Pharmacology II: Pregnancy

• The optometrist must be aware of the physiological changes occurring in the pregnant woman along with
the development stage of the fetus and identify potential adverse drug events occurring in both the mother
and child à being responsible for the health and safety to two persons
o Maternal adaptations in pregnancy: increased progesterone, activated hepatic metabolism,
increased renal blood flow and GFR
o Approximately 90% of the pregnant woman report taking at least one medication, with an
estimated 70% taking at least one prescription medication
§ about two-thirds of pregnant patients take at least one medication
• some drugs are used to treat pregnancy-related conditions (e.g. nausea,
preeclampsia)
o thromboembolic disorders, gestational diabetes and gestational HTN
may occur during pregnancy and must be treated for the safety of both
mother and growing fetus
o antibiotics may be necessary to treat infections acquired during
pregnancy
• some are used to treat chronic disorders (e.g. HTN, diabetes and epilepsy)
o if the patient has a preexisting epilepsy, asthma, HTN or a psychiatric
disorder, it would be unwise to discontinue pharmacotherapy
§ uncontrolled maternal asthma is far more dangerous to the
fetus than the drugs used to treat it
• stillbirth is a consequence
o SSRIs may increase the increase of preterm labor and may cause
withdrawal symptoms in newborns which include agitation, irritability,
trouble feeding, sleeping disturbances and convulsions
• regular use of dependence-producing drugs (e.g. alcohol) during pregnancy can
result in the birth of a drug-dependent infant
o if the infant’s dependence isn’t supported with drugs following birth, a
withdrawal syndrome will ensue
§ symptoms: shrill crying, vomiting and extreme irritability
§ drug therapy is often postponed until after delivery and lactation because the risks for
most drugs are unknown due to the fact that most haven’t been tested during pregnancy
• the goal of pharmacotherapy in pregnant patients is to treat the mother without
causing ill effects for the fetus
o use the smallest effective dose possible with the shortest duration
§ limit systemic absorption of drops by nasolacrimal duct
occlusion
o drugs in pregnancy:
§ first trimester: congenital malformations (teratogenesis)
• first semester is teratogenicity
o teratogen is an agent that by acting during
the embryonic or fetal period produces
morphological or functional malformations
that become apparent postnatal
• common sense tells us that the best way to minimize
use of drugs
o if possible, pregnant patients should avoid
unnecessary drugs entirely
§ second and third trimester: growth and fetal development or
toxic effects on fetal tissues
§ near term: adverse effects on labor or neonate after delivery
• changes in the kidney, liver and GI tract are of particular interest because it
affects dosage
 o by the third trimester, renal blood flow is doubled which causes
increase in glomerular filtration rate = accelerated clearance of drugs
§ dosage must be increased
o increased levels of progesterone causes a decrease in gastric tone and
intestinal motility = delayed gastric emptying
§ drugs remain longer in the GI tract which takes longer to be
absorbed and distributed = delayed onset and duration of
action
o high estrogen levels in the pregnant women cause increased
hydrochloric acid production in the stomach = affects absorption
o progesterone increases pulmonary blood flow which increases
absorption of respiratory agents
o tone and motility of the bowel decrease in pregnancy which causes
intestinal transit time to increase = more time for drugs to be absorbed
• distribution of drugs during pregnancy is affected by changes in the total body
water which may increase over 50%
o highly lipophilic drugs ultimately pass to the breast-feeding infant
o a woman’s heart rate may increase up to 15 beats per minute during
pregnancy = greater drug distribution
• some of the cytochrome P450 enzymes increase (CYP2D6 and 3A4) while
others decrease (CYP1A2)
• excretion of drugs during pregnancy is enhanced by renal plasma flow, which is
increase 50% to 70% during the first two trimesters = increased renal
elimination
• many lipid soluble drugs pass from mother to infant via the placenta (especially
lipophilic drugs) by simple diffusion
o multiple factors impact the transfer of drugs across the placenta
§ plasma drug level in the mother
§ solubility of the drug
§ molecular size
§ protein binding
§ drug ionization
§ blood flow to the placenta
• drugs enter breast milk primarily by passive diffusion but there are relatively
few instances in which breast-feeding must be discontinued due to medication
use
o Negative effects of tobacco smoking on the fetus are well documented and many women convert
to nicotine-replacement therapy (NRT) during pregnancy
Drug Pregnancy Breastfeeding
Tylenol #3 (Acetaminophen + Yes No
Codeine)
Vicodin (Acetaminophen + Yes Yes
Hydrocodone)
Restasis No Unknown
Brimonidine/Dipivefrin (Category Yes No
B)
Beta-blockers Yes after first trimester up to one Yes
week before delivery
Prostaglandins (stimulates uterine No No
contraction and can cause abortion)
Carbonic Anhydrase Inhibitors Oral is contradicted and topical is Yes
preferred

Drug Class Teratogenic Effects

Topical Anesthetics None
(Routine use or dilating drops should be avoided) but Tropicamide 0.5% is recommended if needed
with the lowest concentration and duration
Dilating drops can cause infant systemic hypertension
during breastfeeding
Mydriatic/Cycloplegic Agents Systemic use of Atropine, Epinephrine, Homatropine =
(Category C) minor, non life-threatening malformations
contraindicated due to fetal hypoxia in late Systemic scopolamine and Phenylephrine = fetal
pregnancy and delivery tachycardia and heart rate variability
Sympathomimetics Brimonidine (Alphagan P) caused CNS depression,
somnolence, apnea in neonates and infants
Miotics Systemic Pilocarpine = neonatal hyperthermia, seizures
and restlessness near term
Corticosteroids Systemic corticosteroids = increased risk of stillbirth,
intrauterine growth retardation and adrenal
insufficiency
Antibiotics Erythromycin (relatively safe) & Polymyxin B = no
known congenital defects
Aminoglycosides = hearing loss in animal studies
Fluoroquinolones are not recommended during
pregnancy
Tetracycline (Category D) = permanent discoloration
of teeth in offspring
Anti-Inflammatory Cyclosporine (Restasis) isn’t recommended during
breast milk if used systemically
Medical Marijuana Crosses the placenta and excreted in breast milk

• Once ingested by the infant, a drug is subjected to the usual pharmacokinetic influences but the infant’s
stomach content is quite acidic so some drugs may be destroyed and have reduced bioavailability
o Two primary factors have the potential to influence the oral absorption of drugs in pediatric
patients:
§ increased gastric pH
§ delayed gastric emptying
• gastric acid production may not reach adult levels until age 2 or 3
• slowed gastric motility in very young children will keep the drug in the stomach
longer = more absorption
o Three main factors affecting drug distribution in children are the proportion of water to fat,
immature liver function and the underdeveloped blood-brain barrier
§ the higher proportion of water dilutes water-soluble drugs
§ low percentage of body fat compared to adults
• lipid-soluble drugs would normally be distributed to fat tend to stay in the blood,
raising serum drug levels
o The rate at which drugs are metabolized in children is impacted by the immaturity of the hepatic
cytochrome P450 (CYP450) enzyme system
• Older adults take more medications than any other segment of the population – half the older population
has two or more chronic disorders (the most prevalent being a combination of hypertension and arthritis)
o The higher the number of drugs taken by a patient, the greater the possibility of experiencing
adverse effects and drug interactions
§ polypharmacy is taking two or more drugs that cause renal or liver impairment can result
in additive organ damage in older adults
• occurs when the patient takes OTC drugs
o Marked prolongation of half-life of many drugs
o Older adult patients are more likely to have visual impairment, functional disabilities and
cognitive dysfunction that may be sources of medication errors and nonadherences