Pregnancy-induced changes in pharmacokinetics: a mechanistic-based approach

Gene profiling of maternal hepatic adaptations to pregnancy

BACKGROUND

Maternal metabolic demands change dramatically during the course of gestation and must be co-ordinated with the needs of the developing placenta and fetus. The liver is critically involved in metabolism and other important functions. However, maternal hepatic adjustments to pregnancy are poorly understood.

AIM

The aim of the study was to evaluate the influences of pregnancy on the maternal liver growth and gene expression profile.

METHODS

Holtzman Sprague-Dawley rats were mated and sacrificed at various stages of gestation and post-partum. The maternal livers were analysed in gravimetric response, DNA content by PicoGreen dsDNA quantitation reagent, hepatocyte ploidy by flow cytometry and hepatocyte proliferation by ki-67 immunostaining. Gene expression profiling of non-pregnant and gestation d18.5 maternal hepatic tissue was analysed using a DNA microarray approach and partially verified by northern blot or quantitative real-time PCR analysis.

RESULTS

During pregnancy, the liver exhibited approximately an 80% increase in size, proportional to the increase in body weight of the pregnant animals. The pregnancy-induced hepatomegaly was a physiological event of liver growth manifested by increases in maternal hepatic DNA content and hepatocyte proliferation. Pregnancy did not affect hepatocyte polyploidization. Pregnancy-dependent changes in hepatic expression were noted for a number of genes, including those associated with cell proliferation, cytokine signalling, liver regeneration and metabolism.

CONCLUSIONS

The metabolic demands of pregnancy cause marked adjustments in maternal liver physiology. Central to these adjustments are an expansion in hepatic capacity and changes in hepatic gene expression. Our findings provide insights into pregnancy-dependent hepatic adaptations.

A review of nucleoside reverse transcriptase inhibitor use to prevent perinatal transmission of HIV

Worldwide, women comprise > 50% of all people living with HIV and the vast majority of these women are of childbearing age. In fact, a significant proportion of these women are identified as HIV-infected during pregnancy. Preventing perinatal transmission has been one of the greatest prevention successes of the HIV epidemic with < 2% of live births resulting in an HIV-infected infant. The strategic use of combination antiretroviral therapy has been a critical component of this reduction. With more antiretroviral agents available for HIV, the appropriate selection of therapy is often based on provider familiarity with the various agents. Although benefits of antiretroviral use in pregnancy tremendously outweigh the risks, concerns regarding short- and long-term toxicity in mothers and their children, in addition to the risk of the development of HIV resistance, remain subjects of discussion. The choice of antiretroviral 'backbone' is supported by extensive data showing efficacy in the prevention of HIV vertical transmission. Co-formulated zidovudine/lamivudine is the most commonly used combination in pregnancy. Long-term consequences of in utero exposure to antiretroviral agents are not fully understood. In this article, we review the data regarding nucleoside reverse transcriptase inhibitors with a focus on tenofovir.

Hypoglycemics: pharmacokinetic considerations during pregnancy

A wide range of physiological and hormonal changes occur during pregnancy. Most begin early in the first trimester and increase by the last trimester. These changes can significantly affect pharmacokinetics and pharmacodynamics of drugs and thus may alter their safety and efficacy. Approximately 5% of pregnant women are affected by some form of diabetes, with gestational diabetes being the most prevalent. Several classes of antidiabetic drugs are currently available for the treatment of diabetes, including human insulin, its short and long analogues, and oral hypoglycemic agents. Maternal and fetal responses to these drugs can be affected by changes in absorption, distribution, and elimination in both the mother and the placental-fetal unit. This can dictate the amount of drug that can cross and the amount that is metabolized or eliminated by the placenta. Further studies are needed on the safety of antidiabetic drugs in pregnancy to clarify the extent of their transplacental passage. Specifically, in vitro placental perfusion studies in combination with controlled trials and cord blood measurements can provide insight in to the pharmacokinetics of drug transport across the placenta. This article reviews common types of antidiabetic drugs, focusing on pharmacokinetic considerations that need to be incorporated into the decision on treatment in pregnancy.

Effect of pregnancy on nitrofurantoin disposition in mice

We investigated the effect of pregnancy on nitrofurantoin (NFT) disposition in wild-type and Bcrp1(-/-) mice. Pregnant and non-pregnant mice were administered NFT intravenously (5 mg/kg) or orally (10 mg/kg). Blood samples were collected at various times (5-60 min) after drug administration, plasma NFT concentrations determined by HPLC/UV, and pharmacokinetic parameters estimated. Dose-normalized area under the plasma concentration-time curve (AUC), terminal plasma half-life (T(1/2)), total plasma clearance (CL), and steady-state volume of distribution (V(ss)) of intravenous NFT in wild-type or Bcrp1(-/-) mice were not altered by pregnancy. After oral administration, pregnancy did not affect dose-normalized AUC of NFT in wild-type mice; however, dose-normalized AUC in Bcrp1(-/-) mice was decreased by approximately 70% by pregnancy. In conclusion, since Bcrp1 plays a minor role in the systemic clearance of NFT in female mice, pregnancy did not affect disposition of intravenous NFT despite the fact that Bcrp1 expression in the liver and kidney of mice is significantly induced by pregnancy. On the other hand, pregnancy may affect expression and activity of certain intestinal efflux transporters and/or metabolic enzymes in Bcrp1(-/-) mice, resulting in a drastic decrease in the systemic exposure of oral NFT in pregnant Bcrp1(-/-) mice.

Pharmacokinetic properties of azithromycin in pregnancy

Azithromycin (AZI) is an azalide antibiotic with antimalarial activity that is considered safe in pregnancy. To assess its pharmacokinetic properties when administered as intermittent preventive treatment in pregnancy (IPTp), two 2-g doses were given 24 h apart to 31 pregnant and 29 age-matched nonpregnant Papua New Guinean women. All subjects also received single-dose sulfadoxine-pyrimethamine (SP) (1,500 mg or 75 mg) or chloroquine (450-mg base daily for 3 days). Blood samples were taken at 0, 1, 2, 3, 6, 12, 24, 32, 40, 48, and 72 h and on days 4, 5, 7, 10, and 14 for AZI assay by ultra-high-performance liquid chromatography-tandem mass spectrometry. The treatments were well tolerated. Using population pharmacokinetic modeling, a three-compartment model with zero-order followed by first-order absorption and no lag time provided the best fit. The areas under the plasma concentration-time curve (AUC(0-infinity)) (28.7 and 31.8 mg.h liter(-1) for pregnant and nonpregnant subjects, respectively) were consistent with the results of previous studies, but the estimated terminal elimination half-lives (78 and 77 h, respectively) were generally longer. The only significant relationship for a range of potential covariates, including malarial parasitemia, was with pregnancy, which accounted for an 86% increase in the volume of distribution of the central compartment relative to bioavailability without a significant change in the AUC(0-infinity). These data suggest that AZI can be combined with compounds with longer half-lives, such as SP, in combination IPTp without the need for dose adjustment.

Effects of intrauterine exposure to synthetic glucocorticoids on fetal, newborn, and infant hypothalamic-pituitary-adrenal axis function in humans: a systematic review

BACKGROUND

Synthetic glucocorticoids are commonly used in reproductive medicine. Fetal organ systems are highly sensitive to changes in the intrauterine environment, including overexposure to glucocorticoids. Structural and functional alterations resulting from such changes may persist throughout life and have been associated with diverse diseases. One system that could be particularly sensitive to fetal glucocorticoid overexposure is the hypothalamic-pituitary-adrenal (hpa) axis. Many human studies have investigated this possibility, but a systematic review to identify consistent, emergent findings is lacking.

METHODS

We systematically review 49 human studies, assessing the effects of intrauterine exposure to synthetic glucocorticoids on fetal, neonate, and infant hpa function.

RESULTS

Study quality varied considerably, but the main findings held true after restricting the analyses to higher-quality studies: intrauterine exposure to synthetic glucocorticoids reduces offspring hpa activity under unstimulated conditions after pain but not pharmacological challenge. Although reduced unstimulated hpa function appears to recover within the first 2 wk postpartum, blunted hpa reactivity to pain is likely to persist throughout the first 4 months of life. There is some evidence that the magnitude of the effects is correlated with the total amount of glucocorticoids administered and varies with the time interval between glucocorticoid exposure and hpa assessment.

CONCLUSIONS

This systematic review has allowed the demonstration of the way in which intrauterine exposure to various regimens of synthetic glucocorticoids affects various forms of hpa function. As such, it guides future studies in terms of which variables need to be focused on in order to further strengthen the understanding of such therapy, whilst continuing to profit from its clinical benefits.

Women and epilepsy

Women with epilepsy face additional challenges when compared to their peers. Hormonal influences may increase seizure activity, alter endocrine function, and affect fertility. In this population, antiepileptic drugs (AEDs) reduce the efficacy of contraception methods and increase the risk of fetal malformations. Other pertinent issues to women with epilepsy include breastfeeding as well as bone mineral health. This article summarizes our current, collective knowledge of these issues and makes specific recommendations with respect to management.

Pharmacokinetics of sulfadoxine and pyrimethamine in intermittent preventive treatment of malaria in pregnancy

Malaria during pregnancy is associated with maternal and fetal morbidity and mortality. In order to minimize the burden, sulfadoxine-pyrimethamine (SP) is widely used in Africa as an intermittent preventive treatment of malaria in pregnancy (IPTp). However, only limited data are available on the pharmacokinetics of sulfadoxine and pyrimethamine during pregnancy. We conducted a prospective, self-matched, multicenter study of 98 pregnant women in four African countries in order to determine the effects of pregnancy on SP pharmacokinetics. After adjusting for the effects of potential confounders, blood concentrations (associated with therapeutic efficacy) of pyrimethamine were higher (geometric mean ratio (GMR) 1.33; 95% confidence interval (CI) 1.18-1.51; P < 0.001) and those of sulfadoxine were lower (GMR 0.91; 95% CI 0.84-0.98; P = 0.013) on day 7 after SP administration during pregnancy than after the postpartum period. SP pharmacokinetic parameters differed significantly among the study sites. Given the inconsistency of changes in pharmacokinetic parameters between sulfadoxine and pyrimethamine as well as among the study sites, it is not possible to recommend any dose adjustment to prolong the therapeutic life span of the fixed dose combination of SP for IPTp on the basis of our study findings.

Up-regulation of UDP-glucuronosyltransferase (UGT) 1A4 by 17beta-estradiol: a potential mechanism of increased lamotrigine elimination in pregnancy

Oral clearance of lamotrigine, an antiepileptic drug commonly used in pregnant women, is increased in pregnancy by unknown mechanisms. In this study, we show that 17beta-estradiol (E(2)) up-regulates expression of UDP glucuronosyltransferase (UGT) 1A4, the major enzyme responsible for elimination of lamotrigine. Endogenous mRNA expression levels of UGT1A4 in estrogen receptor (ER) alpha-negative HepG2 cells were induced 2.3-fold by E(2) treatment in the presence of ER alpha expression. E(2) enhanced transcriptional activity of UGT1A4 in a concentration-dependent manner in HepG2 cells when ER alpha was cotransfected. Induction of UGT1A4 transcriptional activity by E(2) was also observed in ER alpha-positive MCF7 cells, which was abrogated by pretreatment with the antiestrogen fulvestrant (ICI 182,780). Analysis of UGT1A4 upstream regions using luciferase reporter assays identified a putative specificity protein-1 (Sp1) binding site (-1906 to -1901 base pairs) that is critical for the induction of UGT1A4 transcriptional activity by E(2). Deletion of the Sp1 binding sequence abolished the UGT1A4 up-regulation by E(2), and Sp1 bound to the putative Sp1 binding site as determined by a electrophoretic mobility shift assay. Analysis of ER alpha domains using ER alpha mutants revealed that the activation function (AF) 1 and AF2 domains but not the DNA binding domain of ER alpha are required for UGT1A4 induction by E(2) in HepG2 cells. Finally, E(2) treatment increased lamotrigine glucuronidation in ER alpha-transfected HepG2 cells. Together, our data indicate that up-regulation of UGT1A4 expression by E(2) is mediated by both ER alpha and Sp1 and is a potential mechanism contributing to the enhanced elimination of lamotrigine in pregnancy.

Role of placental ATP-binding cassette (ABC) transporters in antiretroviral therapy during pregnancy

Highly active anti-retroviral therapy (HAART) is used to treat HIV-infected patients and involves administration of multiple antiretroviral drugs acting at different steps of the HIV life cycle. In treating HIV-infected pregnant patients, the aim of therapy is not only to treat the mother but also to prevent the transmission of the virus to the fetus. Among the antiretroviral drugs used, there are differences in the extent of transfer of these drugs across the placenta; HIV protease inhibitors are particularly poorly transferred. Activities of ABC transporters expressed in the human placenta as well as differences in plasma protein binding may account for the poor transplacental transfer of certain drugs. This review discusses factors affecting the extent of placental transfer of antiretroviral drugs during pregnancy. These issues may also apply to drugs in other therapeutic categories.

Optimizing pediatric dosing: a developmental pharmacologic approach

Many physiologic differences between children and adults can result in age-related differences in pharmacokinetics. Understanding the effects of age on bioavailability, volume of distribution, protein binding, hepatic metabolic isoenzymes, and renal elimination can provide insight into optimizing doses for pediatric patients. We performed a search of English-language literature using the MEDLINE database regarding age and pharmacokinetics (1979-July 2008). We then evaluated the literature with an emphasis on drugs with one primary elimination pathway, such as renal clearance or a pathway involving a single metabolic isoenzyme. Our mechanistic-based analysis revealed that children need weight-corrected doses that are substantially higher than adult doses for drugs that are metabolically eliminated solely by the specific cytochrome P450 (CYP) isoenzymes CYP1A2, CYP2C9, and CYP3A4. In contrast, weight-corrected doses for drugs eliminated by renal excretion or metabolism involving CYP2C19, CYP2D6, N-acetyltransferase 2, or uridine diphosphate glucuronosyltransferases are similar in children and adults. In children, bioavailability of drugs with high first-pass metabolism is decreased for drugs metabolized by CYP1A2, CYP2C9, and CYP3A4. Limited data suggest that by age 5 years, bioavailability of drugs affected by efflux transporters should be equivalent to that of adults. Using a pharmacokinetics-based approach, rational predictions can be made for the effects of age on drugs that undergo similar pathways of elimination, even when specific pharmacokinetic data are limited or unavailable.

Sex differences in the expression of hepatic drug metabolizing enzymes

Sex differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Sex-based differences in drug metabolism are the primary cause of sex-dependent pharmacokinetics and reflect underlying sex differences in the expression of hepatic enzymes active in the metabolism of drugs, steroids, fatty acids and environmental chemicals, including cytochromes P450 (P450s), sulfotransferases, glutathione transferases, and UDP-glucuronosyltransferases. Studies in the rat and mouse liver models have identified more than 1000 genes whose expression is sex-dependent; together, these genes impart substantial sexual dimorphism to liver metabolic function and pathophysiology. Sex differences in drug metabolism and pharmacokinetics also occur in humans and are due in part to the female-predominant expression of CYP3A4, the most important P450 catalyst of drug metabolism in human liver. The sexually dimorphic expression of P450s and other liver-expressed genes is regulated by the temporal pattern of plasma growth hormone (GH) release by the pituitary gland, which shows significant sex differences. These differences are most pronounced in rats and mice, where plasma GH profiles are highly pulsatile (intermittent) in male animals versus more frequent (nearly continuous) in female animals. This review discusses key features of the cell signaling and molecular regulatory mechanisms by which these sex-dependent plasma GH patterns impart sex specificity to the liver. Moreover, the essential role proposed for the GH-activated transcription factor signal transducer and activator of transcription (STAT) 5b, and for hepatic nuclear factor (HNF) 4alpha, as mediators of the sex-dependent effects of GH on the liver, is evaluated. Together, these studies of the cellular, molecular, and gene regulatory mechanisms that underlie sex-based differences in liver gene expression have provided novel insights into the physiological regulation of both xenobiotic and endobiotic metabolism.

Pharmacokinetic properties of sulfadoxine-pyrimethamine in pregnant women

To determine the pharmacokinetic disposition of sulfadoxine (SDOX) and pyrimethamine (PYR) when administered as intermittent presumptive treatment during pregnancy (IPTp) for malaria, 30 Papua New Guinean women in the second or third trimester of pregnancy and 30 age-matched nonpregnant women were given a single dose of 1,500 mg of SDOX plus 75 mg of pyrimethamine PYR. Blood was taken at baseline and 1, 2, 4, 6, 12, 18, 24, 30, 48, and 72 h and at 7, 10, 14, 28, and 42 days posttreatment in all women. Plasma samples were assayed for SDOX, N-acetylsulfadoxine (NASDOX), and PYR by high-performance liquid chromatography. Population pharmacokinetic modeling was performed using NONMEM v6.2.0. Separate user-defined mamillary models were fitted to SDOX/NASDOX and PYR. When the covariate pregnancy was applied to clearance, there was a significant improvement in the base model for both treatments. Pregnancy was associated with a significantly lower area under the concentration-time curve from 0 to infinity for SDOX (22,315 versus 33,284 mg x h/liter), NASDOX (801 versus 1,590 mg x h/liter), and PYR (72,115 versus 106,065 microg x h/liter; P < 0.001 in each case). Because lower plasma concentrations of SDOX and PYR could compromise both curative efficacy and posttreatment prophylaxis in pregnant patients, IPTp regimens incorporating higher mg/kg doses than those recommended for nonpregnant patients should be considered.

Practical guidelines for the use of new generation antipsychotic drugs (except clozapine) in adult individuals with intellectual disabilities

New generation antipsychotic (NGA) drugs introduced to the US market after clozapine (aripiprazole, olanzapine, paliperidone, quetiapine, risperidone, and ziprasidone) are frequently used in individuals with intellectual disabilities (ID). However, there is very limited research to fully establish evidence-based or personalized medicine approaches for their use in this population. These guidelines take a pragmatic approach to establishing frameworks for their use by utilizing the prescribing information and reviewing the available literature on other relevant neuropsychiatric disorders. In the absence of expert consensus guidance and well-controlled comparison trials, we present a set of guidelines to inform initiation, dosing and monitoring of use in adults. Further, in these guidelines we provide practical information on drug-drug interactions and adverse drug reactions, and a brief review of discontinuation syndromes, potential for abuse, use during pregnancy and cost considerations. We also provide drug utilization review forms for each NGA to facilitate implementation of these guidelines, these guidelines provide a practical and necessary resource for practitioners treating psychiatric disorders and challenging behaviors in adult individuals with ID.

Bisphenol A levels in blood depend on age and exposure

We present two approaches to estimate blood concentrations of Bisphenol A (BPA). Simple kinetic principles were applied to calculate steady state plasma concentrations. A physiologically based model was used to simulate the blood concentration time profile in several age groups exploring the influence of not yet fully developed metabolic capacity on the blood concentrations in the newborn. Both approaches gave concordant results and are in excellent agreement with experimental results [Völkel, W., Colnot, T., Csanady, G.A., Filser, J.G., Dekant, W., 2002. Metabolism and kinetics of bisphenol A in humans at low doses following oral administration. Chem. Res. Toxicol. 15, 1281-1287]. The predictions also agree with published results obtained with a different physiologically based model. According to model simulations, BPA is present in the blood of the normal population at concentrations several orders of magnitude lower than most measurements reported in the literature. At the same external exposure level, the newborn is predicted to have 3 times greater blood concentration than the adult. This is due to the not yet fully developed glucuronidation activity in the newborn, not fully compensated by the unimpaired sulfation pathway. For the highest measured external BPA exposure, the predicted blood concentrations of 2.6 pg/ml (steady state concentration) and 8.2 pg/ml (peak concentration) in the adult are lower than the in vitro concentrations at which inhibiting adiponectin release from human adipocytes and stimulation of beta-cell production and secretion were observed.

Urinary excretion of buprenorphine, norbuprenorphine, buprenorphine-glucuronide, and norbuprenorphine-glucuronide in pregnant women receiving buprenorphine maintenance treatment

BACKGROUND

Buprenorphine (BUP) is under investigation as a medication therapy for opioid-dependent pregnant women. We investigated BUP and metabolite disposition in urine from women maintained on BUP during the second and third trimesters of pregnancy and postpartum.

METHODS

We measured BUP, norbuprenorphine (NBUP), buprenorphine glucuronide (BUP-Gluc), and NBUP-Gluc concentrations in 515 urine specimens collected thrice weekly from 9 women during pregnancy and postpartum. Specimens were analyzed using a fully validated liquid chromatography-mass spectrometry method with limits of quantification of 5 microg/L for BUP and BUP-Gluc and 25 microg/L for NBUP and its conjugated metabolite. We examined ratios of metabolites across trimesters and postpartum to identify possible changes in metabolism during pregnancy.

RESULTS

NBUP-Gluc was the primary metabolite identified in urine and exceeded BUP-Gluc concentrations in 99% of specimens. Whereas BUP-Gluc was identified in more specimens than NBUP, NBUP exceeded BUP-Gluc concentrations in 77.9% of specimens that contained both analytes. Among all participants, the mean BUP-Gluc:NBUP-Gluc ratio was significantly higher in the second trimester compared to the third trimester, and there were significant intrasubject differences between trimesters in 71% of participants. In 3 women, the percent daily dose excreted was higher during pregnancy than postpregnancy, consistent with other data indicating increased renal elimination of drugs during pregnancy.

CONCLUSIONS

These data are the first to evaluate urinary disposition of BUP and metabolites in a cohort of pregnant women. Variable BUP excretion during pregnancy may indicate metabolic changes requiring dose adjustment during later stages of gestation.

Therapeutic product disposition in at-risk populations

In an emergency situation, such as a chemical, biological, radionuclide, nuclear or explosion (CBRNE) event, all patient populations are at increased risk of serious adverse events. Therapeutic product (TP) safety and efficacy depend on the disposition of the product through absorption, distribution, metabolism and excretion. The ability of a patient to benefit from or merely tolerate a TP can be modified by many factors, including but not limited to culture, diet, disease, environmental contaminants, genetic predisposition, stress and socioeconomic status and recent life experiences. Metabolism is considered to have the greatest effect on safety and efficacy, as chemicals not metabolised can accumulate to toxic levels. Inter-individual variances in most drug metabolism enzymes may range up to greater than 1000-fold. The fetus, neonates, infants, individuals with hormonal change, infection or prior exposure to licit or illicit products and the elderly are more susceptible to increased risk of serious adverse health effects. The critically ill are the most at risk. The at-risk populations for a serious adverse event are dependent then on the CBRNE event, their physical and cognitive states and the inter-individual intrinsic and extrinsic factors that affect TP disposition.

As in humans, pregnancy increases the clearance of the protease inhibitor nelfinavir in the nonhuman primate Macaca nemestrina

The apparent oral clearance of protease inhibitors (PIs) is increased in pregnant women. Although this phenomenon is reproduced in the mouse, because of the multiplicity of mouse cytochrome P450 isoforms, lack of information on their substrate and inhibitor selectivity, and lack of reagents (e.g., antibodies, purified protein), it is difficult to study the mechanistic basis of this phenomenon in this animal model. To investigate the mechanistic basis of this phenomenon in a more representative model, the nonhuman primate, we first determined whether this phenomenon could be reproduced in Macaca nemestrina, using nelfinavir as a model PI. Consistent with the human and mouse studies, we found that the apparent oral clearance of nelfinavir (NFV) in the macaques was significantly increased (3.14-fold) antepartum (n = 3) versus postpartum (n = 4). This increased apparent oral clearance was a result of an increased systemic clearance (1.9-fold) and a decreased bioavailability (approximately 45%) during pregnancy. In vitro, pregnancy significantly enhanced the rate of NFV depletion in hepatic, but not intestinal S-9 fractions. Human CYP3A inhibitors erythromycin (0.5 mM), ketoconazole (0.5 microM), and troleandomycin (0.01-1 mM), but not the CYP2C inhibitor, sulfaphenazole (3 microM), significantly inhibited the depletion of NFV in hepatic S-9 fractions and expressed rhesus CYP3A64 enzyme. Based on these data, we conclude that increased hepatic activity of NFV-metabolizing enzymes (perhaps CYP3A enzymes) results in increased clearance of PIs during pregnancy in the macaques. The M. nemestrina should be further investigated as a model to study the mechanisms by which the clearance of PIs is increased during pregnancy.

Physiologically based pharmacokinetic model of midazolam disposition during pregnancy

Disposition of drugs in pregnant women is poorly understood in spite of widespread prescription of drugs to women during gestation. We have developed a whole body physiologically based pharmacokinetic (PBPK) model to explore the effects of pregnancy on pharmacokinetics. The model accounts for maternofetal changes over the course of gestation; physiological and drug-specific parameters are taken from literature. Here we preliminarily demonstrate the model's utility to predict midazolam pharmacokinetics following intravenous bolus dosing in women undergoing Caesarian section. Simulations of maternal venous plasma concentrations compare favorably with data extracted from historical studies.

The pharmacokinetics, safety and efficacy of boosted saquinavir tablets in HIV type-1-infected pregnant women

Background

Pregnancy affects the pharmacokinetics of most protease inhibitors. Saquinavir, when administered in a tablet formulation, has not been studied extensively in this setting.

Methods

A pharmacokinetic, prospective, multicentre trial of HIV type-1-infected pregnant women treated with saquinavir (500 mg tablets) boosted with ritonavir at a dose of 1,000/100 mg twice daily plus a nucleoside backbone was conducted. Pharmacokinetic curves were recorded for 12 h in the second trimester (week 20 ±2), the third trimester (week 33 ±2) and post-partum (weeks 4–6). Blood was sampled pre-dosing and at 1, 2, 3, 4, 6, 8, 10 and 12 h post-dosing. Pharmacokinetic parameters were calculated using WinNonlin software version 4.1.

Results

A total of 37 women were included in the analysis. Mean (±sd) values for saquinavir area under the curve (AUC0–12h) were 23.47 h•mg/l (11.92) at week 20 ( n=16), 23.65 h•mg/l (9.07) at week 33 ( n=31) and 25.00 h•mg/l (11.81) post-partum ( n=9). There was no significant difference in the saquinavir AUC0–12h when comparing the data during pregnancy and post-partum. Subtherapeutic plasma concentrations of saquinavir (defined as <0.10 mg/l) were not observed throughout the study. No major safety concerns were noted.

Conclusions

Saquinavir exposure in the new tablet formulation generates adequate saquinavir concentrations throughout the course of pregnancy and is safe to use; therefore, no dose adjustment during pregnancy is needed.

The influence of labour on the pharmacokinetics of intravenously administered amoxicillin in pregnant women

AIMS

Many physiological changes take place during pregnancy and labour. These might change the pharmacokinetics of amoxicillin, necessitating adjustment of the dose for prevention of neonatal infections. We investigated the influence of labour on the pharmacokinetics of amoxicillin.

METHODS

Pregnant women before and during labour were recruited and treated with amoxicillin intravenously. A postpartum dose was offered. Blood samples were obtained and amoxicillin concentrations were determined using high-pressure liquid chromatography. The pharmacokinetics were characterized by nonlinear mixed-effects modelling using NONMEM.

RESULTS

The pharmacokinetics of amoxicillin in 34 patients was best described by a three-compartment model. Moderate interindividual variability was identified in CL, central and peripheral volumes of distribution. The volume of distribution (V) increased with an increasing amount of oedema. Labour influenced the parameter estimate of peripheral volume of distribution (V(2)). V(2) was decreased during labour, and even more in the immediate postpartum period. For all patients the population estimates (mean +/- SE) for CL and V were 21.1 +/- 4.1 l h(-1) (CL), 8.7 +/- 6.6 l (V(1)), 11.8 +/- 7.7 l (V(2)) and 20.5 +/- 15.4 l (V(3)) respectively.

CONCLUSIONS

The peripheral distribution volume of amoxicillin in pregnant women during labour and immediately postpartum is decreased. However, these changes are not clinically relevant and do not warrant deviations from the recommended dosing regimen for amoxicillin during labour in healthy pregnant patients.

Novel biomarkers of prenatal methamphetamine exposure in human meconium

Meconium analysis can detect fetal exposure to drugs taken by the mother during pregnancy. Methamphetamine (MAMP) and amphetamine (AMP) have previously been observed in meconium of MAMP-exposed neonates; the presence of other metabolites has not been investigated. Detection of such analytes may lead to more sensitive identification and thus improved medical treatment of affected infants. Forty-three MAMP-positive meconium specimens were analyzed for newly identified MAMP biomarkers, p-hydroxymethamphetamine, p-hydroxyamphetamine, and norephedrine. Due to MAMP adulteration in illicit ecstasy and to simultaneously monitor 3,4-methylenedioxymethamphetamine and MAMP prenatal exposure, 3,4-methylenedioxymethamphetamine, its metabolites, and related sympathomimetic amines were assayed. MAMP, AMP, and unconjugated p-hydroxymethamphetamine were the most prevalent and abundant analytes present in meconium; however, unconjugated p-hydroxyamphetamine and norephedrine also were identified. It is possible that one of these additional analytes could be important for predicting toxicity or maternal or neonatal outcome measures in fetuses exposed to MAMP at specific gestational ages or with different metabolic capabilities. Although these new biomarkers were present in lower concentrations than MAMP and AMP in the meconium of previously confirmed specimens, additional research will determine if inclusion of these analytes can increase identification of MAMP-exposed neonates. Novel methamphetamine biomarker concentrations were characterized in meconium of infants exposed in utero to MAMP.

Seizure deterioration in women treated with oxcarbazepine during pregnancy

Thirteen pregnancies in ten women on oxcarbazepine (OXC) monotherapy and one pregnancy in a woman on OXC and topiramate therapy were retrospectively analyzed. A significant decrease of ratio plasma concentration of 10-monohydroxy derivate (MHD) of oxcarbazepine to dosage was found by 26.2% during first trimester, by 36.5% during second trimester and by 38.2% during third trimester when compared to pre-pregnant levels. Eight patients experienced seizure deterioration during the pregnancy, five of which had been seizure-free before the pregnancy. In seven pregnancies (50%) the seizure frequency was at least doubled during pregnancy compared to a pre-pregnancy baseline. There was a trend toward a correlation between seizure deterioration and decrease in plasma concentration of MHD.

Cefazolin pharmacokinetics in maternal plasma and amniotic fluid during pregnancy

OBJECTIVE

To study cefazolin pharmacokinetics in maternal plasma and amniotic fluid during pregnancy.

STUDY DESIGN

Newly collected time-concentrations profiles and reported studies investigating cefazolin disposition (plasma, amniotic fluid) were pooled. Nonlinear mixed effect modeling was applied. A 2-compartment linear disposition model was used to fit cefazolin plasma observations. A third compartment was used to model amniotic fluid concentration.

RESULTS

One hundred eighty-seven plasma and 96 amniotic fluid samples were collected in 82 pregnancies (17-40 weeks gestational age). Cefazolin clearance and distribution estimates were 7.44 L/h and 12.04 L without gestational age-dependent trends in maternal plasma. The equilibration half-life (T(eq)) between plasma and amniotic fluid at term gestational age was 4.4 hours, increased with decreasing gestational age, and was 9.09 times longer in patients with polyhydramnios.

CONCLUSION

Cefazolin clearance and distribution volume are increased during pregnancy. The cefazolin T(eq) depends on gestational age and polyhydramnios. On the basis of these observations, dosing regimes to attain higher amniotic fluid concentrations were formulated.

Determination of unbound antiretroviral drug concentrations by a modified ultrafiltration method reveals high variability in the free fraction

Total plasma concentrations are used for therapeutic drug monitoring of antiretroviral drugs, whereas antiviral activity is expected to depend on unbound concentrations. The determination of free (unbound) concentrations by ultrafiltration may be flawed by the irreversible adsorption of many drugs onto the membrane filters and plastic components of the device. The authors describe a modified ultrafiltration method enabling the accurate measurement of unbound concentrations of 10 antiretroviral drugs by liquid chromatography-tandem mass spectroscopy, which circumvents the problem of loss by adsorption in the early ultrafiltration fractions. The method was applied to assess the variability of free fractions of antiretroviral drugs during routine therapeutic drug monitoring in 144 patients with HIV. In in vitro experiments, ultrafiltrate collected in four fractions (0-8, 8-16, 16-24, and 24-30 minutes) gave much lower and more variable free drug concentrations in the first ultrafiltrate fraction than in the last three fractions for lopinavir, nelfinavir, saquinavir, tipranavir, and efavirenz. In the last two fractions, free concentrations remained constant, indicating saturable adsorption. The adsorption was modest for indinavir, amprenavir, and ritonavir, and unnoticeable for atazanavir and nevirapine. Free fraction values obtained with this modified ultrafiltration method reveal substantial interindividual variability, suggesting that monitoring unbound antiretroviral drug concentrations may increase its clinical usefulness, especially for lopinavir, saquinavir, and efavirenz.

Serum concentration/dose ratio of topiramate during pregnancy

PURPOSE

To study the impact of pregnancy on the serum concentration/dose ratio (C/D-ratio) of topiramate (TPM).

METHODS

Twelve women with epilepsy using TPM during pregnancy, and 15 pregnancies were studied. The main target variable was the C/D-ratio at baseline and during pregnancy. Additional variables were changes in TPM dose, concomitant use of other antiepileptic drugs, seizure frequency, and pregnancy outcome. Clinical and pharmacological data were obtained from the women's medical records.

RESULTS

The average C/D-ratios in the second and third trimester were 30% (p = 0.002, n = 11) and 34% (p = 0.001, n = 8) lower than the baseline values, respectively. The interindividual variability was pronounced. Increased seizure frequency was common in pregnant women using TPM, but a correlation to the decline in TPM C/D-ratio could not be established from our data.

DISCUSSION

Dose-corrected serum concentrations of TPM appear to decline gradually throughout pregnancy. The underlying mechanisms are not known. Increased glomerular filtration may play a major role. During pregnancy, therapeutic drug monitoring of TPM may be useful.

Hormonal regulation of hepatic drug-metabolizing enzyme activity during adolescence

Activities of drug-metabolizing enzymes (DMEs) are known to change throughout the course of physical and sexual maturation, with the greatest variability noted during infancy and adolescence. The mechanisms responsible for developmental regulation of DME are currently unknown. However, the hormonal changes associated with puberty/adolescence provide a theoretical framework for understanding the biochemical regulation of DME activity during growth and maturation. Important information regarding potential influences of growth and sex hormones can also be extrapolated from studies that evaluate changes in activities of DMEs occurring as a consequence of physiological, pathological, and/or pharmacological hormonal fluctuations. Collectively, current data support the hypothesis that isoform-specific alterations in DME activity during adolescence are mediated by sex and/or growth hormones. Characterization of the underlying biochemical alterations responsible for developmental changes in DME activity will require additional studies in which relationships between DMEs and important hormonal axes are evaluated during the course of pubertal development.

Steady-state nevirapine plasma concentrations are influenced by pregnancy

OBJECTIVES

Optimal plasma concentrations of antiretroviral drugs are required during pregnancy to treat maternal HIV infection and prevent mother-to-child transmission. We investigated the effect of pregnancy on nevirapine (NVP) plasma concentrations.

METHODS

We included all HIV-1-infected women for whom NVP plasma concentrations were available as part of routine patient care at two university hospitals. Plasma NVP concentrations were compared for pregnant (n=45) and non-pregnant (n=152) women. Univariate and multivariate linear regression analyses were used to identify and adjust for other confounding factors associated with NVP plasma concentrations. For pregnant women who had a plasma NVP concentration available both during and outside pregnancy, a paired analysis was performed.

RESULTS

Steady-state NVP plasma concentrations were lower in pregnant women: 5.2 mg/L (interquartile range 3.9-6.8) vs. 5.8 mg/L (4.3-7.7) (P=0.08). After adjusting for confounders, both pregnancy (regression coefficient=-0.90 mg/L, P=0.046) and African descent (regression coefficient=+1.13 mg/L, P=0.005) influenced NVP concentrations significantly. The paired analysis showed mean concentrations of 4.8 mg/L during pregnancy and 5.8 mg/L outside pregnancy (paired t-test, P=0.073).

CONCLUSIONS

Pregnancy has a moderate but significant lowering effect on NVP plasma concentrations. Being of African descent compensates for the lowering effect of pregnancy on NVP concentrations.

Glomerular Hyperfiltration and Albuminuria in Critically ILL Patients

Glomerular hyperfiltration and albuminuria are two pathological conditions that could alter renal drug elimination, but they have been rarely studied in a critical care setting.

The aims of this descriptive, prospective study performed on 89 critically ill patients are to determine rates of glomerular hyperfiltration (main objective) and albuminuria (secondary objective).

On admission, 17.9% of patients presented with glomerular hyperfiltration, climbing to rates as high as 30% during the first week of admission. Seventy-five percent showed albuminuria on admission, with rates remaining high throughout the week of the study.

Since glomerular hyperfiltration as well as albuminuria are frequent pathophysiological conditions in critical care patients, the implications that these phenomena may have regarding drug elimination need further evaluation.

Where do we go now with low molecular weight heparin use in obstetric care?

The use of low molecular weight heparins (LMWH) in obstetric care has grown considerably since their introduction into clinical practice in the early 1990s. However, because of the physiological changes of pregnancy, the predictable pharmacokinetic profile of LMWH is lost and some uncertainty exists around the optimal dosing regimen for LMWH in obstetric care. Two recent United Kingdom prospective surveys of the management of acute venous thromboembolism (VTE) suggest that despite recommendations from the Royal College of Obstetricians and Gynaecologists (RCOG) for a twice daily LMWH regimen, a once daily regimen is acceptable for the treatment of venous thromboembolism; and that accepted thromboprophylactic doses licensed for non-pregnant individuals may not be applicable during the second and third trimester for VTE thromboprophylaxis. Accepting that randomized clinical studies are difficult in obstetric care, future advances could be made through population-based multi-center studies, coupled with pharmacokinetic modeling studies, which have the potential to determine the optimal dosing regimen for the various obstetric indications.

Pharmacokinetics and therapeutic drug monitoring of antiretrovirals in pregnant women

Highly active antiretroviral therapy is recommended for HIV-infected pregnant women to prevent mother-to-child transmission. The specific physiological background induced by pregnancy leads to significant changes in maternal pharmacokinetics, suggesting potential variability in plasma concentrations of antiretrovirals during gestation. Therapeutic drug monitoring (TDM) of protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) is recommended in certain situations, including pregnancy, but its systematic use in HIV-infected pregnant women remains controversial. This review provides an update of the pharmacokinetic data available for PIs and NNRTIs in pregnant women and highlights the clinical interest of systematic TDM of certain antiretroviral drugs during pregnancy, including nevirapine, nelfinavir, saquinavir, indinavir and lopinavir.

Sex-specific differences in CYP450 isoforms in humans

BACKGROUND

The activity of various CYP isoforms is critical for maintaining the clinical effectiveness of many medications. Therefore, determining the sex-dependent activity of clinically relevant CYP families is highly important for optimal therapeutic effectiveness.

OBJECTIVE

This review examined the sex-dependent activity of CYP3A, CYP1A2, CYP2D6, CYP2C9, CYP2C19 and CYP2E1.

METHODS

This review searched for studies performed in humans and hormonal status was not a limiting factor.

RESULTS/CONCLUSIONS

The current evidence suggests that CYP2E1 and CYP1A2 activity is higher in males than females, while CYP3A, one of the most clinically relevant CYP isoforms, appears to have greater activity in females. Overall, more studies are needed to fully support these conclusions as there are many factors that influence drug metabolism and thus it is very difficult to isolate gender as a sole modulator of CYP activity.

Biological rhythms: a neglected factor of variability in pharmacokinetic studies

Biological rhythms may influence drug response (chronopharmacology) and some chronopharmacological studies have underlined the influence of time of day on drug pharmacodynamics and pharmacokinetics. The aim of the present review is to underline how biological rhythms may interfere with drug kinetics and to try to underline when, how, and why taking into account the moment of administration of a drug. Many physiological factors, possibly implicated in different steps of the fate of drugs in the organism (e.g., absorption, distribution, metabolism, and elimination) vary along the 24 h scale. Taking into account biological rhythms in kinetic studies, should be indicated when the concerned drug will be used in a chronobiological disease (e.g., asthma, cancer, depression, hypertension, gastrointestinal diseases, rheumatisms), etc. In case of a drug characterised by a high inter- and intra-variability, a narrow therapeutic range or when the drug will be further used following a once-a-day formulation. It is of importance to rigorously control factors which are known to influence pharmacokinetic processes in chronokinetic studies. Time of day has to be regarded as an additional variable to influence the kinetics of a drug.

Regulation of UDP-glucuronosyltransferase (UGT) 1A1 by progesterone and its impact on labetalol elimination

The authors recently reported the increased oral clearance of labetalol in pregnant women. To elucidate the mechanism of the elevated oral clearance, it was hypothesized that female hormones, at the high concentrations attainable during pregnancy, enhance hepatic metabolism of labetalol. Labetalol glucuronidation, which is the major elimination pathway of labetalol, was characterized by screening six recombinant human UGTs (UGT1A1, 1A4, 1A6, 1A9, 2B4, and 2B7) for their capacity to catalyse labetalol glucuronidation. The effect of female hormones (progesterone, oestradiol, oestriol, or oestrone) on the promoter activities of relevant UDP glucuronosyltransferases (UGT) was investigated using a luciferase reporter assay in HepG2 cells. The involvement of oestrogen receptor alpha (ERalpha) and pregnane X receptor (PXR) was examined by co-transfecting ERalpha- or PXR-constructs. UGT1A1 and UGT2B7 were identified as the major UGT enzymes producing labetalol glucuronides (trace amount of glucuronide conjugate was formed by UGT1A9). The activities of the UGT1A1 promoter containing PXR response elements were enhanced by progesterone, but not by oestrogens, indicating PXR-mediated induction of UGT1A1 promoter activity by progesterone. Results from semi-quantitative real-time polymerase chain reaction (PCR) assays are consistent with the above findings. This effect of progesterone on UGT1A1 promoter activities was concentration dependent. Promoter activities of UGT2B7 were not affected by either oestrogens or progesterone. The results suggest a potential role for progesterone in regulating labetalol elimination by modulating the expression of UGT1A1, leading to enhanced drug metabolism during pregnancy.

Changes in antidepressant metabolism and dosing across pregnancy and early postpartum

OBJECTIVE

Little information about the disposition of individual antidepressant drugs during pregnancy has been published. We examined the dose requirements and level-to-dose (L/D) ratios of citalopram, escitalopram, and sertraline during pregnancy and after birth.

METHOD

Women aged from 32 to 43 years with major depressive disorder according to the Structured Clinical Interview for DSM-IV Axis I Disorders participated in the study. Doses were charted across each week of gestation and post-partum. Samples were collected at 20, 30, and 36 weeks' gestation; delivery; and at 2 and 12 weeks postpartum. Plasma trough levels were obtained 8 to 15 hours after dose intake. Across pregnancy and postpartum, the mean dose-corrected plasma concentrations (L/D ratios) of S- and R-citalopram and S-sertraline, and the corresponding primary chiral metabolites S- and R-desmethylcitalopram and N-desmethylsertra-line were assessed. The samples were analyzed for concentrations of stereospecific parent drug and metabolites. The study was conducted from 2003 to 2006.

RESULTS

Three women received citalopram, 2 women were treated with escitalopram, and 6 women received sertraline. In 4 of 5 subjects who received citalopram or escitalopram and 5 of 6 subjects who received sertraline, the L/D ratios for the stereoisomers of the parent compound and primary metabolite decreased between 20 weeks gestation and delivery, which reflects increased drug metabolism. By 12 weeks postpartum the L/D ratios were similar to those detected at 20 weeks gestation.

CONCLUSIONS

Our cases illustrate that dose requirements frequently increase during the second half of pregnancy to offset increased drug turnover and maintain optimal pharmacotherapy. These findings replicate and extend earlier published data with other antidepressants.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00279370.

Obstetric anesthesia: outside the labor and delivery unit

The maternal mortality rate in the United States has stagnated for the past 2 decades. To further lower morbidity and mortality, we must take a broader perspective. When a pregnant woman is treated in a nonobstetric part of the hospital, care must adapt quickly to her special needs. Excessive concern as to medication, radiation, and litigation may render her care neither safe, timely, efficient, effective, nor patient-centered. Anesthesiologists can significantly improve the care of the pregnant patient by applying their uniquely broad-based skills, experience, and knowledge outside the labor unit.

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.