1. 7
LECTURE # 05

2. DRUGS IN PREGNANCY
DR. NAHEED BANO
Assistant Professor, Obs/Gynae
Rawalpindi Medical College, Rawalpindi.

4. IMPORTANT ASPECTS
1. Physiological changes of pregnancy
affect DRUG METABOLISM
2. Drug may cross the placenta and affect
the fetus (TERATOCENICITY)

5. PHYSIOLOGICAL CHANGES OF
PREGNANCY THAT AFFECT DRUG
METABOLISM
GIT:
 Nausea
and
vomiting
of
early
pregnancy
 Acid content of the stomach is ↓
 Delayed gastric emptying
Continued:

6. SKIN AND MUCOUS MEMBRANE:
 ↑ Blood flow to the skin leads to more rapid
absorption e.g. glyceryl trinitrate
patches
used to suppress preterm labour
 → Blood flow to nasal and oral mucous
membrane
absorption.
→
leads
to
more
rapid

7. CNS:
↑ Vascularity of epidural space e.g. opiates used
for analgesia are rapidly absorbed
PLASMA AND BLOOD VOLUME:
↑ Plasma and blood volume causes
haemodilution affecting drug concentration
PLASMA PROTEINS:
↓ In plasma proteins affect drugs that are
bound to proteins e.g. diazepam, phenytoin
leading to ↑ free drug in circulation
URINARY SYSTEM:
↑ Renal blood flow and GFR affecting
concentration and elimination of many drugs.

8. TERATOGENICITY
 Drugs that affect organogenesis are described
as TERATOGENIC DRUGS
 Drug exposure accounts for 2-3 % of all birth
defects
 Most critical period is embrogenic period
which is from 2nd to 8th week post conception or
day 31 to day 71 from LMP in a 28 day cycle
 Exposure prior to day 31 produces all or none
effect i.e. either the fetus dies in utero or has
no effect.
 Exposure from day 31 to day 71 may lead to
fetal abnormality or fetal death.

9. FACTORS THAT INFLUENCE
TERATOGENICITY

Nature of the agent

Dose

Route

Frequency of exposure

Duration of exposure

10. FACTORS THAT INFLUENCE
TERATOGENICITY

Gestational timing

Concurrent exposures

Concurrent illness

Genetic susceptibility
* Mother
* Fetus

11. DIAGRAMATIC REPRESENTATION
DRUG TOXICITY
Conception
Heart & CNS
Ear & Palate
Organogenesis
14
31
71
209

12. PRINCIPAL MECHANISMS
OF TERATOGENESIS
Cell growth or proliferation
Cell death
Cell migration
Cell and tissue interactions
Disruptions

13. BIRTH DEFECTS IN CHILDHOOD
Baird et al. AJHG 42:677, 1988

14. FDA CLASSIFICATION OF DRUG
SAFETY IN PREGNANCY
United
States
food
and
drug
administration categories for drug use
in pregnancy
A. Controlled studies show no risk
B. No evidence of risk in humans
C. Risk cannot be ruled out
D. Positive evidence of risk
E. Contra – indicated in pregnancy

15. Awareness of potential advise effects of
drugs increased after THALIDOMIDE
TRAGEDY

16. FETAL HYDANTION SYDROME
Cranio- facial abnormalities , cardiac
defects, IUGR
WARFARIN EMBRYOPATHY
Nasal hypoplasia, hydrocephaly,
microcephaly, IUGR
NON –TERATOGENIC FETAL
CONSEQUENCES
IUGR, mental retardation, intracranial
hemorrhage.

17. DRUGS & BREAST FEESING
Drug may affect the infant in various ways
Drug may inhibit lactation

18. TAKE HOME MESSAGE
DRUGS SHOULD BE PRESCRIBED TO
PREGNANT AND LACTATING
WOMEN WITH EXTREME
CAUTION