Core45: Antibiotic selection considerations - pregnancy, childhood

🤰 High-yield / 要点：In pregnancy and childhood, antibiotic choice must balance infection risk against fetal/child toxicity. Prefer proven older drugs, monotherapy, lowest effective dose, and avoid high-risk classes.

Pregnancy: general principles / 妊娠中の原則

• Antibiotics are common in pregnancy, especially for:
  • UTIs.
  • STIs.
  • Upper respiratory infections.
• Untreated infections can harm the fetus, but antibiotics can also cause fetal adverse effects.
• Pregnancy changes PK:
  • Increased blood/plasma volume.
  • Increased renal blood flow.
  • Altered GI motility.
• Recommendations:
  • Use antibiotics only when clearly indicated.
  • Avoid antibiotics in the 1st trimester if possible.
  • Prefer older drugs with proven safety.
  • Use monotherapy when possible.
  • Use the lowest effective dose.
  • Avoid OTC drugs because of interaction risk.

Pregnancy risk categories / 妊娠中の抗菌薬リスク

Category	Meaning	Antibiotic examples
A	No risk in adequate human studies	None listed
B	No animal risk; use only if clearly needed	β-lactams, macrolides except clarithromycin, fosfomycin, vancomycin, clindamycin, daptomycin, metronidazole, nitrofurantoin, fidaxomicin
C	Risk not ruled out; benefits may outweigh risks	Fluoroquinolones, glycopeptides except vancomycin, polymyxins, antifolates, clarithromycin, chloramphenicol
D	Human fetal risk; should be avoided	Tetracyclines, tigecycline
X	Contraindicated	None listed

Childhood considerations / 小児での考慮点

• Children have different PK/PD from adults.
• Important PK differences:
  • Neonates have larger body water percentage → increased Vd for aminoglycosides.
  • Prolonged hepatic metabolism → chloramphenicol toxicity risk in neonates.
  • Decreased renal function in early childhood → aminoglycoside renal toxicity risk.
• Avoid or restrict:
  • Fluoroquinolones：arthropathy risk; use only for approved indications, resistant pathogens with no alternative, or when oral option is needed and alternatives are IV only.
  • Tetracyclines：tooth calcification impairment/discoloration; use only when benefits outweigh risks, e.g. rickettsial infections, cholera.

Remember / 覚え方

• Pregnancy: treat real infection, avoid unnecessary exposure
• β-lactams are generally safer
• Tetracyclines/tigecycline = avoid in pregnancy
• Children: fluoroquinolones and tetracyclines require special caution