Which of the following drugs can be safely prescribed in pregnancy? (AIIMS Nov 2009)
Drugs safe during pregnancy
Placental drug transport depends upon
- Unionized drug transportation> Ionized drug like thiopentone > Highly ionized drugs (SCh, d-tubocurarine).
- Exception - Salicylates are almost completely ionized at physiological pH, even then fetus level is high because the small amount of salicylate which is not ionized is highly lipid soluble.
- 250 - 500 - Cross placenta easily, depending upon their lipid solubility and degree of ionization
- 500 -1000 - Cross placenta more difficulty
- > 1000 - Cross very poorly
Heparin is a very large polar molecule, so unable to cross the placenta. Though, an acidic drug by nature it should remain unionized in the low pH of placenta. But the drug is a bulky molecule with polar character. Therefore, it fails to enter the blood placenta barrier.
- P- glycoprotein transporter pumps back into the maternal circulation a variety of drugs, including cancer drugs (vinblastine, doxorubicin) and other agent (digoxin). Inhibition of this transporter may cause drug accumulation in the fetus.