Bioavailability

Bioavailability refers to the proportion of a drug or other substance that enters the bloodstream when it is introduced into the body and is thus able to have an active effect.

• Absolute bioavailability compares the bioavailability of the same drug given via a non-intravenous route (e.g., oral) to its bioavailability when given intravenously (IV). IV administration is considered 100% bioavailable.

  ^ Formula: ^
  | **Absolute Bioavailability** = ((AUC_non-IV / AUC_IV) × (Dose_IV / Dose_non-IV)) × 100 |

• Relative bioavailability compares the bioavailability of two different formulations of the same drug.

• First-pass metabolism
• Drug formulation (e.g., tablet vs. liquid)
• Solubility
• Gastrointestinal pH and motility
• Presence of food
• Enzyme activity or transport proteins in the gut/liver

• Important in dosing decisions
• Affects therapeutic equivalence of generic vs. brand-name drugs
• Relevant in drug design and pharmacokinetics studies