The intravenous (IV) route allows direct administration of the drug into the bloodstream, providing immediate systemic circulation. This bypasses absorption barriers such as the gastrointestinal tract and muscle or subcutaneous tissues, resulting in the fastest onset of action. Unlike oral, intramuscular, or subcutaneous routes, IV administration ensures 100% bioavailability with no delay, making it the preferred method when rapid drug effect is critical.

Reference: Goodman & Gilman’s The Pharmacological Basis of Therapeutics, Brunton et al., 13th Edition.