Intravenous

Several sites on the body are used to intravenously administer drugs: the veins of the antecubital area (in front of the elbow), the back of the hand, and some of the larger veins in the foot. On some occasions, a vein must be exposed by a surgical cut down.

Intravenous administration will provide the most rapid onset of action of any parenteral route because there is no barrier to absorption. The drug is completely available to the body. Drugs that are too irritating for intramuscular or subcutaneous administration (e.g., chemotherapy agents) can be given by this route. Many different types of catheters (an indwelling soft tube) or needles are used to administer intravenous formulations. Placement of these devices is crucial to avoid problems of extravasation or infiltration.

There are several complications that can occur from intravenous administration.

• Thrombosis formation can results from many factors: extremes in solution pH, particulate material, irritant properties of the drug, needle or catheter trauma, and selection of too small a vein for the volume of solution injected.
• Phlebitis, or inflammation of the vein, can be caused by the same factors that cause thrombosis.
• Air emboli occur when air is introduced into the vein. The human body is not harmed by small amounts of air, but a good practice is to purge all air bubbles from the formulation and administration sets before use.
• Particulate material is generally small pieces of glass that chip from the formulation vial or rubber that comes from the rubber closure on injection vials. Although great care is taken to elimination the presence of particulate material, a final filter in the administration line just before entering the venous system is a typical precaution.

Solutions are the most commonly administered intravenous formulation. They are usually aqueous but may also have glycols, alcohols, or other nonaqueous solvents in them. Injectable suspensions are difficult to formulate because they must possess syringeability and injectability. Syringeability refers to the ease at which the suspension can be withdrawn from a container into a syringe. It has been demonstrated that parenteral injections containing particles >25µm³ in size and having aspect ratios of >3.1 frequently cause syringe needle blockage. Injectability refers to the properties of the suspension while being injected, properties such as flow evenness, freedom from clogging, etc. Intravenously administered emulsions are heterogeneous formulations that contain both aqueous and non-aqueous components. Fat emulsions and total parenteral nutrition (TPN) emulsions are used to provide triglycerides, fatty acids, and calories for patients who cannot absorb them from the gastrointestinal tract.