Bioavailability

The fraction of an administered dose of a substance that reaches systemic circulation in an unchanged form. Intravenous administration has 100% bioavailability by definition. Subcutaneous injection of peptides typically achieves bioavailability between 50-80%, while oral bioavailability for most peptides remains extremely low due to gastrointestinal degradation. This parameter is essential for understanding effective dosing in research contexts.