Placental Transfer and Lactation

Placental Drug Transfer - Baby's First Dose

Fetal drug exposure begins here.

• Mechanisms:
  • Passive Diffusion: Most common. Favors lipid-soluble, unionized.
  • Facilitated Diffusion: Carrier-mediated (glucose).
  • Active Transport: Needs energy (amino acids, iron).
  • Pinocytosis: For large molecules (IgG).
• Key Factors Influencing Transfer:
  • Maternal: Drug dose, uterine blood flow.
  • Placental: Surface area, thickness (↓ with gestation ↑ transfer), placental age, metabolism (P-gp efflux ↓ transfer).
  • Fetal: pH (ion trapping), blood flow, protein binding.
• Drug Properties Favoring Transfer:
  • High lipid solubility
  • Low Molecular Weight (MW): <500 Da (easy), >1000 Da (poorly)
    • E.g., Warfarin (crosses) vs. Heparin (high MW, doesn't cross)
  • Unionized state
  • Low maternal protein binding (↑ free drug) 📌 Mnemonic: 'PLacenta TRANSFER' (Properties, Lipid solubility, Area, Concentration, Thickness, etc.)

⭐ Most drugs cross the placenta primarily by passive diffusion, driven by concentration gradients and favored by high lipid solubility and low molecular weight.

Teratogenicity & Fetal Effects - Handle With Care

• Teratogen: Agent causing fetal abnormalities.
• Critical Periods of Exposure:
  • 'All-or-None' Period: First 2 weeks post-conception. Exposure: embryo death or normal development.
  • Organogenesis (Embryonic Period): Week 3-8 post-conception. Max susceptibility to major structural anomalies.

    ⭐ The period of maximum susceptibility to major morphological abnormalities (teratogenesis) is the embryonic period, from week 3 to week 8 post-conception.

  • Fetal Period: Week 9 to term. Growth retardation, CNS/functional defects.

• Drug Risk Classification:
  • Old FDA Categories (A,B,C,D,X) replaced by PLLR (Pregnancy, Lactation, Females/Males of Reproductive Potential) for detailed risk.
• Key Teratogens & Effects:

  Teratogen	Defect(s)
  Thalidomide	Phocomelia (limb defects)
  Valproate/Carbamazepine	Neural tube defects (NTDs)
  ACE inhibitors/ARBs	Renal dysgenesis, oligohydramnios (late)
  Warfarin	Nasal hypoplasia, chondrodysplasia
  Isotretinoin (Vit. A)	CNS, craniofacial, CV defects
  Phenytoin	Fetal hydantoin syndrome
  Lithium	Ebstein's anomaly (cardiac)

• 📌 Mnemonic: Warfarin, ACEi, Retinoids (Isotretinoin), Antiepileptics (Valproate, Phenytoin), Thalidomide, Lithium. (Acronym: WARATL)
• Fetal Adverse Drug Reactions (FADRs):
  • Distinct from teratogenicity; occur later, often functional.
  • Examples:
    • NSAIDs (3rd trim): Premature ductus arteriosus closure.
    • Opioids (late): Neonatal withdrawal.
    • Aminoglycosides: Ototoxicity (CN VIII).
    • Tetracyclines: Teeth/bone defects.

Drugs in Lactation - Milk Bar Pharmacy

• Mechanisms: Passive diffusion (lipid-soluble, low MW), active transport (cimetidine, iodine).
• Factors Affecting Excretion:
  • Maternal: Dose, plasma conc., metabolism, timing.
  • Drug: ↑Lipid solubility, ↓MW (<200 Da), ↓Protein binding, pKa (weak bases ↑conc.), ↑half-life.
• Milk/Plasma (M/P) Ratio: [Milk]/[Plasma]; >1 → drug concentrates in milk.
• Relative Infant Dose (RID %): (Infant dose / Maternal dose) wt. adj.; <10% generally safe.
• Ion Trapping: Weak bases (e.g., erythromycin) trapped in acidic milk (pH ~7.0-7.2) vs plasma (pH ~7.4). $pH - pKa = log([B]/[BH+])$.

  ⭐ Weakly basic drugs tend to be trapped and concentrated in the relatively acidic environment of breast milk due to ion trapping, leading to higher M/P ratios.

• Minimize Exposure:
  • Drugs: ↓t½, ↑protein binding, ↓lipid solubility, ↑MW, ↓M/P, ↓RID.
  • Timing: Take drug post-feed or before infant's longest sleep.
• Contraindicated/Caution: Amiodarone, anticancer, lithium, radioisotopes, illicit drugs, ergotamine. (LactMed).
• 📌 BREAST Mnemonic: Bases trapped, RID <10%, Evaluate infant, Amount low, Short half-life, Timing of dose.

High‑Yield Points - ⚡ Biggest Takeaways

• Lipid-soluble, low MW, and non-ionized drugs readily cross the placenta.
• The placental barrier is not absolute; most drugs cross to the fetus.
• Teratogens (e.g., thalidomide, valproate) cause defects during organogenesis.
• FDA pregnancy categories (A, B, C, D, X) help assess fetal risk.
• Most drugs enter breast milk; high lipid solubility & low protein binding favor this.
• Weakly basic drugs undergo ion trapping in acidic breast milk.
• Avoid tetracyclines, warfarin in pregnancy; lithium, amiodarone during lactation.