Question

Which of the following drug does not cross the placenta?

• A. Warfarin
• B. Heparin
• C. Phenindione
• D. Bromocriptine

Hint:

Heparin is a low molecular weight drug that does not cross the placenta, making it safe for pregnant women.

Answer 1

The Correct Option is B

Step 1: Understanding drug placental crossing.
Heparin, unlike Warfarin, does not cross the placenta. This is why it is preferred for use in pregnant women for conditions like deep vein thrombosis, as it does not pose a risk to the fetus.
Step 2: Analyzing the options.
(1) Warfarin: Incorrect, Warfarin does cross the placenta and can cause harm to the developing fetus.
(2) Heparin: Correct — Heparin does not cross the placenta, making it safe for use during pregnancy.
(3) Phenindione: Incorrect, Phenindione crosses the placenta and has similar risks to Warfarin.
(4) Bromocriptine: Incorrect, Bromocriptine can cross the placenta.
Step 3: Conclusion.
The correct answer is (2) Heparin.

Answer 2

The question asks which anticoagulant does not cross the placenta, an important consideration for choosing safe treatment during pregnancy. Let's look at the molecular basis for placental transfer and check each drug against it.

1. Warfarin: Warfarin is a small, lipid-soluble molecule that readily crosses the placental barrier, and it is well known to be teratogenic, causing "warfarin embryopathy" if used in early pregnancy. It clearly does cross the placenta.
2. Heparin: Heparin is a large, highly polar, negatively charged molecule (a mucopolysaccharide). Its large size and charge prevent it from crossing the placental barrier, which is exactly why it is the preferred anticoagulant when anticoagulation is required during pregnancy.
3. Phenindione: Like warfarin, phenindione is an oral anticoagulant of the coumarin/indandione class; being a small lipophilic molecule, it also crosses the placenta and carries similar fetal risks.
4. Bromocriptine: Bromocriptine is a small molecule (a dopamine agonist) that is lipid-soluble enough to cross the placenta, and its use in pregnancy requires caution for that reason.

The determining factor is molecular size and charge — the three small, lipid-soluble drugs all cross the placenta, whereas heparin's large, charged structure is precisely what blocks it from doing so.

Therefore, the correct answer is Heparin.