100% Bioavailability is seen with this route:

Bioavailability is fraction of unchanged drug reaching the systemic circulation following administration by any route.IV route has 100% bioavailability.Routes of administration, bioavailability, and general characteristicsRouteBioavailability (%)CharacteristicsIntravenous (IV)100 (by definition)Most rapid onsetIntramuscular (IM)75 to <=100Large volumes often feasible; may be painfulSubcutaneous (SC)75 to <=100Smaller volumes than IM; may be painfulOral (PO)5 to <100Most convenient; first-pass effect may be importantRectal (PR)30 to <100Less first-pass effect than oralInhalation5 to <100Often very rapid onsetTransdermal80 to <=100Usually very slow absorption; used for lack of first-pass effect; prolonged duration of action