New aspects in deriving health-based guidance values for bromate in swimming pool water

Bromate, classified as a EU CLP 1B carcinogen, is a typical by-product of the disinfection of drinking and swimming pool water. The aim of this study was (a) to provide data on the occurrence of bromate in pool water, (b) to re-evaluate the carcinogenic MOA of bromate in the light of existing data, (c) to assess the possible exposure to bromate via swimming pool water and (d) to inform the derivation of cancer risk-related bromate concentrations in swimming pool water. Measurements from monitoring analysis of 229 samples showed bromate concentrations in seawater pools up to 34 mg/L. A comprehensive non-systematic literature search was done and the quality of the studies on genotoxicity and carcinogenicity was assessed by Klimisch criteria (Klimisch et al., Regul Toxicol Pharmacol 25:1–5, 1997) and SciRAP tool (Beronius et al., J Appl Toxicol, 38:1460–1470, 2018) respectively. Benchmark dose (BMD) modeling was performed using the modeling average mode in BMDS 3.1 and PROAST 66.40, 67 and 69 (human cancer BMDL₁₀; EFSA 2017). For exposure assessment, data from a wide range of sources were evaluated for their reliability. Different target groups (infants/toddlers, children and adults) and exposure scenarios (recreational, sport-active swimmers, top athletes) were considered for oral, inhalation and dermal exposure. Exposure was calculated according to the frequency of swimming events and duration in water. For illustration, cancer risk-related bromate concentrations in pool water were calculated for different target groups, taking into account their exposure using the hBMDL₁₀ and a cancer risk of 1 in 100,000. Convincing evidence was obtained from a multitude of studies that bromate induces oxidative DNA damage and acts as a clastogen in vitro and in vivo. Since statistical modeling of the available genotoxicity data is compatible with both linear as well as non-linear dose–response relationships, bromate should be conservatively considered to be a non-threshold carcinogen. BMD modeling with model averaging for renal cancer studies (Kurokawa et al., J Natl. Cancer Inst, 1983 and 1986a; DeAngelo et al., Toxicol Pathol 26:587–594, 1998) resulted in a median hBMDL₁₀ of 0.65 mg bromate/kg body weight (bw) per day. Evaluation of different age and activity groups revealed that top athletes had the highest exposure, followed by sport-active children, sport-active adults, infants and toddlers, children and adults. The predominant route of exposure was oral (73–98%) by swallowing water, followed by the dermal route (2–27%), while the inhalation route was insignificant (< 0.5%). Accepting the same risk level for all population groups resulted in different guidance values due to the large variation in exposure. For example, for an additional risk of 1 in 100,000, the bromate concentrations would range between 0.011 for top athletes, 0.015 for sport-active children and 2.1 mg/L for adults. In conclusion, the present study shows that health risks due to bromate exposure by swimming pool water cannot be excluded and that large differences in risk exist depending on the individual swimming habits and water concentrations.

Use of mechanistic information to derive chemical-specific adjustment factors - Refinement of risk assessment

When extrapolating data from animal toxicological studies a default factor (dUF) of 100 is applied to derive a heath based guidance value. The UF takes into account the interspecies differences (ID) and the intraspecies variability (IV). When re-evaluating the safety of phosphates used as food additives nephrocalcinosis was identified as the critical endpoint. The underlying mechanism for nephrocalcinosis was attributed to the precipitation of calcium phosphate in the kidney, depending on its solubility, irrespective of the species and the population. Based on the mechanism, the volume of primary urine, for which the glomerular filtration rate (GFR) was used as a proxy, was considered to be the only parameter relevant for ID and IV. Median value of GFR in rats was 4.0 ml/min/kg bw. In humans it was 1.6 ml/min/kg bw in healthy adults and 0.9 in elderly. These values were calculated from the distribution of the GFR data from 8 studies in rats (n = 191), 16 studies in adults (n = 1540) and 5 studies in elderly (n = 2608). Multiplying the distribution of the ratio rat/healthy humans (ID) with the distribution of the ratio healthy humans/elderly human (IV) resulted in a phosphate specific factor of 4.5 (3.3-6.7) (median; 25th - 75th percentile).

Critical evaluation of human health risks due to hydraulic fracturing in natural gas and petroleum production

The use of hydraulic fracturing (HF) to extract oil and natural gas has increased, along with intensive discussions on the associated risks to human health. Three technical processes should be differentiated when evaluating human health risks, namely (1) drilling of the borehole, (2) hydraulic stimulation, and (3) gas or oil production. During the drilling phase, emissions such as NOx, NMVOCs (non-methane volatile organic compounds) as precursors for tropospheric ozone formation, and SOx have been shown to be higher compared to the subsequent phases. In relation to hydraulic stimulation, the toxicity of frac fluids is of relevance. More than 1100 compounds have been identified as components. A trend is to use fewer, less hazardous and more biodegradable substances; however, the use of hydrocarbons, such as kerosene and diesel, is still allowed in the USA. Methane in drinking water is of low toxicological relevance but may indicate inadequate integrity of the gas well. There is a great concern regarding the contamination of ground- and surface water during the production phase. Water that flows to the surface from oil and gas wells, so-called 'produced water', represents a mixture of flow-back, the injected frac fluid returning to the surface, and the reservoir water present in natural oil and gas deposits. Among numerous hazardous compounds, produced water may contain bromide, arsenic, strontium, mercury, barium, radioactive isotopes and organic compounds, particularly benzene, toluene, ethylbenzene and xylenes (BTEX). The sewage outflow, even from specialized treatment plants, may still contain critical concentrations of barium, strontium and arsenic. Evidence suggests that the quality of groundwater and surface water may be compromised by disposal of produced water. Particularly critical is the use of produced water for watering of agricultural areas, where persistent compounds may accumulate. Air contamination can occur as a result of several HF-associated activities. In addition to BTEX, 20 HF-associated air contaminants are group 1A or 1B carcinogens according to the IARC. In the U.S., oil and gas production (including conventional production) represents the second largest source of anthropogenic methane emissions. High-quality epidemiological studies are required, especially in light of recent observations of an association between childhood leukemia and multiple myeloma in the neighborhood of oil and gas production sites. In conclusion, (1) strong evidence supports the conclusion that frac fluids can lead to local environmental contamination; (2) while changes in the chemical composition of soil, water and air are likely to occur, the increased levels are still often below threshold values for safety; (3) point source pollution due to poor maintenance of wells and pipelines can be monitored and remedied; (4) risk assessment should be based on both hazard and exposure evaluation; (5) while the concentrations of frac fluid chemicals are low, some are known carcinogens; therefore, thorough, well-designed studies are needed to assess the risk to human health with high certainty; (6) HF can represent a health risk via long-lasting contamination of soil and water, when strict safety measures are not rigorously applied.

Daily uptake of mycotoxins - TDI might not be protective for nursed infants

Exclusive breast feeding is recommended by international bodies for the first six months of life. Because of the presence of contaminants, breast feeding might lead to toxicologically relevant exposure of the nursed child. Exposure towards mycotoxins is of specific interest because of their widespread occurrence in food and of their toxicological profile. We calculated the relationship between maternal intake at the level of the existing TDIs and the exposure in the nursed infants of several mycotoxins to evaluate whether maternal exposure at the TDI is also safe for the nursed infant. If published information was not available we used in silico methods for estimating toxicokinetic parameters and the lactational transfer. A single dose and a continuous daily intake scenario were considered. Maternal intake at the TDI exceeds the age-adjusted TDI (TDI/3) values for infants in case of deoxynivalenol and patulin in the single dose scenario. Exceedance is particularly pronounced for ochratoxin A in the continuous daily intake scenario (29.2 fold above the child adjusted TDI). According to published data in infants impaired kidney function may result from this exceedance. When setting a TDI, the safety of the exclusively nursed infant should be considered in the continuous daily intake scenario.

Critical evaluation of key evidence on the human health hazards of exposure to bisphenol A

Despite the fact that more than 5000 safety-related studies have been published on bisphenol A (BPA), there seems to be no resolution of the apparently deadlocked controversy as to whether exposure of the general population to BPA causes adverse effects due to its estrogenicity. Therefore, the Advisory Committee of the German Society of Toxicology reviewed the background and cutting-edge topics of this BPA controversy. The current tolerable daily intake value (TDI) of 0.05 mg/kg body weight [bw]/day, derived by the European Food Safety Authority (EFSA), is mainly based on body weight changes in two- and three-generation studies in mice and rats. Recently, these studies and the derivation of the TDI have been criticized. After having carefully considered all arguments, the Committee had to conclude that the criticism was scientifically not justified; moreover, recently published additional data further support the reliability of the two- and three-generation studies demonstrating a lack of estrogen-dependent effects at and below doses on which the current TDI is based. A frequently discussed topic is whether doses below 5 mg/kg bw/day may cause adverse health effects in laboratory animals. Meanwhile, it has become clear that positive results from some explorative studies have not been confirmed in subsequent studies with higher numbers of animals or a priori defined hypotheses. Particularly relevant are some recent studies with negative outcomes that addressed effects of BPA on the brain, behavior, and the prostate in rodents for extrapolation to the human situation. The Committee came to the conclusion that rodent data can well be used as a basis for human risk evaluation. Currently published conjectures that rats are insensitive to estrogens compared to humans can be refuted. Data from toxicokinetics studies show that the half-life of BPA in adult human subjects is less than 2 hours and BPA is completely recovered in urine as BPA-conjugates. Tissue deconjugation of BPA-glucuronide and -sulfate may occur. Because of the extremely low quantities, it is only of minor relevance for BPA toxicity. Biomonitoring studies have been used to estimate human BPA exposure and show that the daily intake of BPA is far below the TDI for the general population. Further topics addressed in this article include reasons why some studies on BPA are not reproducible; the relevance of oral versus non-oral exposure routes; the degree to which newborns are at higher systemic BPA exposure; increased BPA exposure by infusions in intensive care units; mechanisms of action other than estrogen receptor activation; and the current regulatory status in Europe, as well as in the USA, Canada, Japan, New Zealand, and Australia. Overall, the Committee concluded that the current TDI for BPA is adequately justified and that the available evidence indicates that BPA exposure represents no noteworthy risk to the health of the human population, including newborns and babies.

Primary rat hepatocytes as in vitro system for gene expression studies: comparison of sandwich, Matrigel and 2D cultures

Recent studies have presented evidence that in vivo obtained gene expression data can be used for carcinogen classification, for instance to differentiate between genotoxic and non-genotoxic carcinogens. However, although primary rat hepatocytes represent a well-established in vitro system for drug metabolism and enzyme induction, they have not yet been systematically optimized for toxicogenomic studies. The latter may be confounded by the fact that cultured hepatocytes show strong spontaneous alterations in gene expression patterns. Therefore, we addressed the following questions: (1) which culture system is optimal, comparing sandwich, Matrigel and 2D cultures, (2) how critical is the impact of culture period on substance-induced alterations in gene expression and (3) do these substance-induced alterations in cultured hepatocytes occur already at in vivo relevant concentrations? For this purpose we analyzed the expression of four genes, namely Abat, Gsk3beta, Myd116 and Sult1a1 that recently have been reported to be influenced by the antihistamine and non-genotoxic carcinogen methapyrilene (MPy). The most reproducible effects of MPy were observed in sandwich cultures. Induction factors of Gsk3beta and Myd116 at 100 microM MPy were 2 and 4 (medians), respectively, whereas expression of Abat and Sult1a1 were inhibited by factors of 7 and 5, respectively. Similar results were observed in hepatocytes maintained for 24 h or 3 weeks in sandwich culture with respect to the influence of MPy on the expression of Abat, Gsk3beta, Myd116 and Sult1a1. To determine whether MPy influences gene expression at in vivo relevant concentrations, 3.5 mg/kg MPy were administered to male Wistar rats intraperitoneally, resulting in plasma concentrations ranging between 1.72 and 0.32 microM 5 and 80 min after injection. Inhibition of Abat and Sult1a1 expression in vitro already occurred at in vivo relevant concentrations of 0.39 microM MPy. Induction of Myd116 was observed at 6.25 microM which is higher but in the same order of magnitude as in vivo relevant concentrations. In conclusion, the presented data strongly suggest that sandwich cultures are most adequate for detection of MPy-induced gene expression alterations and the effect of MPy was detected at in vivo relevant concentrations.

The role of active metabolites in dihydrocodeine effects

OBJECTIVE

The metabolism of dihydrocodeine to dihydromorphine, a high affinity mu-opioid receptor ligand in membrane homogenates, is catalyzed by CYP2D6. However, it is not clear whether an active CYP2D6 enzyme is required for opioid receptor-mediated effects in man after standard dihydrocodeine doses.

METHODS

Whole cell opioid-receptor affinity and effects on cAMP accumulation of dihydrocodeine and its metabolites were determined in differentiated SH-SY5Y neuroblastoma cells. In a double-blind, 2-period, placebo-controlled randomized crossover pilot study the pharmacokinetics of dihydrocodeine (60 mg single dose) and its metabolites were examined in 5 phenotyped extensive (EMs) and 4 poor metabolizers (PMs) for CYP2D6, and pharmacodynamics were evaluated using a pain threshold model and dynamic pupillometry.

RESULTS

Displacement binding and cAMP accumulation experiments showed clearly higher affinities (100- and 50-fold) and activities (180- and 250-fold) of dihydromorphine and dihydromorphine-6-glucuronide, respectively, whereas the other metabolites had similar or lower affinities and activities as compared to dihydrocodeine. The clinical study revealed no significant difference in plasma or urine pharmacokinetics between EMs and PMs for dihydrocodeine and its glucuronide. Dihydromorphine and its glucuronides were detectable in EMs only. A clear reduction of initial pupil diameters was observed up to 6 hours postdose in both PMs and EMs, with no obvious differences between CYP2D6 phenotypes. In the pain threshold model no effects were observed in either group.

CONCLUSION

CYP2D6 phenotype has no major impact on opioid receptor-mediated effects of a single 60 mg dihydrocodeine dose, despite the essential role of CYP2D6 in formation of highly active metabolites.

Children as a sensitive subgroup and their role in regulatory toxicology: DGPT workshop report

There is increasing discussion that children might be considered as a specific subgroup in public health regulations which could be more sensitive than the average "adult" human being. Differences between children and adults, with regard to susceptibility towards toxicants, may result from a combination of toxicokinetic, toxicodynamic and exposure factors. Kinetic factors are of importance mainly in the early postnatal period, largely as the result of immature elimination systems, i.e. metabolising enzymes and/or renal function. Specific vulnerability may prevail during several time periods, related to the development and maturation of organs (for example, brain, bone, endocrine system). For some substances, it has been shown that children at a specific age are less sensitive than adults. Specific exposures of toddlers to environmental chemicals may be high due to their moving behaviour and hand-to-mouth activities. Existing scenarios and models for exposure of children should be improved, in particular with respect to different ages. The outcome of model calculations must be verified by human biomonitoring analysis. At present, there is ongoing discussion of toxicological test models suitable to delineate human postnatal development. Experience with infant-orientated test systems is scarce (for example in developmental neurotoxicity). In general, tools for predicting toxicological sensitivity of children must be further improved. Regulators should also be aware that reduction of lifestyle-related toxic exposures such as smoking and drug abuse in children and adolescents is now an increasing public health problem in many countries.

Workshop report. Children as a special subpopulation: focus on immunotoxicity. Federal Institute for Health Protection of Consumers and Veterinary Medicine (BgVV), 15-16 November 2001, Berlin, Germany

An international symposium on the impact of environmental hazards, chemicals and drugs on the developing immune system of children was held in Berlin (Germany) organized by the BgVV. Epidemiological evidence indicates that an immature immune system challenged early in life by bacterial antigens may prevent, to some extent, allergic reactions including asthma bronchiale triggered by environmental pollutants. However, the prevalence for infectious disease is increased in childhood, especially when exposure to contaminants takes place in the period of pregnancy and breast-feeding. The effects of chlorinated biphenyls, dioxin, endotoxins, hexachlorobenzene, and direct and indirect in utero tobacco smoke exposure are examples. All participants recommend comparative and follow-up epidemiological studies and clinical examination of infants and children at risk during upbringing. There is ample evidence from experimental studies that indicates adverse effects on the developing immune system after in utero and postnatal exposure to chemicals and drugs. The adverse reactions of aciclovir, benzodiazepines, hexachlorobenzene, organotins (di-n-octyltin dichloride, tributyltin oxide), pesticides (methoxychlor, heptachlor) and polyhalogenated aromatic hydrocarbons (2,3,7,8-tetrachlorodibenzo-p-dioxin) are presented and reviewed. To determine the predictive value of test data in risk assessment for neonates and children, development, differentiation and maturation of the immune system in humans and laboratory rodents is compared in their pre- and postnatal stages. Considering some differences in immunocompetence at birth and after lactation, and differences in the time frame for maturation of the immune system, reaction types are thought to be common, comparable and similar in human childhood and early adolescence and the postnatal lifetime of laboratory rodents. The participants of the symposium felt strongly that regulatory steps urgently need to be initiated to incorporate some relevant aspects into existing test guidelines for testing developmental immunotoxicity. In this context, it is recommended that animals culled otherwise in one- and two-generation studies be examined for developmental immunotoxicity according to the valid methods and parameters discussed. The majority of participants agreed that a safety factor of 10 is too low in risk assessment and management to protect a sensitive subpopulation of children against man-made environmental pollutants.

In vitro prediction of gastrointestinal absorption and bioavailability: an experts' meeting report

The most convenient route of drug administration is peroral. To reach their target, drug molecules must be absorbed from the gastrointestinal tract and enter the systemic circulation in sufficient quantities. For this reason, understanding and anticipating the mechanisms and factors affecting gastrointestinal absorption and metabolism are of the utmost importance in developing new drugs. In contrast to drugs, which are administered intentionally for therapeutic reasons, chemical residues in food and other matrices enter the body unintentionally. Hence, in this case, a low systemic availability would be advantageous. For many reasons, but particularly because of financial and ethical (reduced used of animals) considerations, in vitro and ex vivo approaches to this problem have been pursued over the last few years. The use of in vitro methods, however, inherently creates questions about the validity of extrapolation to the in vivo situation. The purpose of this report is to review the current status of the field and to identify major gaps in our knowledge. Currently, there are a number of in silico, in vitro, cultured cell-based and ex vivo approaches available to predict the cell permeation, absorption and gastrointestinal metabolism of molecules. Some strengths and weaknesses of these approaches are presented, together with a discussion of genetic, environmental, physiological and pathological factors responsible for interspecies and inter-individual variability in these processes. Recent advances in our understanding of active processes such as gut epithelial transporters, involved in absorption, and drug-metabolising enzymes, responsible for intestinal presystemic metabolism, are highlighted. Some major research priorities are identified, including the need for high-quality, information-rich databases against which testing methods being developed can be prevalidated and validated. Preclinical drug development is changing rapidly, and the role of in vitro and ex vivo approaches in this process is becoming increasingly more important. Methods available now are very useful in the drug discovery and development process, including lead compound selection and optimisation and in the design of very early clinical studies, but whether any of them will eventually obviate the need for clinical trials of bioavailability is still very debatable and will require their full validation. It is clear, however, that the results from such in vitro tests are important in shaping drug discovery and the early preclinical drug development process. For other environmental, industrial and household chemicals to which humans are exposed, in particular new chemicals, results from in vitro studies might be the only source of information concerning systemic availability.

The use of toxicodynamics in risk assessment

Risk assessment of xenobiotics is a qualitative and quantitative assessment of toxic properties conventionally based on data resulting from tests in animals exposed to the substance. The assessment of dose-effect relationship includes evaluation of exposure at the site of action. More recently, emphasis is put on understanding the relationship between exposure at the site of action and the resulting effect, i.e. toxicodynamic. In this respect, results from genotoxicity studies may be a measure for exposure and at the same time of an effect. Results of toxicodynamic endpoints such as binding to receptors or release of hormones have been used when replacing default values for interspecies extrapolation. It may also be envisaged to use toxicodynamic endpoints in order to get an estimate of intraspecies variability. It was demonstrated that this approach may be helpful only if the relationship between the toxicodynamic endpoint and the definite endpoint is known by using the example of bisphenol A. Whereas there are clear effects of bisphenol A in in vitro and ex vivo studies, the classical two generation study has not been able to detect an effect on reproduction and/or fertility. Looking in the future development of toxicodynamic endpoints, gene profiling and the analysis of proteins ('proteomics') may be helpful tools employed in screening and being related to the mode of action are explored for their suitability in terms of toxicodynamic endpoints.

CYP2E1 expression in bone marrow and its intra- and interspecies variability: approaches for a more reliable extrapolation from one species to another in the risk assessment of chemicals

When characterizing the health risks for man by exposure to chemicals, species-specific differences have to be taken into consideration, otherwise extrapolation from animal data to the human situation would be inadequate. The site-specific toxicity of chemicals may be explained by the following alternatives: (1) reactive metabolites are generated in the liver and subsequently transported to the target tissue(s); (2) metabolism of the parent compound occurs in the target tissue, a pathway by which the enzymes necessary for activation must be expressed in the target tissue. Cytochrome P450 2E1 (CYP2E1) is an important phase-I enzyme activating several chemicals. In the study described in this paper, myeloid intra- and interspecies variability in the expression of CYP2E1 has been investigated in rats, rabbits and man, because the bone marrow represents an important target organ for toxic effects of several chemicals, e.g. benzene. CYP2E1 at the protein level was detected by Western blotting and enzyme activities were determined by CYP2E1-dependent hydroxylation of chlorzoxazone (CLX). In the bone marrow of Wistar rats, the CLX hydroxylase activities were within the same order of magnitude (range: 0.1-0.4 pmol/mg protein per min) as previously described for mice (range 0.2-0.8 pmol/mg protein per min), whereas the CYP2E1 activities in two strains of rabbits were significantly higher (range: 1.7-4.7 pmol/mg protein per min) than in the rodents (P < 0.05). In human CD34+ bone marrow stem cells, CYP2E1 could also be detected on the protein level by Western blotting. The data demonstrate a presence of CYP2E1 in the bone marrow of all species investigated, thus supporting the hypothesis of CYP2E1-dependent local metabolism of several chemicals as a factor possibly contributing to their myelotoxicity and haematotoxicity. The data show that intraspecies/intrastrain variability of CYP2E1 activity in rodents is small. However, CYP2E1 activity between rodents and a non-rodent species was quite different indicating considerable interspecies variability.

CYP2E1-dependent benzene toxicity: the role of extrahepatic benzene metabolism

Benzene, a ubiquitous environmental pollutant, is haematotoxic and myelotoxic. As has been shown earlier, cytochrome P450 2E1 (CYP2E1)-dependent metabolism is a prerequisite for the cytotoxic and genotoxic effects of benzene, but which of the benzene metabolites produces toxicity is still unknown. The observed differences between the toxicity of benzene and that of phenol, a major metabolite of benzene, could be explained by alternative hypotheses. That is, whether (1) toxic benzene effects are caused by metabolites not derived from phenol (e.g. benzene epoxide, muconaldehyde). which are formed in the liver and are able to reach the target organ(s); or (2) benzene penetrates into the bone marrow, where local metabolism takes place, whereas phenol does not reach the target tissue because of its polarity. To further investigate hypothesis 2, we used various strains of mice (AKR, B6C3F1, CBA/Ca, CD-1 and C57B1/6), for which different toxic responses have been reported in the haematopoietic system after chronic benzene exposure. In these strains, CYP2E1 expression in bone marrow was investigated and compared with CYP2E1 expression in liver by means of two independent methods. Quantification of CYP2E1-dependent hydroxylation of chlorzoxazone (CLX) by high-performance liquid chromatography (HPLC; functional analysis) was used to characterize specific enzymatic activities. Protein identification was performed by Western blotting using CYP2E1-specific antibodies. In liver microsomes of all strains investigated, considerable amounts of CYP2E1-specific protein and correspondingly high CYP2E1 hydroxylase activities could be detected. No significant differences in CYP2E1-dependent enzyme activities were found between the five strains (range of medians, 4.6 12.0 nmol 6-OH-CLX/[mg protein x min]) in hepatic tissue. In the bone marrow, CYP2E1 could also be detected in all strains investigated. However, chlorzoxazone hydroxylase activities were considerably lower (range of medians, 0.2-0.8x10(-3) nmol 6-OH-CLX/[mg protein x min]) compared with those obtained from liver microsomes. No significant (P>0.05) interstrain differences in CYP2E1 expression in liver and/or bone marrow could be observed in the mouse strains investigated. The data obtained thus far from our investigations suggest that strain-specific differences in the tumour response of the haematopoietic system of mice chronically exposed to benzene cannot be explained by differences in either hepatic or in myeloid CYP2E1-dependent metabolism of benzene.

Influence of urine pH and urinary flow on the renal excretion of memantine

AIMS

The present study assessed the influence of urinary flow rate and urine pH on the renal excretion of the NMDA-receptor antagonist memantine.

METHODS

In a randomized, open, four-period cross-over trial, 12 healthy male volunteers received 10 mg memantine daily for 43 days. After reaching steady state conditions the volunteers were allocated to four different regimens to alter urine pH and urinary flow, which were each separated by a 1 week period while the study medication continued (A: acidification of urine pH, low urinary flow; B: acidification of urine pH, high urinary flow; C: alkalinization of urine pH, low urinary flow; D: alkalinization of urine pH, high urinary flow).

RESULTS

The renal clearance of memantine (CL(R)) in regimen A and B was 7-10 fold higher in comparison with regimen C and D (P<0.05). There were small but statistically significant differences of CL(R) between the two regimens with acidic urine pH (A: median: 210.2 ml min(-1) vs B: median: 218.7 ml min(-1)) and between the two regimens with alkaline urine pH (C: median: 19.4 ml min(-1) vs D: median: 30.5 ml min(-1)). The amount of memantine excreted into the urine within one regimen (Ae0-24h) was 5.7-7.4 fold higher in regimens A and B than C and D (P< 0.05). Differences of the AUC(0,24 h) and Cmax/AUC(0,24 h) were significant (P<0.05) between each of the regimens with acidic urine pH (A, B) and regimens (C, D) with alkaline urine pH (A vs C, A vs D, B vs C, B vs D) but not between regimens A vs B or C vs D.

CONCLUSIONS

The present study demonstrated a considerable effect of urine pH, whereas no clinically relevant change of the renal excretion of memantine with urinary flow could be detected. As the renal excretion of memantine may have an impact on therapeutic efficacy changes of dietary habits that may alter urine pH should be avoided during treatment with memantine.

Determination of 2-hydroxyphenylacetic acid (2HPAA) in urine after oral and parenteral administration of coumarin by gas-liquid chromatography with flame-ionization detection

The urinary excretion of 2-hydroxyphenylacetic acid (2HPAA) was studied in human volunteers after oral and parenteral doses of coumarin. The presence of 2HPAA in the urine was confirmed by gas chromatography mass spectroscopy (GC MS). Mass spectra of reference material and samples are presented. The determination of 2HPAA was carried out by GC with flame-ionization detection. Prior to analysis samples were extracted into ethyl ether and the analytes were derivatized with trimethlyphenylammonium hydroxide. A calibration range from 0.3 to 150 micrograms ml-1 was established using 3-hydroxyphenyl acetic acid (3HPAA) as an internal standard. On average less than 10% of the coumarin administered were excreted into the urine in the form of 2HPAA.

Pharmacokinetics and pharmacodynamics of candesartan after administration of its pro-drug candesartan cilexetil in patients with mild to moderate essential hypertension--a population analysis

OBJECTIVE

The pharmacokinetics and pharmacodynamics of the angiotensin (AT) II receptor, AT1-subtype, antagonist candesartan were investigated in a dose-finding study in 232 patients of either gender, aged 28-69 years and weighing 54-110 kg. The study was a double-blind, placebo-controlled trial in which oral doses of 2, 4, 8, 12 and 16 mg once daily were given as the pro-drug candesartan cilexetil from day 0 to day 28.

RESULTS

The population pharmacokinetics of candesartan could be best described by a two-compartment body model, parameterized in terms of clearance (14.1 1.h-1), central volume of distribution (118 1), peripheral volume (272 1) and intercompartmental clearance (15.4 1.h-1). From these model parameters, a cumulation half-life (t1/2, beta) of 29 h was derived. Age and weight were influencing factors for the distribution and elimination of the drug. Systolic and diastolic blood pressure were lowered by the treatment in a dose-dependent fashion. The maximum effect of each dose was reached after repeated administration. The link between plasma concentrations and effect could be described by a linear model when trough concentrations and blood pressure, measured at the same time, were modelled. In this model, the time dependence is implicitly handled as the trough concentrations increased during repeated administration. After treatment with the highest dose used in the trial (16 mg), the population estimate for the diastolic blood pressure was reduced from 103.2 mmHg (pre-dose day 0) to 93.3 mmHg (on day 29) and the systolic blood pressure from 154.6 mmHg (pre-dose day 0) to 137.9 mmHg (on day 29). None of the covariates (age, weight, gender) had an influence on the concentration-effect relationship.

Routine measurement of fluoxetine and norfluoxetine by high-performance liquid chromatography with ultraviolet detection in patients under concomitant treatment with tricyclic antidepressants

A robust and rapid high-performance liquid chromatography (HPLC) method is described for therapeutic drug monitoring of fluoxetine and norfluoxetine in the presence of six frequently-used tricyclic antidepressants and their respective metabolites. Liquid-liquid extraction into n-hexane/acetonitrile is used with reextraction into hydrochloric acid for clean-up. The chromatographic separation is carried out on a CN column. The minimum detectable amount is 3 ng injected on column. In addition to qualitative and quantitative validation data for the assay method, results from patient samples are presented. It is concluded that for patients treated with fluoxetine, therapeutic drug monitoring is valuable for optimizing the therapy.

Pharmacodynamic modelling of the analgesic effects of piritramide in postoperative patients

BACKGROUND

The concentration-effect relationship of piritramide, a synthetic opioid analgesic predominantly used for postoperative analgesia and analgosedation, has not been reported so far.

METHODS

Twenty-four patients of both genders aged 58.1 (11.7) yr (mean (SD)) received inhalational anaesthesia for abdominal surgery. Postoperative pain was assessed with a visual analogue scale (VAS). Analgesia was provided with piritramide, infused at a rate of 7 micrograms.kg-1.min-1 until analgesia was considered sufficient (VAS < 25) or up to a maximum dose of 0.2 mg/kg. The plasma concentrations of piritramide were determined by gas chromatography. An inhibitory fractional sigmoid Emax-model was used to describe the relation between effect site concentration and perceived pain.

RESULTS

The equilibration half-life between plasma and effect site concentrations (T1/2 (keo)) was 16.8 min (median; range: 4.4-41.6 min). The steady-state plasma concentration required to produce 50% of maximum analgesia (EC50) was 12.1 ng/ml (range: 2.9-29.8 ng/ml) and correlated with initial pain intensity. The slope factor gamma was 1.9 (range: 0.5-6.1) and increased with age. Clinically relevant respiratory depression did not occur. Due to the relatively large equilibration half-life of the effect compartment, the context-sensitive half-time of the effect site concentrations after short-time administration (< 2 h) clearly exceeded those of alfentanil, sufentanil, and fentanyl.

CONCLUSIONS

The analgesic effect of piritramide was adequately described by an inhibitory fractional Emax-model. In order to overcome the pronounced hysteresis, piritramide should initially be administered as an intravenous bolus of at least 5 mg.

Fenoterol but not dobutamine increases erythropoietin production in humans

OBJECTIVE

This study assessed the role of adrenergic signal transmission in the control of renal erythropoietin (EPO) production in humans.

METHODS

Forty-six healthy male volunteers underwent a hemorrhage of 750 ml. After phlebotomy, they received (intravenously for 6 hours in a parallel, randomized, placebo-controlled and single-blind design) either placebo (0.9% sodium chloride), or the beta 2-adrenergic receptor agonist fenoterol (1.5 microgram/min), or the beta 1-adrenergic receptor agonist dobutamine (5 micrograms/kg/min), or the nonselective beta-adrenergic receptor antagonist propranolol (loading dose of 0.14 mg/kg over 20 minutes, followed by 0.63 micrograms/kg/min).

RESULTS

The AUCEPO(0-48 hr)fenoterol was 37% higher (p < 0.03) than AUCEPO(0-48 hr)placebo, whereas AUCEPO(0-48 hr)dobutamine and AUCEPO(0-48 hr)propranolol were comparable with placebo. Creatinine clearance was significantly increased during dobutamine treatment. Urinary cyclic adenosine monophosphate excretion was increased only by fenoterol treatment, whereas serum potassium levels were decreased. Plasma renin activity was significantly increased during dobutamine and fenoterol infusion.

CONCLUSIONS

This study shows in a model of controlled, physiologic stimulation of renal erythropoietin production that the beta 2-adrenergic receptor agonist fenoterol but not the beta 1-adrenergic receptor agonist dobutamine is able to increase erythropoietin levels in humans. The result can be interpreted as a hint that signals for the control of erythropoietin production may be mediated by beta 2-adrenergic receptors rather than by beta 1-adrenergic receptors. It appears to be unlikely that an increase of renin concentrations or glomerular filtration rate is causally linked to the control of erythropoietin production in this experimental setting.

Modelling of non-linear pharmacokinetics in sheep after short-term infusion of cardiotoxic doses of imipramine

Imipramine was administered to sheep (n = 10) by intravenous infusion in high doses (450 mg-900 mg) to elicit cardiovascular shock. A cardiac assist device was then employed to manage the acute overdose situation. The concentration-time course of imipramine and its metabolite desmethylimipramine in plasma was measured by HPLC. As an indicator of imipramine's cardiotoxic effect, cardiac output was monitored. The aim of the study was to evaluate the pharmacokinetics under these conditions and to assess the efficiency of a cardiac assist device with (n = 5) and without (n = 5) an integrated haemoperfusion unit in removing drug from the circulation. The kinetics of imipramine could be described by a three compartment body model with concentration-dependent clearance resulting in non-linear kinetics. The changes in cardiac output with time could be linked to the pharmacokinetic model by a linear relationship. The cardiac assist device was found to contribute to the overall elimination of imipramine whereas the haemoperfusion unit had no clinically relevant impact.

Hypokalaemia in pregnant women treated with the beta 2-mimetic drug fenoterol--a concentration and time dependent effect

The effect of tocolytic treatment with fenoterol on plasma potassium concentrations was studied in 83 pregnant women on intravenous tocolytic therapy. Plasma concentrations of fenoterol and potassium were measured simultaneously, the time interval between initiation of therapy and taking the blood sample varying from 2 hours to 100 days. In a subset of 13 patients this blood sample was taken after two hours of therapy and pretreatment potassium concentrations were measured also. Pretreatment potassium concentrations were normal in these 13 patients and declined to 2.88 mmol/L (median) fenoterol concentrations being 320 ng/L through 1164 ng/L. Potassium concentrations measured later than 24 hours after initiation of therapy were all in the normal range corresponding fenoterol concentrations varying from 200 ng/L to 2504 ng/L. The multivariate statistical model for the description of all data showed that the duration of treatment was the only variable which explained the data to a significant extent. This might indicate that tolerance to the potassium lowering effect of fenoterol had developed within 24 hours after initiation of therapy. In the subset of 13 patients pretreatment potassium concentrations were found to be more important in explaining potassium concentrations than fenoterol concentrations at two hours. As we did not observe any adverse events in patients with low potassium concentrations and potassium concentrations were normal within 24 hours, we conclude that hypokalaemia due to fenoterol in the treatment of premature labor is not of clinical concern.

Erythropoietin production in healthy volunteers subjected to controlled haemorrhage: evidence against a major role for adenosine

1. This study was carried out to assess the role of adenosine in the regulation of human erythropoietin (EPO) production. To this end we investigated in healthy volunteers whether the nonspecific adenosine antagonist theophylline increases and the adenosine uptake inhibitor dipyridamole decreases EPO production in response to an haemorrhage of 750 ml. 2. Healthy male nonsmokers received i.v. in a parallel, randomized, single-blind trial theophylline (loading dose 5 mg kg-1 over 20 min, followed by 0.5 mg kg-1 min-1), dipyridamole (0.21 mg kg-1 h-1) or placebo (0.9% NaCl) for 6 h following the phlebotomy. EPO concentrations were followed up to 72 h after phlebotomy. 3. Following blood loss EPO concentrations increased during all treatments. The AUCEPO (0,72 h) were not statistically significantly different (theophylline: 398 +/- 30, dipyridamole: 301 +/- 15, placebo: 332 +/- 57 [mu ml-1 h]). Creatinine clearance and urinary cAMP excretion were unaltered by any treatment. Urinary excretion of adenosine was significantly increased during infusion of dipyridamole. Plasma renin activity was significantly increased during theophylline infusion. 4. In our model of controlled, physiological stimulation of EPO production by haemorrhage, adenosine appears unlikely to play a major role as a mediator of renal EPO production.

Concentration-effect relationship of the positive chronotropic and hypokalaemic effects of fenoterol in healthy women of childbearing age

OBJECTIVE

To analyse fenoterol-induced tachycardia and hypokalaemia, the most important and most frequent adverse effects of tocolytic therapy with beta 2-adrenoceptor agonists in females of childbearing age.

METHODS

The study was performed as a double blind, randomised, placebo controlled, cross over trial. Seven healthy women aged 22-38 y, received intravenous infusions of fenoterol at 3 different rates within the therapeutic range for tocolysis (0.5,1.0, and 2.0 micrograms.min-1) and placebo. The time courses of the plasma concentrations of fenoterol and potassium, and the heart rate were analysed with mixed effects pharmacokinetic-pharmacodynamic (PKPD) modeling using NONMEM.

RESULTS

The plasma concentration-time course followed a linear two compartment model. Fenoterol-induced tachycardia was described by a linear concentration-effect model with baseline. The estimated baseline and slope parameters were 78 beats.min-1 and 0.032 beats.min-1.microgram-1.1, respectively. Fenoterol-induced hypokalaemia could be described by a physiological indirect response model including feedback; the Estimated basal plasma potassium concentration was 3.93 mmol.1-1 and the slope factor for the fenoterol-induced relative increase in the efflux of potassium from the extracellular space was 6.22*10(-4) ng.1(-1).

CONCLUSION

The estimated population parameters permitted calculation of the expected time course of tachycardia and hypokalaemia in women after the initiation of tocolysis with fenoterol over the clinically relevant concentration range, and prediction of its variability. Based on simulation, our model predicted that a continuous infusion of 2.0 micrograms.min-1 (highest rate examined) would increase heart rate to 113 beats.min-1 at steady state and lower the plasma potassium concentration to 2.77 mmol.1(-1) 1.5 h after beginning the infusion. Thereafter, the plasma potassium concentration would slowly return to normal.

Pharmacokinetics of piritramide after an intravenous bolus in surgical patients

BACKGROUND

Piritramide is a synthetic opioid analgesic which is commonly used for postoperative analgesia. It is structurally related to meperidine, exhibiting full mu-receptor agonism. Pharmacokinetic data of the drug have not been reported so far.

METHODS

Plasma protein binding of piritramide was studied in vitro. The kinetics were examined after a single intravenous bolus (0.2 mg/kg) in 10 male patients aged 22-53 years undergoing elective minor surgery. Plasma and urine concentrations were determined by gas chromatography in samples drawn before and after the bolus. The concentration vs. time data were evaluated by nonlinear regression analysis, and the mean values and SD of the individual pharmacokinetic parameters were calculated. A three-compartment body model was fitted to the data.

RESULTS

The volume of distribution at steady state was 4.7 (0.7)l/kg, systemic plasma clearance was 7.8 (1.5) (mean (SD)) ml/kg/min. Renal clearance of unchanged piritramide was negligible (0.13 (0.09) ml/kg/min). The terminal elimination half-life was 8.0 (1.4) h. In vitro, the free fraction in plasma of piritramide did not change over the therapeutic concentration range (5.5 (1.3)% at a pH of 7.35) but decreased considerably with pH within the physiological range.

CONCLUSION

Since the elimination half-life of piritramide appears to exceed the duration of clinically effective analgesia observed during the treatment of acute pain, the dose of piritramide should be titrated carefully during long-term treatment to avoid accumulation that may lead to adverse effects.

Morphine-6-O-beta-D-glucuronide but not morphine-3-O-beta-D-glucuronide binds to mu-, delta- and kappa- specific opioid binding sites in cerebral membranes

We investigated the nature of interaction of morphine-3-O-beta-D-glucuronide (M3G) and morphine-6-O-beta-D-glucuronide (M6G) with opioid binding sites at the mu-, delta- and kappa-opioid receptors (mu-OR, delta-OR and kappa-OR) in cerebral membranes. Saturation binding experiments revealed a competitive interaction of M6G with all three opioid receptors. Inhibition binding experiments at the mu-OR employing combinations of morphine and M6G resulted in a rightward shift of the IC50 for morphine proportional to the M6G concentration, thus strengthening the finding of competitive interaction of M6G at the mu-opioid binding site. Data in absence and presence of M6G were included in a three-dimensional model. Compared to a model with one binding site a model with two binding sites significantly improved the fits. This might indicate that different mu-OR subtypes are involved. Hydrolysis of M6G to morphine was investigated and did not occur. Therefore the effects of M6G on binding to the mu-OR were due to M6G and not due to morphine. In contrast, M3G at the three opioid receptors was found to inhibit binding being about 300 times weaker than morphine. This effect was well explained by the amount of contaminating morphine (about 0.3%) identified by HPLC. We conclude that M6G binds to mu-, delta- and kappa-OR in a competitive manner. Some of our results on the mu-OR suggest two binding sites for agonists at the mu-OR and that M6G binds to both sites. Our results suggest that the high potency of M6G as an analgesic is mediated through opioid receptors. In contrast, M3G does not interact with the mu-, delta- or kappa-OR. We therefore doubt that any effect of M3G is mediated via opioid receptors.

Gender differences in pharmacokinetics

There is growing awareness that the underrepresentation of women in clinical trials and in particular in phase I studies may lead to incorrect handling of drugs. Despite the fact that investigations are not informed in a systematic way, there are a number of examples showing pharmacokinetic differences between gender. From the data actually presented, it can be concluded that the activity of CYP 3A4 activity as measured by elimination in vivo is higher in women compared to men. CYP isoenzymes other than CYP 3A4 seem to be more active in men than in woman, as are conjugation reactions, such as glucuronidation. The influence of changing hormonal levels during the lifetime of a woman has been looked at in some drugs but deserves further systematic investigation. The use of oral contraceptives can interfere with the metabolism of many drugs whereas, in pregnancy, the elimination of antiepileptics is increased which, without dose adjustment, leads to an increased number of seizures. The impacts of hormonal replacement therapy (HRT) on the pharmacokinetics of concomitantly given drugs is an important issue, as HRT is increasingly used, but more research is needed in this field.

Amiodarone in a newborn with ventricular tachycardia and an intracardiac tumor: adjusting the dose according to an individualized dosing regimen

We report the successful management of recurrent ventricular tachycardias in a newborn suffering from an intracardiac tumor. Amiodarone was the only agent able to control the tachycardias and did so as long as an individually titrated plasma concentration above 0.8 mu mol/L was maintained. Because no therapeutic plasma concentration has been defined in children and no kinetic studies are available in this population, we optimized the dosing regimen based on a computer simulation, taking into account the pharmacokinetic parameters of the patient and the individual concentration-effect relation.

[Age as a factor in dose-response relationship of drugs]

Drug therapy in the elderly requires careful individualization of the dosage. Whether dose adjustment is due to altered pharmacokinetic or due to altered pharmacodynamic is a matter of experimental evidence which can be found by performing studies with simultaneous measurements of concentration and effect over time. The kinetic of drugs in the elderly can be characterized by an altered volume of distribution, an altered protein binding, an impaired metabolism and renal excretion. There is a wide interindividual variation of the alterations which are further influenced by environmental factors such as smoking and nutrition. In generalization of the results it can be assumed that the concentration of drugs is elevated in the elderly and that the excretion will be prolonged. Hence, it is safe to reduce the dose in the elderly. The influence of age on factors which determine the effect of drugs is much less investigated than the factors influencing the pharmacokinetic. With respect to side-effects, it seems that the elderly population is a population at special risk. However, it is unclear whether this finding is explained on a pharmacodynamic basis (e.g., enhanced receptor sensitivity, impaired homeostatic mechanisms), as analyses are lacking in investigating the relationship between concentration and effect. As there is no evidence besides a special situation with betablockers that aged patients require higher doses than younger ones, it is wise to use doses at the lower range for the treatment of aged patients. In case of new symptom side-effects of drugs should be considered as the underlying cause.

Transpulmonary disposition of prilocaine, mepivacaine, and bupivacaine in humans in the course of epidural anaesthesia

The pulmonary first-pass kinetics of the amide-linked local anaesthetics prilocaine, mepivacaine and bupivacaine were studied in 33 patients after a single epidural injection. Drug concentrations were monitored before and after lung passage, i.e. in samples withdrawn simultaneously from mixed venous and arterial blood. In most cases, maximum plasma concentrations were observed 10 min after injection (range 2 to 30 min). Two min after injection the local anaesthetics were distinctly extracted by the lung (prilocaine 40%, mepivacaine 20%, and bupivacaine 12%). Prilocaine was retained by the lung more effectively than bupivacaine and mepivacaine. However, a transpulmonary concentration gradient could be observed only for a short time, i.e. maximum 15 min. Altogether, in the case of accidental fast absorption, e.g. inadvertent intravenous injection, arterial peak concentrations of these drugs will be attenuated by passage of the lung. However, the lung will not substantially lower the risk of toxicity by amide-linked local anaesthetics during normal conditions of regional anaesthesia where slow absorption occurs.

Biliary excretion of mezlocillin in patients with hepatic disease

In three patients with liver disease (2 patients with alcoholic liver cirrhosis and 1 patient with chronic cholangitis) total, renal, biliary and metabolic clearance of the acylureidopenicillin mezlocillin was examined under steady state conditions. Mezlocillin was infused for 6 hours at a constant infusion rate of 10 mg/min. Renal clearance was calculated based on urinary excretion rates. Duodenal perfusion and marker dilution technique was applied to determine biliary excretion rates of the drug. Clearances were estimated by dividing the excretion rate by the respective plasma concentration. Total clearance was calculated by dividing the infusion rate by the plasma concentration. Biliary clearance was markedly reduced in the patients compared to the data of 8 healthy controls (0.65 +/- 0.33 ml/min vs 98.6 +/- 42.5 ml/min). Total and renal clearance were diminished (total clearance: 121.4 +/- 21.6 ml/min vs 286.5 +/- 54.6 ml/min, renal clearance, 65.4 +/- 1.0 ml/min vs 137.6 +/- 32.6 ml/min). In contrast, metabolic clearance was not changed (53.3 23.1 ml/min vs 50.3 +/ 24.2 ml/min). As mezlocillin is well tolerated and has a wide margin of safety we do not recommend reduced dosage. On the contrary, it might even be necessary to increase the dose when treating biliary tract infections in patients with cholestasis in order to assure effective drug concentrations in the bile.

An inexpensive and sensitive method for the determination of quinidine in plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive, specific, and rapid high-performance liquid chromatographic method with ultraviolet detection for therapeutic drug monitoring of the cardioactive compound quinidine is described. The method uses only 50 microliters of serum, which is extracted into methyl-t-butylether at an alkaline pH and consequently reextracted into dilute hydrochloric acid. Quinidine is separated from quinine, the internal standard, and dihydroquinidine on a reversed phase C18 column. The minimum detectable amount is 1 ng injected on column. The method is both precise and accurate, as shown by the validation data presented, and can also be of use in pharmacokinetic investigations.