difference between bolus and infusion
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bolus injection versus continuous infusion definition pharmacology
| Feature | Bolus | Infusion |
|---|---|---|
| Meaning | A relatively large dose given rapidly, usually IV | Drug or fluid given slowly and continuously over time |
| Purpose | Produces a rapid effect or quickly reaches a therapeutic concentration | Maintains a steady drug level or controlled fluid delivery |
| Blood concentration | High peak soon after administration, then falls | Lower, more stable concentration while it runs |
| Typical duration | Seconds to a few minutes | Minutes, hours, or longer |
| Examples | IV fluid bolus for low blood pressure; IV antibiotic loading dose | Noradrenaline infusion; insulin infusion; maintenance IV fluids |
| Main concern | High peak can cause adverse effects if pushed too fast | Requires pump/rate monitoring; effect may be slower to establish |
A common approach is bolus followed by infusion: the bolus gives rapid initial action, then the infusion maintains it. For example, lidocaine may be started with a loading bolus followed by a maintenance infusion (Miller's Anesthesia, 10e).
The better method depends on the medicine, clinical objective, and patient's condition. Recent reviews comparing the two approaches in specific situations, such as diuretics in acute heart failure, do not imply that one method is universally superior (Cochrane review, 2024).
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