Showing papers in "Developmental pharmacology and therapeutics in 1992"

Salivary excretion of drugs in children: theoretical and practical issues in therapeutic drug monitoring.

Abstract: Studies suggest that saliva could be used instead of blood in the therapeutic monitoring of many drugs. This has distinct advantages in pediatrics and neonatology as saliva sampling is painless and spares blood. Stimulation of saliva secretion with a chemical stimulus (i.e. citric acid applied over the tongue) facilitates the study of younger patients. Secretory and reabsorptive processes which take place in the ductal system of the salivary glands, and the rate of flow of the secretion play major roles in the determination of the concentration of solutes in saliva. Drug passage into saliva follows the general principles of movement of drugs across biologic membranes. Only the unbound fraction of the drug in plasma is available for diffusion into saliva and a relationship exists between saliva pH and the saliva/plasma concentration ratio of many polar drugs (tolbutamide, propranolol, procainamide, etc.). However, deviations from the pH theory exist and the inter -and intra-individual variations in saliva/plasma concentration ratios of salicylate and procainamide cannot be explained solely on the basis of fluctuations of salivary pH; on the other hand, a useful relationship exists between plasma and saliva phenobarbital concentrations with no need to correct for saliva pH. The use of stimulated saliva has several advantages over resting saliva: a larger volume of the sample is obtained, the pH gradient between plasma and saliva is smaller, the variability in saliva/plasma concentration ratios of some drugs is narrowed, and less specimens are too viscous or discolored to allow drug analysis. Thorough rinsing of the mouth is required prior to saliva sampling as remnants of orally administered medicines may contaminate saliva specimens and give spuriously high values. Deviation from a simple but strict methodology accounts for some of the discrepancies found in the literature. Studies in children uniformly recommend saliva for therapeutic monitoring of phenytoin, carbamazepine and phenobarbital. Saliva sampling for therapeutic monitoring of ethosuximide, primidone and digoxin in infants and children, and of theophylline and caffeine in the neonate is promising, but little pediatric experience is available as yet. The value of saliva in therapeutic monitoring of theophylline in children is still controversial. Little of highly polar compounds such as aminoglycosides, and of polar highly protein bound drugs such as valproic acid is present in saliva. More data are still needed on the excretion of drugs in saliva in infants and in acutely ill children, and few data exist in the premature and full-term neonate.

Comparison of the effect of midazolam or vecuronium on blood pressure and cerebral blood flow velocity in the premature newborn.

Abstract: The effect of midazolam and vecuronium on mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV) was evaluated in premature infants (birthweight 550-2,560 g; gestational age 26-36 weeks) randomised to receive either 0.1 mg/kg midazolam (n = 7) or 0.05 mg/kg vecuronium (n = 8) intravenously. MAP, by means of an indwelling arterial catheter, and MCBFV, by means of non-invasive pulsed-Doppler of the middle cerebral artery, were measured every 5 min, starting at 10 min prior to until 1 h after drug administration. A transient 25-43% decrease in MCBFV (mean 0.06 m/s) dependent on a 8-23% decrease in blood pressure (mean 9 mm Hg) was noted in all patients within 15 min following administration of midazolam, which returned to baseline values within 1 h. In 2 out of 7 infants, a plasma expander was required. In contrast, vecuronium only decreased the MCBFV in 3 of 8 infants. Thus, a bolus of midazolam transiently decreased blood pressure and MCBFV, and should be used cautiously in sick preterm infants.

Cytochrome P450-dependent metabolism of dextromethorphan: fetal and adult studies.

Abstract: Dextromethorphan undergoes O-demethylation to dextrorphan and N-demethylation to 3-methoxymorphinan. 3-Hydroxymorphinan, a didemethylated compound, is secondarily formed. The O-demethylation pathway to dextrorphan is polymorphic and under CYP2D6 genetic control. Adult and fetal studies were performed to characterize the cytochrome P450 families involved in dextromethorphan metabolism and their ontogeny. In adult volunteers in vivo and in vitro studies demonstrate that the O-demethylation pathway to dextrorphan is dependent on CYP2D6 and is predominant in extensive metabolizers and defective in poor metabolizers of the drug. The N-demethylation pathway to 3-methoxymorphinan is accessory and is dependent on the CYP3A subfamily. In human fetal microsomes, CYP2D6 protein and activity are not detectable until birth, while CYP2D6 RNA is present in significant amounts before birth. CYP3A activity is detectable in large amounts as early as the 17th week of gestation. Fetal and adult members of the CYP3A subfamily have close, although different, properties, as demonstrated by immunoinhibition studies.

Studies on developmental neurology in the human fetus.

Abstract: The development of the motor component of the embryonic and fetal central nervous system can be studied by observation of fetal movements, using real-time ultrasound. In this paper data on emergence and development of fetal movement patterns and behavioural states are reviewed in the light of the normal development of the nervous system, identification of disturbances in normal development and testing behavioural teratogenicity in the human.

Hypoxic-ischemic damage in the neonatal brain: excitatory amino acids.

Abstract: Perinatal brain damage is a major clinical problem. Recent studies suggest that excitatory amino acids (EAAs) may be important for the development of hypoxic-ischemic brain injury in the newborn. Experimental work demonstrates that the immature brain is hypersensitive to the toxic effects EAA ('excitotoxicity'), hypoxic-ischemia is accompanied by an extracellular overflow of EAAs and hypoxic-ischemic brain damage is reduced by EAA receptor antagonists. Clinical investigations demonstrate the presence of EAA receptors in vulnerable areas of the newborn human brain and the concentrations of EAAs in the cerebrospinal fluid are higher in asphyxiated than in control infants. Clinical studies are warranted to evaluate the importance of excitotoxicity for development of brain lesions after severe asphyxia.

Developmental aspects of the monoamine-degrading enzyme monoamine oxidase.

Abstract: In the rat heart, monoamine oxidase (MAO)-B activity was shown to predominate in 2- to 3-week-old animals, whereas MAO-A activity was reported to be very low in newborn rats and to increase considerably with age until it predominates. These results are in contrast with those found in the mouse heart, where an age-dependent increase in MAO-B activity with no changes in 5-hydroxytryptamine deaminating activity was found to occur. There is evidence that the adult values of MAO activity are reached early in development in rat kidney and liver. In the rat lung the adult values of MAO-A activity are reached by day 40, whereas MAO-B activity is still increasing by day 80. Important differences have been reported in the developmental pattern of the two forms of MAO in the rat and mouse brain, with a decrease in the MAO-A/MAO-B ratio during postnatal development. In the human brain, the ontogenetic development of MAO-A and MAO-B appears to parallel that observed in the rodent brain. It is worth noting that most of the available data have to be considered with reservation owing to many methodological problems. Further studies are clearly needed to get reliable information on the ontogenesis of MAO in mammalian tissues.

Potential of population pharmacokinetics to reduce the frequency of blood sampling required for estimating kinetic parameters in neonates.

Abstract: Data obtained from neonates receiving zidovudine as part of a phase I study were used to estimate the population pharmacokinetic parameters of this drug and to determine the minimum number of data points necessary to provide accurate estimates of the kinetic parameters and their variability Analysis was performed with 541 concentrations of zidovudine, obtained from 32 infants and with a variety of reduced data sets using NONMEM (nonlinear mixed effect model) The reduced data sets were derived by randomly reducing the number of sampling time points per dosing interval and/or by randomly reducing the number of available subjects We determined that accurate estimates of pharmacokinetic parameters and their variability were obtained with the inclusion of all 32 patients using only two concentration-time points per dose interval, provided that one of the points was obtained during the first 2 h after administration of the drug The parameters themselves were adequately estimated with only 24 subjects and two concentration-time points per dose interval We suggest that NONMEM should be used in addition to the traditional pharmacokinetic analysis to obtain more precise information directly in the population of interest with a minimum of blood sampling from each patient This is especially critical in infants whose blood volumes are limited

Biological markers of intrauterine exposure to cocaine and cigarette smoking.

Abstract: We describe hair tests for assessment of fetal exposure to cocaine and cigarette smoking. Cocaine and its major metabolites are incorporated into hair during the growth of the shaft and stay there for the whole life of the hair. Cocaine crosses the placenta and its metabolite benzoylecgonine, has been found in neonatal urine, meconium and hair. In order to utilize hair measurements of cocaine as a biological marker of systemic exposure, we conducted both animal and human investigations on the dose response characteristics of this phenomenon. Our data suggest that both maternal and fetal accumulation of cocaine and its metabolite follow a linear pattern within the regularly used doses. Similarly, a good correlation was observed in animals between maternal dose and fetal hair accumulation. To date, no biological markers have been identified that can predict the extent of fetal exposure to the adverse effects of toxic constituents of cigarette smoke. We measured maternal and fetal hair concentrations of nicotine and cotinine in mother-infant pairs. Smoking mothers had a mean of 21.3 +/- 18 ng/mg hair nicotine and 6 +/- 9.2 ng/mg of cotinine, significantly more than nonsmokers (0.9 +/- 0.8 ng/mg nicotine and 0.3 +/- 0.5 ng/mg cotinine, p < 0.0001). Babies of smokers had a mean nicotine concentration of 6 +/- 9.2 ng/mg (range 0-27.3) and cotinine of 2.1 +/- 3.7 ng/mg (range 0-12.2), significantly more than babies of nonsmokers (nicotine 0.6 +/- 0.7 ng/mg and cotinine 0.2 +/- 0.5 ng/mg; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Nervous and immune systems as targets for developmental effects of benzodiazepines. A review of recent studies.

Abstract: Prenatal exposure to benzodiazepines (BDZ) can cause behavioral dysfunctions both in humans and in experimental animals. In addition, prolonged impairment of cellular immune functions is found in rats after low dose BDZ exposure (e.g., diazepam 1.25 mg/kg/day) during part of fetal life [gestational days (GD) 14-20]. Analysis of diazepam and its metabolites in maternal and fetal tissues revealed that in this rat model the drug is no longer present at birth, which excludes direct effects of diazepam during the postnatal period. The main target of BDZ in brain, the GABAA receptor complex, is structurally and functionally heterogeneous. Besides alpha- and beta-subunits, gamma 2- or gamma 3-subunit should be coexpressed for a fully functional BDZ response. Signals of mRNAs encoding for alpha 1, beta 2 and gamma 2 are detected in fetal rat spinal cord and lower brainstem by GD 14 and reach telencephalic regions in later fetal life, reminiscent of BDZ receptor ontogeny. Regional subunit distribution differs from the adult brain, one interesting feature being a preponderance of gamma 2 mRNA throughout fetal life. Since subunit composition influences the sensitivity to BDZ, these data suggest that prenatal effects of BDZ depend upon regional subunit compositions present at different developmental stages. The delayed depression of cellular immune responses in prenatally BDZ-exposed rat offspring during the first 2 postnatal months is accompanied by various changes in immune cell biology. Binding characteristics of the peripheral (omega 3) type BDZ receptor are altered until adulthood (8 weeks). Membranes of spleen cell preparations containing mainly lymphocytes exhibit a decrease of affinity for the peripheral ligand [3H]PK11195, splenic macrophage preparations a decrease of maximal binding capacity. Various defects in cytokine production by macrophages and T lymphocytes were observed: Mitogen-stimulated release of macrophage-derived tumor necrosis factor-alpha (TNF-alpha) and of the T cell-derived interleukin-2 (IL-2) was drastically reduced at 2 and 4 weeks of life and recovered in young adulthood, exhibiting the same time course of depression as lymphocyte proliferation in response to immune stimuli. Interleukin-6 (IL-6) release remained diminished until adulthood. In female offspring, additional alterations were found in splenic noradrenaline turnover after immune stimulation. The mechanisms underlying the breakdown of the cytokine network in prenatally diazepam-exposed offspring, and the long-term consequences are as yet unknown.

Placental transport of dioxins from mother to fetus. II. PCBs, dioxins and furans and vitamin K metabolism.

Abstract: Placental transport of dioxins and furans from mother to fetus takes place. It is probably related to the fatty acid transport. Between 10 and 20% of fatty acids in a full-term baby are of maternal origin. In adipose tissue of children that died in the early neonatal period concentrations of +/- 25% were found of three dioxin and furan congeners 12378 P5CDD, 123678 H6CDD, and 23478 P5CDF in relation to a mean concentration of these congeners in the fat of 14 breastmilk samples. Data of concentrations are given as measured in liver and adipose tissue. In the placenta of a Dutch woman an accumulation of dioxins and furans is found in relation to blood. Animal studies support the hypothesis that polychlorobifenyls play a role in the cause of the late hemorrhagic disease in the newborn, in particular the 2, 4, 5, 2, 4, 5-hexachlorobifenyl that is present in relatively high concentrations in breastmilk.

Functional changes implicating dopaminergic systems following perinatal treatments.

Abstract: A series of experiments, involving diverse perinatal treatments of either rats or mice, have been performed in order to investigate the effects of these treatments upon certain selected spontaneous and learned behaviors in the laboratory. Rat dams were administered either metallic mercury, organic tin or neuroleptic compounds, and the offspring of these dams was studied with behavioral tests at adult ages, prenatal studies. Newborn rat pups were administered either 6-hydroxydopamine (6-OHDA) (at various doses), or metallic mercury and then tested at adult ages. Newborn mice were administered either metaclopramide, an antiemetic compound, or haloperidol, a neuroleptic compound, and tested for spontaneous and d-amphetamine induced activity as adults. The behavioral battery the rats were tested with consisted of measures of spontaneous motor activity, including locomotion/ambulation, rearing, and head dipping behaviors, and a parameter under which diverse behaviors were collected, total activity. Alterations to instrumental maze learning performance were studied through application of the spatial learning tasks: the radial arm maze and the circular swim maze. Possible changes in dopaminergic pathways were assessed by measuring the effects of perinatal treatments upon d-amphetamine-induced activity. It was shown that prenatal metallic mercury, organic tin and the neuroleptic compounds, haloperidol and remoxipride altered various parameters of spontaneous motor activity, retarded maze learning in the radial arm maze and potentiated d-amphetamine-induced activity. Metallic mercury rats were not subjected to the amphetamine test and remoxipride rats were not retarded according to the learning task. Postnatal metallic mercury, 6-OHDA, haloperidol and the antiemetic compound, metaclopramide, also altered spontaneous and d-amphetamine-induced activity as well as radial arm maze performance, excluding in this case haloperidol and metaclopramide. None of these treatments altered performance in the circular swim maze, except for 6-OHDA where doses inflicting severe depletions (greater than 85% depletion compared to control values) caused notable impairments. One tentative conclusion from the pattern of behavioral changes, generally in the absence of any measurable neurochemical changes, observed after these treatments is that the functional development of dopaminergic systems had, to a greater or lesser degree, been altered.

Pharmacokinetics of high-dose methylprednisolone in children.

Abstract: Disposition of methylprednisolone was characterized in 11 children receiving the high-dose therapy (26.0 mg/kg on average). After intravenous infusion, methylprednisolone hemisuccinate was rapidly converted to methylprednisolone with a half-life of about 20 min. Methylprednisolone in serum, eliminated monoexponentially in 8 patients and biexponentially in the remaining three, had the mean residence time of about 3 h, and a terminal half-life of 2.5 h. The volume of distribution at steady state, and the clearance were 1.3 liters/kg and 0.5 liters/kg/h, respectively. Although these average pharmacokinetic parameters were comparable to those determined in other studies with conventional low doses, the clearance values in our data were characterized by 5-fold interindividual difference, suggesting large variations in exposures to methylprednisolone among children on the high-dose pulse therapy.

Patient-controlled versus conventional analgesia for postsurgical pain relief in adolescents.

Abstract: We performed a randomized nonblinded, cross-over comparison of patient-controlled analgesia (PCA) with conventional intramuscular analgesia in 10 adolescents (13-18 years) undergoing spinal fusion for idiopathic scoliosis. PCA use afforded more effective pain control (p < 0.02) on a 10-point linear pain intensity scale than did intramuscular injections, while causing an equal amount of sedation and no side effects. PCA appears to be a promising technique for providing postoperative pain relief in this group of adolescents. Further studies are needed to define its role for other pediatric conditions.

Priming as a model of behavioural sensitization

Abstract: Repeated exposure to drugs acting as direct or indirect stimulants of central dopamine transmission results in sensitization to their behavioural stimulant properties (behavioural sensitization). Priming provides a simple model of behavioural sensitization particularly suitable for studies of its neural and molecular mechanisms. The results obtained to date indicate that priming results in an increased responsiveness of postsynaptic dopamine receptor mechanisms in the caudate nucleus, possibly due to an increased affinity of the D-1 receptor for its agonist.

Pregnancy alters the hemodynamic responses to cocaine in the rat.

Abstract: To test our hypotheses that the hemodynamic response to cocaine may be altered during pregnancy, cocaine (0.33 mg/kg/min) was infused intravenously to chronically catheterized pregnant and nonpregnant female rats. Cardiac output and regional blood flow were measured, and cocaine concentrations in plasma and tissues, as well as plasma cholinesterase activity were determined. Results were compared between pregnant and nonpregnant groups. Cocaine produced a significant decrease in heart rate, accompanied by a fall in cardiac output, and decreased cerebral, myocardial, and placental blood flow in pregnant rats. The plasma cocaine concentration in pregnant animals was lower than that of nonpregnant ones, but tissue concentrations were similar in both groups. These results indicate that pregnancy enhances cardiovascular responses to subtoxic doses of cocaine. There was little placental transfer of cocaine with a fetal to maternal plasma concentration ratio of 0.28.

Wilson's disease treatment by triethylene tetramine dihydrochloride (trientine, 2HCl): long-term observations.

Abstract: Wilson's disease is an autosomal recessive disorder characterized by an accumulation of a toxic amount of copper in the body. Triethylene tetramine dihydrochloride (trientine, 2HCl) is a new chelating agent that may be effective in the removal of excess copper but long-term efficacy has not yet been investigated. Here we report the use of trientine over more than 8 years in 2 patients with Wilson's disease who could not tolerate D-penicillamine. We found no significant side effect, except a decreased serum iron concentration without clinical symptoms of anemia. In annual examinations at a steady state, the serum copper levels remained below 20 micrograms/100 ml. The 24-hour urinary copper excretion was less than that found using D-penicillamine, while the basal copper excretion, after 5 days abstinence from trientine, was maintained below 100 micrograms/day. Both hepatic and neurological manifestations except bulbar symptoms were recovered without any initial deterioration.

Sedative/hypnotic effects of chloral hydrate in the neonate: trichloroethanol or parent drug?

Abstract: Although the metabolism and pharmacokinetics of chloral hydrate (CH) have been reported, there have been no attempts to correlate CH or its metabolite, trichloroethanol (TCE) with the sedative or hypnotic effects. In order to determine whether plasma concentrations of CH or TCE reflect the sedative/hypnotic effects, a sedation/agitation scale was developed. Based on the results of the present study, the sedative/hypnotic effects of TCE cannot be ruled out completely. However, in the neonate, the parent drug CH seems to have a more important role than has been previously suggested from human research.

Effects of prenatal cocaine on the ventilatory response to hypoxia in newborn rabbits

Abstract: Recently, investigators have reported an alteration of postnatal respiratory pattern, deficient hypoxic arousal from sleep, and an increased incidence of sudden infant death syndrome (SIDS) among human infants exposed to cocaine prenatally, thus suggesting that prenatal cocaine exposure may perturb the maturation of respiratory control thereby increasing the risk for SIDS. To investigate the effects of prenatal cocaine on postnatal respiration, we evaluated the ventilatory response to 0.21 FIO2 (baseline) and at 0.15, 0.10, and 0.08 FIO2 by the barometric method on days 4-5 of life in 23 New Zealand White rabbit pups born to cocaine-exposed (30 mg/kg/day of cocaine HCl by continuous subcutaneous infusion), pair-fed and free-fed does. The chamber pressure deflection (proportional to VT after appropriate calculation) was computer-sampled at 200 Hz when the unanesthetized pups were resting quietly with no gross body movements. Recording was made after 10 min acclimatization to a specific FIO2. We found that baseline ventilation did not differ significantly among study groups. However, minute ventilation (VI), inspiratory flow (VT/TI), tidal volume (VT), increased significantly with hypoxia to peak values at 0.08 FIO2 in pair-fed and free-fed pups but these measurements did not increase significantly in cocaine-exposed pups. Our finding of a deficient second phase of the hypoxic ventilatory response among cocaine-exposed pups supports the hypothesis that prenatal cocaine perturbs the maturation of respiratory control.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombocyte monoamine oxidase activity and behavior deviances in adolescence.

Abstract: The frequencies of patients with low thrombocyte monoamine oxidase (MAO) activity (defined as having an activity lower than 1 SD below the mean of a respective control group) were studied in 100 consecutive cases admitted to a clinic for child and youth psychiatry. 41 boys and 26 girls (group I) had behavior disorders, attention deficit disorders and/or alcohol and hashish abuse according to DSM III R. 16 boys and 17 girls had other diagnoses (group II). None of the 2 male patient groups differed significantly from the controls. A significantly higher percentage of the girls in group I had low activity of platelet MAO than in the control group (p = 0.015), while the girls in group II did not differ from the controls. Acting out, antisocial behavior and abuse is less accepted in women than in men. Therefore, the girls in the present study might be either more psychiatrically disturbed or have more deviant personalities than the boys, which might explain why our hypothesis about a lower thrombocyte MAO activity in the adolescents with externalizing symptoms (group I) was verified only in the girls.

Placental transfer of phenobarbital: what is new?

Abstract: The placental transfer of phenobarbital was investigated in 35 mother-infant pairs at birth The drug was administered prenatally to the mothers for maternal epilepsy (group 1, n = 5), gestational hypertension and preeclampsia (group 2, n = 20) and prophylaxis of intraventricular hemorrhage in premature deliveries (group 3, n = 10) The phenobarbital levels in arterial cord blood were 100 +/- 28% in group 1, 89 +/- 21% in group 2 and 77 +/- 16% in group 3 with respect to the levels observed in the mothers The most important factor influencing the transplacental passage was the duration of maternal treatment in the infant of group 1 (r = 080, p < 001), the gestational age in the infants of group 2 (r = 074, p < 001) and the arterial cord pH in the infants of group 3 (r = 089, p < 0001)

Vasodilators in persistent pulmonary hypertension of the newborn: a need for optimal appraisal of efficacy.

Abstract: Tolazoline hydrochloride is usually the first choice pulmonary vasodilator in persistent pulmonary hypertension of the neonate (PPHN). The analysis of 26 articles including 467 tolazoline-treated infants has been hindered by many methodological drawbacks. Tolazoline has always been administered to infants suffering refractory hypoxemia, but, unfortunately, pulmonary hypertension has not usually been investigated. Moreover, 80% of the tolazoline-treated neonates had an underlying pulmonary parenchymal disease as a potential cause of severe hypoxemia. Noteworthy is that similar comments apply to all studies dealing with the use of other pulmonary vasodilators in PPHN. Pulsed Doppler echocardiography (PDE) should allow a qualitative and quantitative approach for PPHN and an analysis of both success and failure of vasodilator therapeutics. In the meantime, the use of PDE requires more intense investigation prior to wide application in PPHN.

Methamphetamine detection from meconium and amniotic fluid in guinea pigs depends on gestational age and metabolism.

Abstract: Significant adverse perinatal effects of maternal methamphetamine use have been reported, but little is known about factors influencing methamphetamine screening test results during the perinatal period. We tested the hypothesis that gestational age would affect quantitative recovery of methamphetamine in meconium and amniotic fluid. Time-bred guinea pigs received an intraperitoneal (i.p.) injection of 1 mg/kg methamphetamine at either 44 days (0.65 of term, n = 5), 50 days (0.74, n = 8), 56 days (0.82, n = 9) or 63 days (0.93, n = 4) gestation. At 1 or 7 days after i.p. methamphetamine, meconium and amniotic fluid were collected for quantitative methamphetamine assay by gas chromatography-mass spectrometry. Recovery from amniotic fluid and meconium 1 day after injection was influenced by gestational age. Greater values in amniotic fluid and meconium and a higher percentage of positive samples were seen in older fetuses. Collectively at all gestational ages, combined testing of amniotic fluid and meconium yielded detectable methamphetamine or its metabolites in 87% of guinea pigs 1 day after injection. However, methamphetamine was not detectable 1 week after injection in any sample (n = 63) at either 0.74 or 0.82 of term except for one positive amniotic fluid sample. Finally, demethylation of methamphetamine to amphetamine was higher in older fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)

The valproic acid metabolite E-2-n-propyl-2-pentenoic acid does not induce spina bifida in the mouse.

Abstract: The antiepileptic drug valproic acid (VPA) has been implicated as a human teratogen causing spina bifida aperta. Recently we developed a mouse model inducing spina bifida aperta and occulta with VPA. In a search for novel antiepileptic agents the VPA metabolite E-2-n-propyl-2-pentenoic acid (2-en-VPA) had been developed. In the mouse, 2-en-VPA exhibits anticonvulsive potency similar to VPA but very low teratogenic potency (induction of exencephaly). We have now compared VPA and its metabolite 2-en-VPA in regard to induction of spina bifida in our mouse model. 2-en-VPA was administered 3 times during the period of gestation most sensitive for the induction of spina bifida aperta with VPA: on day 9 of gestation at 0, 6 and 12 h. The following doses were injected (in mmol 2-en-VPA-Na/kg): (a) 3 x 2.1, (b) 3 x 2.7 (the equimolar dose of VPA is the threshold dose for induction of spina bifida aperta) and (c) 3 x 3.0 (the equimolar VPA dose produced spina bifida aperta). 2-en-VPA did not induce spina bifida aperta in the mouse in any of these groups. We then investigated the induction of spina bifida occulta in the three dose groups. Spina bifida occulta is a less serious form of spina bifida and may provide a sensitive method to estimate the potency of a compound to induce more severe forms of spina bifida. This malformation was demonstrated in alcian-blue- and alizarin-red-stained fetal skeletons by measurements of the distance between the cartilaginous ends of each vertebral arch.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostacyclin synthesis and stimulation of cyclic AMP production in ovine fetal vasculature : heterogeneity in pulmonary and systemic arteries

Abstract: Prostacyclin (PGI2) is an important local mediator of vasomotor tone in the fetus and newborn, acting via stimulation of cAMP production by vascular smooth muscle (VSM) adenylate cyclase. In this investigation PGI2 and prostaglandin (PG) E2 synthesis and stimulation of cAMP production were compared in vitro in ovine fetal pulmonary versus systemic (mesenteric) arteries. PGI2 synthesis was similar in the pulmonary and systemic arteries (2.4 +/- 0.2 and 2.6 +/- 0.3 ng/mg protein.h, respectively), as was PGE2 synthesis (1.9 +/- 0.2 and 1.5 +/- 0.2 ng/mg protein.h, respectively); synthesis was greater for PGI2 versus PGE2 in both artery types. 65-71% of PGI2 synthesis and 51-59% of PGE2 synthesis occurred in the endothelium. Basal (nonstimulated) cAMP production was fully attenuated by indomethacin, indicating that it is mediated exclusively by endogenous PG. Basal cAMP production was 3.8-fold less in pulmonary versus systemic arteries, and this was related to a 9.7-fold difference in responsiveness to PG. A 14.7-fold difference in the response to forskolin indicates that underlying mechanism may be a disparity in the quantity and/or function of the adenylate cyclase enzyme complex. Thus, prostacyclin and PGE2 synthesis are comparable in ovine fetal pulmonary versus systemic arteries, but the cAMP response to the prostanoids is markedly greater in the latter artery type due to differences in the activation of adenylate cyclase. This heterogeneity in VSM intracellular signalling may contribute to differential vasomotor tone and responses in the fetal pulmonary and systemic circulation.

Enantiomers: implications and complications in developmental pharmacology.

Abstract: The majority of synthetic drugs with chiral centers are administered as racemates. Thus chemically, and to an even greater extent biologically, a racemic drug is not a single compound, but a 50:50 mixture of two enantiomeric drugs. No generalization can be made concerning whether and to what extent the activity, in either qualitative or quantitative terms, differs between enantiomers. It is not unusual for the enantiomers of a drug to have a high degree of enantioselectivity for one action but no enantioselectivity for another action. For instance S-propranolol is at least two orders of magnitude more potent than R-propranolol with regard to beta-adrenoceptor antagonism. However, the two enantiomers are equipotent with regard to their membrane stabilizing effect. It is often overlooked that enantioselectivity in the activity of enantiomers as determined in vitro cannot be extrapolated to the in vivo situation since enantioselective drug disposition can lead to an enantiomer ratio in vivo which differs substantially from that in the dosage form administered. Enantioselectivity in drug disposition seems to be the rule rather than the exception and, depending on whether the active or less active enantiomer is preferentially affected, there may be amplification or attenuation of in vivo as compared to the in vitro drug potency.

Prophylactic low-dose vancomycin treatment in very-low-birth-weight infants.

Abstract: For the prophylaxis of septicemia with coagulase-negative staphylococci in a high-risk very-low-birth-weight population, we administered 5 mg/kg of vancomycin every 12 h. Distribution volume and half-life of vancomycin were determined. Serum peak and trough levels were obtained on day 3 of treatment. With this low-dose regimen, serum concentrations in the therapeutic range were achieved in 35 of the 45 patients. Distribution volume and half-life were 0.692 liters/kg and 7.4 h, respectively. The distribution volume was not related to the gestational age; the half-life in the group of patients with a gestational age < 30 weeks was considerably higher. The 10 small-for-gestational-age children had a significantly smaller distribution volume. The vancomycin trough levels correlated with the serum creatinine concentrations and, therefore, with the gestational age. Our study indicates that this low vancomycin dose is sufficient in very-low-birth-weight infants to achieve therapeutic serum levels, being suitable for both prophylaxis and sepsis therapy.

Delayed thromboxane synthesis inhibition, but not cholinergic blockade, reverses group B streptococcus-induced pulmonary hypertension.

Abstract: Anisodamine, an anticholinergic drug, is widely used in China for treatment of infants with septic shock and has been reported to inhibit thromboxane synthesis in cultured cells. Thromboxane A2 plays an important role in the early pulmonary hypertension in sepsis; however, the role of thromboxane A2 later in sepsis is unclear. We tested the hypothesis that thromboxane A2 synthesis inhibition with dazmegrel, and cholinergic blockade with anisodamine, would attenuate the later phase of pulmonary hypertension induced by 4 h of group B streptococcus (GBS) infusion. 1 mg/kg of dazmegrel reversed the pulmonary hypertension and slightly increased cardiac output; these hemodynamic improvements persisted for 30-60 min. Plasma thromboxane B2 levels returned toward pre-GBS baseline values after dazmegrel treatment. Thus, thromboxane A2 is still a major mediator of pulmonary hypertension in piglets after 4 h of continuous GBS infusion. 0.5 mg/kg of anisodamine had no significant hemodynamic effect. 2 and 4 mg/kg of anisodamine each caused transient, dose-related decreases in systemic artery pressure; cardiac output also fell after the highest anisodamine dose. Pulmonary hypertension was not alleviated by anisodamine. All hemodynamic changes induced by anisodamine were short-lived and returned to preanisodamine values within 10 min. Anisodamine did not ameliorate thromboxane-mediated pulmonary hypertension in this animal model, and therefore may not inhibit thromboxane synthesis in vivo. The results of this study do not support the use of anticholinergic therapy to improve hemodynamics in GBS sepsis, but do suggest that thromboxane synthesis inhibition may be a clinically useful therapy in advanced GBS sepsis.

Comparison of methods for prediction of nephrotoxicity during development.

Abstract: Drugs with nephrotoxic potential are continuously introduced into perinatal and pediatric medicine, and assessment of their relative toxicity is important. We compared different methods of assessment of renal damage during development in an attempt to establish their relative sensitivity, age and dose dependence. Newborn, 6- to 8-day-old and adult rats were treated for 7 days with intramuscular gentamicin (5, 10 or 20 mg/kg/day) or amikacin (5, 20 or 40 mg/kg/day). Renal damage was assessed by serum and urine creatinine, urine N-acetyl beta-glucosaminidase and beta 2-microglobulin, cortical sphingomyelinase in vivo and in vitro and morphologic changes in light and electron microscopy. As expected, there was a dose-dependent damage, with gentamicin being more nephrotoxic than amikacin, and with newborn rats more resistant. The light- and electron-microscopic assessment were more sensitive than all other methods, followed by urinary N-acetyl glucosaminidase and then by beta 2-microglobulin. Sphingomyelinase changes occurred only at the highest doses of gentamicin.

Stimulation of renal tubular transport of p-aminohippurate in rats of different ages by treatment with adrenocortical steroids.

Abstract: Treatment with prednisolone or dexamethasone is followed by an increase in renal excretion of p-aminohippurate (PAH) and in accumulation of PAH in renal cortical slices, particularly in 5- and 10-day-old rats with immature kidney function. Treatment with triamcinolone is effective both in immature and in 55-day-old rats. There is no stimulation of PAH transport after treatment with mineralocorticoids (desoxycorticosterone, aldosterone).

Albendazole and mebendazole uptake by isolated enterocytes.

Abstract: Uptake of albendazole (ABZ) and mebendazole (MBZ) by isolated rat enterocytes was carried out. These drugs, widely used oral anthelmintics, exhibit a scarce water solubility which reduce its absorption by the oral tract. The present study was designed to assess the captation for ABZ and MBZ in different enterocyte populations isolated from upper to crypt villus. The concentration range used for the absorption experiments was within 10-500 microM for both drugs, using DMSO as solvent. The results obtained show the existence of a passive mechanism for the uptake of ABZ and MBZ at concentrations between 10 and 100 microM, with a maximum intake value around 20 microM/mg protein. No differences were found with respect to the cell populations analyzed. The drug uptake levels seem to be higher for MBZ than for ABZ prior to reaching the maximum plateau.