In medicine, a bolus (from Latin bolus, ball) is the administration of a medication, drug or other compound that is given to raise blood concentration to an effective level. The administration can be given intravenously, by intramuscular or subcutaneous injection.
The placement of the bolus depends on the systemic levels of the contents desired throughout the body. An intramuscular bolus is used in the administration of vaccines to allow a slow release of the antigen to stimulate the body's immune system and allow time to develop antibodies. Subcutaneous injections are used by heroin addicts (called 'skin popping', referring to the bump formed by the bolus of heroin), to sustain a slow release that staves off withdrawal symptoms without producing euphoria.
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. This is typically done at the beginning of a treatment or after a removal of medicine from blood (e.g. through dialysis).
Diabetics and health care professionals use bolus to refer to a dosage of fast-acting insulin with a meal (as opposed to basal rate, which is a dose of slow-acting insulin or the continuous pumping a small quantity of fast-acting insulin to cover the glucose output of the liver).
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