Routes of Drug Administration: Parenteral

Parenteral routes deliver drugs directly into the systemic circulation, which provides high bioavailability as the drugs bypass the harsh GI environment and hepatic metabolism.

In the intravenous route, a bolus injection rapidly administers the complete dose, whereas an IV infusion injects smaller doses slowly and at a constant rate.

The IV route is preferred for irritating solutions as the blood rapidly dilutes them.

IV injections result in rapid and high drug concentrations, so the risk of adverse reactions is high. The route may also introduce infective agents if the administration site is contaminated.

The intramuscular route administers the drug into a muscle. Muscle perfusion by blood aids absorption. Aqueous solutions of drugs are rapidly absorbed, but slower and sustained absorption occurs if nonaqueous vehicles are used.

The subcutaneous route injects the drug into the tissues between the skin and the muscle.

Absorption is relatively slow and constant, which provides sustained effects.

Some drugs are implanted in their solid forms under the skin, allowing for slow absorption and long-term activity.