3.5 : 药物递送：肠外途径

The parenteral route delivers drugs directly into the systemic circulation. It facilitates rapid onset of action and is the preferred route for poorly absorbed or unstable oral drugs.

Primary parenteral routes include intravenous or IV, intramuscular or IM, and subcutaneous or SC.

IV injection releases the drug into the bloodstream directly. IM injection targets muscle, while SC injection reaches deep into the subcutaneous tissue.

In IM and SC administration, drugs diffuse along the gradient toward nearby blood vessels.

Certain IV drugs, like tissue plasminogen activator, are bolus-injected for quick effect, while antibiotics are infused slowly for prolonged action.

IM drugs in aqueous solutions absorb rapidly, while specialized depot preparations release gradually.

Additionally, aqueous solutions injected into the deltoid muscle absorb faster than in the gluteus maximus.

Subcutaneously administered drugs, like insulin or contraceptive implants, have slow absorption, extending their therapeutic effect.

Notably, subcutaneous injection of tissue irritants may cause necrosis and intense pain.