Placental transfer of diphenhydramine in chronically instrumented pregnant sheep

Choline transport via choline transporter-like protein 1 in conditionally immortalized rat syncytiotrophoblast cell lines TR-TBT

Choline is an essential nutrient for phospholipids and acetylcholine biosynthesis in normal development of fetus. In the present study, we investigated the functional characteristics of choline transport system and inhibitory effect of cationic drugs on choline transport in rat conditionally immortalized syncytiotrophoblast cell line (TR-TBT). Choline transport was weakly Na(+) dependent and significantly influenced by extracellular pH and by membrane depolarization. The transport process of choline is saturable with Michaelis-Menten constants (K(m)) of 68microM and 130microM in TR-TBT 18d-1 and TR-TBT 18d-2 respectively. Choline uptake in the cells was inhibited by unlabeled choline and hemicholinium-3 as well as various organic cations including guanidine, amiloride and acetylcholine. However, the prototypical organic cation tetraethylammonium and cimetidine showed very little inhibitory effect of choline uptake in TR-TBT cells. RT-PCR revealed that choline transporter-like protein 1 (CTL1) and organic cation transporter 2 (OCT2) are expressed in TR-TBT cells. The transport properties of choline in TR-TBT cells were similar or identical to that of CTL1 but not OCT2. CTL1 was also detected in human placenta. In addition, several cationic drugs such as diphenhydramine and verapamil competitively inhibited choline uptake in TR-TBT 18d-1 with K(i) of 115microM and 55microM, respectively. Our results suggest that choline transport system, which has intermediate affinity and weakly Na(+) dependent, in TR-TBT seems to occur through a CTL1 and this system may have relevance with the uptake of pharmacologically important organic cation drugs.

The Use of Microdialysis for the Study of Drug Kinetics: Central Nervous System Pharmacokinetics of Diphenhydramine in Fetal, Newborn, and Adult Sheep

The central nervous system (CNS) pharmacokinetics of the H(1) receptor antagonist diphenhydramine (DPHM) were studied in 100- and 120-day-old fetuses, 10- and 30-day-old newborn lambs, and adult sheep using in vivo microdialysis. DPHM was administered i.v. at five infusion rates, with each step lasting 7 h. In all ages, cerebrospinal fluid (CSF) and extracellular fluid (ECF) concentrations were very similar to each other, which suggests that DPHM between these two compartments is transferred by passive diffusion. In addition, the brain-to-plasma concentration ratios were >or=3 in all age groups, suggesting the existence of a transport process for DPHM into the brain. Both brain and plasma DPHM concentrations increased in a linear fashion over the dose range studied. However, the ECF/unbound plasma and CSF/unbound plasma DPHM concentration ratios were significantly higher in the fetus and lambs (approximately 5 to 6) than in the adult (approximately 3). The factors f(CSF) and f(ECF), the ratios of DPHM areas under the curves (AUCs) in CSF and ECF to the plasma DPHM AUC, respectively, decreased with age, indicating that DPHM is more efficiently removed from the brain with increasing age. The extent of plasma protein binding of the drug increased with age. This study provides evidence for a transporter-mediated mechanism for the influx of DPHM into the brain and also for an efflux transporter for the drug, whose activity increases with age. Moreover, the higher brain DPHM levels in the fetus and lamb compared with the adult may explain the greater CNS effects of the drug at these ages.

Area/moment and compartmental modeling of pharmacokinetics during pregnancy: applications to maternal/fetal exposures to corticosteroids in sheep and rats

PURPOSE

The pharmacokinetics of corticosteroids in pregnancy were analyzed to assess maternal/fetal disposition and factors controlling fetal exposure. Area/Moment equations and compartmental models for estimating pharmacokinetic parameters from single dose data during pregnancy were developed.

METHODS

Betamethasone in the maternal/fetal circulations of sheep was measured by HPLC after maternal intramuscular injection (n = 4) of 170 microg kg(-1) of a depot formulation. Additional data for beta-methasone in sheep and dexamethasone pharmacokinetics in rats were obtained from the literature. Area/Moment equations were derived using mass balance concepts, statistical moments, and Laplace theory. Area/Moment analysis, compartmental modeling, and allometric scaling to man for betamethasone were performed using WinNonlin and ADAPT II programs.

RESULTS

Polyexponential maternal/fetal profiles for corticosteroids were observed. Clearance terms for corticosteroid transfer from fetus to mother were 4-fold higher than the clearance term for transfer in the opposite direction. A placental efflux process may restrict fetal access of corticosteroids which are known PGP substrates. The elimination clearance estimates indicate that fetal metabolism plays a minor role in corticosteroid elimination.

CONCLUSIONS

Generalized and specific models for maternal/fetal pharmacokinetics were developed. An efflux transport mechanism, such as the known placental expression of PGP, could explain the limited fetal exposure of corticosteroids.

Apical uptake of choline and cationic drugs in epithelial cell lines derived from human placenta

Many cationic drugs are administered during pregnancy and might enter the fetal circulation by transplacental passage. This study was performed to characterize the apical uptake of choline and several cationic drugs at cultured epithelial cells of the human placenta. Total uptake of [3H]choline in BeWo cells was H(+)-independent and to 65% Na(+)-independent. Uptake rates into both cell lines were saturable with Michaelis-Menten constants (Kt) of 108 microM (BeWo) and 206 microM (JEG-3), respectively. Cationic drugs such as etilefrine, clonidine, ranitidine, diphenhydramine, imipramine and butylscopolamine strongly inhibited the [3H]choline uptake in BeWo cells and in JEG-3 cells, with Ki values ranging from 0.18 to 3.3 mM. In contrast, tetraethylammonium had only little inhibitory effect on [3H]choline uptake. Using high-performance capillary electrophoresis for quantitative analyses, uptake of etilefrine and diphenhydramine into JEG-3 or BeWo cells was measured. Diphenhydramine was transported into JEG-3 cells in a saturable manner with a Kt value of 0.75 mM. In the presence of sodium, diphenhydramine uptake at BeWo cells was inhibited to 69% by the addition of 50 mM choline chloride. Like choline uptake, total diphenhydramine uptake was to 68% Na(+)-independent in BeWo cells. We conclude that in addition to choline, several cationic drugs, in particular diphenhydramine, are taken up by placental epithelial cells from the maternal blood by carrier-mediated processes. Etilefrine, clonidine, ranitidine, diphenhydramine and butylscopolamine interact with the Na(+)-independent placental choline transport system.

A case-control study of congenital abnormality and dimenhydrinate usage during pregnancy

OBJECTIVE

The objective was to determine the teratogenicity of dimenhydrinate, an anti-emetic drug.

METHODS

We compared patients with congenital abnormalities with matched normal controls. Cases were taken from the population-based data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities between 1980 and 1996, while matched controls were from the National Birth Registry of the Central Statistical Office.

RESULTS

Out of 38,151 newborn infants with no congenital abnormalities (control group), 1,726 (4.5%) were treated with dimenhydrinate during pregnancy, while out of 22,843 cases with congenital abnormalities, the number was 914 (4.0%; unadjusted prevalence odds ratio with 95% confidence interval: 0.9, 0.8-1.0). There was thus no indication of teratogenicity with dimenhydrinate. However, a lower rate of obstructive uropathy was found in infants born to mothers treated with dimenhydrinate during the first trimester of pregnancy than in infants whose mothers did not take the drug at that time.

Maternal exposure to diphenhydramine during the fetal period in rats: Effects on physical and neurobehavioral development and on neurochemical parameters

Previous research from our laboratory suggested that the administration of antihistaminics (H(1) receptor antagonists) to pregnant Wistar rats throughout pregnancy altered brain sexual differentiation and dopaminergic physiology of the offspring. In the present study, we assessed the effects of 20 mg/kg diphenhydramine (DPH) administration to pregnant rats during the fetal period of pregnancy [Gestation Days (GDs) 16-21], a critical period for brain sexual differentiation and central nervous system (CNS) maturation. Maternal body weight and water and food consumption were measured during pregnancy and offspring physical and behavioral development were evaluated during lactation. Offspring open-field behavior was assessed at 21 and 100 days of age. After the final open-field test, male and female sexual behavior, stereotypy following an apomorphine challenge, striatal content of dopamine (DA), the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), serotonin (5-HT) and the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were assessed. There were no significant treatment-related changes in maternal reproductive parameters, but DPH treatment decreased maternal body weight gain during the treatment period. Offspring physical parameters were not altered in the treated group, and no significant treatment-related changes were found in female open-field measures, sexual behavior or in striatal neurochemical measurements. However, delayed testis descent and altered patterns of sexual behavior occurred in male offspring accompanied by increased striatal DA, decreased striatal DOPAC as well as reduced DOPAC/DA, HVA/DA and 5-HIAA/5-HT ratios. Taken together, these data suggest that exposure to DPH during the fetal period of rat development altered postnatal CNS maturation and sexual development of male offspring via changes in striatal bioamine systems.

STEREOSELECTIVE PHARMACOKINETICS OF FLUOXETINE AND NORFLUOXETINE ENANTIOMERS IN PREGNANT SHEEP

We examined the stereoselective disposition of fluoxetine (FX) and its metabolite norfluoxetine (NFX) in five pregnant sheep. Racemic FX was administered i.v. to the ewe (50 mg) and the fetus (10 mg) on separate occasions. Maternal and fetal blood, maternal urine, and fetal amniotic and tracheal fluid samples were collected for 72 h. FX and NFX isomers were quantified by gas chromatography-mass spectrometry. They rapidly crossed the placenta [maternal to fetal area under the plasma concentration versus time curve (AUC) ratios 0.59 and 0.65, respectively]. There was significant FX stereoselectivity with S/R FX AUC ratios averaging 1.65 +/- 0.33 and 1.73 +/- 0.29 in ewe and fetus, respectively, after maternal dosing. The maternal clearance and volume of distribution were also higher for (R)-fluoxetine than for (S)-fluoxetine. FX, NFX, and their glucuronides were present in maternal urine but accounted for only 3.4% of maternal drug elimination. In contrast, NFX was not detected in the fetus after fetal FX administration, which is consistent with the absence of measurable fetal nonplacental clearance of the drug and the lack of NFX formation in fetal hepatic microsomal incubations. There was also no fetal production of FX and NFX glucuronides in vivo. Both FX and NFX were extensively and stereoselectively bound in maternal and fetal plasma, with the free fraction S/R FX ratio averaging 0.46 +/- 0.06 and 0.58 +/- 0.10 in ewe and fetus, respectively. Thus, FX exhibits extensive stereoselective disposition, which is likely due to differential plasma protein binding of the FX isomers, and there is no detectable fetal formation of NFX, FX, and NFX glucuronides.

Comparative efficacy of terfenadine, loratadine, and astemizole in perennial allergic rhinitis

Nonsedating H1 antihistamines such as terfenadine, loratadine, and astemizole are widely prescribed for the treatment of allergic rhinitis. The comparative efficacy of these agents has not been thoroughly studied. We studied 14 subjects in an open-label four-way crossover trial. Patients were recruited from an outpatient allergy clinic. Inclusion criteria were documented rhinitis symptoms for at least 2 years before the study and skin-test positivity in response to perennial allergens. Each subject underwent sequential 2-week trials of each of four H1 antihistamines: terfenadine, loratadine, astemizole, and chlorpheniramine. No placebo was included. Outcome measures were subjective rhinitis symptom scores, overall efficacy scores, and concomitant pseudoephedrine use. In addition, nasal-examination scores were obtained by way of physician assessment at the end of each 2-week trial, and side effects were tabulated. Nasal-examination scores for each of the four H1 antihistamines were significantly better than the baseline scores (p < 0.05). No statistically significant differences in rhinitis symptom scores, overall efficacy scores, or concomitant pseudoephedrine use were noted. We detected no clinically significant differences in efficacy among terfenadine, loratadine, astemizole, and chlorpheniramine in the treatment of perennial allergic rhinitis.

Determination of valproic acid and its metabolites using gas chromatography with mass-selective detection: application to serum and urine samples from sheep

An improved method for the quantitative determination of valproic acid (VPA) and sixteen of its metabolites has been developed using gas chromatography-mass spectrometry with selected-ion monitoring. The method is applicable to serum or urine and all metabolites are measured in a single chromatographic run of 29.5 min. Ions selected for quantitative purposes were the characteristic [M-57]+ ions of the tert.-butyldimethylsilyl (tBDMS) derivatives. The method utilizes heptadeuterated VPA as well as six heptadeuterated metabolites as internal standards [i.e. 2-[2H7]propyl-2-pentenoic acid (2-ene[2H7]VPA), 2-[2H7]propyl-4-pentenoic acid (4-ene[2H7]VPA), 2-[2H7]propyl-3-oxopentanoic acid (3-keto[2H7]VPA), 2-[2H7]propyl-4-oxopentanoic acid (4-keto[2H7]VPA), 2-[2H7]propyl-3-hydroxypentanoic acid (3-OH[2H7]VPA), 2-[2H7]propyl-5-hydroxypentanoic acid (5-OH[2H7]VPA)]. The method demonstrates very good accuracy and precision over a large range of concentrations for VPA and all metabolites measured in both human and sheep biological fluids. The assay was applied to the analysis of VPA and metabolites in serum and urine samples collected from three non-pregnant ewes following intravenous bolus administration of a mixture of VPA and [13C4]VPA. Sheep were observed to produce measurable quantities of the majority of metabolites found in humans, with the notable exception of the di-unsaturated compounds (i.e. 2,3'-diene VPA and 2,4-diene VPA). The pharmacokinetics and metabolism of VPA and [13C4]VPA appear to be equivalent in the sheep model. The elimination half-life of VPA and [13C4]VPA in the ewe were estimated to be approximately 3.5 +/- 0.4 and 3.2 +/- 0.4 h, respectively.

Simultaneous analysis of diphenhydramine and a stable isotope analog (2H10)diphenhydramine using capillary gas chromatography with mass selective detection in biological fluids from chronically instrumented pregnant ewes

This report describes both the synthesis of a stable isotope analog of the H1 receptor antagonist diphenhydramine (DPHM), and the simultaneous quantitation of DPHM and a deuterated stable isotope analog of DPHM, viz. (2H10)DPHM in biological fluids from the chronically instrumented pregnant ewe. (2H10)DPHM was synthesized and purified, and both its structure and purity were verified. Biological samples were prepared for analysis using liquid-liquid extraction prior to capillary gas chromatography/mass spectrometry. The method employed electron impact ionization with selective ion monitoring of ions with m/z 165 for DPHM and m/z 173 for (2H10)DPHM. The minimal quantifiable concentration of DPHM and (2H10)DPHM from a 1.0 ml sample was 2.0 ng ml-1 in fetal and maternal plasma, fetal tracheal fluid and amniotic fluid. The method was validated from 2.0 ng ml-1 to 200.0 ng ml-1 for both DPHM and (2H10)DPHM in plasma, fetal tracheal fluid and amniotic fluid. Differences in the disposition between DPHM and (2H10)DPHM were not apparent during a control experiment in which both labeled and unlabeled DPHM were administered to a chronically instrumented fetal lamb. This method provides the required sensitivity and selectivity for the simultaneous quantitation of unlabeled and labeled DPHM during pharmacokinetic experiments conducted in near-term pregnant sheep.

Transplacental and nonplacental clearances of diphenhydramine in the chronically instrumented pregnant sheep

Pharmacokinetic studies of the histamine H1-receptor antagonist diphenhydramine were conducted in eight chronically instrumented pregnant sheep at 126-138 days of gestation. Diphenhydramine was administered by simultaneous intravenous bolus injection and infusion to steady state given 48 h apart, to the ewe and the fetus on separate occasions. Average steady-state drug concentration in plasma after maternal infusion was 212.1 +/- 67.8 ng/mL in the mother and 36.3 +/- 14.4 ng/mL in the fetus, resulting in a fetal-to-maternal concentration ratio of 0.19 +/- 0.10. Following fetal infusions, maternal and fetal steady-state drug concentrations were 31.1 +/- 11.6 and 447.6 +/- 185.2 ng/mL, respectively. The free fraction of diphenhydramine determined in the fetus (0.277 +/- 0.087) was significantly greater than that in the mother (0.141 +/- 0.079). Transplacental and nonplacental clearances were calculated at steady state according to a general two-compartment open model, with drug elimination occurring from both compartments. The total fetal clearance (472.7 +/- 215.7 mL/min) was relatively small compared with the total maternal clearance (3426.1 +/- 905.8 mL/min). The transplacental clearance from fetus to mother (264.4 +/- 138.7 mL/min) was approximately threefold higher than that from mother to fetus (82.4 +/- 40.5 mL/min). Maternal nonplacental clearance (3343.8 +/- 890.7 mL/min) accounted for 97.8 +/- 1.1% of the maternal total clearance, whereas fetal nonplacental clearance (208.4 +/- 80.4 mL/min) accounted for 45.1 +/- 4.7% of the fetal total clearance. It is concluded that in the fetus both the transplacental and nonplacental pathways are important for drug elimination.

Prenatal versus postnatal effects on offspring weight gain of rats exposed to diphenhydramine: a critical evaluation of fostering procedures in rats

1. In order to evaluate the relative contribution of fostering procedures in the analysis of the development of rats prenatally exposed to diphenhydramine (20 mg/kg/day, sc) the weight gain of litters fostered or not by their biological mothers were examined from 2-21 days of age. 2. Maternal behavior and milk production were also assessed. 3. The results showed a decreased weight gain only in offspring fostered by mothers from different prenatal treatments and a lack of effects on maternal behavior and milk production. 4. It was concluded that the reduced weight of cross-fostered litters was mediated through an interference with postnatal mother-offspring interaction, which was not herein identified.

Pharmacokinetics of diphenhydramine after dose ranging in nonpregnant ewes

Studies were conducted to characterize the pharmacokinetics of diphenhydramine in nonpregnant ewes after iv administration of 25-, 50-, 100-, and 200-mg doses of diphenhydramine hydrochloride on a crossover basis. Plasma drug concentration versus time data exhibited multiexponential characteristics. The initial distribution half-life increased from 5 to 9 min and the elimination half-life from 34 to 68 min as the dose was increased. There was also an increase in the volume of distribution (from 3 to 6 L/kg) with increasing dose. The elimination half-life and the volume of distribution after a 200-mg dose were significantly greater than after a 25-mg dose. There was, however, a linear increase in AUC0 infinity as dose was increased. The average total body clearance (approximately 5 L/h/kg) remained unchanged regardless of dose. The free fraction of diphenhydramine determined by equilibrium dialysis averaged 0.229 +/- 0.080, and the extent of drug binding to plasma protein was independent of the drug concentrations encountered (30-780 ng/mL) in the nonpregnant sheep in vivo. Concentration-independent binding of the drug was also confirmed by in vitro binding studies over the drug concentration range 10-2000 ng/mL. Therefore, it appears that changes in the volume of distribution are likely to be a result of changes in tissue uptake or binding of the drug as a function of dose.

Determination of diphenhydramine in rat milk and plasma and its effects on milk composition and mammary gland nucleic acids

To study the excretion of diphenhydramine into rat milk, milk and plasma concentrations of diphenhydramine were determined in lactating rats after single or multiple oral doses. Four hours after a single dose of 40 or 100 mg/kg of diphenhydramine, milk concentrations of the drug averaged 0.30 and 2.2 micrograms/mL, respectively, in two experiments, and the milk:plasma ratios ranged from 4.4 to 7.5. Multiple doses did not significantly affect the plasma or milk concentrations or the milk:plasma ratios, which were similar to the theoretical milk:plasma ratio based on pH partitioning for this compound (i.e., 4.0). Although the concentration of diphenhydramine was higher in milk than in plasma, the estimated dose received by the pups (0.057 mg/kg/d) based on the milk concentrations was much lower than that given to the mother. Oral diphenhydramine treatment at doses which significantly reduced maternal food consumption had no effect on milk solid, lipid, protein, or lactose concentrations, nor on mammary gland RNA or DNA content, indicating that diphenhydramine did not adversely affect lactation.

Metoclopramide pharmacokinetics in pregnant and nonpregnant sheep

The pharmacokinetics of metoclopramide was studied in chronically instrumented pregnant and nonpregnant sheep. Metoclopramide was administered to the ewe by intravenous bolus injections (on a crossover basis) of 10, 20, and 40 mg, with an additional 80-mg dose to the nonpregnant animals. Transfer of the drug to the fetus was rapid with significant concentrations in fetal plasma 1 min after maternal dosing. The ratio of fetal-to-maternal area under the plasma concentration-time curves averaged 0.74, indicating significant fetal exposure to the drug. Maternal metoclopramide administration resulted in minimal fetal effects, with no change in arterial pressure, heart rate, or arterial pH or PCO2, and only a small (approximately 1.8 mmHg) transient decline in PO2. Plasma concentrations in maternal and fetal plasma in most animals were best described by a biexponential equation with rapid distribution and elimination phases. The terminal elimination half-lives in maternal and fetal plasma averaged 71.3 and 86.8 min, respectively, with fetal half-life being significantly longer. The number of fetuses present had no consistent effects on either maternal or fetal pharmacokinetic parameters. Total body clearance and volume of distribution averaged 3.5 L/h/kg and 5.8 L/kg, respectively, in the pregnant ewe, and 4.5 L/h/kg and 6.9 L/kg, respectively, in the nonpregnant animals. The terminal elimination half-life in the nonpregnant ewes averaged 67.5 min. Pharmacokinetic parameters were compared in the pregnant and nonpregnant ewes at the 10-, 20-, and 40-mg doses, and no significant differences were observed in the distribution or elimination rate constants, elimination half-life, or volume of distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug accumulation in lung fluid of the fetal lamb after maternal or fetal administration

The pharmacokinetic characteristics of the antiemetic drug metoclopramide and the antihistamine diphenhydramine have been determined in a chronically catheterized pregnant sheep preparation. Metoclopramide and diphenhydramine were administered by separate maternal and fetal intravenous infusions to a steady state as well as by maternal intravenous bolus dosing. Drug concentrations in the maternal and fetal plasma and the amniotic and tracheal fluids were measured by means of capillary gas-liquid chromatographic assay techniques. Both metoclopramide and diphenhydramine were excreted into tracheal fluid in substantial quantities. Tracheal metoclopramide concentrations were found to exceed fetal plasma levels by about fifteen-fold while diphenhydramine attained maximal excretion in tracheal fluid of about five times that seen in fetal plasma. Drug levels were observed to accumulate slowly in amniotic fluid and eventually to exceed tracheal concentrations. The markedly elevated concentrations of these drugs in fetal lung fluid suggests that the fetal lung may be an important route of drug distribution, elimination, and excretion.

A method to obtain maternal-fetal plasma samples using a microsampling technique in the rat: transplacental passage of cefoxitin

A microsampling technique that allows taking blood samples from the umbilical vein of the pregnant rat is described. Such techniques are needed in order to allow pharmacokinetic and embryo exposure to be correlated with teratogenic endpoints. Cefoxitin was administered intravenously (300 mg/kg) into tracheotomized, pentobarbital anesthetized dams on day 21 in gestation. Blood samples were collected via the carotid artery from the dam and the umbilical vein of the fetus at designated times. Up to three samples of 20 to 30 microliters each, were taken from individual fetuses at 20-min intervals. With few exceptions, fetal cefoxitin concentrations were homogeneous at each sampling period. Fetal concentrations were low compared to maternal concentrations as seen by the small fetal/maternal area under the curve ratio (0.053 +/- 0.006).

Determination of pharmacokinetics of cocaine in sheep by liquid chromatography

Cocaine was administered as 1-, 2-, and 4-mg/kg intravenous bolus doses to each of six sheep. Plasma samples were collected as a function of time and assayed for cocaine using reversed-phase ion-pair HPLC. The assay involved double extraction with ether and UV detection at 229 nm. Using 2 mL of plasma, levels of 1 ng/mL of cocaine can be measured. The concentration versus time data obtained for the plasma samples were analyzed by a "noncompartmental" method. The pharmacokinetic parameters of cocaine in sheep had mean values of 4.0 L/kg, 3.5 L/kg, and 0.29 L X min-1 X kg-1 for Vd, Vdss, and CL respectively. The clearance of cocaine in sheep was much higher than cardiac output. Pulmonary first-pass effect has been suggested as the possible explanation for the large clearance of cocaine in sheep.