared to the contralateral ankle. However, a statistically significant loss of inversion (passive, P = 0.011; active, P = 0.018) and eversion (passive, P = 0.004; active, P = 0.007) was noted when compared to the contralateral ankle. Measurement of isometric eversion strength, using a Cybex 340 Isokinetic device, and functional testing, using a lateral lunge test, revealed no significant loss of peroneal strength. The authors conclude that chronic lateral ankle instability in the general population can be successfully managed with a modified Brostrom procedure augmented with a portion of the peroneus brevis. The procedure remains technically simple and provides a greater static restraint for inversion stress without evidence of dramatic overtightening or loss of peroneal strength.

Cross-correlation study of the temporal interactions between areas V1 and V2 of the macaque monkey

Cross-correlation studies performed in cat visual cortex have shown that neurons in different cortical areas of the same hemisphere or in corresponding areas of opposite hemispheres tend to synchronize their activities. The presence of synchronization may be related to the parallel organization of the cat visual system, in which different cortical areas can be activated in parallel from the lateral geniculate nucleus. We wanted to determine whether interareal synchronization of firing can also be observed in the monkey, in which cortical areas are thought to be organized in a hierarchy spanning different levels. Cross-correlation histograms (CCHs) were calculated from pairs of single or pairs of multiunit activities simultaneously recorded in areas V1 and V2 of paralyzed and anesthetized macaque monkeys. Moving bars and flashed bars were used as stimuli. The shift predictor was calculated and subtracted from the raw CCH to reveal interactions of neuronal origin in isolation. Significant CCH peaks, indicating interactions of neuronal origin, were obtained in 11% of the dual single-unit recordings and 46% of the dual multiunit recordings with moving bars. The incidence of nonflat CCHs with flashed bars was 29 and 78%, respectively. For the pairs of recording sites where both flashed and moving stimuli were used, the incidences of significant CCHs were very similar. Three types of peaks were distinguished on the basis of their width at half-height: T (<16 ms), C (between 16 and 180 ms), and H peaks (>180 ms). T peaks were very rarely observed (<1% in single-unit recordings). H peaks were observed in 7-16% of the single-unit CCHs, and C peaks in 6-16%, depending on the stimulus used. C and H peaks were observed more often when the receptive fields were overlapping or distant by <2 degrees. To test for the presence of synchronization between neurons in areas V1 and V2, we measured the position of the CCH peak with respect to the origin of the time axis of the CCH. Only in the case of a few T peaks did we find displaced peaks, indicating a possible drive of the V2 neuron by the simultaneously recorded V1 cell. All the other peaks were either centered on the origin or overlapped the origin of time with their upper halves. Thus similarly to what has been reported for the cat, neurons belonging to different cortical areas in the monkey tend to synchronize the time of emission of their action potentials with three different levels of temporal precision. For peaks calculated from flashed stimuli, we compared the peak position with the difference between latencies of V1 and V2 neurons. There was a clear correlation for single-unit pairs in the case of C peaks. Thus the position of a C peak on the time axis appears to reflect the order of visual activation of the correlated neurons. The coupling strength for H peaks was smaller during visual drive compared with spontaneous activity. On the contrary, C peaks were seen more often and were stronger during visual stimulation than during spontaneous activity. This suggests that C-type synchronization is associated with the processing of visual information. The origin of synchronized activity in a serially organized system is discussed.

Influence of the antioxidant quercetin in vivo on the level of nitric oxide determined by electron paramagnetic resonance in rat brain during global ischemia and reperfusion

We characterized the changes in nitric oxide (NO) levels in the brain during global forebrain ischemia and reperfusion and tested the ability of the natural flavonoid, quercetin, and a synthetic flavonoid, FB277, to increase the amount of available NO by elimination of the superoxide radicals produced during reperfusion. In Sprague-Dawley rats, we used a four-vessel occlusion model of forebrain ischemia (15 min) and reperfusion (30 min). Brain NO was measured on samples of cerebral cortex and cerebellum ex vivo by electron paramagnetic resonance (EPR) spectroscopy. The spin trap used was diethyldithiocarbamate sodium salt (DETC) associated with ferrous citrate. The complex Fe(DETC)2NO was detected at 77 K as a triplet signal at g = 2.035. Groups of animals were treated with quercetin or FB277 (3-morpholinomethyl-3',4',5,7tetramethoxyflavone) or polyethylene glycol-conjugated superoxide dismutase (PEG-SOD). In control (intact anesthetized animals), the signal was about 3 times greater in the cortex than in the cerebellum. During ischemia, the signal rose to 110% in cortex (NS) and 283% in cerebellum (P < 0.05). In reperfusion, it fell again to 91% of control in cerebellum (NS) and 35% in cortex (P < 0.05). Treatment by quercetin (5 mg/kg i.v.) of intact and ischemia-reperfusion groups did not significantly change the signal amplitude in the cerebellum, but did double it in the cortex (to 76% of control) for the ischemia-reperfusion group (P < 0.05). In contrast, FB277 (3.75 mg/kg i.v.) did not increase the signal in the cortex during ischemia-reperfusion, but did do so in the cerebellum (to 152% of control, P < 0.05). The results obtained for PEG-SOD (10,000 U/kg i.v.) were similar to those for FB277. In separate in vitro measurements, we found that quercetin but not FB277 efficiently scavenged superoxide. We hypothesize that quercetin but not FB277 scavenged superoxide anions released in the cortex during reperfusion, thus diminishing the amount of NO removed by the formation of peroxynitrite. The lack of effect of PEG-SOD may be related to the need for chronic treatment to obtain protection.

[Biosynthesis and transport of sterols in the yeast Saccharomyces cerevisiae]

The yeast Saccharomyces cerevisiae was a powerful tool in the identification of the structural genes involved in sterol biosynthesis in eucaryotes. Among 20 genes, 16 were isolated by genetic techniques using either complementation of mutants or overexpression strategy using specific inhibitors. In spite of this good knowledge concerning the genes of the pathway, little is known about the regulation of the isoprenoid/steroid biosynthetic pathway. However, the existence of two genes encoding HMG-CoA reductase in yeast genome suggests strongly that this enzyme could play a fundamental function in regulation, such as in plants and mammals. The regulation mechanisms could also involve sterol trafficking and storage. Indeed, one enzyme in the pathway, the sterol-C24-methyl transferase is localized in lipid particles that correspond to the storage form of steryl esters. Yeast cells are impermeable towards exogenous sterols in aerobiosis and become permeable in anaerobiosis when ergosterol synthesis is precluded by the absence of molecular oxygen. This phenomenon called aerobic sterol exclusion is dependent on the hem status of the cell. One gene, named SUT1 was identified that directs aerobic sterol uptake in yeast SUT1 gene and his partner SUT2 present strong features common to yeast transcription factors and could regulate the expression of genes involved in sterol uptake or intracellular trafficking.