This document discusses guidelines for postnatal evaluation in developmental and juvenile toxicity studies. It compares EPA and OECD harmonization issues for dosing schedules, assessments, sample sizes, and neuropathology in two-generation reproduction and developmental neurotoxicity studies. The document also discusses guideline requirements for testing pharmaceuticals, including evaluating postnatal outcomes after parental exposure. It considers study design factors like target organ systems, exposure periods, basic principles, and whether direct neonatal exposures are needed.

1. WIL Research Laboratories
Postnatal Evaluation in
Developmental and Juvenile
Toxicity Studies
Joseph F. Holson, Ph.D.

2. Guideline Requirements for
Testing Chemicals
Established and proposed guidelines for studies
which include postnatal assessment
Two-generation reproduction study
OPPTS 870.3800; OECD 416; updating and/or
harmonizing drafts
Developmental Neurotoxicity study
OPPTS 870.6300 and DCI for organophosphate
pesticides; OECD 426; harmonizing drafts

3. EPA vs. OECD Harmonization
Issues
Dosing schedule:
Pre-weaning activity:
Reflex ontogeny:
Sample size:
Neuropathology:
Assignment to testing:
Emerging request:
to PND 10 vs. PND 21
3 vs. 1 assessment
non vs. some
10 vs. 20/sex/group
PND 11 vs. PND 21; some
morphometry vs. tiered
1/litter for each test vs.
1/sex/litter for all behavior
kinetics/biomarker effects

4. Guideline Requirements for
Testing Pharmaceuticals
1994 ICH guidelines for medicinal products
Evaluation of postnatal survival, growth,
development, behavior and reproductive performance
following parental exposure (usually Segment II/III or
I/II/III)
FDA, 1998 – possible direct neonatal exposure
to support pediatric use of medicinal products
Exposure period(s) and endpoints determined on a
case-by-case basis

5. Segments Defined by Parental
Exposure Period(s)
Exposure Conventions
Reproductive and Developmental Toxicity Studies
Segment I
II
Gestation
III
Lactation
Mating

Sexual maturity (F0
 Conception
 Birth
 Weaning
 Implantation
adults)
 Closure of hard palate

6. Manifestations of Developmental
Disruption
Functional Deficits
Growth Alterations
Malformations
Death

7. FDA-Defined Pediatric
Populations
Pre-Term Neonate
Term Neonate
Infant/Toddler
Child
Adolescent
Born at < 38 weeks
Birth to 1 month
1 month to 2 years
2 to 12 years
12 to 16 (or 18) years
Comparable stage/age categories for animal species
dependent on individual organ or system

8. Comparative Age Categories
Human
Rat
Dog
Primate
Minipig
(days)
(wks)
(months)
(wks)
<=9
<=0.5
pre-term
pre-term
10
<3
<0.5
<2
Infant/Toddler
10-21
3-6
0.5-6
2-4
Child
21-45
6-20
6-36
4-14
Adolescent
45-90
20-28
26-48
14-26
Pre-Term
Neonate
Term Neonate
Estimates are based on combined general developmental events occurring in
both sexes, and represent only the overall schedule for CNS and reproductive
development in these species. Note that the end age of the comparative
category to human Infant/Toddler corresponds roughly to the usual age at
weaning for laboratory species.

9. Study Design Considerations:
Target Organ Systems
Organ systems and endpoints of greatest
concern are those that continue to
develop postnatally in humans, e.g.:
Nervous System
Immune System
Kidney
Bone
Reproductive System
Metabolizing Enzymes
Lung
Growth

10. Study Design Considerations: Parental
or Maternal Exposure Studies
Chemicals:
Exposure periods and endpoints specified in
guidelines
Pharmaceuticals:
Standard sample sizes, exposure periods,
and reproductive and developmental
endpoints measured in the offspring
Occasionally include additional assessments
for target organ characterization

11. Study Design Considerations:
Basic Principles
Study design directly affects interpretation of
developmental outcome
Preliminary studies often very useful
Critical period(s) of exposure – TK/PK value
Critical period(s) for assessment of age- and
sex-specific expressions of toxicity
“Litter” is the largest contributor to outcome
Via maternal exposure and maintenance
Similarity among siblings increases with age

12. Study Design Considerations: Are
Direct Exposures Needed?
Rule #1: Talk to the FDA or EPA
Gaps in existing data and/or exposures
Pharmaceutical Considerations:
Medical condition
Target Population
Duration of treatment
Clinical trial schedule
Labeling for pediatric efficacy/safety
Outcome of standard nonclinical
reproductive and developmental studies

13. Study Design Considerations:
Pharmaceutical Direct-Exposure Studies
Therapeutic usage in children –
Primary or secondary therapeutic population
Treatment duration – acute vs. chronic
Probable age(s) at initiation of treatment
What and when to monitor –
Standard toxicity evaluations
Standard developmental evaluations
During and/or after exposure

14. Study Design Considerations:
Direct-Exposure Studies
Case-by-Case Decisions
Exposure period(s) – value of PK/TK information
Assessment period(s) – during/after treatment
One vs. two species
Within-litter vs. between litter designs
Feasibility of studies in animal model
Direct-dosing issues
Compound- and/or age-specific evaluations