**Relative bioavailability (RBA)** is the systemic availability of the drug from a dosage form as compared to a reference standard given by the same route of administration. Relative bioavailability is calculated as the ratio of the AUC for the dosage form to the AUC for the reference dosage form given in the same dose.

A relative bioavailability of 1 (or 100%) implies that drug bioavailability from both dosage forms is the same but does not indicate the completeness of systemic drug absorption. The determination of relative bioavailability is important in generic drug studies (e.g., bioequivalence studies). Bioequivalence is a relative bioavailability study.

**Relative Bioavailability (RBA) Calculation Formula**

**Absolute bioavailability (F)** is the fraction of drug systemically absorbed from the dosage form. F is calculated as the ratio of the AUC for the dosage form given orally to the AUC obtained after intravenous (IV) drug administration (adjusted for dose). A parenteral drug solution given by IV administration is considered to have 100% systemic absorption (i.e., F=1). An F value of 0.80 (or 80%) indicates that only 80% of the drug was systemically available from the oral dosage form.

**Absolute Bioavailability (F) Calculation Formula**

**Read also:** F1 and F2 Calculation Formula

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