51. Drug treatment in pregnancy and teratogens
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How do drugs cross from maternal to fetal circulation?
By passive diffusion across the placenta.
What types of drugs diffuse most easily across the placenta?
Lipophilic and/or uncharged drugs.
Why does thiopental cross the placenta easily?
It is highly lipophilic.
What is a fetal effect of thiopental crossing the placenta?
It can cause sedation in the newborn.
Why does succinylcholine cross the placenta poorly?
It is a highly charged quaternary amine.
What is the likelihood of succinylcholine affecting the newborn?
Unlikely, due to poor placental transfer.
How do drugs cross from maternal to fetal circulation?
By passive diffusion across the placenta.
What types of drugs diffuse most easily across the placenta?
Lipophilic and/or uncharged drugs.
Why does thiopental cross the placenta easily?
It is highly lipophilic.
What is a fetal effect of thiopental crossing the placenta?
It can cause sedation in the newborn.
Why does succinylcholine cross the placenta poorly?
It is a highly charged quaternary amine.
What is the likelihood of succinylcholine affecting the newborn?
Unlikely, due to poor placental transfer.
How does molecular weight affect placental diffusion?
Drugs with MW < 500 diffuse easily; MW > 1000 diffuse poorly.
Why is heparin safe for anticoagulation during pregnancy?
It has a high molecular weight and is charged, so it doesn't cross the placenta well.
Why is warfarin harmful to the fetus?
It has a low molecular weight and crosses the placenta easily.
What placental function starts in the second trimester related to IgG?
Transport of maternal IgG to the fetus.
What is the benefit of maternal IgG transfer to the fetus?
It provides passive immunity before the newborn's humoral immunity is active.
When can maternal antibodies be harmful to the fetus?
In Rh incompatibility or when the mother is treated with biologics like anti-TNF agents.
What happens in Rh incompatibility?
Maternal anti-Rh antibodies cross the placenta and can cause fetal anemia.
When can anti-TNF antibodies affect the fetus?
Starting in the second trimester.
What does P-glycoprotein do in the placenta?
It actively transports some drugs back into maternal circulation.
What are two drug classes that are substrates of P-glycoprotein?
Anti-tumor drugs and viral protease inhibitors.
What role can the placenta play in drug metabolism?
It can metabolize drugs, decreasing or increasing fetal exposure.
What happens to pentobarbital in the placenta?
It is oxidized to an inactive metabolite, reducing fetal exposure.
What happens to ethanol in the placenta?
It can be converted to a more active or toxic metabolite.
Why is prednisolone safe in pregnancy?
The placenta converts it to inactive prednisone.
Why are corticosteroids given when premature delivery is likely?
To promote fetal lung maturation.
What drug is used to induce fetal hepatic enzyme expression?
Phenobarbital.
How does phenobarbital help prevent neonatal jaundice?
It induces glucuronidation enzymes that help process bilirubin.
What is neonatal abstinence syndrome (NAS)?
Withdrawal symptoms in a newborn after in utero drug exposure.
Which drugs can lead to NAS?
Illicit drugs like opioids and licit drugs like antidepressants and benzodiazepines.
How is NAS treated?
With supportive care and medications for withdrawal symptoms.
What is known about long-term effects of NAS?
Long-term risks are unclear.
What is a teratogen?
An agent that causes a characteristic set of malformations.
What does the selectivity of a teratogen indicate?
It targets specific organs.
When do teratogens exert their effects?
During specific stages of fetal development, especially organogenesis.
How does dose affect teratogenicity?
Effects show dose-dependent incidence or severity.
Are all teratogens drugs?
No, they also include infections and environmental exposures.
What are examples of infectious teratogens?
Rubella, cytomegalovirus, herpes, Zika.
What are examples of environmental teratogens?
Radiation, hyperthermia, mercury, lead.
What percentage of all births involve major congenital defects?
Up to 3%.
What percentage of congenital defects are caused by drugs?
Only about 2–3%.
What are other contributors to congenital defects besides drugs?
Genetic risks, non-drug teratogens, and combined factors.
What birth defect is thalidomide most known for causing?
Phocomelia (failure of long-bone growth).
Why was thalidomide removed from the market?
It caused severe congenital defects.
What regulatory response did thalidomide trigger in the U.S.?
FDA required animal testing for reproductive toxicity in NDAs.
What data must NDAs now include for reproductive safety?
Effects on fertility, congenital defects, fetal survival, and birth weight in two species.
What is isotretinoin used for?
Severe acne.
Why is isotretinoin contraindicated in pregnancy?
It causes severe birth defects, especially in the first trimester.
What is tretinoin (Retin-A) used for?
Topical treatment for acne.
Why is tretinoin less risky than isotretinoin in pregnancy?
It has much lower systemic absorption and no clear evidence of fetal harm.
What determines the impact of ethanol exposure during pregnancy?
Dose, frequency, and timing of exposure.
What is the estimated prevalence of Fetal Alcohol Spectrum Disorder (FASD)?
1–5%.
What are facial features associated with FASD?
Small head, flat nasal bridge, smooth philtrum, thin upper lip.
What are other risks for children with FASD?
Low birth weight, behavioral, and neurodevelopmental disorders.
Why is tobacco considered a teratogen?
It increases risk of fetal growth restriction and other complications (implied from syllabus context).
Why are anti-seizure medications considered teratogenic?
Many have known associations with birth defects (e.g., neural tube defects).
Why are statins avoided in pregnancy?
They may disrupt fetal cholesterol synthesis and development.
Why are ACE inhibitors contraindicated in pregnancy?
They can cause fetal renal and cardiovascular defects.
What was the purpose of the FDA teratogenic risk categories (1970–2015)?
To classify drug safety in pregnancy (A, B, C, D, X).
Why was FDA Category C problematic?
Over 70% of drugs were placed in it with limited additional guidance.
What has replaced the FDA letter categories for drug risk?
A narrative format with Risk Summary, Clinical Considerations, and Data.
What is the benefit of the new FDA format for pregnancy drug safety?
It allows more informed, individualized risk–benefit decisions.
Why is post-exposure counseling important in pregnancy?
Many exposures happen before pregnancy is known; patients need accurate risk information.
What does FDA pregnancy category A mean?
Controlled studies in women show no fetal risk.
What does FDA pregnancy category B mean?
Animal studies show no risk OR animal risk not confirmed in human studies.
What does FDA pregnancy category C mean?
Animal studies show fetal risk OR no studies in animals or humans.
What does FDA pregnancy category D mean?
Human fetal risk exists, but benefits may outweigh risks in serious conditions.
What does FDA pregnancy category X mean?
Fetal risk is confirmed and outweighs any possible benefit—contraindicated in pregnancy.