Prescribing in Pregnant Women Flashcards
Old FDA Pregnancy Category labeling system
A: controlled studies show no risk
B: no risk in humans; chance of fetal harm remote
C: risk not excluded; adequate studies lacking; fetal benefits outweigh harm
D: Positive evidence of risk. Studies in humans show fetal risk. Benefit MAY outweigh risk
X: contraindicated
Cons of using old labeling system for pregnancy risk
- often based on animal studies
- does not include adequate info on drug use in lactation
Pregnancy-related physiologic considerations in regards to pharmokinetics
Expanded intravascular volume
Increased progesterone activated hepatic metabolism
Increased renal blood flow and GFR
Decreased albumin
Decreased GI motility
Increased thinning of feto-maternal barrier with advancing gestation
What is the critical time when organogenesis to occurs during gestation?
first 8 weeks after fertilization (1st trimester)
Most drugs cross the placenta via ________ at a rate directly related to difference between maternal and fetal blood concentrations.
simple diffusion
Which types of substances diffuse rapidly into fetal circulation?
lipophilic
low molecular weight
Which types of substances do not diffuse into fetal circulation?
protein-bound drugs
large molecular weight
(eg. heparin, insulin)
Most drugs enter fetus via what vessel?
umbilical vein
Describe how blood gets to fetal systemic circulation from umbilical vein
60-80% perfuses liver and rest is shunted to inferior vena cava via ductus venosus
inf vena cava -> right atrium -> shunted to body via foramen ovale and ductus arteriosus to bypass lungs
How is fetal brain tissue different than adults?
low myelin content
higher water content
Why are drugs that are originally eliminated by fetus then recirculated?
fetus can swallow drug previously eliminated into amniotic fluid
What is the most sensitive time in fetal development for developing malformations? Why?
first 8 weeks after fertilization (1st trimester) when organogenesis is occurring
Ways fetus eliminates drugs?
Renal excretion
Circulation back through placenta
Which systems are developed earliest and most susceptible to teratogenic effects of drugs and toxins?
brain and heart
What are the embryonic and fetal periods? Which is more sensitive phase?
Embryonic: fertilization to 8 weeks **more sensitive
Fetal: 8 weeks to birth (wk 38)
Significance of ion trapping in fetus
Fetal pH is slightly lower than maternal (7.32 to 7.38), thus most unionized drugs are “ion trapped” to a degree, even in a healthy fetus
What characteristics of drug would minimize fetal exposure?
Low lipid solubility High protein binding Lowest dose possible Short half-life High molecular weight
methotrexate use during pregnancy
Category X
craniofacial deformities, limb deformities
anticonvulsants use during pregnancy
Category D
must assess benefit of seizure prevention vs risk of harm to fetus
Magnesium is safe seizure med
oral isotretionoin use during pregnancy
Category X
causes cleft palate, PTH deficiency, ear and thymus gland abnormalities, CV issues
Warfarin effects on fetus
Category X
Fetal warfarin syndrome when given in 1st trimester - nasal hypoplasia, hypoplasia of extremities, and developmental retardation
Chondrodysplasia punctata - nasal hypoplasia, bone stippling seen on XR, ophthalmologic abnormalities, and mental retardation
Thyroid medication effects on fetus
scalp defects (aplasia cutis) in infants and a higher incidence of maternal side effects
How is morning sickness treated?
Treatment should begin with diet - Carb snacks
Consider Acupressure and acupuncture
Antihistamines (Meclizine, doxylamine, diphenhydramine): decreasing stimulation of vomiting center
Doxylamine (Unisom) is OTC sleep aid
Vitamin B6 with Doxylamine
Ginger (thought to stimulate GI motility and saliva, bile, and gastric sections)
Ondansetron (Zofran)
First line treatment for “aches and pains” of pregnancy
acetaminophen
