Which statement about oral bioavailability is correct?

• A. The drug must be in solution to be absorbed
• B. The drug must be fully ionized to be absorbed
• C. The drug must be bound to plasma proteins to be absorbed
• D. The drug must be hydrolyzed before absorption

Answer: (A)

The essential prerequisite for absorption from the gut is that the drug be in solution. If a drug isn’t dissolved in the gastrointestinal fluids, there’s nothing available to pass the mucosal barrier, so none of the dose can reach the bloodstream, no matter how well it could cross membranes in theory. Ionization and membrane permeability matter, but they don’t override the need for dissolution; many drugs are absorbed in their unionized form because it favors diffusion, while being fully ionized would generally hinder absorption. Plasma protein binding occurs after the drug has entered systemic circulation, not during the absorption process from the gut. Hydrolysis before absorption happens only for certain compounds (like some prodrugs) and is not a universal requirement. So being in solution is the best description of what enables oral bioavailability.