Bolus (medicine)

An intramuscular injection of vaccines allows for a slow release of the antigen to stimulate the body's immune system and to allow time for developing antibodies.

[2] A bolus delivered directly to the veins through an intravenous drip allows a much faster delivery which quickly raises the concentration of the substance in the blood to an effective level.

[3] In veterinary medicine a bolus is a large time-release tablet that stays in the rumen of cattle, goats, and sheep.

It can also refer to a dose of liquid injected subcutaneously with a hypodermic needle, such as saline solution administered either to counteract dehydration or especially to mitigate kidney failure, a common ailment in domestic cats.

Before it is fully absorbed, which can take several minutes or longer, the liquid remains in the form of a bolus, a ball or lump under the animal's skin.