Lecture 1 - Drug Absorption and Distribution

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Read: Rang and Dale, Ch. 1 & 7 SWBAT: - describe the main processes in drug absorption and distribution - explain the chemical and biological factors influencing them - define "volume of distribution" - illustrate how these determine the route of drug administration

Mechanisms for drugs crossing membranes

1. passive diffusion
2. facilitated diffusion
3. active transport
4. pinocytosis

Main plasma proteins involved in drug binding

- albumin
- beta-globulin and acid glycoprotein

GIT

GastroIntestinal Tract

Advantages of Oral Administration of drugs

easy, safe, economical

Disadvantages of Oral Administration of drugs

slow, less predictable, first-pass metabolism, patient compliance

Absorption after oral administration is influenced by...

GI motility
blood flow
drug formulation
physiochemical factors

Route of Oral Administration (before reaching systemic circulation)

1. passes through stomach (acid stable)
2. diffuses from lumen through cells into blood stream
3. drug metabolism in gut wall and/or liver (aka "first-pass metabolism")

Administration Routes

Oral
Enteral (absorb through GIT)
- sublingual
- rectal
Parenteral (absorb outside of GIT)
- injection
- topical
- inhalation

Volume of Distribution

The apparent volume into which drug is distributed after IV injection
Vd = D/C0
where: Vd is volume in liters
D is dose of drug in mg
C0 is concentration (mg/L)

Interpreting Vd (Volume of Distribution)

IF:
Vd < 5L, drug stays in blood

Vd < 15L, drug restricted to extracellular fluid, crossing capillary walls but not cell membranes

Vd > 15L, drug distributed through total body water, or concentrated in certain tissues (usually body fat)

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