Bolus

Bolus is a term used in medicine, physiology, nutrition, and veterinary science to describe a single, rounded mass of material that is swallowed or delivered to the body. The meaning varies by context: it can refer to a mass of chewed food formed in the mouth and swallowed as a unit, or to a dose of a drug given all at once to achieve a rapid effect.

In pharmacology and clinical medicine, a bolus dose is a relatively large amount of drug administered quickly, often intravenously, to reach therapeutic levels promptly. This is typically followed by a slower infusion or maintenance doses. Bolus injections are used to rapidly achieve anesthesia, correct hypotension, deliver contrast for imaging, or initiate antibiotic therapy.

In nutrition and enteral care, bolus feeding delivers a specific volume of formula or expressed breast milk into the stomach in a short period, usually several times a day, using a syringe or pump. This method contrasts with continuous feeding, which supplies nutrients steadily over many hours.

In diagnostic imaging and veterinary practice, a contrast bolus describes the rapid introduction of radiopaque material into the bloodstream to opacify vessels and tissues during CT or MRI. In veterinary contexts, bolus commonly refers to a large oral dosage form given to animals to ensure adequate dosing.

Overall, the concept of a bolus centers on delivering a concentrated amount of material—whether food, medication, or contrast agent—in a single, controlled, rapid event to elicit a timely physiological response.