Bioavailability
Also known as: F · systemic availability
The fraction of an administered peptide dose that reaches systemic circulation in an active, unmetabolized form.
Bioavailability is expressed as a percentage of the injected dose that ends up available at target receptors. Intravenous administration is by definition 100% bioavailable. Subcutaneous and intramuscular injection typically range between 60–95% depending on compound, injection site, and local blood flow. Oral administration of most peptides collapses bioavailability below 2% due to gastric acid degradation and first-pass hepatic metabolism — which is why injectable research protocols dominate.
Practitioner-validated data suggests that abdominal subcutaneous injection yields higher bioavailability than thigh injection for most GLP-1 analogs, and that consistent site selection matters more for PK predictability than absolute absorption maximization.
Related Terms
Subcutaneous Absorption Rate
The speed at which a peptide injected into subcutaneous tissue reaches systemic circulation.
AUC (Area Under Curve)
The integrated total exposure of the body to a peptide over time, calculated as the area under the concentration-time curve.
Clearance Rate
The volume of plasma cleared of a peptide per unit time, typically by renal filtration, hepatic metabolism, or proteolytic degradation.
Volume of Distribution
A theoretical volume describing how extensively a peptide distributes from plasma into tissues.
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