This document discusses teratogenicity studies and provides details on how to conduct prenatal developmental toxicity tests according to OECD Guideline 414. It defines key terms like teratogen and teratology. Historical teratogens like thalidomide, Accutane, DES, and alcohol are described along with their effects. The FDA pregnancy drug categories and critical periods of development are outlined. Test procedures include selecting animal species, housing, dosing, observations, post-mortem examinations of dams and fetuses, and results reporting. The goal is to identify effects of substances on prenatal development and discriminate between general toxicity and developmental toxicity.

1. Presented by:
MERLIN VARKEY
M PHARM
DEPARTMENT OF PHARMACOLOGY
TERATOGENICITY STUDIES-
SEGMENT 2

2. Teratogenicity
 Teratogenicity is the ability to cause
developmental abnormalities in foetus.
 Developmental toxicity is any morphological or
functional alteration caused by chemical or
physical insult that interfere with normal growth ,
homeostatis , development, differentiation and or
behavior.

3. Teratogen
 A teratogen is an agent that can produce a
permanent alteration of structure or function in an
organism exposed during embyronic or fetal life.
Teratology
 Teratology is the study of abnormalities of
physiological development.

4. Critical period
Drug can affect the fetus at 3 stages:
 Pre-implantation : embryonic lethality
 Implantation to organogenesis : morphological
defects.
 Fetal to neonatal stage : functional disorders ,
growth retardation, carcinogenesis
 The sensitivity of embryo to the induction of
morphological defects is increased during the
period of organogenesis.

5. Historical teratogens
Thalidomide
• Thalidomide is a sedative-hypnotic drug used in
Europe from 1957 to 1961.
• It was marketed for morning sickness , nausea and
insomnia .
• Malformation : phocomelia ,absence of auricle with
deafness, defects of the muscles of the eye and face,
malformation of heart ,bowel uterus and gallblader.

6. Accutane [isotetrinoin]
• It is used to treat acne.
• Birth defects : facial malformation, heart defects,
mental retardation.
Diethylstilbesterol [DES]
• From 1940 to 1970 ,DES was used to help maintain
pregnancy.
• Women who were exposed in utero often developed
vaginal neoplasia, vaginal adenosis, and cervical
erosion.
• Effects were not seen in offspring until they reach
puberty.

7. Alcohol
• Heavy drinking during the early pregnancy greatly
increases the risk of cluster of birth difects known as
fetal alcohol syndrome.
o Fetal alcohol syndrome :
• This syndrome includes a small skull [microcephaly],
abnormal facial features, and heart defects, often
accompined by impeded growth and mental
retardation.
• Signs and symptoms : poor body weight, poor
memory, learning disabilities, speech and language
delay, difficulty with attension.

8. FDA category of drugs used in pregnancy
Category A
 Adequate studies in human demonstrate no risks.
 Safest category
Category B
 Animal studies indicate no risk, but there are no
adequate studies in human.
 Animal studies show adverse effects, but adequate
studies in human have not demonstrated a risk.
Category C
 Animal studies indicated adverse effects and there are
no data from human studies.

9.  These drugs may be used when potential benefits
outweight the potential risk.
Category D
 There is evidence of human fetal risk, but the potential
benefits to the mother may be acceptable.
Category X
 Studies in animals or humans show adverse reaction
reports or both have demonstrated fetal abnormalities.
 Absolutely contraindicated for use during pregnancy

10. OECD guideline for testing of
chemicals :414
Prenatal developmental toxicity studies
PRINCIPLE
• The test substance is administered to pregnant animals
atleast from implantation to one day prior to the day of
scheduled kill.
• Shortly before caesarean section , the females are killed,
the uterine contents are examined and the foetuses are
evaluated for soft tissue and skeletal changes.

11. PREPARATION FOR THE TEST
Selection of animal species
 The preferred rodent species is rat.
 The preffered non-rodent species is rabbit.
 Justification should be provided if another species is
used.
Housing and feeding conditions
 Mating procedure should be carried out in cages
suitable for this purpose.
 Individual housing of mated rat is preffered.
 Group housing in small numbers is also accepted.

12. Preparation of animals
 Healthy animals which have been acclimated to
laboratory conditions for at least 5 days and have not
been subjected to previous experimental procedures,
should be used.
 Young adult nulliparus female animals should be
used at each dose level.
 The females should be mated with males of same
species and strains.
 Mating of siblings should be avoided.
 For rodents day 0 of gestation is the day on which a
vaginal plug and/or sperm are observed.
 Mated females should be assigned in an unbaised
manner to the control and treatment group.

13. PROCEDURE
Number and sex of animal
 Each test and control group should contain a sufficient
no.of females to result in approximately 20 female
animals with implantation sites at necropsy.
Preparation of dose
 If a vehicle or other addictive is used to facilitate
dosing, cosideration should be given to the following
characteristics:
effects on aborption, distribution,metabolism,
excretion of the test substance.
 The vehicle should neither be developmentally toxic
nor have effects on reproduction.

14. Dosage
 Normally, the test substance should be administered
daily from implantation to the day prior to scheduled
caesarean session.
 At least 3 dose levels and a concurrent control should
be given.
 The highest dose should be chosen with the aim to
induce some developmental and/or maternal toxiciy
but not death or severe suffering.
 Intermidiate dose level should produce minimal
obserable toxic effects.
 The lowest dose level should not produce any
evidence of either maternal or developmental toxicity.

15.  Dose levels should be selected taking into account
any existing toxicity data as well as additional
information on metabolism and toxicokinetics of the
test substance.
 A concurrent control group should be used.
 Animal in the control group should be handled in an
identical manner to test group animals.
 Sham treated control or vehicle control group is used.
Administration of dose
 The test substance or vehicle is usually administered
orally by intubation.
 The test substance should be administered at approx
the same time each day.

16.  The dose to each animal should normally be based on
the most recent individual body weight determination.
 If excess toxicity is noted in the treated dams, those
animals should be humianly killed.
Observations of the dams
 Clinical observations should be made and recorded at
least once a day, preferably at the same time each
day.
 Mortality, moribundity, pertinent behavioural changes,
and all signs of overt toxicity are recorded.
 Body weight : animal should be weighed on day 0, on
the first day of dosing, at least every 3 days during the
dosing period and on the day of scheduled kill.

17. Post-mortem examination
 Females should be killed one day prior to the
expected day of delivery.
 At the time of termination or death during the study,
the dam should be examined macroscopically for any
structural abnormalities or pathological changes.
Examination of uterine contents
 Uteri that appear non-gravid should be further
examined [ ammonium sulfide staining for rodents and
Salewski staining for rabbit] to confirm non-pregnant
status.
 Gravid uteri including the cervix should be weighed.

18.  The no.of corpora lutea should be determined for
pregnant animals.
 The uterine contents should be examined for no.of
embryonic or fetal deaths and viable fetus.
Examination of fetuses
 The sex and body weight of each foetus should be
determined.
 Foetus should be examined for skeletal and soft
tissue alterations.
 For rodents, approx one-half of each litter should be
prepared and examined for skeletal alteration. Other
half should be examined for soft tissue alteration.

19.  For non-rodents all foetuses should be examined for
both soft tissue and skeletal alterations.
Results
 Maternal toxic response data by dose:
 The no.of animal at the start of the test, the no.of
animal surviving, the number pregnant, the number
aborting, number of animals delivering early.
 Data from animals that do not survive to the
scheduled kill should be reported
 Body weight, body weight changes and gravid uterine
weight

20.  Food and water consumption.
 Necropsy findings, including uterine weight.
 NOAEL values for maternal and developmental
effects should be reported.
 Developmental endpoints by dose for litters with
implants, including:
 No.of corpora lutea
 No.of implantations, number and percent of live and
dead foetuses and resorption
 Number and percent of pre and post implantation
losses.

21.  Developmental endpoints by dose for litters with live
foetuses, including:
 Number and percent of live offspring
 Foetal body weight , sex ratio
 External, soft tissue, and skeletal malformation and
other relevant alterations.
Interpretation of results
 A prenatal developmental toxicity study will provide
information on the effects of repeated oral exposure to
a substance during pregnancy.
 The results of the study will allow for the discrimination
between developmental effects occuring in the
absence of general toxicity and those which are only
expressed at levels that are toxic to the maternal
animals.

23. Reference
 OECD guideline :414
 Medical database in studies of drug
teratogenicity: article
 COVID-19 vaccination during pregnancy

24. Thank you