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A developing fetus must always be carefully considered when drugs are
administered to a pregnant woman. Each drug prescribed for a woman during
pregnancy must be evaluated for its utmost effectiveness while weighing this
against its potential adverse effects. Considering this:
Identify how normal physiologic changes with pregnancy alter the
pharmacokinetics of drug therapy.
Prescription and over-the-counter medications use is common in pregnancy, with the average
pregnant patient in the US and Canada using more than two drugs during the course of their
pregnancy. One reason for this is that some women enter into pregnancy with pre-existing medical
conditions, such as diabetes, hypertension, asthma, and others gestational disorders complicate
women’s pregnancies and require treatment. The majority of organ systems are affected by
physiologic changes during pregnancy, with many of these changes beginning in early gestation.
The purpose of this review is to summarize some of the physiologic changes during pregnancy
that may affect medication pharmacokinetics.
The physiological changes with pregnancy alter the pharmacokinetics of drug therapy:
Due to the increase in estrogen concentrations in pregnancy, the respiratory system undergoes
anatomic changes leading to increased vascularity and edema of the upper respiratory mucosa.
This may explain the increased prevalence during pregnancy. Although it is a theoretical risk and
no studies have shown increased toxicity, inhaled medications, such as steroids used to treat
asthma, may be more readily absorbed by pregnant patients. The decrease in functional residual
capacity may predispose pregnant patient to hypoxemia during induction of general anesthesia.
The vital capacity remains unchanged, as the decreased expiratory reserve volumes are
accompanied with increased inspiratory reserve volumes
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The effects of progesterone and relax on smooth muscles are also seen in the urinary system
leading to dilation of the urinary collecting system with consequent urinary stasis, predisposing
pregnant women to urinary tract infections. This is more common on the right side secondary to
dextrorotation of the pregnant uterus, and the right ovarian vein that crosses over the right ureter.
Both renal blood flow and glomerular filtration rate (GFR) increase by 50%, as early as 14 weeks
of pregnancy.
In pregnancy, the rise in progesterone leads to delayed gastric emptying and prolonged small bowel
transit time. Drug absorption is also decreased by nausea and vomiting early in pregnancy. This
results in lower plasma drug concentrations. For this reason, patients with nausea and vomiting of
pregnancy are routinely advised to take their medications when nausea is minimal. Moreover, the
increased prevalence of constipation and the use of opiate medications to ease pain during labor
slow gastrointestinal motility, and delay small intestine drug absorption.
Plasma iodide concentration decreases in pregnancy because of fetal use and increase in maternal
clearance of iodide. This predisposes the thyroid gland to increase in size and volume in almost
15% of women. In addition to anatomic changes, the thyroid gland increases production of thyroid
hormones during pregnancy.
Other factors that affect thyroid hormones metabolism and levels in pregnancy include:
(1) The increase in maternal renal iodine excretion (secondary to increase in GFR)
(2) The higher maternal metabolic demands and rate during pregnancy
(3) The increase in thyroid hormones transplacental transport to the fetus early in pregnancy
(4) The increase in activity of placental type
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Profound physiologic and anatomic changes occur in virtually every organ system during
pregnancy. These have significant consequences on the pharmacokinetic and pharmacodynamics
properties of various medications when used by pregnant women. Data are lacking on the
implications of these changes on variety of therapeutic agents, and future research is desperately
Differentiate the classification of drugs for use in pregnancy:
Pregnancy Category: A
Definition: In human studies, pregnant women used the medicine and their babies did not have
any problems related to using the medicine.
Examples of Drugs:
Folic acid
Levothyroxine (thyroid hormone medicine)
Pregnancy Category: B
In animal studies, pregnant animals received the medicine, and some babies had problems. But in
human studies, pregnant women used the medicine and their babies did not have any problems
related to using the medicine.
Examples of Drugs:
Some antibiotics like amoxicillin.
Zofran (ondansetron) for nausea
Glucophage (metformin) for diabetes
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Some insulins used to treat diabetes such as regular and NPH insulin.
Pregnancy Category: C
Definition: In humans, there are no good studies. In animals, pregnant animals treated with the
medicine had some babies with problems. However, sometimes the medicine may still help the
human mothers and babies more than it might harm.
Examples of Drugs:
Ventolin (albuterol) for asthma
Zoloft (sertraline) and Prozac (fluoxetine) for depression
Pregnancy Category: D
Definition: Studies in humans and other reports show that when pregnant women use the
medicine, some babies are born with problems related to the medicine. However, in some serious
situations, the medicine may still help the mother and the baby more than it might harm.
Examples of Drugs:
Paxil (paroxetine) for depression
Some cancer chemotherapy
Pregnancy Category: X
Definition: Studies or reports in humans or animals show that mothers using the medicine during
pregnancy may have babies with problems related to the medicine. There are no situations where
the medicine can help the mother or baby enough to make the risk of problems worth it. These
medicines should never be used by pregnant women.
Examples of Drugs:
Accutane (isotretinoin) for cystic acne
Thalomid (thalidomide) for a type of skin disease
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Adverse Effect from use
in pregnancy
Place in therapy
Fetus: hemolytic anemia
Fetus: neural tube defects
Not recommended
in pregnancy
Fetus: Low birth weight
Safe for used in 2
and 3
Define Teratogenic effect:
A teratogen is something that can cause birth defects or abnormalities in a developing embryo or
fetus upon exposure. Teratogens include some medications, recreational drugs, tobacco products,
chemicals, alcohol, certain infections, and in some cases, health problems such as
uncontrolled diabetes in pregnant people. Exposure to a teratogen can occur through ingestion or
environmental exposure during pregnancy.
Teratogenicity is the ability to cause developmental abnormalities in the fetus. Congenital
malformations non reversible functional or morphological defects present at birth. Teratology is
the study of abnormalities of physiological development. A teratogen is the agent that can disturb
the development of the embryo or fetus.
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Tabulate teratogenic and non-teratogenic adverse fetal effects of different
drugs during pregnancy:
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