Drugs usage in pregnant women and lactating women

1. DRUG USE IN PREGNANCY AND LACTATION
 Drug use during pregnancy and lactation requires special consideration because both the
mother and the child are affected.
 Many pregnant or lactating women take drugs for acute or chronic disorders or habitual
use of alcohol and tobacco
 Pregnant women pose a set of therapeutic problems that must be considered before
prescribing medication
 She can exhibit altered pharmacokinetic and pharmacodynamics response to a number of
drugs
 She is subject to diseases unique in pregnancy e.g eclampsia
 Drugs are used in over half of all pregnancies and prevalence of use is increasing
 The most commonly used drugs include anti-emetics, antacids, antihistamines, analgesics,
antimicrobials, diuretics, hypnotics, tranquilizers, and social and illicit drugs.
 Over 90 % of expectant mothers take 3 or 4 drugs at some stage of pregnancy.
 Indications range from chronic illness such as epilepsy and depression to those commonly
associated with pregnancy such as hypertension, UTI and GIT complications
 All drugs administered to pregnant women have the potential to cross placenta and effects
on fetus
 Many drugs have potential for teratogenicity during 1st
trimester
 During the first trimester, an older safe drug is preferred over a newer drug of unknown
teratogenicity.
 Live virus vaccines (measles, mumps, polio, rubella) should be avoided because of possible
harmful effects to the fetus.
 Inactive virus vaccines (influenza, rabies, hepatitis B) and toxoids (diphtheria, tetanus) are
considered safe for use.
 Human gestation period is approx. 40 weeks.
 Divided into 1st
2nd
and 3rd
trimester each lasting 3 months
 Another classification is according to stage of fetal development
1) Pre – embryonic stage: first 17 days post conception and involves implantation of
fertilized ovum
2) Embryonic stage: days 18-56 major organ systems are formed
3) Fetal stage: days 8-38 involves maturation, development and growth

2. Placental transfer of drugs:
 Most drugs diffuse easily across placenta and thus enter the fetal circulation to some extent
 Some drugs are administered to treat fetal disorders e.g. flecainide to resolve fetal
tachycardia
 Drugs with large molecular weight like insulin and heparin have negligible transfer
 Drugs that are small, uncharged at physiological pH and highly lipid soluble cross placenta
rapidly e.g thiopental
 Charged drugs that are highly ionized at physiological pH diffuse across placenta more
slowly e.g. heparin and succinylcholine
 Some enzymes and transporters in placenta may facilitate or restrict the drug transfer
 Molecular weight of drug and extent of maternal plasma protein binding will also influence
the extent of diffusion
Considerations in pregnancy:
 Two major considerations:
1. Effect of drug on the pregnancy, fetus or neonate (teratogenicity and pharmacological
effects)
2. Effect of pregnancy on drug handling (Pharmacokinetics)
Altered pharmacokinetic and pharmacodynamics:
 During pregnancy mothers cardiac output increases up to 40 %
 Renal blood flow, GFR, and plasma volume increases
 Plasma albumin decreases
 All these result in altered pharmacokinetic and pharmacodynamics
 50% Increase in plasma volume and body water:
 Water soluble drugs are distributed and “diluted” more than in the non-pregnant state
 Drug dosage requirements may increase
 Increased weight (~14 Kg) and body fat:
 Fat-soluble drugs are distributed more widely.
 Drugs distributed to fatty tissues tend to linger in the body because they are slowly released
from storage sites

3.  Decreased serum albumin: The rate of albumin production is increased. However, serum
levels fall because of plasma volume expansion
 Many plasma protein-binding sites are occupied by hormones that increase during
pregnancy
 More free drug is available for therapeutic or adverse effects on the mother and for
placental transfer to the fetus.
 Increased renal blood flow and glomerular filtration rate secondary to increased cardiac
output.
 Increased excretion of drugs by the kidneys, especially those excreted primarily unchanged
in the urine (digoxin, lithium)
 In late pregnancy, the increased size of the uterus decreases renal blood flow in supine
position
 This results in decreased excretion and prolonged effects of renally excreted drugs.
 Pregnancy is hyper dynamic state, drug clearance may be increased (by renal
elimination/liver met) so maintenance doses of drugs often need to be raised
 Vd may be increased by 20 % for both lipid and water soluble drugs so increase in loading
dose may be required
 Measured drug concentration of highly PB drugs may be lower e.g. phenytoin
Normal physiological changes:
 Maternal plasma volume, cardiac output, and glomerular filtration increase by 30% to 50%
as body fat increases during pregnancy
 Nausea and vomiting, as well as delayed gastric emptying, may alter the absorption of
drugs
 Pregnancy-induced increase in gastric pH may affect the absorption of weak acids and
bases.
 Higher levels of oestrogen and progesterone alter liver enzyme activity and increase the
elimination of some drugs but result in accumulation of others
Effects of drugs on pregnancy:
 Majority of drugs attain concentrations in fetus close to those of maternal plasma
 Exposure during 1st
16 weeks of pregnancy is associated with an increased incidence of
physical malformation
 Less obvious effects e.g. decreased neuronal function or intellectual development may
occur following exposure later in pregnancy

4.  Able to disturb the growth and development of an embryo or foetus.
 Drugs are classified as class A, B, C, D and X

5. Teratogenic:
A drug's effect on the fetus is determined largely by fetal age at exposure, drug potency, and
drug dosage. Fetal age affects the type of drug effect:
1. Before the 20th day after fertilization: Drugs given at this time typically have an all-or-
nothing effect, killing the embryo or not affecting it at all. Teratogenesis is unlikely during
this stage
2. During organogenesis (between 20 and 56 days after fertilization): Teratogenesis is
most likely at this stage. Drugs reaching the embryo during this stage may result in
spontaneous abortion, a sublethal gross anatomic defect (true teratogenic effect), or covert
embryopathy (a permanent subtle metabolic or functional defect that may manifest later in
life), or the drugs may have no measurable effect.
3. After organogenesis (in the 2nd and 3rd trimesters): Teratogenesis is unlikely, but drugs
may alter growth and function of normally formed fetal organs and tissues. As placental
metabolism increases, doses must be higher for fetal toxicity to occur.
Pharmacological risks:
 NSAIDS may cause premature closure of ductus arteriosus in later stage of pregnancy

6.  Beta blockers can cause fetal bradycardias and hypoglycemia
 Ethanol and cocaine can cause teratogenic and toxic effects at birth as well as withdrawal
symptoms in neonates
General principles:
 Avoid all drugs if possible
 Avoid drugs in 1st
trimester
 Choose drugs of proven safety or least toxicity
 Use short course and smallest doses
DRUGS DURING LACTATION
 Breastfeeding mothers should avoid taking drugs if possible.When drug therapy is
necessary, the mother should avoid contraindicated drugs and drugs that suppress lactation
(bromocriptine levodopa)
 When drug treatment is necessary, the safest known alternative should be used
 Drugs pass into milk by passive diffusion of free (unbound) and unionized form
 They are distributed within aqueous, protein and lipid phase of milk
 So drugs which are highly lipid soluble with low protein binding and unionized at
physiological pH achieve higher conc. in milk
 Nursing infants could ingest significant amount of drugs if it were present in breast milk in
higher conc.
 Nursing infants might be at high risk of toxicity as their renal, hepatic drug excretion is
immature, Sulphonamides, INH, Li, barbiturates, morphine, heroin, chloramphenicol,
methotrexate cyclophosphamide should be avoided
Drugs Contraindicated for Breastfeeding Mothers:
 Dicumarol
 Warfarin
 Cytotoxic drugs (Cyclophosphamide, Methotrexate
 Diazepam, antipsychotics
 Corticosteroids