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

Changes in maternal liver Cyp2c and Cyp2d expression and activity during rat pregnancy

During human pregnancy, CYP2C9, CYP2C19, and CYP2D6 activities are altered. The aim of the current study was to determine if this phenomenon can be replicated in the rat, and to evaluate the mechanisms that contribute to the changes in Cyp2c and Cyp2d activity during pregnancy. The intrinsic clearance of dextromethorphan O-demethylation, a measure of Cyp2d2 activity, was decreased 80% at both days 9 and 19 of gestation when compared to non-pregnant controls. The decreased intrinsic clearance was a result of both decreased V(max) and increased K(m)-values at both days of gestation. Quantitative RT-PCR revealed that transcripts of Cyp2d2 and Cyp2d4 were significantly decreased at day 19 of pregnancy (p<0.05) when compared to day 9 and non-pregnant controls. The decrease in Cyp2d mRNA levels correlated with a decrease in several nuclear receptor mRNA levels (RARalpha, RXRalpha, HNF1 and HNF3beta) but not with the mRNA levels of nuclear receptors usually associated with regulation of P450 enzymes (PXR, CAR and HNF4alpha). In contrast, Cyp2c12 and Cyp2c6 transcription and protein expression were not significantly altered during rat pregnancy although the intrinsic clearance of Cyp2c6 mediated diclofenac 4'-hydroxylation was increased 2-fold on day 19 of gestation when compared to non-pregnant controls. The increase in intrinsic clearance was due to a decrease in the K(m)-value for 4'-hydroxydiclofenac formation. These data show that pregnancy significantly alters the expression and activity of drug metabolizing enzymes in an enzyme and gestational stage specific manner. These changes are likely to have toxicological and therapeutic implications.

Serum concentration/dose ratio of levetiracetam before, during and after pregnancy

PURPOSE

To investigate changes in levetiracetam (LEV) serum concentration/dose ratio (C/D-ratio) in relation to pregnancy.

METHODS

Altogether 21 consecutive pregnancies in 20 women with epilepsy receiving LEV during gestation were studied retrospectively. The main target variable was the C/D-ratio before and during pregnancy, and in the post partum period. Secondary target variables were changes in LEV dose, concomitant use of other antiepileptic drugs and seizure frequency. Student's paired t-test and two-sample t-test for independent samples were used to test for statistically significant changes in C/D-ratio means.

RESULTS

Mean C/D-ratio in the third trimester was 50% of the mean C/D-ratio at baseline (p<0.001, n=11). Baseline levels were reached within the first weeks after pregnancy. The interindividual variability was pronounced.

CONCLUSIONS

Serum concentrations of LEV declined significantly in the third trimester of pregnancy and increased rapidly after delivery.

Ritodrine pharmacokinetics in twin pregnancy patients

OBJECTIVES

To establish a rational ritodrine therapy in relation to serum ritodrine concentration, we examined 14 twin pregnancy patients and determined their pharmacokinetic data.

METHODS

We measured serum concentrations of ritodrine in twin pregnancy patients using high-performance liquid chromatography (HPLC).

RESULTS

The twin pregnancy patients all exhibited linear ritodrine pharmacokinetic profiles. There was a statistically significant but slight negative correlation between gestation period and ritodrine clearance (y=-0.038x+2.75, r=0.349, p<0.001) among all patients. However, when analyzed on an individual basis, there was a high correlation found in three of the 14 patients.

CONCLUSION

Due to a decrease in total body clearance in three of the 14 patients, overall serum concentration of ritodrine increased at the end of the pregnancies. To further characterize ritodrine kinetics, additional studies are needed to determine an effective and safe therapy for ritodrine use in twin pregnancy patients.

Pharmacokinetic modelling of the placental transfer of nelfinavir and its M8 metabolite: a population study using 75 maternal-cord plasma samples

AIMS

A population pharmacokinetic model was developed to characterize the transfer of nelfinavir and its active metabolite M8 from maternal to cord plasma and amniotic fluid.

METHODS

Concentration data were obtained from 75 women on the day of delivery and for whom maternal, umbilical plasma and amniotic fluid samples were collected. Data from 53 pregnant, 61 nonpregnant and seven consecutively pregnant and non pregnant women were then added to the database, the contents of which were analyzed using NONMEM.

RESULTS

Nelfinavir and M8 concentrations in maternal plasma, umbilical plasma and amniotic fluid were described by six connected compartments. Mean (% intersubject variability) population estimates were: absorption rate 00.67 h(-1), lag time 00.87 h, oral clearance and volume of distribution: 39.5 l h(-1) (53%), and 557 l for non pregnant and pregnant women, respectively, and 115 l h(-1) (132%) and 1626 l, respectively, on the day of delivery, M8 formation clearance 0.77 l h(-1) and M8 elimination rate constant 03.41 h(-1) (74%). For nelfinavir and M8, respectively, the mother-to-cord parameters were 0.058 l h(-1) (34%), and 00.35 h(-1) (76%), the cord-to-amniotic fluid rate constants were 0.23 and 00.59 h(-1), and the elimination rate constants from amniotic fluid were 0.36 and 00.49 h(-1). The nelfinavir fetus : maternal concentration ratio was 25% for maternal concentrations between 0.1 and 2.5 mg l(-1), between the 31 and 41st week of gestation.

CONCLUSIONS

The low transfer of nelfinavir from the placenta is unlikely to protect the fetus from vertical HIV-1 transmission.

The fate and effects of xenobiotics in human placenta

During past decades, knowledge on placental drug metabolism and mechanisms of placental transfer has increased significantly. Most pharmaceutical drugs administered during pregnancy cross the placenta to some extent. The important properties determining the placental transfer by passive diffusion are molecular weight, pK(a), lipid solubility and protein binding. In addition to passive diffusion, compounds may cross the placenta via active transfer, facilitated diffusion, phagocytosis and pinocytosis. This review gives an update of efflux transporter proteins and xenobiotic-metabolizing enzymes that modify the fate and effects of drugs in the placenta.

The Food and Drug Administration Office of Women's Health: Impact of Science on Regulatory Policy

In 1994, the Food and Drug Administration Office of Women's Health (FDA-OWH) was created to provide leadership and policy direction for the Agency regarding issues of women's health. Within its first year, the FDA-OWH established a science program for women's health research, promoting the development of sound policy and regulation. In a little over a decade, the program has provided approximately 14 million dollars to fund more than 100 women's health research studies covering a broad range of health topics affecting women across their lifespan. Some studies, such as those elucidating drug effects on QT prolongation in women and drug-dietary supplement interaction, have had significant influence on regulatory decisions. Other studies have provided sound scientific data on sex and gender differences supporting FDA guidelines to protect women's health. This paper describes the science program at the FDA-OWH, providing examples of how funded research impacts regulatory policy.

Pharmacokinetics of Levetiracetam during Pregnancy, Delivery, in the Neonatal Period, and Lactation

PURPOSE

To study pharmacokinetics of levetiracetam (LEV) during pregnancy, delivery, lactation, and in the neonatal period.

METHODS

Fourteen women with epilepsy receiving LEV treatment during pregnancy and lactation contributed with 15 pregnancies to this prospective study in which LEV concentrations in plasma and breast milk were determined. Trough maternal plasma samples were collected each trimester, and at baseline after delivery. Blood samples were obtained at delivery from mothers, from the umbilical cord, and from newborns during 2 days after delivery. LEV concentration was also determined in breast milk and in plasma collected from 11 of the mothers and their suckling infants after birth.

RESULTS

The umbilical cord/maternal plasma concentration ratios ranged from 0.56-2.0 (mean 1.15, n=13). LEV plasma concentrations in the neonates declined with an estimated half-life of 18 h (n=13). The mean milk/maternal plasma concentration ratio was 1.05 (range, 0.78-1.55, n=11). The infant dose of LEV was estimated to 2.4 mg/kg/day, equivalent to 7.9% of the weight-normalized maternal dose. Plasma concentrations in breastfed were approximately 13% of the mother's plasma levels. Maternal plasma concentrations during third trimester were only 40% of baseline concentrations outside pregnancy (p<0.001, n=7)

CONCLUSIONS

Our observations suggest considerable transplacental transport of LEV and fairly slow elimination in the neonate. Plasma concentrations of LEV in nursed infants are low despite an extensive transfer of LEV into breast milk. Pregnancy appears to enhance the elimination of LEV resulting in marked decline in plasma concentration, which suggests that therapeutic monitoring may be of value.

Lornoxicam and ondansetron for the prevention of intrathecal fentanyl-induced pruritus

PURPOSE

In this randomized, double-blind study, we aimed to compare the effectiveness of lornoxicam and ondansetron for the prevention of intrathecal fentanyl-induced pruritus in patients undergoing cesarean section.

METHODS

One hundred and eight parturients (American Society of Anesthesiologists [ASA] I-II status) requesting neuraxial analgesia by a combined spinal-epidural (CSE) technique were recruited for this study. A CSE technique was performed and anesthesia was achieved with fentanyl 25 microg and hyperbaric bupivacaine 12 mg. Patients were randomly allocated to three groups, each with 36 participants. Immediately following delivery, patients received either lornoxicam 8 mg IV (group L; n = 36), ondansetron 8 mg IV (group O; n = 36), or normal saline 2 ml IV (group P; n = 36). Pruritus, pain, and nausea and vomiting scores were recorded during the initial 24 h postoperatively.

RESULTS

The incidence of pruritus was significantly lower in group O from 4 to 12 h postoperatively when compared to that in group L and group P. According to the pruritus grading system we used, the number of patients without pruritus was significantly higher in group O when compared to that in group L and group P. The number of patients experiencing moderate pruritus was significantly lower in group O when compared to that in group P.

CONCLUSION

We observed that the administration of 8 mg IV lornoxicam failed to prevent intrathecal fentanyl-induced pruritus in parturients. Also, our data confirmed that ondansetron is likely to attenuate intrathecal fentanyl-induced pruritus.

Transplacental Passage of Vancomycin in Noninfected Term Pregnant Women

OBJECTIVE

To evaluate the transplacental passage of vancomycin in term, uninfected pregnant women.

METHODS

A single vancomycin 1-g dose was administered intravenously at four separate time intervals to 13 uncomplicated nonlaboring women undergoing scheduled cesarean delivery. Samples of maternal blood and fetal cord blood were collected at time of delivery and vancomycin concentrations assayed.

RESULTS

Vancomycin concentrations in maternal serum ranged from 2.6 to 19.8 mcg/mL. In cord blood samples, vancomycin concentrations ranged from 2.8 to 9.4 mcg/mL and persisted above the group B streptococci vancomycin breakpoint of 1 mcg/mL. Only 6 of 13 women received the full 1-g vancomycin dose because 53.8% (7 of 13) had some manifestation of red man syndrome during the infusion. No other short term sequelae were identified in any patients or their fetuses. A strong correlation (r(2)=0.93, P<.001) between cord and maternal serum concentrations versus time was noted. Cord vancomycin concentrations approached maternal serum concentrations 4 hours after the infusion ended.

CONCLUSION

Vancomycin crosses the placenta in a predictable manner in concentrations that exceed the usual group B streptococci breakpoint. Adverse events were common, suggesting that longer infusion times and weight adjusted doses should be used.

Obstetric clinical pharmacology: coming of age

Little is known about changes in drug disposition and effect during pregnancy. In this issue, which is devoted to maternal and child health, Andrew and colleagues from the University of Washington present research describing significant changes in the disposition of amoxicillin during pregnancy. The clinical significance is the potential for inadequate dosing during pregnancy of compounds that are renally cleared. Further research is needed to guide the appropriate, safe, and effective medical treatment of pregnant women. In 2003, the National Institute of Child Health and Human Development (NICHD) formed the Obstetric Pharmacology Research Units Network. This network serves in part as a proof-of-concept platform, to demonstrate that clinical investigations can be performed in pregnant women.

Kinetics of glyburide metabolism by hepatic and placental microsomes of human and baboon

Glyburide (glibenclamide) is under investigation for treatment of gestational diabetes. Two metabolites of glyburide have been previously identified in patients, namely, 4-trans-(M1) and 3-cis-(M2) hydroxycyclohexyl glyburide. Recently, the metabolism of glyburide by microsomes of liver and placenta from humans and baboons revealed the formation of four additional metabolites: 4-cis-(M2a), 3-trans-(M3), and 2-trans-(M4) hydroxycyclohexyl glyburide, and ethyl-hydroxy glyburide (M5). The aim of this investigation was to determine the kinetics for the metabolism of glyburide by cytochrome P450 (CYP) isozymes of human and baboon placental and hepatic microsomes. The metabolism of glyburide by microsomes from the four organs revealed saturation kinetics and apparent K(m) values between 4 and 12 microM. However, the rates for formation of the metabolites varied between organs and species. M1 was the major metabolite (36% of total), formed by human hepatic microsomes with V(max) of 80+/-13 pmol mg protein(-1)min(-1), and together with M2, accounted for only 51% of the total. M5 was the major metabolite (87%) formed by human placental microsomes with V(max) of 11 pmol mg protein(-1)min(-1). In baboon liver, M5 had the highest rate of formation (V(max) 135+/-32 pmol mg protein(-1)min(-1), 39% of total), and in its placenta, was M4 (V(max) 0.7+/-0.1 pmol mg protein(-1)min(-1), 65%). The activity of human and baboon hepatic microsomes in metabolizing glyburide was similar, but the activity of human and baboon placental microsomes was 7% and 0.3% of their respective hepatic microsomes. The data obtained suggest that more than 1 CYP isozyme is responsible for catalyzing the hydroxylation of glyburide.

Human Teratogens and Evidence-based Teratogen Risk Counseling: The Motherisk Approach

There are only a limited number of drugs proven to be human teratogens including thalidomide, isotretinoin, coumarin derivates, valproic acid, and folate antagonists. In some cases, the combination of 2 drugs may increase the teratogenic risk. The risk of birth defects may also vary with the time at which the drug is administered during pregnancy and the dose. There are some examples of drugs in which the dose has proven to be a major determinant of their teratogenicity in humans. There is more safety information for older than for newer drugs. Proactive teratogen risk counseling should include a critical appraisal of all available data including the consequences of the untreated maternal condition.

Using pharmacokinetics to predict the effects of pregnancy and maternal-infant transfer of drugs during lactation

Knowledge of pharmacokinetics and the use of a mechanistic-based approach can improve our ability to predict the effects of pregnancy for medications when data are limited. Despite the many physiological changes that occur during pregnancy that could theoretically affect absorption, bioavailability does not appear to be altered. Decreased albumin and alpha(1)-acid glycoprotein concentrations during pregnancy will result in decreased protein binding for highly bound drugs. For drugs metabolised by the liver, this can result in misinterpretation of total plasma concentrations of low extraction ratio drugs and overdosing of high extraction ratio drugs administered by non-oral routes. Renal clearance and the activity of the CYP isozymes, CYP3A4, 2D6 and 2C9, and uridine 5'-diphosphate glucuronosyltransferase are increased during pregnancy. In contrast, CYP1A2 and 2C19 activity is decreased. The dose of a drug an infant receives during breastfeeding is dependent on the amount excreted into the breast milk, the daily volume of milk ingested and the average plasma concentration of the mother. The lipophilicity, protein binding and ionisation properties of a drug will determine how much is excreted into the breast milk. The milk to plasma concentration ratio has large inter- and intrasubject variability and is often not known. In contrast, protein binding is usually known. An extensive literature review was done to identify case reports including infant concentrations from breast-fed infants exposed to maternal drugs. For drugs that were at least 85% protein bound, measurable concentrations of drug in the infant did not occur if there was no placental exposure immediately prior to or during delivery. Knowledge of the protein binding properties of a drug can provide a quick and easy tool to estimate exposure of an infant to medication from breastfeeding.

Gaps in knowledge in treating pregnant women

Because studies are often undertaken without knowledge of the pharmacokinetics of a drug, efficacy is difficult to assess in pregnant women. To address this lack, basic and clinical research within the National Institute of Child Health and Human Development is focusing on expanding knowledge of pharmacology during pregnancy. Although medication use, including prescription, over-the-counter, and herbal products, is common during pregnancy, physicians may not be aware of the nonprescription products their patients are taking or the interactions these products may have with prescribed medications. A number of studies have found sex differences in oxidative metabolism and transport, as well as pharmacologic and toxicologic differences in hepatic metabolism, that are ultimately reflected in pharmacokinetics. Sex differences exist in distribution volumes, transport proteins, and drug clearance. Beyond these sex differences, pregnancy itself affects the absorption, distribution, metabolism, and elimination of a drug. Women experience more adverse drug reactions (ADRs) than do men, and these reactions tend to be more severe. QT prolongation (torsades de pointes) and hepatic toxicity are two of the most severe ADRs, frequently causing withdrawal of a drug from the market. Women may also metabolize drugs more quickly than do men, and drugs metabolized by cytochrome P3A4 are cleared more rapidly during pregnancy. A substantial increase in the clearance of drugs eliminated by renal mechanisms also has been noted. A significant number of women are clinically depressed during pregnancy and postpartum, and eliminating treatment for depression during pregnancy may have negative consequences for both mother and fetus. Among women with depression who are treated with selective serotonin reuptake inhibitors, the dose needed to maintain efficacy increases across the course of pregnancy. Drug disposition and response not only can differ between men and women, but also between pregnant and nonpregnant women. Research is needed to understand how pregnancy alters the pharmacokinetics and pharmacodynamics of drugs; then, efficacy trials can be initiated. Alternative strategies also need to be developed to characterize safety information.

Pharmacokinetics and Therapeutic Drug Monitoring of Newer Antiepileptic Drugs During Pregnancy and the Puerperium

The treatment of epilepsy in pregnancy is particularly challenging in that the fetal and maternal risks associated with maternal seizures need to be balanced against the potential teratogenic effects of antiepileptic drugs (AEDs). Pregnancy is known to affect the pharmacokinetics of older-generation AEDs. Understanding such alterations is important in the effort to optimise drug therapy since they may affect seizure control as well as fetal drug exposure. Therapeutic drug monitoring has therefore been recommended to control for changes in the disposition of the older-generation AEDs during pregnancy. Much less is known about gestation-induced alterations in the pharmacokinetics of the newer AEDs that have been introduced in the last 15 years. Lamotrigine is by far the most extensively studied of the newer AEDs. Pronounced alterations have been reported in the apparent clearance of lamotrigine, with an increase of >300% from baseline in late pregnancy in some patients on monotherapy, most likely due to enhanced metabolism. The available data suggest that the corresponding decline in plasma concentrations can be associated with loss of seizure control. More limited data indicate that a similar decline in plasma concentrations of the active monohydroxy derivative of oxcarbazepine may occur in late pregnancy. Preliminary experience also suggests that a significant fall in plasma concentrations of levetiracetam may occur during pregnancy. No systematic information is available on the pharmacokinetics during pregnancy of other newer AEDs (e.g. gabapentin, pregabalin, tiagabine, topiramate or zonisamide). Given the importance of maintaining optimal treatment of epilepsy during pregnancy, therapeutic drug monitoring appears to be justified for lamotrigine and oxcarbazepine in particular. Systematic studies of the effects of pregnancy on the pharmacokinetics of the other newer-generation AEDs are urgently needed.

Pharmacokinetics of oral cefatrizine in pregnant and non-pregnant women with reference to fetal distribution

OBJECTIVE

To investigate the effect of gestation on the pharmacokinetics of orally administered beta-lactams, choosing cefatrizine as the model antibiotic.

SETTING

A tertiary teaching hospital.

DESIGN

Prospective study.

METHODS

In 20 women with affected fetuses, 17 by beta-thalassemia major and 3 with congenital malformations, termination of gestation between 19 and 24 weeks was induced by intra-amniotic administration of prostaglandin F(2)(alpha). Pharmacokinetics of cefatrizine in maternal and fetal blood were studied after the administration of three 1 g doses of oral cefatrizine, every 12 h. Twenty female non-pregnant volunteers consisted the control group.

RESULTS

Gestation was found to decrease substantially both cefatrizine oral bioavailability and maximum serum plasma concentration (42.8 and 44.5%, respectively) but increased elimination half-life. This effect can be attributed to a substantial increase of the apparent volume of distribution of cefatrizine in relation to a moderate increase of clearance that occurs during pregnancy. Fetal serum cefatrizine levels were lower for the first few hours after administration and then exceeded the corresponding maternal ones.

CONCLUSIONS

Our results indicate that gestation decreases the oral bioavailability of cefatrizine. A delay in the maternal drug elimination compared to non-pregnant controls was more pronounced in the fetus.

A comparison of the steady-state pharmacokinetics of nevirapine in men, nonpregnant women and women in late pregnancy

AIMS

To evaluate the pharmacokinetics of nevirapine and any possible influencing factors in pregnant women (n = 16), nonpregnant women (n = 13) and men (n = 14), who received nevirapine 200 mg twice daily together with nucleoside reverse transcriptase inhibitors.

METHODS

Blood samples were taken for 12 h at steady state. Nevirapine concentrations were measured by liquid chromatography-tandem mass spectrometry. The influence of gender, age, body weight and comedication on minimum and maximum concentrations (C(min), C(max)), area under the concentration-time curve (AUC), total clearance (CL(tot)), half-life (t(1/2)) and volume of distribution (V(d)) was analysed by multivariate techniques.

RESULTS

Mean [95% confidence interval (CI)]C(max), AUC(ss) and clearance were 5221 ng ml(-1) (4267, 6175), 50 789 ng (-1)h ml(-1) (43 453, 58 125) and 69.9 ml min(-1) for men, 5871 ng ml(-1) (4848, 6895), 57 045 ng h(-1) ml(-1) (45 997, 68 093) and 65.6 ml min(-1) for nonpregnant women and 4505 ng ml(-1) (3644, 5366), 44 579 ng h(-1) ml(-1) (36 564, 52 594) and 82.1 ml min(-1) for pregnant women. The differences between pregnant and nonpregnant women (% difference, 95% CI) in C(max) (-30.3; -28.5, -33.0), AUC(ss) (-28.0; - 25.8, - 29.5) and clearance (20.2; 26.6, 15.6) reached statistical significance (P = 0.010, P = 0.028 and P = 0.028, respectively). The multivariate analysis underscored the influence of bodyweight on the plasma exposure to nevirapine.

CONCLUSIONS

Pregnant women exhibited an increased nevirapine clearance and comparably low plasma concentrations, whereas women with a low bodyweight achieved high plasma nevirapine concentrations. The large variability in nevirapine concentrations in women may lead to loss of efficacy and viral resistance, or drug toxicity, and therefore these patients should be monitored frequently.