Pharmacokinetics of clorazepate in pregnant and non-pregnant women

Clinical Pharmacokinetic Studies in Pregnant Women and the Relevance of Pharmacometric Tools

BACKGROUND

In clinical pharmacokinetic (PK) studies, pregnant women are significantly underrepresented because of ethical and legal reasons which lead to a paucity of information on potential PK changes in this population. As a consequence, pharmacometric tools became instrumental to explore and quantify the impact of PK changes during pregnancy.

METHODS

We explore and discuss the typical characteristics of population PK and physiologically based pharmacokinetic (PBPK) models with a specific focus on pregnancy and postpartum.

RESULTS

Population PK models enable the analysis of dense, sparse or unbalanced data to explore covariates in order to (partly) explain inter-individual variability (including pregnancy) and to individualize dosing. For population PK models, we subsequently used an illustrative approach with ketorolac data to highlight the relevance of enantiomer specific modeling for racemic drugs during pregnancy, while data on antibiotic prophylaxis (cefazolin) during surgery illustrate the specific characteristics of the fetal compartments in the presence of timeconcentration profiles. For PBPK models, an overview on the current status of reports and papers during pregnancy is followed by a PBPK cefuroxime model to illustrate the added benefit of PBPK in evaluating dosing regimens in pregnant women.

CONCLUSIONS

Pharmacometric tools became very instrumental to improve perinatal pharmacology. However, to reach their full potential, multidisciplinary collaboration and structured efforts are needed to generate more information from already available datasets, to share data and models, and to stimulate cross talk between clinicians and pharmacometricians to generate specific observations (pathophysiology during pregnancy, breastfeeding) needed to further develop the field.

A Physiologically Based Pharmacokinetic Model for Pregnant Women to Predict the Pharmacokinetics of Drugs Metabolized Via Several Enzymatic Pathways

BACKGROUND

Physiologically based pharmacokinetic modeling is considered a valuable tool for predicting pharmacokinetic changes in pregnancy to subsequently guide in-vivo pharmacokinetic trials in pregnant women. The objective of this study was to extend and verify a previously developed physiologically based pharmacokinetic model for pregnant women for the prediction of pharmacokinetics of drugs metabolized via several cytochrome P450 enzymes.

METHODS

Quantitative information on gestation-specific changes in enzyme activity available in the literature was incorporated in a pregnancy physiologically based pharmacokinetic model and the pharmacokinetics of eight drugs metabolized via one or multiple cytochrome P450 enzymes was predicted. The tested drugs were caffeine, midazolam, nifedipine, metoprolol, ondansetron, granisetron, diazepam, and metronidazole. Pharmacokinetic predictions were evaluated by comparison with in-vivo pharmacokinetic data obtained from the literature.

RESULTS

The pregnancy physiologically based pharmacokinetic model successfully predicted the pharmacokinetics of all tested drugs. The observed pregnancy-induced pharmacokinetic changes were qualitatively and quantitatively reasonably well predicted for all drugs. Ninety-seven percent of the mean plasma concentrations predicted in pregnant women fell within a twofold error range and 63% within a 1.25-fold error range. For all drugs, the predicted area under the concentration-time curve was within a 1.25-fold error range.

CONCLUSION

The presented pregnancy physiologically based pharmacokinetic model can quantitatively predict the pharmacokinetics of drugs that are metabolized via one or multiple cytochrome P450 enzymes by integrating prior knowledge of the pregnancy-related effect on these enzymes. This pregnancy physiologically based pharmacokinetic model may thus be used to identify potential exposure changes in pregnant women a priori and to eventually support informed decision making when clinical trials are designed in this special population.

Assessment of induced CYP3A activity in pregnant women using 4β-hydroxycholesterol: Cholesterol ratio as an appropriate metabolic marker

AIMS

This study was aimed at evaluating changes in CYP3A activity following and during pregnancy by analyzing metabolic markers for CYP3A activity, which can help avoid unnecessary drug exposure and invasive sampling.

METHODS

Forty-eight pregnant women and 25 non-pregnant women were enrolled in this study. Plasma and urine samples were collected from the pregnant women during each trimester and from the non-pregnant women for evaluation of metabolic markers for CYP3A activity. Metabolic markers for CYP3A activity were measured using GC-MS.

RESULTS

An increased 4β-hydroxycholesterol/cholesterol ratio, consistent with high CYP3A activity, was observed in pregnant women compared with that in non-pregnant women; however, no differences were observed among trimesters. No significant differences were observed in urinary markers.

CONCLUSIONS

We observed an increase in the activity of CYP3A following but not during pregnancy when measured using the 4β-hydroxycholesterol/cholesterol ratio. In addition, based on our results, we suggest that the plasma 4β-hydroxycholesterol/cholesterol ratio be used to measure CYP3A activity in pregnant women.

Pregnancy-Associated Changes in Pharmacokinetics: A Systematic Review

BACKGROUND

Women are commonly prescribed a variety of medications during pregnancy. As most organ systems are affected by the substantial anatomical and physiological changes that occur during pregnancy, it is expected that pharmacokinetics (PK) (absorption, distribution, metabolism, and excretion of drugs) would also be affected in ways that may necessitate changes in dosing schedules. The objective of this study was to systematically identify existing clinically relevant evidence on PK changes during pregnancy.

METHODS AND FINDINGS

Systematic searches were conducted in MEDLINE (Ovid), Embase (Ovid), Cochrane Central Register of Controlled Trials (Ovid), and Web of Science (Thomson Reuters), from database inception to August 31, 2015. An update of the search from September 1, 2015, to May 20, 2016, was performed, and relevant data were added to the present review. No language or date restrictions were applied. All publications of clinical PK studies involving a group of pregnant women with a comparison to nonpregnant participants or nonpregnant population data were eligible to be included in this review. A total of 198 studies involving 121 different medications fulfilled the inclusion criteria. In these studies, commonly investigated drug classes included antiretrovirals (54 studies), antiepileptic drugs (27 studies), antibiotics (23 studies), antimalarial drugs (22 studies), and cardiovascular drugs (17 studies). Overall, pregnancy-associated changes in PK parameters were often observed as consistent findings among many studies, particularly enhanced drug elimination and decreased exposure to total drugs (bound and unbound to plasma proteins) at a given dose. However, associated alterations in clinical responses and outcomes, or lack thereof, remain largely unknown.

CONCLUSION

This systematic review of pregnancy-associated PK changes identifies a significant gap between the accumulating knowledge of PK changes in pregnant women and our understanding of their clinical impact for both mother and fetus. It is essential for clinicians to be aware of these unique pregnancy-related changes in PK, and to critically examine their clinical implications.

Pregnancy does not increase CYP3A or P-glycoprotein activity in the non-human primate, Macaca nemestrina

Plasma concentrations of protease inhibitors are lower in pregnant women than in nonpregnant women or men. Using nelfinavir as a model protease inhibitor, we have shown that this phenomenon can be reproduced in a representative non-human primate model, Macaca nemestrina (J Pharmacol Exp Ther 329:1016-1022, 2009). Nelfinavir is cleared from the body predominantly by CYP3A metabolism and P-glycoprotein (P-gp) efflux. Therefore, using midazolam (MDZ) as a CYP3A probe and digoxin (DIG) as a P-gp probe, we determined the antepartum (73-118 days) and postpartum (61-130 days) in vivo intestinal and hepatic CYP3A or P-gp activity in the macaque. Although the systemic clearance of MDZ was significantly increased ( approximately 70%) during pregnancy after intra-arterial (IA) administration of the drug ((15)N-labeled MDZ; 40 microg/kg), pregnancy did not affect the oral clearance of the drug administered simultaneously (1 mg/kg p.o.) with the IA dose. In vitro studies in hepatic and intestinal S-9 fractions indicated no effect of pregnancy on CYP3A activity or protein expression in the small intestine or liver. In contrast, neither the oral (100 microg/kg) nor the IA (10 microg/kg) clearance of DIG was significantly altered by pregnancy, indicating no effect of pregnancy on P-gp activity. Assuming that MDZ and DIG are selective substrates of the macaque CYP3A enzymes and P-gp, respectively, these results suggest that factors other than increased CYP3A or P-gp activity contribute to the increased clearance of protease inhibitors during M. nemestrina pregnancy.

Effects of pregnancy on CYP3A and P-glycoprotein activities as measured by disposition of midazolam and digoxin: a University of Washington specialized center of research study

The objectives of the study were to evaluate the effects of pregnancy on CYP3A and P-glycoprotein (P-gp) activities, as measured by disposition of midazolam and digoxin, respectively. Thirteen women received digoxin (0.25 mg p.o.) and midazolam (2 mg p.o.) in random order, separated by 1-2 weeks at 28-32 weeks gestation, and the same order was repeated at 6-10 weeks postpartum. Plasma and urine concentrations were determined by liquid chromatography-mass spectrometry and analyzed by noncompartmental methods. Midazolam CL/F(unbound) (593 +/- 237 l/min vs. 345 +/- 103 l/min; P = 0.007), digoxin CL(Renal, unbound) (272 +/- 45 ml/min vs. 183 +/- 37 ml/min; P < 0.002) and digoxin CL(secretion,) (unbound) (109 +/- 34 ml/min vs. 58 +/- 22 ml/min; P < 0.002) were higher during pregnancy than postpartum. These data are consistent with increased hepatic and/or intestinal CYP3A and renal P-gp activities during pregnancy.

Pharmacokinetics and safety of indinavir in human immunodeficiency virus-infected pregnant women

Human immunodeficiency virus-infected women (n=16) received indinavir (800 mg three times a day) plus zidovudine plus lamivudine from 14 to 28 weeks of gestation to 12 weeks postpartum. Two women and eight infants experienced grade 3 or 4 toxicities that were possibly treatment related. Indinavir area under the plasma concentration-time curve was 68% lower antepartum versus postpartum, suggesting increased intestinal and/or hepatic CYP3A activity during pregnancy.

Changes in pharmacokinetics of anti-HIV protease inhibitors during pregnancy: the role of CYP3A and P-glycoprotein

Human immunodeficiency virus (HIV)-infected women have reduced exposure [area under the curve (AUC)] to anti-HIV protease inhibitors [e.g., nelfinavir (NFV)] during pregnancy. To determine the mechanistic basis of this phenomenon, we administered NFV mesylate orally (2.5 mg) or intravenously (0.625 mg) to timed pregnant (gestational age: 18-19 days) and non-pregnant FVB mice. After oral but not after i.v. administration, the plasma clearance of NFV was higher (by 134%, p < 0.05) and bioavailability was lower (by 32%, p < 0.05) in pregnant (n = 3) versus nonpregnant mice (n = 3). These effects of pregnancy were not due to changes in plasma protein binding of NFV. The half-life of NFV depletion in hepatic S-9 fractions of pregnant mice (n = 8) was 2.2-fold faster (p < 0.05) than that in nonpregnant mice (n = 7). Hepatic CYP3A activity (testosterone 6beta-hydroxylation, n = 4) and expression (n = 8) were significantly higher (by 138 and 49%, p < 0.05) in pregnant mice than that in nonpregnant mice. In the intestine, no CYP3A activity was detected and CYP3A protein expression (n = 6, p > 0.05) was not significantly different between the two groups. P-glycoprotein expression (n = 6) in hepatic and intestinal tissue of pregnant mice was not significantly different from that in nonpregnant mice. These changes in disposition of NFV during pregnancy are predominately due to a change in its bioavailability. An increase in hepatic CYP3A can explain the reduced bioavailability of NFV during pregnancy. If such upregulation of hepatic CYP3A activity occurs in pregnant women, it has important implications for dose adjustment of a variety of drugs ingested by pregnant women and cleared predominately via CYP3A metabolism.

In vitro inhibition of cellular immune responses by benzodiazepines and PK 11195. Effects on mitogen- and alloantigen-driven lymphocyte proliferation and on IL-1, IL-2 synthesis and IL-2 receptor expression

In vitro mitogen-driven lymphocyte proliferation tests (Con A, LPS) on murine lymph node and spleen cells revealed inhibition of T and B cell stimulation by different benzodiazepines and by PK 11195, with IC50 values in the low micromolar range. T cell responses as a consequence of recognition of alloantigens, as measured in mixed lymphocyte cultures (MLC), were affected in an analogous way. In all systems, agonists at peripheral type benzodiazepine receptors (Ro 5-4864 and the non-benzodiazepine compound PK 11195) and diazepam which acts on both, central and peripheral type benzodiazepine receptors, were most potent; clonazepam, a central type agonist, proved about half as active. The central type antagonist Ro 15-1788 failed to antagonize the action of diazepam and clonazepam. Variations among cells from several congenic strains of mice were modest. Cytotoxicity could not be made responsible for drug effects. The most susceptible stage of mitogen-triggered T and B lymphocyte proliferation was found to be at incipience. Radioresistant, adherent spleen cells, upon LPS-stimulation formed only small amounts of the cytokine IL-1. Its release was affected only at very high drug concentrations. Similar small amounts of IL-1 were generated during MLC; in this case, the drugs were about 10 times less potent than in mitogen-induced proliferation assays. Peripheral agonists were more active on IL-1 synthesis. Spleen cells stimulated with Con A and cultivated with the highest concentration of diazepam and clonazepam formed markedly greater amounts of IL-2 than those cultivated in medium, while at this concentration PK 11195 allowed no formation of the lymphokine.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal diazepam induced persisting depression of cellular immune responses

Treatment of pregnant Long Evans rats with a low dose of diazepam (1.25 mg/kg per day s.c.) from gestational day (GD) 14 to 20 resulted in severe and long lasting depression of cellular immune responses in male and female offspring. T lymphocyte proliferation, induced by allogeneic stimulation in mixed lymphocyte culture (MLC) or geneic stimulation in mixed lymphocyte culture (MLC) or mitogenic stimulation (concanavalin A), decreased by 50 % or more over a postnatal period of about 2 months. Treatment of the pregnant dam during the early fetal period, from GD 12 to GD 16, did not significantly affect these immune parameters, whereas treatment during later gestation, from GD 16 to 20, significantly affected T lymphocyte function. Clonazepam, a benzodiazepine with high affinity for the central type benzodiazepine site, also affected cellular immune response in offspring. Our data indicate that benzodiazepine treatment during the fetal period may result in persistent postnatal deficiency of cellular immune responses. The relative role of central and peripheral type benzodiazepine receptor and possible interactions with maternal and fetal pituitary - adrenocortical systems are discussed.

Effects of pregnancy on antiepileptic drug utilization

Pregnancy is associated with characteristic changes in the disposition of antiepileptic drugs; recent findings on this aspect of drug utilization are presented. In one study involving 48 pregnancies, the mean level-dose ratio of phenytoin decreased by 34%. In another study of 111 patients, phenytoin clearance increased gradually over the first 32 weeks of pregnancy and reached twice the preconception value. In two studies with phenobarbital, levels tended to decrease, although this effect was less pronounced than for phenytoin. Similarly for primidone, pregnancy had little effect on steady-state levels; however, levels of phenobarbital formed from primidone exhibited large decreases during pregnancy followed by increases after delivery. This effect was quite consistent. Carbamazepine clearance tended to increase to a relatively small extent. Limited data indicate that valproate levels decrease by 30 to 40% during pregnancy. The mechanisms responsible for these effects have not been elucidated and possibly include decreased bioavailability or compliance, increased metabolic clearance, or decreased plasma protein binding. Since the patient at risk of an increase in seizure frequency cannot be identified prior to conception, therapeutic monitoring is imperative during and after pregnancy.

Intramuscular bioavailability of chlorazepate as compared to diazepam

Dipotassium chlorazepate (DPC) and diazepam (DZM) were given i.m. and i.v. to 6 healthy volunteers in doses of 20 mg (48.9 mumol) DPC and 15 mg (52.0 mumol) DZM. The interval between the injections was at least 1 week. Plasma samples were analyzed for DPC and DZM by HPLC. The bioavailability of DPC and DZM after i.m. administration, determined from computer calculated AUCs, was 1.04 and 0.85, respectively.

Sex-related differences in drug disposition in man

Sex-related differences in the disposition of some analgesics, anxiolytics and hypnotics have recently been reported. With certain benzodiazepines, sex has been shown to be a more important determinant of variability in drug disposition than age, while with other benzodiazepines an age-related decline in clearance was more pronounced in men than women. In young healthy adults these sex-related differences in drug disposition were related to the phase of the menstrual cycle, oral contraceptive steroid administration, and variations in plasma concentrations of albumin, alpha 1-acid glycoprotein, free fatty acids and sex hormones. While none of the sex-related differences so far reported necessitates the modification of a therapeutic dosage regimen, it is prudent that future protocols for pharmacokinetic studies should regard age, sex, the menstrual cycle and oral contraceptive steroids as potential sources of variability.

Hepatic drug metabolism in pregnancy

The results of both isolated tissue and whole animal experimentation, whilst showing some unexplored inconsistencies, suggest that late pregnancy is associated with a reduced ability of the liver to metabolise foreign compounds. The mechanism of this reduced capacity and the physiological reason for it are unclear but such change does have implication for therapeutic response in pregnancy. Available results from the limited and often poorly structured studies of drug levels in pregnant women neither prove nor disprove the existence of similar changes in hepatic monooxygenase activity during human pregnancy.

High-performance liquid chromatography determination of dipotassium clorazepate and its major metabolite nordiazepam in plasma

A rapid and sensitive high-performance liquid chromatographic method is described for the quantitative analysis of dipotassium clorazepate (CZP) and its major metabolite nordiazepam (ND) in fresh human and dog plasma. The method consists of two separate selective ND extractions from a plasma sample without and with conversion of all the CZP to ND. For quantitation, diazepam (DZP) is used as the internal standard. The chromatographic phase utilized in a reversed-phase Hibar EC-RT analytical column prepacked with LiChrosolv RP-18 with a solvent system consisting of acetonitrile-0.05 M sodium acetate buffer, pH 5.0 (45:55). The UV absorbance is monitored at 225 nm using a variable-wavelength detector. The mean assay coefficient of variation over a concentration range of 20-400 ng per ml of plasma is less than 3% for the within-day precision. Recoveries of ND, DZP and CZP (as ND) are essentially quantitative at all levels investigated. The calibration curves of ND are rectilinear (r2 = 0.99) from the lower limit of sensitivity (2 ng/ml) to at least 2000 ng/ml in plasma. Applicability of the method to CZP and ND disposition studies in the anaesthetized mongrel dog is illustrated. When the two separate selective nordiazepam extractions from plasma cannot be performed immediately after blood sampling, an extrapolation kinetic method is suggested for the estimation of CZP concentration. In all previous in vivo studies, CZP has been determined only with gas-liquid chromatographic methods.

Pharmacokinetics of chlorazepate after intravenous and intramuscular administration

Dichlorazepate (DPC) was given to eight healthy volunteers aged 22-38 years (five males and three females). The dose was 20 mg (48.9 mumol) given either as an IV or an IM injection. The interval between the injections was at least 1 week. Plasma samples were analysed for desmethyldiazepam (DMD) by HPLC before and after acid hydrolysis. The kinetics after both IV and IM administration could be explained by a one or two compartment open model. By comparing values before and after hydrolysis an estimate of di- and/or monopotassiumchlorazepate (MPC) could be made. The bioavailability was almost 100% after IM administration. The plasma half lives of DPC and DMD were independent of the form of administration (2.42 and 46.0 h respectively after IV and 2.29 and 45.1 h respectively after IM injection).

Placental drug transfer: effects of gestational age and species

The available evidence suggests that for most drugs, adverse effects in the fetus may vary with gestational state and among species due to: (i) changes in the fetal exposure to the drug (i.e. due to changes in the pharmacokinetics of the drug in the mother and/or the fetus), or to (ii) changes in the susceptibility of the fetus to the drug. The fetal exposure to a drug during gestation is influenced more by the varying capacity of mother and/or fetus to eliminate the drug than by any intrinsic 'barrier' phenomenon at the placenta. Although differential maternal/fetal protein binding, active transplacental transport processes and 'ion-trapping' effects may influence the fetal exposure of some drugs, the main mechanisms by which fetal exposure may be modulated during pregnancy are via the capacity for irreversible drug elimination--by the fetus or, less often, by the placenta. The susceptibility of a fetus to adverse drug reactions is determined by the ontogeny of vital processes and the nature of the interaction between the drug and the process. Hence 'gestational state' and 'species' dependent differences in adverse drug effects, in the presence of a constant level of exposure of drug, reflect the time dependent appearance of these processes and the differences in ontogeny of the processes among species. At present, no studies have attempted to relate the measured fetal drug exposure to the intensity of a drug response at different stages of gestation or among species. Although there is a dearth of information in this field, it is apparent that in all species the placentas of all species pose little obstruction to the passage of xenobiotics (including drugs), to the fetus. The consequence of this exposure will depend on a myriad of pharmacokinetic and pharmacodynamic considerations for a given substance in a given species. Hence the outcome cannot be predicted, but must be empirically determined. Extrapolation of findings among different drugs, species and gestational states must be undertaken with caution, recognizing the above considerations and limitations.

Propoxyphene and acetaminophen. Possible effects on the fetus

Propoxyphene (Darvon) and acetaminophen (Tylenol) are widely prescribed analgesic agents. Both can cross the placenta, and propoxyphene can produce serious withdrawal symptoms in newborns. Neither propoxyphene nor acetaminophen is considered a teratogen, yet, three malformed infants who were antenatally exposed to propoxyphene have previously been reported. We report a fourth case of an infant, with withdrawal symptoms and cranial-facial and digital malformations, born to a women who used propoxyphene and acetaminophen throughout her pregnancy. We suggest that possibility that the antepartum use of propoxyphene and acetaminophen, in combination, may be teratogenic.

Prolongation of drug half-life due to obesity: studies of desmethyldiazepam (clorazepate)

Desmethyldiazepam pharmacokinetics were determined after oral administration of its precursor, clorazepate, to 12 obese subjects (mean weight: 105.4 kg; mean percent ideal body weight: 170%) who were matched for age, sex, and smoking habits with 12 normal controls (66.5 kg; percent ideal body weight: 103.3%). After an overnight fast, a single 15-mg clorazepate capsule, equivalent to 10.3 mg of desmethyldiazepam, was administered. Multiple plasma samples drawn 10-42 days postdose were analyzed for desmethyldiazepam by electron-capture GLC. Obese subjects compared to controls had a prolonged desmethyldiazepam elimination half-life (t1/2) (154.1 hr versus 57.1 hr; p less than 0.005). Assuming quantitative conversion of clorazepate to desmethyldiazepam and 100% systemic availability, volume of distribution (Vd) was greatly increased in the obese (158.8 liters versus 63.3 liters; p less than 0.001). The value of Vd remained greater even after correction for body weight (1.52 liter/kg versus 0.94 liter/kg; p less than 0.005). However, clearance of desmethyldiazepam was not different between groups (13.2 ml/min in obese versus 13.4 ml/min in controls). The percent ideal body weight was highly correlated with Vd (r = 0.82), as was total body weight (r = 0.86). The value of t1/2 was correlated highly with Vd (r = 0.89) but only weakly with clearance (r = -0.38). Therefore, the large increase in the desmethyldiazepam t1/2 value seen in obese subjects is predominantly due to the disproportionate distribution of this lipid-soluble drug into body fat as opposed to lean tissue. The contribution of clearance to desmethyldiazepam t1/2 was of much less importance than was Vd in this obese study population.

Use of benzodiazepines during pregnancy, labour and lactation, with particular reference to pharmacokinetic considerations

Knowledge of the pharmacokinetic properties of the benzodiazepines is playing an increasingly important role in their use during pregnancy, labour and lactation. All of the benzodiazepine derivatives are lipophilic, undissociated agents which readily penetrate membranes. Thus, they exhibit rapid placental transfer with significant fetal uptake of the drug. In the first trimester of pregnancy there is seldom a clear indication for the use of benzodiazepines. In late pregnancy and at parturition there may be more clear indications for their use. During delivery, the lowest effective dose should be used, since after high doses the so-called 'floppy infant syndrome' may occur, and the slow elimination of these agents by the newborn should be considered. Oxazepam, lorazepam, nitrazepam and, especially, flunitrazepam, appear to penetrate the human placenta more slowly than diazepam, but the clinical significance of this phenomenon remains uncertain. All of these derivatives appear in human milk, but only high clinical doses might be expected to exert a possible effect on the nursing newborn.

Concentrations of N-descyclopropylmethylprazepam in whole-blood, plasma, and milk after administration of prazepam to humans

After oral doses of 30 mg of prazepam to humans, N-descyclopropylmethylprazepam (desalkylprazepam, N-desmethyldiazepam) is the only major drug-related compound in plasma. Neither the parent drug, nor its major urinary metabolites were detected in plasma. The overall concentration-time profile of desalkylprazepam in the plasma of females was lower than, and significantly different (p less than 0.001) from that in the plasma of males. However, the mean peak desalkylprazepam concentrations in the plasma of females (265 ng ml-1 +/- 60 S.D.) were not significantly different (p greater than 0.05) from those in males (342 ng ml-1 +/- 60 S.D.). Concentrations declined in the plasma of either sex with similar half-lives (mean 60 h, range 37-93 h). Apparent plasma desalkylprazepam clearances were also similar (mean 60 h, range 37-93 h). Apparent plasma desalkylprazepam clearances were also similar (mean 1.09 l h-1), range 0.74-1.84 l h-1). At 12 h after the last of multiple doses of prazepam (60 mg d-1 for 3 days) to lactating women, mean plasma concentrations of desalkylprazepam were 823 ng ml-1 +/- 200 S.D. and declined with a mean half-life of about 60 h over the time-course studied. There was only slight uptake of desalkylprazepam into blood cells; plasma; whole blood concentration ratios were constant at about 1.6. Concentrations of desalkylprazepam in milk were low at about 10 per cent of the corresponding plasma levels (e.g. 86 ng ml-1 +/- 37 S.D. at 12 h). The data suggest that, expressed on a mg kg-1 basis, exposed neonates could receive about 4 per cent of the maternal dose of prazepam as desalkylprazepam.

Pharmacokinetics of the placental transfer and distribution of clorazepate and its metabolite nordiazepam in the feto-placental unit and in the neonate

Clorazepate 20 mg was given i.m. to 49 mothers during the first stage of labour. The elimination of the drug was studied in 27 newborns produced by these mothers. The same dose was given to 13 women who underwent amniocentesis and to 7 women who were breast-feeding. "Total nordiazepam", i.e. the sum of clorazepate and its metabolite nordiazepam, was determined by gas-liquid chromatography in maternal blood, umbilical cord blood (both arterial and venous), amniotic fluid and in milk. Clorazepate was found to cross the placental barrier slowly, but nordiazepam was transferred more rapidly. Nordiazepam was found in the milk and in the blood of neonates after breast-feeding had started.