Toxicodynetics: A new discipline in clinical toxicology.

OBJECTIVES: Regarding the different disciplines that encompass the pharmacology and the toxicology, none is specifically dedicated to the description and analysis of the time-course of relevant toxic effects both in experimental and clinical studies. The lack of a discipline devoted to this major field in toxicology results in misconception and even in errors by clinicians. MATERIAL AND METHODS: Review of the basic different disciplines that encompass pharmacology toxicology and comparing with the description of the time-course of effects in conditions in which toxicological analysis was not performed or with limited analytical evidence. RESULTS: Review of the literature clearly shows how misleading is the current extrapolation of toxicokinetic data to the description of the time-course of toxic effects. CONCLUSION: A new discipline entitled toxicodynetics should be developed aiming at a more systematic description of the time-course of effects in acute human and experimental poisonings. Toxicodynetics might help emergency physicians in risk assessment when facing a poisoning and contribute to a better assessment of quality control of data collected by poison control centres. Toxicodynetics would also allow a quantitative approach to the clinical effects resulting from drug-drug interaction.

Population pharmacokinetics and pharmacodynamics of imipenem in neutropenic adult patients.

OBJECTIVE: Imipenem is recommended in patients with chemotherapy-induced febrile neutropenia. Although alterations of antibiotic pharmacokinetic parameters have been reported in such patients, little data is available on imipenem. METHODS: Prospective, single-center, non-interventional pharmacokinetic cohort study in adults with chemotherapy-induced febrile neutropenia. Critically ill patients were excluded. Imipenem was administered as a 30-min infusion of 1000 mg/8h. Total imipenem plasma concentrations were assayed by high-performance liquid chromatography during neutropenia and just after neutrophil recovery. We estimated population pharmacokinetic parameters of imipenem by non-linear mixed-effect modelling using the SAEM algorithm. RESULTS: Sixteen patients were included in the study, including nine women (56.3%), median age 37 years (range, 18.3; 78.3). Eight patients had an hematological malignancy (50.0%) and seven had a solid tumor (43.8%). Imipenem pharmacokinetics were best described by a one-compartment model with first-order elimination. Mean values for imipenem were: clearance 14.3L/h and 10.9L/h and volume of distribution 20.7L and 14.5 L during neutropenia and after recovery, respectively. Imipenem plasma area under the curve at steady state was reduced by 23% during neutropenia. However, all patients achieved a pharmacodynamic target of %fT>MIC ≥ 40% with a regimen of 1000 mg/8 h or 500 mg/6 h, for MICs up to 2 mg/L. The pharmacodynamics profile for a target of %fT > MIC = 100% was however less favorable with 500 mg/6 h or 1000 mg/8 h either during or after neutropenia. CONCLUSION: Pharmacokinetic/pharmacodynamic goals for imipenem were similar in patients during and after neutropenia, despite reduced plasma exposure.

False-Positive Ethanol Level in Urine and Plasma Samples of a Resuscitated Infant.

We report the case of an 11-month-old male infant with a complex congenital heart disease who was admitted in the intensive care unit following cardiorespiratory arrest at home. Toxicological urine screening reported an ethanol concentration of 0.65 g/L using an enzymatic assay, without suspicion of alcohol intake; a significant amount of ethanol concentration was found in two plasma samples using the same enzymatic assay. Plasma and urine ethanol concentrations were below the limit of quantification (LOQ) when tested using a gas chromatography method. Urine ethanol level was also below the LOQ when tested by enzymatic assay after an initial urine ultrafiltration. These results confirmed our suspicion of matrix interference due to elevated lactate and lactate dehydrogenase levels interfering in the enzymatic assay. This analytical interference, well-known in postmortem samples, extensively studied in vitro, has been rarely reported in vivo, especially in children. To the best of our knowledge, this case is only the sixth one reported in an infant's plasma and the first initially discovered from urine. Indeed, as for ethanol, this last matrix has not been studied in the context of this artifact that may induce false-positive ethanol results while seeking a diagnosis in life-threatening or fatal situations that are potentially subject to forensic scrutiny. In parallel to a synthetic literature review, we propose a simple, informative decision tree, in order to help health professionals suspecting a false-positive result when performing an ethanol assay.

Assessment of vitamin A status of preschool children in a sub-Saharan African setting: comparative advantage of modified relative-dose response test.

A nationally-representative sample of 2,696 preschool children living in Congo was examined during Au gust-September 2003 to determine the rates of vitamin A deficiency. Ninety clusters of 30 children, aged six months to six years, were selected, using a randomized two-level cluster-sampling method. Vitamin A deficiency was determined by assessing the prevalence of active xerophthalmia (nightblindness and/or Bitot spots) in the cross-over sample of 2,696 individuals. A semi-quantitative seven-day dietary questionnaire was concurrently applied to the mothers of children enrolled to estimate the latter's consumption of vitamin A-rich food. Vitamin A status was assessed by performing the modified relative dose-response test (MRDR) on dried blood spots (DBS) from a subsample of 207 children aged less than six years and the impression cytology with transfer (ICT) test on a subsample of 1,162 children. Of the children enrolled, 5.2% suffered from nightblindness, 8.0% had Bitot spots, and 2.5% had other vitamin A deficiency sequellae. Fifty-three percent of the ICT tests showed the presence of vitamin A deficiency. The biochemical MRDR test showed that the vitamin A status of 30% of the study children was critical. Twenty-seven of them had retinol levels of < 10 microg/dL [mean +/- standard deviation (SD) 7.02 +/- 2.0 microg/dL], and 50% had retinol levels of 10-20 microg/dL (mean +/- SD 14.2 +/- 2.83 microg/dL). The poor health status and low rates of consumption of vitamin A-rich food are the main factors determining critical status. Vitamin A deficiency, reflecting poor nutrition and health, is a serious public-health issue among children aged less than six years in Congo.

Assessment of the targeting specificity of a fluorescent albumin conceived as a preclinical agent of the liver function.

In the context of increasing liver diseases, no contrast agent is currently available in Europe and the United States to directly assess the liver function. Only neolactosylated human serum albumin is being clinically used in Asia. In order to perform preclinical studies in the context of liver diseases, we conceived a fluorescent lactosylated albumin for the quantification of liver functional cells (l-Cyal). Precise characterization was achieved in order to determine the amounts of lactose and Cyanine 5 (Cy5) coupled to the albumin. In addition, potential aggregation was characterized by asymmetrical flow field-flow fractionation hyphenated to multi-angle light scattering (AF4-MALS). The optimal functionalized albumin exhibited a mass greater than 87 kDa which corresponds to the addition of 34 lactose moieties per protein and 1-2 Cy5 labels. Also, no significant formation of aggregates could be identified due to the modification of the native albumin. In healthy mice, the accumulation of l-Cyal in the liver and its selectivity for hepatocyte cells were shown by optical imaging and flow cytometry. Administration of l-Cyal to mice bearing liver metastases showed a reduced signal in the liver related to a decrease in the number of hepatocytes. The l-Cyal bioimaging contrast agent could be particularly useful for assessing the state of liver related diseases.

Preferential expression of domain cassettes 4, 8 and 13 of Plasmodium falciparum erythrocyte membrane protein 1 in severe malaria imported in France.

OBJECTIVES: Severe Plasmodium falciparum malaria (SM) involves cytoadhesion of parasitized red blood cells, mediated by P. falciparum erythrocyte membrane protein 1, which is encoded by var genes. Expression of var gene group A and B or encoding domain cassettes DC4, DC5, DC8 and DC13 has been implicated in SM in African children, but no data exist in the context of imported malaria. The aim of this study was to investigate var gene expression linked to clinical presentation and host factors in SM imported into France. METHODS: Expression level of var gene groups A, B, C, var1, var2csa, var3 and var genes encoding DC4, DC5, DC8 and DC13 was measured by quantitative RT-PCR and expressed in transcript units. Seventy SM and 48 uncomplicated malaria (UM) P. falciparum cases were analysed according to disease severity, epidemiological characteristics (migrants or travellers) and anti-P. falciparum antibodies. Cluster analysis was performed to identify gene expression profiles. RESULTS: Var1 and B/C expression were higher in UM than SM (0.66 (0-1.1) and 1.88 (1.3-2.4); p <0.04, respectively). Group C expression differed between migrants and travellers (0.21 (0-0.75) versus 0 (0-0); p 0.002). Group A differed in naive and pre-exposed patients (1.1 (0.7-1.5) versus 0.4 (0-1.1); p 0.01). Population clusters revealed increased expression from group A and B var genes, and DC4, DC8 and DC13 in SM. CONCLUSIONS: These results corroborate the implication of DC4, DC8 and DC13 in severe imported malaria cases as African children, and their expression depends of host factors.

Quantification of urinary allantoin by capillary zone electrophoresis during recombinant urate oxydase (rasburicase) therapy.

OBJECTIVES: Rasburicase (Fasturtec) is used to prevent or treat hyperuricemia associated with chemotherapy. We developed a capillary zone electrophoresis method to measure urinary allantoin, the degradation product of uric acid by rasburicase. DESIGN AND METHODS: Electrophoresis was performed using a P/ACE 5500 system (Beckman) with a fused silica capillary tube and a UV-visible detector set at 214 nm. Urine samples from 10 patients with non-Hodgkin's lymphoma were analyzed to validate the technique. RESULTS: Using a sodium tetraborate running buffer, urinary allantoin was separated from related compounds and internal standard in less than 30 min. The method was linear up to 1.25 g/L (quantification limit: 30 mg/L); precision was below 10%. The total amount of allantoin excreted in patients treated by rasburicase ranged from 1.5 g to 7.9 g/4 days. CONCLUSION: This CZE assay is a simple, rapid and reproducible method to measure allantoin in urine. Different elimination profiles have been found in patients treated with rasburicase.

Prevalence of infant Vitamin A deficiency and undernutrition in the Republic of Congo.

OBJECTIVES: A representative sample of 5722 pre-school children living in rural and urban areas of the Congo was examined between July and September 1999 for assessing Vitamin A deficiency. METHODS: Using a randomized two-level cluster sampling method, 190 clusters of 30 children aged from 6 months to 6 years were selected in order to assess the prevalence of active xerophthalmia (night blindness and/or Bitot spots). Concurrently, the children's height and weight were determined. A semi-quantitative seven-day dietary questionnaire was applied to the mothers of 5722 children to estimate the latter's consumption of Vitamin A rich foodstuffs. The prevalence of biochemical deficiency was assessed based on the serum retinol concentrations analyzed in dried blood spots from a sub-sample of 300 children living in the Pointe-Noire area. RESULTS: Among the 5722 children studied, 0.7% were found to suffer from night blindness and 7.7% had Bitot spots. The weekly intake of Vitamin A rich foods was estimated in 5722 children. Our data suggest that Vitamin A rich food consumption was lower in rural zones than in urban area according to the food frequency method threshold values. The serum retinol levels were lower than 10 microg/dl in 18% (95% confidence interval [C.I.]: 13.7, 22.3) [8.04+/-2.87 microg/dl] and less than 20 microg/dl in 49% (95% C.I.: 43.4, 54.6) [15.05+/-2.76 microg/dl] of the 300 studied children. We have established a significant relation between mean serum retinol levels and high rate of Vitamin A food intake (chi-square=59.64, 2 d.d.l., p<0.05) in the sample studied. The mean serum retinol concentrations did not differ significantly between the various Z-scores of weight for age (W/A) and height for age (H/A) patterns. But children with a weight for height (W/H) ratio below -2 standard deviation (S.D.) had significantly lower serum retinol values [9.33+/-1.3 microg/dl] than those with a W/H ratio greater than or equal to -2S.D. [10.82+/-4.84 microg/dl]. CONCLUSION: These data suggest that Vitamin A deficiency is still a serious public health problem in rural areas of the Congo in which this study was carried out.

Effects of acute ethanol administration on the uptake of 59Fe-labeled transferrin by rat liver and cerebellum.

The uptake of iron by the liver and cerebellum was measured in rats using [59Fe]transferrin. An acute ethanol load (50 mmol/kg body wt., i.p.) elicited a significant increase in the hepatic and cerebellar non-heme iron concentration. The uptake of 59Fe by the liver and the cerebellum was significantly greater in the ethanol-treated rats than in control animals. The administration of allopurinol prior to the ethanol load prevented the changes in liver and cerebellar non-heme iron content. Moreover pretreatment with allopurinol reduced the ethanol-induced enhancement of 59Fe uptake by the liver and completely prevented the changes in 59Fe uptake by the cerebellum. These effects of allopurinol lead us to suggest that oxygen-derived free radicals are involved in the ethanol-induced disturbances of iron uptake both at the hepatic and cerebellar level.

Changes in some pro- and antioxidants in rat cerebellum after chronic alcohol intake.

Some pro- and antioxidants were measured in the cerebellum from ethanol-fed rats using ethanol administration in drinking water as a model of moderate alcohol intoxication. After 4 weeks of ethanol intake, a 30% increase in the nonheme iron content in the cerebellum occurred in ethanol-fed rats as compared to control animals. The low-molecular-weight-chelated iron (LMWC-Fe) content as well as the percentage of total nonheme iron represented by LMWC-Fe were increased in the cerebellar cytosol after chronic ethanol administration. Cerebellar copper and selenium concentrations were lower and zinc concentration higher in ethanol-fed rats than in controls. Ethanol consumption decreased the cerebellar vitamin E level. Glutathione S-transferase [EC 2. 5. 1. 18] activity was higher, whereas glutathione peroxidase [glutathione: H2O2 oxidoreductase, EC 1. 11. 1. 9] activity was not altered by ethanol treatment. No significant changes in cerebellar lipid peroxidation, carbonyl protein content, or glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming) EC 6. 3. 1. 2] activity were observed. These results suggest that adaptative increases in some elements of the antioxidant defense may counteract the increase in LMWC-Fe, a pro-oxidant factor, and prevent the occurrence of overt cellular lipid and protein damage. However, after 8 weeks of ethanol intake, the activity of glutamine synthetase, an enzyme specially sensitive to inactivation by oxygen radicals, was decreased, suggesting that this prevention was not totally achieved.

Effect of acute ethanol administration on the subcellular distribution of iron in rat liver and cerebellum.

An acute ethanol load (50 mmol/kg, i.p.) produced altogether a decrease in the non-heme iron content of the serum and an increase in the iron content in liver and cerebellum. Subcellular fractionation studies indicated that the non-heme iron accumulated by the liver, 4 hr after the ethanol load, was recovered in light mitochondria, microsomes and cytosol, and that iron accumulated by the cerebellum was localized in heavy mitochondria, light mitochondria, microsomes and cytosol. The low molecular weight chelatable (LMWC) iron content as well as the percentage of total non-heme iron represented by LMWC-iron were increased in the cytosol of liver and cerebellum after the ethanol load. These results suggest that an acute ethanol load induces (i) a shift in the distribution between circulating and tissular non-heme iron; (ii) an increase in the cytosolic LMWC-iron which, by favouring the biosynthesis of reactive free radicals, may contribute to lipid peroxidation in liver and cerebellum.

Preclinical evaluation of an automated closed fluid management device: Cytomate, for washing out DMSO from hematopoietic stem cell grafts after thawing.

Infusion of dimethylsulfoxide (DMSO) contained in cryopreserved and thawed hematopoietic stem cell (HSC) grafts is frequently associated with mild or moderate adverse reactions, and occasionally with more severe events including neurological symptoms. The severity of these complications is related to the amount of residual DMSO. We evaluated a recently available, closed, automated and 'cgmp (current good manufacturing practice) compliant' device (CytoMate) for its ability to wash out DMSO at the expense of a limited loss of viable CD34(+) cells. A total of 16 procedures were carried out with 39 blood HSC bags intended for destruction. Mean amounts of DMSO for each cellular product (one, two or three bags) were between 12.2 and 39.6 g before thawing; after the washing procedure, residual DMSO quantities were between 0.1 and 3.7 g. When set up to reproducibly allow for a more than 96% elimination of DMSO, processing of thawed cells with the CytoMate cell processor resulted in a mean recovery of viable total cells, CD34(+) cells and lymphocyte subsets above 60%. We conclude that this simple and efficient washing technique is suitable for routine processing of HSC grafts. Clinical studies will demonstrate whether a reduction in the incidence of adverse effects associated with DMSO infusion is observed.

Effects of respiratory acidosis and alkalosis on the distribution of cyanide into the rat brain.

The aim of this study was to determine whether respiratory acidosis favors the cerebral distribution of cyanide, and conversely, if respiratory alkalosis limits its distribution. The pharmacokinetics of a nontoxic dose of cyanide were first studied in a group of 7 rats in order to determine the distribution phase. The pharmacokinetics were found to best fit a 3-compartment model with very rapid distribution (whole blood T(1/2)alpha = 21.6 +/- 3.3 s). Then the effects of the modulation of arterial pH on the distribution of a nontoxic dose of intravenously administered cyanide into the brains of rats were studied by means of the determination of the permeability-area product (PA). The modulation of arterial blood pH was performed by variation of arterial carbon dioxide tension (PaCO2) in 3 groups of 8 anesthetized mechanically ventilated rats. The mean arterial pH measured 20 min after the start of mechanical ventilation in the acidotic, physiologic, and alkalotic groups were 7.07 +/- 0.03, 7.41 +/- 0.01, and 7.58 +/- 0.01, respectively. The mean PAs in the acidotic, physiologic, and alkalotic groups, determined 30 s after the intravenous administration of cyanide, were 0.015 +/- 0.002, 0.011 +/- 0.001, and 0.008 +/- 0.001 s(-1), respectively (one-way ANOVA; p < 0.0087). At alkalotic pH the mean permeability-area product was 43% of that measured at acidotic pH. This effect of pH on the rapidity of cyanide distribution does not appear to be limited to specific areas of the brain. We conclude that modulation of arterial pH by altering PaCO2 may induce significant effects on the brain uptake of cyanide.

Comparison of urinary markers for bone resorption in multiple myeloma.

Multiple myeloma causes extensive bone remodeling. Classical biochemical markers such as urinary calcium have poor sensitivity for detecting multiple myeloma bone remodeling. New biochemicals have been developed including a carboxyterminal telopeptide of collagen I (CTX). We used an immunoenzymatic assay to determine urinary CTX in 60 patients with multiple myeloma. This marker was evaluated with regard to total pyridinolines, urinary calcium, radiological features, pain and response to treatment with bisphosphonates. In patients with bone involvement, CTX concentrations were significantly higher (+230%) than those of deoxypyridinoline (DPD) (+175%) and pyridinolines (PYD) (+130%). In all patients we have found a close correlation between CTX and DPD but not between CTX and PYD. Compared to radiological features, CTX was more sensitive (97%) and specific (96%) than DPD. After treatment by bisphosphonates, the fall in CTX concentrations was paralleled to urinary calcium and more marked than pyridinolines. Although our results need to be confirmed, CTX appears to be a potential marker to explore bone involvement in multiple myeloma.

Urinary carboxyterminal telopeptide of collagen I as a potential marker of bone metastases chemotherapy monitoring in breast cancer.

Breast cancers frequently have osteoclastic bone metastases that are difficult to monitor and treat. Bone scintigraphy with 99mTc-labeled biphosphonates is still the reference method for detecting and localizing bone involvement. Classical biochemical markers such as urinary calcium have poor sensitivity for detecting and monitoring metastases of breast cancers. New biochemical markers for the study of bone remodeling have recently been developed, including a degradation product of the C-terminal end of the telopeptide of type I collagen (CTX). We used an immunoenzymatic assay technique for urinary CTX in 84 pre- and post-menopausal women and demonstrated a correlation between scintigraphic scores and urinary CTX concentrations. CTX values are significantly different between the control group and patients with bone metastasis, except those with score 0. There is a regular increase in urinary CTX concentration from score 0 (no abnormal uptake) to score 4 (diffuse carcinomatosis). There is no significant variation between control population and score 0 to 3 for urinary calcium. Only women with scintigraphic score 4 have significantly increased urinary calcium concentrations. Measuring CTX in pre- and post-menopausal patients during breast cancer chemotherapy might be of great interest for monitoring the development of metastases and the therapeutic efficacy of chemotherapy.

Steady-state population pharmacokinetics of sustained release theophylline in adult asthmatic patients.

The steady-state population pharmacokinetics of theophylline were studied in 52 asthmatic adult patients who received sustained-release theophylline as armophylline or euphylline. A total of 92 steady-state plasma theophylline concentration-dosage pairs were analyzed using a nonlinear mixed effects model. The pharmacokinetic model used was a one-compartment open model with single path Michaelis-Menten elimination. Dosage was adjusted to body weight. The effects of age, gender, alcohol consumption, cigarette smoking, dosage form, concurrent treatment with beta-agonists or steroids, outpatient dosing, and plasma caffeine concentration on maximum elimination rate (Vm) and Michaelis constant for theophylline metabolism (Km) were investigated. Hypothesis testing produced a final model in which Km = 0.42 (mg/l), and Vm (mg/kg per day) was based on cigarette smoking and dosage form, with Vm = 7.54 + 2.01 (smoking) + 1.08 (euphylline). Estimated coefficients of variation for interindividual variability in Km and Vm were 162.6% and 48.1%, respectively. Residual variability in dosage rates was estimated as 0.90 mg/kg per day. The identification of factors influencing theophylline disposition should prove useful for the a priori design of theophylline dosage regimens and monitoring of drug levels during therapy.

1-Methyl-4-phenylpyridinium (MPP+) does not exhibit paraquat-like immunoreactivity.

The structural analogy of paraquat with 1-methyl-4-phenylpyridinium (MPP+) has been implied in the aetiology of Parkinson's disease. The cross-reactivity of MPP+ to a specific antibody to paraquat was assessed by radioimmunoassay and was found to be very low. The results suggest that this polyclonal paraquat antibody does not mimic the MPP+ receptor.

Toxicokinetics of paraquat in humans.

1. The toxicokinetics of paraquat were studied in 18 cases of acute human poisoning using a specific radioimmunoassay. Plasma paraquat concentration exhibited a mean distribution half-life (t1/2 alpha) of 5 h and a mean elimination half-life (t1/2 beta) of 84 h. Cardiovascular collapse supervened early during the course of the intoxication and was associated with the distribution phase. Death related to pulmonary fibrosis occurred late and was associated with the elimination phase. 2. Pharmacokinetic analysis of urine paraquat excretion confirmed the biphasic decline of paraquat. Moreover, renal paraquat and creatinine clearances were not correlated but renal paraquat clearance was never higher than the renal creatinine clearance. 3. Tissue paraquat distribution was ubiquitous with an apparent volume of distribution ranging from 1.2 to 1.6 l/kg. Muscle could represent an important reservoir explaining the long persistence of paraquat in plasma and urine for several weeks or months after poisoning.

Efficacy of 4-methylpyrazole in ethylene glycol poisoning: clinical and toxicokinetic aspects.

Potentially fatal ethylene glycol intoxication in an adult with normal renal function was treated with 4-methylpyrazole administered three hours after the incident occurred. The plasma ethylene glycol concentration was 3.5 g l-1 on admission. The metabolic acidosis present on admission resolved within four hours, and the subsequent clinical course was uneventful. The apparent plasma half-life of ethylene glycol was 16 h and the mean renal and plasma clearances of ethylene glycol were 24 and 25 ml min-1, respectively. These results support the hypothesis that complete blockade of hepatic metabolism of ethylene glycol is achieved by 4-methylpyrazole. The only side-effect observed as a result of treatment was a transient slight increase in serum transaminase activity.

[Microassay of serum iron by induced plasma emission spectrometry]. / Microdosage du fer sérique par spectrométrie d'émission par plasma induit HF (SEPIHF).

The authors describe a new micromethod for iron quantification in serum by ICPAES. Because the high temperature of quantification, the results are not affected by the iron chelating drugs used for the treatment of major thalassaemia (desferrioxamine).