Classification of teratogens

Classification of teratogens

Teratogenicity is a very difficult cause-and-effect relationship to prove, although many case reports exist that associate major malformations with drug use during a particular pregnancy. Animal studies cannot be true predictors of teratogenicity due to wide inter- and intraspecies variations in the pharmacokinetic properties of drugs, including placental transfer.

The following categories are distinguished: A: no fetal risk shown in controlled human studies. B: no human data available and animal studies show no fetal risk

or animal studies show a risk but human studies do not show fetal risk. C: no controlled studies on fetal risk available for humans or animals or fetal risk shown in controlled animal studies but no human data available. (Benefit of drug use must clearly justify potential fetal risk in this category). D: studies show fetal risk in humans (use of drug may be acceptable even with risks, such as in life-threatening illness or where safer drugs are ineffective). X: risk to fetus clearly outweighs any benefits from these drugs.