Teratogenicity of Drugs and Teratogenicity Tests.

1. Teratogenicity of Drugs
&
Teratogenicity Tests

2. Teratogenicity
of
Drugs

3. • Any substance that can induce or
increase the incidence of a congenital
malformation
• Recognition of human teratogens
offers the opportunity to prevent
exposure

4. • Frequency of congenital malformations
in women exposed is greater
• This data is sometimes not available for
humans & is not unbiased
• There are clearly species differences
between teratogenic effects

5. • Drugs are classified as to their teratogenic
potential, based on anecdotal information
or animal studies
• Less than 2% of congenital malformations
are caused by drugs or chemicals
• Teratogenic drugs should be avoided either
during or prior to conception

6. • Women to avoid all medications in the first 8
weeks after conception
• Effects of teratogens, during the
developmental period, results in an “all or
none effect.”

7. Drugs can affect the foetus at 3 stages:
• Fertilization & implantation – conception to 17
days
• Organogenesis- 18 to 55 days of gestation
• Growth & development-56 days onwards

8. Risk Category of Drugs during Pregnancy:
• Cat A- Adequate studies in pregnant women have
failed to demonstrate a risk to the foetus
• Cat B- Adequate human studies are lacking, but
animal studies demonstrate a risk to foetus
• Cat C- No adequate studies in pregnant women &
animal studies are lacking or have shown an adverse
effect on foetus, but potential benefit may require
use in pregnant women.

9. • Cat D- There is evidence of human foetal risk,
but the potential benefits from use of the drug
may be acceptable despite the potential risk.
• Cat X- Studies in animals or humans have
demonstrated foetal abnormalities, and
potential risk clearly outweighs possible
benefits.

10. TERATOGENIC MECHANISMS:
• Folate antagonism
• Neural crest cell disruption
• Endocrine disruption
• Oxidative stress
• Vascular disruption and specific receptor
• Enzyme-mediated teratogenesis

11. Proven Human Teratogens:
Drug Abnormality
Thalidomide Phocomelia, multiple defects
Anti-neoplastic drugs Multiple defects, foetal death
Androgens Virilization, esophageal, cardiac defects
Progestins Virilization of female foetus
Stilboestrol Vaginal carcinoma
Tetracyclines Discoloured teeth, bone defects
Warfarin Nose, Eye, Hand defects, Growth retardation
Phenytoin Cleft lip/palate, microcephaly, hypoplastic
phalanges

12. Alcohol Low IQ, Growth Retardation, Foetal alcohol
syndrome
ACE inhibitors Hypoplasia of organs, growth retardation, foetal
loss
Lithium Foetal goiter, Cardiac abnormality
Antithyroid
Drugs
Foetal goiter, hypothyroidism
Indomethacin Premature closure of ductus arterious
Isotretinoin Craniofacial, Heart & CNS defects

13. Thalidomide: (Thalidomide disaster 1958-61)
• Hypnotic agent widely used in Europe in 1959
• An estimated 7000 infants born with
thalidomide syndrome or focomelia
• Characteristic features
include limb abnormalities

14. • Other malformations - Absence of the internal
and external ears, hemangiomas, congenital
heart disease & urinary tract malformations
• Critical period of exposure  24 to 36 days
after fertilization

15. Retinoic acid or Vitamin A derivatives:
• Even at very low doses
isotretinoin is potent teratogen
• Malformations include
 Craniofacial dysmorphisms,
 Cleft palate,
 Thymic aplasia
 Neural tube defects
• Critical period of exposure 2nd to 5th week of
gestation.

16. Anti-neoplastic/chemotherapeutic agents:
• Highly teratogenic  inhibit rapidly dividing
cells
• Malformations include cranial defects,
leukopenia and malformed extremities
• Occasionally used in the 3rd trimester when
they are urgently needed to treat the mother.

17. Anticonvulsants:
• Use of anticonvulsants leads to double the risk
for malformations
• Malformations like cleft lip, cleft palate,
congenital heart disease, neural tube defects,
microcephaly

18. Anticoagulants :
• Warfarin (Coumarin) has been associated with
Chondrodysplasia punctata
• Other malformations like nasal hypoplasia,
bone stippling seen on radiologic examination,
bilateral optic atrophy and mental retardation

19. Thyroid and Antithyroid Drugs
• Propylthiouracil (PTU) and methimazole both
cross the placenta and may cause some
degree of fetal goiter
• Goal of such therapy during pregnancy is to
keep the mother slightly hyperthyroid to
minimize fetal drug exposure.

20. Tetracycline:
• Protein synthesis inhibitor
• Readily cross the placenta.
• Brown discoloration of the deciduous teeth,
hypoplasia of the enamel, and inhibition of bone
growth
• Critical period of exposure- 2nd & 3rd trimester

21. Streptomycin and Kanamycin:
• Associated with congenital deafness
• Ototoxicity was reported with doses as low 1 g
streptomycin
• Critical period of exposure- 1st trimester

22. Androgenic Steroids:
• Androgens may masculinize a developing
female fetus
• Danazol to produce mild clitoral enlargement
and labial fusion
• Critical period of exposure 10 to 12 weeks
after conception

23. ACE Inhibitor:
• It can cause-
fetal hypotension
renal failure
oligohydromnios
death
• Critical Period of exposure 2nd – 3rd trimester

24. Lithium:
• Malformations caused are
–Hypotonia
–Cyanosis
–Lethargy
• Critical period of exposure 1st Trimester

25. Nicotine:
• Constrict blood vessels
• This decreases oxygen delivery to the fetus

26. Alcohol:
• Malformation caused are
–Low IQ
–Growth Retardation
–Foetal alcohol syndrome

27. Teratogenicity Test:

28. • Only Mammalian Species are to be used
• Studies are carried in two animal species (rats
& rabbits)
• Drug is given after mating, during the period of
organogenesis
• Foetus is then examined for visceral or skeletal
abnormalities

29. Testing Protocols:
• Under the guidelines of FDA
• Under the guidelines of ICH
(International Conference on
Harmonisation)

30. Test under FDA:
• Multigenerational studies
• Single generational studies
a) Segment I:Evaluation of Fertility and
Reproductive Performance
b) Segment II: Assessment of Developmental
Toxicity
c) Segment III: Postnatal Evaluation

31. Multigenerational Study:
The animals are
mated.
Continuous exposure
of a rodent species
(usually mice)
F1
Exposed shortly after
weaning (30–40 days
of age)
The effects of the test
is monitored through
each generation.
The measured parameters :
Fertility
Litter size
Neonatal viability
F2F3

32. Evaluation of Fertility and Reproductive
Performance:
Male rodents are treated for 70 days and nonpregnant
females for 14 days .
Treatment is continued in the females during
Mating
Pregnancy
Lactation
50% of the females are sacrificed and the foetus are
examined for presence of malformations. The other 50% are
allowed to give birth.
After weaning, these offspring are sacrificed and examined

33. Assessment of Developmental Toxicity:
Treatment of pregnant females only during
implantation through organogenesis
One day prior to birth, the animals are sacrificed
Fetuses examined for
1. Viability
2. Bodyweight
3. Presence of malformation

34. Postnatal Evaluation:
Pregnant animals are treated from the last trimester of
pregnancy until weaning.
Evaluation:
• Parturition process
• Late fetal development
• Neonatal survival
• Growth
• Presence of any malformations

35. Test under ICH:
• Fertility Assessment
• Postnatal Evaluation and Pregnancy State
Susceptibility
• Assessment of Developmental Toxicity

36. Fertility Assessment:
• 1.
• 3.
Males Females
Exposed for four weeks
before mating
Two weeks before mating
Evaluation Evaluation
Reproductive organs weight Fertility
Histological analysis Litter size
Sperm count & mobility Viability of conceptus

37. Postnatal Evaluation and Pregnancy State
Susceptibility:
Comparing the degree of toxicity of the non pregnant
female to that of the pregnant female
Evaluation :
Maternal toxicity
Growth
Functional development(off springs)

38. Assessment of Developmental Toxicity:
Pregnant animals are exposed from implantation through
organogenesis
The study is conducted using atleast two species, one
rodent and one non rodent.
One day prior to birth , the animals are killed &
foetus are examined.
Evaluation : Viability
Body weight
Presence of malformation

39. Alternative Test Methods:
• Micro mass test ( cells from the limb buds &
brains of rat embroys)
• Whole embryo culture test(whole embryos of
rats)
• Embryonic stem cell test

40. Conclusions:
 Understanding the mechanisms of the induction
of birth defects is key to determine how to
prevent these effects
 Further increasing the accuracy of experimental
animal extrapolation will aid in the
interpretation of experimental data in order to
more accurately determine the risk of a given
compound to elicit birth defects in humans

41. Thank you