Means within - or administered through - a vein (a blood vessel). The term is often abbreviated I.V.. Additional Info: Intravenous administration of medicines or withdrawal of a blood sample is usually done with a syringe tipped with a small hollow needle. I.V. lines (tubes or catheters) are used when a large volume of fluid (such as saline) or blood needs to be delivered in a controlled fashion. Solutions that are administered intravenously must have their electrolytes properly adjusted to avoid damaging the blood cells and/or causing serious bodily damage or death. Not all injections are intravenous. For example, flu vaccines are administered directly into muscles (intramuscular or IM injection). MSDS Relevance: On an MSDS, this term usually appears in one of two contexts: (1) In describing how the LD₅₀ value on a test animal such as a mouse was determined. (2) In an instruction for emergency medical personnel to, for example, administer fluids or an antidote. See also: Intraperitoneal, LC₅₀