An infusion delivers drug slowly into a vein, usually over 30 minutes to several hours. It is different from a bolus injection, which pushes the drug in all at once. The slow rate matters for drugs that cause irritation, that need to be diluted, or that must maintain a steady blood level. Many biologics, chemotherapy agents, and antibiotics are given by infusion.

The setup is familiar. A bag of fluid containing the drug hangs on a pole. Tubing runs through a pump that controls the rate, then to a catheter or needle in the patient's arm. For longer treatments, a central line or a port under the skin may be used. Nurses monitor vital signs, watch for reactions, and adjust the rate if needed. Some infusions can be given at home with a portable pump, but most happen in a clinic or hospital.

Common reasons for infusion:

• Irritant drugs. Slower delivery reduces vein damage.
• Steady levels. Continuous infusion maintains a constant blood concentration.
• Large volumes. Drugs that require dilution need time to deliver.
• Biologics. Many cannot be given orally and are infused.

Infusion reactions can happen. Mild ones include rash, fever, and chills. Severe reactions, including anaphylaxis, require stopping the infusion and treating immediately.