Teratogenecity of drugs

What are teratogens?

Some Drugs or chemicals are fatal to embryo development. 

Those drugs and chemical substances which produce deviations and abnormalities in the development of embryo and foetal growth, are termed as teratogens. . 

Hence foetas is more sensitive to drugs than mother as foetal hepatic enzyme function is minimum and rapidly growing foetal tissues are more susceptible to the effect. 

During gestation, the plasma proteins poorly bind the drugs and resulting in more free drugs. Drugs are teratogenic only at specific times during embryogenesis. You all must know about The Thalidomide.

Depending on the stage of development a teratogen may show different adverse effects. or even no effect.

Thalidomide when  taken After 21-22 days of gestation effects are observed :
— the absence of external 👂 ears
— paralysis of cranial nerves 

After about 24 – 27 days
— the phocomelia effect ( shortening or complete absence of limbs)

After 27 days defects of legs occur.

This sensitivity period terminates after 34 to 36 days of gestation. 

Teratogens in 1st trimester -> Steroids, salicylates, phenylbutazone, amphetamine, LSD, Antihistamines 

Teratogens throughout pregnancy -> chloramphenicol(grey baby syndrome), Quinine (deafness), Antidiabetics (tolbutamide),Insulin.

Teratogens Prior to delivery -> Reserpine,  tranquilizers, salicylates.

Some drugs also excreted in milk -> Reserpine, tetracycline, anti-histamine, heavy metals like mercury, lead and arsenicals.