Drug and environmental factors associated with adverse pregnancy outcomes. Part I: Antiepileptic drugs, contraceptives, smoking, and folate

Association of paternal smoking with the risk of neural tube defects in offspring: A systematic review and meta-analysis of observational studies

PURPOSE

The present study aimed at providing some epidemiological evidences to assess the association of paternal smoking with the risk of neural tube defects (NTDs) and its specific subtypes in offspring, and explore the possible dose-response relationship between paternal smoking and risk of NTDs.

METHODS

English and Chinese databases were systematically searched from 1984 to May 2020. Either a fixed- or a random-effects model was used to calculate the overall combined risk estimates. We also examined the dose-response relationship between parental smoking and risk of NTDs in offspring. Subgroup analyses and sensitivity analyses were conducted to explore possible sources of heterogeneity.

RESULTS

A total of 10 case-control studies involving 2,593 cases of NTDs and 45,100 controls were included for analysis. Findings from our study showed that paternal smoking was significantly associated with risk of total NTDs (odds ratio [OR] = 1.68; 95% confidence interval (CI): 1.48-1.92) and two subtypes including anencephaly (OR = 1.41; 95% CI: 1.06-1.86) and encephaloceles (OR = 2.90; 95% CI: 1.00-8.41). Additionally, a linear dose-response relationship between paternal smoking and risk of NTDs was observed, which indicated that the risk of NTDs in offspring was significantly increased by 45% (OR = 1.45, 95% CI: 1.14-1.84) for each increment of half a pack of cigarettes per day. Sensitivity analyses yielded consistent results. No evidence of publication bias was found.

CONCLUSIONS

Paternal smoking is significantly associated with the risk of NTDs in offspring. Therefore, it should be recommended that fathers quit smoking before pregnancy to prevent NTDs in offspring.

Prevalence of highly effective contraception use by women with epilepsy

OBJECTIVE

To determine (1) the proportion of women with epilepsy (WWE) at risk of unintended pregnancy who use highly effective contraception, (2) demographic predictors, and (3) folic acid (FA) use.

METHODS

These cross-sectional data come from 311 US WWE, 18-47 years, who participated in the Epilepsy Birth Control Registry (EBCR) web-based survey in 2017. They provided demographic, epilepsy, antiepileptic drug (AED), contraceptive, and FA data. We report frequencies of highly effective contraception use and use logistic regression to determine demographic predictors. We report the proportion who take FA.

RESULTS

A total of 186 (59.8%) of the 311 WWE were at risk of unintended pregnancy. A total of 131 (70.4%) used a highly effective contraceptive category; 55 (29.6%) did not. An additional 13 (7.0%) used a combination of generally effective hormonal contraception with an enzyme-inducing AED, which poses increased risk of unintended pregnancy. Overall, 68 (36.6%) of the 186 WWE at risk did not use highly effective contraception. Increasing income (p = 0.004) and having insurance (p = 0.048) were predictors of highly effective contraception. A total of 50.0% took FA supplement. There was no significant difference in relation to the use or lack of use of highly effective contraception.

CONCLUSION

A total of 36.6% of WWE in the EBCR did not use highly effective contraception and 50.0% did not take FA in 2017 despite the important negative consequences of unintended pregnancy on pregnancy outcomes. There is a need for more readily available information and counseling on safe and effective contraception and FA use for this community.

Medicines associated with folate-homocysteine-methionine pathway disruption

Folate is vital for cell development and growth. It is involved in one-carbon transfer reactions essential for the synthesis of purines and pyrimidines. It also acts in conjunction with cobalamin (vitamin B₁₂) as a fundamental cofactor in the remethylation cycle that converts homocysteine to methionine. A deficiency in folate or vitamin B₁₂ can lead to elevated homocysteine level, which has been identified as an independent risk factor in several health-related conditions. Adequate folate levels are essential in women of childbearing age and in pregnant women, and folate deficiency is associated with several congenital malformations. Low folate levels can be caused by dietary deficiencies, a genetic predisposition or treatment with medicines that affect folate concentration. Women who are pregnant or of child-bearing age commonly use medicines, so it is important to identify the basic biochemical mechanisms by which medicines interfere with the folate-homocysteine-methionine pathway. This review focuses on prescription medicines associated with folate disruption. It also summarizes their undesirable/toxic effects. Recommendations regarding folate supplementation during medical therapy are also reviewed.

Maternal use of oral contraceptives and risk of birth defects in Denmark: prospective, nationwide cohort study

STUDY QUESTION

Is oral contraceptive use around the time of pregnancy onset associated with an increased risk of major birth defects?

METHODS

In a prospective observational cohort study, data on oral contraceptive use and major birth defects were collected among 880,694 live births from Danish registries between 1997 and 2011. We conservatively assumed that oral contraceptive exposure lasted up to the most recently filled prescription. The main outcome measure was the number of major birth defects throughout one year follow-up (defined according to the European Surveillance of Congenital Anomalies classification). Logistic regression estimated prevalence odds ratios of any major birth defect as well as categories of birth defect subgroups.

STUDY ANSWER AND LIMITATIONS

Prevalence of major birth defects (per 1000 births) was consistent across each oral contraceptive exposure group (25.1, never users; 25.0, use >3 months before pregnancy onset (reference group); 24.9, use 0-3 months before pregnancy onset (that is, recent use); 24.8, use after pregnancy onset). No increase in prevalence of major birth defects was seen with oral contraceptive exposure among women with recent use before pregnancy (prevalence odds ratio 0.98 (95% confidence interval 0.93 to 1.03)) or use after pregnancy onset (0.95 (0.84 to 1.08)), compared with the reference group. There was also no increase in prevalence of any birth defect subgroup (for example, limb defects). It is unknown whether women took oral contraceptives up to the date of their most recently filled prescription. Also, the rarity of birth defects made disaggregation of the results difficult. Residual confounding was possible, and the analysis lacked information on folate, one of the proposed mechanisms.

WHAT THIS STUDY ADDS

Oral contraceptive exposure just before or during pregnancy does not appear to be associated with an increased risk of major birth defects.

FUNDING, COMPETING INTERESTS, DATA SHARING

BMC was funded by the Harvard T H Chan School of Public Health's Maternal Health Task Force and Department of Epidemiology Rose Traveling Fellowship; training grant T32HD060454 in reproductive, perinatal, and paediatric epidemiology and award F32HD084000 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development; and grant T32CA09001 from the National Cancer Institute. The authors have no competing interests or additional data to share.

Risk of spina bifida and maternal cigarette, alcohol, and coffee use during the first month of pregnancy

This study was conducted to assess the association between the risks of spina bifida (SB) in relation to cigarette, alcohol, and caffeine consumption by women during the first month of pregnancy. Between 1988–2012, this multi-center case-control study interviewed mothers of 776 SB cases and 8,756 controls about pregnancy events and exposures. We evaluated cigarette smoking, frequency of alcohol drinking, and caffeine intake during the first lunar month of pregnancy in relation to SB risk. Logistic regression models were used to calculate adjusted odds ratios and 95% confidence intervals. Levels of cigarette smoking (1–9 and ≥10/day), alcohol intake (average ≥4 drinks/day) and caffeine intake (<1, 1, and ≥2 cups/day) were not likely to be associated with increased risk of SB. Further, results were similar among women who ingested less than the recommended amount of folic acid (400 μg/day).

New perspectives on folate transport in relation to alcoholism-induced folate malabsorption--association with epigenome stability and cancer development

Folates are members of the B-class of vitamins, which are required for the synthesis of purines and pyrimidines, and for the methylation of essential biological substances, including phospholipids, DNA, and neurotransmitters. Folates cannot be synthesized de novo by mammals; hence, an efficient intestinal absorption process is required. Intestinal folate transport is carrier-mediated, pH-dependent and electroneutral, with similar affinity for oxidized and reduced folic acid derivatives. The various transporters, i.e. reduced folate carrier, proton-coupled folate transporter, folate-binding protein, and organic anion transporters, are involved in the folate transport process in various tissues. Any impairment in uptake of folate can lead to a state of folate deficiency, the most prevalent vitamin deficiency in world, affecting 10% of the population in the USA. Such impairments in folate transport occur in a variety of conditions, including chronic use of ethanol, some inborn hereditary disorders, and certain diseases. Among these, ethanol ingestion has been the major contributor to folate deficiency. Ethanol-associated folate deficiency can develop because of dietary inadequacy, intestinal malabsorption, altered hepatobiliary metabolism, enhanced colonic metabolism, and increased renal excretion. Ethanol reduces the intestinal and renal uptake of folate by altering the binding and transport kinetics of folate transport systems. Also, ethanol reduces the expression of folate transporters in both intestine and kidney, and this might be a contributing factor for folate malabsorption, leading to folate deficiency. The maintenance of intracellular folate homeostasis is essential for the one-carbon transfer reactions necessary for DNA synthesis and biological methylation reactions. DNA methylation is an important epigenetic determinant in gene expression, in the maintenance of DNA integrity and stability, in chromosomal modifications, and in the development of mutations. Ethanol, a toxin that is consumed regularly, has been found to affect the methylation of DNA. In addition to its effect on DNA methylation due to folate deficiency, ethanol could directly exert its effect through its interaction with one-carbon metabolism, impairment of methyl group synthesis, and affecting the enzymes regulating the synthesis of S-adenosylmethionine, the primary methyl group donor for most biological methylation reactions. Thus, ethanol plays an important role in the pathogenesis of several diseases through its potential ability to modulate the methylation of biological molecules. This review discusses the underlying mechanism of folate malabsorption in alcoholism, the mechanism of methylation-associated silencing of genes, and how the interaction between ethanol and folate deficiency affects the methylation of genes, thereby modulating epigenome stability and the risk of cancer.

Folate status in various pathophysiological conditions

Folate is the generic term for compounds that have vitamin activity similar to that of pteroylglutamic acid. Folate acts as a coenzyme in several single carbon transfers involved in biosynthesis of purine nucleotides and deoxythymidylic acid essential for DNA and RNA synthesis. In addition, folate provides one-carbon unit for methylation of a wide variety of biological substances including DNA, proteins, phospholipids, and neurotransmitters, thereby regulating their function. Recent epidemiological-clinical and experimental studies suggest the association of folate deficiency with the risk of various cancers, birth defects, and cardiovascular diseases. Thus, it is important to consider the conditions that are associated with altered folate status and their consequences. The impairment in folate status has been found in number of pathophysiological conditions like inflammatory bowel disease, cancer, alcoholism, pregnancy, neonatal growth, and during administration of some drugs. The recent advances dealing with mechanistic aspects of impaired folate status in these conditions have been discussed in this review.

Spontaneous abortion and the prophylactic effect of folic acid supplementation in epileptic women undergoing antiepileptic therapy

BACKGROUND

Antiepileptic drugs (AEDs) like phenytoin (PHE), carbamazepine (CBZ), barbiturates and valproic acid (VPA) interfere with folic acid absorption and metabolism, which in turn can be the cause of adverse pregnancy outcome.

OBJECTIVE

To study the prophylactic effect of folic acid supplementation with regard to spontaneous abortion and preterm delivery (fetal demise after week 20 of gestational age) in pregnant women receiving AED therapy, as well as benefits of most common dosage and preconceptional commencement.

METHODS

Prospective examination of 104 patients, registered in EURAP from 1999-2004 at a single center and a retrospective analysis of data from our epilepsy databank completed with medical records and patients interviews of the Department of Neurology of Innsbruck University Hospital from 1971 to 1999.

RESULTS

388 pregnancies in 244 patients were analyzed. Pregnancies with folic acid supplementation showed significant reduction of spontaneous abortion. With regard to monotherapies, in the group of women taking VPA, supplementation of folic acid had significant benefit. Other examined monotherapies (CBZ, PHE, and PB) known to interfere with folic acid showed no significant results.

CONCLUSIONS

This study confirms the prophylactic effect of folic acid supplementation on spontaneous abortion. For AED therapy, folic acid supplementation should be part of the therapy of every pregnant epileptic woman, especially for those treated with VPA.

Maternal use of oral contraceptives and risk of fetal death

Intrauterine exposure to artificial sex hormones such as oral contraceptives may be associated with an increased risk of fetal death. Between 1996 and 2002, a total of 92 719 women were recruited to The Danish National Birth Cohort and interviewed about exposures during pregnancy. Outcome of pregnancy was identified through linkage to the Civil Registration System and the National Discharge Registry. The authors analysed the risk of fetal death after recruitment to the cohort by using proportional hazards regression models with gestational age as the underlying time scale. In total, 1102 (1.2%) women took oral contraceptives during pregnancy. Use of combined oestrogen and progesterone oral contraceptives (COC) or progesterone-only oral contraceptives (POC) during pregnancy was not associated with increased hazard ratios of fetal death compared with non-users, HR 1.01 [95% CI 0.71, 1.45] and HR 1.37 [95% CI 0.65, 2.89] respectively. Neither use of COC nor POC prior to pregnancy was associated with fetal death. Stratification by maternal age and smoking showed elevated risks of fetal death for women <30 years and smokers using oral contraception during pregnancy, but the interactions were not significant. In conclusion, there was no evidence that oral contraceptive use before or during pregnancy is associated with an increased risk of fetal death.

The use of folic acid antagonists and the risk of colorectal cancer

PURPOSE

Since folate is associated with a reduced risk of colorectal cancer, we hypothesized that folic acid antagonists might increase the risk. We used data from a population-based case control study of medication use and colorectal cancer to evaluate the hypothesis.

METHODS

Case patients with adenocarcinoma of the colon or rectum were ascertained from participating hospitals in Massachusetts and the Massachusetts cancer registry (MCR) from January 1, 2001, through November 30, 2004. Age-, sex-, and precinct-matched control subjects were chosen from Massachusetts town lists. Information on folic acid antagonist use and other relevant data were obtained from 1809 cases and 1809 matched controls by telephone interview and by a self-administered dietary questionnaire. We used logistic regression models to estimate odds ratios among 1229 case patients and 1165 control subjects who provided satisfactory dietary information and did not have Crohn's disease or ulcerative colitis.

RESULTS

The odds ratio for colorectal cancer among regular users of folate-containing supplements was 0.7 (95%CI 0.6-0.9). The odds ratio for regular use of folic acid antagonists was 1.3 (95%CI 0.9-1.9). Contrary to expectation, the odds ratio was reduced in the highest category of alcohol consumption (OR = 0.5, 95%CI 0.2-1.2). The odds ratio was higher among users of drugs that inhibit dihydrofolate reductase (OR = 1.6, 95%CI 0.9-2.8) than drugs that work through other mechanisms (OR = 1.2, 95%CI 0.7-1.9).

CONCLUSIONS

Our data provide little support for the hypothesis that regular folic acid antagonist use increases the risk of colorectal cancer. However, there is a suggestion that dihydrofolate reductase inhibitors specifically may increase the risk.

Folate modulates Hox gene-controlled skeletal phenotypes

Hox genes are well-known regulators of pattern formation and cell differentiation in the developing vertebrate skeleton. Although skeletal variations are not uncommon in humans few mutations in human HOX genes have been described. If such mutations are compatible with life, there may be physiological modifiers for the manifestation of Hox gene-controlled phenotypes, masking underlying mutations. Here we present evidence that the essential nutrient folate modulates genetically induced skeletal defects in Hoxd4 transgenic mice. We also show that chondrocytes require folate for growth and differentiation and that they express folate transport genes, providing evidence for a direct effect of folate on skeletal cells. To our knowledge, this is the first report of nutritional influence on Hox gene-controlled phenotypes, and implicates gene-environment interactions as important modifiers of Hox gene function. Taken together, our results demonstrate a beneficial effect of folate on skeletal development that may also be relevant to disorders and variations of the human skeleton.

Anencephaly: MRI findings and pathogenetic theories

We describe the MRI appearances of an anencephalic newborn who survived for 13 h; particularities of this case are male gender and the absence of other associated malformations. Moreover, we discuss the pathogenetic theories of anencephaly, correlating MRI findings with embryological data. An exencephaly-anencephaly sequence due to amnion rupture is hypothesized.

Low maternal dietary intakes of iron, magnesium, and niacin are associated with spina bifida in the offspring

Evidence about the preventive effects of nutrients other than folate on the occurrence of spina bifida is scarce. Therefore, the aim of this work was to investigate the role of maternal nutritional intake and the risk of spina bifida in the offspring. In 106 cases and 181 controls, the mothers' nutrient intakes were obtained by an FFQ approximately 24 mo after conception of the index pregnancy. Energy-adjusted mean nutrient intakes were compared, and odds ratios (OR) and 95% CI were calculated. Although mean nutrient intakes were comparable to the Dutch food consumption survey data, fat, cholesterol, iron, and folate intakes were below the 1998 Dutch Recommended Daily Allowances. Case mothers had significantly lower intakes of plant proteins (7%), polysaccharides (4%), fiber (7%), iron (6%), magnesium (6%), and niacin (4%) than control mothers. Mono- and disaccharide intakes were significantly higher (6%) in the case mothers than in control mothers. The adjusted OR (95% CI) in the lowest quartiles for plant proteins was 5.4 (2.3-12.4), for fiber 3.1 (1.5-6.8), for iron 3.5 (1.4-8.3), for magnesium 1.9 (0.9-4.1), and for niacin 2.5 (1.2-5.2). Mono- and disaccharide and polysaccharide intakes in the highest quartile had ORs (95% CI) of 2.9 (1.4-6.3) and 0.5 (0.3-1.0), respectively. The nutritional intake of Dutch women from food groups containing iron and folate seems to be compromised. Low preconceptional intakes of plant proteins, iron, magnesium, and niacin are associated with a 2- to 5-fold increased risk of spina bifida.

The etiology of neural tube defects: the role of folic acid

DISCUSSION

While the cause of neural tube defects in humans is considered to be multifactorial, it is apparent that folic acid can prevent 70% of open neural tube defects. Even in laboratory animals with known genetic defects, folic acid can prevent the genetic expression.

CONCLUSION

While some of the metabolic pathways for folic acid are known, the true effects of folic acid on closure of the neural tube have yet to be discovered.

Amelioration of sodium valproate-induced neural tube defects in mouse fetuses by maternal folic acid supplementation during gestation

Infants of epileptic women treated with valproic acid (VPA) during pregnancy have a higher risk of developing spina bifida than those of the general population. VPA induces exencephaly in experimental animal embryos. But the pathogenetic mechanism remains rather elusive. Antiepileptic drugs (AED) in general accentuate pregnancy-imposed fall in maternal folate levels. Periconceptional folic acid supplementation is reported to protect embryos from developing neural tube defects (NTD). Conflicting results have been reported by experimental studies that attempted to alleviate VPA-induced NTD by folic acid. Our objectives were to determine the critical developmental stages and an effective dose of folic acid for the prevention of VPA-induced exencephaly in mouse fetuses. A single teratogenic dose of 400 mg/kg of VPA was administered to TO mice on gestation day (GD) 7 or 8. It was followed by (1) a single dose of 12 mg/kg of FA (folinic acid) or (2) 3 doses of FA 4 mg/kg each. In experiment (3), FA (4 mg/kg) was administered thrice daily starting on GD 5 and continued through GD 10. These animals received VPA on GD 7 or 8. VPA and B12 concentrations were determined by radioimmunoassay. The single heavy dose of FA had no rescue effect on NTD. Three divided doses of FA on GD 7 and continuous dosing of FA from GD 5 through GD 10 substantially reduced the VPA-induced exencephaly in the fetuses. In the later experiments, the neural folds elevated faster than the non-supplemented group. VPA considerably reduced maternal plasma folate and B12 concentrations. The heavy dose of FA only moderately improved vitamin levels. Three divided doses of FA elevated the vitamin levels slightly better but it was the prolonged dosing of FA that was associated with sustained elevation of plasma levels higher than the control levels and acceleration of neural tube closure thus accounting for the pronounced protection against VPA-induced NTD development. These data suggest that plasma levels of FA and B12 have to be kept substantially elevated and maintained high throughout organogenesis period to protect embryos against VPA-induced NTD in this mouse model.

The effect of B-vitamins on hyperhomocysteinemia in patients on antiepileptic drugs

Patients on antiepileptic drugs (AEDs) may have elevated levels of plasma total homocysteine (p-tHcy). The aim of this study was to assess the effect of B-vitamin supplementation on the levels of p-tHcy and markers of endothelial activation and lipid peroxidation. A total of 33 adult patients on AEDs were identified with either fasting (Group 1, n=23) or post methionine load (PML) (Group 2, n=10) hyperhomocysteinemia. Subjects were supplemented with B-vitamins for 30 days: folic acid 0.4 mg, pyridoxine 120 mg and riboflavin 75 mg per day. After supplementation, serum folate and pyridoxal phosphate had increased, while fasting and PML p-tHcy had decreased (P<0.0001) by 36 and 26%, respectively. Prior to supplementation, the Group 1 patients had elevated levels of P-selectin and von Willebrand factor (vWF) (P=0.05 and 0.03, respectively). After supplementation, the levels of intercellular cell adhesion molecules had decreased (P=0.01) and E-selectin decreased nonsignificantly (P=0.07). However, the levels of vascular cell adhesion molecules had increased (P<0.0001), while lipid peroxidation were unchanged. In conclusion, the combined supplementation with folic acid, pyridoxine and riboflavin reduced fasting and PML hyperhomocysteinemia in patients on AEDs. Patients with fasting hyperhomocysteinemia had elevated levels of P-selectin and vWF, which may indicate an increased risk of cardiovascular disease. Furthermore, B-vitamin supplementation influenced endothelial activation, although the clinical implication is uncertain.

Drugs in pregnancy. Anticonvulsants and drugs for neurological disease

The use of anticonvulsant drugs in pregnancy presents unique challenges to clinicians and their patients. The need for control of maternal epilepsy must be balanced with the fetal and neonatal risks associated with anticonvulsant drugs. Anticonvulsant drugs may have potential effects on embryogenesis, neurological development, growth and subsequent paediatric progress. Drug selection and dose adjustment must be appropriate and based on a combination of known maternal and fetal risks as well as the clinical status of the patient. Overall, no one drug can be specifically recommended but monotherapy with most of the recognized first-line drugs will result in a satisfactory outcome. Polytherapy is associated with an increase in congenital malformations and should be avoided if possible. It is possible that newer second-line agents, for example, gabapentin, may be safer as add-on therapy. Neurological disorders such as migraine, and the less common conditions of myasthenia gravis and multiple sclerosis, may require the use of drugs which have not been well studied in pregnancy. Information is provided about the use of drugs to control symptoms and prevent disease progression in these disorders during pregnancy.

Birth Defects and Supplemental Vitamins

Women of childbearing age who are capable of becoming pregnant should ingest 0.4 mg of folic acid per day to reduce the incidence of neural tube defects (anencephaly, spina bifida, and encephalocele). This may also reduce the incidence of conotruncal heart defects, limb defects, renal anomalies, pyloric stenosis, and possibly oral-facial clefts. Women who are at increased risk of having an affected fetus because of having had a previously affected fetus should take 4 mg of folic acid daily. Women with epilepsy, particularly those taking antiepileptic drugs, should follow the same guidelines as nonepileptic women; however, women with epilepsy should take the lowest dose and the fewest number of antiepileptic drugs needed to control the epilepsy. Physicians and the public should be educated about the benefits of supplemental folic acid and the consumption of folate-rich foods and fortified foods in reducing the incidence of neural tube defects and other congenital anomalies. They should be made aware that neural tube defects occur between 23 and 28 days of gestation, often before women know they are pregnant. Therefore, folic acid supplements need to be taken at least 1 month before the beginning of pregnancy. Because many pregnancies are unplanned, women should take folic acid supplements routinely.

Correlation between maternal toxicity and embryo/fetal effects

It has been widely debated whether embryo/fetal toxicity is secondary to maternal toxicity. This argument has led to great difficulties for administrative decision makers involved in public health evaluation of drugs or chemicals. The present study sought to characterize whether there is a correlation between maternal toxicity and embryo/fetal toxicity. Developmental data from control and treated animals in our laboratory were collected and evaluated. Maternal toxicity, defined here as maternal body weight change, was statistically correlated with embryo/fetal parameters. The result showed that embryo/fetal parameters did not correlate with the body weight change. It can be concluded that maternal toxicity does not always lead to embryo/fetal toxicity; therefore, findings should be handled on a case by case basis and causal relationships should be established.

Lamotrigine Use in Pregnancy

Objective:

To review the literature on the proposed mechanisms of teratogenicity of older antiepileptic drugs (AEDs) compared with lamotrigine.

Data Sources:

Published articles on the use of AEDs during pregnancy were identified from a comprehensive MEDLINE search of the English-language literature (January 1966-January 1998). Additional articles were selected from the references. Search terms included antiepileptic drugs, lamotrigine, and pregnancy.

Study Selection:

Only human clinical and pharmacokinetic trials and case studies performed in Europe and the US were included.

Data Synthesis:

Pharmacologic characteristics of the older AEDs that appear to contribute to teratogenicity include antifolate effects, metabolism to oxide metabolites, induction of the hepatic cytochrome P450 system, and a high degree of protein binding. The pharmacokinetics and pharmacodynamics of lamotrigine may offer advantages over other AEDs in terms of teratogenicity because lamotrigine is metabolized by the glucuronidation pathway and is not known to induce the hepatic cytochrome P450 system or to form oxide metabolites. The protein-binding capacity of lamotrigine is considerably lower than that of older AEDs, and antifolate effects have not been observed in humans.

Conclusions:

Although few data are available, lamotrigine appears to have pharmacokinetic and pharmacodynamic properties that suggest a safer outcome with its use in pregnancy compared with older AEDs.

Drug and environmental factors associated with adverse pregnancy outcomes. Part III: Folic acid: pharmacology, therapeutic recommendations, and economics

OBJECTIVE

To review folic acid's mechanism of action, adverse effects, therapeutic recommendations, compliance, and cost.

DATA SOURCES

A MEDLINE search was conducted through December 1997. Additional sources were obtained from Current Contents and citations from the references obtained. Search terms included folate, folic acid, neural tube defect, homocysteine, and methylenetetrahydrofolate reductase.

STUDY SELECTION

Animal and human studies examining the effects of folate were reviewed.

DATA EXTRACTION

Data collected included mechanism of action, safety issues, dosing recommendations, compliance with recommendations, and economics.

DATA SYNTHESIS

Folic acid decreases neural tube defect risk through an effect on methionine-homocysteine metabolism. In addition, increased folate intake may reduce cardiovascular morbidity and mortality. Since toxicity is minimal, everyone can potentially benefit from increased folate consumption. To help achieve this, the Food and Drug Administration has mandated that cereal grain be fortified with 140 micrograms of folic acid per 100 g of grain, which will add approximately 0.1 mg of folate to the average diet. Studies recommend supplementing with 0.2 mg to promote optimal homocysteine concentrations and for preventing neural tube defects.

CONCLUSIONS

Despite fortification, most women will still receive less folate than the 0.4 mg/d recommended by the Public Health Service. All population groups would benefit from increased folate intake. Current studies indicate 200 micrograms/d may be the minimum effective amount of fortification needed for normalizing homocysteine concentrations and preventing a significant number of neural tube defects; thus, a higher level of food fortification may be warranted.

Drug and environmental factors associated with adverse pregnancy outcomes. Part II: Improvement with folic acid

OBJECTIVE

To provide a comprehensive review of periconceptional folic acid supplementation and factors affecting folate supplementation trials.

DATA SOURCES

A MEDLINE search was conducted through December 1997. Additional sources were obtained from Current Contents and citations from the references obtained. Search terms included folate, folic acid, neural tube defect, spina bifida, and anencephaly.

STUDY SELECTION

Relevant animal and human studies examining the effects of folate were reviewed.

DATA EXTRACTION

Data collected included: type of study, folate dosing, dietary folate intake, serum and red blood cell folate concentrations, type of defect(s) studied, vitamin usage, parental risk factors, factors affecting trial results.

DATA SYNTHESIS

Nine key factors have been identified that affect outcomes of folic acid supplementation trials. Daily doses of 0.8 mg decreased the occurrence and doses of 4 mg decreased the recurrence of neural tube defects in randomized clinical trials. Since lower folic acid doses were effective in nonrandomized trials, research is needed to determine the lowest effective dosage. Other benefits involving pregnancy outcome are suggested.

CONCLUSIONS

Women of childbearing age should take a daily folic acid supplement to reduce the risk of pregnancies resulting in infants with a neural tube defect and other potential adverse pregnancy outcomes. Further health benefits from folic acid supplementation are reviewed in Part III of this series.