Core11: Absorption of drugs

💊 High-yield / 要点：Route determines speed, completeness, first-pass metabolism, and risk. IV is fastest/complete; oral is convenient but variable; sublingual avoids first-pass.

Main routes / 投与経路

Route	Key feature	Absorption factors / notes
Oral	Through GI tract	Gastric emptying, GI pH, food, formulation; affected by first-pass metabolism
Sublingual	Fast absorption	Avoids first-pass metabolism
Rectal	Useful when oral route difficult	Partly avoids first-pass metabolism
Subcutaneous	Injected into tissue between skin and muscle	Blood flow, hydration, molecule size, solubility
Intramuscular	Injected into muscle	Blood flow, muscle mass, solubility; avoid in anticoagulated patients
Intravenous	Directly into vein	Rapid and complete; higher adverse-effect risk; inject slowly when needed
Intraosseous	Into bone marrow circulation	Emergency alternative when IV access is difficult
Transdermal	Through skin via patch/cream	Local effect, e.g. hydrocortisone; systemic effect, e.g. fentanyl
Inhalational	Through lungs	Local antiasthmatics or systemic anesthetics; depends on lung concentration, lipid-water partition, pulmonary blood flow
Intrathecal	Directly into CSF	Spinal anesthesia, antibiotics, chemotherapy, pain management
Nasal	Through nasal mucosa	Can provide local or systemic effect

First-pass metabolism / 初回通過効果

• Oral drugs often undergo first-pass metabolism in gut/liver.
• Sublingual avoids first-pass and can act quickly.
• Rectal partly avoids first-pass, depending on venous drainage.

Absorption principles / 吸収に影響する因子

• Blood flow at administration site.
• Drug solubility and molecule size.
• Local pH and tissue conditions.
• Formulation: tablet, depot injection, patch, cream, aerosol.
• Food and gastric emptying for oral drugs.

Remember / 覚え方

• IV = 100% bioavailability
• Sublingual = fast + no first-pass
• Oral = convenient but variable
• IM/SC = blood-flow dependent
• Transdermal = slow sustained systemic option