Clinical relevance of therapeutic drug monitoring during pregnancy

Therapeutic Drug Monitoring in Pregnant Patients

During pregnancy, there are several physiological changes during each trimester that can affect the absorption, distribution, metabolism, and elimination of drugs. Although there is a potential need to understand the pharmacokinetics and pharmacodynamics of drugs in pregnant patients, therapeutic drug monitoring is not well established for various drug classes due to ethical and safety concerns regarding the neonate. Potential risks from in utero drug exposure to the fetus may impact growth and development and may cause malformations or teratogenesis. The clinician must consider the benefits of drug treatment for the pregnant mother versus the risk to the fetus, before prescribing medications during pregnancy. The objective of this review is to aid clinicians, pharmacists, and laboratorians in understanding the pharmacokinetic and pharmacodynamic changes during pregnancy, to provide drug class recommendations for monitoring therapy throughout pregnancy via therapeutic drug monitoring, and to highlight the recent directives of governing agencies on maternal and fetal health.

In-utero exposure to antihypertensive medication and neonatal and child health outcomes: a systematic review

BACKGROUND

Although medication is generally avoided wherever possible during pregnancy, pharmacotherapy is required for the treatment of pregnancy associated hypertension, which remains a leading cause of maternal and fetal morbidity and mortality. The long-term effects to the child of in-utero exposure to antihypertensive agents remains largely unknown.

OBJECTIVE

The aim of this study was to systematically review published studies on adverse outcomes to the child associated with in-utero exposure to antihypertensive medications.

METHODS

OVID, Scopus, EBSCO Collections, the Cochrane Library, and Web of Science databases were searched for relevant publications published between January 1950 and October 2016 and a total of 688 potentially eligible studies were identified.

RESULTS

Following review, 47 primary studies were eligible for inclusion. The Critical Appraisal Skills Programme checklist was used to assess study quality. Five studies were of excellent quality; the remainder were either mediocre or poor. Increased risk of low birth weight, low size for gestational age, preterm birth, and congenital defects following in-utero exposure to all antihypertensive agents were identified. Two studies reported an increased risk of attention deficit hyperactivity disorder following exposure to labetalol, and an increased risk of sleep disorders following exposure to methyldopa and clonidine.

CONCLUSION

The current systematic review demonstrates a paucity of relevant published high-quality studies. A small number of studies suggest possible increased risk of adverse child health outcomes; however, most published studies have methodological weaknesses and/or lacked statistical power thus preventing any firm conclusions being drawn.

[Affective disorders during pregnancy : Therapy with antidepressants and mood stabilizers]

BACKGROUND

It is not rare that the first manifestation or relapse of an affective disorder occurs during pregnancy. Should a pharmacological treatment be indicated, the selection of a suitable substance should be made on a basis which is as safe as possible. Even when treating women of childbearing age it should be assured that the psychotropic drug selected is safe to use during pregnancy as a high percentage of pregnancies are unplanned.

OBJECTIVE

When assessing the risks and benefits of psychopharmacotherapy in women who are or wish to get pregnant, not only the exposure of the child to potentially teratogenic drug effects but also potential complications during or after pregnancy and long-term neuropsychological issues need to be addressed.

METHODS

This article provides an overview of the currently available literature on the use of antidepressants and mood stabilizers during pregnancy.

RESULTS

A growing body of increasingly reliable data for many antidepressants and mood stabilizers are available, which allow a good prediction of their suitability for use during pregnancy and lactation.

CONCLUSION

When treating affective disorders during pregnancy an individual assessment of the benefits and risks for mother and child is required. The benefit of an appropriate treatment for the mother by including medication which may be potentially harmful to the child versus the risk of an insufficient treatment for the mother by excluding medication which may be potentially harmful to both the mother and the child need to be weighed up. When a suitable psychopharmacotherapy during pregnancy has been selected, the risk for mother and child can be minimized by incorporation of therapeutic drug monitoring.

[Psychopharmacotherapy during pregnancy : Which antipsychotics, tranquilizers and hypnotics are suitable?]

BACKGROUND

When administering psychotropic drugs during pregnancy not only the potential teratogenic effects on the child must be addressed but also the fetotoxic implications for pregnancy and/or the peripartum phase as well as possible neurocognitive developmental disorders must be considered.

OBJECTIVE

Evaluation of the risks and benefits of administering psychotropic drugs during pregnancy or for women who wish to become pregnant.

METHODS

The literature has been reviewed with the purpose of providing information on psychotropic drugs which can safely be administered during pregnancy. The review considers antipsychotics as well as tranquilizers and hypnotics.

RESULTS

Data are available for a multitude of psychotropic drugs that allow a safe estimation on their suitability for use during pregnancy.

CONCLUSION

When treating mental illnesses during pregnancy the option of administering drugs must not principally be ruled out. What is required is an individual assessment of benefits and risks. The risk of an untreated mental illness versus the benefit of a suitable treatment, which may include the use of medication and the potential harm to the infant must be evaluated. If certain rules are observed and a suitable drug is selected the risk to the newborn child and/or mother during pregnancy can be minimized. During pregnancy, therapeutic drug monitoring is indicated and increases the safety for use of drugs and preventing harm to both mother and infant.

Salivary Monitoring of Antiepileptic Drugs

Therapeutic drug monitoring is widely used in the anticonvulsant treatment of persons with epilepsy. Most monitoring uses serum, but many anticonvulsant drugs can as easily be monitored using saliva, including phenobarbital, phenytoin, carbamazepine, lamotrigine, oxcarbazepine, topiramate, levetiracetam, and gabapentin. For highly protein-bound medications such as phenobarbital, phenytoin, and carbamazepine, saliva has the advantage of providing an approximation of the serum free level, the free level presumably being the active moiety. Salivary therapeutic drug monitoring offers a number of advantages over serum therapeutic drug monitoring, including lack of pain, lower cost, and wide potential acceptability by patients and physicians. It has the potential to open new approaches to treatment with strategic at-home monitoring at the time a seizure or adverse event occurs and to allow the collection of cohort-based, pharmacokinetic, and pharmcodynamic data for populations of persons of varying ages and with different medical conditions who require anticonvulsant medications.

Maternal-Fetal Cancer Risk Assessment of Ochratoxin A during Pregnancy

Increasing evidence has demonstrated that in utero exposure to environmental chemicals may interfere with fetal development and increase the risk of disease and cancer development later in life. Ochratoxin A (OTA) has been proven to induce diverse toxic effects including teratogenicity, carcinogenicity, immunotoxicity and potential endocrine disruption. Due to the continuous and widespread occurrence of OTA as a potential contaminant of staple foods, there is increasing concern of in utero exposure of fetus to this mycotoxin. In this study, maternal-fetal risk assessment of OTA during pregnancy was conducted using the benchmark dose approach for genotoxic carcinogens. The daily intake of OTA for Egyptian pregnant women was estimated based on their serum OTA level using the refined Klaassen equation for pregnancy. Fetal exposure level was also estimated based on the maternal data. Comparison between the estimated daily exposure and the negligible cancer risk intake (NCRI), and the calculation of margin of exposure (MOE) implicated that OTA exposure from dietary intake would be of low health concern for this general subpopulation of Egyptian women. This subpopulation of pregnant women was generally estimated not to be in high-risk for toxicity induced by OTA.

Pharmacokinetics of efavirenz and treatment of HIV-1 among pregnant women with and without tuberculosis coinfection

BACKGROUND

Pregnancy and tuberculosis treatment or prophylaxis can affect efavirenz pharmacokinetics, maternal human immunodeficiency virus type 1 (HIV-1) treatment outcomes, and mother-to-child transmission (MTCT) risk.

METHODS

We evaluated a prospective cohort of pregnant, HIV-infected women with and without tuberculosis in Soweto, South Africa. Pharmacokinetic sampling was performed at gestation week 37 and during the postpartum period. Efavirenz trough concentrations (Cmin) were predicted using population pharmacokinetic models. HIV-viral load was measured at delivery for mothers and at 6 weeks of age for infants.

RESULTS

Ninety-seven women participated; 44 had tuberculosis. Median efavirenz Cmin during pregnancy was 1.35 µg/mL (interquartile range [IQR], 0.90-2.07 µg/mL; 27% had an efavirenz Cmin of < 1 µg/mL), compared with a median postpartum value of 2.00 µg/mL (IQR, 1.40-3.59 µg/mL; 13% had an efavirenz Cmin of < 1 µg/mL). A total of 72% of pregnant women with extensive CYP2B6 genotypes had an efavirenz Cmin of <1 µg/mL. Rifampin did not reduce the efavirenz Cmin. Isoniazid (for prophylaxis or treatment), though, reduced the rate of efavirenz clearance. At delivery, median durations of ART were 13 weeks (IQR, 9-18 weeks) and 21 weeks (IQR, 13-64 weeks) for women with and those without tuberculosis, respectively; 55% and 83%, respectively, had a viral load of <20 copies/mL (P = .021). There was 1 case of MTCT.

CONCLUSIONS

Pregnancy increased the risk of low efavirenz concentrations, but MTCT was rare. A detectable HIV-viral load at delivery was more common among pregnant women with tuberculosis, in whom ART was generally initiated later.

Perceptions by pregnant and childbearing-age women in southern Brazil towards teratogenic risk from medicines and radiotherapy

Mistaken perception of teratogenic risk can keep pregnant women from using safe medicines. The current study analyzed women’s concepts and perceptions towards teratogenic risk from medicines and exposure to radiotherapy during pregnancy. The quantitative data resulted from interviews with 287 pregnant and non-pregnant women. Two qualitative focus groups were conducted. No significant differences were observed between the two groups in terms of perceptions of teratogenic risk. Median perceptions of non-teratogenic exposures (paracetamol and metoclopramide) were close to the expected values, while higher values were found for teratogenic exposures (misoprostol and radiotherapy). The logic women used to estimate risk was classification of medicines as “strong” or “weak”. Medicines perceived as “weak” by the women do not pose any teratogenic risk, as shown by the median perceptions close to the true values. Meanwhile, “strong” medicines were viewed as dangerous, thus explaining the high median perceptions of teratogenic exposures.

Effects of nanoparticle size and gestational age on maternal biodistribution and toxicity of gold nanoparticles in pregnant mice

Gold nanoparticles (GNPs) have considerable applications in biomedicine, such as in bio-sensing, bio-imaging, drug delivery and photothermal therapeutics. However, currently there are limited information regarding the impact of pregnancy on their biodistribution, elimination and toxicity. In this study, we investigated the biodistribution and potential toxic effects of different-sized GNPs (1.5, 4.5, 13, 30 and 70 nm in diameter) in non-pregnant and pregnant mice at different gestational ages (E5.5, 7.5, 9.5, 11.5 and 13.5). 5h after intravenous injection, GNPs exhibited size-dependent biodistribution profiles; however, regardless of size, no significant biodistribution changes were observed between non-pregnant and pregnant mice. Kinetic studies showed that 4.5 nm GNPs were primarily excreted through urine within 5h, whereas 30 nm GNPs had a more prolonged blood circulation time. No apparent toxic effects (e.g., increased mortality, altered behavior, reduced animal weight, abnormal organ morphology or reduced pregnancy duration) were observed with different-sized GNPs in pregnant mice. However, treatment with 30 nm GNPs induced mild emphysema-like changes in lungs of pregnant mice. These results indicated that the maternal biodistribution patterns of GNPs in pregnant mice depended on particle size, but not gestational age; organ-specific adverse effects may arise with treatment with some GNPs according to their size.

Therapeutic drug monitoring in a developing nation: a clinical guide

Therapeutic drug monitoring is aimed at using drug concentration measurements to manage a patient's medication requirement and optimise clinical outcome, particularly in respect of drugs with narrow therapeutic index. Typically, immunoassay methods of various techniques are employed with the advantage of rapid turnaround time and ease of operation. The chromatographic methods are specific and cost effective, though more demanding and require technical expertise. The most crucial aspect of any therapeutic drug monitoring service is the expert clinical interpretation of drug concentration measurements taking into consideration individual pharmacokinetic variability in drug disposition across different populations. The setting up of a therapeutic drug monitoring service requires enormous resources, both in terms of equipment and trained personnel. This poses considerable constraints in developing countries due to limited scarce resources, coupled with ignorance among health practitioners on the relevance of therapeutic drug monitoring in clinical practice. Consequently, the need for advocacy, training and encouragement of health practitioners on the usefulness of therapeutic drug monitoring in enhancing patient care and overall clinical outcome in a developing country such as Nigeria can never be over-emphasised.

Concentrations of venlafaxine and its main metabolite O-desmethylvenlafaxine during pregnancy

WHAT IS KNOWN AND OBJECTIVE

Depression during pregnancy is common and includes risks for mother and child. Pharmacokinetics of venlafaxine may be changed during pregnancy. This study aimed to describe changes in metabolic ratios and concentrations of venlafaxine and its main metabolite O-desmethylvenlafaxine during and after pregnancy.

METHODS

To study this, we used data from our study of compliance to Antidepressants During Pregnancy (the ADAP study) to investigate the course of venlafaxine and O-desmethylvenlafaxine concentrations during pregnancy and in the period post-partum.

RESULTS AND DISCUSSION

We found that the venlafaxine concentration significantly changed during pregnancy when compared to the post-partum period (P = 0·028). The median concentration of venlafaxine in the first trimester was 98·9% (54·2-292·0%), the second 100·0% (46·5-264·0%) and the third trimester 87·0% (61·5-217·2%). We did not found differences in O-desmethylvenlafaxine concentrations in the different trimesters of pregnancy compared with the post-partum period, P = 0·565. Also the ratio of O-desmethylvenlafaxine/venlafaxine concentrations increased significantly from 76·9% (range 32·8-142·0%) in the first trimester to 196·7% (range 83·3-427·6%) in the third trimester compared with the post-partum period, P = 0·004. Further, three of seven patients had concentrations below the therapeutic reference range (100-400 μg/L) in any period of pregnancy, whereas no one had subtherapeutic concentrations in the post-partum period.

WHAT IS NEW AND CONCLUSION

Venlafaxine concentrations decreases during pregnancy, and the ratio of the concentrations of O-desmethylvenlafaxine/venlafaxine increases during pregnancy. Pregnant women using venlafaxine are at risk for subtherapeutic concentrations, therefore routine monitoring of concentrations venlafaxine and O-desmethylvenlafaxine is recommendable during pregnancy.

Ochratoxin A: developmental and reproductive toxicity-an overview

Ochratoxin A (OTA) is nephrotoxic, hepatotoxic, reprotoxic, embryotoxic, teratogenic, neurotoxic, immunotoxic, and carcinogenic for laboratory and farm animals. Male and female reproductive health has deteriorated in many countries during the last few decades. A number of toxins in environment are suspected to affect reproductive system in male and female. OTA is one of them. OTA has been found to be teratogenic in several animal models including rat, mouse, hamster, quail, and chick, with reduced birth weight and craniofacial abnormalities being the most common signs. The presence of OTA also results in congenital defects in the fetus. Neither the potential of OTA to cause malformations in human nor its teratogenic mode of action is known. Exposure to OTA leads to increased embryo lethality manifested as resorptions or dead fetuses. The mechanism of OTA transfer across human placenta (e.g., which transporters are involved in the transfer mechanism) is not fully understood. Some of the toxic effects of OTA are potentiated by other mycotoxins or other contaminants. Therefore, OTA exposure of pregnant women should be minimized. OTA has been shown to be an endocrine disruptor and a reproductive toxicant, with abilities of altering sperm quality. Other studies have shown that OTA is a testicular toxin in animals. Thus, OTA is a biologically plausible cause of testicular cancer in man.

Characteristics and publication patterns of obstetric studies registered in ClinicalTrials.gov

Physiologic changes during pregnancy alter the pharmacokinetics, safety, and efficacy of many drugs. For clinicians, there is often uncertainty regarding the safety of these drugs due to a scarcity of published data. This study aimed to comprehensively evaluate the characteristics and publication patterns of obstetric studies registered in ClinicalTrials.gov from 2007 to 2012. Primary outcome measures, funding sources, inclusion criteria, and the reporting of study results were evaluated. A manual review of Medline/PubMed was performed to identify publications associated with studies registered in ClinicalTrials.gov. Of 93,709 total studies, there were 5,203 (6%) obstetric studies registered in ClinicalTrials.gov. Interventional studies accounted for 70% and 30% were observational. Clinical trials of drugs (49%), procedures (13%), and behavioral interventions (12%) were most common. Among interventional drug trials, 84% featured randomized allocation to study arms and 93% included measures of safety and/or efficacy as primary endpoints. Of 946 (18%) studies completed more than 2 years ago, only 11% had reported results and <7% had been published. In an area with a great need for evidence of safe and effective therapies, the low publication rate of completed studies incorporating elements of high-quality trial design is concerning. The sources of this trend should be closely investigated.

Therapeutic drug monitoring in pregnancy

Therapeutic drug monitoring (TDM) is commonly recommended to optimize drug dosing regimens of various medications. It has been proposed to guide therapy in pregnant women, in whom physiological changes may lead to altered pharmacokinetics resulting in difficulty in predicting the appropriate drug dosage. Ideally, TDM may play a role in enhancing the effectiveness of treatment while minimizing toxicity of both the mother and fetus. Monitoring of drug levels may also be helpful in assessing adherence to prescribed therapy in selected cases. Limitations exist as therapeutic ranges have only been defined for a limited number of drugs and are based on data obtained in nonpregnant patients. TDM has been suggested for anticonvulsants, antidepressants, and antiretroviral drugs, based on pharmacokinetic studies that have shown reduced drug concentrations. However, there is only relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Further studies are required to determine whether implementation of TDM during pregnancy improves outcome and is associated with any benefit beyond that achieved by clinical judgment alone. The cost effectiveness of TDM programs during pregnancy also remains to be examined.

When one drug affects 2 patients: a review of medication for the management of nonlabor-related pain, sedation, infection, and hypertension in the hospitalized pregnant patient

One of the most difficult challenges health care providers encounter is drug selection for pregnant patients. Drug selection can be complex as efficacy and maternal side effects must be weighed against potential risk to the embryo or fetus. Verification of an individual drug's fetal safety is limited as most evidence is deduced from epidemiologic, prospective cohort, or case-control studies. Medication selection for the pregnant inpatient is a particularly complex task as the illnesses and conditions that require hospitalization mandate different medications, and the risk versus benefit ratio can vary significantly compared to the outpatient setting. Some degree of acute pain is not uncommon among inpatients. Acetaminophen is generally considered the drug of choice in pregnancy for mild to moderate acute pain, while most opioids are thought to be safe for short-term use to manage moderate to severe pain. Providing sedation is particularly challenging as the few options available for the general population are further limited by either known increased risk of congenital malformations or very limited human pregnancy data. Propofol is the only agent recommended for continuous sedation, which has a Food and Drug Administration classification as a pregnancy category B medication. Treatment of infections in hospitalized patients requires balancing the microbiology profile against the fetal risk. Older antimicrobials proven generally safe include beta-lactams, and those with proven fetal risks include tetracyclines. However, little to no information regarding gestational use is available on the newer antimicrobials that are frequently employed to treat resistant infections more commonly found in the inpatient setting. Management of maternal blood pressure is based on the severity of blood pressure elevations and not the hypertensive classification. Agents generally considered safe to use in hypertensive pregnant patients include methyldopa, labetolol, and hydralazine, while angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, hydrochlorothiazide, and atenolol should be avoided.

Fate of the teratogenic and carcinogenic ochratoxin A in human perfused placenta

Ochratoxin A (OTA) is one of the most frequent mycotoxins detected in human blood worldwide. Apart from its well known nephrotoxicity, OTA-induced teratogenicity and carcinogenicity proven in animals are potential effects also in humans. Pregnant women have been exposed to this food contaminant via dietary exposure in a continuous and widespread manner. Although the transplacental transfer of OTA has been demonstrated in laboratory animals and the presence of OTA in human fetal samples has been reported, little is known about the role of human placenta in OTA toxicokinetics. In this study, human perfused placenta was used to reveal the actual placental toxicokinetics of OTA using concentrations found in serum of pregnant women. Moreover, the effect of protein concentration and biological significance of placental transporters on the OTA transfer in human placenta were also determined. Our study is the first to pursue the transfer of OTA through perfused human placenta. The transfer of OTA through term human placenta was barely detectable in all perfusions. Inhibitors of neither ABCG2 nor ABCC2 increased the transport of OTA to fetal circulation in placental perfusion, and thus these transporters apparently do not have biological significance in inhibiting transplacental transfer of OTA. Human albumin has inhibited OTA transfer through a tight monolayer of BeWo b30 cells. Finding from this study clearly contradict the existing epidemiological studies reporting higher OTA levels in fetal than in maternal circulation in vivo.

Metabolism of bupropion by baboon hepatic and placental microsomes

The aim of this investigation was to determine the biotransformation of bupropion by baboon hepatic and placental microsomes, identify the enzyme(s) catalyzing the reaction(s) and determine its kinetics. Bupropion was metabolized by baboon hepatic and placental microsomes to hydroxybupropion (OH-BUP), threo- (TB) and erythrohydrobupropion (EB). OH-bupropion was the major metabolite formed by hepatic microsomes (Km 36±6 μM, Vmax 258±32 pmol mg protein(-1) min(-1)), however the formation of OH-BUP by placental microsomes was below the limit of quantification. The apparent Km values of bupropion for the formation of TB and EB by hepatic and placental microsomes were similar. The selective inhibitors of CYP2B6 (ticlopidine and phencyclidine) and monoclonal antibodies raised against human CYP2B6 isozyme caused 80% inhibition of OH-BUP formation by baboon hepatic microsomes. The chemical inhibitors of aldo-keto reductases (flufenamic acid), carbonyl reductases (menadione), and 11β-hydroxysteroid dehydrogenases (18β-glycyrrhetinic acid) significantly decreased the formation of TB and EB by hepatic and placental microsomes. Data indicate that CYP2B of baboon hepatic microsomes is responsible for biotransformation of bupropion to OH-BUP, while hepatic and placental short chain dehydrogenases/reductases and to a lesser extent aldo-keto reductases are responsible for the reduction of bupropion to TB and EB.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

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.

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.

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.

Therapeutic monitoring of antiepileptic drugs during pregnancy and in the postpartum period: is it useful?

As in all patient populations, epilepsy is common in pregnant women. Consequently, approximately 1 in 200 pregnancies is exposed to antiepileptic drugs (AEDs). Although exposure to AEDs in utero has been associated with an increased risk of major fetal malformations, most women with epilepsy require medication throughout pregnancy, since seizures themselves may be potentially harmful not only for the mother but also for the developing fetus. Physiological changes during pregnancy result in a reduction in the serum concentrations of most AEDs, particularly in late pregnancy. Changes in protein binding lead to a greater reduction in total than free (active) drug concentrations. Pharmacokinetic changes in pregnancy show interindividual variability and are not well understood for most newer AEDs. However, recent studies have shown that changes in lamotrigine clearance are particularly marked, with increases in each trimester and a significant fall in plasma concentrations, leading to consequent breakthrough seizures in some women. Concentrations may then rise precipitously after delivery, leading to symptoms of lamotrigine toxicity. Therapeutic drug monitoring could theoretically guide adjustment of AED dosage to achieve good seizure control while minimising fetal exposure, although there are several limitations to such monitoring. Firstly, there are wide interindividual variations in serum drug concentrations, with seizure control often correlating poorly with a given therapeutic range. Secondly, therapeutic ranges have not been well defined for newer AEDs and their measurement is often not always available. Thirdly, for highly protein-bound drugs, although measurement of free drug concentrations may more accurately reflect drug availability during pregnancy than total drug concentrations, assays for this are not always available and may be unreliable. Thus, it may be useful, prior to pregnancy, to establish the total and free drug concentrations required to achieve optimal seizure control in a given individual. Regular monitoring of AEDs has been advocated in each trimester and shortly after delivery, with adjustment of dosage to avoid seizure precipitation during pregnancy or symptoms of toxicity after birth. More frequent monitoring has been recommended for lamotrigine. However, aggressive drug monitoring of any AED has yet to be proven to be effective in improving seizure control or care. Furthermore, higher doses may be associated with a greater potential for teratogenicity and it is not yet known whether longer term adverse effects may be related to in utero exposure in the latter half of pregnancy. There is limited evidence about the relationship of maternal serum drug concentrations and teratogenicity. While there is a theoretical role for therapeutic drug monitoring in improving the risk-to-benefit ratio of AED therapy during pregnancy, there are many practical limitations. Future work is needed to clarify its role in improving seizure control during pregnancy and identifying serum drug concentrations that may be considered safe for fetal exposure.

Therapeutic drug monitoring of psychoactive drugs during pregnancy in the genomic era: challenges and opportunities

Various symptoms of mental illness occur commonly during pregnancy. It is estimated that serious mental disorders, including major depression, bipolar disorder, schizophrenia, panic and other anxiety disorders, occur with a frequency of 10 to 25% in community samples of US women in their child-bearing years. As a result, approximately a third of all women take at least one psychoactive drug during pregnancy. Fetal drug exposure has been documented for all psychoactive drugs studied to date. However, the rate and extent of placental transfer within and between psychoactive drug classes remains ill defined. The contribution of various genetic factors such as the role of polymorphic drug metabolizing enzymes and drug transporters in controlling the variability of fetal drug exposure is also unclear. Therapeutic drug monitoring (TDM) has traditionally played an important role in psychiatric pharmacotherapy during pregnancy to ensure an adequate drug dose to achieve desired benefits while avoiding excessive fetal accumulation for drugs. In the genomic era, individualized treatment with specific drugs tailored to the mother's and fetus's genotype should eventually become the standard of care. Several methodological problems need to be overcome for this prediction to become reality. One approach to this goal taken by the Specialized Center of Research on Sex and Gender Factors Affecting Women's Health at the Emory University Women's Mental Health Program is described. This research is grounded on TDM of pregnant women receiving antidepressants, antipsychotics, anti-epileptic drugs and mood stabilizers. The use of pharmacokinetic and pharmacogenetic models to predict maternal plasma drug concentrations, fetal drug exposure, and maternal and neonatal outcomes, is expected to improve our understanding of dose-response relationships of psychoactive drugs in pregnancy.

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

Observational studies have documented that women take a variety of medications during pregnancy. It is well known that pregnancy can induce changes in the plasma concentrations of some drugs. The use of mechanistic-based approaches to drug interactions has significantly increased our ability to predict clinically significant drug interactions and improve clinical care. This same method can also be used to improve our understanding regarding the effect of pregnancy on pharmacokinetics of drugs. Limited studies suggest bioavailability of drugs is not altered during pregnancy. Increased plasma volume and protein binding changes can alter the apparent volume of distribution (Vd) of drugs. Through changes in Vd and clearance, pregnancy can cause increases or decreases in the terminal elimination half-life of drugs. Depending on whether a drug is excreted unchanged by the kidneys or which metabolic isoenzyme is involved in the metabolism of a drug can determine whether or not a change in dosage is needed during pregnancy. The renal excretion of unchanged drugs is increased during pregnancy. The metabolism of drugs catalysed by select cytochrome P450 (CYP) isoenzymes (i.e. CYP3A4, CYP2D6 and CYP2C9) and uridine diphosphate glucuronosyltransferase (UGT) isoenzymes (i.e. UGT1A4 and UGT2B7) are increased during pregnancy. Dosages of drugs predominantly metabolised by these isoenzymes or excreted by the kidneys unchanged may need to be increased during pregnancy in order to avoid loss of efficacy. In contrast, CYP1A2 and CYP2C19 activity is decreased during pregnancy, suggesting that dosage reductions may be needed to minimise potential toxicity of their substrates. There are limitations to the available data. This analysis is based primarily on observational studies, many including small numbers of women. For some isoenzymes, the effect of pregnancy on only one drug has been evaluated. The full-time course of pharmacokinetic changes during pregnancy is often not studied. The effect of pregnancy on transport proteins is unknown. Drugs eliminated by non-CYP or non-UGT pathways or multiple pathways will need to be evaluated individually. In conclusion, by evaluating the pharmacokinetic data of a variety of drugs during pregnancy and using a mechanistic-based approach, we can start to predict the effect of pregnancy for a large number of clinically used drugs. However, because of the limitations, more clinical, evidence-based studies are needed to fully elucidate the effects of pregnancy on the pharmacokinetics of drugs.

Managing drugs safely

There is hard data to show that newborn infants are more likely than adults to experience adverse reactions to drugs. Paradoxically, drug-related legislation to ensure safe and effective drug use in humans neglected neonates until 2002, when the Best Pharmaceuticals Act for Children was signed into law in the USA. The situation for neonates should now catch up with that for adults and neonates will be prescribed more licensed drugs in the near future. If we are to be able to analyze the underlying system errors to improve the safe use of drugs in the studied patient population, reporting of adverse drug events and reactions needs to happen in a blame free environment. In addition, computerized physician order entry will certainly further improve the current situation by preventing errors in ordering, transcribing, verifying, and transmitting medication orders.

Nelfinavir plasma concentrations are low during pregnancy

Plasma nelfinavir concentration ratios (CRs) were calculated for all pregnant (n=27) and nonpregnant (n=48) human immunodeficiency virus type 1-infected women receiving the drug who visited our outpatient clinic. In pregnant women, mean and median nelfinavir CRs were significantly lower (P=.02 and P=.04, respectively), and 51% of the CRs were below the clinically relevant threshold of 0.90, compared with 35% of the CRs in nonpregnant women. After we adjusted for confounders, we found that the mean nelfinavir CR was 34% lower in pregnant women (P=.02). With targeted interventions, subsequent CRs in pregnant women showed a significant increase (median increase, 0.31; P=.01).