Core31: Special groups - drug interactions: pregnancy

🤰 High-yield / 要点：In pregnancy, drug choice must consider placental transfer, teratogenicity, perinatal effects, and safer alternatives.

Core risks / 基本リスク

• Many drugs can cross the placenta and affect the fetus.
• Important harmful effects:
  • Teratogenicity：negative effect on fetal development → congenital abnormalities.
  • Classic example: thalidomide/Contergan scandal.
  • Perinatal undesired effects：harm after birth without necessarily altering intrauterine development.
  • Example: oral antidiabetics may cause neonatal hypoglycemia.
• Route of administration can matter, e.g. retinoid derivatives.

Pregnancy categories / 妊娠カテゴリー

Category	Meaning	Examples
A	Controlled studies in pregnant women show no fetal risk	Levothyroxine
B	Animal studies show no harm; insufficient human data	Methyldopa, amoxicillin
C	No adequate animal/human studies	Ibuprofen, topical isotretinoin
D	Human data show fetal risk, but benefits may outweigh risk	Doxycycline, lithium
X	Contraindicated in pregnancy or possible pregnancy	Methotrexate, systemic tretinoin

Contraindicated drugs and substitutes / 禁忌薬と代替薬

Indication	Avoid	Reason	Alternative
Fever/pain/inflammation	COX inhibitors: ibuprofen, naproxen	Ductus arteriosus closure	Paracetamol
Anticoagulation	Warfarin	Teratogenic, abortion risk	Low molecular weight heparin
Hypertension	ACE inhibitors, ARBs	Fetal renal/cranial abnormalities	Nifedipine, methyldopa
Hyperlipidemia	Statins	Teratogenicity	Bile acid sequestrant
Gestational diabetes	Oral antidiabetics	Placental transfer; potential harm	Insulin
Hyperthyroidism	Thiamazole	Teratogenic	Propylthiouracil
Epilepsy	Valproate	Teratogenic	Levetiracetam, lamotrigine

Uterine effects / 子宮への作用

• Tocolytics relax uterine muscle and help sustain pregnancy.
  • β2 agonist: terbutaline.
  • Oxytocin receptor antagonist: atosiban.
  • Magnesium.
• Drugs causing uterine contraction may induce labor or abortion.
  • Oxytocin.
  • Misoprostol.

Remember / 覚え方

• Pregnancy = placenta + fetus + timing
• Warfarin/ACEi/statins/valproate are high-yield avoid drugs
• Paracetamol, LMWH, methyldopa/nifedipine, insulin are common safer choices