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Biomedical subjects

H Nau

Publications and source records attributed to H Nau.

At least 181 records · Page 10Linked to original sources
PubMed1987

Clinical pharmacokinetics in pregnancy and perinatology. II. Penicillins.

Ampicillin has been most thoroughly studied in regard to placental transfer. Both during the first/second trimester and at term, fetal drug levels rose slowly to reach values similar to those in the maternal circulation 1-3 h after maternal drug administration; thereafter, fetal drug levels exceeded corresponding maternal values. Amniotic fluid levels were low during early gestational periods; during late gestation these levels were significant and even exceeded corresponding maternal values 6-8 h after drug administration. Slow exchange rates and fetal micturation may be responsible for the elevated ampicillin levels during late gestation. Administration via the intramuscular (recommended with 0.5 g every 4-6 h) or intravenous routes, but not by the oral route, resulted in adequate drug levels. Because of increased plasma clearance of ampicillin during pregnancy, a dose increase in pregnant patients may be necessary to obtain adequate drug levels. Amoxillin and azidocillin have been suggested to give effective drug levels even after oral administration, except during labor. The fetal levels of epicillin and benzylpenicillin (Penicillin G) were lower than the corresponding maternal values; amniotic fluid concentrations of these two drugs were elevated during late, but very low during early gestation, similar to the situation with ampicillin. Methicillin and sulbenicillin were effectively transferred across the placenta (similar to ampicillin), while dicloxacillin was not. The low concentrations of dicloxacillin in the fetus and amniotic fluid may be the results of extensive protein binding (greater than 90%) of this drug in maternal blood. Other highly bound penicillins such as cloxacillin and flucloxacillin have not yet been investigated in regard to placental transfer. Excretion of penicillins in human milk was usually very limited. Following therapeutic doses, the mean milk concentrations were 0.1-0.6 microgram/ml for amoxicillin, 0.1-0.2 microgram/ml for epicillin, about 0.5 microgram/ml for sulbactam, 2-2.5 micrograms/ml for ticarcillin, and 0.1-0.4 microgram/ml for aztreonam.

Amniotic Fluid↗
PubMed1987

Ventral duplication of the autopod: chemical induction by methoxyacetic acid in rat embryos.

Administration of 2-methoxyethanol to pregnant rats on day 12 of gestation induced ventral duplication of the autopod, presumably via its oxidative metabolite, methoxyacetic acid. Morphological observations indicate that the limb bud periderm is severely damaged by methoxyacetic acid so that large patches of this structure are actually missing during an extended period of limb bud development. A high concentration of methoxyacetic acid (10 mM) was found in the extraembryonic fluid and we postulate that the damage to the periderm was initiated from this extraembryonic exposure. The ventral duplication of the autopod is thought to arise through an attempt by the embryo to repair the periderm lesion.

Abnormalities, Drug-Induced↗
PubMed1986

Direct determination of folate monoglutamates in plasma by high-performance liquid chromatography using an automatic precolumn-switching system as sample clean-up procedure.

A simple and rapid technique for the simultaneous isolation and analysis of folate monoglutamates (folic acid, 7,8-dihydrofolic acid, 5,6,7,8-tetrahydrofolic acid and 5-formyl-, 5-methyl- and 10-formyl-5,6,7,8-tetrahydrofolic acids) was developed using reversed-phase high-performance liquid chromatography with an automatic precolumn-switching system. The plasma or the dissolved diet samples were directly injected onto a short precolumn flushed with 50 mM phosphate buffer. The folate vitamers absorbed on the precolumn were backflushed onto the analytical column with a 25 mM phosphate buffer containing 5% methanol and then detected by UV absorption at 280 nm. A linear response was found between the injected sample amounts and the integrated areas for all vitamers analysed. The detection limit was 1-10 pmol and the precision ranged from 1.6 to 10%, depending on the metabolite studied. The recovery rates of folates in plasma were 90-95%. Decomposition of the unstable folates was avoided. Our method was applied to the analysis of mouse plasma and animal diets.

Animals↗
PubMed1986

Serum protein binding of valproic acid in fetus-mother pairs throughout pregnancy: correlation with oxytocin administration and albumin and free fatty acid concentrations.

The protein binding (expressed as percent free drug fraction) of the antiepileptic drug valproic acid (VPA) was studied in 65 fetus-mother pairs from weeks 13 to week 41 of gestation. The fetal free fractions (expressed as percent of total concentrations) of VPA were exceedingly high (greater than 50%) during weeks 13 to 16 of gestation; these values decreased to 20% by week 20 and further decreased gradually to 10% at term. There was a highly significant negative correlation between free VPA fractions and fetal albumin concentrations. Maternal free fractions of VPA gradually increased from 10% during early pregnancy to 20% at term. The free fractions of VPA were significantly higher in mothers who had received oxytocin. Thus, protein binding in the fetus exceeded that of the mother at term, whereas the converse was true during early gestation. These results agree with previous in vivo findings. It is likely that the free concentrations in the mother determine the drug effects and toxicity in both the mother and the fetus. Intermittent drug administration--particularly of large single doses--could result in a transient increase of the free concentrations of VPA, particularly because of the strong concentration dependence of VPA protein binding. Increased free fractions can also be expected from increased concentrations of displacing agents of endogenous or exogenous origin (other drugs).

Adolescent↗
PubMed1986

Transfer of valproic acid and its main active unsaturated metabolite to the gestational tissue: correlation with neural tube defect formation in the mouse.

The pharmacokinetics of the antiepileptic drug valproic acid (2-propyl-pentanoic acid; VPA) and its main active metabolite 2-en-VPA (2-propyl-2-pentenoic acid) in mouse serum and gestational material were studied and correlated with the drastic differences between the two compounds in their embryotoxicity. The peak levels of VPA reached after 0.5 hours were only slightly higher than that of 2-en-VPA (both in mother and gestational material). The free concentrations of VPA and 2-en-VPA in maternal serum also peaked at 0.5 hours. After that time the free maternal serum levels of 2-en-VPA decreased much more rapidly than the concentrations in the gestational materials. The area under the concentration/time curves (AUC) values of 2-en-VPA in mother and embryo were lower than corresponding values of VPA; the higher clearance of 2-en-VPA was predominantly due to an increased volume of distribution. Since we have previously shown that the peak concentrations and not the AUC values of VPA correlated with the teratogenicity of this compound, our present data indicate that the low teratogenic and embryotoxic potential of 2-en-VPA is a result of the intrinsic activity of this compound and not of lower peak concentrations reached in mother and embryo.

Administration, Oral↗
PubMed1986

Transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via placenta and milk, and postnatal toxicity in the mouse.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was found to be efficiently transferred to mouse neonates and offspring by lactating mothers. During the first 2 postnatal weeks the pups received doses of TCDD via the milk which were, on a body weight basis, similar to those which had been administered prenatally to their mothers. The distribution of TCDD in the offspring (high in liver, low in other tissues) was similar to that found in the maternal organism. Maternal TCDD levels rapidly decreased during the lactation period while tissue levels in the nursing pups increased, resulting in offspring tissue levels which greatly exceeded those of their mothers at the respective 3-week periods after birth. The postnatal development of pups from mothers treated on days 14-17 of gestation and nursed by untreated foster mothers was studied. Postnatal mortality was increased. Surviving animals did not exhibit visible signs of abnormal development, although the reduced number of pups per litter may have contributed to this apparently normal development. In small rodents excretion into milk constituted a major pathway for the elimination of maternal TCDD. Whether the same holds true for man is still unknown, but the measurement of TCDD levels in breast milk may be an appropriate and practical method for the assessment of human exposure to this substance.

Aging↗
PubMed1986

Pharmacokinetic aspects of drug effects in vitro: effects of serum protein binding on concentration and teratogenicity of valproic acid and 2-en-valproic acid in whole embryos in culture.

Pharmacokinetic studies were performed in connection with culture experiments. Using the technique of cultivating whole rat embryos of the early postimplantation stage, we measured the concentration of valproic acid (VPA) and 2-en-VPA in the culture medium (free and protein-bound form) and in embryonic tissue. The following results were obtained: The concentrations of VPA and 2-en-VPA reached in the embryos were lower than corresponding total concentrations added to the culture medium, but exceeded the free concentrations in the medium. The concentrations of 2-en-VPA found in the embryo were lower than the comparable VPA total levels because of the more extensive protein binding of 2-en-VPA in the culture serum. The percentage of binding to serum proteins decreased with increasing total drug concentrations in the medium; the concentration of the free drug in the medium increased overproportionally with increasing total drug concentrations. Therefore, the free drug concentrations in the medium were not proportional to the dose of the drug dissolved in the medium (for a drug bound to plasma proteins). The concentrations of VPA and 2-en-VPA found in the embryos after incubation in vitro were not proportional to the drug concentrations dissolved in the medium. This result has to be taken into account when dose-response relationships are evaluated. VPA concentrations of 40 micrograms/g wet weight and above in the embryos clearly induced abnormal development in about 30% of the embryos, while 2-en-VPA concentrations as high as 200 micrograms/g embryo (wet weight) were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Drug-Induced↗
PubMed1986

Valproic acid teratogenicity in mice after various administration and phenobarbital-pretreatment regimens: the parent drug and not one of the metabolites assayed is implicated as teratogen.

The antiepileptic drug valproic acid (VPA) was administered via four different routes in the mouse during gestational stages sensitive for interference with neural tube defect formation: a single oral intubation or injection, sc or ip, on Day 8, or infusion via subcutaneously implanted osmotic minipumps from Day 7 1/2 to 8 1/2 of gestation. Embryotoxicity was evaluated on Day 18 (incidence of exencephaly, embryolethality and fetal weight retardation). Oral intubation of VPA resulted in significantly lower peak concentrations of VPA as well as lower embryotoxicity as compared to sc and ip administration. The metabolites of the beta-, omega- and omega-1 oxidation pathways were present in both maternal serum and gestational tissues in very low concentrations (usually less than 2% of corresponding VPA levels). Infusion of VPA via osmotic minipumps (lower steady-state VPA levels as compared to peak levels following injection of VPA) resulted in embryolethality and fetal weight retardation, but little exencephaly. The metabolic pattern was similar in all four administration experiments. Phenobarbital pretreatment of the dams (previously shown to reduce VPA serum concentrations and induce the omega- and omega-1 oxidation pathways) reduced the embryotoxicity of VPA. These results suggest that VPA embryotoxicity is mediated by the parent drug, and not one of the metabolites considered in this study.

Administration, Oral↗
PubMed1986

Pharmacologic evaluation of various metabolites and analogs of valproic acid: teratogenic potencies in mice.

A number of metabolites of the anticonvulsant drug valproic acid (VPA) as well as related substances were tested in regard to their teratogenicity in the mouse following single sc injections of 600 mg/kg on Day 8 of gestation. VPA was highly teratogenic at this dose level and over 60% of live fetuses had neural tube defects (exencephaly). Homologous compounds with shorter or longer alkyl chains were less teratogenic. Substitution of the alpha-H atoms in related branched carboxylic acids by methyl or ethyl groups abolished the teratogenic response. Introduction of a double bond in the omega-position of VPA (4-en-VPA) did not change the teratogenicity of VPA, while omega-2 double bond (2-en-VPA) abolished teratogenicity. The other VPA metabolites tested as well as two straight-chain acids (n-octanoic acid and 4-pentenoic acid) and the two clinically used substances valpromide (valproic acid amide) and ethosuximide did not induce neural tube defects, although some of them induced slightly increased resorption rates and fetal weight retardation. The serum protein binding capacities of the various compounds did not correlate with the teratogenic response. Also the concentrations reached in the gestational material did not predict the teratogenicity of the substances tested. Our results indicate that the teratogenicity of the class of compounds studied represents a more specific effect than the anticonvulsant activity which could lead to the development of alternative antiepileptic drugs with low embryotoxic potential.

Animals↗
PubMed1986

Predicting the human teratogenic potential of the anticonvulsant, valproic acid, from a non-human primate model.

The anticonvulsant, valproic acid (VPA) is a suspected human teratogen. This study, employing the rhesus monkey as an animal model, demonstrates that VPA has a significant teratogenic potential in the monkey. Timed pregnant monkeys were exposed orally to VPA at approx. 1X, 10X, and 30X (20, 200, and 600 mg/kg/day, respectively) the human therapeutic dose, daily, during organogenesis (gestation days 21-50). All fetuses of mothers exposed to greater than 1X exhibited some form of embryotoxicity. The highest dose, 30X, was 100% embryolethal, while offspring of the 10X dose group exhibited craniofacial and skeletal defects, and low body weights. Maternal pharmacokinetic parameters and plasma metabolites were determined for VPA on the first and last day of dosing for the 10X dose group. Comparison of the kinetic and metabolite data with that obtained for man indicates that the rhesus monkey is a good model for predicting the teratogenic potential of VPA in the human.

Abnormalities, Drug-Induced↗
PubMed1986

Fetal growth, major malformations, and minor anomalies in infants born to women receiving valproic acid.

The association of fetal and neonatal distress, birth measurements, major malformations, and minor anomalies was studied prospectively in 14 infants of women with epilepsy who were receiving valproic acid (VPA) monotherapy and in 12 infants of women with epilepsy who were receiving VPA in combination with other anticonvulsant drugs. Comparison was made with 26 matched-pair controls and 116 controls from a larger study of antiepileptic drugs. During the first trimester, total VPA serum concentrations were well above therapeutic levels (100 to 184 micrograms/ml) in two women receiving high VPA doses (2000 and 1500 mg daily). Although dosage remained the same, serum concentrations decreased during pregnancy to therapeutic levels (33.9 to 57.0 micrograms/ml). The VPA percent free fraction increased in the third trimester and was threefold higher at birth. Almost half of the infants exposed to VPA monotherapy were distressed during labor, and 28% had low Apgar scores. Fetal and neonatal distress may be caused by the high VPA percent free fraction during labor and at birth. Mean body measurements at birth after VPA monotherapy were comparable to those in the matched control group, but were reduced in the group of infants receiving VPA combination therapy. Four infants exposed to VPA monotherapy were born with major malformations. The median number of minor anomalies was four times higher in infants whose mothers received VPA alone or VPA combination therapy than in controls. Seven infants had a pattern of craniofacial and digital anomalies that was distinctly different from that observed after in utero exposure to other anticonvulsant medications. The occurrence of major malformations and the number of minor anomalies may be dose related.

Abnormalities, Drug-Induced↗
PubMed1986

Species differences in pharmacokinetics and drug teratogenesis.

Interspecies differences in regard to the teratogenicity of drugs can be the result of differing pharmacokinetic processes that determine the crucial concentration-time relationships in the embryo. Maternal absorption, as well as distribution, of the drugs does not usually show great species differences. The first-pass effect after oral application is often more pronounced in animals than man (e.g., valproic acid, 13-cis-retinoic acid), although in some cases the reverse was found (e.g., hydrolysis of valpromide). Existing differences can be adjusted by appropriate choice of the administration route and measurements of drug levels. Many variables determine the placental transfer of drugs: developmental stage, type of placenta, properties of the drug. Even closely related drugs (e.g., retinoids) may differ greatly in regard to placental transfer. Maternal protein binding is an important determinant of placental transfer, since only the free concentration in maternal plasma can equilibrate with the embryo during organogenesis; this parameter differs greatly across species (e.g., valproic acid: five times higher free fractions in mouse and hamster than in monkey and man). The metabolic pattern has not yet been demonstrated to be a major cause of species differences, although recent evidence on phenytoin and thalidomide support the hypothesis that some species differences can be the result of differing activation/deactivation pathways. Laboratory animals usually have a much higher rate of drug elimination than man. Drastic drug level fluctuations are therefore present during teratogenicity testing in animals, but not to the same degree in human therapy. It must, therefore, be investigated if peak concentrations (such as for valproic acid and possibly caffeine) or the area under the concentration-time curve (AUC) (such as for cyclophosphamide and possibly retinoids) correlate with the teratogenic response. Only then is a rational and scientific basis for interspecies comparison possible. It is concluded that the prediction of the human response based on animal studies can be improved by consideration of the appropriate pharmacokinetic determinants.

Abnormalities, Drug-Induced↗
PubMed1986

Serum protein binding of diazepam and propranolol in the feto-maternal unit from early to late pregnancy.

Paired samples of maternal and fetal serum were obtained in 65 pregnancies between 13 and 41 weeks gestation. Concentrations of albumin, alpha 1-acid glycoprotein (alpha 1-AGP) and free fatty acids (FFA) were estimated in all samples and the in-vitro binding of diazepam and propranolol was estimated. The free fraction of diazepam in fetal serum was very high in early gestation and decreased with advancing gestation to reach maternal values around the 30th week. After 35 weeks gestation, values were generally lower in fetal than in maternal serum. Fetal serum binding of diazepam correlated with fetal albumin levels and gestational age. The ratio of the fetal/maternal free diazepam fraction correlated negatively with the fetal/maternal serum albumin concentration ratio. The maternal/fetal free diazepam fraction ratio correlated positively with gestational age. The free fraction of propranolol in fetal serum was higher than in maternal serum in early pregnancy and decreased with advancing gestation but always remained higher than the maternal values. The fetal/maternal free propranolol fraction ratio was negatively correlated with the fetal/maternal alpha 1-AGP serum concentration ratio. The maternal/fetal free propranolol fraction ratio was positively correlated with gestational age. Serum protein binding of propranolol was correlated with serum albumin concentrations in fetal samples but not in maternal samples. Serum FFA concentrations were not correlated with serum protein binding except for maternal serum binding of diazepam. For toxicological reasons it is advisable to monitor maternal blood for free concentrations of drugs that exhibit concentration-dependent protein binding or which can be displaced from binding sites by other drugs or endogenous compounds such as FFA.

Adolescent↗
PubMed1985

Teratogenic valproic acid concentrations: infusion by implanted minipumps vs conventional injection regimen in the mouse.

The dosage-regimen-dependent teratogenicity as well as plasma and tissue levels of the antiepileptic drug valproic acid (VPA) were studied in the mouse by comparing various injection regimens and infusion of the drug via implanted osmotic minipumps. Concentrations of 225-248 micrograms VPA/ml maternal plasma (about 2X above the therapeutic concentration range) and 70-75 micrograms VPA/g gestational material (on gestation Day 8) resulted in a significant incidence of neural tube defects (exencephaly in the mouse). Similar effects were produced if those concentrations were reached several times after multiple injections or by steady-state application via implanted pumps. A single injection was less effective than multiple injections, although drug accumulation did not occur. The doses (or area under the concentration-time curve values) did not correlate with the teratogenic response of the different administration regimens: much higher (factor 10) doses were needed with the infusion regimen to produce exencephaly rates comparable to those obtained with the injection regimen. The pattern of embryotoxicity was also schedule dependent: steady-state concentrations produced predominantly embryolethality and fetal weight retardation, while intermittent injections produced a high incidence of exencephaly (up to 60% of live fetuses). The dose of VPA (and the areas under the concentration-time curves) correlated with the embryolethality and fetal weight retardation of the drug, while the peak or steady-state concentrations reached in mother and gestational material correlated with the incidence of neural tube defects.

Animals↗
PubMed1985

Effects of pregnancy on seizure threshold and the disposition and efficacy of antiepileptic drugs in the mouse.

The effects of pregnancy on seizure excitability as well as antiepileptic drug disposition and efficacy were studied in the mouse during late gestation. Phenytoin and carbamazepine concentrations in brain were increased in pregnant animals, which was related to increased free concentrations in plasma. Little changes were observed for valproic acid and phenobarbital. The seizure threshold in untreated pregnant mice was significantly higher than in the nonpregnant group. The efficacy of carbamazepine and valproic acid in the pregnant animals was increased as compared to the control group; little changes were observed for phenobarbital and phenytoin. Our study indicates that - in contrast to the general clinical opinion - pregnancy has little influence or even a slight beneficial effect on the seizure propensity as well as the efficacy of antiepileptic drugs.

Animals↗
PubMed1985

Oxidation and glucuronidation of valproic acid in male rats--influence of phenobarbital, 3-methylcholanthrene, beta-naphthoflavone and clofibrate.

The influence of phenobarbital, clofibrate, 3-methylcholanthrene and beta-naphthoflavone on omega- and beta-oxidation as well as on glucuronidation of valproic acid (n-dipropylacetic acid) was evaluated in male Sprague-Dawley rats by determination of urinary excretion of its metabolites by GC-MS after administration of 100 mg/kg. In controls 12% of the dose was excreted within 24 hours, primarily as glucuronides; metabolites formed by oxidation amounted to about 4%. Phenobarbital treatment led to stimulation of 4-hydroxyvalproic acid [(omega-1)-oxidation], 5-hydroxyvalproic acid and n-propylglutaric acid (omega-oxidation) excretion. Clofibrate enhanced the excretion of 4-hydroxyvalproic acid and 3-keto-valproic acid, a product of peroxisomal beta-oxidation. beta-Naphthoflavone slightly increased the excretion of 5-hydroxyvalproic acid. The most specific effect was found for 3-methylcholanthrene, which was effective in stimulating the formation of 3-hydroxyvalproic acid which might be formed by (omega-2)-oxidation. The addition of fatty acids (olive oil in which 3-methylcholanthrene and beta-naphthoflavone were suspended) led to increased excretion of 3-keto-valproic, 4-hydroxyvalproic and n-propylglutaric acid. The excretion of 3-hydroxyvalproic acid was completely suppressed by olive oil. Such specific effects were not observed for glucuronidation of valproic acid and its metabolites, although stimulation was attained after phenobarbital, clofibrate and 3-methylcholanthrene treatment, because of instability of glucuronide conjugates. Stimulation of valproic acid metabolism was also shown by increased plasma clearance after treatment with phenobarbital. In contrast, clofibrate given once 1 hr before valproic acid inhibited excretion of valproic acid, possibly by competition during renal tubular secretion. Determination of valproic acid metabolites in urine provides a useful tool for evaluation of inducer specificity of short chain fatty acid metabolism and differentiation between microsomal and peroxisomal enzyme activity.

Animals↗
PubMed1985

Enzyme cytochemistry combined with electron microscopy, pharmacokinetics, and clinical chemistry for the evaluation of the effects of steady-state valproic acid concentrations on the mouse.

A number of organs from adult female mice were investigated after continuous application of the anticonvulsant drug valproic acid (VPA) by enzyme cytochemistry, light and electron microscopy, pharmacokinetics and clinical chemistry. VPA plasma levels were maintained between 55 micrograms/ml and 67 micrograms/ml for three days following subcutaneous implantation of drug reservoirs. Effects detectable by enzyme cytochemical or electron microscopical means were mainly observed in liver, kidney, thymus and spleen. A strict concentration-dependency of drug effects could not be found. In the liver, the activities of some surface-membrane hydrolases were increased at the biliary pole; the activities of other hydrolases were decreased or unchanged. Electron microscopically, number and length of microvilli of hepatocytes were increased and many of them showed fat inclusions, mitochondrial swellings and autophagic vacuoles. In some of the proximal convoluted tubules of the kidney, the reaction product originating from microvillous and lysosomal hydrolases was diffusely distributed and its amount lowered. This was paralleled by tubular cells with an increased number of fat droplets and swollen mitochondria or destroyed tubular cells, as demonstrated by electron microscopy. Additionally, peritubular endothelial cells were arranged in a garland-like pattern. Alkaline phosphatase was activated in the straight portion of the proximal tubules. Increased glucose, creatinine and total protein concentrations and increased gamma-glutamyl transpeptidase and alkaline phosphatase activities in the urine reflected well the damage of the proximal renal tubules. Cortical and medullary morphology varied considerably in the thymus. In extreme cases, the cortical zone was either reduced in size or the medulla showed a cortex-like structure or vice versa (inverted type of thymus). The thymic cortical reticular cells showed increased aminopeptidase A activity accompanied by a generalized aminopeptidase M and alkaline phosphatase reaction. Our data indicate that--in addition to the liver--also the kidney, thymus and spleen are target organs of VPA-induced toxicity in the mouse.

Alkaline Phosphatase↗