Duration of action of i.v. administered drug depends on:

Once a drug has gained access to the bloodstream (by iv route), it gets distributed to other tissues that initially had no drug, concentration gradient being in the direction of plasma to tissues. The extent of distribution of a drug depends on its lipid solubility,ionization at physiological pH (a function of its pKa), extent of binding to plasma and tissue proteins, presence of tissue-specific transpoers, differences in regional blood flow, clearance Ref ;KD Tripathi Pharmacology 7th edition (page no;17)