Core27: Pharmacokinetic drug interactions - at the level of absorption

🍽️ High-yield / 要点：Absorption-level pharmacokinetic interactions occur when one drug/food changes another drug’s rate or extent of absorption.

Definition / 定義

• Pharmacokinetic interaction at absorption = one agent alters absorption of another drug.
• This changes drug exposure before the drug reaches systemic circulation.

Mechanisms / 機序

Mechanism	Effect	Example / note
Adsorption	Drug sticks to a large surface area	Less free drug available for absorption
Binding / chelation	Forms insoluble complex	Aluminum antacids + ciprofloxacin
Gastric pH change	Changes solubility/ionization	Can increase or decrease absorption
GI motility change	Changes rate of absorption	Prokinetics enhance; anticholinergics delay
Transport protein effect	Changes influx/efflux	P-glycoprotein, organic anion transporters
Food interaction	Can increase or reduce absorption	Milk reduces doxycycline absorption

High-yield examples / 重要例

• Prokinetics：increase GI motility → may enhance absorption rate.
• Anticholinergics：slow GI motility → may delay absorption.
• Aluminum-containing antacids + ciprofloxacin：
  • Chelation/insoluble complex.
  • Decreased antibiotic absorption.
• Milk + doxycycline：
  • Reduced doxycycline absorption.

Remember / 覚え方

• Absorption interactions happen before blood
• Chelation = less absorption
• Motility changes rate
• pH/transporters change exposure