〔教学要求〕

1、掌握：吸收及生物利用度概念、吸收和生物利用度的影响因素。

2、熟悉生物利用度的测定方法。

3、了解药物吸收过程。

Oral Administration

Advantages:

Most convenient, most economical

Disadvantages:

Emesis (drug irritation of the gastrointestinal mucosa)

Digestive enzymes/gastric acidity destroys the drug

Unreliable or inconsistent absorption due to food or other drug effects

Metabolism of the drug by gastrointestinal flora

Factors determining rate of drug effect onset

Primary factor:

Rate and absorption extent by GI tract

Absorption Site:

Mainly small intestine because of large surface area

Drug ionization state:

Nonionized (lipid-soluble) forms favor absorption

Weak acids may be highly ionized in the alkaline intestinal pH (not favoring absorption) but this effect is counterbalanced by the large surface-area effect.

Drugs which are weak acids are readily absorbed in the stomach

First-Pass Effect

Drugs absorbed from the GI tract passes through the  portal venous system then through the liver and finally into the systemic circulation when drugs interact with receptors in target tissues.

Extensive hepatic metabolism/extraction result in minimal drug delivery to the systemic circulation for certain agents.

Drugs with large first pass effect exhibit significant differences in pharmacological effects comparing oral vs. IV administration